Xylan esters as bio-based nucleating agents for poly (l-lactic acid)

Xylan esters of varying alkyl chain lengths (C2-C12) were screened for their effect on the crystallization of poly(l-lactic acid) (PLLA). Among the xylan esters, only xylan propionate (XylPr) and xylan butyrate (XylBu) exhibited a nucleating effect on PLLA during non-isothermal crystallization. Blending of 1% XylPr or XylBu with PLLA led to a decrease in the crystallization temperature (Tc) of PLLA from 125 °C to 96 or 97 °C, respectively. Similar results were also obtained for 0.1% blends of the same ester. Isothermal crystallization studies revealed that the PLLA blends exhibited faster crystallization rates, higher crystallinities and smaller spherulites than neat PLLA. Consequently, the PLLA blends possessed lower degrees of haze than neat PLLA and their thermal expansion values were also lower than that of neat PLLA when heated above their glass transition temperature (60 °C), indicating their resistance to heat deformation. The mechanism of nucleation was proposed based from the WAXD analysis results.