调控超临界CO2发泡聚合物过程中溶解扩散行为的复合添加剂设计及其协同作用机制

The solubility and diffusivity of gas in polymer matrix play crucial roles in controlling the polymer/CO2 foaming process and the foam structure. The low solubility and the high diffusion coefficient of CO2 in the polymer lead to the difficulty of controlling the CO2 foaming process. The solubility and diffusion of CO2 can be partially changed via introducing the additive of the polymer matrix or the co-blowing agent. However, it is difficult to meet the requirement of CO2 solubility and diffusion at different stages of foaming by using a single additive. The interaction between supercritical CO2, CO2-philic polymer additives and the co-blowing agent will be studied by the multi-scale molecular simulation and a series of high pressure experiments. According the research results of interaction, the CO2-philic polymer additive and co-blowing agent will be matched considering the difference of the environment at different foaming stages. Then the effect of CO2-philic polymer additive and co-blowing agent on the solubility and diffusion of CO2 in the polymer matrix will be quantitatively investigated, and the solubility and diffusion coefficient of CO2 in the polymer will also corrected by the equation of state and free volume model, where the modified version will introduce the parameters accounting for the effect of additives. Meanwhile, the effect of additives on bubble nucleation and bubble growth will be investigated with in-situ observations and numerical simulation. The action mechanism of additives in different foaming stages will be identified by correlating the solubility and diffusion of CO2, the change of polymer properties and the bubble nucleation and bubble growth process. On the basis of understanding the action mechanism of complex additives, a good match of CO2-philic polymer additive and co-blowing agent will achieve a synergistic effect to control the cell density of bubbles and affect the cell size. The results will expand the control methods of supercritical CO2 foaming process, as well as provide theoretical basis and fundamental data for optimizing CO2 foaming process and regulating foams structure. Therefore, this work has high theoretical value and potential application prospect.

气体在聚合物中的溶解扩散行为对于聚合物发泡过程及泡孔结构控制影响显著。CO2在聚合物中溶解度较低、泡孔生长过程中扩散较快，导致超临界CO2发泡过程难以控制。通过引入添加剂改性聚合物基体或改变气体性质可以部分改善CO2的溶解扩散，但单一添加剂难以满足发泡不同阶段对CO2溶解扩散的需求。本项目计划采用多尺度模拟和实验结合，利用发泡不同阶段的CO2环境差异，合理匹配聚合物基体添加剂和小分子发泡助剂， 定性定量考察添加剂对CO2在聚合物基体中溶解扩散的影响，建立相应的溶解-扩散模型；同时通过气泡成核生长过程的在线观测和数值模拟，关联CO2的溶解扩散行为及其引起的聚合物性质改变，辨识复合添加剂在发泡不同阶段的作用机制，优化添加剂的设计匹配，协同增效，提高聚合物发泡过程效率、控制泡孔形貌。研究结果将拓展超临界CO2发泡过程的调控方法和手段，为优化发泡过程、控制泡孔结构提供理论依据和基础数据。

超临界CO2作为环保绿色发泡剂，在聚合物发泡中的应用越来越广泛。相较于目前工业常用的烷烃类等发泡剂，CO2在聚合物中溶解度小，在气泡生长阶段解吸速率快，发泡推动力不足，发泡倍率低，发泡过程难以控制。本项目基于改善CO2在聚合物中溶解扩散行为，提高发泡过程效率，优化调控聚合物泡孔形貌。通过亲CO2聚合物添加剂PDMS的引入，增强聚合物基体与CO2间的相互作用，实现饱和阶段高效扩散、增强溶解，解吸阶段扩散减缓，提高了PS发泡倍率的同时，降低了泡孔孔径；对于结晶形聚合物PP，PDMS在PP中具有提高CO2溶解扩散和促进结晶的双重作用。醇类共发泡剂的引入，也有效提高了CO2在溶解扩散并减缓了CO2的解吸扩散，复合型共发泡剂可以提高PS泡孔密度和发泡倍率；对于PP，共发泡剂促进CO2在PP中的溶解扩散的同时影响结晶行为，拓宽发泡温度的上下限。通过复合添加剂的协同调控CO2溶解扩散，实现双峰孔结构发泡材料的可控制备。建立了可视化系统和气泡生长数值模型，结合添加剂对CO2溶解扩散和聚合物基体性质的影响，分析辨识了不同添加剂对气泡生长的控制因素和作用机制。合理匹配亲CO2添加剂和共发泡剂，可实现大小分子添加剂的协同增效，调控聚合物发泡行为。研究结果为添加剂调控优化超临界CO2发泡聚合物行为提供了新机制和新途径。