Controlling crystal phase transition from form II to I in isotactic poly-1-butene using CO2

Abstract

Controlling crystal phase transition from modification II to I in isotactic Poly-1-butene (iPB-1) using CO2 is presented in this article. The intrinsic kinetics of CO2-induced phase transition from modification II to I in iPB-1 at 40 °C and different CO2 pressures were detected using in situ high-pressure Fourier transform infrared spectroscopy (FTIR) and correlated by Avrami equation. Sorption of CO2 in iPB-1 matrix was measured at 40 °C and different CO2 pressures using both FTIR and magnetic suspension balance (MSB) and the diffusivity was determined by Fick's second law. An algorithm combining the CO2 diffusion and induced phase transition was subsequently proposed to calculate the CO2 concentration as well as the phase transition degree in the iPB-1 matrix with different thickness at different saturation time. The calculated phase transition degree in the iPB-1 agreed well with the FTIR results. In addition, the yield stresses of iPB-1 specimens annealed in the air and 6 MPa CO2 at 40 °C with different durations were also experimentally investigated. The algorithm was applied to predict the phase transition degree of the iPB-1 specimens. The appropriate CO2 treatment time for getting high yield stress was in consistent with that predicted by the algorithm.