Molecular composites composed of castor oil-modified poly(ε-caprolactone) and self-assembled hydroxystearic acid fibers

After (R)-12-hydroxystearic acid (HSA) was mixed at 100 °C with the castor oil-modified poly(ε-caprolactone) (CO-PCL) prepared by the ring-opening polymerization of ε-caprolactone in the presence of castor oil, the mixture was gradually cooled to room temperature to give a solidified CO-PCL/HSA composite. The CO-PCL/HSA sample showed an exothermic peak at around 67-71 °C which was lower than the melting point of HSA (76.8 °C), indicating the formation of mesogenic HSA aggregates. The rheological measurement of the CO-PCL/HSA revealed the formation of HSA organogel at around 67-55 °C during the cooling process from the melt. Furthermore, the polarized and normal optical microscopic analyses of CO-PCL/HSA on the cooling stage revealed that anisotropic fibrous materials are formed at around 60 °C and then the fibrous network propagated over the matrix polymer. The flexural modulus and storage modulus of the CO-PCL/HSA composite increased with increasing HSA content. The CO-PCL/HSA composite annealed at 60 °C for 2 h on the cooling process had a higher flexural and storage modulus than the sample without annealing.