聚丁烯-1的结晶行为和形变机理
文献类型：学位论文
| 作者 | 王要涛 |
| 学位类别 | 博士 |
| 答辩日期 | 2015-04 |
| 授予单位 | 中国科学院研究生院 |
| 授予地点 | 中国科学院长春应用化学研究所 |
| 导师 | 门永锋 |
| 关键词 | 聚丁烯-1 结晶 记忆效应 塑性形变 空洞化 |
| 中文摘要 | 结晶高分子通常可以被看成是由相互关联的片晶构成的硬骨架网络和缠结的非晶软网络的互穿网络，其结晶行为和形变机理是高分子物理和工业领域的重要内容，对于探寻高分子材料的结构特征与宏观力学性能的关系有着实际意义。本论文选择多晶型聚合物聚丁烯-1和丁烯-1/乙烯共聚物作为研究对象，利用示差扫描量热法（DSC）、 偏光显微镜（POM）、同步辐射小角和广角X射线散射（SAXS/WAXS）等多种方法，对其结晶行为、形变过程中的晶型转变和结构演化、空洞化现象等进行了研究，主要结论如下： 1.分子量对聚丁烯-1的结晶和熔融行为的影响； 利用温度依赖的SAXS在线跟踪了三种不同分子量的聚丁烯-1的等温结晶及其后续加热过程的结构演化行为，并建立了片晶厚度和温度之间的关系，发现存在三条具有不同的斜率和相同的平衡结晶温度的结晶线，但是只存在一条共同的重结晶线和熔融线。这是由于由小晶块组成的原生晶的表面自由能会随着分子量的增加而升高，进而导致结晶线的斜率的增加。然而，在原生晶通过稳定化逐渐形成稳定晶的过程中，不同分子量造成的表面能的差异逐渐消失，最终导致一条重结晶线和熔融线。这个结果进一步验证了Strobl提出的聚合物结晶的多阶段模型，从熔体到结晶相的过程中经历一个中介相。 2.记忆效应对丁烯-1/乙烯共聚物结晶行为的影响； 研究了丁烯-1/乙烯共聚物结晶过程中记忆效应的影响，通过调控熔体温度直接得到晶型II或者晶型I’，这两种晶型的形成，依赖于熔体的温度，与初始的晶体结构无关。低温的不均匀的熔体，存在预有序链段堆积结构，易于晶型I’的成核；高温的无规分布熔体，则导致晶型II的产生。该部分工作为加工过程提供一条便捷的方法，可以实现直接从聚丁烯-1的共聚物的熔体中在常温下直接得到稳定态的晶型I’。 3.应力诱导的熔融重结晶机理的实验判据； 研究了聚丁烯-1的晶型I在高温下拉伸的结构演变，发现了亚稳态的晶型II的形成。由于链构象和晶格尺寸限制，稳定态的晶型I不可能直接通过滑移过程转变为晶型II，因此，晶型I必须通过两步形成晶型II。首先，由于倾斜方向晶型I的微晶承受较大的剪切力，其在应力诱导下逐渐熔融；然后，熔融形成的自由分子链重结晶形成沿拉伸方向取向的亚稳态的晶型II。这个实验现象为应力诱导的熔融重结晶机理提供了直接判据。 4.聚丁烯-1本体结晶和应力诱导结晶之间的关系； 对比了本体结晶和拉伸诱导结晶这两种不同的结晶行为，发现在相同温度下，熔体结晶样品的片晶厚度远大于形变诱导结晶样品的片晶厚度，并且得到两个形成无限厚片晶相对应的极限平衡温度，这两种相似过程的不同结果可以通过考虑应力对熔体和结晶过程的热力学参数的影响而得以解释，结果表明拉伸诱导结晶不需要经过中介相，直接从局部有序的熔体形成结晶相。 5.丁烯-1/乙烯共聚物的不同晶型的塑性形变行为 研究了丁烯-1/乙烯共聚物的不同晶型（通过晶型II固固相转变得到的晶型I和直接从熔体结晶得到的晶型I’）的塑性形变行为。相同结晶温度下，晶型I具有更高的熔点、更大的长周期。形变过程中，晶型I具有更高的机械稳定性，处于倾斜方向的晶体在形变的最后阶段可以保存下来，形成长周期较小的新片晶；晶型I’则完全破碎熔融，沿着拉伸方向形成新片晶和微纤结构。值得注意的是，拉伸诱导的片晶具有相同的长周期，只取决于拉伸温度，与初始的晶型结构和长周期无关，证明了形变过程中应力诱导的熔融重结晶机理。 6.聚丁烯-1的空洞化行为 通过精确控制片晶厚度和拉伸温度等参数，我们利用同步辐射超小角X射线散射和广角X射线衍射，研究了聚丁烯-1空洞化行为，构建了空洞化随这片晶厚度和拉伸温度变化的相图，提出了空洞化的模型。形变过程中，空洞化的演化存在三种不同的模式：片晶最薄时，不发生空洞化；片晶较厚在任何温度或者较薄片晶在低温拉伸时，生成的圆盘状空洞径向首先垂直于拉伸方向，大形变时转向至拉伸方向；较薄的片晶在高温拉伸时，空洞始终沿着拉伸方向。 |
| 英文摘要 | Semicrystalline polymers are composed of stacked crystalline lamellae and entangled amorphous polymeric chains in between. The crystallization and deformation behavior in semicrystalline polymers are the two important topics in polymer physics and industry field, which are important to affect the structure features and final properties of polymeric materials. In this thesis, by means of a combination of differential scanning calorimetry (DSC), polarizing optical microscope (POM), and synchrotron small/wide angle X-ray scattering (SAXS/WAXS) techniques, we investigated the crystallization, phase transition, microstructure evolution during deformation process including plastic deformation and cavitation in polybutene-1 (PB-1). The main results are summarized as follows: 1. Molecule weight dependency of crystallization and melting in polybutene-1. By means of temperature-dependent small-angle X-ray scattering experiments, we investigated the isothermal crystallization and subsequent melting processes in three PB-1 samples with different molecule weight, and established the relationship between the lamellar thickness and temperature. Three crystallization lines with different slopes but same limiting temperature and only one common recrystallization line and one melting line were observed. The results can be understood as follows. The surface free energy of the native crystals formed from the mesomorphic blocks increases with molecular weight in PB-1, leading to an increase of the slop of the crystallization line for samples with higher molecular weight. However, during the stabilization process after the formation of native crystals forming stable crystals the surface free energy decreases to such an extent that the di?erences among samples of different molecular weight vanish so that a common recrystallization line and melting line were observed. The results proofed the multistage model of crystallization in semicrystalline polymer where it involved a mesomorphic phase from the melt state to crystalline phase during crystallization process. 2. Memory effect on the crystallization of butene-1/ethylene copolymer The memory effect on the crystallization of butene-1/ethylene copolymer was investigated. By manipulating the melt temperature, form II or form I′ can be obtained directly from the melt state, independent of the initial crystal structure. Even though the material was brought to temperatures higher than the equilibrium melting temperature of the copolymer, heterogeneities of segmental segregation character were preserved which promoted massive nucleation of form I’ crystallites, which makes it possible that the material is able to crystallize into pure form I’. Only if when the melt temperature was high enough where all heterogeneities of the above-mentioned character were erased can the material be crystallized into pure form II. The effect is found independent of the previous crystalline form, meaning that the helical conformation of chains in the heterogeneous melt does not affect the nucleation of stable form I’. 3. Evidence for the stress-induced melting and recrystallization mechanism Stretching-induced structural changes in PB-1 with stable crystalline modification of form I at elevated temperature was investigated by means of the in-situ synchrotron wide-angle X-ray diffraction technique. It was found that oriented metastable form II crystallites with the polymer chain aligned along the stretching direction gradually appear during tensile deformation. Based on the fact that a solid state I to II phase transition cannot take place due to the restriction in chain conformations and lattice dimensions in both phases, the observed occurrence of transition from form I to form II must proceed via a two-step process. First, those form I crystallites with their polymer chain direction tilted with respect to the stretching direction undergo a stress-induced melting process because they experience lar |
| 语种 | 中文 |
| 公开日期 | 2016-05-03 |
| 源URL | [http://ir.ciac.jl.cn/handle/322003/64481]  |
| 专题 | 长春应用化学研究所_长春应用化学研究所知识产出_学位论文 |
| 推荐引用方式 GB/T 7714 | 王要涛. 聚丁烯-1的结晶行为和形变机理[D]. 中国科学院长春应用化学研究所. 中国科学院研究生院. 2015. |
入库方式： OAI收割
来源：长春应用化学研究所
浏览0
下载0
收藏0
其他版本
除非特别说明，本系统中所有内容都受版权保护，并保留所有权利。