开合模微孔发泡注塑成型轻质高强隔热聚乳酸泡沫及其性能研究

The polylactic acid (PLA) foams have very important practical application values for energy conservation and environment protection. The PLA foam fabricated by mold-opening foam injection molding has the lightweight strong and high-insulating properties as well as biodegradability, and thus it has been getting more attention in recent years. At present, due to the low melt strength and slow crystallization speed, PLA has poor foaming ability, and the systematic study on foaming PLA by using mold-opening foam injection molding has not been carried out yet. Additionally, the structure-function relationship between the micro structure and the macro mechanical and heat transfer property of the molded PLA foams can not be analyzed by using the current theoretical models, attributing to their complex cell structures. To this end, this project will reveal the mechanism to regulate the melt strength and crystallization properties of the gas-solid/liquid homogeneous system, through an in-depth study of the in-situ fibrillation mechanism of the reinforcing phase as well as the effect of fibrillated fibrils on the rheological properties and crystallization behavior of PLA matrix. Based on the relationship between the properties of the homogeneous system and the cell nucleation and growth, the viscosity field model of the homogeneous system during the mold-opening foam injection molding will be established, to accurately regulate the cell structure of the molded foams. Furthermore, through analyzing the mechanical and heat transfer mechanisms, the mechanical and heat transfer mathematical model will be created to clarify the relationship between the micro structure and the macro mechanical and heat transfer property of the microcellular PLA foam, which was used to optimize the foam cell structure. This project not only has a pronounced value for reducing energy consumption and promoting environment protection, but also has a scientific significance for enriching the polymer foaming theory as well as the mechanical and heat transfer theory through microcellular materials.

聚乳酸泡沫对于节能环保具有重要的应用价值。基于开合模微孔发泡注塑成型聚乳酸泡沫因具有轻质高强隔热以及可生物降解性能而备受关注。目前，聚乳酸因熔体强度低、结晶速度慢导致发泡能力差，针对聚乳酸泡沫开合模微孔发泡注塑成型机理的研究尚未系统展开，并且其成型泡沫的泡孔结构复杂，无法应用现有理论研究其微观结构与宏观力学和传热的构效关系。为此，本项目拟深入研究增强相的原位成纤机理以及其对聚乳酸流变和结晶行为的影响规律，揭示气固/液均相体系的熔体强度和结晶特性的调控机制，研究均相体系特性与泡孔成核长大之间的映射关系，建立开合模微孔发泡注塑成型熔体粘度场模型，实现泡孔结构的精确调控，研究聚合物泡沫力学与传热学机理，建立微观结构与宏观力学与传热性能之间的构效关系模型，进而优化设计泡孔结构。本研究不仅对于节能减排、保护环境具有重要应用价值，而且对于丰富聚合物发泡成型、多孔材料的力学与传热理论具有重要的科学意义。

高性能、轻量化、环保塑件对于节材降耗、节能减排和可持续发展具有重要意义。微发泡注塑是一种以超临界二氧化碳/氮气为发泡剂的环境友好型塑料成型加工技术，而聚乳酸是一种生物质且可生物降解的环保材料，聚乳酸微发泡注塑成型是制备高性能、轻量化、环保塑件的一种很有潜力的技术途径，但目前该技术存在塑件外观品质不良、力学性能差、减重有限等瓶颈问题。为此，在国家自然科学基金青年项目的支持下，围绕轻量化高性能微孔聚合物构件绿色发泡注塑成型技术开展了系统深入的基础理论和关键共性技术研究，实现了原位微纤增强聚乳酸复合材料可控制备、高温高压环境下聚合物凝聚态结构及泡孔成核及长大过程的原位观测与表征、微发泡注塑成型泡孔结构的精确调控，建立了聚合物泡沫力学与传热学机理，建立聚合物微观泡孔结构与泡沫宏观力学、传热、降噪、吸油及油水分离等性能之间的构效关系模型，为高性能微孔聚合物构件绿色发泡注塑成型制造技术体系的建立提供了理论依据及技术支持。研制的轻量化高性能塑件对航空航天、汽车、电器通讯、医疗等重要领域的绿色可持续发展具有重大作用，有助于提升终端产品的综合性能和轻量化水平，降低材料和能源消耗，对推动和加快我国“碳达峰、碳中和”战略进程意义重大。