Effects of CO2 on crystallization kinetics of polypropylene

When CO2 dissolves into a polypropylene (PP), its crystallization kinetics changes. These changes were studied, in the expectation that the informatio n would reflect on the behavior of other semicrystalline polyolefins. The i sothermal crystallization rate of the PP-CO2 solutions was measured using a high-pressure differential scanning calorimeter (DSC), which performed cal orimetric measurements while keeping the polymer in contact with pressurize d CO2. Although the measured crystallization rate followed the Avrami equat ion, the value of the crystallization kinetic constant was different from t hat measured for PP crystallized in air under atmospheric pressure. The dis solved CO2 decreased the overall crystallization rate of PP within the nucl eation dominated temperature region. This suggests that the dissolved CO2 d ecreases the melting and the glass transition temperatures and prevents for mation of critical size nuclei.