Improvement of the rheological properties of trans-1,4-polyisoprene from Eucommia ulmoides Oliver by tri-branched poly(ricinoleic acid)

Abstract

This study investigated fully bio-based blends of trans-1,4-polyisoprene from Eucommia ulmoides Oliver (EuTPI) and linear poly(ricinoleic acid) (LPRA) or tri-branched poly(ricinoleic acid) (BPRA). LPRA and BPRA were synthesized using an immobilized lipase as the catalyst. Blends of EuTPI with LPRA or BPRA in various mixing ratios were examined. Scanning electron microscope observations suggest that BPRA was uniformly distributed in the EuTPI matrix in contrast to the poor distribution of LPRA, and BPRA was effectively incorporated into the crosslinked network of EuTPI by curing with dicumyl peroxide. Rheological studies indicate that BPRA was more effective than LPRA at improving the processability of EuTPI. The storage modulus, loss modulus and complex viscosity (η) of EuTPI over a frequency (ω) range from 0.1 to 100 rad s-1 at 80 °C clearly decreased with an increase in BPRA content. At low frequency, the rheological behavior of EuTPI changed from that of an elastic gel to that of a liquid when 15wt% of BPRA was added. Moreover, η dramatically decreased to ∼5% of that of the pure EuTPI at ω=0.1 rad s-1. Thermogravimetric analysis results suggest that the blending of BPRA would not compromise the thermal stability of EuTPI. BPRA was found to promote the formation of more stable α-phase crystallites in EuTPI by differential scanning calorimetry analysis.