Applied Study Of The Swelling And Synergistic Plasticizing Effect In CO₂-Osmolyte-Polymer Ternary System On The Acid Hydrolysis Of PET

Supercritical C02(SCCO2) is considered to be an environmentally friendly fluid with outstanding dissolving capacity, diffusibility, low cost, etc. The physical properties of polymer will be changed once CO2dissolves into polymer, then SCCO2is widely used in the synthesis and modification of polymer. The solubility of CO2in polymer and the CO2plastization induced the glass transition temperature (Tg) reduction behavior of polymer are the two important properties in the CO2-polymer binary system. As the deep progress in research, the above two basic data have been unable to keep up with development. In practice, what is more important is to carry other small molecules (osmolyte) to penetrate into the polymer with SCCO2, making them play a functional role in the modification of polymer, such as the transfer and controlled release of drug molecules and graft of polymers, etc. In the CO2-osmolyte-polymer ternary system, not only can CO2dissolve into polymer, but also the osmolyte, plasticizing the polymer and inducing the Tg reduction. Therefore the solubility of osmolyte in polymer, osmolyte plastization effect, and the synergistic plasticizing effect of CO2and osmolyte on the Tg of polymer become the more important properties. It will be useful theoretical guidance and engineering significance to obtain these thermodynamic data with experimental methods and simulation.CO2and drug molecules have rather low solubility in some polymer, or the partitioning coefficient of drug molecules between polymer and SCCO2is very small. The traditional determination for the solubility of small molecules in polymer can not obtain the accurate data due to the low equipment accuracy. As an accurate and sensitive in situ analytical technique that can monitor extremely small changes in mass (10"6-10"9g), the quartz crystal microbalance (QCM) has been extensively applied to exactly measure the solubilities of CO2in polymer for CO2-polymer binary systems. However, in ternary systems, it needs to improve the device to obtain the accurate data. In this study, we establish the multifunctional dual QCM device for the first time, and manage to determine the solubilities of CO2and IBU in PMMA, PAA, PMAA, and PMA, respectively.In this study, the adsorption of N2and CO2on the surface of bare polished and unpolished crystals at different pressure and temperature were investigated using QCM technique to illustrate the reason why the plot of true frequency shift as temperature and pressure changed could intuitively exhibit the adsorption behavior of gas molecules on bare crystals. An anomalous solubility maximum of CO2in polymer thin film in the vicinity of critical temperature and pressure has not been clearly understood up to now when quartz crystal microbalance (QCM) technique is used in determining the sorption of CO2into PMMA film. The mechanism of non-absorbed CO2transitorily stayed in the interspace between PMMA film and crystal surface was explained by the morphology change of PMMA film. The assumption of "Passer-by CO2" was satisfactorily proved to explain the anomalous sorption behavior of CO2into PMMA film in the vicinity of critical CO2temperature and pressure. The sorption of CO2into polymer at different temperature, pressure, and thickness of polymer film were also investigated, the accurate solubility of CO2in polymer film could be obtained by an improved data correction method from the linear relation between true frequency shift and polymer film mass, and the anomalous solubility maximum could be corrected by this method.With an multifunctional dual QCM device and corresponding method for determination, the solubilities of ibuprofen (IBU) in supercritical carbon dioxide (SCCO2), and the CO2/IBU compound into PMMA, PAA, PMAA, PMA films at different temperature and pressure were determined, respectively, then the solubility of IBU in the four polymer film and the partitioning coefficient of IBU between each polymer and SCCO2were calculated according to the theory of infinite dilute solution. Both CO2and IBU molecules can plasticize the polymer in CO2-polymer and drug-polymer systems, for the CO2-IBU-polymer ternary system, the glass transition temperature reduction behavior of polymer versus the pressure of CO2and proportion of IBU in polymer was investigated with a high-pressure visual cell, which would illustrate the synergistic plasticizing effect of CO2and IBU on the glass transition temperature of polymer.Compared to PMMA, PET is one of the polyester plastic which has more broader market application. Based on the research foundation of SCCO2-osmolyte-polymer ternary system, hydrolysis of waste PET using solid acid catalyst in SCCO2is presented in this work for the first time. The mechanism of PET chains scission was proved to be a combination of chain end and random chain scission by FT-IR and titration analysis. A new reaction kinetics model of PET hydrolysis in SCCO2was set up by introducing the Arrhenius equation into an ordinary reaction rate equation, the frequency factor and apparent activation energy were expressed in terms of temperature and CO2pressure, respectively. With this reaction kinetics model, the effects of temperature, and pressure were investigated. An interesting mechanism was proposed to describe the reaction process that both water molecules and hydroniums were carried and penetrated into the amorphous regions of the swollen PET by SCCO2, subsequently hydrolysis reaction preferentially took place in the amorphous regions of both surface and bulk of PET matrix.