Study On Synthesis, Structure And Properties Of Degradable Polyurethane Modified By Lactic Acid

In this paper, a series of polyurethane elastomer with different structure were synthesized using liquefaction modified MDI> HTPB and PLA-OH as materials. The effect of PLA-OH with different content and molecular weight, the ratio of NCO/OH, crosslinker concentration and the molecular weight of HTPB on the mechanical properties, and thermal stability were investigated by tensile test, hardness test, thermogravimetry (TG), differential scanning calorimetry (DSC) and scanning electron microscope (SEM). In addition, the degradation of PUin different conditions and medias was studied by the method of weight loss and were certified by SEM.The results indicated that PU of different constitutes shows different mechanical properties. The elongation of break increased at first, but then decreased with increasing content of the PLA-OH. The tensile strength and the hardness displayed the best overall performance, when the content of PLA-OH is 20%. The results of the thermal analysis showed that the thermal stability became poor with the increasing of PLA-OH. The results of the degradation test indicated that PU modified by PLA-OH could perform degradation, the weight loss of the modified PU in base media was the most significant and would increased with the increasing of content of PLA-OH. The results were certified by the research of SEM as well. Furthermore the phenomenon that degradation occurred in the inner was faster than on the surface of the modified PU could be inspected by SEM. That is to say the degradation of PU is not well-distributed.In addition, a series of hydroxyl- terminated polyether- polyol- co-polyester were synthesized by the direct polycondensation with different constitute of the polyether-polyol (2000) and the lactic acid. Degradable polyurethanes were prepared by the reaction between the polyether -polyol-co-polyester and liquefication MDL It's characteristic includedtensile properties by stress-strain measurements, thermal properties by TG and DSC, degradation properties by weight loss was also studied.The result indicated that the hardness of PU was very well, the tensile strength decreased at first, but then increased, while the elongation of break decreased and the thermal stability became poor with increasing content of the lactic acid, but degradable behaviors were improved. Weight loss of the PU was monitored gravimetrically along with time changing, tensile properties monitored as a function of degradation time that indicated the modified PU could be degraded, when the weight ratio of polyether-polyol and lactic acid was 1.25, and the temperature is 80 the sample became fragments and lost the properties of utilization after 50 hours of degradation in water.