Effects of CO₂ on crystallization kinetics of polypropylene

Abstract

When CO2 dissolves into a polypropylene (PP), its crystallization kinetics changes These changes were studied, in the expectation that the information would reflect on the behavior of other semicrystalline polyolefins. The isothermal crystallizatior rate of the PP‐CO2 solutions was measured using a high‐pressure differential scanning calorimeter (DSC), which performed calorlmetric measurements while keeping the polymer in contact with pressurized CO2. Although the measured crystallizatior rate followed the Avrami equation, the value of the crystallization kinetic constant was different from that measured for PP crystallized in air under atmospheric pressure. The dissolved CO2 decreased the overall crystallization rate of PP within the nucleation dominated temperature region. This suggests that the dissolved CO2 decreases the melting and the glass transition temperatures and prevents formation of critical size nuclei.

Biodegradable polylactide/hydroxyapatite nanocomposite foam scaffolds for bone tissue engineering applications

“…T sat was therefore decreased to 175°C and 165°C and P sat was varied between 100 and 250 bars. Although these T sat are below the nominal melting point of the as-received PLLA (about 180°C), they remain well above the melting point of PLLA in the presence of CO 2 at comparable pressures (about 130°C [41,42]). T sat and P sat were maintained for 10 min to allow adequate diffusion of the supercritical CO 2 into the molten PLLA.…”

Effect of dissolved carbon dioxide on the glass transition and crystallization of poly(lactic acid) as probed by ultrasonic measurements

“…In the case of poly(ethylene terephthalate) (PET), Takada and Ohshima 4 demonstrated that the presence of CO 2 increased the overall crystallization rate of PET, whatever the isothermal T c was. In a previous study on polypropylene (PP), 5 they observed that the dissolved CO 2 reduced the overall crystallization rate within the nucleation-dominated temperature region, that is, in the high T c range. In the case of PLA, Takada et al 6 demonstrated that the crystallization rate was accelerated by the presence of CO 2 molecules in the crystal-growth-controlled region, whereas it was depressed in the nucleation-controlled region.…”

Experimental and computational micro-mechanical investigations of compressive properties of polypropylene/multi-walled carbon nanotubes nanocomposite foams

“…The nanocomposite base material and the foaming preparation conditions -the temperature changes, foaming agents, and nanofillers properties-can affect the crystallinity of the PP matrix as shown by Takada et al (2001); Leelapornpisit et al (2005). The change of the crystallinity degree leads to different mechanical behaviors of the PP phase in neat PP, in nanocomposites, and in the cell walls of nanocomposite foams.…”

“…The PP matrix is a semi-crystalline polymer whose crystallinity can be modified during the foaming process according to the heat treatment, absorbed amount of blowing agent (Takada et al, 2001), or nano-fillers properties (Leelapornpisit et al, 2005). Super-critical carbon dioxide (ScCO 2 ) is used as blowing agent during the one-step batch foaming process.…”