Phase Structure and Mechanical Property of Blends of Organosolv Lignin Alkyl Esters with Poly(ε-caprolactone)

Abstract

Organosolv lignin (OSL) alkyl esters (carbon number n, 2–5) were synthesized by homogeneous reaction with different acyl anhydrides/4-dimethylamino pyridine in pyridine solution. Miscibility of the esterified OSL with poly(ε-caprolactone) (PCL) was investigated through DSC, morphological observation, and spectroscopy. DSC revealed a composition-dependent shift in Tg for blends of OSL esters (n = 3–5) with PCL; thus these three systems can be regarded as miscible on a Tg-detection scale. AFM indicated that no remarkable phase separation occurred in these blends. In observations of crystallization behavior of the PCL component, the OSL derivatives of n = 4 and 5, the alkyl ester substituents of which make a higher similarity in chemical structure with a repeating unit of PCL, exhibited a higher level of miscibility with the aliphatic polyester, compared to the other OSL derivative of n = 3. Thermal-molded blend sheets of OSL esters of n = 3–5 with PCL attained ≥500% of elongation at rupture at 20 °C even when the blends contained 50 wt% of the respective esterified lignin components, reflecting the good miscibility of these OSL esters with PCL.