Development of a new engineered wood product for structural
applications made from trembling aspen and paper birch
Katherina Beck
Alain CloutierAlexander Salenikovich
Robert Beauregard
Annual meeting of IAWS 2011 - StockholmAugust 31, 2011
Context
Engineered Wood Product
Utilization of existing
installations
Use of under-utilized species
Oriented Strand Lumber
• A structural composite lumber that combines parallel aligned wood strands with structural adhesive to form lumber-like structural products
• Can be produced in OSB mills• Using paper birch and trembling aspen
Four Problems
1. Conventional hot platen pressing results in a pronounced vertical density profile.
2. OSB production parameters are adapted to low density species.
3. Adequate bending strength to compete with engineered wood products on the market must be achieved.
4. Panel thickness limited by press opening.
Step1
Step 2
Step 3
Step 1: Develop a Pressing Procedure and Evaluate the Effect of Species
- Background -
• Problem: Conventional hot platen pressing results in a pronounced vertical density profile (VDP).
• Step-closure pressing significantly changes the traditional shape of the VDP (Wang et al. 2000).
conventional step-closure
VDP
Step 1: Develop a Pressing Procedure and Evaluate the Effect of Species
- Background –
• Problem: OSB production parameters are adapted to low density species.
• Panels produced from higher density species tend to have inferior bending properties compared to aspen panels (Blankenhorn et al. 1989, Brunette 1992).
• Thinner strands improve mechanical properties of birch panels (Au and Gertjejansen 1989, Yong et al. 1992).
• Specific surface:
SS =e · ρ
2Particle Mass
Particle Surface=~
e = strand thicknessρ = oven-dry wood density
Thin, slender particles
Step 1: Developing a Pressing Procedure and Evaluating the Effect of Species
- Materials and Methods -
• Trembling aspen (benchmark) and paper birch
• Similar specific surfaces for both species
• Three adhesive contents (3.5%, 5%, 7%)
• Unidirectional strand alignment
• Three-step-closing pressing procedure
Step 1: Production Parameters
Oven-Dry Wood
Density ρ [kg/m3]
Strand Thickness
e [mm]
Strand Length
ℓ [mm]
Target Panel
Density [m3/kg]
Specific Surface
SS1
[m2/kg]
Adhesive Content²
Powder PF
Liquid PF Total
Aspen 451 0.69 105 650 6.4
1.0% 2.5% 3.5%
1.43% 3.57% 5.0%
2.0% 5.0% 7.0%
Birch 617 0.51 105 650 6.4
1.0% 2.5% 3.5%
1.43% 3.57% 5.0%
2.0% 5.0% 7.0%
¹
² Percent per oven-dry wood weightPF = Phenol formaldehyde
ρ⋅=
eSS
2
+ =
Vertical Density Profiles
low adhesive content (3.5%)medium adhesive content (5%)high adhesive content (7%)
0
250
500
750
1000
1250
0 2 4 6 8 10 12 14 16Position (mm)
Den
sity
(kg/
m³)
Aspen
0
250
500
750
1000
1250
0 2 4 6 8 10 12 14 16Position (mm)
Birch
Den
sity
(kg/
m³)
- Results -
0.345 MPa
Internal Bond
• Internal bond (IB):- Adhesive content:
significant effect- Species:
no significant effect
AspenN = 230.63
(14.9)B
BirchN = 180.68
(39.6)B
7.0%
AspenN = 210.47
(14.1)A
AspenN = 220.55
(19.0)AB
BirchN = 160.45
(21.8)A
BirchN = 190.67
(33.1)B
0
0.2
0.4
0.6
0.8
1.0
3.5% 5.0%Adhesive Content
IB (M
Pa)
OSB O-2 (CSA-O437): 0.345 MPa
- Results -
Flatwise Bending
• Modulus of Rupture (MOR):- Adhesive content: no
significant effect- Species: no significant
effect
• Modulus of Elasticity (MOE):- Adhesive content: no
significant effect- Species: significant effect
360180180
[mm]
TimberStrand®
Aspen11.8(8.2)
A
Aspen72.2
(12.6)A
Birch10.6
(13.1)
B
Birch64.4
(27.5)A
0
25
50
75
0
4
8
12
100 16
MOR
(MPa
)
MOE
(GPa
)
Modulus of Elasticity
Modulus of Rupture
TimberStrand®
- Results -
• Modulus of Rupture:Means adjusted for short term loading; COV of 15%; thicknesses up to 89 mm; marketed in Canada
• TimberStrand® LSL40.2 MPa
• Modulus of Elasticity:• TimberStrand® LSL
9 700 MPa
• Modulus of Rupture (MOR):- Adhesive content: no
significant effect- Species: no significant
effect
• Modulus of Elasticity(MOE):- Adhesive content: no
significant effect- Species: no significant
effect
• Modulus of Rupture:Means adjusted for short termloading and 30 mm depth; COV of 15%; marketed in Canada
• TimberStrand® LSL40.2 to 55.1 MPa
• SolidStart® LSL43.6 to 59.4 MPa
• Modulus of Elasticity:• TimberStrand® LSL
9 000 to 10 700 MPa• SolidStart® LSL
9 300 to 10 700 MPa
Edgewise Bending180 180 180
540
[mm]
Birch10.3
(15.4)
A
Aspen10.6(8.4)
A
Aspen43.4
(16.0)
A
Birch43.0
(41.6)A0
20
40
60
80
100
MOR
(MPa
)
0
3
6
9
12
15
MOE
(GPa
)
Modulus of Elasticity
Modulus of Rupture
MOR:40 to 60
MPa
MOE:9 000
to 10 700
MPa
- Results -
Step 2: Evaluate Interaction Between Slenderness Ratio, Specific Surface, Species,
and Performance
- Background -
• Problem: Adequate bending strength to compete with engineered wood products on the market.
• Particle geometry: - Strand length ↑ → bending properties ↑
(Barnes 2001, and others).- Slenderness ratio (length-to-thickness ratio) ↑
→ bending properties ↑ (Post 1958, Barnes 1988, and others).
Step 2: Evaluate Interaction Between Slenderness Ratio, Specific Surface, Species,
and Performance- Materials and Methods -
• Trembling aspen and paper birch
• Three strand lengths
• Two strand thicknesses
• 7% adhesive content
• Unidirectional strand alignment
• Three-step-closing pressing procedure
Step 2: Production Parameters
Oven-Dry Wood Density ρ [kg/m3]
Strand Thickness e
[mm]
Strand Lengthℓ [mm]
Specific SurfaceSS [m2/kg]
Slenderness Ratio SR¹
Trembling Aspen 459
0.49 77.6 8.8 1580.53 105.0 8.3 2000.45 142.1 9.8 3180.75 77.6 5.8 1030.71 105.0 6.2 1490.66 142.1 6.6 217
Paper Birch 624
0.46 77.6 7.0 1700.47 105.0 6.8 2230.43 142.1 7.4 3300.75 77.6 4.3 1040.71 105.0 4.5 1490.71 142.1 4.5 199
e
=RS¹
Internal Bond
• Internal Bond (IB):- Species:
no significant effect- Strand thickness:
no significant effect- Strand length:
no significant effectOSB O-2
OSB O-2 (CSA-O437): 0.345 MPa
N = 910.68
(21.0)A
N = 1160.76
(26.2)A0
0.4
0.8
1.2
IB (M
Pa)
Aspen Birch
- Results -
Flatwise Bending360
180180
[mm]
Flatwise Bending
• Species, thickness, and length: significant effect
• Slenderness ratio: significant effect
• Specific surface: significant effect
360180180
[mm]
S = shortM = mediumL = long
40.3(19.3)
48.9(19.3)
53.5(26.8)
66.0(15.3)
54.5(21.1)
65.5(15.7)
65.4(24.3)
77.6(15.9)
62.0(26.2)
85.1(20.2)
90.1(16.4)
99.2(19.5)0
30
60
90
120
MOR
(MPa
)MO
E (M
Pa)
TimberStrand®
S M LS M L S M L S M L
8943(7.1)
8189(7.9)
7766(18.6)
6395(15.1)
11642(9.4)
10391(11.7)
9647(11.9)
8218(11.5)
13581(14.9)
12624(13.4)
12107(7.0)
10002(11.0)0
4000
8000
1200016000 Modulus of Elasticity
Aspen Birchthin thick thin thick
Modulus of Rupture
TimberStrand®
• Modulus of Rupture:Means adjusted for short term loading; COV of 15%; thicknesses up to 89 mm; marketed in Canada
• TimberStrand® LSL40.2 MPa
• Modulus of Elasticity:• TimberStrand® LSL
9 700 MPa
- Results -
• Species, thickness, and length: significant effect
• Slenderness ratio: significant effect
• Specific surface: significant effect
• Modulus of Rupture:Means adjusted for short term loading and 30 mm depth; COV of 15%; marketed in Canada• TimberStrand® LSL
40.2 to 55.1 MPa• SolidStart® LSL
43.6 to 59.4 MPa
• Modulus of Elasticity:• TimberStrand® LSL
9 000 to 10 700 MPa• SolidStart® LSL
9 300 to 10 700 MPa
Edgewise Bending180 180 180
540
[mm]
MOR
(MPa
)MO
E (M
Pa)
42.7 (9.7)
35.0 (15.0)
38.8 (26.8)
28.8 (19.2)
51.4 (18.3)
45.3 (18.3)
41.8 (24.9)
29.1 (22.1)
66.3 (21.3)
55.4 (22.0)
65.7 (14.9)
40.3 (29.0)0
30
60
90
8371(6.7)
6971(6.7)
7901(12.6)
6493(14.7)
10799(6.0)
9641(8.5)
9614(16.7)
8249(13.5)
13505(7.9)
12163(6.4)
13203(4.9)
10494(11.6)0
4000
8000
12000
16000
S M LS M L S M L S M L
Aspen Birchthin thick thin thick
Modulus of Rupture
Modulus of Elasticity
S = shortM = mediumL = long
MOR:40
to 60 MPa
MOE:9 000
to 10 700
MPa
- Results -
0
2000
4000
6000
8000
10000
12000
14000
16000
0 50 100 150 200 250 300 350 400Slenderness Ratio SR [mm/mm]
MOE
[MPa
]
MOE Values, AspenMOE Values, BirchMOE Regression, Aspen @ 725kg/m³MOE Regression, Birch @ 725 kg/m³
Edgewise Bending - Regression
Aspen:MOE = -1803 + 9.6 Density + 27.4 SR
R² = 0.81
Birch:MOE = -10403 + 20.4 Density + 24.4 SR
R² = 0.88
A B
M
Compression
• Species and strandlength: significanteffect
• Strand thickness: no significant effect
10.8(18.4)
14.5 (15.2)
9.1 (19.1)
11.1 (14.7)
9.7 (22.4)
10.4(15.3)
0
5
10
15
20
Stre
ngth
(MPa
)
2254(23.1)
2852 (15.2)
1318(24.6)
1418(20.9)
1101(31.4)
1219(22.7)
0
1000
2000
3000
4000
MO
E (M
Pa)
Aspen BirchCompressive Strength
S L S M L
Compressive MOE
S = shortM = mediumL = long
- Results -
Step 3: Evaluate a Laminated OSL Prototype
- Background -
• Problem: Panel thickness limited by press opening in OSB mills.
• Face-lamination of thin panels allows to achieve adequate thickness.
Step 3: Evaluate a Laminated OSL Prototype
- Materials and Methods -
• Trembling aspen and paper birch panels- 0.55 mm thick, 142 mm long strands; 7% PF
content
• Industrial webstock OSB
• Phenol-resorcinol adhesive
• Small scale testing
• Larger scale testing
Edgewise Bending – Small Scale
« Birch, aspen OSL» « OSB »
9.9(3.0)
10.6(3.0)
5.2(6.4)
0
3
6
9
12
15
Aspen Birch OSB
MOE
(GPa
)
52.0 (4.7)
58.4 (11.4)
26.4(6.1)
0
30
60
90
Aspen Birch OSB
MOR
(MPa
)
Modulus of Elasticity
Modulus of Rupture
- Results -
• Modulus of Rupture:Means adjusted for short termloading and 30 mm depth; COV of 15%; marketed in Canada
• TimberStrand® LSL40.2 to 55.1 MPa
• SolidStart® LSL43.6 to 59.4 MPa
• Modulus of Elasticity:• TimberStrand® LSL
9 000 to 10 700 MPa• SolidStart® LSL
9 300 to 10 700 MPa
MOR:40 to 60
MPa
MOE:9 000
to 10 700
MPa
45
30
[mm]180 180 180
540
4515 15 15
30 30
[mm] 4611.5 11.5 11.5 11.5
Edgewise Bending – Larger Scale
[mm]
2160720 720 720
46120
• Modulus of Rupture:Means adjusted for short termloading and 120 mm depth; COV of 15%; marketed in Canada
• TimberStrand® LSL39.2 to 53.5 MPa
• SolidStart® LSL41.8 to 57.0 MPa
• Modulus of Elasticity:• TimberStrand® LSL
9 000 to 10 700 MPa• SolidStart® LSL
9 300 to 10 700 MPa
Edgewise Bending – Larger Scale
26.8(3.8)
24.0(4.8)
0
10
20
30
40
smallbeams
large beams
MOR (
MPa)
10%
46.7 52.60
30
60
90
Aspen BirchMO
R (MP
a)9.9 10.6
0
3
6
9
12
15
Aspen Birch
MOE (
GPa)
Modulus of Elasticity
Modulus of Rupture
Modulus of Elasticity
Modulus of Rupture
¹ No size effect indicatedin literature → ignored.
- Results -
MOR:39 to 57
MPa
MOE:9 000
to 10 700
MPa
4.9(6.4)
5.2(2.6)
0
3
6
9
small beams
large beams
MOE (
GPa)
( )¹6%
Conclusions
• Step 1: Develop a Pressing Procedure and Evaluate the Effect of Species- Using a three-step closing schedule, a near-homogenous VDP
was achieved.- Respecting similar specific surface for both species, comparable
internal bond and bending properties were achieved.
• Step 2: Evaluate Interaction Between Slenderness Ratio, Specific Surface, Species, and Performance- Not only strand geometry and species had an effect on bending
properties; the slenderness ratio and specific surface also played a role.
- Strand length is a compromise between bending and compression performance.
Conclusions (2)
• Step 3: Evaluate a Laminated OSL Prototype- Average MOR and MOE values make laminated aspen and birch
OSL competitive with similar EWPs.
Engineered Wood Product
Utilization of existing
installations
Use of under-utilized species
Laminated Oriented Strand
Lumber
The properties of theselaminated OSL products
offer an affordable, viable alternative to similar
products on the market.
These laminated OSL products can be
manufactured in existingOSB mills, allowing them
to react to marketdemand by alternatingbetween OSB and OSL.
Paper birch, currently an underutiziled species,
can be given added value.
Three Advantages
In the Future…
• Other species
• Mill trials
• Full size testing
• Panel combinations
• Panel jointing
• Connections
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