Study On The Preparation And Properties Of The Fully-degradable Hemp Fiber/polylactic Acid Composite

Material is one of the most important foundations of human social development, and environment is the prerequisite of sustainable development of human social. But now lots of waste materials left which has become a prominent problem because of the development of society. In recent years, the development of biodegradable materials shows a new way to resolve this issue. However, the biodegradable materials are mostly linear polymers, due to a single structure, which are difficult to meet society requirements because of the performance deficiencies. Therefore, improving the performance of biodegradable materials, to replace the common plastic of high pollution and energy consumption, has the far-reaching significance.Polylactic acid (PLA), as the most widely used biodegradable materials currently, has the demerit of high brittleness, which has affected its more widely application. Aiming at this problem, in this study, hemp fibers were used to reinforce PLA for preparing the fully-biodegradable composite, to improve the mechanical properties of PLA and expand the scope of its application. Two kinds of methods, mixing-hot pressing and laminating were used to prepare the hemp fiber/PLA composites. And the effects of preparation method, fiber content and interface adhesion on the properties of composites were also investigated in detailed.The best fabricating processes of the two preparing methods were determinate. For the mixing-hot pressing method, the best process was that PLA was mixed for 6 min at a rate of 20 r/min(150℃), and then pressed for 6 min under a pressure of 15Mpa (160℃). The properties of the composite reached up to the best when the content of hemp fiber was 30(wt)%, of which the impact strength has been improved for 65.9%, and the tensile and flexural strength of the composite increased by 38.5% and 39.7% respectively. And for the laminating method, the best condition was applying two kinds of pressure,5Mpa and 15Mpa, and the heating rate was 5℃/min, and the final temperature when pressed was 155℃. The properties of the composite reached up to the best when the content of hemp fiber was 40(wt)%, the tensile, flexural and impact strength reached up to 102.3 MP,130.6MPa and 17.23KJ/m2 respectively. And the pretreatment of hemp fiber using silane coupling agent (KH550) and the addition of nucleating agent (talcum powder) can both improve the mechanical properties of composites via the proving of tests on universal testing machine, scanning electron microscopy (SEM), differential scanning calorimetry (DSC). Finally, the degradation property of the composites was tested. Results showed that the degradation rate of composite materials was very low in the natural condition, but in soil the rate was significantly higher. Hydrolysis rate of composite was higher than pure PLA, and in alkaline condition, the degradation rate was highest, a bit lower in the acidic condition, and in the neutral condition was the lowest.