| Research Abstract |
Poly(L-lactic acid) is biodegradable polymer made from sustainable resources such as corn starch. But it begins to be softening above the gloss transition temperatue (50℃). Therefore, PLLA was mixed with triallyl isocyanurate (TAIC). After mixed with TAIC, PLLA was irradiated at various irradiation doses. Gel fraction and degree of swelling were measured and evaluated crosslinking formation. At 3% concentration of TAIC, 50 kGy of irradiation dose were the best condition for modification of PLLA. For this sample, gel fraction and degree of swelling were 85% and 6%, respctively. Thermo- mechanical analysis (TMA) of untreated PLLA showed softening above glass transition temperature(Tg) and significant elongation at around 90℃, while crosslinked sample treated under above conditions showed slight softening above Tg and melting point Tm, however it retains original shape even at above Tm. Thermal stability of PLLA was also obtained by annealing at around 90℃, however, the crosslinked sample
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showed not only the heat stability but also chemical proofing with good solvent for PLLA, such as chloroform. Moreover, the crosslinked PLLA showed properties of shape memory, even after once melted. Melt-quenced PLLA has very low crystallinity, which causes poor heat stability, so we tried annealing PLLA sample mixed with TAIC followed by irradiation. This method showed TMA behavior of partially crosslinked PLLA, i.e., partially softening at Tm but retained its shape above Tm. Biodegradability of the crosslinked PLLA was retarded slightly by introduction of crosslinking, however, usually it proceeds biodegradation after hydrolysis, there are no problem after the treatment in practice.
Other chemically synthesized biodegradable polymers (e.g., bionolle)were treated with blending with inorganic particles or TAIC or TMAIC. Thermal stable and shape memory biodegradable polymers were obtained by these methods. These chemically synthesized biodegradable polymers were biodegraded with bacteria. 33 strain of bacteria were isolated, which were investigated by physiologicolly and morphologically, ond they are found to be gram negative and gram positive bacteria and fungi. Less
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