微型注塑条件下聚乳酸基共混物的原位微纳米纤维化、取向及机理研究

One of the important fundamental scientific problems in the high-performance of the biomedical polymer microparts is how to realize the formation of highly oriented micro/nano fiber structures and their structuring during microinjection molding process, which is worthy to be investigated. This project will design a blend composed of a biodegradable polymer (BDP) with low melting point and low melt viscosity such as Poly(ε-caprolactone) as the dispersed phase and poly(lactic acid)(PLA) with relatively higher melting point and melt viscosity as the matrix resin, design different micromold cavity dimension and runner structure to construct the shear stress field and devise different mold temperature gradient to construct the temperature field. The in-situ micro/nano fibrillation and the orientation of the dspersed phase in PLA/BDP blend could be accordingly realized under the strong shear stress field generated in the designed micromold cavity. For this purpose, the hierarchical structure, the interfacial compatibility, the in-situ micro/nano fibrillation of dispersed phase, the orientation and the related mechanism occuring in the blend under the different external field will be investigated. The related micro-scale rheological behavior in the confined space of the micromold cavity will be also investigated. The dependence of the melting piont and the rheological property including melt viscosity of the dispersed phase on its micro/nano fibrillation and orientation will be invstigated. The rheological behavior ~ structure ~ performance relationship will be finally established. The novel technology for the high performance of biomedical PLA microparts will be accordingly developed. This would surely lay a good foundation for preparation of high performance micro vascular clamps and micro bone screws. The studies in this project will provide novel technology and novel theory for the polymer microinjection molding and of course will make innovations and important theoretical and practical significance.

在微注塑加工过程中如何实现聚合物中高度取向微纳米纤维的形成及定构是生物医用聚合物微型制品高性能化中值得研究的重要基础科学问题。本项目拟通过设计低熔点低粘度可生物降解聚合物(BDP)如聚己内酯为分散相和相对较高熔点和熔体粘度聚乳酸(PLA)为基体组成共混物，设计和研制不同模具模腔尺寸和流道结构构建剪切场，不同模温梯度构建温度场，实现PLA/BDP共混物中分散相在微型模腔强剪切力场作用下的原位微纳米成纤及取向。研究不同外场作用下共混物中多层次结构，界面相容性，分散相原位微纳米纤维化、取向规律及机理，研究微型注塑受限空间的微流变行为，弄清分散相熔点、熔体粘度等流变性能与分散相微纳米纤维化及取向的关系，建立流变行为~结构~性能关系，建立生物医用聚乳酸微型制品高性能化新技术，为制备高性能微型血管夹和微型骨钉奠定基础。本项目研究将为聚合物微型注塑加工提供新技术新原理，具有创新性和重要的理论和实际意义。

针对传统微型血管夹、微型骨钉等生物医用微型器件力学强度不理想脆性大等缺点，本项目通过创新构建由两种具有明显熔点差和熔体粘度差的可完全生物降解且具良好生物相容性的聚合物组成的聚乳酸（PLA）基共混物体系，具体包括聚乳酸(PLA)/聚己内酯(PCL)、聚乳酸(PLA)/聚丁二酸丁二醇酯(PBS)、聚乳酸(PLA)/聚丁二酸-己二酸丁二醇酯(PBSA)等为代表的共混物体系，利用微型注塑加工过程中微型模腔内产生的强大剪切拉伸应力场以及高温度梯度（快速冷却）特点，实现了共混物中的分散相在微型注塑过程中原位形成高度取向的微纳米纤维以及高度取向的shish-kebab串晶结构（结合退火技术），大幅改善了共混物微型制品力学性能，如相对于传统注塑，微型注塑制品的力学性能拉伸强度提高了20-30%，表征韧性的断裂伸长率提高幅度最高达到了近2700%；深入研究了微型注塑加工条件下分散相微纳米纤维的形成机理及界面相容性问题，实现了理论创新；结合Moldex 3D、Moldflow、Polyflow等模流分析软件设计研制不同模腔尺寸和流道结构的模具以及通过改变微型注塑加工条件构建剪切场，通过设计温度梯度构建温度场，实现了聚乳酸基共混物中高度取向结构的形成和定构，建立了聚乳酸基共混物微型注塑加工的形态与结构调控新技术，实现了高分子材料生物医用微型制品如聚乳酸基共混物微型血管夹、微型骨钉等的高性能化；建立了聚乳酸基共混物微型注塑加工条件下微尺度流变行为～分散相微纳米纤维化～力学性能之间的关系；我们还积极参与了与微型加工相关的学科平台如四川大学-英国Bradford大学国际聚合物微型加工中心等的建设，建立和发展了国内一流国际先进的聚合物微型加工平台。项目在国内外重要学术期刊发表了学术研究论文9篇，其中SCI论文6篇，EI论文2篇；发表学术会议论文3篇，其中，国际会议1 篇，国内会议2篇；申请中国发明专利3项，其中获准授权1项；基于本项目的研究成果，项目负责人是获得第十七届中国青年女科学家奖团队奖的“高分子功能材料和器件先进制造”团队成员（2021年1月）。