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

4

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

5

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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Thank you very much for your attention!Thank you very much for your attention!

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