| COMPUTATIONAL SIMULATION |
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| Macromolecular Solidification Mechanism of the Isotropic Polypropylene (iPP) Material During the Injection Cooling Stage |
| CAO Wenhua, XIN Yong, LIU Donglei, YU Xuan
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| School of Mechanical & Electrical Engineering, Nanchang University, Nanchang 330031 |
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Abstract In response to the micro-mechanism of the liquid-solid phase transition and macromolecular structure evolution of the isotropic polypropylene (iPP) material during the injection molding cooling process, the macromolecular solidification and confi-guration evolution mechanism was studied based on the molecular dynamic simulation method. The different iPP cell systems were built, of which the polymerization degree were 24, 36, 51, 72, 120 and chain number were 36, 24 and 16, successively. The energy initialization was performed using the smart minimization method followed by the simulated annealling (SA) method. Coupling with the periodic boundary conditions, COMPASS force field and the velocity-verlet algorithm, the cooling simulation was launched. The results indicate that the glass transition temperature (Tg) of each simulated cell coincides well with the Flory’s free volume theory. The bond length as well as bond angle presents a Gaussian distribution, the lower the temperature, the more concentrated distribution of them, agreeing with the cooling free relax process of the macromolecular. The 〈h〉 and 〈Rg〉 of the polymer chains are all increasing with the polymerization degree. 〈h〉 shows a Gaussian distribution during the declining of the temperature, while 〈Rg〉 exhibits a shrinkage trend, which indicates the macromolecular chains configuration tangle again during this stage from the orientated phase, and another crystallize phase is taken place. The migration and solidification rate give a negative correction with the increasing polymerization degree. And the diffusion coefficient exhibits steeper declining trend with higher polymerization degree when the temperature is above the glass transition temperature.
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Published: 25 October 2017
Online: 2018-05-05
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2017, Vol. 31 
