Robust, transparent films of propylene ethylene copolymer through isotropic-orientation transition at low temperature accelerated by adjustment of ethylene contents
Robust, transparent films of propylene ethylene copolymer through isotropic-orientation transition at low temperature accelerated by adjustment of ethylene contents
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通过调节乙烯含量加速低温下各向同性取向转变的丙烯乙烯共聚物的坚固透明薄膜
DOI：
10.1016/j.polymer.2019.122099
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发表时间：
2020
期刊：
影响因子：
4.6
通讯作者：
Li Zhong-Ming
中科院分区：
文献类型：
--
作者：
Yang Sheng;Wei Qiu-Yang;Gao Xin-Rui;Zhou Li;Xu Ling;Tnag Jian-Hua;Zhong Gan-Ji;Ji Xu;Li Zhong-Ming
在较低的加工温度下，通过对丙烯-−-乙烯共聚物(COPP)的单轴拉伸，制备了高性能的透明取向薄膜。与PP相比，乙烯含量为4wt%(CoPP4)的COPP可使加工温度降低约50℃，拉伸强度达到约259.2 Mpa，高于PP的约215.9 Mpa。由于CoPP4@7.5(拉伸倍数后加“@”)的结晶度和取向度均低于PP@4.5，小角X射线散射(SAXS)和扫描电子显微镜(SEM)表明，这种反常现象是由于CoPP4@7.5中存在纤维状晶体所致。结构分析表明，薄膜的拉伸性能与层状晶体形态密切相关，尤其是纤维状晶体。在拉伸过程中，适量的乙烯含量可以促进由COPP球晶变形而形成的纤维状晶体的形成和完善，从而有利于拉伸强度的提高。有趣的是，随着乙烯含量的增加，拉伸薄膜的最终分子取向有显著的线性下降(R2=40.98)。此外，拉伸工艺对COPP的结晶度和长周期的影响不大，这与PP拉伸的情况有明显的不同。同时发现，除了coPP16外，乙烯链段还会导致大量γ晶型的生成，在拉伸过程中，CoPP16有向α晶型转变的趋势。
Transparently oriented films with high performance are fabricated by uniaxial stretching of propylene−ethylene copolymers (coPPs) at a low processing temperature. The coPP with ethylene content of 4 wt% (coPP4) can reduce processing temperature by approximately 50 °C compared to polypropylene (PP) and reach a tensile strength about 259.2 MPa, which is higher than that of PP about 215.9 MPa. As both crystallinity and orientation of coPP4@7.5 (draw ratio value followed by “@“) is lower than that of PP@4.5, this abnormal phenomenon is ascribed to the fibrillar crystals existing in coPP4@7.5 revealed by small angle X-ray scattering (SAXS) and scanning electronic microscopy (SEM). Structure analysis attests to that the tensile properties of the films are closely related to the hierarchically crystalline morphology especially in the fibrillar crystals. During the stretching process, it is intriguing that an appropriate amount of ethylene contents can accelerate the formation and perfection of fibrillar crystals originated from the deformation of coPPs spherulites, which are favorable for the enhancement of tensile strength. Interestingly, there is a significant linear decrease (R2= 0.98) of the ultimate molecule orientation of stretched films with the increase of ethylene content. Furthermore, the stretching processing has little effect on crystallinity and long period for coPPs, which is distinctly different from the case of PP stretching. Meanwhile, it is found that ethylene segments lead to formation of lots of γ-form except for coPP16, which tends to transform to α-form during stretching of coPPs.