Research On The Preparation Of CPVC In Gas-Solid Phase Method

Chlorinated polyvinyl chloride, a new type of resin, which is an important modification of PVC by chlorination. Comparing with PVC, CPVC has some excellent performance, such as corrosion resistance, fire resistance, heat resistance, and high mechanical strength. CPVC has a widely application in all kinds of areas like plastics, construction materials, medical, electricity, agriculture, coatings, paper, shipping, and packaging.Nowadays, the preparation of CPVC mostly employs the method of aqueous suspension. Though chloride content can be improved by increasing the temperature, pressure or adding oxidants, these will lead to fracture of the polymer chain which may diminish the molecular weight, and degrades the mechanical performance. Therefore, the application of CPVC is limited. Comparatively, chlorination can be achieved at low temperatures in the Gas-solid phase method, and the same chloride content can be attained. More importantly, the fracture of polymer chains will be depressed, which meets the mechanical requirement. In addition, this method, producing much less waste, is a green technology.In this thesis, Gas-solid phase method is applied in the preparation of CPVC. By studying the time, temperature, flow of Cl2 and rate of stirring, which are the influence factor of the chlorine content and the molecular weight, the optimization are supplied. The results indicate that the chlorine content will increase by rising the temperature, extending the time, or increasing the flow. Though the number average molecular weight of CPVC will decline slightly when rising the temperature, the weight average molecular weight will increase. Extending the time, both molecular weights will increase. Rate of stirring is not a predominant factor. Pre-chlorination could profit the heat resistance of PVC, which will allow the chlorination at a high temperature. The optimizations are as follows:Time of pre-chlorination is 1h, temperature of pre-chlorination is 55℃, time of chlorination is 6h,temperature is 100℃, flow of chlorine is 500 mL/min, rate of stirring is 80r/min. The performances of the product, which was obtained in the optimization, were measured, such as the content of chlorine, the density, the volatile component and the molecular weight. The results indicate that the performances meet the standard of the aqueous suspension method. Some of the performances are much better, most close to the product abroad.Self-rotating reactor is employed in this experiment, instead of mechanical stirring. CPVC could be well-proportioned in this reactor.Further, the kinetics of the reaction, inside the particles of PVC, was investigated. The equation of kinetics in gas-solid phase reaction was deduced. The rate constants of reaction in different temperatures are calculated. Finally, the apparent activation energy and the frequency factor are calculated by the equation of Arrhenius. The apparent activation energy is Ea=22.118kJ/mol, and the frequency factor is 0.001355 (mol·m-3)-1·s-1.