To achieve higher clarity of polypropylene sheets while keeping a certain level of crystallinily and maintaining mechanical properties, supercritical CO
2 (SCF-CO
2) is used when blending a nucleating agent with polypropylene powder. The nucleating agent is initially dissolved in SCF-CO
2 together with an entrainer (1-propanol), and then the polypropylene powder is exposed to the SCF CO
2/entrainer/nucleating agent system. The SCF-CO
2 enhances the diffusivity of the nucleating agent into the polypropylene powder and enables a better dispersion of the nucleating agents in the polymer. The better dispersion increases the number of nuclei and reduces the size of the spherulites. The reduction of spherulite size improves the clarity of the polypropylene sheets. Comparison of the clarity of polypropylene sheets made from SCF-CO
2 treated powder with those made from powder dry-blended with nucleating agents clearly shows the positive effect of the SCF-CO
2 treatment. The experimental results also show that a higher density of SCF-CO
2 increases the clarity of polypropylene sheet and an entrainer, with a solubility close to that of the nucleating agent, is effective for improving the clarity.
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