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001 Wood/water
relationships during kiln drying and reconditioning of softwoods
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22
may 2007
Wood/water relationships during kiln drying and reconditioning
of softwoods
Prepared for the
Forest and Wood Products Research and Development Corporation
by
R. Northway and I. Burgar
The FWPRDC is jointly funded by the Australian forest and wood products industry and the Australian Government.
© 2007 Forest and Wood Products Research and Development Corporation All rights reserved.
Publication: Wood/water relationships during kiln drying and reconditioning of softwoods
The Forest and Wood Products Research and Development Corporation (“FWPRDC”) makes no warranties or assurances with respect to this publication including merchantability, fitness for purpose or otherwise. FWPRDC and all persons associated with it exclude all liability (including liability for negligence) in relation to any opinion, advice or information contained in this publication or for any consequences arising from the use of such opinion, advice or information.
This work is copyright under the Copyright Act 1968 (Cth). All material except the FWPRDC logo may be reproduced in whole or in part, provided that it is not sold or used for commercial benefit and its source (Forest and Wood Products Research and Development Corporation) is acknowledged. Reproduction or copying for other purposes, which is strictly reserved only for the owner or licensee of copyright under the Copyright Act, is prohibited without the prior written consent of the Forest and Wood Products Research and Development Corporation.
Project no: PN04.2001 Researchers: R. Northway Ensis
Private Bag 10, Clayton South, Vic 3169 I. Burgar
CSIRO
Private Bag 33, Clayton South MDC, Vic 3169
Final report received by the FWPRDC in May 2007.
Forest and Wood Products Research and Development Corporation PO Box 69, World Trade Centre, Victoria 8005 T +61 3 9614 7544 F +61 3 9614 6822 E [email protected] W www.fwprdc.org.au
Table of contents
Executive summary.................................................................................... 1
Introduction ............................................................................................... 3
Conclusions .............................................................................................. 5
Part 1 Exploratory tests ........................................................................ 6
Materials and methods ............................................................................... 6
Results and discussion ............................................................................... 7
NMR measurements and preliminary analysis ........................................... 7
Part 2 Detailed tests ........................................................................... 12
Materials and methods ............................................................................. 12
Results and discussion ............................................................................. 16
Detailed drying runs 6 and 7: radiata pine heartwood ............................... 17
Detailed drying run 15: radiata pine near-pith sapwood ........................... 20
Detailed drying runs 16 and 17: radiata pine heartwood ........................... 23
Detailed drying test runs 10, 11 and 12: slash pine heartwood ................. 27
Detailed test drying runs 13 and 14: slash pine heartwood ....................... 31
NMR measurements and analysis ............................................................ 35
Part 3 Experimental kiln trials ............................................................. 47
Materials and methods ............................................................................. 47
Results and discussion ............................................................................. 49
Kiln runs ................................................................................................. 49
Environmental conditions ........................................................................ 50
Moisture content ..................................................................................... 51
Distortion ................................................................................................ 53
Stiffness .................................................................................................. 55
NMR measurements ................................................................................ 56
Gaussian parameters ................................................................................ 59
Lorentzian parameters ............................................................................. 59
Project results and discussion ................................................................. 62
Acknowledgements ................................................................................. 64
Disclaimer ................................................................................................ 64
1
EXECUTIVE SUMMARY
Objective
For this project, the principal objectives were to identify and characterize the bonding states
of water in softwoods during kiln drying, subsequent high humidity and/or steam treatment
and later stabilization or storage periods, and to recommend improved kiln schedules and
conditioning processes to reduce timber storage time with improved stability.
The specific objectives, derived from the results of the previous Softwood Drying Project,
were:
1. Identify and characterize the bonding states of water in softwoods during kiln drying
and subsequent high humidity and/or steam treatment, and also during later
stabilization or storage periods.
2. Identify links between changes to the bonding states of water, internal stresses and
distortion on release from restraint and on machining.
3. Identify high temperature kiln drying schedule modifications and/or high humidity or
steam treatments that improve stability.
4. Identify stabilization treatments to reduce the time to a stable state.
5. Identify differences between Heart-in and Free of Heart material.
6. Recommend modification to current commercial practices to minimize kiln drying
time, steaming time and storage periods to produce stable dried softwood timber.
Key results
The role of water in wood stability
The simple bound/free water model is inadequate to explain the role of water in wood shape
and stability. It is possible to use NMR measurements to identify the energy state and hence
the bonding of water in wood before, during and after processing. Other components of wood
than water are additional sources of protons and contribute to NMR signals. High field NMR
was needed to separate these different contributions. Techniques have been developed to
analyse low field NMR signals to identify other components and to separate signals from
structural components and water in dry wood. Indications of links between proportions of two
types of bound water and wood stability have been identified but further development will be
needed to develop technique that can be correlated to wood stability.
Improved kiln schedules and conditioning processes to reduce storage time
with improved stability
There are indications that steaming after drying increases the mobility of water, particularly
near the surfaces of timber, although any effect on stability was not demonstrated. Modifying
the later stages of kiln schedules can eliminate or reduce the need for steaming after drying,
with similar product stability.
Application of results
The low field NMR surface probe takes measurements from only a small volume of wood at
the surface. This technology can be used to monitor moisture content and surface uniformity
of green and dry wood. Other available equipment cannot be used to assess and re-assess the
same location on a specimen which would be desirable. Current technology requires physical
samples to be taken for more intensive low field and for high field classical NMR
2
measurements. This is destructive and limits the scope of sampling, leaving the results subject
to normal wood characteristic variation.
While the same stability can be achieved without steaming, the drying time is extended,
although not by as much as the time used for the traditional steaming treatment. The benefit to
industry of reduced total processing time and reduced energy usage may be outweighed by the
increased kiln residence time and consequent need for more kilns rather than the much
cheaper steaming chambers.
The strategy of eliminating steaming is probably not appropriate for timber to be re-sawn
during machining (e.g. as 2-out) because of the possibility of wet centres of boards being
exposed and further drying causing distortion.
3
INTRODUCTION
Plantation grown softwood is subject to distortion during drying because of longitudinal
shrinkage associated with spiral grain and microfibril angle. High temperature drying and
steam conditioning while under restraint from concrete blocks is current industry practice to
produce structural softwood timber. This is generally satisfactory, but producers find it
necessary to store dried timber for varying periods before machining, to maximise product
straightness and stability. This is particularly the case if the moulder is also used to separate a
dried board into several products e.g. splitting wide boards, commonly known as 2-outing.
The stability in shape of wood products in service is dependent on the maintenance of internal
structural accommodations that were made during drying under restraint. Any changes in void
space in the structure will affect bound water bonding sites. Stability is thus associated with
the bound water remaining in stable positions. While moisture exchange between wood and
the environment is predictable, internal movement of water and its significance is not fully
understood.
FWPRDC Softwood Drying Project PN008.96 explored the relationships between the wood
structure and water during drying operations with a range of technologies and the possibilities
of modelling the drying process, stress and distortion development during drying. The next
step, to gather information on the wood/water relationships linked to measured changes in
wood behaviour so that the drying/processing models can incorporate this knowledge, was the
principal objective of this project. Nuclear Magnetic Resonance, NMR, was the primary
technology used in this investigation.
Water in wood
Water in hydrophilic polymers, Wc, is generally assigned 1 as a sum of non-freezing water
(structural water or tightly bound to cell walls), Wnf; freezing bound water or water associated
with walls and smaller reservoirs, Wfb; and free water or essentially unbound water in cell
lumens, Wf. The closely studied relationship between these categories can be summarised as
follows: water is in bound non-freezing condition at very low moisture concentration (MC),
then the freezing bound water contribution appears at low total moisture, around 10%, and
after around 12% of total moisture, or normal wood moisture, the free water contribution is
becoming evident. Therefore, in the dry wood samples, where MC is around 10%, the main
moisture contribution will be from bound water (freezing and non-freezing). Such
interpretation was supported by Guzenda et al.2, who concluded that loss of free water in the
drying process (moisture content going below the fibre saturation point) is evident also from
NMR data, in particular, the spin-lattice relaxation time T1, which normally reveals two decay
components in green wood, becomes a single component parameter below the fibre saturation
point.
The division of water in wood between bound and free states and something between is not
the complete story. Depending on the experimental method used one can detect all different
phases or some time average those according to the detection time scale and dynamic
exchange rate between these phases.
Attempts to use NMR spectroscopy, with the assumption that the proton NMR signal is
predominantly the water signal, led to ambiguity in the interpretation of NMR data on the
1 H. Hatakeyama and T. Hatakeyama, Interaction between water and hydrophilic polymers,
Thermometrica Acta, 308 (1998) 3-22 2 R. Guzenda, W.Olek, H.M. Baranowska, 12
th International symposium on non-destructuve testing of
wood (2000), Sopron, Hungary
4
water types, due to the fact that there are also other proton bearing mobile organic molecules
which contribute to the NMR signal. To understand the NMR data collected from the samples
from wood drying process therefore required further detailed analysis of the proton NMR
signal; in particular, we were trying to identify the organic components like resin and other
volatile wood components in the proton NMR signals observed at low (and/or high) magnetic
fields. The results of our investigation not only give the evidence of such organic components,
but also reveal further evidence for the fast dynamical exchange of NMR signals between
organic and two types of bound water molecules.
Wood deformation and moisture behaviour during drying
The deformation of the wood structure during drying is a consequence of moisture loss and
induced strain in the structures. Theoretical prediction of total strain rate was assumed to be
the sum of elastic strain rate, moisture strain rate and mechano-sorptive strain rate (intake
moisture from the environment after drying). 3
The rate of drying of softwood is clearly influenced by board properties (green moisture
content, wood basic density, sapwood/heartwood mixture in a single board, board thickness
and ring orientation pattern), drying schedule and drying conditions. 4
Swelling and shrinking of wood occurs when the moisture in wood falls below the fibre
saturation point, FSP, (when the cell walls are saturated and the cell lumen is empty) –
assumed to be around 30% moisture content for softwood. Of course, there is no such ideal
situation in the wood as FSP, as the real weight used in the moisture content estimate is also
affected by the density of the wood, its structure, and chemical composition (extractives). 5
Especially, the amount of extractives and moisture left behind after drying depends on wood
porosity (estimated to be up to 74% for softwood) and its permeability (ability to release
water from the structure) and they play an essential role in the realistic estimates for drying
regime. All these factors influence the value of NMR parameters such as relaxation times and
resonance intensities due to the variations in the intermolecular interaction caused by the
heterogeneous nature of wood.
The NMR relaxation times T1 and T2 are defined as the spin-lattice relaxation time T1
associated with the energy transfer and therefore NMR signal lost to the lattice, and spin-spin
relaxation time T2 associated with the signal decay by losing coherence in the spin system
without loss of any energy (spin-spin interaction).
The T1 NMR data interpretation has already been established in view of FSP moisture content
but the T2 relaxation times have not previously been proven useful in the analysis due to their
large dependence on other environmental variables.
Our intention here was to find the correlation between the moisture measurements by NMR
methods (in particular to use the T2 measurements) and the deformation of wood. The T2 data
collected here can be taken only as a relative comparison through a set of boards. It is
reasonable to assume that the large structural variations of samples on the molecular level will
also affect the results. Therefore, it may be difficult to find a clear correlation between NMR
parameters and the detected structural deformations.
3 O. Dahlblom et al. Ann.Sci.For (1996) 53, 857-866
4 S.Pang, Chemical Eng. J. 86 (2002), 103-110
5 J.Kopac et al., J. of Materials Processing Technology 133 (2003), 134-12
5
CONCLUSIONS
It was possible to use low field NMR to follow the distribution of water during the kiln drying
and reconditioning of softwood. The NMR equipment available is capable of taking
measurements, which can be analysed to identify the states of water, generally as expected
from the literature. High field NMR can further distinguish between water and other proton
sources in wood and identify structural changes from different drying and conditioning
processes. With further development NMR will be able to help identify processing methods to
obtain greater wood stability.
The specific conclusions from Low Field NMR studies are: 1) The NMR signal intensity
correlates to the wood moisture content as determined by the oven-drying method; 2) Multi-
component NMR signal decay, T1 and T2, are related to different environments (moisture
type); 3) There is a trend of changes in the dynamics of the bound water components and
increased wood deformation, (despite the fact that structural effects frequently overtake these
changes); 4) Clear changes were detected in the amount and dynamics of reconstituted
moisture after the equilibration of dry wood in different moisture (humidity) environments. In
summary, the sensitivity of the NMR data to the board properties (structure etc.) is so large,
that it frequently prevents establishing a straight correlation between the NMR parameters and
wood structural changes.
The MOUSE analysis clearly demonstrated the ability of the NMR surface analyser to
identify the moisture in the green wood samples. The data also shows that there are numerous
variations due to the water mobility, wood structure, porosity, and composition. In particular,
after the proper evaluation of all these influences, there can be further improvements on such
analysis to obtain an accurate estimate of removable moisture and information on resin
content.
NMR investigation by low field NMR MOUSE methods clearly depicted the mobile organic
signal as well in green wood as in fresh dried wood beside the predominant water protons
NMR signal. Variations in the molecular mobility of organics and water is therefore in
general overlapped and further development of NMR methods to separate these components
in detection is probably the only way to provide reliable NMR data, which will be correlated
to short and long term stability of wood structure after drying.
Dry wood samples were analysed by NMR methods on core samples from boards or
specimens. The sensitivity and accuracy of data is a prerequisite for reasonable evaluation but
it has not been possible to sample sufficiently to determine these matters accurately.
Moisture distribution through the board depth is obtainable from measurements on cores and
our data is in agreement with the results of classical methods that take a much longer time and
greater work effort to obtain.
The solid-state NMR methods provide further confirmation of dynamical changes in the water
mobility as result of drying process. The interactions between residual water and organic
components in wood, as reflected in both the water and organic resonance line widths and
corresponding relaxation times, confirm the existence of the so-called plasticised zones in the
wood structure. The distribution and density of these zones may be essential in the
interpretation of the dried wood distortions.
6
Part 1 EXPLORATORY TESTS
This first part of the project was a preliminary test with matched boards dried with and
without restraint, using an industry standard high temperature schedule. Nuclear Magnetic
Resonance, NMR, tests were made on samples from the boards in green and dry states, and
from sections of the dry boards to normal, drier and wetter environments.
MATERIALS AND METHODS
A sample of green radiata pine boards was supplied by Wespine, Bunbury, WA. This
comprised (23) boards, 6.0m long, 100 x 40mm section and approximately equal numbers of
heart-in (HI) and sapwood (Sap). The boards were crosscut to each produce (2) kiln
specimens 2.8m long, with (3) sections cut to determine moisture content and density (Fig. 1).
The offcuts were used for NMR measurements, primarily on the surfaces.
Pairs of boards were separated and one of each pair dried with restraint and one dried without
restraint. Two kiln drying runs were conducted using kiln drying and steam reconditioning
schedules as used by Wespine for HI and Sap timber. Specimen distortion was measured after
drying.
Each 2.8m long board was cut to produce (3) specimens 0.8m long, (2) sections for MC
determination and (2) cores 35mm diameter for NMR measurements (Fig. 2).
Specimens were weighed and distortion measured. Specimens were then placed in controlled
environment chambers, A specimens in 5% equilibrium moisture content (EMC) conditions,
B specimens in 12% EMC conditions and C specimens in 17% EMC conditions.
After one month, seven specimen sets, selected to represent the range of NMR measurements
from the dry boards, were weighed, distortion measured and cores cut for NMR measurement.
For two of these sets another set of cores was cut for NMR measurement and MC gradient
determination. One set of cores was further divided to compare NMR measurements directly
with MC determined by oven drying.
Green offcut 1-1 Green offcut 1-2 Green offcut 1-3
MC section 1a MC section 1b MC section 1c
Board 1-1 Board 1-2
2.8m 2.8m
Figure 1 Kiln boards from 6.0m long boards
1-1-A 1-1-B 1-1-C 1-2-A 1-2-B 1-2-C
Core for NMR 1-1a Core for NMR 1-1c Core for NMR 1-2a Core for NMR 1-2c
MC section 1-1a MC section 1-1c MC section 1-2a MC section 1-2c
Figure 2 Specimens for controlled environments from dry 2.8m long kiln boards
7
RESULTS AND DISCUSSION
This work showed that NMR could identify the quantity and energy states of water in green
and dry wood and that the latter were to some extent indicative of shape changes. It was also
found that there was considerable sensitivity of the NMR measurements to features of the
wood structure in addition to water. Further development to NMR measurement and analysis
techniques were needed. This was described in the Milestone 2 Report.
NMR measurements and preliminary analysis
Green board sections
The NMR surface analyser, MOUSE, (shown in Figure 3 and Figure 4), clearly demonstrated
the ability of NMR analysis to identify the moisture in the green wood samples. The MOUSE
data also shows that there are numerous variations in the data due to the water mobility, wood
structure/porosity and grain orientation. After the proper evaluation of all these influences,
one can further improve these analyses to obtain an accurate estimate of removable moisture
and information on resin content.
Figure 3 The NMR surface analyzer, MOUSE, set up.
Figure 4 A green wood sample as measured on the MOUSE; surface facing the white/red zone
The water distribution changes from centre of the stem towards the sap wood, as shown by the
NMR signal from board #19 in Figure 5. The NMR signal clearly shows the expected
difference between the moisture status of heartwood (inside) and sapwood (outside)
8
35
30
25
20
15
10
5
Sig
na
l
2015105
Time(ms)
19_2 top heart 19_2 top sap
19_3 top inside 19_3 top outside
Figure 5 NMR signals from green board sections using the surface analyser, showing the
differences between inner (heartwood) and outer (sapwood) faces of sections
19-2 and 19-3.
Dry boards and specimens
The kiln dry wood samples were to be investigated using the NMR MOUSE in a similar
procedure to the green wood sample measurements. However, the amount of moisture in the
small part of the surface of the dry wood samples measured by the MOUSE proved to be too
low and the T2 relaxation times were much shorter, so that the MOUSE spin-echo signal
(S/N) was insufficient to be properly analysed (only two or three available points at the best).
The alternative measurement using the NMR MINISPEC PC 110 was utilised to collect
sufficient signals from a large bulk sample – core 35mm in diameter and approximately 38
mm in length - which was drilled from the dried boards, through the thickness.
The data were collected in three different sets:
• two signal magnitude measuring points: first at time 30 microseconds and second at 50
microseconds after the rf pulse;
• T2 measurements with the spin-echo sequence, spacing 50 microseconds, where only one
T2 component was observed;
• T1 measurements by inversion recovery method, where two components, long and short
T1, were identified.
The free induction decay (FID) signal intensity can be related to the overall moisture content
as shown in Figure 6. The first set (blue diamonds) had much more dispersed values than the
second (red squares) values, which were also further away. The improved correlation of the
second data set (further away) to measured moisture content is probably due to signal sources
additional to moisture, contributing to the proton signal at the beginning of the ‘FID’.
9
6
5
4
3
2
1
0
Sig
na
l
14121086420
AvMCmoisture(%)
Figure 6 Two sets of the ‘FID’ signals and their relationship to average moisture content.
The specimens equilibrated in different controlled humidity environments (A = 5% EMC, B =
12% EMC, and C = 17% EMC) were sampled by coring. The core samples from boards 10
and 12 were analysed by NMR methods as whole cores. Figure 7 shows a clear trend in T2
measurements of samples from the 5, 12 and 17% moisture content environments in samples
10-1, 10-2, and 12-2. The sample 12-1C (17% equilibrium moisture content (EMC)) had a
lower than anticipated T2 signal amplitude, but this may be due to factors other than moisture,
such as the wood structure of that particular sample.
0
200
400
600
800
1000
1200
1400
1600
1800
10-
1Ax
10-
1Bx
10-
1Cx
10-
2Ax
10-
2Bx
10-
2Cx
12-
1Ax
12-
1Bx
12-
1Cx
12-
2Ax
12-
2Bx
12-
2Cx
Amplitude of T2 data
Figure 7 Amplitude of T2 measurement from cores at different moisture content
for boards 10 and 12.
Moisture distribution through board depth is obtainable and our data are in agreement with the
traditional method of determining moisture content by oven drying samples. The traditional
is expensive in terms of time and work effort, and NMR appears to be able to clearly
10
undertake these measurements rapidly. The optimisation of methods to measure moisture
content gradients by NMR is in progress.
Wood deformation and moisture during drying
The deformation of the wood structure during drying is a consequence of moisture loss and
induced strain in the wood structure. The theoretical prediction of total strain rate was
assumed to be the sum of elastic strain rate, moisture strain rate and mechanosorptive strain
rate (exchange of moisture with the environment after drying)6. The intention in this project
was to find the correlation between the moisture measurements by NMR methods and the
deformation of wood. From the literature it is clear that moisture is only partially responsible
for wood deformation. A reasonable correlation can be expected only when the moisture
movement dominantly drives wood movement/deformation. The wood drying process
includes the removal of free (mobile) moisture in the wood in addition to partially releasing
the water from the wood structure. Residual (bound) water that is present below fibre
saturation is assumed to be closely associated with the cell structure. These water molecules
should have a strong interaction with solid wood and therefore short relaxation times T1 and
T2. The major effect on these relaxation times is not only the interaction with solid surfaces,
but also the size of the spaces available for water to occupy. If the pores (voids) are large,
then the relaxation times will be longer due to the intermolecular interaction between the
molecules and their isotropic motion. According to NMR theory, the relaxation times will
follow the distribution of pore sizes, but the experimental results will normally present the
average achieved in the NMR timescale (a few nano-seconds (10-9
) for T1 and milli-seconds
(10-6
) for T2). The difference in the NMR data fitting with a single or a double exponential
function shows that there are more components than water alone, in the relaxation time data.
This suggests that:
• The mobility of water molecules is so restrictive in the dried wood that (internal) surface
interactions dominate the relaxation rates.
• The exchange rate between the different pores is slow in comparison to the NMR
timescale; different statistically averaged relaxation time values will be produced.
The rate of drying of softwood is clearly influenced by board properties (green moisture
content, wood basic density, sapwood/heartwood mixture in a single board, board thickness
and growth ring orientation pattern), drying schedule and drying conditions7. Assuming that
in our case the last two were kept constant, it becomes obvious that board properties in all
their variations will be the major factor in the final moisture content distribution. Therefore
the NMR data may vary largely because of these board property variations. Due to the fact
that the board properties varied in the set of 23 boards studied, it can be expected that
individual board properties such as density, sapwood/heartwood distribution and grain pattern
will contribute to the variations in the measured NMR parameters, T1, T2 and signal intensity.
In the first analysis of the collected data the trend in these correlations was evident. Further
data processing is required to build a model which will be relevant to the wood industry.
Swelling and shrinking of wood occur when the moisture in wood goes below the fibre
saturation point, ((FSP) - when the cell walls are saturated and the cell lumen is empty of
water – assumed to be around 30% moisture content for softwood). Of course there is no such
ideal FSP state in wood, therefore the real weight, used in the moisture content estimate, is
affected by the density of the wood, its structure, extractives and chemical composition8. In
particular the amount of extractives and moisture left behind depends on wood porosity,
which has been estimated to be up to 74% for softwood, and its permeability (ability to
6 O. Dahlblom et al. Ann.Sci.For (1996) 53, 857-866
7 S. Pang, Chemical Eng. J. 86 (2002), 103-110
8 J. Kopac et al., J. of Materials Processing Technology 133 (2003), 134-142
11
release the water from the structure). In addition density (and amount of water at a particular
moisture content) varies across growth rings. With comparisons usually made between
matched specimens the composition of the samples contained similar material overall. All of
these factors further affect the value of NMR parameters such as relaxation times and
intensities due to differences in the intermolecular interaction, which govern NMR properties.
The dried wood specimens clearly show the correlation between the magnitude of the detected
signal from the water and its relaxation rates to the moisture content. The measured relaxation
rates are directly proportional to the wood porosity or to the ability of water to enter the wood
structure; as a consequence of drying, pores become more available and interconnected for
water movement.
Successful attempts have already been made to establish the T1 NMR data interpretation with
respect to FSP moisture content9 but the T2 relaxation times have not been proven as useful in
the analysis due to its large dependence on other environmental variables. The T2 data
collected in this project indicate the expected correlations as relative trends through the set of
boards. To use such data as a reliable base to determine the correlations with deformation in
the wood structure can be achieved. For that it is necessary to evaluate all board property
correlations and further develop and apply the theoretical model needed for the interpretation
of the NMR data.
The current NMR data set has revealed:
• good correlation with wood moisture content as determined by the oven drying method;
• differences between the moisture relaxation times, T1 and T2, as assigned to different
environments of water molecules;
• variation of the T2 times through the board profile;
• variation in the amount (using NMR dynamic parameters) of reconstituted moisture after
the equilibrium of dry wood to different moisture environments;
• clear trends of changes of the bound water component dynamics in relation to the
increased wood deformation; and
• sensitivity of the NMR data to board properties is considerable. This prevents the
establishment of clear correlations between NMR parameters and wood structural
changes.
9 Presentation on 21-4-2004 by Group from Poland
12
Part 2 DETAILED TESTS
Milestone Report 3 for this project reported on detailed tests conducted in a laboratory dryer
with short lengths of Radiata Pine and Slash Pine boards. Moisture location and bonding as
measured by NMR did not fully explain changes in shape, with or without moisture content
change. NMR measurements were affected by other proton sources within the wood.
MATERIALS AND METHODS
Material and specimen preparation
A sample of green Radiata pine boards, 6.0m long, 100 x 40mm section, was supplied by
GTFP, Mt Gambier, SA. This included both heart-in (H) and sapwood (S). Boards with
consistent cross-section along the length were selected and crosscut to each produce kiln
specimens 475mm long, avoiding knots where possible. Specimens were identified in
sequence from the butt end with letters: A, B, C etc. Sections from between specimens were
cut to determine moisture content and density and for NMR measurements (Figure 8).
A sample of Slash pine boards was supplied by Hyne & Son, Tuan, Qld, and prepared in the
same manner.
Green offcut
MC section Rh1a
Core for NMR
MC section
Rh1E
Rh1F
Rh1B
Rh1C
Rh1D
Rh1A
Figure 8 Drying specimens 475mm long from green boards
Sets of matched boards were prepared for each drying run. In each run one specimen was weighed
continually, one fitted with an array of thermocouples to monitor internal temperature, and two
specimens removed at intervals to be cored for determination of radial moisture content profile
(19mm diameter core) and NMR measurements (35mm diameter core). Core holes were sealed
with silicon sealant. Also in each run one (two in later runs) specimen was dried with restraint
against twist; the restrained specimen was matched to at least one other specimen in the run dried
without restraint. For all specimens distortion was measured before and after drying and again
after steaming and cooling, except for the restrained specimens, which could not be measured
while in the restraining frames.
13
Drying test procedure
Seventeen drying runs were conducted with drying and steam-reconditioning schedules as
used by GTFP and Weyerhaeuser for HI and Sap timber of each species (Table 1).
Table 1 Drying schedules used in the experimental dryer
Radiata Slash
Air velocity 7-9 m/s; 2-hourly reversals 11 m/s; 2-hourly reversals
Kiln Heatup 140o DB/98
o WB over 1 hour 140
o /98
o over 2 hours
Drying 140
o /90
o; WB ramped down over
approx. .0.5 hr 140
o /90
o
Cool Outside kiln; 0.5-1 hour Outside kiln, 2 hours
Reconditioner heatup To 98o DB in 0.5 hour To 98
o DB in 0.5-1 hour
Recondition 3 hours @ DB>95o 3 hours @ DB>95
o
Cooling Outside immediately
The procedure for a typical run is outlined in below:
1. Select specimens.
2. Coat ends of specimens with silicon sealant and aluminium foil.
3. Weigh and measure distortion & dimensions of specimens.
4. Drill holes and insert thermocouples in selected specimen.
5. Clamp restraint specimen(s) in restraining frame(s).
6. Load specimens in dryer.
7. Start dryer and implement planned drying schedule.
8. Commence schedule ramp-down in temperature at appropriate stage.
9. At selected stages remove specimen(s) for coring from dryer, weigh, cut one 35mm
diameter core and one 19mm core through the specimen thickness, weigh, seal hole(s)
with silicon sealant, weigh and return to dryer; typical time 5 minutes.
10. At end of drying unload specimens and take cores from specimens, as in Step 9,
except restrained and thermocouple specimens; measure distortion & dimensions on
specimens, except restrained specimens.
11. Cool for selected time.
12. Steam in steam chamber, restraint specimens still in frames.
13. Cool at controlled rate and hold overnight.
14. Remove thermocouples from specimen; remove restrained specimen(s) from frame(s).
15. Weigh, measure distortion & dimensions and take cores from all specimens.
16. Slice three 6mm discs from each face of 19mm cores and determine moisture content
distribution; saw two 5mm thick discs at 6mm spacing from each face of the 35mm
diameter cores (1mm saw kerf) for NMR measurements.
17. Make Low field MOUSE NMR measurements on each face of discs.
14
Flexible wires from loadcell
to Data logger
W Specimen weighed continuously
T Specimen with thermocouples
C Specimen cored at stages during run
R Specimen restrained against twist
R
R
W T
C C
Figure 9 Specimen positions in dryer for detailed tests
Variations were made to the standard schedules to generate different treatments: for some
runs the DBT was ramped down over the latter stages; steaming times were reduced for some
runs and no steaming conducted for some runs. Later runs were in pairs, with and without
variations, and with specimens matched.
Details of each run are shown in Table 2. Further details and results for runs with Radiata
heartwood (Runs 6 & 7; 15; 16 & 17) and Slash pine heartwood (Runs 10, 11 & 12; 13 & 14)
are shown below.
Table 2 Details of drying runs and specimen allocation
Run
No.Species
Type
#
Board
No.
Initial
MC %
Drying
Schedule
Air
speed
m/s
Rate of
humidity
buildup
Ramp
down?
Start
Ramp
down
hrs
Drying
Time
hrs
Cool'g
Time,
hrs
Steam
Time,
hrs
Cool
down
rate
after
steam
Spec'ns
paired to
Run
Weighed
spec'n
Spec'n
with
T/Cs
Spec'ns
cored
during
drying
Restrained
specimens
1 Radiata S Rs7 52-129 140/90 11 slow No 5.5 0 Rs7H Rs7BRs7A
Rs7C
2 Radiata S Rs11 96-115 140/90 9 slow No 9 1 4 Slow Rs11G Rs11DRs11E
Rs11HRs11F
3 Radiata S Rs10 48-123 140/90 9 slow Yes 6.5 9.5 1 3 Slow Rs10G Rs10BRs10A
Rs10CRs10E
4 Radiata S Rs4 63-110 140/90 9 fast Yes 7 9.25 1 3 Fast 5 Rs4B Rs4CRs4A
Rs4HRs4D
5 Radiata
S
S
S
Rs2
Rs4F
Rs11A
74-114
95 96140/90 9 fast Yes 7 10 1 3 Mod. 4 Rs2A Rs11A
Rs2B
Rs4FRs2C
6 RadiataH
H
Rh1,
Rh10
29-39 32-
33140/90 9 slow No 4 1 3 Fast 7 Rh1G Rh1C
Rh1A
Rs10IRh1I
7 RadiataH
H
Rh1,
Rh10
30-34 26-
32140/90 9 slow Yes 2.3 5.75 1 3 Fast 6 Rh1E Rh1D
Rh1B
Rs10J
Rs1H
Rs10K
8 SlashS
S
Ss1,
Ss2
101-109
80-86140/90 11 slow No 1 8 1 3 Mod. 9 Ss1C Ss1F
Ss1D
Ss2E
Ss1A
Ss2C
9 SlashS
S
Ss1,
Ss2
90-107
86140/90 11 slow Yes 4.5 8.5 1 3 Mod. 8 Ss1G Ss1H
Ss1E
Ss2F
Ss1B
Ss2D
10 SlashH
H
Sh3,
Sh4
31-40 50-
62140/90 11 fast No 6 1 3 Mod. 11, 12 Sh4E Sh3F
Sh3A
Sh4G
Sh3C
Sh4C
11 SlashH
H
Sh3,
Sh4
33-44 51-
74140/90 11 fast No 6.25 1 2 Mod. 10, 12 Sh4F Sh3G
Sh3H
Sh4H
Sh3B
Sh4D
12 Slash
H
H
H
Sh2
Sh3
Sh4
89-91 45-
46 47-51140/90 11 fast Yes 3 9 0 Fast 10, 11 Sh4A Sh2G
Sh3E
Sh2H
Sh3D
Sh4B
13 SlashH
H
Sh5,
Sh6
91-104
75-110140/90 11 fast No 6.5 1 3 Mod. 14 Sh5E Sh6D
Sh5A
Sh6F
Sh5C
Sh6B
14 SlashH
H
Sh5,
Sh6
91-110
81-122140/90 11 fast Yes 3 9 1 3 Mod. 13 Sh5F Sh6E
Sh5B
Sh6G
Sh5D
Sh6C
15 Radiata S/H Rsh3 48-80 140/90 9 fast Yes 3 9 0 Fast Rsh3F Rsh3CRsh3E
Rsh3B
Rsh3D
Rsh3G
16 RadiataH
H
Rh2,
Rh6
31-35
34-37140/90 9 fast Yes 3 6 0 Fast 17 Rh2A Rh6G
Rh2D
Rh6E
Rh2F
Rh6C
17 RadiataH
H
Rh2,
Rh6
31-36 35-
39140/90 9 fast No 4 1 3 Fast 16 Rh2B Rh6H
Rh2E
Rh6F
Rh2G
Rh6D
# S = Sapwood H = heartwood/juvenile wood
15
After all runs were completed specimens were weighed and distortion measured. Specimens
were then placed in a 12% EMC controlled environment room. After one week specimens
were re-measured and placed in another room at 17% EMC, then at weekly intervals in a 5%
EMC room and back to the 12% EMC room. NMR discs from 35mm cores were measured
after exposure to 12% and 17% conditions.
Specimens from early runs had up to 2 months storage before the cycling which may have
allowed moisture re-distribution and stress relaxation.
The results of the drying runs with heartwood material are presented below. These specimens
had a maximum of 5 weeks storage.
16
RESULTS AND DISCUSSION
Figure 10 gives an example of the detection signals from MOUSE. Amplitude and relaxation
time T2 shown are the results of curve fitting.
Figure 10 MOUSE detection signals from slices taken from specimen 5ER of Run 13
X axis is time, ms; Y axis is signal amplitude
Data for the heartwood runs follows
17
Detailed drying runs 6 & 7: radiata pine heartwood
SWW Run RH6
0
20
40
60
80
100
120
140
160
1:00 2:00 3:00 4:00 5:00
Drying Time, hrs
Tem
pera
ture
, C
0
5
10
15
20
25
30
35
40
MC
%
DBT WBT Stack AvMC Specimen AvMC
SWW Run RH7
0
20
40
60
80
100
120
140
160
1:00 2:00 3:00 4:00 5:00 6:00
Drying Time, hrs
Tem
pera
ture
, C
0
5
10
15
20
25
30
35
40
MC
%
DBT WBT Stack AvMC Specimen AvMC
(a) Dryer conditions for Run 6 (b) Dryer conditions for Run 7
SWW Run RH6 Air & Wood Temperature
0
20
40
60
80
100
120
140
160
0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00
Drying Time, hrs
Te
mp
era
ture
, C
T in T out T surf T 3mm T 9mm T 15mm T 21mm T - 9mm
SWW Run RH7 Air & Wood Temperature
0
20
40
60
80
100
120
140
160
0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00
Drying Time, hrs
Te
mp
era
ture
, C
T in T out T surf T 3mm T 9mm T 15mm T 21mm T - 9mm
(c) Air and wood temp. during Run 6 (d) Air and wood temp. during Run 7
Figure 11 Drying plots for Run 6 and Run 7
For Run 6, DBT was held constant for the 4 hour drying period; for Run 7 DBT was ramped
down to 120C after 2 hours and 20 minutes for 5:40 drying time. WBT was reached much
more quickly in Run 7 than in Run 6. For both runs 3 hours steaming was given.
MC Profiles Run Rh6
0
2
4
6
8
10
12
0 1 5 8 9
Slice
MC
, %
RH1Ir RH1Gd RH1Gr RH1Cr RH1Fr
MC Profiles Run Rh7
0
2
4
6
8
10
12
0 1 5 8 9
Slice
MC
, %
RH1Hd RH1Hr RH1Ed RH1Er RH1Dr
(a) MC profiles for Run 6 (b) MC profiles for Run 7
Figure 12 Profiles of moisture content through the thickness of specimens, generally radial, determined by oven drying, for Run 6 and Run 7.
Slices 0, 1, 8 & 9 are 6mm thick, slice 0 from the outer face and slice 9 from the inner face
(near pith). Labels ending d = at the end of drying; r = after steam reconditioning and cooling
overnight.
Figure 12 shows that moisture content is more uniform through the thickness after steaming.
18
Run 6 NMR measurements
0
1
2
3
4
5
6
7
8
9
10
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9
Slice
Am
plitu
de
Rh1IR* Rh1GD Rh1GR Rh1CR Rh1FR
Run 6 NMR measurements
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9
Slice
1/T
2 m
s-1
Rh1IR* Rh1GD Rh1GR Rh1CR Rh1FR
Run 7 NMR measurements
0
2
4
6
8
10
12
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9
Slice
Am
pli
tu
de
Rh1HD* Rh1HR* Rh1ED Rh1ER Rh1DR
Run 7 NMR measurements
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9
Slice1
/T2
m
s-1
Rh1HD* Rh1HR* Rh1ED Rh1ER Rh1DR
(a) NMR profiles for Run 6 (b) NMR profiles for Run 7
Figure 13 Low field MOUSE NMR measurements on slices from cores through the thickness
of specimens, generally radial, for Run 6 and Run 7.
Slices 0, 1, 8 & 9 are 5mm thick (sawn at 6mm spacing).
Comparison of Figure 12 and Figure 13 shows that amplitude generally mirrors the moisture
content determined by oven drying.
Steaming results in more mobile water near the wood surfaces, indicated by the elevated 1/T2
in surface slices.
MC Run 6
0
5
10
15
20
25
30
35
G D F T3 12% 17% 5% 12%
Condition
MC
, %
Rh1I Rh1G Rh1F Rh1C
MC Run 7
0
5
10
15
20
25
30
35
G D F T3 12% 17% 5% 12%
Condition
MC
, %
Rh1H Rh1E Rh1D
(a) MC records for Run 6 (b) MC records for Run 7
Figure 14 Average specimen moisture content of specimens of Run 6 and Run 7 during drying
and later environmental cycling.
G = Green; D = Dry; F = final (Reconditioned and cooled or cooled); T3 = Condition before humidity cycling; 12% = after 1 week at 12% EMC; 17% = after 1 week at 17% EMC; 5% = after 1 week at 5% EMC; 12% = after 1 week at 12% EMC;
19
Twist Run 6
-5.5
-5
-4.5
-4
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
G D F T3 12% 17% 5% 12%
Condition
Tw
ist,
deg
rees
Rh1I Restrained Rh1G Weighed Rh1F Rh1C T/Cs
Twist Run 7
-5.5
-5
-4.5
-4
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
G D F T3 12% 17% 5% 12%
Condition
Tw
ist,
deg
rees
Rh1H Restrained Rh1E Weighed Rh1D T/Cs
(a) Twist records for Run 6 (b) Twist records for Run 7
Figure 15 Twist of specimens of Run 6 and Run 7 during drying and later environmental
cycling.
G = Green; D = Dry; F = final (Reconditioned and cooled or cooled); T3 = Condition before humidity cycling; 12% = after 1 week at 12% EMC; 17% = after 1 week at 17% EMC; 5% = after 1 week at 5% EMC; 12% = after 1 week at 12% EMC;
Effect of drying conditions and restraint
• The amount of twist during drying varied between specimens. As can be seen in the
photos below, the specimens with the greatest twist, Rh1C and D has pith at one face and
similar knots. Specimen Rh1G twisted much more than E, possibly because it included a
loop of pith.
• Specimen Rh1H increased in twist by almost 50% over the cycling whereas Rh1I did not.
Rh1H had slightly lower surface moisture content after drying and increased in mass a
little more up to the 17% condition. This would be expected to have reduced twist.
• All other specimens showed little change in twist over the cycling, showing no difference
between the two runs.
• Comparing the specimens restrained against twist, I and H, with the most closely
matching unrestrained specimens,Rh1E and F, show no apparent effect of the restraint.
Figure 16 Specimens of Run 6 and Run 7 after tests with ends trimmed. Specimens are in a
sequence A, B…I, cut from Radiata Pine heartwood Board 1
20
Detailed drying run 15 – radiata pine near-pith sapwood
For Run 15 kiln temperature ramped down in two stages and no steam reconditioning was
used (Figure 17).
SWW Run Rsh15
0
20
40
60
80
100
120
140
160
0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00
Drying Time, hrs
Te
mp
era
ture
, C
0
10
20
30
40
50
60
70
80
MC
%
DBT WBT Corr. Stack AvMC Specimen AvMC
SWW Run Rsh15 Air & Wood Temperature
0
20
40
60
80
100
120
140
160
0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00
Drying Time, hrs
Te
mp
era
ture
, C
T in T out T surf T 3mm T 15mm T 21mm T -9mm
(a) Dryer conditions for Run 15 (b) Air and wood temperatures during Run 15
Figure 17 Drying records for Run 15
MC Profiles Run Rsh15
0.0
5.0
10.0
15.0
20.0
25.0
0 1 5 8 9
Slice
MC
, %
Rsh3Df Rsh3Gf Rsh3Ff Rsh3Cf
Figure 18 Profiles of moisture content from sliced cores through the thickness of specimens,
generally radial, determined by oven drying, for Run 15.
Slices 0, 1, 8 & 9 are 6mm thick, slice 0 from the outer face and slice 9 from the inner face (near pith). Labels ending d = at the end of drying; r = after steam reconditioning and cooling overnight; f = final where no reconditioning applied
21
g
Run 15 Restrained vs Non-restrained
0
2
4
6
8
10
12
14
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9
Slice
Am
plitu
de
Rsh3DF* Rsh3CF
Run 15 Restrained vs Non-restrained
0
2
4
6
8
10
12
14
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9
Slice
Am
plitu
de
Rsh3DF* Rsh3CF Rsh3DF* 12% Rsh3CF 12%
Run 15 Restrained vs Non-restrained
0
1
1
2
2
3
3
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9
Slice1/T
2 -
m
s-1
Rsh3DF* Rsh3CF Rsh3DF* - 12% Rsh3CF - 12%
Run 15 Restrained vs Non-restrained
0
1
1
2
2
3
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9
Slice
1/T
2 -
m
s-1
Rsh3DF* Rsh3CF
Figure 19 Low field MOUSE NMR measurements on slices from cores through the thickness
of specimens, generally radial, for Run 15.
Slices 0, 1, 8 & 9 are 5mm thick (sawn at 6mm spacing).
• The moisture content profiles from Run 15 show that ramping down without steaming
after drying resulted in significant gradients; final moisture contents were high, however.
MC Run 15
0
10
20
30
40
50
60
70
80
G D F T3 12% 17% 5% 12%
Condition
MC
, %
Rsh3D Rsh3B Rsh3C
MC Run 15
0
10
20
30
40
50
60
70
80
G D F T3 12% 17% 5% 12%
Condition
MC
, %
Rsh3G Rsh3E Rsh3F
Twist Run 15
-1
-0.5
0
0.5
1
1.5
2
2.5
G D F T3 12% 17% 5% 12%
Condition
Tw
ist,
deg
rees
Rsh3D Restrained Rsh3B Cored Rsh3C T/Cs
Twist Run 15
-0.5
0
0.5
1
1.5
2
G D F T3 12% 17% 5% 12%
Condition
Tw
ist,
deg
rees
Rsh3G Restrained Rsh3E Cored Rsh3F Weighed
Figure 20 Average specimen moisture content and twist of specimens of Run 15 during
drying and later environmental cycling.
22
• Although most specimens dried further between stages F and T3, twist did not change to
any extent.
• Only Specimen Rsh3D increased significantly in twist during cycling.
Figure 21 Specimens of Run 15 after drying and cycling.
Note: Ends trimmed to show grain patterns.
23
Detailed drying runs 16 & 17: radiata pine heartwood
For Run 16 kiln conditions were ramped down in two stages and no steam reconditioning was
used; Run 17 followed the full Radiata test schedule.
SWW Run Rh16
0
20
40
60
80
100
120
140
160
0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00
Drying Time, hrs
Tem
pera
ture
, C
0
5
10
15
20
25
30
35
40
MC
%
DBT WBT Corr. Stack MC Specimen AvMC
SWW Run Rh17
0
20
40
60
80
100
120
140
160
0:00 1:00 2:00 3:00 4:00 5:00
Drying Time, hrs
Te
mp
era
ture
, C
0
5
10
15
20
25
30
35
40
MC
, %
DBT WBT Corr. Stack MC Specimen AvMC
(a) Dryer conditions for Run 16 (b) Dryer conditions for Run 17
SWW Run Rh16 Air & Wood Temperature
0
20
40
60
80
100
120
140
160
0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00
Drying Time, hrs
Tem
pera
ture
, C
T in T out T surf T 3mm T 9mm T 15mm T 21mm T -9mm
SWW Run Rh17 Air & Wood Temperature
0
20
40
60
80
100
120
140
160
0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00
Drying Time, hrs
Tem
pera
ture
, C
T in T out T surf T 3mm T 15mm T 21mm T -9mm
(c) Air and wood temperatures during Run 16 (d) Air and wood temperatures during Run 17
Figure 22 Drying records for Run 16 and Run 17
MC Profiles Run Rh16
0
5
10
15
0 1 5 8 9
Slice
MC
, %
Rh2Ff Rh2Af Rh6Cf Rh6Gf
MC Profiles Run Rh17
0
5
10
15
20
0 1 5 8 9
Slice
MC
, %
Rh6Dd Rh6Dr Rh6Hr
MC Profiles Run Rh17
0
5
10
15
20
0 1 5 8 9
Slice
MC
, %
Rh2GD Rh2Gr Rh2Bd Rh2Br
(a) MC profiles for Run 16 (b) MC profiles for Run 17
Figure 23 Profiles of moisture content through the thickness of specimens, generally radial,
determined by oven drying, for Run 16 and Run 17.
Slices 0, 1, 8 & 9 are 6mm thick, slice 0 from the outer face and slice 9 from the inner face (near pith). Labels ending d = at the end of drying; r = after steam reconditioning and cooling overnight; f = final where no reconditioning applied.
24
Run 16 Restrained vs Non-restrained
0
2
4
6
8
10
Slice 0 Slice 1 Slice 7/5 Slice 8 Slice 9
Slice number
Am
pli
tud
eRh6GR Rh6CR*
Run 16 Restrained vs Non-restrained
0
2
4
6
8
10
Slice 0 Slice 1 Slice 7/5 Slice 8 Slice 9
Slice number
Am
pli
tud
e
Rh2AR Rh2FR*
Run 16 Restrained vs Non-restrained
0
1
2
3
4
Slice 0 Slice 1 Slice 7/5 Slice 8 Slice 9
Slice number
1/T
2 -
ms
-1
Rh6GR Rh6CR*
Run 16 Restrained vs Non-restrained
0
1
2
3
4
5
6
Slice 0 Slice 1 Slice 7/5 Slice 8 Slice 9
Slice number
1/T
2 -
ms
-1
Rh2AR Rh2FR*
(a) NMR measurements for Run 16
Run 17 Restrained vs Non-restrained
0
2
4
6
8
10
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9
Slice
Am
plitu
de
Rh6DR* Rh6HR Rh6DD*
Run 17 Restrained vs Non-restrained
0
1
2
3
4
5
6
7
8
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9
Slice
Am
plitu
de
Rh2GR* Rh2BR Rh2GD* Rh2BD
Run 17 Restrained vs Non-restrained
0.00
1.00
2.00
3.00
4.00
5.00
Slice 0 Slice 1 Slice 7/5 Slice 8 Slice 9
Slice
1/T
2 m
s-1
Rh2GR* Rh2BR Rh2GD* Rh2BD
Run 17 Restrained vs Non-restrained
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9
Slice
1/T
2 m
s-1
Rh6DR* Rh6HR Rh6DD*
(b) NMR measurements for Run 17
Figure 24 Low field MOUSE NMR measurements on slices from cores through the thickness
of specimens, generally radial, for Run 16 and Run 17.
Slices 0, 1, 8 & 9 are 5mm thick (sawn at 6mm spacing).
• Run 17 shows that moisture content becomes more uniform through the thickness from
steaming.
• Steaming results in more mobile water near the wood surfaces, indicated by the elevated
1/T2 in surface slices, slices 0 and 9.
• The moisture content profiles from Run 16 were not excessive; ramping down can
minimise gradients.
25
MC Run 16
0
5
10
15
20
25
30
35
40
G D F T3 12% 17% 5% 12%
Condition
MC
, %
Rh6C Rh6E Rh6G
MC Run 17
0
5
10
15
20
25
30
35
40
G D F T3 12% 17% 5% 12%
Condition
MC
, %
Rh6D Rh6F Rh6H
MC Run 16
0
5
10
15
20
25
30
35
40
G D F T3 12% 17% 5% 12%
Condition
MC
, %
Rh2F Rh2D Rh2A
MC Run 17
0
5
10
15
20
25
30
35
40
G D F T3 12% 17% 5% 12%
Condition
MC
, %
Rh2G Rh2E Rh2B
Figure 25 Average specimen moisture content of specimens of Run 16 and Run 17 during
drying and later environmental cycling
Twist Run 16
-4.0
-3.5
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
G D F T3 12% 17% 5% 12%
Condition
Tw
ist,
deg
rees/4
50m
m
Rh6C Restrained Rh6E Cored Rh6G T/Cs
Twist Run 17
-4.0
-3.5
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
G D F T3 12% 17% 5% 12%
Condition
Tw
ist,
deg
rees/4
50m
m
Rh6D Restrained Rh6F Cored Rh6H T/Cs
Twist Run 16
-4.0
-3.5
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
G D F T3 12% 17% 5% 12%
Condition
Tw
ist,
deg
rees/4
50m
m
Rh2F Restrained Rh2D Cored Rh2A Weighed
Twist Run 17
-4.0
-3.5
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
G D F T3 12% 17% 5% 12%
Condition
Tw
ist,
deg
rees/4
50m
m
Rh2G Restrained Rh2E Cored Rh2B Weighed
Figure 26 Twist of specimens of Run 16 and Run 17 during drying and later environmental
cycling
26
• Moisture content estimates were particularly difficult for cored specimens; the actual MC
of Rh6E and Rh2D were higher than plotted. The environment in the laboratory is close
to 10% EMC.
Effect of drying conditions and restraint
• Twist changes generally followed moisture changes with environmental changes.
• The restrained specimens in both runs showed increased twist over the cycling process.
• There is apparently more distortion in Run 17 specimens, but this is not consistent and
may be due to variation in wood characteristics along the boards.
Figure 27 Specimens of Run 16 and Run 17 after tests with ends trimmed.
Specimens are in a sequence A, B…I, cut from Radiata Pine heartwood Boards 2 and 6
27
Detailed drying test runs 10, 11 and 12: slash pine heartwood
Runs 10 and 11 differ only in the shorter steaming time for Run 11; Run 12 had no steaming after
two stages of ramp-down of temperature, and with humidity increased for the final stage (Figure 28).
SWW Run Sh10
0
20
40
60
80
100
120
140
160
0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00
Drying time, hrs
Te
mp
era
ture
, C
0
10
20
30
40
50
60
MC
%
DBT WBT Stack AvMC Specimen AvMC
SWW Run Sh11
0
20
40
60
80
100
120
140
160
1:00 2:00 3:00 4:00 5:00 6:00 7:00
Drying Time, hrs
Te
mp
era
ture
, C
0
10
20
30
40
50
60
70
MC
%
DBT WBT Stack AvMC Specimen AvMC
SWW Run SR12
0
20
40
60
80
100
120
140
160
1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00
Drying Time, hrs
Te
mp
era
ture
, C
0
10
20
30
40
50
60
70
80
MC
%
DBT WBT Stack AvMC Specimen AvMC
Radiata heartwood
specimens out
(a) Dryer conditions for Run 10 (b) Dryer conditions for Run 11 (c) Dryer conditions for Run 12
SWW Run Sh10 Air & Wood Temperature
0
20
40
60
80
100
120
140
160
0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00
Drying Time, Hrs
Tem
pera
ture
, C
T in T out T surf T 3mm T 9mm T 15mm T 21mm T - 9mm
SWW Run Sh11 Air & Wood Temperature
0
20
40
60
80
100
120
140
160
0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00
Drying Time, hrs
Tem
pera
ture
, C
T in T out T surf T 3mm T 9mm T 15mm T 21mm T -9mm
SWW Run SR12 Air & Wood Temperature
0
20
40
60
80
100
120
140
160
0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00
Drying Time, hrs
Tem
pera
ture
, C
T in T out T 3mm T 9mm T 15mm T 21mm T -9mm
(d) Air and wood temp. for Run 10 (e) Air and wood temp. for Run 11 (f) Air and wood temp. for Run 12
Figure 28 Drying records for Run 10, Run 11 and Run 12
Final MC levels and profiles were similar after all three runs
(a) Moisture profiles for Run 10 (b) Moisture profiles for Run 11 (c) Moisture profiles for Run 12
Figure 29).
MC profiles Run Sh10
0
5
10
15
20
0 1 5 8 9Slice
MC
, %
Sh3Cd Sh3Cr Sh3Fr
MC profiles Run Sh11
0
5
10
15
20
0 1 5 8 9Slice
MC
, %
Sh3Bd Sh3Br Sh3Gr
MC Profiles Run Sh12
0
5
10
15
20
0 1 5 8 9Slice
MC
, %
Sh3Df Sh3Ef
(a) Moisture profiles for Run 10 (b) Moisture profiles for Run 11 (c) Moisture profiles for Run 12
Figure 29 MC profiles through the thickness of specimens from Board 3, by oven drying, for
Runs 10, 11 & 12
Run 10 NMR measurements
0
2
4
6
8
10
12
14
16
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9
Slice
Am
plit
ud
e
Sh3CD* Sh3CR* Sh3FR
Run 10 NMR measurements
0
1
2
3
4
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9
Slice
1/T
2 m
s-1
Sh3CD* Sh3CR* Sh3FR
Run 11 NMR measurements
0
2
4
6
8
10
12
14
16
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9Slice
Am
plit
ud
e
Sh3BD* Sh3BR* Sh3GR
Run 11 NMR measurements
0
1
2
3
4
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9
Slice
1/T
2 m
s-1
Sh3BD* Sh3BR* Sh3GR
Run 12 NMR measurements
0
2
4
6
8
10
12
14
16
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9
Slice
Am
plitu
de
Sh3DF* Sh3EF
Run 12 NMR measurements
0
1
2
3
4
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9Slice
1/T
2 m
s-1
Sh3DF* Sh3EF
(a) NMR profiles for Run 10 (b) NMR profiles for Run 11 (c) NMR profiles for Run 12
Figure 30 Low field MOUSE NMR measurements on slices through the thickness of
specimens from Board 3, for Runs 10, 11 & 12
28
MC profiles Run Sh10
0
5
10
15
20
0 1 5 8 9Slice
MC
, %
Sh4Cd Sh4Cr Sh4Ed Sh4Er
MC profiles Run Sh11
0
5
10
15
20
0 1 5 8 9Slice
MC
, %
Sh4Dd Sh4Dr Sh4Fd Sh4Fr
MC Profiles Run Sh12
0
5
10
15
20
0 1 5 8 9Slice
MC
, %
Sh4Bf Sh4Af
(a) Moisture profiles for Run 10 (b) Moisture profiles for Run 11 (c) Moisture profiles for Run 12
Figure 31 MC profiles through the thickness of specimens from Board 4, by oven drying, for
Runs 10, 11 & 12
Run 10 NMR measurements
0
2
4
6
8
10
12
14
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9
Slice
Am
plitu
de
Sh4CD* Sh4CR* Sh4ED Sh4ER
Run 10 NMR measurements
0
1
2
3
4
5
6
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9
Slice
1/T
2,
ms-1
Sh4CD* Sh4CR* Sh4ED Sh4ER
Run 11 NMR measurements
0
2
4
6
8
10
12
14
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9
Slice
Am
plit
ud
e
Sh4DD* Sh4DR* Sh4FD Sh4FR
Run 11 NMR measurements
0
1
2
3
4
5
6
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9
Slice
1/T
2,
ms-1
Sh4DD* Sh4DR* Sh4FD Sh4FR
Run 12 NMR measurements
0
2
4
6
8
10
12
14
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9Slice
Am
plit
ud
e
Sh4BF* Sh4AF
Run 12 NMR measurements
0
1
2
3
4
5
6
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9Slice
1/T
2,
ms-1
Sh4BF* Sh4AF
(a) NMR profiles for Run 10 (b) NMR profiles for Run 11 (c) NMR profiles for Run 12
Figure 32 Low field MOUSE NMR measurements on slices through the thickness of
specimens from Board 4 for Runs 10, 11 & 12
Final MC levels and profiles for matched specimens from both boards 3 and 4 were similar
after all three runs.
MC Run 10
0
5
10
15
20
25
30
35
40
45
50
G D F T3 12% 17% 5% 12%Condition
MC
, %
Sh3C Sh3A Sh3F
MC Run 11
0
5
10
15
20
25
30
35
40
45
50
G D F T3 12% 17% 5% 12%
Condition
MC
, %
Sh3B Sh3H Sh3G
MC Run 12
0
5
10
15
20
25
30
35
40
45
50
G F T3 12% 17% 5% 12%
Condition
MC
, %
Sh3D Sh3E
(a) Av. Spec’n MC for Run 10 (b) Av. Spec’n MC for Run 11 (c) Av. Spec’n MC for Run 12
Figure 33 Average MC of specimens from Board 3, for Runs 10, 11 & 12
29
Twist Run 10
-4.5
-4.0
-3.5
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
G D F T3 12% 17% 5% 12%
Condition
Tw
ist, d
egre
es
Sh3C Restrained Sh3A Cored Sh3F T/Cs
Twist Run 11
-4.5
-4.0
-3.5
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
G D F T3 12% 17% 5% 12%
Condition
Tw
ist,
de
gre
es
Sh3B Restrained Sh3H Cored Sh3G T/Cs
Twist Run 12
-4.5
-4.0
-3.5
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
G F T3 12% 17% 5% 12%Condition
Tw
ist, d
egre
es
Sh3D Restrained Sh3E Cored
(a) Twist for Run 10 (b) Twist for Run 11 (c) Twist for Run 12
Figure 34 Twist of specimens from Board 3 for Runs 10, 11 & 12
• Specimens in Runs 10 & 11 lost moisture after drying (F > T3) and twist increased.
• Specimens in Run 10 increased twist during cycling (T3 > 12%) more than those in Run
11 which had less steaming although average MC returned to almost the same values.
Specimens in Run 12 without steaming twisted less during cycling.
• Restrained specimens seemed slightly more stable with less steaming.
MC Run 10
0
10
20
30
40
50
60
70
80
G D F T3 12% 17% 5% 12%
Condition
MC
, %
Sh4C Sh4G Sh4E
MC Run 11
0
10
20
30
40
50
60
70
80
G D F T3 12% 17% 5% 12%
Condition
MC
, %
Sh4D Sh4H Sh4F
MC Run 12
0
10
20
30
40
50
60
70
80
G F T3 12% 17% 5% 12%Condition
MC
, %
Sh4B Sh4A
(a) Av. Spec’n MC for Run 10 (b) Av. Spec’n MC for Run 11 (c) Av. Spec’n MC for Run 12
Figure 35 Average MC of specimens from Board 4, for Runs 10, 11 & 12
Twist Run 10
-4.5
-4.0
-3.5
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
G D F T3 12% 17% 5% 12%
Condition
Tw
ist, d
eg
ree
s
Sh4C Restrained Sh4G Cored Sh4E Weighed
Twist Run 11
-4.5
-4.0
-3.5
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
G D F T3 12% 17% 5% 12%Condition
Tw
ist,
de
gre
es
Sh4D Restrained Sh4H Cored Sh4F Weighed
Twist Run 12
-4.5
-4.0
-3.5
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
G F T3 12% 17% 5% 12%Condition
Tw
ist, d
egre
es
Sh4B Restrained Sh4A Weighed
(a) Twist for Run 10 (b) Twist for Run 11 (c) Twist for Run 12
Figure 36 Twist of specimens from Board 4 for Runs 10, 11 & 12
• All specimens maintained stable mass after drying (F to T3), but the restrained specimen
(Sh4C) in Run 10 and several un-restrained specimens increased in twist.
• The restrained specimen (Sh4C) in Run 10 increased in twist during cycling (T3 to 12%).
• Restrained specimens seemed more stable with less steaming (<3 hours), and finished
with less twist than un-restrained specimens.
30
Figure 37 Specimens of Runs 10, 11 & 12 from Board 3 after tests & with ends trimmed
• Specimens B, C and H contained the pith and might be expected to twist more; other
specimens generally had the pith in or near the face.
Figure 38 Specimens of Runs 10, 11 & 12 from Board 4 after tests & with ends trimmed
• All specimens contained the pith and might be expected to twist in similar manner;
generally they did so.
31
Detailed test drying runs 13 and 14: slash pine heartwood
SWW Run Sh13
0
20
40
60
80
100
120
140
160
1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00
Drying Time, hrs
Tem
pera
ture
, C
; M
C%
DBT WBT Stack AvMC Specimen AvMC
SWW Run Rh14
0
20
40
60
80
100
120
140
160
1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00
Drying Time, hrs
Tem
pera
ture
, C
; M
C%
DBT WBT Corr. Stack AvMC Specimen AvMC
(a) Dryer conditions for Run 13 (b) Dryer conditions for Run 14
SWW Run Sh13 Air & Wood Temperature
0
20
40
60
80
100
120
140
160
0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00
Drying Time, hrs
Te
mp
era
ture
, C
T in T out T surf T 3mm T 9mm T 15mm T 21mm T -9mm
SWW Run Sh14 Air & Wood Temperature
0
20
40
60
80
100
120
140
160
0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00
Drying Time, hrs
Te
mp
era
ture
, C
T in T out T surf T 3mm T 9mm T 15mm T 21mm T -9mm
(c) Air and wood temp. during Run 13 (d) Air and wood temp. during Run 14
Figure 39 Drying records for Run 13 and Run 14
For Run 14 temperature was ramped down in two stages and no steam reconditioning was
used; Run 13 followed the Slash test schedule.
MC profiles Run Sh13
0.0
5.0
10.0
15.0
20.0
25.0
0 1 5 8 9
Slice
MC
, %
Sh5Cd Sh5Cr Sh5Ed Sh5Er
MC Profiles Run Sh14
0
5
10
15
20
25
0 1 5 8 9
Slice
MC
, %
Sh5Dd Sh5Dr Sh5Fd Sh5Fr
(a) MC profiles for Run 13 (b) MC profiles for Run 14
Figure 40 Profiles of moisture content from sliced cores through the thickness of specimens
5, generally radial, determined by oven drying, for Run 13 and Run 14
Slices 0, 1, 8 & 9 are 6mm thick, slice 0 from the outer face and slice 9 from the inner face (near pith). Labels ending d = at the end of drying; r = after steam reconditioning and cooling overnight; f = final where no reconditioning applied.
32
Runs 13 NMR measurements
0.0
0.5
1.0
1.5
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9
Slice number
1/T
2 -
ms
-1
Sh5CD* Sh5CR* Sh5ED Sh5ER
Runs 13 NMR measurements
0
2
4
6
8
10
12
14
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9
Slice number
Am
plitu
de
Sh5CD* Sh5CR* Sh5ED Sh5ER
Runs 14 NMR measurements
0
2
4
6
8
10
12
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9
Slice number
Am
plitu
de
Sh5DD* Sh5DR* Sh5FD Sh5FR
Runs 14 NMR measurements
0.0
0.5
1.0
1.5
2.0
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9
Slice number
1/T
2 -
ms
-1
Sh5DD* Sh5DR* Sh5FD Sh5FR
(a) NMR profiles for Run 13 (b) NMR profiles for Run 14
Figure 41 Low field MOUSE NMR measurements on slices from cores through the thickness
of specimens 5, generally radial, for Run 13 and Run 14.
Slices 0, 1, 8 & 9 are 5mm thick (sawn at 6mm spacing).
MC profiles Run Sh13
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
0 1 5 8 9
Slice
MC
, %
Sh6Bd Sh6Br Sh6Dr
MC Profiles Run Sh14
0
2
4
6
8
10
12
14
16
0 1 5 8 9
Slice
MC
, %
Sh6Cd Sh6Cr Sh6Er
(a) Oven-dry MC profiles for Run 13 (b) Oven-dry MC profiles for Run 14
Figure 42 Profiles of moisture content from sliced cores through the thickness of specimens
6, generally radial, determined by oven drying, for Run 13 and Run 14
Slices 0, 1, 8 & 9 are 6mm thick, slice 0 from the outer face and slice 9 from the inner face (near pith). Labels ending d = at the end of drying; r = after steam reconditioning and cooling overnight; f = final where no reconditioning applied.
33
Runs 13 NMR measurements
0
2
4
6
8
10
12
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9
Slice number
Am
plitu
de
Sh6BD* Sh6BR* Sh6DR
Runs 13 NMR measurements
0.0
0.5
1.0
1.5
2.0
2.5
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9
Slice number
1/T
2 -
ms
-1
Sh6BD* Sh6BR* Sh6DR
Runs 14 NMR measurements
0
2
4
6
8
10
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9
Slice number
Am
plitu
de
Sh6CD* Sh6CR* Sh6ER
Runs 14 NMR measurements
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Slice 0 Slice 1 Slice 5/7 Slice 8 Slice 9
Slice number
1/T
2 -
ms-1
Sh6CD* Sh6CR* Sh6ER
(a) NMR profiles for Run 13 (b) NMR profiles for Run 14
Figure 43 Low field MOUSE NMR measurements on slices from cores through the thickness
of specimens 6, generally radial, for Run 13 and Run 14.
Slices 0, 1, 8 & 9 are 5mm thick (sawn at 6mm spacing).
MC Run 13
0
10
20
30
40
50
60
70
80
90
100
110
120
130
G D F T3 12% 17% 5% 12%
Condition
MC
, %
Sh5C Sh5A Sh5E
MC Run 14
0
10
20
30
40
50
60
70
80
90
100
110
120
130
G D F T3 12% 17% 5% 12%Condition
MC
, %
Sh5D Sh5B Sh5F
(a) Av. Specimen MC for Run 13 (b) Av. Specimen MC for Run 14
Figure 44 Average MC of specimens from board 5 in Run 13 and Run 14 during drying and
later environmental cycling.
Twist Run 13
-3
-2.5
-2
-1.5
-1
-0.5
0
0.5
G D F T3 12% 17% 5% 12%
Condition
Tw
ist,
deg
rees
Sh5C Restrained Sh5A Cored Sh5E Weighed
Twist Run 14
-3
-2.5
-2
-1.5
-1
-0.5
0
0.5
G D F T3 12% 17% 5% 12%
Condition
Tw
ist,
de
gre
es
Sh5D Restrained Sh5B Cored Sh5F Weighed
(a) Specimen twist for Run 13 (b) Specimen twist for Run 14
Figure 45 Twist of specimens from board 5 in Run 13 and Run 14 during drying and later
environmental cycling.
34
MC Run 13
0
10
20
30
40
50
60
70
80
90
100
110
120
130
G D F T3 12% 17% 5% 12%Condition
MC
, %
Sh6B Sh6F Sh6D
MC Run 14
0
10
20
30
40
50
60
70
80
90
100
110
120
130
G D F T3 12% 17% 5% 12%
Condition
MC
, %
Sh6C Sh6G Sh6E
(a) Av. Specimen MC for Run 13 (b) Av. Specimen MC for Run 14
Figure 46 Average MC of specimens from board 6 in Run 13 and Run 14 during drying and
later environmental cycling
Twist Run 13
-3
-2.5
-2
-1.5
-1
-0.5
0
0.5
G D F T3 12% 17% 5% 12%
Condition
Tw
ist,
deg
rees
Sh6B Restrained Sh6F Cored Sh6D T/Cs
Twist Run 14
-3
-2.5
-2
-1.5
-1
-0.5
0
0.5
G D F T3 12% 17% 5% 12%
Condition
Tw
ist,
de
gre
es
Sh6C Restrained Sh6G Cored Sh6E T/Cs
(a) Specimen twist for Run 13 (b) Specimen twist for Run 14
Figure 47 Twist of specimens from board 6 in Run 13 and Run 14 during drying and later
environmental cycling
Figure 48 Specimens of Run 13 and Run 14 after tests with ends trimmed.
Specimens are in a sequence A, B…I, cut from Slash Pine heartwood Boards 5 and 6
35
NMR measurements and analysis
NMR Surface Analyser
The NMR MOUSE (MObile Universal Surface Explorer) is a novel NMR device designed for
relaxation measurements on surfaces of arbitrary shaped samples. The design of the mobile
probe with the permanent magnets and transmitter and receiver coil system allows measurements
of the proton NMR signals (15.9MHz) from various samples.
The NMR surface analyzer, MOUSE, detects the signal from water via the special imaging
sequence, spin echo, which gives the NMR signal predominantly of water close to the surface.
The observation volume is about 1mm in depth over a 0.5cm2. The observed signal is detected
only from the moisture with a sufficient mobility or a long enough relaxation time, but not the
signal from the protons of solid organic molecules, whose relaxation time is in general shorter.
The data are presented as probability 1/T2 for water to be bound and the amplitude reflects the
overall number of protons (water molecules) detected. The scale is given in relative terms and is
proportional to total moisture content.
High field Solid-state NMR spectroscopy
The solid wood samples were investigated by solid-state proton NMR spectroscopy - Varian
Unity Plus 300 MHz NMR spectrometer. The method used was the proton magic angle spinning
NMR spectroscopy, which in a typical spectrum of a wood sample would normally give the
broad water resonance band (bound water) and small but sharp signals from the organic
molecules. By using a standard spin-echo pulse sequence (CPMG – sequence) we found that the
water signal disappears faster with the increased spin-echo time than the organic signal. The
standard CPMG sequence was used in order to determine the relaxation time T2 of these two
components, and the inversion recovery sequence, 180°-90°, was used to determine the spin
lattice relaxation time T1.
Model for wood drying NMR parameters
The general concept reported in 1999 (PN008.96 Softwood Drying Research Project) for NMR
signal of water in wood was adopted as follows:
“Studies of T2 relaxation of water suggest:
essentially unbound water in cell lumens,
water associated with walls and smaller reservoirs – droplets & cracks
tightly bound cell wall water.
Short T2 ranges from 0.2 ms to 1 ms, medium T2 ranges from 5 ms to 40 ms, and long T2
ranges from 50 ms to 800 ms.”
In the current investigation of the drying process and moisture effects on wood structural
changes this model and water categories were investigated in detail in order to establish the
specific moisture deformation correlations where previous data was not conclusive. In such a
study we found it essential to investigate first the limitations of the above definition and to
suggest a more comprehensive description of the drying process yielding potentially better
control of this process for the industry. The investigation was conducted in two directions: first
the definitions and physical differentiation (especially by NMR parameters) between the
proposed categories of water in wood, and second the more comprehensive analysis of NMR
spectral data in the view of the above definitions.
1) The general definition of water in the hydrophilic polymers is correctly stated in the previous
report and it can be found in general literature on this subject where water content, Wc, is a sum
36
of non-freezing water (structural water or tightly bound to cell walls), Wnf, freezing bound water
or water associated with walls and smaller reservoirs, Wfb, and free water or essentially unbound
water in cell lumens, Wf.10,11
The relationship between these categories was studied closely and
the characteristic finding by H & T Hatakeyama can be graphically summarised as shown here11
.
Figure 49 from Hatakeyama11
This diagram indicates that in the dry wood samples where MC is around 10% one can expect
mainly bound water (freezing and non-freezing). Such interpretation was given by R Guzenda et
al.3 at the 12th International symposium on non-destructive testing of wood, Hungary 2000, who
concluded that lost of free water in the drying process (moisture going below the fibre saturation
point) is evident from NMR data where the relaxation spin-lattice time T1, which reveals two
components in green wood, becomes a single component parameter below the fibre saturation
point. In our investigation we quickly confirmed the above conclusion (milestone report) but
investigating further the spin-spin relaxation time T2 we also expected to see some difference
between the bound waters (freezing and non-freezing), especially in correlation to the drying
regime and to conditioning after drying. But again as in the previous project report we reached a
similar conclusion:
“There are large and inconsistent variations in the proportions of water in each bonding state for
different samples inconsistent with respect to other parameters or drying conditions. Lesser
variability was observed after further conditioning of the wood and proportion of bound water
was higher than for freshly dried samples - moisture content after drying exhibited large
variation from matched samples, masking any consistent relationship”.
This fact by itself was leading us to the assumption that in the proton NMR spectra we are
observing too large variations due to the additional species such as resin and other wood
components, which possess the protons in their molecular structure (as already indicated in the
previous milestone report). The results of a detailed investigation have now been incorporated
into the improved model for NMR data interpretation as outlined below.
2) The assumption that the proton NMR signal analysed in the wood is mainly coming from water
in different states of interaction with the solid matrix needs to be revised. The water definition
10
S.L. Maunu, NMR studies of wood and wood products, Progress in Nuclear Magnetic Resonance Spectroscopy, 40 (2002) 151-174 11
H. Hatakeyama and T. Hatakeyama, Interaction between water and hydrophilic polymers, Thermometrica Acta, 308 (1998) 3-22
37
statement in the first report assumed that the whole proton NMR signal, as analysed by the T2
measurements using FID (free induction decay) method, is coming from water in the wood. This
simplified picture is not always correct because the protons from other components of wood such
as cellulose, hemicellulose and lignin (major ones) may appear in the signal as well, especially
when their molecular mobility is comparable to the mobility of water molecules. Proton NMR
polarisation, which was investigated by NMR methods in wood samples, is therefore from both
water molecules and organic components (cellulose, hemicellulose and lignin). These protons can
be detected as separate species but they also interact at the interfaces yielding the additional NMR
polarisation exchange, which further changes the proton NMR signal.
The dried sample 2AR (Run 16) is used here as an example where the difference between two
slices is evident in the signal obtained by the NMR MOUSE instrument in around 21/2 minutes.
The dried wood samples all have a short T2 and only one T1 component but in these two spectra,
Figure 50 below, it is obvious that we have a longer and shorter component in signal decay. The
MOUSE detection utilizes the spin-echo sequence at a certain time where all the signal from
materials with the shorter T2 component (for solid wood) is already gone (relaxed) and only the
mobile part of the organic components can be detected. It was assumed that the longer T2
component belongs to the water molecules alone, but it is evident from our investigation that
such organic components do exist and they are likely to be organic extractable compounds or
mobile parts of cellulose/hemicellulose polymers.
(a)
20
15
10
5
0
Sig
na
l
160140120100806040200
Time(ms)
Run 16 sample 2AR slice 5
(b)
20
15
10
5
0
Sig
na
l
30252015105
Time(ms)
Run 16 sample 2AR slice 8
Figure 50 The NMR signal, MOUSE, from two slices (a) with pith and (b) without.
In order to separate different molecular species in the proton NMR spectrum one needs to use the
high field solid-state NMR methods. Fast magic angle spinning is one of them12,13
and it can
differentiate the resonances of water and other species. These methods are most effective when
the magnetic environment of protons is sufficiently different (chemical shift difference) and they
are not fast exchanging NMR polarisation. Recent work of A.M. Gill and co-workers13
shows
that proton high-resolution magic angle spinning spectra of natural polymeric materials like
wood yield sufficient information to identify the proton resonances in these materials. Their
conclusion, spectral assignment, is presented in Table 3 below:
12
R. Guzenda, W.Olek, H.M. Baranowska, Identification of free and bound water content in wood by means of NMR relaxometry, 12
th International symposium on non-destructuve testing of wood (2000),
Sopron, Hungary 13
A.M. Gill, M.H. Lopes, C. Pascoal Neto, and J. Rocha, Very high-resolution 1H MAS NMRE spectra of
natural polymeric material, Solid State Nuclear Magnetic Resonance, 15 (1999) 59-67
38
Table 3 From Gill et al13
Their spectral interpretation and assignment did help us to compare our solid-state NMR spectra
with theirs and to identify the additional species detected by NMR method in the proton
spectrum. 1H MAS NMR spectra of lignin, cellulose and hemicellulose, as shown below, show
the different spectral appearance of these species13
.
Figure 51 From Gill et al13
39
Solid-state NMR analysis
The carbon CPMAS (cross-polarisation magic angle spinning) spectrum of wood, sample 1BR from
Radiata Run RH7, is presented in Figure 52. This spectrum is a characteristic spectrum of wood
samples revealing cellulose, hemicellulose and lignin components.1,5 The central resonances from
50 ppm to 110 ppm are clearly from cellulose, crystalline and amorphous, as well as hemicellulose.
The broad resonance peaks from 110 ppm to 160 ppm are mainly from the lignin aromatic carbons.
The standard proton MAS (magic angle spinning) spectrum, Figure 52, reveals mainly a large
and broad water signal – bound water (3 ppm to 8ppm) – and small additional peaks due to the
organics components in wood (probably cellulose, hemicellulose, and lignin). These resonances,
sharp peaks at 1.2 ppm and 1.6 ppm, and smaller at 1.9 ppm and 2.3 ppm, in comparison with the
spectra from reference 13 are most likely due to the cellulose/hemicellulose species.
In order to further identify these resonances in the proton MAS spectrum it is proper to recall the
general wood structure model. The general model for the cell walls in the wood predicts that it is
comprised of cellulose polymers, which form microfibrils, that are bound together by
hemicellulose. A low, or reduced, hemicellulose content has been associated with the high
dimensional stability of wood structure. It may then be postulated that hemicellulose in particular
in the hydration state (plasticised by water) will be the main contributor in relation to the wood
distortion. Therefore, if in our 1H NMR MAS spectra we are able to observe and quantify the
hemicellulose that is hydrated (in physical contact with the bound water), we may have the
detection tool to estimate the potential distortion in the wood after drying.
The 1H MAS NMR spectra were obtained at 300MHz and a magic angle spinning speed of
around 9000 Hz. According to the literature13
only very high spinning speeds can provide the
sufficient line narrowing (30 kHz) for such resolution. It may be quickly assumed that we are
observing a broad line of water and narrow lines from cellulose due to the fact that the bound
water and hemicellulose interact (fast exchanging the magnetic polarisation) due to direct
contact. Therefore further relaxation studies of T1 and T2 for both species is required to confirm
their contact.
The spin-lattice relaxation time, T1, determined for the water proton peak, resonance at 4.8 ppm, and
the peak at 1.6 ppm (-CH2- in cellulose and hemicellulose) are nearly the same at 300 MHz; 324 ms
and 334 ms respectively. This may be interpreted as confirmation that water and ‘hemicellulose’
ends are closely associated – exchanging the magnetic polarisation in the NMR time scale.
The spin-spin relaxation time, T2, measured by the spin echo technique using a CPMG pulse
sequence, is on the other hand, quite different; around 1ms for water and 20 ms for cellulose.
This indicates that the bound water is in fast exchanging rate between immobile state (“non-
freezing” - attached to cell wall surface) and semi-free state in the pores (”freezing bound”),
whilst the organic protons (cellulose, hemicellulose and lignin) are different from the water
relaxation time. The solid crystalline component is expected to have a very short relaxation time,
but an amorphous more flexible structure may have quite a long T2 in comparison to the water.
So far the hemicellulose model of hydration is not in contradiction with the obtained results.
Using the spin-echo method with variable spin-echo time will further provide the separation of
these two components, bound water and organic signal, making a final better identification of
these organics. If we are using spin-echo detection with variable detection time, the NMR signal
from protons with a shorter T2 will disappear from the spin-echo signal before the proton signal
from the components with a long T2. Therefore, the presence of the organic protons in the signal
can be enhanced by making the abundant, but short-lived, water signal disappear.
In Figure 54, one can easily see the relative larger intensities from the organic components in
relation to the water. By using the spin-echo time, which is a few times longer than the water
relaxation time T2, completely removes the water signal from the NMR spectrum, Figure 55.
40
We used the spin echo technique with variable delays to define the relaxation time T2 of the
residual water (bound) signal and it was found to be always short, smaller than 1 ms. Therefore
one can conclude that we have a bound water signal that can not be differentiated further into
separate categories at room temperature by these NMR measurements. On the other hand, the
measurement of water T1 also reveals only one T1 component. The bound water, which may
come from two physical states, non-freezing bound water bonded to cell walls and freezing
bound water which is H-bonded to non-freezing bound water, seems to appear as one under the
room temperature and dry wood sample conditions. Of course the so-called “free” water was
evidently removed in the drying cycle.
Single component in T2 analysis indicates that the NMR signal from water molecules in the
“non-freezing” state and in the “freezing bound” state is averaged out due to fast exchange rate
between these molecules in the NMR time-scale (at room temperature) and strong spin-spin
interactions. The detected NMR signals (NMR is a bulk detection method of atomic magnetic
properties) are averaged in space and time in the NMR timescale through all different positions
or sites. This makes interpretation of bound and free water from NMR data alone more complex
due to the fact that relaxation times of the individual molecules may be different at different
positions in the wood structure.
It can also be assumed that there is a continuous distribution of the relaxation times T2 in the
‘certain’ range of values, but yielding only the average value in the final analysis as stated above.
ppm20406080100120140160180
Figure 52 The carbon CPMAS spectrum of wood – sample 1BR.
ppm-1-012345678910111213
Figure 53 The proton MAS spectrum of wood – sample 1BR.
41
ppm-1-0123456789101112
Figure 54 The proton MAS spectrum of sample 1BR using spin echo at 1 ms.
ppm-1-0123456789101112
Figure 55 The proton MAS spectrum of sample 1BR using spin echo at 4ms.
Figure 56 The proton MAS spectra of sample 1BR using different spin-echo times,
from 0.4ms to 2.4ms.
42
Dimensional changes in wood
Wood is an anisotropic material, that is, its dimensions change differently in three dimensions:
tangentially, radially and longitudinally. Tangential dimensional change has the highest rate of
change due to parallel orientation of microfibrils along the axis of the cell wall. Radial change is
the second largest and longitudinal change is negligible for most practical applications. In
general, dimensional change is expressed as a percentage as a function of initial dimension and
ratio of moisture content over fibre saturation point. This simple model denotes that the change
of moisture content in drying below fibre saturation point is proportional to the variation in the
shape.
Dimensional changes in wood could be calculated using the following formula14
100**
FSP
CMCOD
SV
DC=
where DC is dimensional change due to change in moisture content (CMC), OD is original
dimension, SV is shrinkage value from green to oven dry moisture content, and FSP is fibre
saturation point. Assuming that FSP is around 28% and it does not change much between the
softwood samples the rate of distortion change, DC/SV, is proportional to the rate of moisture
change, CMC/FSP.
On the other hand there is also a direct relationship between the density of wood and shrinkage values14
. Species with higher density shrink more than those with lower density. There have been many studies aimed at stabilizing the cell wall (resin treatment and alike) so that shrinkage of wood can be controlled, however none of these methods has been put into practical use due to economical and technical considerations
14.
Water dynamics in wood
Results of measuring the relaxation time T1 ( NMR solid-state methods)
The relaxation time T1 of water was measured in dry samples with high field solid state NMR
method in order to observe any differences which may arise from the difference in treatment (run
16 no steaming versus run 17 with 3 hour steaming) or in restrained versus non-restrained boards
during drying.
0.00
100.00
200.00
300.00
400.00
500.00
600.00
700.00
800.00
2A,2B 6G,6H 2F,2G 6C,6D
Run16 Run17
Figure 57 Effect of steaming: T1
14
Source: http://www.agweb.okstate.edu, “Dimensions Changes in Wood”, S. Hiziroglu
43
0.00
100.00
200.00
300.00
400.00
500.00
600.00
700.00
800.00
2A,2F 6G,6C 2B,2G 6H,6D
unrestrained restrained
Figure 58 Effect of restraint: T1
A similar comparison is given on the T2 data collected at high field solid-state NMR which
isolate the water resonance from the organic protons.
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
2A,2B 6G,6H 2F,2G 6C,6D
Run16 Run17
Figure 59 Effect of steaming: T2
44
0.00
0.20
0.40
0.60
0.80
1.00
1.20
2A,2F 6G,6C 2B,2G 6H,6D
unrestrained restrained
Figure 60 Effect of restraint: T2
Discussion *(solid-state data):
T1 data of water resonance at 300 MHz (MAS NMR spectroscopy) exhibit some kind of trend
between the runs 16 and 17, one without steaming and other with steaming, at the end of the
drying cycle. After steaming, the T1 becomes shorter, even more so for the boards having a
longer initial T1. It seems that steaming enhanced the exchange between different types of bound
water making relaxation T1 shorter. The restrain on the other hand is making the similar
enhancement in exchange and shorten T1.
T2 data, collected at 300 MHz, presented here are given here for water resonance by using spin
echo decay (CPMG method). Changes in these T2’s don’t show any significant correlation as
function of steaming or restrain. There may be some shortening trend in T2 with the restrain but
the body of data is too small to make this observation certain. More data were collected by
Mouse that can be analysed further in order to identify the correlations to drying conditions:
steaming or restrain.
MOUSE relaxation data
Mouse relaxation data on slices 0 and 1 have been averaged into one set (see Table 4 below).
They reveal some relationship to the steaming and non-steaming drying regime as well as to the
restraint and non-restraint condition during drying.
45
Table 4 The average amplitude and T2 for slices 0 and 1 of samples (run16 and 17).
Samples Condition Comparison Amplitude T2(ms)
2AR-2BR R Steaming -/+ 4.90 ; 6.11 0.457 ; 0.547
12% 4.79 ; 5.24 0.452 ; 0.510
17% 6.58 ; 7.27 0.642 ; 0.680
2FR-2GR R Steaming -/+ 5.26 ; 5.19 0.345 ; 0.538
12% 5.98 ; 5.08 0.360 ; 0.478
17% 5.53 ; 6.63 0.578 ; 0.608
2AR-2FR R Restrained -/+ 4.90 ; 5.26 0.457 ; 0.345
12% 4.79 ; 5.98 0.452 ; 0.360
17% 6.58 ; 5.53 0.642 ; 0.578
2BR-2GR R Restrained -/+ 6.11 ; 5.19 0.547 ; 0.538
12% 5.24 ; 5.08 0.510 ; 0.478
17% 7.27 ; 6.63 0.680 ; 0.608
6GR-6HR R Steamed -/+ 3.77 ; 5.97 0.375 ; 0.508
12% 5.13 ; 5.95 0.412 ; 0.540
17% 6.13 ; 7.12 0.622 ; 0.720
6CR-6DR R Steamed -/+ 5.36 ; 4.68 0.330 ; 0.778
12% 5.19 ; 4.97 0.378 ; 0.635
17% 5.36 ; 7.28 0.648 ; 0.748
6GR-6CR R Restrained -/+ 3.76 ; 5.36 0.375 ; 0.330
12% 5.13 ; 5.19 0.412 ; 0.378
17% 6.13 ; 5.36 0.622 ; 0.648
6HR-6DR R Restrained -/+ 5.97 ; 4.68 0.508 ; 0.778
12% 5.95 ; 4.97 0.540 ; 0.635
17% 7.12 ; 7.28 0.720 ; 0.748
Discussion (MOUSE data):
The data from un-steamed, Run 16, versus steamed, Run 17 of the same board always gives the
longer T2 component for steamed samples. The expected higher amplitude for the steam samples
is not always detected as such, because there are other factors (structural) that influence the
amount of re-adsorbed moisture by steaming.
The data or non-restrained and restrained boards shows less correlation, but it still can be said
that on average, the relaxation time T2 is generally shorter for restrained board samples in
comparison to the same board non-restrained sample. However, on the other hand, the signal
amplitude shows no correlation to the changes between the restrained and non-restrained regime
indicating that other (structural) factors prevail in determining the total amount of bound water in
the samples.
Correlation between high field solid-state NMR data and low field Mouse data
Assuming that water in our dried wood samples is mainly bound water that plays a structural role
(non-freeze bound water) and small pores role (freeze bound water), it can be accepted that first
type of water will have a much shorter T2 than the other one due to the difference in the
molecular mobility. The measured relaxation time is therefore the average between these two as
defined by the following relationship:
fbnfT
pT
pT
+=222
1)1(
11
Steaming does increase the contribution of the second term, which results in the overall longer
T2. If a similar relationship is used for the T1, the steaming should increase the second part as
well, but the overall effect, as experimentally determined, is a shorter T1 after steaming. The
46
possible explanation for this discrepancy between the two relaxation times behaviour can be
found in the theory of the relaxation time and phase of the materials.
T1
T2
log (T1,2)
log ( c)o c = 1
Figure 61 Relaxation times T1 and T2 as a function of mobility correlation time c
It can be seen that the difference between the measured T1 and T2 values indicate already that we
are at the bottom of the T1 curve or even to the right side of it, where small changes in T2 (larger
correlation time tc) means larger changes in T1. Or in other words, the water correlation time is
longer than 10-8
s, indicating bound water.
47
Part 3 EXPERIMENTAL KILN TRIALS
Trials were conducted in an experimental kiln with Radiata Pine corewood to determine the
extent to which NMR could explain the differences in wood behaviour from different drying
schedules, particularly those identified in the detailed tests as showing equivalent stability, i.e.
using a longer kiln schedule with ramped-down temperature and no final steaming compared to a
standard high temperature schedule with steaming after drying. Boards were monitored for three
weeks after processing, with regular measurements of moisture content, shape and stiffness and
sampling for NMR measurements. These experimental kiln trials are described in Ensis Client
Report No. 1678.
MATERIALS AND METHODS
Procedure
One pair of kiln runs was conducted:
Material
Radiata pine boards from typical resources were provided by Green Triangle Forest Products:
Approximately (120) “heart in” (HI) 100 x 40mm boards, 6.0m long, were provided, plastic
wrapped and trucked to Clayton. As these were from production HI material there was
considerable variation in board characteristics; many boards were partly sapwood, often at one
end.
Preparation
Boards were selected by grain pattern, near-pith or with pith included, and with uniform
grain pattern along the length.
(72) boards were cut to each produce (2) 2.8m long end-matched specimens.
Cross-sections were cut from each end and at the centre of each board, and moisture
content (MC) and basic density (BD) were determined by oven drying.
The 2.8m long specimens were end-coated and weighed.
Acoustic wave velocity (AWV) was measured on the green specimens.
The paired specimens were allocated alternately to (2) kiln loads to ensure equal numbers
of butt and top specimens in each stack.
Stack
6 boards wide; 12 boards high; full length in kiln
25mm thick stickers
2.8m long x 1.2m wide x 200mm thick concrete weight – equivalent to 400mm thick
weight (800kg/m3 stack top area)
top baffle to weight
Kiln runs
Conditions
As for detailed test runs 16 & 17. (Part 2)
48
Table 5 Drying conditions for Run 1 and Run 2 of the kiln trials
Drying Cooling Steaming Cooling
Run 1 140/90 for 4+ hours outside kiln 1 hour
4 hrs outside kiln with weight
Run 2 140/90 for 3 hours; ramp to 120/90 over 1 hour; 120/90 for 1 hours; 110/95 for 1 hour; total drying 6 hours
none none outside kiln
Monitoring
DBT and WBT in the kiln were monitored during drying; wood temperature near the core
of several boards was monitored in each run during drying, steaming and cooling. Boards
for temperature monitoring were selected from near the left, centre and right sides of the
stack, looking from the door.
Restraint
The stack weight was left on the stack overnight (at least 12 hours after drying).
Measurements after drying
Mass and AWV of 2.8m length specimens were measured.
All specimens were cut to 2.4m length and sections taken for MC determination; the
sections removed were from the end cut to separate the specimen from its pair.
Mass & AWV of the 2.4m length specimens were measured. Distortion was measured
over 1.2m gauge length for each half-length and the centre half-length; measurements
were combined to give total distortion.
Boards from each run were re-stacked with stickers.
Stability during storage
Conditions
The two stacks of 2.4m long boards were stored for 21 days with stickers, without
restraint in a well-ventilated building.
Monitoring
Temperature and humidity were logged during storage
Weekly measurements
Mass and distortion were measured. Average moisture content for the specimens was
calculated from the mass, assuming the average green MC was the average of the MC at
each end. Where the section MCs were different, the calculation was done assuming that
the kiln-dried MC was that of the dry section cut after drying.
Sample cores for MC distribution and NMR measurements were taken from 12 boards
from each run (the two middle layers of the test stack).
Dynamic stiffness of core samples – ultrasound along and across grain – were not
measured as equipment could not be acquired.
AWV were measured,
Stiffness on flat, 3-point bending
49
RESULTS AND DISCUSSION
Kiln runs
The planned schedules were followed as detailed in Table 6. However, due to an error in
programming the kiln controller, the conditions were not logged for either Run 1 or Run 2. The
screen image at the end of Run 2 is reproduced in Figure 62.
Table 6 Kiln trial conditions and times
Drying Cooling Steaming Cooling Process time
Run 1 140/90 for 4+ hours outside kiln 1 hour
4 hrs outside kiln with weight
9 hours + cooling
Run 2 140/90 for 3 hours; ramp to
120/90 over 1 hour; 120/90 for 1 hours; 110/95 for 1 hour; total drying 6 hours
none none outside kiln 6 hours + cooling
Figure 62 Kiln controller screen for Run 2
Wood temperatures were logged for Run 1 from approximately halfway through drying (Figure
63) and for all of Run 2 (Figure 64).
50
Core wood temperature in 3 specimens during Kiln Trial 1
0
20
40
60
80
100
120
0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00
Elapsed Time, hours
Te
mp
era
ture
, C
Temp in board at left side of stack
Temp in board at centre of stack
Temp in board at right side of stack
Figure 63 Core temperatures of three specimens during drying, steaming and cooling – Run 1
Core wood temperature in 3 specimens during Kiln Trial 2
0
20
40
60
80
100
120
0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00
Elapsed Time, hours
Te
mp
era
ture
C
Temp in board at left side of stack
Temp in board at centre of stack
Temp in board at right side of stack
Figure 64 Core temperatures of three specimens during drying and cooling – Run 2
Environmental conditions
The conditions during the three weeks of monitoring are shown in Figure 65.
Environment in Factory
0
10
20
30
40
50
60
70
80
90
2-Sep-05 9-Sep-05 16-Sep-05 23-Sep-05
Tem
peratu
re, C
; R
H%
0
5
10
15
20
25
30
35
40
45
EM
C%
Temperature
RH%
EMC%
96 per. Mov. Avg. (EMC%)
A B C D
Figure 65 Environmental conditions for period of storage and monitoring
51
Moisture content
These runs followed quite closely the schedules used in the laboratory dryer tests. In each run
there were specimens from near sapwood boards with higher moisture content which skewed the
result. Specimens in Run 1 were slightly higher in MC than specimens in Run 2 (Figure 66).
Figure 66 and Figure 67 show the distribution of average moisture content and the change of average
moisture content during storage for each run. From Run 1 moisture content was higher than intended
and it reduced during storage to stage B and again to Stage D, as might be expected from the
environmental conditions (Figure 65) when starting with moist surfaces after steaming. Specimens in
Run 2 generally gained throughout storage, the initially drier surfaces taking up moisture.
The average moisture contents of the runs were significantly different throughout the period of
observation.
MC Distribution after drying - Run 1
0
10
20
30
40
50
60
5 10 15 20 25 More
MC% Category upper limit
No
. S
pe
cim
en
s Av. MC 14.2%
MC Distribution after drying - Run 2
0
10
20
30
40
50
60
5 10 15 20 25 More
MC% Category upper limit
No
. s
pe
cim
en
sAv. MC 12.8%
(a) Run 1 (b) Run 2
Figure 66 Moisture content of sections cut from all specimens after drying
Average MC of Specimens during storage
11.0
11.5
12.0
12.5
13.0
13.5
14.0
14.5
15.0
15.5
A B C D
Stage, weekly intervals
MC
%
Run 1
Run 2
#
# ##
$$
$ $
Figure 67 Average moisture content of all specimens in each run, weekly during storage. Points
which do not share the same symbol are significantly different (Scheffe Test).
The moisture content of the specimens from which NMR cores and MC cores were taken is shown in
Figure 68. Most specimens initially gained moisture, particularly those from Run 2 which were not
steamed after drying. Core MC is from 19mm cores cut adjacent to the 35mm cores cut for NMR, and
cut at the same time. The moisture content of cores was quite variable; some of the variation may be
52
from varying degrees of wetness in the centre of specimens. Some variation may be along the boards;
this variation may influence interpretation of the NMR measurements over storage time.
The paired specimens are presented here in a set labelled Set A. This has five pairs which were
well matched in initial moisture content and grain pattern.
(a) Av. MC of specimens
from mass
Average MC of Specimens during storage - Set A
8.0
9.0
10.0
11.0
12.0
13.0
14.0
15.0
16.0
2/09/2005
A
9/09/2005
B
15/09/2005
C
23/09/2005
D
Date; Stage
Av. M
C %
31-2
36-1
37-2
39-2
42-1
31-1
36-2
37-1
39-1
42-2
(b) Av. MC of cores
Av. MC of cores taken during storage - Set A
8.0
9.0
10.0
11.0
12.0
13.0
14.0
15.0
16.0
2/09/2005
A
9/09/2005
B
15/09/2005
C
23/09/2005
DDate; Stage
Av.
MC
%
31-2
36-1
37-2
39-2
42-1
31-1
36-2
37-1
39-1
42-2
(c) Av. Surface MC of cores
Surf. MC of cores taken during storage - Set A
7.0
8.0
9.0
10.0
11.0
12.0
13.0
14.0
15.0
2/09/2005
A
9/09/2005
B
15/09/2005
C
23/09/2005
D
Date; Stage
Av. M
C %
31-2
36-1
37-2
39-2
42-1
31-1
36-2
37-1
39-1
42-2
Figure 68 Average Moisture Content of a set of five paired specimens, estimated from specimen
mass and MC of cores taken from specimens.
Solid symbols/lines = Specimens from Run 1; Open symbols/dotted lines = Specimens from Run 2.
53
Distortion
Figure 69 shows the change in average twist, spring and bow for all specimens of each run
during the storage period. Run 2 had more twist than Run 1 but the behaviour during the storage
period is similar. Spring and Bow behaviour after the initial period is also similar.
(a) Twist over 2.4m length
Av. Twist of specimens during storage
-7.5
-7.0
-6.5
-6.0
-5.5
-5.0
-4.5
-4.0
-3.5
-3.0
A B C D
Stage, weekly intervals
Tw
ist
ov
er 2
.4m
, d
eg
re
es
Run 1
Run 2
#
$$
$
&
&,%
%%
(b) Spring at centre of 2.4m length
Av. Spring of specimens during storage
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
A B C D
Stage, weekly intervals
Sp
rin
g a
t cen
tre o
f 2.4
m, m
m
Run 1
Run 2
#
##
#
#
##
#
(c) Bow at centre of 2.4m length
Av. Bow of specimens during storage
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
A B C D
Stage, weekly intervals
Bo
w a
t cen
tre o
f 2.4
m, m
m
Run 1
Run 2
#
%,@%,@
[]
#,@
$
$
#,%
Figure 69 Average distortion of all specimens in each run during storage.
Points which do not share the same symbol are significantly different (Scheffe Test).
54
The distortion of 10 sets of paired specimens is shown in Figure 70. After the initial period when
some specimens exchanged moisture at the surface there was generally little change in all forms
of distortion.
(a) Twist over 2.4m length
Twist during storage - Set A
-12.0
-11.0
-10.0
-9.0
-8.0
-7.0
-6.0
-5.0
-4.0
-3.0
-2.0
-1.0
0.0
1.0
2.0
2/09/2005
A
9/09/2005
B
15/09/2005
C
23/09/2005
D
Date
Tw
ist,
de
gre
es
ov
er 2
.4m
31-2
36-1
37-2
39-2
42-1
31-1
36-2
37-1
39-1
42-2
(b) Spring at centre of 2.4m length
Spring during storage - Set A
-6.0
-5.0
-4.0
-3.0
-2.0
-1.0
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
2/09/2005
A
9/09/2005
B
15/09/2005
C
23/09/2005
D
Date
Sp
rin
g,
mm
, a
t c
en
tre
31-2
36-1
37-2
39-2
42-1
31-1
36-2
37-1
39-1
42-2
(c) Bow at centre of 2.4m length
Bow during storage - Set A
-6.0
-5.0
-4.0
-3.0
-2.0
-1.0
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
2/09/2005
A
9/09/2005
B
15/09/2005
C
23/09/2005
D
Date
Bo
w,
mm
, a
t c
en
tre
31-2
36-1
37-2
39-2
42-1
31-1
36-2
37-1
39-1
42-2
Figure 70 Twist, Spring and Bow of a set of paired specimens measured at weekly interval
during storage.
Solid symbols/lines = Specimens from Run 1; Open symbols/dotted lines = Specimens from Run 2 Sign of spring has no intrinsic meaning; +ve bow is concave on the inner (near pith) face.
55
Stiffness
Figure 71 shows average stiffness for all specimens in each run calculated from two
measurement methods. For each run stiffness measured by bending on flat appears to increase
during storage; this is less evident for that from acoustic measurements. With the bending tests
which were done without rotating specimen supports, after the first set of measurements a wedge
was used to eliminate the point load from twisted specimens at the non-rotating loading points;
this may explain part of the increase from B to C. Figure 72 shows stiffness for selected pairs of
specimens.
Av. Stiffness from of specimens during storage - Acoustic Meast
8.0E+09
8.2E+09
8.4E+09
8.6E+09
8.8E+09
9.0E+09
9.2E+09
9.4E+09
A B C D
Stage, weekly intervals
E
Run 1
Run 2
#,$#
$
#,$
&#,&
#,$
#,$
Av. Stiffness of specimens during storage - 3-pt bending flat
6.0E+09
7.0E+09
8.0E+09
9.0E+09
1.0E+10
1.1E+10
1.2E+10
B C D
Stage, weekly intervals
E
Run 1
Run 2
#
$ $
#
$ $
(a) Stiffness (acoustic tests) (b) Stiffness (3-point bending on flat
Figure 71 Average Stiffness calculated from (a) acoustic tests and from (b) bending on flat for all
specimens of each run.
Points which do not share the same symbol are significantly different (Scheffe Test).
Stiffness during storage - acoustic - Set A
4.0E+09
6.0E+09
8.0E+09
1.0E+10
1.2E+10
1.4E+10
1.6E+10
1.8E+10
2/09/2005
A
9/09/2005
B
15/09/2005
C
23/09/2005
D
Date
Sti
ffn
ess, E
31-2
36-1
37-2
39-2
42-1
31-1
36-2
37-1
39-1
42-2
Stiffness during storage - 3-point bending flat - Set A
4.0E+09
6.0E+09
8.0E+09
1.0E+10
1.2E+10
1.4E+10
1.6E+10
1.8E+10
9/09/2005
B
15/09/2005
C
23/09/2005
D
Date
Sti
ffn
ess, E
31-2
36-1
37-2
39-2
42-1
31-1
36-2
37-1
39-1
42-2
(a) (b)
Figure 72 Stiffness calculated from (a) acoustic tests and from (b) bending on flat.
Set A has the five best matched pairs. Solid symbols/lines = Specimens from Run 1; Open symbols/dotted lines = Specimens from Run 2.
56
NMR measurements
Figure 73 Solid echo signals for six of the dried specimens of Run 1.
Plots of the solid echo signals for the initial measurements of cores from six specimens of Run 1
are shown in Figure 73 and for matched specimens of Run 2 in Figure 74.
The solid echo signal is the response from all protons in the sample at the frequency. All
different protons, moisture and organic mobile components, contribute to the signal resulting in
the clearly separate contributions to the free induction decay signal (FID): the first is the solid
part with decay generally described by the Gaussian decay function; the second is the semi-
mobile part (from moisture and small organic molecules – like resins) with longer relaxation
times and with decay described by a common Lorentzian function. Therefore the FID signal
from the solid-echo sequence analysed by the combination of Gaussian and Lorentzian functions
gives the characteristic parameters for solid matrix and hydrolysed semi-mobile phases. The
latter is a combination of “bound” water and softened organic matrix where the protons quickly
exchange the spin magnetization between different molecules.
57
Figure 74 Solid echo signals for six of the dried specimens of Run 2.
As a result of these interactions only one T2 value is detectable as an average of these different
sites. Increasing amounts of water soften more organic molecules and the overall dynamic of this
phase increases (longer T2) and as well as the overall signal intensity. On the other hand the
redistribution of moisture in the sample also enhances the magnetization exchange between the
molecules resulting in a sharper (longer T2) and taller (increased intensity) resonance band. In
the proper equilibrium one can expect to have a proportional increase in amplitude and T2 of
longer component (Lorentzian) at different, increasing moisture content. When moisture
redistribution is not in equilibrium the data can be expected to deviate from this proportionality.
The deviation or scattering of the data amplitude versus T2 therefore can reflect the stage of
moisture distribution as well as its changes with different scattering at different times after the
drying process.
Parameters of NMR measurements of cores taken from the specimens are presented in Table 7.
58
Table 7 NMR Solid Echo Results for Cores on Minispec 10 MHz
Run 1A Run 2A
BoardAmp
(Gauss)% (G/L)
T2
(Gauss)
T2
(Loren)
Amp
(Loren)Board
Amp
(Gauss)% (G/L)
T2
(Gauss)
T2
(Loren)
Amp
(Loren)
31-2 643.1 76.24 0.0136 0.2208 200.5 31-1 816.4 75.45 0.0133 0.2214 265.7
32-1 552.7 59.81 0.0136 0.3115 371.4 32-2 625.2 60.47 0.0139 0.3266 408.7
33-2 612.2 71.68 0.0135 0.2661 241.9 33-1 695.4 74.73 0.0139 0.3150 235.2
34-1 653.1 63.10 0.0139 0.3709 381.9 34-2 655.5 64.32 0.0137 0.3461 363.6
35-2 761.6 73.06 0.0139 0.2607 280.9 35-1 793.0 75.50 0.0136 0.2518 257.4
36-1 559.1 67.98 0.0135 0.2705 263.4 36-2 688.9 77.21 0.0137 0.2244 203.3
37-2 608.4 78.76 0.0133 0.1973 164.1 37-1 755.9 72.93 0.0136 0.2887 280.6
38-1 626.3 66.11 0.0135 0.3551 321.1 38-2 661.5 63.41 0.0142 0.3908 381.7
39-2 870.6 75.42 0.0141 0.3396 283.8 39-1 944.0 77.62 0.0138 0.3097 272.1
40-1 599.3 50.18 0.0134 0.3004 595.0 40-2 598.2 65.68 0.0137 0.2694 312.6
41-2 721.1 56.05 0.0140 0.3878 565.5 41-1 666.8 39.30 0.0144 0.6348 1029.8
42-1 672.7 75.50 0.0134 0.2113 218.3 42-2 816.1 66.74 0.0140 0.3338 406.8
Run 1B Run 2B
BoardAmp
(Gauss)% (G/L)
T2
(Gauss)
T2
(Loren)
Amp
(Lor)Board
Amp
(Gauss)% (G/L)
T2
(Gauss)
T2
(Loren)
Amp
(Lor)
31-2 701.3 71.98 0.0138 0.2963 273.0 31-1 723.5 55.04 0.0138 0.4331 591.0
32-1 636.5 54.74 0.0139 0.3950 526.3 32-2 648.1 59.56 0.0134 0.3443 440.0
33-2 706.4 66.79 0.0137 0.3368 351.3 33-1 721.8 77.11 0.0137 0.2616 214.3
34-1 640.5 72.24 0.0139 0.2976 246.1 34-2 612.9 63.67 0.0138 0.3359 349.7
35-2 720.2 76.69 0.0136 0.2305 218.8 35-1 809.2 67.02 0.0138 0.2980 398.2
36-1 738.5 69.59 0.0139 0.3272 322.7 36-2 651.4 77.26 0.0138 0.1959 191.7
37-2 752.5 74.15 0.0138 0.3158 262.3 37-1 742.0 74.40 0.0139 0.2602 255.3
38-1 671.0 70.14 0.0135 0.3025 285.6 38-2 682.8 73.39 0.0135 0.2735 247.6
39-2 919.5 74.04 0.0137 0.3327 322.3 39-1 904.7 76.47 0.0139 0.3150 278.4
40-1 613.5 54.99 0.0137 0.3481 502.1 40-2 632.8 69.71 0.0139 0.2274 275.0
41-2 749.0 65.08 0.0138 0.3265 401.8 41-1 689.8 45.51 0.0140 0.4496 826.0
42-1 827.7 70.37 0.0139 0.3076 348.5 42-2 753.7 78.25 0.0136 0.2246 209.5
Run 1C Run 2C
BoardAmp
(Gauss)% (G/L)
T2
(Gauss)
T2
(Loren)
Amp
(Lor)Board
Amp
(Gauss)% (G/L)
T2
(Gauss)
T2
(Loren)
Amp
(Lor)
31-2 704.7 62.51 0.0137 0.2796 422.7 31-1 729.5 63.27 0.0136 0.2684 423.6
32-1 641.5 53.84 0.0137 0.3627 549.9 32-2 642.2 60.71 0.0136 0.3393 415.6
33-2 748.3 72.86 0.0137 0.2934 278.7 33-1 724.9 79.53 0.0135 0.2097 186.6
34-1 638.5 72.27 0.0134 0.2538 245.0 34-2 619.8 65.68 0.0136 0.2840 323.8
35-2 729.7 73.70 0.0136 0.2487 260.4 35-1 799.9 76.46 0.0135 0.2174 246.2
36-1 693.8 68.84 0.0135 0.2592 314.0 36-2 656.1 72.61 0.0137 0.2361 247.5
37-2 770.5 76.48 0.0137 0.2464 236.9 37-1 601.8 76.57 0.0133 0.2107 184.2
38-1 704.9 64.75 0.0136 0.3427 383.8 38-2 687.0 69.11 0.0134 0.2786 307.0
39-2 915.1 77.01 0.0135 0.2461 273.2 39-1 867.8 78.06 0.0133 0.2475 243.9
40-1 626.7 63.98 0.0137 0.2484 352.8 40-2 649.0 71.02 0.0138 0.2406 264.9
41-2 665.1 54.56 0.0138 0.3932 554.0 41-1 687.9 43.37 0.0138 0.4829 898.3
42-1 806.7 65.84 0.0142 0.3428 418.5 42-2 734.1 73.00 0.0134 0.2488 271.4
Run 1D Run 2D
BoardAmp
(Gauss)% (G/L)
T2
(Gauss)
T2
(Loren)
Amp
(Lor)Board
Amp
(Gauss)% (G/L)
T2
(Gauss)
T2
(Loren)
Amp
(Lor)
31-2 585.1 76.27 0.0138 0.2194 182.0 31-1 721.8 56.27 0.0137 0.3838 561.0
32-1 617.8 57.22 0.0137 0.3482 462.0 32-2 647.2 48.63 0.0139 0.4542 683.8
33-2 729.2 73.46 0.0135 0.2675 263.5 33-1 727.7 79.88 0.0137 0.2413 183.3
34-1 625.3 72.56 0.0136 0.2381 236.5 34-2 638.4 71.64 0.0137 0.2589 252.7
35-2 697.5 73.65 0.0137 0.2676 249.5 35-1 804.1 75.83 0.0136 0.2387 256.3
36-1 678.3 76.48 0.0136 0.2131 208.5 36-2 650.3 75.21 0.0138 0.2265 214.4
37-2 673.8 77.28 0.0134 0.2043 198.1 37-1 733.9 71.82 0.0138 0.3108 288.0
38-1 658.5 71.11 0.0134 0.2713 267.6 38-2 622.0 59.78 0.0133 0.3369 418.5
39-2 847.5 78.04 0.0137 0.2637 238.5 39-1 892.2 78.24 0.0137 0.2803 248.2
40-1 652.5 64.44 0.0139 0.2822 360.1 40-2 610.0 72.75 0.0141 0.2087 228.5
41-2 669.5 56.22 0.0140 0.3918 521.2 41-1 682.7 42.28 0.0139 0.4555 931.8
42-1 776.7 68.88 0.0137 0.2688 350.9 42-2 799.9 78.76 0.0137 0.2576 206.9
23/9/2005 23/9/2005
16/9/2005 16/9/2005
2/09/2005
9/09/2005
2/09/2005
9/09/2005
59
Gaussian parameters
Gaussian parameters (Figure 75) relate to the solid wood matrix. The variation of amplitude and T2 seen in Figure 75 can not be taken to be meaningful as it is of the same order as the error in the signal.
T2 Gaussian during storage - Set A
0.0128
0.013
0.0132
0.0134
0.0136
0.0138
0.014
0.0142
0.0144
���� 2/09/2005
A
���� 9/09/2005
B
���� 16/09/2005
C
���� 23/09/2005
D
Date; Stage
31-2
36-1
37-2
39-2
42-1
31-1
36-2
37-1
39-1
42-2
Amplitude Gaussian during storage - Set A
0
100
200
300
400
500
600
700
800
900
1000
����� 2/09/2005
A
���� 9/09/2005
B
�� 16/09/2005
C
�� 23/09/2005
D
Date; Stage
31-2
36-1
37-2
39-2
42-1
31-1
36-2
37-1
39-1
42-2
(a) Amplitude Gaussian (b) T2 Gaussian
Figure 75 Gaussian parameters of NMR measurements of cores taken during storage.
Set A has the five best matched pairs. Solid symbols/lines = Specimens from Run 1; Open symbols/dotted lines = Specimens from Run 2.
Lorentzian parameters
Amplitude Lorentzian during storage - Set A
0
100
200
300
400
500
600
700
���� 2/09/2005
A
���� 9/09/2005
B
���� 16/09/2005
C
���� 23/09/2005
D
Date
31-2
36-1
37-2
39-2
42-1
31-1
36-2
37-1
39-1
42-2
T2 Lorentzian during storage - Set A
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
����� 2/09/2005
A
����� 9/09/2005
B
���� 16/09/2005
C
���� 23/09/2005
DDate
31-2
36-1
37-2
39-2
42-1
31-1
36-2
37-1
39-1
42-2
(a) Amplitude Lorentzian (b) T2 Lorentzian
Figure 76 Lorentzian parameters of NMR measurements of cores taken during storage.
Set A has the five best matched pairs. Solid symbols/lines = Specimens from Run 1; Open symbols/dotted lines = Specimens from Run 2.
Figure 76 shows the Lorentzian parameters for the cores taken from specimens at weekly stages
during storage. Amplitude Lorentzian is most strongly influenced by moisture content; T2
Lorentzian is an indicator of moisture mobility.
The peaks of Amplitude generally seem to correspond with high core MC (Figure 68).
60
Figure 77 and Figure 78 show the Amplitude Lorentzian for cores taken from specimens at
stages during storage plotted against the average moisture content of matching smaller cores
taken at the same time, for Run 1 and Run 2 respectively. It can be seen in these figures that
Amplitude Lorentzian is generally linearly related to moisture content. Data from two poorly
matched pairs of specimens with higher moisture content have been omitted as the NMR
analysis was “tuned” to moisture content below about 15%.
Amplitude Lorentzian v MC - Run 1
100
200
300
400
500
600
700
8 9 10 11 12 13 14 15 16
Core Av. MC%
Am
plitu
de L
oren
tzia
n
Av. Core MC A
Av. Core MC B
Av. Core MC C
Av. Core MC D
Fitted to all
Figure 77 Amplitude Lorentzian plotted against Av. MC of matching cores – Run 1.
Amplitude Lorentzian v MC - Run 2
100
200
300
400
500
600
700
8 9 10 11 12 13 14 15 16
Core Av. MC%
Am
plitu
de L
oren
tzia
n
Av. Core MC A
Av. Core MC B
Av. Core MC C
Av. Core MC D
Fitted to all
Figure 78 Amplitude Lorentzian plotted against Av. MC of matching cores – Run 2.
Figure 79 and Figure 80 show T2 Lorentzian for cores taken from specimens (set A of previous
figures) at stages during storage plotted against the average moisture content of matching smaller
cores taken at the same time, for Run 1 and Run 2 respectively. T2 Lorentzian indicates the
mobility of water molecules, as well as other organic molecules associated with water. Water
therefore provides the major part of the signal. For each set of points the steepness of the fitted
line can be taken to indicate increasing water mobility. The fitted lines for specimens of Run 1
(Figure 79), which was steamed after drying are initially steep (Set A; dark blue line) then
61
recline to that at C (orange line) then become slightly steeper at D (plum line). This may indicate
that water in the wood, particularly that added to the surface during steaming, becomes more
strongly “bound” during storage, and during the period C to D the water added to the surface
from the atmosphere is likely to be initially more mobile.
T2 Lorentzian v MC - Run 1
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
8 9 10 11 12 13 14 15 16
Core Av. MC%
T2
Lo
re
ntz
ian
Av. Core MC A
Av. Core MC B
Av. Core MC C
Av. Core MC D
Fitted to all
Linear (Av. Core MC A)
Linear (Av. Core MC B)
Linear (Av. Core MC C)
Linear (Av. Core MC D)
Figure 79 T2 Lorentzian plotted against Av. MC of matching cores – Run 1.
The fitted lines for specimens of Run 2 (Figure 80) which was not steamed after drying follow
quite a different progression; the blue line for state A is shallow, indicating low water mobility
and the lines for states B and D are progressively steeper. State C seems out of step with this
progression. For these specimens the surface moisture content was low at A and the specimens
gained moisture during storage (Figure 68).
T2 Lorentzian v MC - Run 2
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
8 9 10 11 12 13 14 15 16
Core Av. MC%
T2
Lo
re
ntz
ian
Av. Core MC A
Av. Core MC B
Av. Core MC C
Av. Core MC D
Fitted to all
Linear (Av. Core MC A)
Linear (Av. Core MC B)
Linear (Av. Core MC C)
Linear (Av. Core MC D)
Figure 80 T2 Lorentzian plotted against Av. MC of matching cores – Run 2.
These explanations for the observed differences are only the best attempt to interpret these data;
they may not be completely consistent, because the moisture content of the cores seems to show
more variation, perhaps along the (about 300mm) length of the specimens from which successive
cores were taken at each weekly stage (Figure 68 (b)).
62
PROJECT RESULTS AND DISCUSSION
1. Bonding states of water during processing and stabilization
Non-freezing water, Wnf, (structural water or tightly bound to cell walls) and freezing bound
water, Wfb, (water associated with walls and smaller reservoirs) can not be differentiated at
room temperature through NMR spectroscopy detection due to the fast exchange between
them that gives rise to only one average parameter (like chemical shift and relaxation time) in
the NMR signal.
Additional moisture taken in or lost by the wood in conditioning rooms or during storage is a
relatively quick process, in days, and it is not free water but becomes a part of the total bound
water, Wnf + Wfb. This bound water has, as expected, higher NMR signal amplitude when
external humidity is higher but it also has a longer T2 component. Assuming that a fast
exchange mechanism is in place between Wnf and Wfb one can say that the majority of added
moisture becomes firstly Wfb type moisture. This is expected to have a longer T2 (more
mobile) and therefore moves the averaged value for all bound water to a longer T2 at higher
overall moisture content. This is true only when the total moisture content is below the FSP
(around 28%).
The further separation and evaluation of the major NMR parameters (relaxation mechanisms)
has produced an improved physical description of the moisture states in softwood and thus
contribute to the development of a comprehensive softwood drying model incorporating
moisture state as well as location.
The solid echo signal is the response from all protons in the sample at the frequency. All
different protons, moisture and organic mobile components, contribute to the signal resulting
in the clearly separate contributions to the free induction decay signal (FID): the first is the
solid part with decay generally described by the Gaussian decay function; the second is the
semi-mobile part (from moisture and small organic molecules – like resins) with longer
relaxation times and with decay described by a common Lorentzian function. Therefore the
FID signal from the solid-echo sequence analysed by the combination of Gaussian and
Lorentzian functions gives the characteristic parameters for solid matrix and hydrolysed
semi-mobile phases. The latter is a combination of “bound” water and softened organic
matrix where the protons quickly exchange the spin magnetization between different
molecules.
As a result of these interactions only one T2 value is detectable as an average of these
different sites. Increasing amounts of water soften more organic molecules and the overall
dynamic of this phase increases (longer T2) and as well as the overall signal intensity. On the
other hand the redistribution of moisture in the sample also enhances the magnetization
exchange between the molecules resulting in a sharper (longer T2) and taller (increased
intensity) resonance band. In the proper equilibrium one can expect to have a proportional
increase in amplitude and T2 of longer component (Lorentzian) at different, increasing
moisture content. When moisture redistribution is not in equilibrium the data can be expected
to deviate from this proportionality. The deviation or scattering of the data amplitude versus
T2 therefore can reflect the stage of moisture distribution as well as its changes with different
average mobility at different times after the drying process.
2. Bonding states of water, internal stresses and distortion
The variation in structural wood distortion and variations of moisture content seems to be
inconsistent with the expected correlation between moisture and shape change – indicating
that the whole measured moisture is determined by other factors as well. Only the cell wall
63
moisture content, which is only one part of the measured total moisture, is commonly
thought to relate to the structural changes.
The variation between the end of the drying cycle and the later conditioning is not all related
to the cell walls moisture (Wnf) and therefore the moisture content corresponding to the shape
change could not be clearly established from the current data. In order to achieve this
correlation further investigation is needed to find a novel NMR method to quantitatively
identify these two types of bound water. The low field NMR can be used finally after the
high-field solid-state methods prove a satisfactory differentiation and quantification of the
two types of bound water.
Other components of wood may be involved in wood shape changes independent of
moisture. This requires further technique development with solid-state high field NMR
measurements.
3. High temperature kiln drying schedule modifications and/or
treatments that improve stability
A HT kiln schedule modified with ramped reductions in temperature with increasing
humidity instead of steam reconditioning, produced similarly straight and stable timber to the
conventional HT schedule with stream reconditioning, over the three weeks period of
monitoring. The project did not incorporate a longer period.
4. Stabilization treatments to reduce the time to a stable state
No treatments for reducing the time to stable products have been identified.
Solid-state NMR investigation indicates that the process of steaming after drying results in
increased water mobility; the tests of specimen stability during humidity cycling only
showed indications of this. To the extent that moisture changes are related to wood shape
stability it may be best to minimise final steaming. This seems to be one possible direction
for further work and should be investigated in experimental trials.
5. Differences between Heart-in and Free of Heart material
A clear difference in the ‘FID’ signal of green wood was also detected for different wide
faces of the board, when one face of the board consists mainly of sapwood as opposed to
heartwood (Appendix 1).
Knots and bluestain are also distinguishable by analysis of the FID signal.
6. Modification to current commercial practices to minimize kiln
drying time, steaming time and storage periods to produce stable
dried softwood timber
A HT kiln schedule modified with later reductions in temperature and higher humidity and
no steam reconditioning, produced similarly stable timber to the conventional HT schedule
and stream reconditioning. Although the drying time was increased, processing time was the
same. The benefit will need to be clearly established for this to be adopted, as kiln
productivity would be reduced unless initial drying temperatures were increased.
This project has not identified a clear link between storage time and product stability.
64
ACKNOWLEDGEMENTS
This research was undertaken with assistance from the Forests and Wood Products Research and
Development Corporation (www.fwprdc.org.au) which is funded by industry and the Australian
Government.
Timber for experiments was kindly provided by Weyerhaeuser Australia through Green Triangle
Forest Products, Hyne Timber and Wespine Industries. The support and advice of Chris Lafferty
(FWPRDC), Tony Haslett (formerly with Weyerhaeuser Australia, now with Ensis), Stephen
Bolden (formerly with Hyne Timber) and Richard Schaffner (Wespine) is gratefully
acknowledged.
DISCLAIMER
The opinions provided in this Report have been provided in good faith and on the basis that
every endeavour has been made to be accurate and not misleading and to exercise reasonable
care, skill and judgment in providing such opinions. However, CSIRO as project manager, and
the parties to the joint venture known as ensis which carried out the research ('ensis') (CSIRO
and Forest Research NZ) do not guarantee or warrant the accuracy, reliability, completeness or
currency of the information in this report unless contrary to law. Neither ensis nor any of its
staff, contractors, agents or other persons acting on its behalf or under its control accept any
responsibility or liability in respect of any opinion provided in this Report by ensis or any person
acting in reliance on the information in it.
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