9. Conclusions

Wood, plastic and the uses of these composites in our daily life has been described in first chapter followed by the surface treatment and additives used for preparation of wood–plastic composites in subsequent chapter.

In the third chapter, machinery and testing techniques for making of wood–plastic composites has been discussed. Because, the authors think that proper machinery is the main important part to produce a good quality WPC. Fourth chapter is described about the research work done by other researchers in recent past.

One of the objectives of this research is to achieving the effects of screw configuration, screw speed, silica content and various compatibilizer on the physico-mechanical and foaming properties of wood-fiber/PP composites. Wood-fiber/PP composites were produced on the intermeshing co-rotating twin screw extruder. Microcellular closed cell wood-fiber/PP composite foams were prepared using pressure-quench batch process method. First, an attempt has been made to determine the optimum conditions of extrusion that involve are screw configurations, screw speed. The experimental results showed that wood-fiber/PP composite prepared under the configuration C (Fig. 5.​1) at screw speed of 150 rpm have higher mechanical properties and narrower cell size distribution, due to the improved dispersion of the wood-fiber in the composites. And then, the effect of the silica content on properties of wood-fiber/PP/silica composites showed that the relationship between silica content and mechanical properties was obvious. The property enhancements were controlled mainly by the extension of silica agglomeration. The foam density is governed by the combined effect of cell nucleation, cell growth, and cell coalescence, as a nucleation agent, the silica in wood-fiber/PP composite created a large amount of heterogeneous nucleation sites during foaming. The heterogeneous nucleations increased the cell density and decreased the cell size and foam density. This phenomenon disappears at high content of silica due to big agglomerates. Finally, the results of physico-mechanical properties of wood-fiber/PP composite with various compatibilizer showed that the PP-g-MA and SEBS-g-MA enhanced adhesion between the WF and PP matrix, Wood-fiber/PP composite with addition of PP-g-MA as compatibilizer showed highest tensile strength and stiffness. Composites with SEBS-g-MA showed the higher impact strength, elongation at break and tensile strength compared to composite systems with SEBS. The batch foaming result of PP/WF composites with various compatibilizer showed relationships between cell morphology and their crystallinity and stiffness. Higher crystallinity, showed higher stiffness and higher relative density.