Development of Supercritical CO_2 assisted polymer-processing techniques

CO_2在高分子材料加工中的应用日益广泛，由于其对环境无害的特性和加工聚合物的优越性能，CO_2已被公认为是挥发性有机溶剂的有效替代品。CO_2在加工过程中对聚合物起到增塑作用，保证加工后的材料不含任何溶剂残留。在这个为期三年的项目中，可以实现以下三个主要进展。1)利用CO_2对聚合物的塑化作用，将染料、PEG、碳纳米管（CNT）等低分子化学物质注入热塑性聚合物表面。提出了CO_2辅助表面改性注射成型的新方案。2)当CO_2/聚合物体系减压时，由于聚合物中扩散系数的差异，scCO_2从聚合物中扩散出去，而溶质保留下来。溶质注入的程度取决于溶质在scCO_2中的溶解度和溶质对聚合物基体的亲和力。为了改变溶质在scCo_2中的溶解度，通常使用醇和丙酮等助溶剂。本文采用近红外光谱和悬浮天平研究了CO_2和醇（丙醇和/或乙醇）在熔融低密度聚乙烯（LDPE）中的扩散率和溶解度。3)利用CO_2的增塑效应，开发了CO_2辅助纳米压印压印方案。在高压冲模机上溶解CO_2对聚合物制品表面进行塑化处理，在不加热制品的情况下，将冲压件表面纳米尺度的精细图案转移到塑化表面。通过CO_2的压力水平和CO_2的吸收时间，可以将塑化层的厚度控制在纳米级。图案转移可以在室温下进行，而不会变形产品的整体形状。少

The application of CO_2 for processing the polymeric materials has been dramatically increased and CO_2 is being recognized as an efficient alternative to volatile organic solvents due to its environmentally benign characteristics as well as its advantageous properties of processing polymer. CO_2 can provide plasticization effect on polymer during the processing and ensure that the processed material does not contain any trace of solvent residue after processing.In this three-year project, the following three major progresses could be achieved.1)Utilizing the plasticization effect of CO_2 on polymer, dye, low molecular chemicals, such as PEG and carbon nanotube (CNT) were infused into the surface of thermoplastic polymers. Furthermore, the new CO_2 assisted surface modification injection molding scheme was proposed.2)When the CO_2/polymer system is depressurized, scCO_2 diffuses out from the polymer while solute remains due to the difference of diffusivity in the polymer. The degree of … More solute infusion is dependent on the solubility of the solute in the scCO_2 and the affinity of the solute for the polymer matrix. To change the solubility of solute in the scCo_2, co-solvents such as alcohol and acetone are often used. In this study, the diffusivity and solubility of CO_2 and alcohol (propanol and/or ethanol) in molten low-density polyethylene (LDPE) was studied using near infrared spectroscopy and magnetic suspension balance.3)Utilizing the plasticization effect of CO_2, a CO_2 assisted nano-imprinting and embossing scheme was developed. The surface of polymer product was plasticized by dissolving CO_2 in a high pressure mold stamping machine and the nanometer-scale fine pattern on the mold stamper was transferred to the plasticized surface without heating up the product. The thickness of the plasticized layer could be controlled in nanometer thickness by pressure level of CO_2 and CO_2 absorption time. The pattern transfer could be performed at room temperature without deforming the overall shape of the product. Less