Preparation And Research Of Polylactic Acid Composite Materials For Ecological Vehicles

With the rapid development of the automobile industry,environmental problems such as lack of oil resources and air pollution have become increasingly prominent.The Ministry of Industry and Information Technology of the People’s Republic of China has put forward requirements for the greening of the automobile industry.Biodegradable bio-based materials have the advantages of naturalness and environmental protection.The use of bio-based composite materials to replace petroleum-based materials in non-metallic products in the automotive industry is a major trend in the future.However,in practical applications,there are generally restrictions on toughness,mechanical properties and thermal properties compared with petroleum-based materials.In this paper,the poly(lactic acid)and poly(butyleneadipate-co-terephthalate)(PLA/PBAT)were melt-blended to improve the tenacity of PLA.The 4,4′-methylene diphenyl diisocyanate(MDI,0.5% of the total resin)which acted as a reactive chain extender was added to strengthen the interface compatibility of the blended PLA/PBAT.Co-polymers PLA-PBAT-MDI with basalt fiber(BF)were melted to improve the strength of(PLA-PBAT-MDI)/BF blends,and the comprehensive performance of the composites could be affected by varying the ratios of BF.Through comprehensive comparison of composite material microstructure,wide-angle X-ray diffraction(WAXS),Fourier infrared spectroscopy(FTIR)and other analysis and detection results,the microstructure composition,crystallinity and mixing uniformity of composite materials were analyzed;the strength and toughness and fatigue fracture mechanism of composite materials were explored through static tensile test,tensile fatigue test(stress ratio=0.1),fatigue SN curve and fatigue fracture morphology.Differential scanning calorimetry(DSC)is used to research the thermal stability and crystallinity of composite materials.DSC and WAXS analysis show that the addition of BF can effectively improve the strength and toughness,and crystallinity and thermal stability of the copolymer are also improved at varying degrees.The tensile fracture morphology shows that the addition of PBAT caused the co-polymer fracture to be obviously rough,which is transformed from brittle fracture to plastic deformation.It means that under the action of a small amount of compatibilizer MDI,the toughness of the co-polymer obtained by melt blending with PLA is enhanced.With the increase of BF,the fracture morphology gradually changes from crazing to fiber pullout and fiber fracture.However,although the co-polymer under the ratio of 40%BF+60%(PLA-PBAT-MDI)(hereinafter referred to as 40%BF)shows fiber breakage,the connection between BF fiber and the matrix is still very good.Fatigue S-N curve and fatigue fracture morphology analysis show that 40% BF co-polymer has the highest life,20% BF co-polymer second,and 10% BF co-polymer the lowest under the same stress level.Co-polymers with the same BF mass fraction,the life of objects under low stress levels is higher than that under high stress levels.The fatigue fracture of 10% BF is dominated by silver streaks and shear bands,while 20% BF and 40% BF are dominated by fiber fracture and fiber pull-out.The fibers are tightly combined with the matrix,and no obvious cracks are found in the matrix.The battery box upper cover model is established,subsequently,the two sets of material mechanical properties of 40% BF and the original cover material SMC are assigned.The modal analysis,static analysis,random vibration analysis and random vibration fatigue analysis can find that the performance of bio-based composite materials are better than SMC materials,which can replace SMC materials in battery box cover plates.The finite element model of the auxiliary instrument panel assembly is established based on the vehicle model,and the corresponding material parameters are assigned.Perform unit load static analysis on each hard point on the connected vehicle model in finite element method,and import all analysis results into n Code Design Life.Based on the Duty Cycle,the load spectrum that can be used for fatigue research is compiled,and a "five block diagram" was built in n Code.Using the obtained fatigue load of the entire vehicle life cycle as the fatigue life assessment target of the parts,assign the S-N curve obtained by the material fatigue performance test so that the fatigue life cloud diagram of the entire vehicle was received.The fatigue performance of the sub-instrument panel under the material parameters was studied,and the cloud chart showed that the damage value of the auxiliary instrument assembly does not exceed 1,which verifies the feasibility of the application of bio-based composite materials.This paper has carried out a series of design and research on bio-based composite materials,and verified its application in automotive products through simulation.The results show that 40% BF bio-based materials have superior performance and can replace petroleum-based materials in product design.It provides a way for in-depth exploration of bio-based composite materials to promote the ecological and green automotive industry.