The Reinforcement And Biodegradation Of Poly (D,L-Lactic Acid) By Equal Channel Angular Extrusion

Poly(lactic acid), a biomedical material, with excellent biocompatibility and biodegrdability, has a bright application future. Normally, poly(D,L-lactide) is moulded by common processing method, whose mechanical ability can not satisfy the clinic demand. So here we will take the way of the Equal Channel Angular Extrusion (ECAE) to process poly(D,L-lactide) to improve its properties. Degradation properties are tested by ECAE.The experiment of moulding poly(D,L-lactide) is undertaken in the method of ECAE in three times above Tg and the tests of properties and structural characteristics should be used the apparatus, such as electronic mechanic machine, DTA, TGA and SEM. Poly(D,L-lactide) is tested in vitro degradation and thermal degradation experiments. Then their degradation changes were analysed.The results are as follows. The mechanical strengths of poly (D,L-lactide) are obviously improved At Tg throughout ECAE. The mechanic strengths of the samples increase with the increasing in ECAE temperature. The mechanic strength researched the biggest at 75℃by ECAE. With the increasing of extrusion time its mechanic strength gradually enhances. When extruded at 75℃for three times, its tensile strength and bending strength either was 61.25MPa and 182MPa, contrast original sample them improve by 193.37% and 97.83%.Under analysis of SEM of the longitudinal split surface of poly(D,L-lactide) the result indicated that the sample of poly(D,L-lactide) definitely had formed in orientation.Under analysis of DTA of poly(D,L-lactide) we conclude that with increasing time of extrusions, the Tg and the decompound temperature of the sample have enhanced. During the experiment, the Tg of sample, extruded at 75℃for three times, has increased from 75℃to 65℃whose span is the biggest increase. the thermo gravimetric temperature of poly(D,L-lactide) should be between 200℃-370℃. With the increasing extrusion times the temperature of thermal lost-weight was gradually increased and poly(D,L-lactide) thermal stability was increased. In vitro degradation experiments, at first molecular weight was degradated, degradation products which embedded in the sample can not dissolve in the outside media. So weight loss lagged behind molecular weight degradation. With the further degradation, Oligomer continued to degradation and weight loss was larger. Change of bending strength had liner relation with molecular weight degradation. The time of poly(D,L-lactide) degradation will be longer.