PVC-based wood plastic composites (WPC) and its discoloration issue: Application, challenges and opportunities of nanotechnologies

So far, the biggest issue of PVC-based WPCs for outdoor application is the discoloration overtime. Over the years zinc oxide (ZnO) nanoparticles have attracted much interest, because they possess various remarkable physical and chemical properties, like good transparency and UV absorption properties. The incorporation of nano-ZnO as UV-protecting agent into a polymer matrix have attracted particular interest in academic and industrial research. In this work we have tested the colour-fading resistance properties of innovative PVC-based WPCs, filled in many ways with different kind of ZnO and functionalized ZnO nanoparticles. The effectiveness of ZnO nanoparticles for protection of WPCs against discoloration were studied under controlled UV ageing conditions, both "only dry" and "dry / wet" conditions ("dry / wet" conditions were used to obtain a more realistic aging of the materials). The first results showed that the UV-induced photodegradation effects could be only slightly reduced as compared with neat polymer. We discovered that the potential anti-UV activity of nano-ZnO was masked by the strong discoloration of the wood matrix, which is always induced by moisture. Due to this fact we understood that a protection of the wood particles against moisture seems to be mandatory, so we started using alternative approaches in order to do that. In collaboration with all the involved partners, new kind of hydrophobic additives were tested into the WPCs, in association with nano-ZnO, trying to obtain a synergistic effect by increasing hydro-repellency and anti-UV properties. The protection of the wood particles against moisture seemed to be the right way to go through, so new functionalized nano-ZnO additives were developed by the partners and we tested the resistance of the so produced WPCs, verifying an improvement of the resistance against moisture- and UV-induced discoloration. Also an improvement of the dimensional stability of WPCs under wet conditions was achieved.A secondary approach was to use a pretreated wood flour called Thermowoodr (ThermoWoodr is a registered trademark owned by International ThermoWood Association), which should be more resistant to the atmospheric agents.Thanks to their improved durability against decay, the products made with this kind of wood are well suited to applications involving demanding weather conditions.Sovere made a preliminary.