Interface optimisation and bonding mechanism of rubber-wood-plastic composites

Abstract

The incorporation of waste tyre rubber into thermoplastics to develop a class of polymer composites with both elastomeric and thermoplastic behaviour has gained a lot of attention and is becoming one of the most straightforward and preferred options to achieve the valorisation of waste tyres. In view of the unique properties rubber possesses and the rapid expansion and versatile application of wood plastic composites (WPC) materials, the inclusion of tyre rubber as raw material into WPC to develop an entirely new generation of WPC, namely rubber-wood-plastic composites (RubWPC), was presumed to be another highly promising solution to turn waste tyres into value-added materials. This research starts with the interfacial optimisation of Rubber-PE composites and WPC by the use of maleated and silane coupling agents, aiming at addressing their poor constituent compatibility and interfacial bonding, thus enabling the optimal design of RubWPC. Chemical, physical and mechanical bonding scenarios of both untreated and treated composites were revealed by conducting ATR-FTIR, NMR, SEM and FM analyses. The contribution of the optimised interface to the bulk mechanical property of the composites were assessed by carrying out DMA and tensile property analysis. The influence of the coupling agent treatments on the in situ mechanical property of WPC was first determined by nanoindentation analysis, which led to a thorough understanding of the interfacial characteristics and the correlation between in situ and bulk mechanical properties. This research focuses on the novel formulation of RubWPC and the understanding of bonding mechanism. Chemical bonding and interface structure studies revealed that interdiffusion, molecular attractions, chemical reactions, and mechanical interlocking were mutually responsible for the enhancement of the interfacial adhesion and bonding of the coupling agent treated RubWPC. The improved interface gave rise to the increase of bulk mechanical properties, while the continuous addition of rubber particle exerted an opposite influence on the property of RubWPC. The composite with optimised interface possessed superior nanomechanical properties due to the resin penetration into cell lumens and vessels and the reaction between cell walls and coupling agents.