International Topical Meeting on Nuclear Research Applications and Utilization of Accelerators
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AP/P3-14 WAXD and FTIR Studies of Electron Beam Irradiated Biodegradable Polymers Y. Kodama1, C. Giovedi2, N.B. Lima1, L.D.B. Machado1, K. Nakayama3, and W.A.P. Calvo4 1Instituto de Pesquisas Energéticas e Nucleares, IPEN–CNEN/SP, Sao Paulo, Brazil Corresponding Author: ykodama@ipen.br The problem of non-biodegradable plastic waste remains a challenge due to its negative environmental impact. 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. Poly(lactic acid) (PLLA) is a poly(α-hydroxy acid) and poly(ε-caprolactone) (PCL) is a poly(ω–hydroxy acid). PLLA is a hard, transparent and crystalline polymer. On the other hand, PCL can be used as a polymeric plasticizer because of its ability to lower elastic modulus and to soften other polymers. To improve some desirable properties two or more polymers can be mixed to form polymeric blends. PLLA/PCL blends have attracted great interest as temporary absorbable implants in human body, but they suffer from poor mechanical properties due to macro phase separation of the two immiscible components, and to poor adhesion between phases. Chemical structure influences the biodegradation of solid polymers. Enzymatic and non enzymatic degradations occur easier in the amorphous region. 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. Moreover, both polymers, PLLA and PCL, require a proper sterilization process when used in biomedical applications. Nowadays, the most suitable sterilization method is high energy irradiation. Radiation has been known to alter the physical properties of polymers through main-chain scission and crosslinking. Usually both these processes take place simultaneously in many polymers. The combination of two radicals leads to cross-linking in the amorphous phase or recombination in the crystalline region, whereas chain transfer and the subsequent splitting result in chain scission 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, sheets of PCL and PLLA homopolymers and blend with PLLA:PCL weight ratio of 50:50 (w:w) were prepared using a twin screw extruder (Labo Plastomill Model 150C, Toyoseki, Japan) equipped with a T-die (60 mm width and 1.05 mm thickness). Twin screw extruded sheets 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 blends. Wide-angle X-ray diffraction (WAXD) patterns of non irradiated and irradiated samples were obtained using a diffractometer Rigaku Denki Co. Ltd., Multiflex model, Cu Ka radiation; 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. The amorphous phase of PLLA decreased with radiation dose. Although it had been presented in the literature that PLLA crystallinity decreases with radiation dose up to 80 kGy, it was not possible to observe this fact in this study. Furthermore, it was observed that PLLA crystallite size increases with radiation dose above 100 kGy in the studied dose range. Also this occurrence can be observed for the PLLA in the blend. PCL samples, non irradiated and irradiated show the two strongest reflections at Bragg angles 2θ =21.4° and 2θ =23.7° that have been attributed in the literature to the (110) and (200) reflections, respectively. For as extruded irradiated PLLA samples it was observed broad diffusion peaks corresponding to amorphous polymer. PLLA samples annealed under temperature of 140°C during half an hour, showed reflections at Bragg angles 2θ =16.4° and 2θ =18.7° previously attributed in the literature to distorted 103 (α-form) helices. PLLA as extruded samples are amorphous and crystallize by thermal treatment. On the other hand, FTIR results have shown that the ionizing radiation does not promote degradation of the studied homopolymers and blends, also do not affect the miscibility of the blends.
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