On-line acoustic attenuation spectroscopy of emulsions stabilized by vinyl alcohol-vinyl acetate copolymers: a model system for the suspension polymerization of vinyl chloride

BACKGROUND: Poly[(vinyl alcohol)-co-(vinyl acetate)] (PVA) copolymers obtained by partial hydrolysis of poly(vinyl acetate) are currently used as industrial stabilizers in the suspension polymerization of vinyl chloride monomer (VCM). Their molecular characteristics, mainly the average degree of hydrolysis ((DH) over bar) and average degree of polymerization ((DPw) over bar), have a major influence on the monomer droplet size and the properties of the final poly(vinyl chloride) resin. RESULTS: The average droplet size and size distribution of chlorobutane/water emulsions, as a model system for VCM/water emulsions, were studied using acoustic attenuation spectroscopy on-line with an agitated laboratory reactor. The emulsions were stabilized by PVA with (DH) over bar values between 73 and 88 mol% and (DPw) over bar values between 450 and 2500. The effects of agitation speed, stirring time and concentration of the PVA copolymers were investigated. An attempt was made to correlate the interfacial tension and the droplet size. CONCLUSION: On-line acoustic spectroscopy appears to be a suitable technique for the real-time control of the droplet size of monomer suspensions. The advantages and limitations of the technique are outlined. The validity and the application limits of the commonly cited correlation between the droplet size and the Weber number are established for polymeric surfactant-stabilized emulsions. (C) 2009 Society of Chemical Industry