原位红外研究聚乳酸（PLA）的冷结晶行为

发布时间：2018-10-20 14:06

【摘要】：作为一种环境友好型聚合物材料,聚乳酸(PLA)本身具有良好的生物相容性和可降解性,在载药、生物支架、骨组织再生等方面具有广阔的应用前景。然而,由于该材料结晶速率慢,在实际加工过程中极易形成非晶制品,使其热稳定性和力学性能大幅下降,限制了该材料的实际应用。众多研究表明,对聚乳酸进行再处理(退火、外力场等)是改变聚乳酸制品的微观结构进而改变其性能的重要手段。因此,本课题利用原位红外检测技术研究了聚乳酸非晶薄膜在温度场和应力场条件下的冷结晶行为,内容简述如下:(1)采用溶液法制备了聚乳酸薄膜,通过熔融-淬冷法得到了聚乳酸淬火样品,并利用WAXD、DSC和FTIR检测技术对初始样品进行结构表征,发现聚乳酸淬火样品为非晶态结构。(2)利用原位FTIR分析技术研究了退火过程中的聚乳酸非晶样品的结构演变情况,并讨论了温度对聚乳酸结晶结构完善程度的影响。结果表明,在63~68oC之间存在一个临界结晶温度。当退火温度高于该临界结晶温度时,聚乳酸非晶样品可以通过分子链的局部调整实现冷结晶行为,反之,冷结晶将不能发生。冷结晶过程中总是先出现中间相,最后发生中间相和晶体相的转变;中间相的形成总是通过分子链的构象有序和分子链间的堆砌调整实现,两者同时发生;退火温度越高,中间相出现的越早,最终得到的晶体结构越规整。(3)利用原位偏振FTIR技术并结合微型拉伸热台研究了聚乳酸非晶样品的结构演变以及与力学行为之间的关系,并探讨了温度对聚乳酸冷结晶行为的影响。结果表明,样品在结晶前期需经过结构调整。并且在拉伸过程中没有中间相出现,直接发生了非晶相到晶体相的转变;同时,样品在原位拉伸过程中由于发生了取向致使分子链间的堆砌更加规整,达到临界结晶应变后样品的结晶度开始迅速提高,使得晶体结构越来越完善。当拉伸温度低于63oC时,应变诱导聚乳酸结晶主要是受形变作用的影响;而当高于63oC时,随着拉伸温度的升高热驱动力的影响会越来越明显,从而加速分子链堆砌并降低结晶前期非晶相的临界取向。另外,高于临界结晶应变时发生了明显的应变硬化现象,这与拉伸温度对结晶度的变化趋势几乎一致,意味着拉伸过程中结晶度的变化导致了应变硬化现象。
[Abstract]:As a kind of environment-friendly polymer, Polylactic acid (PLA) has good biocompatibility and biodegradability. It has a broad application prospect in drug loading, biological scaffold, bone tissue regeneration and so on. However, due to the slow crystallization rate, amorphous products are easily formed in the process of practical processing, which greatly reduces its thermal stability and mechanical properties, which limits the practical application of the material. Many studies have shown that reprocessing polylactic acid (annealing, external force field, etc.) is an important means to change the microstructure of polylactic acid products and then change their properties. Therefore, the cold crystallization behavior of polylactic acid amorphous films under the condition of temperature and stress field is studied by in situ infrared detection technique. The main contents are as follows: (1) Polylactic acid films were prepared by solution method. Poly (lactic acid) quenched samples were obtained by melt-quenching method. The initial samples were characterized by WAXD,DSC and FTIR. It is found that the as-quenched polylactic acid samples are amorphous. (2) in situ FTIR analysis is used to study the structure evolution of polylactic acid amorphous samples during annealing and the effect of temperature on the perfection of polylactic acid crystal structure is discussed. The results show that there is a critical crystallization temperature between 63~68oC. When the annealing temperature is higher than the critical crystallization temperature, the amorphous polylactic acid sample can realize the cold crystallization behavior through the local adjustment of molecular chain, whereas the cold crystallization will not occur. The formation of mesophase is always realized by the conformational order of molecular chain and the adjustment of stacking between molecular chains. The higher the annealing temperature, the higher the annealing temperature. The earlier the mesophase appears, the more regular the final crystal structure is. (3) the structure evolution of the amorphous polylactic acid sample and its relationship with mechanical behavior are studied by in situ polarization FTIR technique and a micro tensile hot table. The effect of temperature on the cold crystallization behavior of polylactic acid was discussed. The results show that the structure of the sample needs to be adjusted in the early stage of crystallization. There is no mesophase in the tensile process, and the transition from amorphous phase to crystalline phase occurs directly, and the stacking between molecular chains is more regular due to the orientation of the sample during in-situ stretching. After the critical crystallization strain, the crystallinity of the sample increases rapidly, which makes the crystal structure more and more perfect. When the tensile temperature is lower than 63oC, the effect of strain induced polylactic acid crystallization is mainly affected by deformation, but when the tensile temperature is higher than 63oC, the effect of thermal driving force becomes more and more obvious. Thus, the molecular chain stacking is accelerated and the critical orientation of the amorphous phase in the precrystalline phase is reduced. In addition, the phenomenon of strain hardening occurs when the critical crystallization strain is higher than the critical crystallization strain, which is almost consistent with the trend of tensile temperature on crystallinity, which means that the change of crystallinity in tensile process leads to strain hardening.
【学位授予单位】：郑州大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：O633.14

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