| In order to improve the strength,wear resistance and flame retardancy of plastics as mechanical parts or vehicle decoration materials,it is necessary to modify them.Humanity is aware that traditional plastics derived from petrochemicals can accumulate in the environment and cause long-term harmful effects.Polylactic acid is a bio-based thermoplastic that is degradable,renewable and has good biocompatibility.However,due to its poor toughness,poor wear resistance and flammability,it limits some of its application fields.The coir fiber and bamboo fiber are used as raw materials.In order to realize the multi-integrated high value-added modification with low addition amount,the modified polylactic acid composite material is prepared.The chemical structure of the modified materials was characterized,and the thermal stability,mechanical properties,friction and wear and flame retardant properties of the composites with different fiber contents were tested and analyzed.The corresponding strengthening and toughening,low friction and wear resistance mechanism are preliminarily explored.The main research contents of this paper are as follows:（1）The coir fiber was chemically pretreated with a mixed solution of hydrogen peroxide and sodium hydroxide,and a coupling agent was added,silicon nitride and graphene microplatelets were used to obtain modified coconut fiber.Five kinds of polylactic acid modified composites with different fiber contents were prepared by controlling the ratio of modified coconut fiber to PLA.The composite showed good tensile strength（54.8 MPa）,elongation at break（10.3%）,toughness（3.16 MJ/m3）,average friction coefficient（0.48）and average wear rate(7.0×10-7 g/r)in mechanical tests,and the wear surface was smoother and flatter.（2）Bamboo fiber modified PLA composites with higher specific strength and specific modulus were selected and modified by the same method to explore the effect of bamboo fibers on the performance of PLA composites.The carbon residue rate of bamboo fiber with the same modification treatment was 24.15 wt%,and the temperature corresponding to the maximum thermal weight loss rate was 385°C.Compared with the coir fiber,the carbon residue rate was increased by 107.8%,and the temperature corresponding to the maximum thermal weight loss rate was increased by 10.9%.thermal stability and carbon-forming ability.The silicon nitride graphene microplatelets modified bamboo fiber PLA composite has better mechanical properties,lower average friction coefficient（0.44）and average wear rate(6.5×10-7 g/r)in the test,and the friction and wear properties are further improved.（3）A highly efficient phosphorus-containing flame retardant polyhydroxyethyl methacrylate phosphate（PHEMAP）was synthesized via free radical polymerization and loaded onto the silicon nitride graphene microplatelets modified bamboo fibers in the previous chapter,to realize the high value-added modification of the flame retardancy,mechanics and friction and wear properties of composite materials under low addition amount.The carbon residue rates of PHEMAP-BF,FG/PHEMAP-BF and Si3N4/GNPs/PHEMAP-BF were 36.8 wt%,34.7 wt%and 45.3 wt%,respectively,showing excellent carbon formation effect.PLA/Si3N4/GNPs/PHEMAP-BF reached V-0 grade at 3 wt%addition,the maximum heat release rate（PHRR）was 326 k W/m2,the total heat release（THR）was103.9 MJ/m2,and the carbon residue rate was Compared with PLA/3-PHEMAP-BF,it is 128%higher,and has greater tensile strength and toughness in mechanical tests.The fracture surface is covered with a large number of microscopic pits.The composite material changes from brittle fracture to ductile fracture,and reaches the optimum in this paper.The average friction coefficient and average wear rate are higher,the wear surface is smoother and smoother,and there is no obvious peeling pit and wear debris. |
