Model For Methyl Methacrylate Casting Bulk Polymerization And Process Optimization

Poly(methyl methacrylate)(PMMA)is a major commodity plastic and widely used as organic glass due to its excellent transparency.In the production of the casting organic glass,the polymerization is easy to be out of control since the reaction heat is great while the heat transfer is difficult,resulting the unstability of structure and property of the product and the decrease of production efficiency.In this thesis,the models for MMA bulk polymerization were proposed on the basis of the elementary reactions and species mass balance and evaluated firstly,then the polymerization kinetics - heat transfer combined model for MMA sheet casting polymerization was established,simulated and discussed.The study of the thesis is helpful to instruct design of the production recipe and the process conditions in the organic glass production.The kinetics of MMA bulk polymerization initiated by the new peroxides initiators(Luperox10 and Luperox575),and structure and the properties of the product were investigated.It is showed that the polymerization rate increased while the molecular weight of PMMA decreased with the increase of the temperature and concentration of the initiators.Compared with the polymerization initiated by AIBN, the final conversion increased and the polymerization rate became uniform for MMA polymerization initiated by Luperox10/Luperox575 composite initiator with various composite ratios.At the similar conversion,the organic sheet prepared by using the composite initiator with Luperox10/Luperox575 ratio of 1/3,had the highest number average molecular weight,the narrowest molecular weight distribution,a higher glass transition temperature and lower thermal weight loss.MMA bulk polymerization models were established on the basis of the elementary reactions and species mass balance,and considering the influences of cage,gel and glass effects on the rate constants and volume shrinkage during the polymerization course.The effects of time,temperatures,type and concentration of initiators on the conversion,molecular weight and volume shrinkage in the polymerization process were simulated by the models,and compared with experimental data,with good fitness.The proposed models are applicable for design of the polymerization recipe and operation conditions for the MMA bulk polymerization.One and two dimensional heat transfer models were established,respectively, according to water bath method and drying chamber method in sheet organic glass production.The polymerization kinetics-heat transfer combined models for MMA casting sheet polymerization were deduced based on the reaction heat build up and the heat transfer in the micro unit.The boundary conditions,hypothesis conditions for simplification and mathematic analysis methods of the models were discussed.Based on the polymerization kinetics-one dimension heat transfer combined model for MMA sheet polymerization,temporal and spatial distribution of temperature, conversion,molecular weight and molecular weight distribution of PMMA in the system was obtained through simulation.It is showed that temporal and spatial distribution of temperature is uneven as parabola distribution with the thickness of the sheet,having the highest temperature in the center and lowest temperature on edges(excluding the high-temperature heat preservation stage).Corresponding to the polymerization kinetics,the temperature of polymerization system increased with the polymerization time initially,reached to the maximum temperature at the gel stage, decreased after the gel effect and increased again at the high-temperature heat preservation stage.PMMA molecular weight usually increased from the center to the edges because of the temperature change.The simulated results of the various initiators,mode of heat transfer and sheet thickness showed that temperature gradient can be decreased by low-temperature polymerization,obtaining product with high molecular weight and narrow molecular weight distribution.The temperature of the reactor and the uniformity of the time-space distribution of the molecular structure can be improved by heating processes of gradual increasing and decreasing temperatures.The suitable initiator system should be adopted according to the requirements of the product properties and heating process,since the types of the initiator have significant influence on the temperature distribution,conversion, molecular weight and molecular weight distribution in the casting sheet polymerization system.The heat build up increased with the increase of initiator concentration and the thickness of the sheet,resulting the greater variation of the product structure and properties.Therefore,the lower temperature should be applied and the initiator system should be selected according to the heating process for producing thicker PMMA sheet with uniform structure and properties.