Polymer–leather composites. II. Kinetics of the deposition of selected acrylate monomers by polymerization into chrome-tanned cattlehide

Abstract

Limited kinetic information on a convenient process for depositing polymer in 5-oz cattlehide is presented in this article. The work includes a systematic study of the total polymerization rate and of the derived rates of deposition into the fibrous matrix, of bound polymer formation, and of polymer production in the external aqueous phase (the float) for three acrylic monomers. The monomers used, with a persulfate–bisulfite redox initiating system at 27°C, were methyl methacrylate (MMA), n-butyl acrylate (BA) and a fixed mixture of n-butyl acrylate and methyl methacrylate (BA + MMA). The effects of the reaction variables on rate, as measured by their intensity exponents, were not in agreement with a rate expression proposed to describe grafting in homogeneous polymerization, nor were they wholly compatible with classical and modified Smith–Ewart theories for heterogeneous emulsion polymerization. The experimental behavior, however, was in harmony with self-nucleation in the aqueous phase. Exponential orders of dependence were initiator > 0.5 (MMA, 0.72; BA + MMA, 0.66); monomer, zero; surfactant, ∼0.5. The approximately 0.6 order dependence (MMA, 0.9) on leather amount was shown to be largely apparent and to decline as total polymerization proceeded. Thus a dominant grafting reaction was not supported. In support of this conclusion, simple impregnation of the matrix with preformed emulsion polymer yielded the same amount of bound polymer as that formed in situ. It was concluded that monomer is initiated largely from active centers formed initially near fibers or fibrils to form embryo polymer particles, which join penetrating swollen polymer particles and become unstable. These nucleate a polymer front, containing occluded radicals, which grows by diffusion regulated transport of monomer to complete deposition.