Study On Preparation And Properties Of Poly (l-lactic Acid)/ Starch Composites Foams

Polylactic acid (PLA) has good biocompatibility and degradtion, but the costs of PLA foam is relatively high. Poly L-lactic acid (PLLA) was modified by using cheap and easily obtained starch to prepare the PLLA/starch composite foams in this thesis, moreover, the structure and properties of the relative products were characterized and tested also.PLLA/starch composites were prepared by microwave melt-blending method from L-lactic acid (LLA) and starch. The structure of composites was characterized by FT-IR, XRD and SEM, and the properties were tested. Maleic anhydride and glycerin work as chemical bridge between PLLA and starch in PLLA/ starch composite, resulting in the improving of compatibility, but theαorthonormal structure for PLLA is undistorted. The optimzing conditions for PLLA / starch composites from reaction time, coupling agent and other conditions were as following: the mass ratio of the water in gelatinized starch to starch is 1.5:1, maletic anhydride and glycerol contents were 1.2% and 0.6%, the composites were heated 5 min by microwave heating device, then heated extra 3 min after the composites which had been taken out were disbersed for 2 min.According to the characteristics of microbial degradation and enzymatic degradation of PLLA / starhc blends, the speed of degradation was controlled by adjusting the ratio of polylactic acid to starch. In the progress of degradating, the tensile strength decreased. The results by testing PLLA / starch composites hydrolysis showed that starch in composites were degradated completely after 2h degradation in 60℃, but PLLA was partly degradated. The effects of hydrolysis are better than soil burial test, PLLA tensile strength was decreased gradually.PLLA/starch foam was prepared by respectively using azobisisobutyronitrile, ammonium bicarbonate and sodium bicarbonate as the foaming agent. The best process parameters to prepare PLLA / starch composites were obtained by studing the influencing factors on starch, foaming agents, crosslinking agent, reaction temperature, reaction time: starch is 15% of the total composite foams, the ratio of composite foams blowing agent to sodium bicarbonate azobisisobutyronitrile is 1:1, borax is 0.03%, guar gum is 10% of the total mass, the ratio of water to starch to starch is 8:1, foaming temperature is 100℃, the reaction time is 7h.