超声增强拉伸流场制备聚乙烯复合材料的性能及串晶形成机理研究

发布时间：2018-01-03 20:24

本文关键词：超声增强拉伸流场制备聚乙烯复合材料的性能及串晶形成机理研究　出处：《华东理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：高密度聚乙烯(HDPE)具有优异的耐热性、耐化学腐蚀性和力学性能等,广泛应用于生产生活,但是HDPE产品存在韧性和耐磨性差等缺点。而超高分子量聚乙烯(UHMWPE)凭借优异的耐磨性、抗冲击强度以及韧性等优点受到了工业界及学术界的广泛关注。UHMWPE与HDPE分子组成与结构相近,同其他聚合物相比,二者相容性更好。在特殊流场作用下,UHMWPE中较长的分子链可以延展作为晶核,吸引其他分子链附着,形成串晶结构(ShishKebab),以获得优异的性能。由于Shish的"核-壳"结构存在清晰边界,流场诱导晶体结构的转变存在一个临界转变点。目前,研究人员提出了一系列控制因素如熔融焓、剪切应力、剪切速率、应变等,但仍缺乏对复合材料分子链结构影响晶体结构转变方面的研究。因此,本文设计了 HDPE与UHMWPE分子量之比分别为5.6:1、12.5:1、25:1和50:1,通过溶液共混,再借助超声辅助挤出设备共混,并通过注塑和压片制备HDPE/UHMWPE复合材料,进一步研究超声增强拉伸流场下,UHMWPE含量和分子量对复合材料流变性能、结晶行为及串晶结构形成及形态演变的作用,以及其对力学性能的影响。首先,借助高温流变仪考察UHMWPE含量以及分子量对复合材料流变行为的影响。结果发现,复合材料未发生相分离,UHMWPE以分子水平分散到HDPE基体内;随着UHMWPE的含量增加和分子量增大,复合材料的储能模量、损耗模量和复数粘度变大,且分子链的缠结程度增大,分子弹性强度增大。其次,借助差示扫描量热仪考察了 UHMWPE含量和分子量对基体材料非等温结晶动力学、等温结晶动力学和片晶厚度及分布的影响。结果发现,由于UHMWPE与HDPE发生缠结,对HDPE分子链的约束增强,使得HDPE更多地参与到UHMWPE形成的晶核发生链折叠结晶,片晶增厚,结晶度增大。最后,在超声增强拉伸流场作用下,研究UHMWPE含量和分子量对注塑过程中串晶结构形成,以及拉伸过程中串晶结构的形态演变的作用。结果发现,UHMWPE含量越高,分子量越大,复合材料越容易形成单一取向的串晶结构;UHMWPE束缚部分HDPE形成Shish核,在串晶形成中起到主导作用。串晶结构的形成明显影响到复合材料的屈服强度、拉伸强度和断裂伸长率。
[Abstract]:High density polyethylene (HDPE) has excellent heat resistance, chemical corrosion resistance and mechanical properties, so it is widely used in production and life. However, HDPE products have some shortcomings, such as poor toughness and wear resistance, while UHMWPE has excellent wear resistance. The advantages of impact strength and toughness have been widely concerned by industry and academia. The composition and structure of UHMWPE and HDPE molecules are similar to those of other polymers. The longer molecular chains in UHMWPE can be extended as nuclei to attract other molecular chains to attach and form a strand structure. In order to obtain excellent performance, there is a critical transition point for the flow field induced crystal structure transformation due to the clear boundary of the "core-shell" structure of Shish. Researchers have proposed a series of control factors such as enthalpy of melting shear stress shear rate strain and so on but there is still no research on the influence of molecular chain structure on crystal structure transformation. The molecular weight ratio of HDPE to UHMWPE was designed to be 5.6: 12. 5: 1 and 50: 1, respectively. The blend was prepared by solution blending and then by ultrasonic assisted extrusion equipment. The HDPE/UHMWPE composites were prepared by injection molding and compression, and the rheological properties of UHMWPE composites were further studied under ultrasonic reinforced tensile flow field with the content of UHMWPE and the molecular weight of UHMWPE. The effect of crystallization behavior and the formation and evolution of the crystal structure and morphology, and its effect on the mechanical properties. First of all. The effects of UHMWPE content and molecular weight on the rheological behavior of composites were investigated by means of high temperature rheometer. UHMWPE was dispersed into the HDPE group at molecular level. With the increase of UHMWPE content and molecular weight, the energy storage modulus, loss modulus and complex viscosity of the composites increase, and the degree of molecular chain entanglement increases, and the molecular elastic strength increases. The effects of UHMWPE content and molecular weight on the nonisothermal crystallization kinetics, isothermal crystallization kinetics and the thickness and distribution of lamellar crystals were investigated by differential scanning calorimetry. Because of the entanglement between UHMWPE and HDPE, the restriction of HDPE molecular chain is enhanced, which makes HDPE participate more in the chain folding and crystallization of UHMWPE formed nucleus and increase the thickness of the wafer crystal. Finally, under the action of ultrasonic enhanced tensile flow field, the formation of string crystal structure during injection molding with UHMWPE content and molecular weight was studied. The results show that the higher the content of UHMWPE, the higher the molecular weight of the composite, and the easier it is to form a single oriented crystal structure. UHMWPE bound part of HDPE forms Shish nucleus, which plays a leading role in the formation of string crystal. The formation of string crystal structure obviously affects the yield strength, tensile strength and elongation at break of the composite.
【学位授予单位】：华东理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ325.12;TB332

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