流动诱导聚乳酸结构熔体结晶

发布时间：2018-04-05 12:52

  本文选题：聚乳酸　切入点：熔体结构　出处：《郑州大学》2017年硕士论文

【摘要】：聚乳酸(PLA)作为一种半结晶高分子材料,具有良好的生物可降解性和生物相容性。PLA制品的力学性能、耐热性和降解性能依赖于其成型过程中形成的结晶形态结构。由于PLA成核困难、结晶速率慢,导致通常成型条件下常得到非晶制品,从而限制了其应用。提高成核效率可以促进PLA结晶并改善其性能,PLA成核调控的相关研究引起了广泛关注。为了提高聚乳酸制品的结晶度,常采用加入成核剂以提高聚乳酸的成核密度。高分子的成核与结晶行为是影响其结晶形态结构的关键因素,其中流动与自成核能明显加快成核并提高成核密度。本文主要研究了流场作用下聚乳酸有序熔体对结晶行为的影响,主要研究内容和结果如下:采用原位X射线散射和衍射的方法研究了聚乳酸的熔融和结晶行为。通过改变部分熔融温度和部分熔融时间的方式,制备了具有不同热历史的聚乳酸熔体,在随后的静态等温结晶实验中发现:(1)随着部分熔融温度的升高,结晶度逐渐降低;(2)随着部分熔融时间的延长,结晶度略有降低;(3)从有序熔体降温结晶过程中,最快结晶温度在110℃至120℃之间,在110℃等温结晶5 min时,结晶度达到5%左右。在120℃等温结晶5 min时结晶度达到3%左右。对含有初始有序结构的熔体施加剪切,在随后的等温结晶过程中发现:(1)与空白熔体相比,有序熔体施加剪切后结晶度都有明显提高;(2)与有序熔体静态结晶过程相比,施加剪切后的结晶度明显提高;(3)随着部分熔融温度的升高,结晶度逐渐降低;(4)随着剪切应力的增加,样品取向程度逐渐增大,结晶进程逐渐加快;(5)施加剪切后聚乳酸有序熔体的结晶速度明显加快,在110℃和120℃等温结晶5 min时都可以达到40%以上的结晶度。
[Abstract]:Polylactic acid (PLA), as a semi-crystalline polymer, has good biodegradability and biocompatibility. The mechanical properties, heat resistance and degradation properties of PLA products depend on the crystalline structure formed during the molding process.Due to the difficulty of nucleation and the slow crystallization rate of PLA, amorphous products are often obtained under normal forming conditions, which limits its application.Increasing nucleation efficiency can promote the crystallization of PLA and improve its performance.In order to improve the crystallinity of polylactic acid products, nucleating agent is often used to increase the nucleation density of polylactic acid.Nucleation and crystallization behavior of polymers are the key factors affecting their crystalline morphology, in which flow and self-forming nuclear energy can obviously accelerate nucleation and increase nucleation density.In this paper, the effect of polylactic acid ordered melt on crystallization behavior under the action of flow field is studied. The main contents and results are as follows: in situ X-ray scattering and diffraction are used to study the melting and crystallization behavior of polylactic acid.Polylactic acid melts with different thermal histories were prepared by changing the partial melting temperature and partial melting time. In the subsequent static isothermal crystallization experiments, it was found that: 1) with the increase of partial melting temperature,The crystallinity decreased gradually with the prolongation of partial melting time, and the crystallinity decreased slightly. During the cooling crystallization process of the ordered melt, the fastest crystallization temperature was between 110 鈩，

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