本文選題：剪切場(chǎng) + 結(jié)晶動(dòng)力學(xué)�。� 參考：《中國科學(xué)技術(shù)大學(xué)》2017年博士論文

【摘要】：聚合物在實(shí)際加工過程中必然受到各種剪切場(chǎng)的作用,導(dǎo)致聚合物結(jié)晶動(dòng)力學(xué)及結(jié)晶形貌與靜態(tài)條件下的巨大差異,從而嚴(yán)重影響聚合物制品的最終性能。為使目前的剪切場(chǎng)結(jié)晶理論與實(shí)際加工過程更好的結(jié)合,有必要將研究對(duì)象擴(kuò)展到具有應(yīng)用價(jià)值的聚合物材料體系中。本工作通過選取除了純線性聚合物之外的體系為研究對(duì)象,主要通過流變法和偏光顯微鏡搭配剪切熱臺(tái)系統(tǒng)研究不同聚合物體系中長(zhǎng)鏈支化、預(yù)存在結(jié)構(gòu)、熔體-基底界面、共混物等在剪切場(chǎng)作用下結(jié)晶動(dòng)力學(xué)和結(jié)晶形貌演變過程。主要研究?jī)?nèi)容包括以下四個(gè)方面:1.通過在線性聚乳酸(linear PLA)中加入三官能度單體,三羥甲基丙烷三丙烯酸酯(TMPTA),在利用伽馬射線輻照的辦法,制備了一系列具有不同支化度的長(zhǎng)鏈支化聚乳酸(LCB PLA)樣品。動(dòng)態(tài)頻率掃描測(cè)試表明,LCB PLA樣品的松弛時(shí)間譜被拓寬,尤其是在最長(zhǎng)松弛時(shí)間區(qū)域。將結(jié)晶中的LCB PLA模型化為類懸浮體系,可以獲得半結(jié)晶時(shí)間。對(duì)于LCB PLA,結(jié)晶速率的加速效應(yīng)會(huì)在一定的剪切時(shí)間下達(dá)到飽和,且LCB PLA的支化程度越高,飽和剪切時(shí)間則越低。通過流變得到的空間填充率利用Avrami方程計(jì)算成核密度,也出現(xiàn)了成核密度隨剪切時(shí)間飽和的現(xiàn)象。這種足夠長(zhǎng)剪切時(shí)間下的飽和現(xiàn)象與偏光顯微鏡觀察到的結(jié)晶形貌從球晶到取向晶型的轉(zhuǎn)變有著對(duì)應(yīng)的關(guān)系。LCB PLA取向晶體形貌的形成機(jī)理與拉伸后的長(zhǎng)鏈支化分子鏈網(wǎng)絡(luò)被抑制的松弛特性有關(guān)。不同支化度的LCB PLA結(jié)晶速率的大幅提高和結(jié)晶形貌的轉(zhuǎn)變對(duì)于提高PLA的加工效率,以及對(duì)PLA高性能制品的生產(chǎn)提供了潛在的理論指導(dǎo)。2.從形態(tài)學(xué)角度研究了預(yù)存在球晶和剪切場(chǎng)對(duì)iPP的結(jié)晶行為的共同作用。對(duì)已存在球晶的iPP熔體施加剪切場(chǎng)后,結(jié)晶形貌發(fā)生了從球晶到另外兩種獨(dú)特形貌的轉(zhuǎn)變。這兩種形貌的產(chǎn)生與球晶在熔體-基底表面不同的相互作用有關(guān)。較低剪切溫度時(shí),球晶與基底有很好的依附作用,導(dǎo)致球晶周圍剪切強(qiáng)度比本體內(nèi)高,且固定在球晶表面的分子鏈自由端更容易發(fā)生高度的伸展和取向,因此形成了密集堆砌的晶核聚集體為中心結(jié)構(gòu)。而提高剪切溫度,球晶的高程度熔融導(dǎo)致其在剪切中發(fā)生與熔體-基底的相對(duì)移動(dòng),誘導(dǎo)了基底表面大量較為疏散的異相成核,且生長(zhǎng)為為微小球晶為聚集體的中心結(jié)構(gòu)。隨著結(jié)晶時(shí)間的增加,在該兩種中心結(jié)構(gòu)的外沿發(fā)生了片晶的大量生長(zhǎng),最終形成了兩種不同結(jié)構(gòu)的柱形形貌。該工作對(duì)聚合物在加工中所面臨的熔體-基底作用,預(yù)存在晶體或其他添加的粒子等對(duì)聚合物結(jié)晶形貌的影響具有一定的指導(dǎo)意義。3.主要從形態(tài)學(xué)角度研究了聚乳酸/聚己內(nèi)酯(PLA/PCL)共混物這一典型的生物可降解共混物體系在剪切場(chǎng)下的結(jié)晶行為。首先使用DSC研究了其基本的熱性能,證實(shí)了 PCL相能顯著提升PLA的冷結(jié)晶行為。流變研究了PLA/PCL共混物基本的粘彈性行為,表征了該體系PCL相界面的松弛效應(yīng)對(duì)粘彈性行為的影響。靜態(tài)結(jié)晶行為表明PCL的加入對(duì)PLA的成核和晶體生長(zhǎng)并未產(chǎn)生較大影響。然而施加剪切場(chǎng)之后,發(fā)現(xiàn)隨著剪切強(qiáng)度的提高或結(jié)晶溫度的降低,PLA/PCL共混物發(fā)生了從球晶形貌到取向的串珠狀形貌的轉(zhuǎn)變。雖然不同剪切條件下PCL相均發(fā)生了取向,然而PLA取向結(jié)構(gòu)的形成則主要是由PLA的成核和PCL相在剪切后的松弛相互競(jìng)爭(zhēng)從而導(dǎo)致PLA在PCL相界面出誘導(dǎo)成核所影響。雖然取向排列的串珠狀形貌并非shish-kebab,但是對(duì)加工該生物可降解共混物材料或其他共混體系的聚合物具有一定的指導(dǎo)意義。4.研究了不同螺桿轉(zhuǎn)速制備的左旋聚乳酸/右旋聚乳酸/乙烯-甲基丙烯酸縮水甘油酯共聚物(PLLA/PDLA/EGMA)共混物在剪切場(chǎng)下的結(jié)晶行為。首先使用DSC研究了其基本的熱性能,證實(shí)了螺桿轉(zhuǎn)速的提高能顯著提升EGMA對(duì)PLA的冷結(jié)晶行為的促進(jìn)作用。流變研究了 PLLA/PDLA/EGMA共混物基本的粘彈性行為,表征了該體系SC晶體和EGMA相界面的松弛效應(yīng)對(duì)粘彈性行為的影響。施加剪切場(chǎng)之后,發(fā)現(xiàn)不同螺桿轉(zhuǎn)速制備的PLLA/PDLA/EGMA共混物形成了不同的結(jié)晶形貌。較低轉(zhuǎn)速下,結(jié)晶形貌為分散均勻的小尺寸球晶,而當(dāng)轉(zhuǎn)速提高后,結(jié)晶形貌轉(zhuǎn)變?yōu)椴痪坏膱F(tuán)狀晶體甚至為云霧狀的晶體形貌。該現(xiàn)象受SC晶體,EGMA相區(qū)尺寸和EGMA與基體的界面作用共同控制。本論文主要?jiǎng)?chuàng)新點(diǎn):1)探索了長(zhǎng)鏈支化聚乳酸中不同的支化程度對(duì)剪切場(chǎng)下結(jié)晶動(dòng)力學(xué)和結(jié)晶形貌的影響,以及通過流變手段將結(jié)晶動(dòng)力學(xué)的變化與結(jié)晶形貌建立了聯(lián)系,為該生物可降解材料的加工以及應(yīng)用范圍的拓展提供了理論支持。2)強(qiáng)調(diào)了聚合物熔體中預(yù)存在晶體對(duì)剪切場(chǎng)下結(jié)晶行為的影響,以及聚合物-基底界面所扮演的角色。3)對(duì)聚乳酸不相容共混物的剪切結(jié)晶行為進(jìn)行了系統(tǒng)研究,發(fā)現(xiàn)了不相容共混物在剪切場(chǎng)下形成了區(qū)別于shish-kebab的獨(dú)特的取向晶體形貌,為共混物的加工過程中的形態(tài)結(jié)構(gòu)演變提供了直觀的了解。
[Abstract]:In actual processing, polymers are bound to be affected by various shear fields, leading to the huge difference between the crystallization kinetics and the crystalline morphology and static conditions of the polymer, which seriously affects the final properties of the polymer products. In this work, the system of polymer materials which is of applied value has been developed. By choosing a system other than pure linear polymer as the research object, the long chain branching, the pre existence structure, the melt base interface, the blends, etc. are studied by the rheological method and the polarizing microscope with the shear thermal platform system. The main contents include four aspects as follows: 1. by adding three functional monomers, three hydroxymethyl propane three acrylate (TMPTA) in linear polylactic acid (linear PLA), a series of long chain branched polylactic acid with different branching degrees was prepared by gamma ray irradiation. (LCB PLA) samples. The dynamic frequency scanning test shows that the relaxation time spectrum of the LCB PLA sample is widened, especially in the longest relaxation time region. The LCB PLA model in the crystallization is transformed into a class suspension system, and the semi crystallization time can be obtained. For LCB PLA, the accelerating effect of crystallization rate should be saturated at a certain shear time and LCB PLA. The higher the branching degree is, the lower the saturated shear time is, the nucleation density is calculated by the Avrami equation, and the nucleation density is saturated with the shear time. The saturation phenomenon in the long enough shear time and the transformation of the crystalline morphology observed by the polarizing microscope from spherulite to orientation crystal are observed. The formation mechanism of the corresponding.LCB PLA oriented crystal morphology is related to the relaxation characteristics of the long chain branched molecular chain network after stretching. The significant increase in the crystallization rate of LCB PLA and the transformation of the crystalline morphology of the different branching degrees provide a potential reason for improving the processing efficiency of PLA and the production of PLA high performance products. The common effect of pre existence of spherulites and shear fields on the crystallization behavior of iPP was studied from the morphological point of view. After applying the shear field to the iPP melts of the existing spherulites, the crystallization morphology changed from spherulites to the other two unique morphologies. The production of the two morphologies was different from that of the spherulites on the melt substrate surface. When the shear temperature is lower, the spherulite and the substrate have a good dependence on the substrate. The shear strength around the spherulites is higher than that in the body, and the free ends of the molecular chain fixed on the surface of the spherulite are more prone to high extension and orientation. Therefore, the core aggregates of dense stacked nuclei are formed as the central structure. The shear temperature and the high degree of spherulites are improved. Melting leads to the relative movement of the melt and substrate in the shear, which induces a large number of dispersed hetero nucleates on the surface of the substrate, and grows to be the central structure of the small spherulites. With the increase of the crystallization time, the growth of the two kinds of central structures in the outer edge of the central structure has resulted in the formation of two different junctions. This work has a certain guiding significance for the influence of melt basement, pre existence of crystals or other particles on the crystalline morphology of polymers in the process of processing..3. mainly studies the biodegradable blend of polylactic acid / polyhexyllactone (PLA/ PCL) blends from the morphological point of view. The crystallization behavior of an object under the shear field. First, the basic thermal properties were studied by DSC. It was confirmed that the PCL phase could significantly improve the cold crystallization behavior of PLA. The rheological behavior of the PLA/PCL blends was studied by rheology. The effect of the relaxation effect on the PCL phase of the system on the viscoelastic behavior was characterized. The static crystallization behavior indicated that the PCL was the static crystallization behavior. The addition has no significant effect on the nucleation and crystal growth of PLA. However, after the shear field was applied, it was found that with the increase of shear strength or the decrease of crystallization temperature, the PLA/PCL blends changed from spherulite morphology to orientation. Although the orientation of the PCL phase occurred under different shear conditions, the PLA orientation structure was observed. The formation is mainly caused by the nucleation of PLA and the relaxation of the PCL phase after shear, resulting in the effect of PLA on the induced nucleation of the PCL phase interface. Although the bead like morphology of the orientation arrangement is not shish-kebab, it has a certain guiding significance for the processing of the biodegradable blends or other blends. The crystallization behavior of the blends of L-polylactic polylactic acid / polylactic lactic acid / ethylene glycidyl methacrylate copolymer (PLLA/PDLA/EGMA) prepared by different screw speeds was studied under the shear field. First, the basic thermal properties were studied by using DSC. It was proved that the improvement of screw speed could significantly enhance the cold crystallization behavior of EGMA to PLA. The basic viscoelastic behavior of PLLA/PDLA/EGMA blends was studied by rheology. The effect of relaxation effect on the interface between SC crystal and EGMA phase on the viscoelastic behavior was characterized. After applying the shear field, it was found that the PLLA/PDLA/EGMA blends prepared at different screw rotational speeds formed different crystalline morphology. When the rotational speed is increased, the crystalline morphology changes into uneven mass and even cloud like crystal morphology. This phenomenon is controlled by the interface of SC crystal, EGMA phase size and EGMA with the matrix. The main innovation of this paper is: 1) the different branching degree of the long chain branched polylactic acid was explored. The influence of crystallization kinetics and crystal morphology under the tangent field, and the relationship between the change of crystallization kinetics and the crystalline morphology by rheological means, which provide theoretical support for the processing of the biodegradable material and the extension of its application range,.2) emphasized the effect of the pre existence of the crystals on the crystallization behavior under the shear field. As well as the role of the polymer substrate interface (.3), the shear crystallization behavior of poly (lactic acid) incompatible blends was systematically studied. It was found that the incompatible blends formed a unique orientation crystal morphology different from shish-kebab under the shear field, providing a visual understanding of the morphological structure evolution of the blends during the process of processing.

【學(xué)位授予單位】：中國科學(xué)技術(shù)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類號(hào)】：O631.13

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