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1st Workshop - Basics for Chemistry of Wood Surface Modification
April 25-26, 2012, Kuchl/Salzburg, Austria
S f difi ti f WPC d t t S f difi ti f WPC d t t Surface modification of WPC products toSurface modification of WPC products toimprove bonding strengthimprove bonding strength
J. Leßlhumer 1, J. Sinic 1, M. Reif 1, A. Haider 1 , D. Cascorbi 2
1 Competence Centre for Wood Composites and Wood Chemistry2 PINUFORM GmbH & Co. KG
ContentContent
• Introduction Wood K plus
• Motivation
• Materials / MethodsMaterials / Methods
• Results
• Conclusions
2
Wood K plusWood K plus
• R&D Institute for wood-based
materials wood composites andmaterials, wood composites and
wood chemistry
• 95 scientific employees
Mark
innov
Wood- and
cellulose
Solid wood
and wood-
based95 scientific employees
• 50 projects
ket
analy
vatio
n re
chemistrybased
materials
• Budget: 7.0 mio € p.a.
• 4 business units, one cross ysis
and
searc
h
W3C: Surface
technologies
and logistics
Wood polymer
composites
sectional market research field
3
R&D services R&D services -- Division WPCDivision WPC
• Consulting
• Raw material characterizationRaw material characterization
– Wood and fiber analytics
– Polymer analytics
• Material characterization
– Compound analytics
Material testing– Material testing
– Component testing
• Extrusion trials – Pilot plantExtrusion trials Pilot plant
• Injection molding
• Material & Process development
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MotivationMotivation
• Wood Polymer Composites (WPC) are made of lignocellulosic
material based on different thermoplastics
New applications require print- and glueability
• Problems caused by thermoplastic matrixProblems caused by thermoplastic matrix
– Hydrophobic
– Non polar
Low surface energy– Low surface energy
activate and/or modify the surface to
– improve wettability
– increase surface energy
– increase bonding strength
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g g
Materials / Raw materialsMaterials / Raw materials
Material Manufacturer Description
Wood J. Rettenmaier & Söhne spruce wood fibers
Polyethylene Borealis high density polyethylene intended for blow moulding products
Polypropylene Borealis nucleated polypropylene homopolymer for thermoforming packaging
Coupling agent - PE BYK Altana maleic anhydride-grafted linear low density polyethylene
Coupling agent - PP BYK Altana maleic anhydride-grafted polypropylene
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Materials / AdhesivesMaterials / Adhesives
• Epoxy-based adhesive
– Two-component adhesive
– Curing at room temperature
• Acrylate-based adhesive
– Two-component adhesive
S l t f
• Epoxy-based adhesive (commercial)
– Two-component adhesive
– Solvent-free
– Curing at room temperature
– Solvent-free
• Polyurethane-based adhesive
• Wood glue (commercial)
– Water-based
S l t fPolyurethane based adhesive
– One-component adhesive
– Solvent-free
– Fast-drying (5 minutes)
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Materials / SamplesMaterials / Samples
Code Wood PP PE CAPP CAPE
W60PP38 60 38 2
W70PP28 70 28 2
wt-%
W70PP28 70 28 2
W60PE38 60 38 2
W70PE28 70 28 2
• Profiles were manufactured on a
Cincinnati fiberex K38 conical counter-
rotating twin-screw extruder
Specimen preparation by milling/sawing• Specimen preparation by milling/sawing
– 80 x 20 x 4 mm
– 65 x 20 x 4 mm
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Methods / PretreatmentMethods / Pretreatment-- II
• Sanding crosswise to the direction of stress
– Roughen and enlarge the surface area
– BOSCH disc grinder
– 120-grit sandpaper
• Flame treatment
– Oxidation mechanism
– Bunsen burner
– Distance to blue cone: 2 cm
– Time: 1 second
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Methods / PretreatmentMethods / Pretreatment -- IIII
• Plasma can be defined as partially ionized gas
• Plasma cleans and activates the surface and causes a very high
f ith id bl l tsurface energy with a considerable polar component
• Formation of hydroxyl and carboxyl groups
• Conditions
– Plasmatreat Openair® plasma system
– Feed rate: 6 m/min
– Process gas: air
– Distance to nozzle: 10 mm
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Methods / TestingMethods / Testing
• DIN EN 205 – Test methods for wood adhesives for non-structural
applications; determination of tensile shear strength of lap joints
S f ( tt bilit )
Insufficient adhesion of the bondline Material failure through high adhesion and cohesion
• Surface energy (wettability)
– Test inks (Plasmatreat, 28 - 72 mN/m, Ethanol, non toxic, suitable for most
surfaces) )
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bad wetting of the surface good wetting of the surface
ResultsResults -- II
Surface energy [mN/m]
Sample untreated plasma treated after one month storage
W60PP38 28 72 72
W70PP28 28 72 72
Surface energy [mN/m]
W60PE38 28 72 > 66 / < 72
W70PE28 28 72 > 66 / < 72
– Significant increase of the surface energy through plasma treatment
Hardly any change after one month storage (l b t t t )– Hardly any change after one month storage (laboratory, room temperature)
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ResultsResults -- IIII
6
7
2]
W60PP38
4
5
6
gth
T [
N/m
m2
untreated
2
3
4
e s
hear
str
en
g untreated
sanded
f lame
plasma
0
1
epo pol rethane epo ood gl e acr late
Ten
sil
e
• Acrylate-based adhesive no treatment needed
• Significant increase through surface treatment especially in combination with two
epoxy polyurethane epoxy (commercial)
wood glue acrylate
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• Significant increase through surface treatment, especially in combination with two
component adhesives
• Best values after flame treatment (except acrylate-based adhesive)
ResultsResults -- IIIIII
6
2]
W70PP28
4
5
gth
T [
N/m
m2
untreated
2
3
e s
hear
str
en
g untreated
sanded
f lame
plasma
0
1
l th d l l t
Ten
sil
e
• Significant increase through surface treatment best values after plasma
treatment (feasible method for existing production lines)
epoxy polyurethane epoxy (commercial)
wood glue acrylate
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treatment (feasible method for existing production lines)
ResultsResults -- IVIV
• The results of PE-based samples show hardly any differences in the trends
observed (except the absolute values due to the lower mechanical properties of
PE)
• Storage:
• Duration: 1 month
• Conditions: 23°C / 50 rH
• Influence on the results compared to “fresh” samples:
treatment W60PP38 W70PP28 W60PE38 W70PE28
flame decrease no effectincrease small
flame decrease no effect(except PU) decrease
plasmaincrease
(except acrylate)no effect decrease
small
increase
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ConclusionsConclusions
• PP- and PE-based samples showed the same trends
f• Pretreatment is not necessary for acrylate-based adhesive
• Flame and plasma treatment are efficient modification techniques for
surface modification of WPCsurface modification of WPC
• Plasma treatment is easy to install inline in existing production lines
• Polyurethane based adhesives are not suitable for WPCPolyurethane based adhesives are not suitable for WPC
• The wood glue and the commercial epoxy based-adhesive are applicable
for non-bearing applications after appropriate pretreatment
• WPC surface energy is influenced by pretreatment, sample handling and
storage time
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