WAXD and FTIR studies of electron beam irradiated biodegradable polymers

Abstract

Poly(L-lactic acid) (PLLA) and poly(ε-caprolactone) (PCL) have been receiving much attention lately due to their biodegradability in human body as well as in the soil, biocompatibility, environmentally friendly characteristics and non-toxicity. Morphology of biodegradable polymers affects the rate of their biodegradation. A polymer that has high degree of crystallinity will degrade at a slower rate due to the inherent increased stability. PCL homopolymer cross-linking degree increases with increasing doses of high energy radiation. On the other hand, the irradiation of PLLA homopolymer promotes mainly chain-scissions at doses below 250 kGy. In the present work, twin screw extruded films of PLLA and PCL biodegradable homopolymers and 50:50 (w:w) blend were electron beam irradiated using electron beam accelerator Dynamitron (E = 1.5 MeV) from Radiation Dynamics, Inc. at doses in the range of 50 to 1000 kGy in order to evaluate the effect of electron beam radiation on the homopolymers and blend. Wide-angle X- ray diffraction (WAXD) patterns of non irradiated and irradiated samples were obtained using a diffractometer Rigaku Denki Co. Ltd., Multiflex model; and FTIR spectra was obtained using a NICOLET 4700, ATR technique, ZnSe crystal at 45°. By WAXD patterns of as extruded non irradiated and irradiated PLLA it was observed broad diffusion peaks corresponding to amorphous polymer. There was a slight increase of the mean crystallite size of PCL homopolymer with increasing radiation dose. PCL crystalline index (CI) was 68% and decreased with radiation dose above 500 kGy. On the other hand. PLLA CI was 10% and increased with radiation dose above 750 kGy. On the other hand, PLLA presence on the 50:50 blend did not interfere on the observed mean crystallite size increase up to 250 kGy. From 500 kGy to 1 MGy the crystallite size of PCL was a little bigger in the blend than the homopolymer. Also it could be observed that the PLLA peak increase at 14.2° was affected by PCL presence on the blend above 750 kGy. In contrast, FTIR results have shown that this technique was not sensitive enough to observe the degradation promoted by ionizing radiation of the studied homopolymers and blends, and neither on the miscibility of the blends.