The Application Study On Using Recycled Polypropylene In Wood Plastic Composites

With the steady development of our economy in recent years, polymer matetials, which were produced and used in every corner of our life, have induced a lot of recycled plastic. It is so important for environmental protection and resources regeneration that we have to make some research on the recovery and reuse of the waste plastic. Plastic is one of the four basic materials which can achieve"reduction, reuse, recycle". Most of the plastic can be recycled, so it is a kind of resource-conserving and environment-friendly material actually. Nowadays, a new industry named"Plastic recycling", which has a practical significance of"circular economy"and"sustainable development strategy", is growing quickly. On the other hand, the demand of woods soars, while most of the countries make strict restrictions on deforestation with the growing awareness of environmental protection. Therefore, the research on finding a material as a replacement for woods, which can be made from the waste plant fiber such as wood powder(WP), rice chaff, bamboo powder(BP), sisal, straw and so on has attracted people'attention.In this paper, wood powder and maleic anhydride grafted polypropylene(MAPP) as an interface modifier were combined with the new and recycled polypropylene(RPP) matrix to make wood-plastic composites(WPC). Glass fiber and calcium carbonate were also introduced in order to reinforce the WPC. It was knew that polyethylene wax(PEW) as a kind of universal lubricant can enhance the processing ability of the WPC, but decrease the mechnical properties simultaneously. So we also studied how to graft maleic anhydride(MAH), methyl methacrylate(MMA) and butyl acrylate(BA) on PEW through melt copolymerization, then applied the reaction production(GPEW) on the WPC to demonstrate the influence of GPEW on the mechnical property, processing and heat resistance ability of the composite.The results showed that MAPP can effectively enhance the combination property of both PP/WP and RPP/WP composites. When the ratio of MAPP and wood powder is 0.20, the combination property of PP/WP composite reaches the best level. The tensile strength of the PP/WP(100/50) system is increased by 46%, non-notched impact strength is elevated by 72% and the flexural strength is raised by 24%. As a coupling agent, MAPP is also used in RPP/WP and RPP/BP composites. We find that the combination property of RPP/plant fiber(100/50) composites reaches best when the ratio of MAPP and plant fiber is 0.25. Generally, the property of composite with wood powder is little better than with bamboo powder. The tests of SEM, DSC and TG illustrate that MAPP can effectively improve the interface compatibility, accelerate the crystallizing ability and enhance the heat resistance of both PP/WP and RPP/WP composites.Glass fiber can also enhance the combination and heat resistance property of both PP/WP and RPP/WP composites, but decrease the processing ability. After adding the proper weight of MAPP, RPP/WP/GF(100/50/20) has greater property than RPP/WP(100/50), the tensile strength is increased by 20%, non-notched impact strength is elevated by 30% and the flexural strength is raised by 25%. MAPP can improve the interface compatibility of wood powder and glass fiber with PP matrix. Glass fiber can distribute the stress when the composite is damaged. calcium carbonate can enhance the mechanical properties of new PP/WP composite, but has little effect on the RPP/WP/CaCO3 composite. MAPP can improve the dispersion of calcium carbonate in the WPC.GPEW was synthesized under different ratio of functional monomers and the weight of initiator, reaction time, temperature, the best reaction condition was studied through comparing the effects of GPEW on the tensile strength of PP/WP(100/100). The influence of GPEW on the processing and heat resistance ability of PP/WP and RPP/WP composites was also investigated. The results showed that the best outcome of grafting was gained by adding 8 phr MAH, 8 phr MMA , 2 phr BA and 2 phr BPO in 100 phr PEW at 120℃after reacting 4 hours. The test of TG illustrated that GPEW was stabler than PEW when it was heated. The test of DTA demonstrated that GPEW was more hydrophilic than PEW. After adding GPEW and PEW, the balance torch of PP/WP(100/50) was decreased, however,PEW was a little effective. The addition of GPEW and PEW had the same effect on decreasing the viscosity of the composites. The tests of DSC and TG illustrated that GPEW and PEW would impaire the heat resistance ability of the PP/WP composite, but PEW was more harmful.