Behavior of hydrolysis of plasma-treated poly(L-lactic acid)

The degradation behavior of plasma-treated poly(l-lactic acid) (PLLA) was studied. The plasma treatment was carried out in air environment and sample surfaces were analyzed by electron spectroscopy for chemical analysis (ESCA) and water contact angle measurement. For determining the degradation rates of samples the mass loss was determined from the dry weights before and after degradation. The glass transition temperature (T-g) and crystallinity of the specimens were measured using a differential scanning calorimeter (DSC). The surface morphology of specimens was examined with a scanning electron microscope (SEM). The oxygen content of the PLLA surface was increased by the air-plasma treatment and its water contact angle decreased accordingly. However, after degraded for 4 weeks, the water contact angles of the plasma-treated PLLA became to be almost the same as those of the normal PLLA presumably due to the degradation of the hydrophilic surface formed by the air-plasma treatment. The degradation rates of the plasma-treated samples were faster than those of the normal samples in initial periods presumably because of the hydrophilic surface of the plasma-treated PLLA. However, the weight losses of the normal and plasma-treated samples became to be similar after 6 weeks degradation, which may be due to the loss of the hydrophilic surface of the plasma-treated PLLA by hydrolysis. The T-g and crystallinity of the normal and plasma-treated samples increased in initial degradation periods. The increasing rates of T-g and crystallinity of the plasma-treated samples were faster than those of the normal samples.