Polymer–leather composites. III. Morphology and water absorptivities of selected acrylic polymer–leather composite materials

Abstract

The morphology of composite materials made by polymerizing methyl methacrylate into chrome-tanned cattlehide was examined by both light and scanning electron microscopy. The composites were selected from a series previously prepared and characterized, and their kinetics were reported. Micrographs of the polymer phase of the composites, prepared by preferential removal of collageneous material with 6N hydrochloric acid, yielded negative replicas of the fiber conformations. These provided evidence in support of proposed mechanisms of polymer deposition for two different methods of composite preparation. One method involved emulsion polymerization of monomer into hydrated leather and the other, preferentially filling leather free space. Both light and scanning electron microscopy of all composites and replicas revealed poly(methyl methacrylate) deposited largely in coarse aggregates around individual fibers. In emulsion systems, fiber bundles expanded with continuous deposition. No difference was observed in the morphology of bound and deposited polymers. However, high magnification of bound-polymer replicas exposed polymer surrounding some fibril traces. Deposition of polymer in the fine structure of bulk or solution prepared composites was not found; instead, all free space was occupied. A theory specifying polymer location in previous publications of this series, and extended here to define replica parameters, was abundantly supported by measured physical properties. A dominant grafting mechanism was precluded because the large domains limited points of possible attachment. Water absorptivities of emulsion prepared composites and controls were identical when the data were corrected to neat leather, although the rates were slightly perturbed. In contrast, both rate and equilibrium absorption data of the bulk and solution composites were retarded by polymer presence.