ASPECTS OF THE THERMAL, PHOTODEGRADATION AND PHOTOSTABILIZATION OF WATER-BORNE FLUORINATED-ACRYLIC COATING SYSTEMS

Emulsions based on a polymerised 50:50 formulation of methyl methacryl ate (MMA) and butyl acrylate/fluorinated acrylates have been prepared with and without reactive acrylated hindered piperidine and benzotriaz ole stabilisers. The rates of oxidation during irradiation are monitor ed by both hydroperoxide formation and functional group changes by usi ng reflectance Fourier transform infra-red spectroscopy. De-esterifica tion and hydroperoxide formation are found to be important processes d uring latex photooxidation and highly dependent upon the comonomer rat io, while the addition of low levels of comonomer, methacrylic acid, t o the emulsion gives latices with improved photostability. The effects of co-reactive acrylated hindered piperidine and benzotriazole stabil isers were found to be concentration-dependent, with the latter exhibi ting the greater effect. Scanning electron microscopy of unstabilised films showed rough and crazed surfaces before and after irradiation, r espectively, while the co-reacted stabilised films retained a smooth s urface before and after extensive periods of light exposure. Different ial scanning calorimetry showed that the fluorinated copolymers were m uch less stable, exhibiting two main endotherms due to the destabilisi ng effect of the fluorine component. Addition of the co-stabilisers, h owever, increased the thermal stability of the MMA latex. (C) 1997 Els evier Science Limited.