Crystallization behavior in miscible blends of poly(ε‐caprolactone) and poly(hexylene adipate) with similar thermal properties studied by time‐resolved Fourier transform infrared spectroscopy

Melt crystallization behavior in miscible crystalline blends of poly(-caprolactone) (PCL) and poly(hexylene adipate) (PhAd) was investigated by Differential Scanning Calorimetry (DSC), Polarized Optical Microscopy (POM), Wide Angle X-Ray Diffraction (WAXD) and time resolved Fourier Transform Infrared Spectroscopy (FTIR). Both polymers were highly crystalline, had similar thermal properties and formed negative birefringence spherulites. Non-isothermal cooling thermograms showed fractional crystallization of PCL in blends with less than 40 wt% PCL. The crystallization kinetics of the polyesters was investigated by monitoring the absorbance intensities of the crystalline bands at 841 cm-1 and 911cm-1 for PCL and PhAd respectively at 47 oC. For all of the blends examined in this study, simultaneous onsets of crystallization were found although the neat polymers showed very different crystallization kinetics. PCL exhibited a longer induction period with slow crystallization rate while PhAd kinetics were completely opposite. Furthermore, for the PCL/PhAd (80/20) blend, the coincident values of the relative crystallinity were found for both the components. As for the 40/60 and 20/80 blends, the induction period of PCL were much shortened, which is due to PhAd playing a role of the nucleation agent. WAXD ruled out co-crystallization. These findings are important to the field of polymer physics.