Electron Beam Radiation Modification on Chemical, Thermal and Crystalline Properties of Poly (L-lactic acid)

Abstract

The paper presents the effect of electron beam (EB) irradiation on poly (L-Lactic acid) (PLLA). The resultant physicochemical properties were investigated using Electron spin resonance spectrometer (ESR), Fourier transform infrared spectrometer (FTIR), Differential scanning calorimetry (DSC), X-ray Diffraction (XRD) and Scanning electron microscopy (SEM). The results suggest that PLLA undergoes random chain scission producing two types of free radicals ~Ċ(CH3)~ (I) and ĊH(CH3)~ (II) at room temperature. Presence of these free radicals has been confirmed by the ESR method and computer simulation studies using easyspin tool. FTIR results depict that the intensity of the absorption band 1745 cm-1 is reduced by 12% for 90 kGy dose. DSC studies indicate that both glass transition temperature (Tg) and melting temperature (Tm) of PLLA decrease following radiation dose. However melting enthalpy (ΔH) and degree of crystallinity (XC) increased initially up to 30 kGy of radiation dose followed by a decrease after 30 kGy. These results confirm the existence of two types of crystalline lamellar are present in PLLA. Measurements of XC by XRD also confirm the same aspect. The surface of PLLA is composed of micro-cracks when exposed to higher radiation doses.