本文關(guān)鍵詞：超聲增強(qiáng)拉伸流場制備聚乙烯復(fù)合材料的性能及串晶形成機(jī)理研究　出處：《華東理工大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 聚乙烯復(fù)合材料 流變 結(jié)晶動(dòng)力學(xué) 拉伸流場 串晶

【摘要】：高密度聚乙烯(HDPE)具有優(yōu)異的耐熱性、耐化學(xué)腐蝕性和力學(xué)性能等,廣泛應(yīng)用于生產(chǎn)生活,但是HDPE產(chǎn)品存在韌性和耐磨性差等缺點(diǎn)。而超高分子量聚乙烯(UHMWPE)憑借優(yōu)異的耐磨性、抗沖擊強(qiáng)度以及韌性等優(yōu)點(diǎn)受到了工業(yè)界及學(xué)術(shù)界的廣泛關(guān)注。UHMWPE與HDPE分子組成與結(jié)構(gòu)相近,同其他聚合物相比,二者相容性更好。在特殊流場作用下,UHMWPE中較長的分子鏈可以延展作為晶核,吸引其他分子鏈附著,形成串晶結(jié)構(gòu)(ShishKebab),以獲得優(yōu)異的性能。由于Shish的"核-殼"結(jié)構(gòu)存在清晰邊界,流場誘導(dǎo)晶體結(jié)構(gòu)的轉(zhuǎn)變存在一個(gè)臨界轉(zhuǎn)變點(diǎn)。目前,研究人員提出了一系列控制因素如熔融焓、剪切應(yīng)力、剪切速率、應(yīng)變等,但仍缺乏對(duì)復(fù)合材料分子鏈結(jié)構(gòu)影響晶體結(jié)構(gòu)轉(zhuǎn)變方面的研究。因此,本文設(shè)計(jì)了 HDPE與UHMWPE分子量之比分別為5.6:1、12.5:1、25:1和50:1,通過溶液共混,再借助超聲輔助擠出設(shè)備共混,并通過注塑和壓片制備HDPE/UHMWPE復(fù)合材料,進(jìn)一步研究超聲增強(qiáng)拉伸流場下,UHMWPE含量和分子量對(duì)復(fù)合材料流變性能、結(jié)晶行為及串晶結(jié)構(gòu)形成及形態(tài)演變的作用,以及其對(duì)力學(xué)性能的影響。首先,借助高溫流變儀考察UHMWPE含量以及分子量對(duì)復(fù)合材料流變行為的影響。結(jié)果發(fā)現(xiàn),復(fù)合材料未發(fā)生相分離,UHMWPE以分子水平分散到HDPE基體內(nèi);隨著UHMWPE的含量增加和分子量增大,復(fù)合材料的儲(chǔ)能模量、損耗模量和復(fù)數(shù)粘度變大,且分子鏈的纏結(jié)程度增大,分子彈性強(qiáng)度增大。其次,借助差示掃描量熱儀考察了 UHMWPE含量和分子量對(duì)基體材料非等溫結(jié)晶動(dòng)力學(xué)、等溫結(jié)晶動(dòng)力學(xué)和片晶厚度及分布的影響。結(jié)果發(fā)現(xiàn),由于UHMWPE與HDPE發(fā)生纏結(jié),對(duì)HDPE分子鏈的約束增強(qiáng),使得HDPE更多地參與到UHMWPE形成的晶核發(fā)生鏈折疊結(jié)晶,片晶增厚,結(jié)晶度增大。最后,在超聲增強(qiáng)拉伸流場作用下,研究UHMWPE含量和分子量對(duì)注塑過程中串晶結(jié)構(gòu)形成,以及拉伸過程中串晶結(jié)構(gòu)的形態(tài)演變的作用。結(jié)果發(fā)現(xiàn),UHMWPE含量越高,分子量越大,復(fù)合材料越容易形成單一取向的串晶結(jié)構(gòu);UHMWPE束縛部分HDPE形成Shish核,在串晶形成中起到主導(dǎo)作用。串晶結(jié)構(gòu)的形成明顯影響到復(fù)合材料的屈服強(qiáng)度、拉伸強(qiáng)度和斷裂伸長率。
[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.
【學(xué)位授予單位】：華東理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TQ325.12;TB332

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