(180j) Controlling Crystal Phase Transition From Form II to I in Isotactic Poly-1-Butene Using CO2 | AIChE

(180j) Controlling Crystal Phase Transition From Form II to I in Isotactic Poly-1-Butene Using CO2


Xu, Y., East China University of Science and Technology
Li, L., East China University of Science and Technology
Zhao, L., East China University of Science and Technology

Controlling Crystal Phase Transition
from Form II to I in Isotactic Poly-1-butene Using CO2

Xu, Tao Liu*, Lei Li and Ling Zhao*

State Key Laboratory of Chemical Engineering, East China
University of Science and Technology, Shanghai 200237, People's Republic of

whom correspondence should be addressed. E-mail: liutao@ecust.edu.cn, zhaoling@ecust.edu.cn.

poly-1-butene (iPB-1) is a polymorphous semicrystalline
Crystallized from
melt under atmospheric pressure, form II can be obtained
and gradually transform into form I in more than 3 months. The phase transition
is beneficial to the mechanical, thermal and physical properties of iPB-1
products. Li et al. [1] discovered that pressurized CO2 can
effectively promote the phase transition of form II to I, during which CO2
diffusion and CO2-induced the phase transition take place
simultaneously. In this work, a model combining CO2 diffusion in and
CO2-induced phase transition was proposed to calculate the CO2
concentration as well as the phase transition in iPB-1 sheets.

intrinsic kinetics of CO2-induced phase transition from form II to I
at 40 oC was investigated using in-situ
high-pressure Fourier transform infrared spectroscopy and correlated
by Avrami equation. Thin iPB-1 films (20-30 µm) were used to eliminate the effect of CO2
diffusion. As shown in Fig. 1, the CO2-induced phase transition can
be divided into three stages. The duration of the first stage decreased with
increasing CO2 pressure and disappeared at pressures upper than 3 MPa. The rate constant and apparent Avrami
exponent of the second stage both increased with CO2 pressure.

Fig. 1. Avrami
curves of the phase transition from II to I in thin iPB-1 films at 40 oC and different CO2 pressures.

Fig. 2. Flow chart of the coupling model.

Fig. 3.
Calculation from the proposed model (solid lines) and FTIR results (points) in
iPB-1 sheets with thicknesses of 0.2 mm (blue) and 0.4 mm (red) at 40 oC and CO2 pressures of 6 MPa (upper) and 4 MPa (lower).

the phase transformation only occurs in the crystal regions, the diffusion of
CO2 in iPB-1 is considered to be independent from the phase transition.
The flow chart of the coupling model is depicted in Fig. 2. The iPB-1 sheet was
divided into 2n+1 slices in the thickness direction. The solubility (SCO2) and diffusivity (D) of CO2 at 40 oC and a desired pressure were experimentally
measured using magnetic suspension balance, and the distribution of CO2
concentration (Ct,y)
was calculated from the Fick's second law. The intrinsic
kinetic data were used to determine the relative content of form I in each
slice at the next time point. In order to verify the proposed model, 0.2 and
0.4 mm thick iPB-1 sheets were treated with 4 and 6 MPa
CO2. The model values (lines) agreed well with the experiment
results (points), as illustrated in Fig. 3.

Li L, Liu T, Zhao L,
Yuan W-k. Macromolecules 2009;42:2286-90.