Hydrolytic degradation studies of bio-composites of poly(L-lactic acid)/Oligo(L-lactic acid) grafted and non-grafted microcrystalline cellulose

Abstract

This study investigates the hydrolytic degradation properties of poly(L-lactic acid) (PLLA)- based biodegradable polymer composites which were prepared with oligo(L-lactic acid) (OLLA) grafted and non-grafted microcrystalline cellulose (MCC) (OLLA-g-MCC and Non-g-MCC). MCC was obtained through the simple hydrolysis reaction of cellulose and then it was grafted with OLLA. The grafted MCC was characterized by FTIR, SEM and WAXD analyses. Composite of PLLA with OLLA-g-MCC (PLLA/OLLA-g-MCC) and Non-g-MCC (PLLA/Non-g-MCC) were prepared using the solution casting method. The hydrolytic degradation properties of composite samples were tested in a buffer solution at pH 7.4 and 37 °C. The changes in samples after degradation were monitored by analyzing the mechanical properties: thermal stability, crystallinity, degradability and making a comparison with that of PLLA. Both OLLA-g-MCC and Non-g-MCC enhanced the hydrolytic degradation of PLLA, which was observed by evaluating weight loss percentage. The initial weight loss rates of PLLA/OLLA-g-MCC (0.22 % day⁻¹) and PLLA/Non-g-MCC (0.27 % day⁻¹) were higher than that of PLLA (0.12 % day⁻¹). The hydrolysis phenomenon is comparatively linear (Regression coefficient 0.9693) for PLLA, whereas nonlinearity is shown in the case of PLLA/Non-g-MCC composite. The PLLA/OLLA-g-MCC exhibits a higher K_e than that of PLLA/Non-g-MCC and PLLA. The decline in pH indicates the generation of acidic substances. DSC shows that the degradation temperature of hydrolytically degraded samples declined sharply with hydrolytic degradation time up to 130 days and then the rate slowed down. Initial rapid increase in crystallinity was observed which may due to segmental mobility during hydrolytic degradation of the composites and polymer.