Applied Study Of The Diffusion And Synergistic Plasticizing Effect In CO₂-Micromolecule-Polymer Ternary System On The Chlorination Of Polymer

Supercritical carbon dioxide(SCCO2),for its liquid-like density and gas-like diffusivity,has tremendous potential in polymer modification and processing.In these processes,the solubility of CO2 in polymer and the CO2 plasticization induced the glass transition temperature(Tg)reduction behavior of polymer are the two important properties in the CO2-polymer binary system.In practical application,the addition of a small amount of micromolecule into polymer can affect the properties of polymer.Meanwhile,the respective solubilities,as well as the total solubility,and synergistic plasticizing of CO2 and micromolecule on polymer are the most important thermodynamic property for CO2-micromolecule-polymer ternary systems.It will be useful theoretical guidance and engineering significance to obtain these thermodynamic data with experimental methods or simulation.To develop the methodology to accurately determine the respective solubilities of micromolecules in polymer,the respective solubilities of CO2 and ethanol in PS and the synergistic plasticizing of CO2 and micromolecule on polymer in CO2-ethanol-PS ternary system at elevated pressure and temperature were studied.However,in the process of study,pressure gradients and temperature gradients drive nucleation,and cells occur.These cells will predictably influence the diffusion of micromolecule in polymer,whereas the reports on the diffusion of micromolecule in polymer with cells(noted as foamed-polymer)is less,therefore,Foamed-Non-Fickian Diffusion model(FNFD model)was proposed to regress the desorption data obtained by gravimetric method.Results showed that FNFD model could accurately describe the diffusion behavior of CO2 from foamed PS,and the solubility estimated by FNFD model agreed well with the solubility determinated by QCM.Furthermore,based on the assumption that CO2 in the cells of foamed PS would adsorb to the wall of the cells,diffuse into the matrix,and desorb from the polymer during the desorption process.The mass of CO2 in the cells of foamed PS is expressed as a model of the function of swelling temperature and pressure.Results showed that the values obtained by this model agreed well with the values obtained by the FNFD model,except for the data near the critical point.Meanwhile,the FNFD model was used to regress the the desorption data of ethanol in PS for ethanol-PS binary system.Results showed that FNFD model could accurately describe the diffusion behavior of ethanol from foamed PS.The diffusion coefficient of CO2 in PS obtained by FNFD model is about 10-10m2/s,which is proximate with ethanol in PS(about 10-11 m2/s)and it is difficult to determinate the respective solubilities of CO2 and ethanol in PS.Therefore,Sanchez-Lacombe equation of state(S-L EoS)was adopted to calculate the respective solubilities and total solubilities of CO2 and ethanol in PS.Results showed that the total solubility of CO2 and ethanol obtained from calculation agreed well with values obtained by FNFD model.Furthermore,the respective and total solubilities of CO2 and ethanol at 313.15 k,338.15 K,and 343.15 K were calculated by S-L EoS.Results indicated that the respective solubilities of ethanol in PS is much larger than that for ethanol-PS binary system and the solubilities of CO2 in PS for the CO2-PS binary system are bigger than the respective solubilities of CO2 in PS for CO2-ethanol-PS ternary system.To study the synergistic plasticizing of CO2 and micromolecule on polymer,the glass transition temperature reduction behavior of PS versus the pressure of CO2 and ethanol in polymer was investigated with a high-pressure visual cell,which would illustrate the synergistic plasticizing effect of CO2 and ethanol on the glass transition temperature of PS.Furthermore,the Chow’s EoS was used to correlate the the respective solubilities of CO2 and ethanol in PS and the Tg of PS for CO2-ethanol-PS ternary system.Results indicated that the glass transition temperature reduction behavior of PS was resulted in by the effect of CO2 and ethanol.Compared with PS,PVC is one of the thermoplastic plastics which has more broader market application.Based on the research foundation of CO2-micromolecule-polymer ternary systems,SCCO2 and acetone were adopted to assist synthesis of chlorinated polyvinyl chloride(CPVC)with uniform distribution of chlorine for the first time.The chlorine content of CPVC obtained by this method had exceeded 0.65 g/g.The analysis of particle diameter and morphology of pretreated PVC showed that the preliminary foaming treatment had enlarged particle diameter and inner pore structure.GPC,DSC,and 13C-NMR analysis showed that the obtained CPVC had narrow molecular weight distribution,excellent thermal properties,and uniform chlorine distribution.Furthermore,an improved kinetics model was proposed to indicate the crucial step of the chlorination.The frequency factor was expressed as the ratio of the particle volume of the foamed PVC to that of original PVC.Consequently,the model values of chlorine content agreed well with experimental values.Meanwhile,CO2 and acetone were applied to assist synthesis of chlorinated polypropylene(CPP)with high chlorine content for the first time.The results indicated that acetone and SCCO2 can "break" the film of commercial PP.The chlorine content of CPP had exceeded 0.5726 g/g.