流动场下聚合物分子链响应与结晶关系的研究

发布时间：2018-03-13 16:08

本文选题：聚合物　切入点：X射线散射　出处：《中国科学技术大学》2017年博士论文　论文类型：学位论文

【摘要】：结晶型聚合物在成型过程中往往都要经历复杂流场的作用,这会对聚合物熔体中分子链的伸展和取向情况产生影响,从而影响其结晶动力学、晶体结构和晶体形态等结晶行为。因此,有必要对流动场下聚合物的结晶行为进行充分系统的研究。尽管目前有许多理论能够定量或半定量地描述流动诱导结晶的过程并预测流动诱导结晶的结果,但这些结论大多都是基于均匀流场的假设。在通常的加工条件下,处于非线性区高分子熔体的非线性流动行为会使得分子链对流场的响应变得非均匀。而即便是均匀流场,分子链对流场的响应也不会宏观外场完全一致。因此为了更为准确地理解流动诱导结晶的本质,有必要对流动诱导结晶实验中分子链对流场的响应进行关注。本论文主要着眼于非均匀流场和均匀流场下分子链对流场的响应及其对结晶的影响。通过自主研发的与X射线联用剪切装置,同时采集聚合物流变信息和结晶过程中结构演化信息,将不同均匀性流场下分子链响应与结晶行为相关联,得到不同流动模式熔体与结晶之间的关系。同时,针对均匀流场(拉伸流场),结合小角中子散射技术定量描述了链变形程度和串晶生成之间的关系。主要结果和结论总结如下:(1)采用交联氘/氢聚乙烯共混体系,研究了拉伸场下串晶生成前后分子链真实变形情况,结果显示串晶的形成不需要很大的分子链形变,这说明链内构象并不是影响串晶生成的唯一要素,而链内构象和链间密度耦合才更为关键。此外,在拉伸之后的结晶过程中,分子链运动行为与样品所处的拉伸状态密切相关。对于拉伸至硬化区的样品,体系内会有周期性高浓度氘代聚乙烯区域的产生。相反的,拉伸程度较弱的样晶体系内不会形成周期性高浓度氘代聚乙烯区域。(2)设计并制造了一台与X射线联用具有快速降温功能的剪切装置,该装置的快速降温的功能使得我们能够在高温对样品进行剪切并快速降温至较低温度进行等温结晶,将样品流变性能和结晶行为进行对应,研究不同链响应导致的不同流动行为与结晶的关系。(3)使用自主研发的快速降温装置,研究了瞬时和缓慢两种电机加速方式对样品流变和结晶行为的影响。实验结果显示缓慢加速能够消除剪切过程中流场的非均匀性,提高分子链对流场的响应,使样品取向度增加,提高流场对聚合物熔体的作用效果。同时,比对不同剪切速率和加速时间样品的结晶行为发现,对于不同剪切速率,流动诱导结晶对于加速时间有依赖性。(4)使用快速降温剪切装置并结合广角X射线散射,采用不同剪切速率和加速时间对不同流动模式下聚合物流变和结晶行为进行了研究。结果显示不同加速模式下分子链初始对流场的响应不同会引起熔体解缠结行为出现差异,从而对熔体流变行为和结晶动力学以及晶体取向造成影响。
[Abstract]:The crystallization kinetics of crystalline polymer is affected by the effect of complex flow field during the molding process, which will affect the stretching and orientation of molecular chain in polymer melt. Crystalline behavior such as crystal structure and crystal morphology. It is necessary to study fully and systematically the crystallization behavior of polymers in flow field, although there are many theories that can describe the process of fluid-induced crystallization quantitatively or semi-quantitatively and predict the results of fluid-induced crystallization. However, most of these conclusions are based on the assumption of uniform flow field. Under the normal processing conditions, the nonlinear flow behavior of polymer melt in the nonlinear region will make the response of the flow field of the molecular chain non-uniform, and even the homogeneous flow field. The response of the flow field of the molecular chain is not completely consistent with that of the external field. Therefore, in order to understand more accurately the essence of fluid-induced crystallization, It is necessary to pay attention to the response of the molecular chain flow field in the flow induced crystallization experiment. This paper focuses on the response of the molecular chain flow field and its effect on the crystallization under the inhomogeneous flow field and the uniform flow field. In conjunction with an X-ray shearing device, At the same time, the rheological information of polymer and the information of structure evolution during crystallization were collected, and the molecular chain response and crystallization behavior under different homogeneity flow fields were correlated, and the relationship between melt and crystallization in different flow modes was obtained. For the uniform flow field (tensile flow field), the relationship between chain deformation and crystal formation is quantitatively described in combination with small angle neutron scattering technique. The main results and conclusions are summarized as follows: 1) the cross-linked deuterium / hydrogen-polyethylene blend system is used. The real deformation of molecular chains before and after the formation of string crystals under tensile field is studied. The results show that the formation of string crystals does not require a large amount of molecular chain deformation, which indicates that the conformation of chains is not the only factor affecting the formation of string crystals. Moreover, in the crystallization process after stretching, the molecular chain movement behavior is closely related to the tensile state of the sample. There will be periodic high concentration deuteriated polyethylene regions in the system. A shearing device with rapid cooling function in conjunction with X-ray was designed and manufactured in a sample system with weak tensile degree, which does not form periodic high concentration deuterium polyethylene region. The rapid cooling function of the device enables us to shear the samples at high temperatures and rapidly drop them to lower temperatures for isothermal crystallization, which corresponds to the rheological properties and crystallization behavior of the samples. To study the relationship between different flow behavior and crystallization caused by different chain responses. The effects of instantaneous and slow motor acceleration modes on the rheology and crystallization behavior of the samples are studied. The experimental results show that the slow acceleration can eliminate the inhomogeneity of the flow field in the shear process and improve the response of the molecular chain flow field. At the same time, comparing the crystallization behavior of samples with different shear rates and accelerating time, it is found that, for different shear rates, the effect of flow field on polymer melts is improved. Fluid-induced crystallization is dependent on acceleration time. 4) using a rapid cooling shear device combined with wide-angle X-ray scattering, The rheology and crystallization behavior of polymer in different flow modes were studied by using different shear rates and acceleration time. The results show that the different responses of initial flow field of molecular chain in different accelerated modes will lead to the difference of melt unentanglement behavior. Thus, the melt rheological behavior, crystallization kinetics and crystal orientation are affected.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O631.1

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