In order to solve the practical problem of heat transfer during the hot pressing process of a novel wood-plastic composite plywood, this paper investigates the perforation treatment of polyvinyl chloride (PVC) plastic films and their plywood composites. The PVC films were pretreated by the physical punching method, and the effects of PVC perforation diameter, hot pressing time and hot pressing temperature on the mechanical properties of the plywood composites were investigated by orthogonal experimental design. The results showed that the optimum hot pressing time was 7 min, the hot pressing temperature was 170 °C, and the PVC perforation diameter was 15 mm for the optimum mechanical properties. The punching pretreatment of PVC films gave rise to a reduction of the hot pressing time by 51 s due to improved heat transfer and heat loss by 5.06%, and allowed an increase in the initial moisture content of the veneer by 2–3%, thereby cutting down the drying cost in the veneer production process, which is conducive to energy conservation and environmental protection.
Wood based composites, such as plywood, particleboard, oriented strand board (OSB), medium density fiberboard (MDF), laminated veneer lumber (LVL) and Glulam, are commonly used for both structural and non-structural applications.1–3 These composites are usually produced using aldehyde adhesives, such as urea–formaldehyde resins (UF) and phenol–formaldehyde resins (PF), the production and products of which can release free formaldehyde.4–6 In particular, most of these composite panels are for indoor applications and release of harmful gases is very detrimental to people's health. In order to reduce the toxicity of wood-based composites, some researchers have attempted biomass-adhesives for the production, e.g. plant protein adhesives, blood glue, starch glue and bone glue.7–9 However, these adhesives have high viscosity and are difficult to apply evenly, which may lead to unstable bonding of glue lines. In addition, biomass adhesives are prone to mildew and deterioration, and are not suitable for use in high humidity environments. Wood-plastic composite plywood have also recently been considered as one of alternative in some applications of wood based composites and the advantages of which are light weight, easy processing, good thermal insulation performance, rich texture and importantly no release of formaldehyde,10 and wood plastic composites have also the characteristics of water resistance, mildew resistance and chemical resistance.