초임계 이산화탄소를 이용한 Polycarbonate에 Docosane 함침

Abstract

Supercritical fluid(SCF) is defined as a solvent above its critical temperature and pressure. SCF is a highly nonideal fluid which has unique features in physical properties like a blending of gas and liquid. Especially, carbon dioxide is the most widely used SCF because it is inexpensive, no toxic residue, and is not flammable. And it has a relatively low critical temperature. Also, supercritical carbon dioxide(ScCO₂) is known as a low-volatile plasticizing agent for many polymer. Recently, some promising applications has been developed where mass transfer in the polymer phase by means of a SCF is major importance. The application of phase change materials(PCMs) for solar thermal energy storage capacities has received considerable attention in recent years due to their large storage capacity and isothermal nature of the storage process. Paraffin waxes are cheap and have moderate thermal energy storage density but low thermal conductive, and hence, require large surface area. Hydrated salts have larger energy storage density and higher thermal conductivity but supercooling and phase segregation, and hence, their application requires the use of some nucleating and thickening agents. Docosane, a sort of paraffin waxes, is one of the attractive organic PCMs for use in latent heat storage at 42℃. This paper is about impregnation of docosane into Polycarbonate(PC) using ScCO₂ The impregnation apparatus consisted of a low temperature bath, a high pressure pump, two consecutive high pressure cylinders and auxiliary facilities. After docosane and PC were loaded in each cylinder, the cylinders were heated to a desired temperature and purged with carbon dioxide during 20min to eliminate air inside cylinders. Liquid carbon dioxide was then added into the cylinders to achieve a desired pressure. The experiments were recorded at temperatures from 35℃ to 50℃ and pressures from 2,000psi to 4,000psi. Polycarbonate was bound on cylindrical stainless steel net inside equilibrium cylinder and was impregnated with supercritical solution of docosane. The weight change in impregnated PC after depressurization was gradually decreased until 7 days due to the desorption of carbon dioxide from impregnated PC. The impregnation ratio of docosane in PC was showed 0.5 ~ 1.1 wt% according to the experimental conditions, and increased with pressure and decreased slightly with temperature. From SEM images, it is turned out docosane was unevenly impregnated inside the processed PC. And impregnated PC showed high energy storage and release capacities around the melting point of docosane. From these results, it can be concluded that docosane was successfully impregnated into PC using supercritical carbon dioxide.