Plasma-assisted synthesis of chlorinated polyvinyl chloride (CPVC) characterized by online UV–Vis analysis

Abstract

An online UV–Vis analysis system is established to reveal the dynamic characteristics of plasma-assisted synthesis of chlorinated polyvinyl chloride (CPVC). Dielectric barrier discharge (DBD) plasma is generated in a vibrated-bed reactor intermittently so that the decoupled processes, i.e., the plasma initiated chlorination step and the chlorine migration step, are mimicked and operated repeatedly at atmospheric pressure. The instant chlorine consumption rate shows corresponding cyclic curves, illustrating evident plasma initiation followed by chlorine migration inside particles. The mechanism of process decoupling concept is therefore demonstrated vividly. Under the same power density of plasma, temperature is ascertained as a key factor to influence the PVC chlorination process. PVC particles with smaller sizes tend to be chlorinated easily, while other particle properties such as specific surface area and microstructure also exert complicated effect on the chlorination process. SEM results show that plasma can destroy the film layer on the particle surface, which makes the secondary sub-particles inside a PVC particle expose to the environmental chlorination gas and plasma. A pyrolysis GC–MS analysis helps to identify the molecular structure of CPVC product in terms of the compositions of chlorobenzene and dichlorobenzene in the pyrolized products, which are formed by chlorine atoms bonded on polymer chains.