Effect of Isothermal Annealing on Degree of Crystallinity,Mechanical Properties and Degradation Behavior of PLLGA85/15

The effect of isothermal annealing on the degree of crystallinity,mechanical properties and degradation behavior of a random copolymer poly(L-lactic-co-glycolic acid) with monomer molar ratios of 85/15 (PLLGA85/15) was investigated.The polymer was annealed at the optimal annealing temperature of 130℃.Its crystallization behavior after annealing was observed by X-ray diffraction (XRD),and the mechanical properties were tested by universal mechanical experimental machine.The degradation experiments of PLLGA85/15 with different annealing times were performed,and the changes of water adsorption rate,weight loss rate and pH of solution after degradation were observed.The change of polymer molecular weight after degradation was determined by gel chromatography (GPC),change of mechanical properties was measured by differential scanning calorimetry (DSC),and the change of micro-morphology of samples was observed by scanning electron microscopy (SEM).As shown by the experimental results,the degrees of crystallinity and mechanical properties were increased with the increasing of annealing time,while kept constant when reached the maximum data.Long time annealing led to accelerated thermal degradation and reduced molecular weight,while short time annealing resulted in increase of the degree of crystallinity and reduction of degradation rate.