Study On Preparation And Interface Stability Of Wood Plastic Composites

Wood Plastic Composite(WPC)is a kind of composite materials with excellent per-formance,which is obtained by compounding plant fibers,plastics and other additives with a series of processing techniques.Compared to original materials,the composites have a variety of excellent characteristics,such as better stability and strength,corrosion resistance,light weight and environment-benign,and have a very high practical value.However,the poor interfacial bonding between the resin matrix and the reinforcing material is an important problem in wood-plastic composites.Therefore,how to improve the compatibility of the two phases is the key factor to promote the development of WPC industry.It is urgent to prepare a high performance interface modifier with simple process techniques.Recently,a new kind of multi-monomer graft copolymer prepared by copolymerizing multiple monomers has become a highly effective compatiblizer for WPC.As the compatibilizer of WPC,the multi-monomer graft copolymer has potential practical values in terms of high graft degree,effective interfacial compatibilization and low cost.Therefore,it is necessary to prepare a highly effective ternary monomer graft copolymer that can be used as an interface modifier for WPC and systematically study the effect of graft copolymer on the interfacial compatibility and mechanical properties of WPC,which is of great significance to the industrial production of composite materials.Firstly,maleic anhydride(MAH),methyl methacrylate(MMA),and butyl acrylate(BA)were grafted on polypropylene(HDPE)and polypropylene(PP)by using melt grafting method and solid phase grafting method,respectively.Then,thermogravimetric analysis(TG),differential scanning calorimetry(DSC),Fourier transform infrared spectroscopy(FTIR),polarized light microscopy(POM)were used for analysis and testing.The results of FTIR analysis showed that the polar monomers were successful in grafting on polyolefin backbones.The interfacial modifiers PP-g-MAH/MMA/BA(SP-GPP)and HDPE-g-MAH/MMA/ BA(SP-GPE)were successfully prepared by solid phase grafting and the interfacial modifiers PP-g-MAH/MMA/BA(M-GPP)and HDPE-g-MAH/MMA/BA(M-GPE)were successfully prepared by melt grafting.The results of POM and DSC show that the crystallization temperature and crystallinity of graft copolymers decrease compared to the original polyolefin because the introduction of polar monomers into polyolefin increases the intermolecular interactions and changes the crystalline form and crystallization rate of polyolefin during the crystallization process.Then the interfacial modifier was compounded with polyolefin and the effect of interfacial modifier on the performance of the polyolefin was inve stigated in order to obtain the adding reference for the interfacial modifier in the WPC.The results show that with the increasing of the adding content of modifier M-GPP or SP-GPP,the mechanical properties of the polyolefin gradually increase.when the adding content of interface modifier is 7 phr,the properties tends to be stable or slightly increase.At the time,the mechanical properties of the polyolefin are relatively stable.With the increasing of the adding content of interfacial modifier M-GPE or SP-GPE,the mechanical properties of the polyolefin gradually decrease.When the adding content of modifier is 9 phr,it gradually decreases and tends to be stable.Secondly,four interfacial modifiers such as SP-GPP,SP-GPE,M-GPP and M-GPE were used to improve the interfacial compatibility of wood plastic composites.The testing results of mechanical properties show that the mechanical properties first increase and then generally maintain stability with the increase of the modifier content.The effec t of the interface modifier by melt grafting method is greater than that by solid phase grafting method.When the adding content of interface modifier M-GPP is 5 phr,the comprehensive mechanical properties of wood/PP composites reach the best va lue.The tensile strength,flexural strength and notch impact strength increase by 63.1%,53.5% and 20.3% respectively.When the the adding content of modifier M-GPE is 7 phr,the mechanical properties of wood/HDPE composites reach the best val ue.The tensile strength,flexural strength and notch impact strength reach the best value at 7 phr,increasing by 24.5%,22.05% and 45.2% respectively.SEM directly shows that the interface state between the two phases changes from visible before the addition of the interface modifier to obscure after the addition of the interface modifier.FTIR shows that the modifier has an esterification reaction with the hydroxyl group in wood powder and plays a bridge role in the materials.The calculated results by the mathematical model show that with the increase of fiber content,the interfacial bond strength parameter B of composites decreases.Thirdly,the steaming and cooking technics were used to pretreat the wood fiber and bagasse fiber.FTIR results showed that there was no major chemical reaction happened inside the fibler after steaming and cooking,only a physical process.SEM was used to observe the microstructure changes of plant fibers after the pretreatments.Results showed that there is no distinct morphological change except that a few small molecule impurities are reduced on the surface of fibler and the surface becomes slightly smooth after cooking.The mechanical properties tests show that the cooking fiber has the better reinforcing effect on polyolefin than the steaming fiber.Finally,melt grafting method was used to modify polypropylene wax(PPW)and polyethylene wax(PEW)and prepare the interfacial modifiers PPW-g-MAH/MMA/BA(M-GPPW)and PEW-g-MAH/MMA/BA(M-GPEW).M-GPPW and M-GPEW were coordinated with M-GPP and M-GPE to obtain the compound interfacial modifiers M-GPP/GPPW and M-GPE/GPEW.M-GPP/GPPW and M-GPE/GPEW were used to improve the interfacial compatibility of pretreated-fibers filled WPC.Results show that the compound modifier has a greater impact on the mechanical properties of the wood plastic composite than the single modifier.The optimum ratio of the compound modifier M-GPP/GPPW and M-GPE/GPEW is 8/2,where the mechanical properties of the material are the best.