Grafting of acrylic acid onto flax fibers using Mn(IV)-citric acid redox system



When the flax fibers (machine tow) were treated with KMnO4 solution, MnO2 was deposited over-all the fiber surface. The amount of MnO2 deposited relied on the KMnO4 concentration. Subjecting the flax-containing MnO2 to a solution consisting of monomer (acrylic acid, AA) and citric acid, CA (or any acid used in this work) resulted in formation of poly(AA)-flax graft copolymer. Dependence of the polymer criteria, namely, the total percentage conversion (%TC) and the carboxyl content of the grafted flax fibers on various grafting parameters, viz., concentrations of the redox pair as well as AA, material-to-liquor ratio (M/R), duration and temperature of polymerization, kind of the acid and kind of the flax fibers pretreatment was studied systematically. The results indicated that the polymerizability of AA molecules, expressed as %TC (i.e., counting both grafting and homopolymerization) and thence the carboxyl content (i.e., evaluating the extent of AA grafting along the flax backbone) was optimized with the following conditions: [AA], 100% (based on weight of flax fibers, owf); [CA], 0.4 meq/1 g flax; [MnO2], 0.4 meq/1 g flax; polymerization temperature, 40°C; polymerization time, 30 min; and the M/R, 1 : 50. A tentative mechanism for grafting of flax fibers with AA using MnO2-acid redox system was elucidated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3028–3036, 2006