Preparation Of Polylactic Acid/Wood Fiber Composites And Their Compatibilization Modification

With the enhanced awareness of environmental protection and increase the global energy crisis,biodegradable materials has attracted more and more attention.Polylactic acid,as the green material that has the potential to replace traditional petroleum-based plastics,shows a bright future.However,the high price,poor heat resistance and low crystallinity have always limited the widespread application and production of polylactic acid.On the other hand,there are a large number of forestry resources in the world,but the utilization rate of wood materials is very low at present,and a large amount of discarded wood materials have the potential for secondary recycling.The combination of polylactic acid and wood materials to prepare a new type of green material can not only fully exploit the advantages of both degradation and no pollution,but also make full use of a large amount of wood materials.In-depth study and preparation of polylactic acid-based wood-plastic composites with good compatibility is of great significance for the development of wood-plastic composites and biodegradable materials.In this paper,firstly,the hyperbranched polyester is used as a compatibilizer to improve the compatibility of polylactic acid and wood fiber.It has been found that hyperbranched polyesters can weaken the intramolecular hydrogen bonds of wood fiber molecules,and the main role of compatibilizing polylactic acid and wood fibers is hydrogen bonding.When the content of hyperbranched polyester in wood fiber is 15%,the mechanical properties of the composite are the best,the tensile strength is increased by 14.75 MPa,and the tensile modulus is increased by 379.04 MPa.According to SEM analysis,the addition of hyperbranched polyester can weaken the interface polarity difference between polylactic acid and wood flour and improve the compatibility of the two phases.The hyperbranched polyester has an amorphous structure and does not change the crystal form of wood fiber and polylactic acid.As an effective nucleating agent,wood fiber can promote the crystallization of polylactic acid.The addition of hyperbranched polyester has a strong inhibitory effect on the crystallization of polylactic acid.Then,the polylactic acid was grafted with maleic anhydride,and the wood fiber was alkali treated,silane treated and esterified.The research showed that: When PLA:MA:DCP mass ratio is 100:4:0.4,it is most suitable to prepare polylactic acid grafted maleic anhydride(MPLA).The tensile strength and tensile modulus of MPLA and silane coupling agent treated wood fiber composites were the highest,64.72 MPa and 2194.38 MPa,respectively,and the SEM image of the tensile section was the roughest.The mechanical properties of MPLA and esterified wood fiber composites were the worst,and there were a lot of voids and particle pull-out in the SEM image of the tensile section.The MPLA/esterified wood fiber composite has a relative crystallinity of 50% for a minimum of 1.65 minutes.The alkali-treated wood fiber crystal form changed from cellulose type I to cellulose type II.Finally,ethylene butyl acrylate grafted with glycidyl methacrylate(EBA-GMA),citric acid(CA),polyethylene oxide(PEO),ethylene acrylic acid copolymer(EAA)four compatibilizers to further improve MPLA / alkali-treated wood fiber composites.The results showed that EBA-GMA,citric acid and PEO significantly improved the mechanical properties of MPLA/ alkali-treated wood fiber composites.The addition of EBA-GMA,citric acid and PEO make the cross-sectional SEM image of the composite material more uniform,and the phase interface is more blurred,showing better compatibility,and the hydrophobic properties of the composite material are also obviously improved.The phase interface of the MPLA/alkali-treated wood fiber composite with EAA added still has micropores and uneven particle distribution,but the composite exhibits good heat resistance.