Production of colloidally stable latices from low molecular weight ethylene–propylene–diene copolymers

Abstract

The best impact modifiers for coatings and engineering plastics include fixed morphology core-shell particles. For the present work, ethylene–propylene copolymers (EPM) and ethylene–propylene–diene copolymers (EPDM) were chosen, for their good resistance to stringent conditions, like UV-irradiation or high temperatures, to prepare the core of the desired particles. The solution-emulsification technique was used to produce artificial latices based on low molecular weight EPM and EPDM materials. Conventional emulsification techniques as well as ‘miniemulsification’ methods have been investigated. In both cases, a larger volume of polymer is reduced into smaller sub-units using the mechanical energy of comminution techniques, i.e. an Ultra-Turrax ® and a homogenizer operating at a pressure of 300 bar and with a shear rate of approximately 3.2×10 7 s −1. The difference between conventional emulsification and miniemulsification resides in the stabilizing system. For the conventional emulsification method, an equimolar mixture of anionic (sodium dodecyl benzene sulfonate, SDBS) and nonionic (polyoxyethylene (100) stearyl ether, Brij 700) surfactants was found to be the optimal surfactant system. For the miniemulsification method, a combination of SDBS as surfactant and hexadecane or cetyl alcohol as costabilizer was the most suitable system. Both conventional emulsification and miniemulsification lead to latices with monomodal particle size distributions and volume-average diameters ranging from 300 to 400 nm, determined with light scattering techniques. The low molecular weight elastomers, exhibiting viscosities lower than 1 Pa s at 20 °C, were easily emulsified without addition of organic solvent.