Graft polymerization of methyl methacrylate onto short leather fibers

Abstract

SummaryIn this work, the graft polymerization of methyl methacrylate (MMA) monomer ontoshort leather fibers (SLF) was investigated as a function of the monomer/leather fiber ratio.This chemical modification was made by aqueous emulsion polymerization initiated by aredox system. The effect of' the monomer concentration on the grafting parameters(deposited and grafted polymer, as well as grafting efficiency) were determined.Composites formulated with SLF without chemical modification have showed lower tensileand impact properties in comparison with composites formulated with treated fibers.However, the elongation at break values for both systems remained similar as the MMAcontent changed. The morphology of SLF grafted with MMA was examined by both opticallight microscopy (OLM) and scanning electron microscopy (SEM). Micrographs haveshown polymer deposition on individual fibers and bundles of SLF. They have alsorevealed that PMMA may interpenetrate the SLF network and be deposited in large andcoarse aggregates around individual fibers, but without occupation of the free space in thefiber net.IntroductionResidues and wastes of organic fibers are used as fillers or reinforcements inthermosets and thermoplastic polymers, such as polyethylene (PE), polypropylene (PP),polyvinyl chloride (PVC), polystyrene (PS), polymethyl metacrylate (PMMA), etc. Thecomposites formulated offer significant weight advantages, a combination of goodmechanical properties with a low specific mass, and provide the economic benefit of lowercost (1-5). Taking into account that organic fillers or fibers are derived from renewablenatural resources; most of them show a common limitation in applications. The limitation isa poor compatibility between the hydrophilic filler (high level of moisture absorption by thefiber) and the hydrophobic thermoplastic polymer. However, a large number of attemptshave been made to improve the adhesion between polymeric matrices and natural fiberssuch as coconut, wood, nutshell flour, hemp, jute, sisal, and cellulose (6-9). These attemptshave included modifying the chemistry of the fiber surface or the polymer matrix.Some investigations into chemical modification of leather fibers have beenconducted on leather products (10-11). The aims of these investigations were to producenew leather products, such as leather boards, while retaining the natural appearance ofleather. These investigations demonstrated that acrylic monomers, such as methylmethacrylate (MMA), butyl acrylate (BA) and others, can be grafted onto tanned oruntanned leather fibers with an improvement in the mechanical properties (12). However,this system (acrylic-leather) has special characteristics, not all the polymer generated isgrafted onto the leather fibers. Usually the efficiency of grafting reactions is a function of