动态剪切场作用下纳米添加剂引入对异相气泡成核的作用机理研究

The phase of bubble nucleation in the moulding process for microcellular plastics plays a decisive role in determining the microstructure and mechanical performance of final foam products。The effect of steady shear, dynamic shear and the introduction of nano-additives on extrusion foaming of plastics will be conducted with a self-designed dynamic extrusion foaming machine in-situ with a transparent slit die.Based on the concept of shear energy, bubble nucleation model in steady shear flow field and dynamic shear flow field will be set up from the viewpoint of energy, and the contribution of each process variables to shear energy will be studied through the numeric simulation, and the effect of shear stress in different direction on the cell morphology will be investigated. With the presence of nano-additives, the discontinuity between the nano-additives and the surrounding polymer may lead to a local pressure field that differs from the bulk pressure as a result of pressure release. The concept of negative pressure is introduced and taking into account the irregular shape of the additive surface, a probability density function is proposed to account for the randomness of the semi-conical angle.Through the research on mechanism for cell nucleation with the presence of nano-additives,the constitutive equation corresponds to polymer melt/gas two-phase system will be built and qualitative description of the relationship between the nano-particles shape, dispersion and cell morphology will be clarified. Furthermore,a theoretical model will be established.The research of the project will contribute to clarifying the effect of dynamic processing parameters and configuration of nano-additives on bubble nucleation,providing theoretical guidance for preparation of the ideal microcellular plastics.

微孔塑料成型过程中的气泡成核阶段对制品的微观结构和力学性能起着决定性的作用。项目采用自行设计的动态挤出发泡机配以可视化模头，在线研究稳态剪切、动态剪切及纳米添加剂的加入对塑料挤出发泡的影响。根据剪切能的概念，从能量的角度提出稳态剪切流场和动态剪切流场中的气泡成核模型，通过对模型的数值模拟研究各工艺变量对剪切能和剪切应力的贡献，考察不同方向上的剪切应力对泡孔形态的影响。考虑到纳米添加剂存在时，压力的释放会导致纳米添加剂局部区域的压力与周围熔体的压力不同，引入负压力的概念并考虑到纳米添加剂表面形状的不规则性，将概率密度函数引入到空穴成核半锥角的分析中。通过对纳米添加剂存在条件下的气泡成核机理研究，构建聚合物熔体/气体两相体系的本构方程，定性描述纳米粒子形态及其分散与泡孔形态的关系，建立理论模型。项目研究有助于探明动态加工参数及纳米添加剂形态对气泡成核的影响，为制备理想的微孔塑料提供理论指导。

微孔塑料成型过程中的气泡成核阶段对制品的微观结构和力学性能起着决定性的作用，其引发和增强机制尚未完全清楚，项目通过研究稳/动态剪切及添加剂引入对塑料挤出发泡的影响，阐明了动态加工参数及纳米添加剂含量、形态等对气泡成核的影响。本课题创新点在于首次发现或揭示了：1）通过对微孔塑料的气泡成核过程进行宏观的能量描述，从能量角度建立了微孔塑料挤出发泡中稳/动态剪切流场中的气泡成核模型，并通过Matlab软件对该模型进行数值模拟，分析了剪切和振动参数对剪切能的贡献以及对泡孔形态的影响；2）将具有高超临界CO2溶解度的PDMS相引入到聚丙烯（PP）微发泡成型过程并研究了其对PP气泡成核和长大的影响；3）研究了稳/动态条件下纳米黏土（Nano-clay）引入对不同聚合方式PP发泡性能的影响；4）研究了聚苯乙烯（PS）与Nano-clay 引入对PP发泡性能的协同作用；5）研究了增塑剂、改性剂、气泡成核剂和加工工艺参数对聚氯乙烯（PVC）微孔发泡泡孔形态及力学性能的影响并对其作用机制进行了阐明。项目研究成果对采用超临界CO2挤出成型制备微孔聚合物材料的科学实践，具有重要的基础理论和应用指导意义。目前，相关研究成果在《Journal of Vinyl & Additive Technology》（SCI）、《Materials Science Forum》（EI）、《Advanced Materials Research》（EI）等期刊及会议上发表学术论文8篇，其中SCI/EI收录论文6篇（含已录用）。此外，另有两篇基金资助论文已分别投稿至SCI期刊《Journal of Applied Polymer Science》和《Cellular Polymers》上，目前正在审稿阶段。