Wood-coating interactions

One key factor for producing acceptable WPCs is the interaction between the wood and thermoplastic components (wood-polymer interface). It is difficult to achieve wood/plastic interaction because the hydrophobic thermoplastic (nonpolar) and hydrophilic wood (polar) are energetically different [2, 4]. During wood/plastic mixing, the thermoplastic must first coat or spread over the wood fiber surface to interact [4]. It is observed in Figure 26.2 that the polymer-fiber interface and a poor surface adhesion lead to fiber slipping from the matrix. 

Wood-filled PVC has inferior mechanical properties because of lack of interaction. Treatment of wood filler with aminosilane improves acid-base interaction between filler and polymer to the extent that impact strength and tensile properties of composite are improved over unfilled PVC. Tensile properties of PVC were deteriorated when leather particles were used as a filler. But, after filler particles were treated with ethylene-vinyl acetate copolymer, a coating was produced on the surface of filler particles that promoted adhesion with PVC and improved mechanical properties.These are some recent examples of many applications of filler preparations to improve its interaction with PVC. 

The influence of secondary interactions on the development of interfacial structure in composites of wood and amorphous thermoplastic polymers is not well understood. Inverse gas chromatography is used to investigate the effect of different polymers on the surface energy of partially or fully coated white pine wood meal. In this way, the development of the interphase is monitored as a function of polymer depth on the wood surface. The polymers are selected to provide a range of functional groups and include PS, PMMA, PVC,... 

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