Development of Supercritical CO_2 assisted polymer-processing techniques

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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