A Study On Polypropylene/Wood Flour Composites

Wood plastic composite (WPC) is a kind of new composites developed in the last few years, which has combined the advantages of the plastics and wood. Polypropylene (PP) is a widely used plastic with excellent mechanical properties. PP has been used as the matrix material in WPCs for a long time. However, several disadvantages of linear PP restricted the application of PP/wood flour composites. In this thesis, several methods have been adopted to improve the performance of PP-based WPCs.1. In order to improve the mechanical properties of PP/WF composites, linear polypropylene was modified by melt branching reaction in Haake mixer. Long chain branching (LCB) polypropylene/wood flour composite was made in one step. Fourier Transformed Infrared Sepctra (FTIR spectra) indicated that macro-radical recombination reactions took place and PETA had been grafted onto PP backbone in the composites. Various rheological plots including viscosity curve, storage modulus, loss angle, Cole-Cole plot were used to show the existence of LCB. Mechanical tests showed that LCB increased the Izod notched impact strength and tensile strength. Moreover, LCB PP/WF composites have a better thermal stability than linear PP/WF composites according to TGA test. While scanning electron microscopy (SEM) indicated that LCB PP had a stronger affinity with the wood particles. It is expected that there is an interaction between LCB PP and the wood particles formed in reactive mixing, which would improve the mechanical properties of the composites. 2. Several methods were used to improve the compatibility between wood flour and polypropylene, such as using MA-g-polyolefin, micro-wave treatment, and silane coupling agent. All the methods have improved the Izod impact strength of WPCs. Then we used MA-g-polyolefin and silane to treat the wood flour together, and studied the synergetic effects on Izod impact strength. It is proved that the synergetic effects improved the impact strength of WPCs greatly. Scanning electron microscopy (SEM) also indicated that PP had a stronger affinity with the wood particles treated by MA-g-polyolefin and silane. There may be some chemical reaction happened to improve the interfacial campatibility.Both of the two solutions above have improved the capabilities of the WPCs, and there are some innovative points of reactive methods in wood treatments.