基于RHCM与CIM熔接痕形成的分子形态演化研究
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摘要
针对注塑成型中的熔接痕问题,建立了聚合物流动前锋汇合时垂直取向的初始界面模型。采用分子动力学方法,通过对比分析传统注塑成型(Conventional injection molding, CIM)和快速热循环注塑成型(Rapid heat cycle molding, RHCM)熔接痕界面分子链的迁移扩散、分子链取向、回转半径及界面结合能,研究了熔接痕界面弱连接与强连接的分子形态演化规律。结果表明,温度低、冷却速率快的CIM熔接痕表层和中间层分子取向快速冻结,分子链运动受阻,扩散速率慢,使得熔接痕界面分明,界面结合能低,分子形态变化不大,形成弱连接;而RHCM熔接痕及CIM熔接痕芯层高温保持时间较长,保压阶段冷却速率缓慢,有利于分子链的迁移扩散,同时促进分子链松弛,解取向明显,回转半径减小,使聚合物分子链团呈缠绕卷曲状态,界面分子链穿绕缠结在一起,界面结合能也增大,形成强连接。因此,熔接痕界面聚合物分子形态演化的实质是取向分子链的松弛和相互扩散的过程,而RHCM工艺则极大促进了分子形态演化进程,显著改善了熔接痕的弱连接问题。
Aimed at the problem of weld line during injection molding process, the initial interface model of vertical orientation was established when polymer flow fronts meet. Based on the molecular dynamic simulation method, molecular morphology evolution mechanism of poor and strong bond was researched by comparing migration and diffusion of molecular chain, chain orientation, radius of gyration and bonding energy at CIM and RHCM weld line interface. The results indicate that the molecular orientation of the surface and intermediate layer of CIM weld line is rapidly frozen with low temperature and fast cooling rate. Molecular chain motion is blocked and the diffusion rate is low. The weld line interface is ob-vious and interface bonding energy is low. The molecular morphology changes little, so the interface forming poor bond. However, RHCM weld line and the core layer of CIM weld line have a long time to maintain high temperature and the cooling rate is slow at packing stage, which is beneficial to the migration and diffusion of molecular chain and promotes the relaxation of molecular chain. Chain disorientation is obvious and the ra-dius of gyration reduces. The polymer molecular chains show winding and curling state and intertwine together at the interface. So the interface bonding energy increases and the interface forms strong bond. Therefore, the essence of molecular morphology evolution at weld line interface is the process of the relaxation and interdiffusion of oriented molecular chain. RHCM process greatly promotes the course of molecular morphology evolution and dramatically improves poor bond of weld line.
Aimed at the problem of weld line during injection molding process, the initial interface model of vertical orientation was established when polymer flow fronts meet. Based on the molecular dynamic simulation method, molecular morphology evolution mechanism of poor and strong bond was researched by comparing migration and diffusion of molecular chain, chain orientation, radius of gyration and bonding energy at CIM and RHCM weld line interface. The results indicate that the molecular orientation of the surface and intermediate layer of CIM weld line is rapidly frozen with low temperature and fast cooling rate. Molecular chain motion is blocked and the diffusion rate is low. The weld line interface is ob-vious and interface bonding energy is low. The molecular morphology changes little, so the interface forming poor bond. However, RHCM weld line and the core layer of CIM weld line have a long time to maintain high temperature and the cooling rate is slow at packing stage, which is beneficial to the migration and diffusion of molecular chain and promotes the relaxation of molecular chain. Chain disorientation is obvious and the ra-dius of gyration reduces. The polymer molecular chains show winding and curling state and intertwine together at the interface. So the interface bonding energy increases and the interface forms strong bond. Therefore, the essence of molecular morphology evolution at weld line interface is the process of the relaxation and interdiffusion of oriented molecular chain. RHCM process greatly promotes the course of molecular morphology evolution and dramatically improves poor bond of weld line.
引文
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3 Fellahi S,Meddad A,Fisa B,et al.Advances in Polymer Technology,1995,14 (3),169.
4 Fathi S,Behravesh A H.Polymer-Plastics Technology and Engineering,2008,47 (7),666.
5 Zhou Y,Mallick P K.Polymer Composites,2011,32(2),268.
6 Wu C H,Liang W J.Polymer Engineering and Science,2005,45,1021.
7 Ozcelik B,Kuram E,Topal M M.International Communications in Heat and Mass Transfer,2012,39(2),275.
8 Dzulkipli A A,Azuddin M.Procedia Engineering,2017,184,663.
9 Zhao G Q,Wang G L,Guan Y J.Journal of Plasticity Engineering,2009,16 (1),190.
10 Marco F,Giovanni L.AIP Conference Proceedings,2011,1353,797.
11 Zhao G Q,Wang G L,Guan Y J,et al.Polymers for Advanced Technologies,2011,22(5),476.
12 Chen S C,Jong W R,Chang J A.Journal of Applied Polymer Science,2006,101(2),1174.
13 Ling C J,L X Y,Fan F C,et al.Chemical Engineering Science,2012,84,292.
14 Paul W G.Polymer,2004,45(11),3901.
15 Shi M N,Zhang Y C,Cheng L S,et al.Journal of Physical Chemistry B,2016,120(37),10018.
16 Zhou M Y,Jiang B Y,Weng C.Computational Materials Science,2016,120,36.