Changes in the crystallinity and mechanical properties of poly(l-lactic acid)/poly(butylene succinate-co-l-lactate) blend with annealing process

Biodegradable polymer blends of poly(l-lactic acid) (PLLA) and poly(butylene succinate-co-l-lactate) (PBSL) at various blending ratios are prepared. The blending of PLLA with PBSL results in an increase in the ductility and thermal stability of the blend. However, flexural strength and modulus, as well as loss modulus, decrease with an increase in PBSL content. Annealing is employed to increase blend crystallinity and subsequently improve the mechanical properties of the PLLA/PBSL blend. The influences of annealing time on the crystal modification, thermal properties, and mechanical properties of the PLLA/PBSL blend are investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and three-point bending test, respectively. Crystalline peaks are found in the XRD patterns of all annealed samples. DSC analysis reveals that the degree of crystallinity is enhanced with an increase in annealing time. The flexural modulus also increases with annealing time due to the change in crystalline phases. However, longer periods of annealing, especially over 20 h, result in thermal degradation and subsequently reduce the modulus value of the PLLA/PBSL blend.