Numerical simulation of polypropylene foaming process assisted by carbon dioxide: Bubble growth dynamics and stability |
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| Authors: | Yan Li Zhen Yao Zhen-hua Chen Kun Cao Shao-long Qiu Fang-jun Zhu Changchun Zeng Zhi-ming Huang |
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| Affiliation: | aState Key Laboratory of Chemical Engineering, Zhejiang University, Hangzhou 310027, China;bInstitute of Polymerization and Polymer Engineering, Department of Chemical and Biological Engineering, Zhejiang University, Hangzhou 310027, China;cHigh Performance Materials Institute, Florida State University, Tallahassee, FL 32310, USA;dDepartment of Industrial and Manufacturing Engineering, FAMU-FSU College of Engineering, Tallahassee, FL 32310, USA |
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| Abstract: | A mathematical model was established to simulate the bubble growth process during foaming of polypropylene (PP) by carbon dioxide, taking into account of a wide range of physical and rheological properties (solubility, diffusivity, surface tension, long-chain branching, zero shear viscosity, relaxation time, strain hardening), as well as processing conditions. By employing the Considère construction the possibility of growth instability and bubble rupture at later stage of bubble growth was predicted. The simulation revealed that the improvement of foamability of polypropylene by introducing long-chain branching was due to the well-defined viscoelastic characteristics of the melt. Rheological factors that impede bubble growth are beneficial in stabilizing the bubble growth. Stability during bubble growth is further facilitated by moderate strain hardening characteristics and elastics properties of the polymers. The diffusivity and solubility characteristics also have profound impact on the bubble growth stability, while the influence of the surface tension is negligible. |
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| Keywords: | Foam Long-chain branched polypropylene Polymer processing Rheology Simulation Supercritical fluid |
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