Introduction Wood K plus. Motivation. Results. Conclusions. J. Leßlhumer 1, J. Sinic 1, M. Reif 1, A. Haider 1, D. Cascorbi 2

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1 1 st Workshop - Basics for Chemistry of Wood Surface Modification April 25-26, 2012, Kuchl/Salzburg, Austria Surface modification of WPC products to improve 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 Chemistry 2 PINUFORM GmbH & Co. KG Content Introduction Wood K plus Motivation Materials / Methods Results Conclusions 2

2 Wood K plus R&D Institute for wood-based materials, wood composites and wood chemistry 95 scientific employees 50 projects Budget: 7.0 mio p.a. 4 business units, one cross sectional market research field Mark innov ket analy vation re ysis and search Wood- and cellulose chemistry W3C: Surface technologies and logistics Solid wood and wood- based materials Wood polymer composites 3 R&D services - Division WPC Consulting Raw material characterization Wood and fiber analytics Polymer analytics Material characterization Compound analytics Material testing Component testing Extrusion trials Pilot plant Injection molding Material & Process development 4

3 Motivation Wood Polymer Composites (WPC) are made of lignocellulosic material based on different thermoplastics New applications require print- and glueability Problems caused by thermoplastic matrix Hydrophobic Non polar Low surface energy activate and/or modify the surface to improve wettability increase surface energy increase bonding strength 5 Materials / 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 6

4 Materials / Adhesives Epoxy-based adhesive Two-component adhesive Curing at room temperature Epoxy-based adhesive (commercial) Two-component adhesive Solvent-free Polyurethane-based adhesive One-component adhesive Acrylate-based adhesive Two-component adhesive Solvent-free Curing at room temperature Wood glue (commercial) Water-based Solvent-free Fast-drying (5 minutes) 7 Materials / Samples wt-% Code Wood PP PE CA PP CA PE W60PP W70PP W60PE W70PE Profiles were manufactured on a Cincinnati fiberex K38 conical counterrotating twin-screw extruder Specimen preparation by milling/sawing 80 x 20 x 4 mm 65 x 20 x 4 mm 8

5 Methods / Pretreatment- I 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 9 Methods / Pretreatment - II Plasma can be defined as partially ionized gas Plasma cleans and activates the surface and causes a very high surface 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 10

6 Methods / Testing DIN EN 205 Test methods for wood adhesives for non-structural applications; determination of tensile shear strength of lap joints Insufficient adhesion of the bondline Material failure through high adhesion and cohesion Surface energy (wettability) Test inks (Plasmatreat, mn/m, Ethanol, non toxic, suitable for most surfaces) bad wetting of the surface good wetting of the surface 11 Results - I Surface energy [mn/m] Sample untreated plasma treated after one month storage W60PP W70PP W60PE > 66 / < 72 W70PE > 66 / < 72 Significant increase of the surface energy through plasma treatment Hardly any change after one month storage (laboratory, room temperature) t 12

7 Results - II 7 W60PP38 Tensile e shear streng gth T [N/mm2 2] untreated sanded flame plasma 0 epoxy polyurethane epoxy wood glue acrylate (commercial) Acrylate-based adhesive no treatment needed Significant increase through surface treatment, especially in combination with two component adhesives Best values after flame treatment (except acrylate-based adhesive) 13 Results - III 6 W70PP28 Tensile e shear streng gth T [N/mm2 2] untreated sanded flame plasma 0 epoxy polyurethane epoxy wood glue acrylate (commercial) Significant increase through surface treatment best values after plasma treatment (feasible method for existing production lines) 14

8 Results - IV 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 increase small flame decrease no effect (except PU) decrease plasma increase (except acrylate) no effect decrease small increase 15 Conclusions PP- and PE-based samples showed the same trends Pretreatment is not necessary for acrylate-based adhesive Flame and plasma treatment are efficient modification techniques for surface modification of WPC Plasma treatment is easy to install inline in existing production lines Polyurethane 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 16

9 Thank you very much for your attention! 17