本文選題：聚乙烯 + 共混��； 參考：《太原理工大學(xué)》2017年碩士論文

【摘要】：注塑成型是聚乙烯最主要的加工方式,在成型過(guò)程中控制聚乙烯的微觀結(jié)構(gòu)演變能夠直接影響制品的性能。注塑成型的聚乙烯制品通常具有力學(xué)性能較差、結(jié)晶度較低等缺陷。增加成核密度能夠提高結(jié)晶度并使晶形發(fā)生改變,從而改善制品性能。本文依據(jù)誘導(dǎo)結(jié)晶的試驗(yàn)現(xiàn)象,通過(guò)不同分子量誘導(dǎo)結(jié)晶和剪切應(yīng)力誘導(dǎo)結(jié)晶兩種方式,對(duì)注塑成型過(guò)程中聚乙烯的結(jié)晶機(jī)理進(jìn)行探究,主要研究?jī)?nèi)容包括:(一)采用直接共混法將不同種類(分子量不同)的聚乙烯用雙螺桿擠出機(jī)擠出,制備共混物�？疾炝瞬煌壤�、不同種類聚乙烯混合料對(duì)制品的影響。表征了共混物的熔體流動(dòng)性、分子量分布情況、制品力學(xué)性能和結(jié)晶度等性能。通過(guò)對(duì)共混物流動(dòng)性和分子量變化的分析,探討了分子量的改變以及長(zhǎng)鏈和短鏈在誘導(dǎo)結(jié)晶中的作用。結(jié)果表明,在中等分子量聚乙烯(5000S)中添加4%的低分子量聚乙烯(2911)或者4%的高分子量聚乙烯(1158)能大幅提高制品的結(jié)晶度。同時(shí)向5000S中添加4%2911和4%1158不僅能大幅提高制品的結(jié)晶度,而且制品的拉伸性能有了巨大的提升,伸長(zhǎng)率達(dá)到846%。(二)采用控制剪切應(yīng)力的方式對(duì)中等分子量聚乙烯進(jìn)行試驗(yàn),通過(guò)改變注塑機(jī)的注射壓力和模具溫度來(lái)調(diào)整聚乙烯熔融體受到的剪切應(yīng)力。利用電子萬(wàn)能試驗(yàn)機(jī)、差示量熱掃描儀和掃描電鏡對(duì)試樣進(jìn)行表征,對(duì)剪切應(yīng)力與晶形的關(guān)系進(jìn)行了分析。通過(guò)對(duì)聚乙烯結(jié)晶過(guò)程的分析探討,闡述了受剪切作用的剪切層和芯層取向及結(jié)晶狀況。結(jié)果表明,當(dāng)熔融體受到持續(xù)的剪切時(shí),制品的剪切層會(huì)持續(xù)變厚,力學(xué)性能也會(huì)隨之提升。剪切速率能夠直接對(duì)晶形的結(jié)構(gòu)、形狀和大小產(chǎn)生影響。當(dāng)剪切速率大于一定值時(shí),分子鏈開(kāi)始發(fā)生明顯的取向。(三)運(yùn)用分子模擬軟件,利用分子鏈模型和粗�；Ｐ蛯�(duì)聚合物分別受到剪切和拉伸作用的情況進(jìn)行模擬,研究了聚合物分子鏈在剪切應(yīng)力場(chǎng)中的取向行為以及在拉伸應(yīng)力作用下微觀結(jié)構(gòu)的變形情況。在力學(xué)測(cè)試中,采用兩種不同的系綜來(lái)考察拉伸速率與應(yīng)力應(yīng)變曲線之間的關(guān)聯(lián)。根據(jù)非鍵勢(shì)能和總能量的變化情況來(lái)分析外部應(yīng)力對(duì)晶形的影響。結(jié)果表明,拉伸時(shí)采用NVT系綜能夠有效避免空穴現(xiàn)象的產(chǎn)生。在剪切應(yīng)力或拉伸應(yīng)力的作用下,分子鏈結(jié)構(gòu)均會(huì)發(fā)生明顯的取向行為。
[Abstract]:Injection molding is the main processing method of polyethylene. Controlling the microstructure evolution of polyethylene during the molding process can directly affect the properties of products.Injection molding polyethylene products usually have poor mechanical properties, low crystallinity and other defects.Increasing nucleation density can improve the crystallinity and change the crystal shape, thus improving the properties of the products.Based on the experimental phenomena of induced crystallization, the crystallization mechanism of polyethylene in injection molding process was studied by means of different molecular weight induced crystallization and shear stress induced crystallization.The main research contents are as follows: (1) different kinds of polyethylene (with different molecular weight) were extruded by twin-screw extruder by direct blending method to prepare the blends.The effects of different proportion and different kinds of polyethylene mixture on the products were investigated.The melt fluidity, molecular weight distribution, mechanical properties and crystallinity of the blends were characterized.Based on the analysis of the fluidity and molecular weight of the blends, the changes of molecular weight and the roles of long and short chains in the induction of crystallization were discussed.The results show that the crystallinity of the product can be greatly improved by adding 4% low molecular weight polyethylene (LMWPE) 2911) or high molecular weight polyethylene (HMWPE) 4% to 5000S).At the same time, the crystallinity and tensile properties of the products were greatly improved by adding 4C11 and 4C58 to 5000S, and the elongation reached 8466a.(2) the medium molecular weight polyethylene (MMWPE) was tested by controlling the shear stress, and the shear stress of the melt was adjusted by changing the injection pressure and mold temperature of the injection molding machine.The relationship between shear stress and crystal shape was analyzed by means of electronic universal testing machine, differential scanning calorimeter and scanning electron microscope.Based on the analysis of the crystallization process of polyethylene, the orientation and crystallization of shear layer and core layer subjected to shear action are described.The results show that when the melt is shearing continuously, the shear layer will continue to become thicker and the mechanical properties will be improved.The shear rate can directly affect the structure, shape and size of the crystal shape.When the shear rate is greater than a certain value, the molecular chain begins to have obvious orientation.(3) using molecular simulation software, using molecular chain model and coarse graining model to simulate the effect of shear and tensile on polymer, respectively.The orientation behavior of polymer chains in shear stress field and the deformation of microstructure under tensile stress were studied.In mechanical testing, two different ensembles are used to investigate the relationship between tensile rate and stress-strain curve.The influence of external stress on crystal shape is analyzed according to the change of non-bond potential energy and total energy.The results show that NVT ensemble can effectively avoid the hole phenomenon.Under the action of shear stress or tensile stress, the orientation behavior of the molecular chain structure is obvious.
【學(xué)位授予單位】：太原理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TQ325.12

【參考文獻(xiàn)】

相關(guān)期刊論文 前10條

1 段芳莉;金義礦;顏世鐺;;半晶態(tài)聚合物拉伸變形的微觀機(jī)理[J];力學(xué)學(xué)報(bào);2016年02期

2 Dong Liu;Kunpeng Cui;Ningdong Huang;Zhen Wang;Liangbin Li;;The thermodynamic properties of flow-induced precursor of polyethylene[J];Science China(Chemistry);2015年10期

3 梁曉坤;袁霞;王偉鈴;李楊;羅筑;;有機(jī)硅對(duì)LLDPE/MH/有機(jī)硅無(wú)鹵阻燃復(fù)合體系性能的影響[J];塑料;2015年04期

4 王寧;趙立朋;李莉;;熱處理對(duì)硼酸改性聚乙烯醇體系結(jié)構(gòu)與性能的影響[J];塑料;2015年02期

5 Juan Li;Yi-jing Nie;Yu Ma;胡文兵;;STRESS-INDUCED POLYMER DEFORMATION IN SHEAR FLOWS[J];Chinese Journal of Polymer Science;2013年11期

6 段芳莉;顏世鐺;;半晶態(tài)聚合物的分子動(dòng)力學(xué)模擬[J];計(jì)算物理;2012年05期

7 高春雨;;我國(guó)聚烯烴生產(chǎn)工藝現(xiàn)狀及發(fā)展[J];合成樹(shù)脂及塑料;2012年01期

8 莫志深;;一種研究聚合物非等溫結(jié)晶動(dòng)力學(xué)的方法[J];高分子學(xué)報(bào);2008年07期

9 王文生,王旭霞;聚合物結(jié)晶度對(duì)注塑制品性能影響的研究[J];科技情報(bào)開(kāi)發(fā)與經(jīng)濟(jì);2002年03期

10 張志英;測(cè)定高聚物結(jié)晶動(dòng)力學(xué)參數(shù)的非等溫理論和方法[J];高分子通報(bào);1994年03期

相關(guān)博士學(xué)位論文 前3條

1 鄧聲威;非均質(zhì)聚合物材料力學(xué)性能的計(jì)算機(jī)模擬[D];華東理工大學(xué);2014年

2 王碩;注塑成型過(guò)程模腔內(nèi)熔體流動(dòng)速度與壓力檢測(cè)控制方法研究[D];浙江大學(xué);2012年

3 王錦燕;注塑成型中結(jié)晶形態(tài)演化的數(shù)值模擬[D];鄭州大學(xué);2012年

，

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