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利用自行研制的能够方便改变工艺条件的新型动态保压注射成型(DPIM)装置,研究了中等分子量聚丙烯(PP)注射成型试样的结构与性能。研究表明:所得中等分子量PP试样的结构与性能与注射成型过程中的工艺条件有密切关系,如:振动压力、熔体温度等。振动压力、熔体温度对试样性能的影响呈二次曲线关系,拉伸强度随着振动压力的升高先提高而后减小,有一个最大值。拉伸强度同样也随着熔体温度的升高先提高后减小,有一个最大值。DSC曲线表明:动态试样熔融呈现明显的脊纤维晶和片晶两个熔融峰,而静态试样呈现明显的片晶熔融单峰。SEM照片显示静态试样剪切层结晶形态主要为球晶结构,动态试样剪切层产生明显的高度取向串晶结构。所有的测试结果表明:中等分子量PP在动态保压单向流动场中所得试样内部结晶由静态试样中的球晶转变成了串晶,且性能明显提高。
The structure and properties of medium molecular weight polypropylene (PP) injection molded specimens were investigated using a novel dynamic holding pressure injection molding (DPIM) device which was developed by ourselves. The results show that the structure and properties of the obtained medium molecular weight PP samples are closely related to the process conditions in the injection molding process, such as vibration pressure, melt temperature and so on. The influence of vibration pressure and melt temperature on the properties of the sample shows a quadratic curve. The tensile strength first increases and then decreases with the increase of the vibration pressure, and has a maximum value. Tensile strength also increases with the melt temperature first and then decrease, there is a maximum. The DSC curves show that the melting of dynamic specimen shows two melting peaks of spine fiber and lamella, while the static specimen shows obvious single melting of lamella. The SEM images show that the crystal morphology of the shear layer of the static sample is mainly the spherulite structure, and the dynamic shear layer of the sample produces a significant highly oriented crystal string structure. All of the test results show that the internal crystallization of the medium molecular weight PP in the dynamic pressure-holding unidirectional flow field is transformed from spherulites in the static samples into string crystals, and the performance is obviously improved.