| The polyvinyl alcohol (PVA) is a polymer which is biodegradable completely. PVA can be a good performance plastic membrane that can instead of polyvinyl chloride and polystyrene. But degradation time of the pristine PVA is too long, which limits the application itself. In this study, the polyvinyl alcohol was modified by sterification and blend, and PVA with a faster degradation rate was made.The PVA cross-linked citric acid polymer was synthesized firstly by esterification. Hydroxyl group from PVA reacted with carboxyl groups from citric acid, which can create esterfunction that was biodegradable easily. The samples were characterized by Fourier transform infrared (FT-IR) spectroscopy. The mass ratio, reaction temperature and time of PVA and citric acid were discussed by orthogonal experiment which had effect on the degree of esterification. For this graft polymerization system, the optimum conditions were determined. Feed ratio m(citric acid): m(PVA) was 4:1, reaction temperature was 60℃, reaction times was 3 hours, the yield of the product up to 47.12% . Through the TG, DSC studied the thermal properties of CA-PVA. It showed that CA-PVA thermal degradation process was divided into two stages. One stage will focus on the thermal degradation of CA-PVA material, the other stage is mainly the thermal degradation of PVA . It was found from the DSC curve that the thermal decomposition temperature of PVA was reduced by the introduction of citric acid.Membranes were prepared from modified PVA polymer with starch or poly(vinyl pyrrolidone) (PVP) as plasticizer by the tape casting method in aqueous solution. Mechanical properties and light transmission rate of modified PVA membranes was examined and films morphology were characterized by electron microscope.It showed that tensile strength and elongation at break of Starch/CA-PVA film increased first and then decreased with increasing of the amount of starch filled, and transmittance shown a downward trend. But when the amount of starch filled reached about 50%, mechanical properties and transmission of the membranes undergone a sharp decline. So the best amount of starch filled was 50%. In this condition, the membranes had the best mechanical properties, tensile strength and fracture elongation rate reached 7.7 MPa and 32.20% respectively, and light transmission rate was above 70%. Tensile strength of PVP/CA-PVA film increased first and then decreased with increasing of the amount of PVP filled, elongation at break shown a downward trend and transmittance gradually decreased. But when the amount of PVP filled reached about 50%, mechanical properties and transmission of the membranes undergone a sharp decline. So the best amount of starch filled was 50%. In this condition, tensile strength of the membranes reached 5.3MPa, fracture elongation rate reached 13.6% respectively, and light transmission rate was above 95%.Degradation characteristic of the modified PVA was investigated which could be degraded in vitro or buried under the soil. The results showed that: in vitro degradation the Starch/CA-PVA membrane's weight loss rate can be up to 85% in 24 hours; while buried in the soil Starch/CA-PVA membrane can loss 30% after 6 months. However, pure PVA film's weight loss rate is only 70% in vitro degradation after 24 hours, 12% when buried in the soil degradation after 6 months. When test the mechanical properties of the degradation of the Starch/CA-PVA membrane, we found that the tensile strength of thin film was gradually decreasing and the trend of the elongation at break shown the first increase then a sharp decrease.
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