Effect Of Adding Wheat Straw Fiber And Nano-Powder On The Mechanical Property And Crystallinity Of PLA Composites

Polylactic acid (PLA) resin and its related composite is a kind of material which has the abilityof bio-deterioration. And as the advantages in the environment engineering, PLA has huge potentialmarkets both in research and application. However, the poor performances on impact strength and theheat resistance, which are indirectly influenced by the crystalline, lead to the limitation of PLA insome areas. According to these reasons, studying the mechanical properties and the crystalline of PLAmaterials is necessary.In this project, the three kinds of wheat straw fibers consist of different size, which were selectedby the defibrator process, the coupling treatment and the screen separation, were selected to mix withPLA powder. And the samples of composites were made by extruding and injection molding. Theeffect of coupling treatment was detected by the Fourier transform infrared spectrum analysis; Andthe variation tendency of mechanical properties was studied by the mechanical properties test and theSEM analysis; The DSC test results showed the variation tendency of glass transition temperature andthe degree of crystallinity of the composite. The results, which had been found through the integratedanalysis, showed that the formulation adding15%(mass fraction) wheat straw fiber treated bydefibering, coupling and screen separation into PLA is relatively good. At this point, the glasstransition temperature and the degree of crystallinity of the composite were63.53℃and38.44%,which were respectively increased by6%and14.5%. But the tensile strength, flexural strength andimpact strength of the composite respectively became to51.07MPa，55.16MPa，4.08KJ/m2, whichwere decreased appreciably.The four kinds of inorganic particle were chosen to mix with PLA powder as differentformulations, such as the nano-SiO2/PLA, the nano-ZnO/PLA, the nano-SiO2/mico-ZnO mixedpowder which was made by ball milling and the nano-SiO2/mico-ZnO mixed powder which was madeby high-speed mixer. And the samples of each formulation were made by extruding and injectionmolding. The data of mechanical property and the degree of crystallinity were collected through therelated performance testing. The best formulation, which had been found through the integratedanalysis, was adding0.5%(mass fraction) nano-SiO2/mico-ZnO ball grinded powder into PLA. Atthis point, the glass transition temperature, the degree of crystallinity, the impact strength, the tensilestrength and the flexural strength of the composite became to41.45%,65.22℃,68.82MPa,59.67MPaand4.92KJ/m2, which respectively increased by23.4%,8.8%,4.5%,9.1%and5.4%.