The poly (lactic acid) (PLA) was modified with three kinds of light stabilizer

UV-944

UV-531

UV-9 and antioxidant 7910

glycidyl methacrylate (GMA) and Triphenyl phosphate (TPP). The thermal stabilities of all modified specimens were studied by gel permeation chromatography (GPC) and rheological tests. The results showed that weight- average molecular weights of neat PLA pellet declined from 136000 to 101000 by melt-blending and press-molding. After heat treatment at 180℃ for 5h

weight-average molecular weight of pure PLA declined from 101000 to 37000

while that of PLA modified with 0. 25%(wt) TPP decreased from 101000 to 91000. The storage modulus and complex viscosity of PLA modified with 0. 25 % (wt) TPP remained constant within the studied range. These results indicate that the introduction of TPP effectively prevent thermal degradation of PLA. Weight-average molecular weights of PLA modified with UV-944 and antioxidant 7910 were maintained at about 133000 and 121000

respectively. UV-944 and antioxidant 7910 effectively improve the thermal stability of the PLA matrix. UV-944 and antioxidant 7910 together have a synergetic effect on the improved thermal stability of PLA

while other compound additives have little improvement on thermal stability of the matrix.