STUDIES ON GRAFT COPOLYMERIZATION ON CELLULOSE FROM THE BINARY MIXTURES OF THE VINYL MONOMERS

Abstract

The property modification of natural and synthetic polymers has been carried out by number of ways but modification by graft copolymerization is an easiest and effective technique to obtain polymers with desired properties. The grafting is accomplished either by growing a polymer chain onto cellulose backbone or by implanting preformed polymer chain onto cellulose backbone. However, the preformed polymers have restricted diffusion and provide limited choice for their distribution onto the backbone of the cellulose, hence modification by growing polymer chains onto cellulose backbone using vinyl monomer in the solution has been a preferred choice in comparison to grafting of preformed polymers. The graft copolymerization taking mixture of monomers in the solution phase provides ample opportunities to obtain cellulose with desired properties. The graft copolymerization onto natural and synthetic polymers is carried out by different techniques but in these techniques, the formation of homopolymers has predominated over the graft copolymerization. Amongst the various chemical methods of graft initiation, the eerie (IV) ions have shown high efficiency for grafting on varieties of natural and synthetic polymers because eerie (IV) ions participate in the formation of active sites onto cellulose than on vinyl monomers present in the reaction mixture. The modification of cellulose with binary mixture of the comonomers using eerie (IV) ions as initiator has been found very fascinating to obtain cellulose with desired properties and size of the grafted chains. The graft copolymerization of acrylonitrile and methylacrylate has been carried out using eerie ammonium nitrate as initiator in presence of nitric acid. The affinity of acrylonitrile has improved for grafting onto cellulose in presence of methylacrylate comonomer in the reaction mixture due to the synergistic effect of methylacrylate. The extent of graft yield has been studied by varying the feed molarity from 0.60 mol dm"3 to 4.20 mol dm"3, feed composition (fAN) from 0.25 to 0.80 and concentration of eerie ammonium nitrate has been varied from 0.20xl0"3 mol dm-3 to 15.50x10° mol dm"3. As the activity ofeerie (IV) ions depends upon the concentration ofthe nitric acid, hence the grafting parameters of acrylonitrile-methylacrylate comonomers were also evaluated by varying nitric acid concentration from 0.50x10"2 mol dm"3 to 20.0x10"2 mol dm"3 at constant concentration of eerie ammonium nitrate (6.0x10"3 mol dm"3). The graft copolymerization of acrylonitrile and methylacrylate has been found to be maximum at a feed molarity of 3.0 mol dm"3. The compositional data of grafted chains determined with IR and nitrogen content measurement were used to estimate the reactivity ratios of the acrylonitrile (r,) and methylacrylate (r2) which have been found to be 1.45 and 0.90 respectively. The rate of graft copolymerization has varied to square concentration of the feed molarity and shown half order dependence on the concentration of the eerie ammonium nitrate. The thermal stability of the cellulose was improved on grafting. The isothermal and non-isothermal methods of analysis were used to estimate the energy of activation of decomposition and other characteristic thermal decomposition temperatures. The dye uptake capacity has also increased on grafting cellulose with mixture of acrylonitrile and methylacrylate monomers . In order to analyze the effect of substituent on comonomer, the graft copolymerization has also been carried out taking methyl methacrylate and ethyl methacrylate as comonomer along with acrylonitrile in the reaction mixture. In case of acrylonitrile-methyl methacrylate comonomers system, the maximum graft yield and other grafting parameter were obtained at a feed molarity of 4.0 mol dm" and 8.0x10"2 mol dm"3 concentration of eerie ammonium nitrate at 3.0x10" mol dm" concentration of nitric acid. The graft copolymerization has shown dependence on concentration of nitric acid, nitrate ions, hydrogen ions and the composition of the reaction mixture. The composition of the grafted chains has varied on varying the feed composition, concentration of nitric acid, nitrate ions, hydrogen ions and the temperature of the reaction mixture. The reactivity ratio of acrylonitrile and methyl methacrylate was found to be 0.74 and 1.03 respectively which suggested the alternate arrangement of the repeat units in the grafted copolymer chains. The rate of graft copolymerization has shown square dependence on feed molarity and square root to the concentration of eerie ammonium nitrate. The poly(acrylonitrile-co-methyl methacrylate) copolymer grafted cellulose has shown higher thermal stability than poly(acrylonitrile-co-methylacrylate) copolymer grafted cellulose. The dye uptake capacity was also improved on graft copolymerization of cellulose with mixture of acrylonitrile and methyl methacrylate monomers. The extent of grafting has also been studied taking ethyl methacrylate monomer along with acrylonitrile in presence of eerie ammonium nitrate as initiator. The graft copolymerization of ethyl methacrylate adds antimicrobial properties to the cellulose and has not been reported for graft copolymerization onto cellulose along with acrylonitrile. The extent of graft copolymerization has been found to be maximum at a feed molarity of 2.5 mol dm"3 and 7.54x10"3 mol dm"3 concentration of the eerie ammonium nitrate at 10.0xl0'3 mol dm'3 concentration of the nitric acid. The reactivity of acrylonitrile in presence ofethyl methacrylate has been found to be low, hence all graft m copolymerization were carried out at a feed composition (fAN) of 0.6. The graft yield and composition ofthe grafted poly(acrylonitrile-co-ethyl methacrylate) copolymer have been found to be dependent on concentration of nitric acid, nitrate ions and hydrogen ions. The maximum yield was observed at 20.30x10"2 mol dm"3 concentration of the nitric acid and 12.50x10' mol dm"3 concentration of the hydrogen ions at 12.0xl0"3 mol dm'3 concentration of eerie ammonium nitrate. The order of graft copolymerization reaction with respect to feed molarity and eerie (IV) ions has been found to be two and half respectively. The reactivity ratios ofacrylonitrile and ethyl methacrylate have been found 0.68 and 1.45 respectively, hence the sequences of acrylonitrile and ethyl methacrylate monomers in the copolymers were considered in alternate fashion. The thermal stability of the poly(acrylonitrile-co-ethyl methacrylate) copolymer grafted cellulose has been found be less than poly(acrylonitrile-co-methylmethacrylate) copolymer grafted cellulose. Dye uptake capacity of poIy(acrylonitrile-co-ethyl methacrylate) copolymer grafted cellulose has been found to be low in comparison to the poly(acrylonitrile-comethyl methacrylate) copolymer grafted cellulose. However, the dye uptake capacity of poly(acrylonitrile-co-ethyl methacrylate) copolymer grafted cellulose has been found to be higher than pure cellulose and cellulose grafted individually with poly(acrylonitrile) or poly(ethyl methacrylate). The graft copolymerization of acrylonitrile-ethylacrylate comonomers onto cellulose has also been studied at different feed molarity ranging from 0.60 mol dm"3 to 3.0 mol dm"3 and feed composition ranging from 0.20 to 0.80 at constant temperature (35° C) and reaction time (120 min.) .The graft yield and other grafting parameters were maximum at afeed molarity of 2.10 mol dm"3 and at fAN =0.60. The graft yield and other IV parameters were also estimated as a function of reaction time and temperature and found to be optimum at 120 minutes and 35 C. The effect of concentration of nitric acid, nitrate ions and hydrogen ions was also investigated on graft copolymerization and yield was found maximum at lO.OxlO"2 mol dm"3 concentration of nitric acid and at lO.OxlO"3 mol dm"3 concentration of the eerie ammonium nitrate. The graft yield and other grafting parameters have shown decreasing trend on increasing nitrate ions concentration in the reaction mixture. The order of graft copolymerization has been found to be two on feed molarity and half on concentration of eerie ammonium nitrate. The reactivity ratios of acrylonitrile (ri) and ethylacrylate (r2) estimated with IR and elemental analysis, have been found to be 0.62 and 1.32 respectively. As the product of reactivity ratios (n, r2) was less than unity, hence the sequence of acrylonitrile and ethylacrylate were considered as arranged in alternate fashion. The poly(acrylonitrile-co-ethylacrylate) copolymer grafted cellulose has shown low thermal stability in comparison to poly(acrylonitrile-co-methyl methacrylate) copolymer grafted cellulose because the energies of activation of decomposition of poly(acrylonitrile-co-ethylacrylate) copolymer grafted cellulose determined by different methods are lower than poly(acrylonitrile-co-methyl methacrylate) copolymer grafted cellulose. The dye uptake capacity of the poly(acrylonitrile-co-ethylacrylate) polymer grafted cellulose has been found to be low in comparison to poly(acrylonitrile-co-methyl methacrylate) copolymer grafted cellulose. The graft copolymerization of acrylonitrile-butylacrylate comonomer has been carried at different feed molarity ranging from 0.40 mol dm"3 to 3.60 mol dm" , feed composition from 0.20 to 0.80. The graft yield has been found to be maximum at feed molarity of 2.40 mol dm"3, feed composition (fAN) of 0.60. The graft copolymerization has been found to be optimum at 35° C. The composition and yield have shown variation on varying the concentration of nitric acid, nitrate ions, and hydrogen ions. The order of graft copolymerization reaction has been found to be two with respect to feed molarity and half with respect to eerie ammonium nitrate. The composition of grafted chains has varied on varying feed molarity, concentration of nitric acid, nitrate ions, hydrogen ions and reaction temperature. The reactivity ratios of acrylonitrile (ri) and butylacrylate (r2) were found to be 0.56 and 1.76 respectively, hence the sequence lengths of acrylonitrile and butylacrylate in the grafted copolymers were arranged in alternate fashion.The thermal stability of poly(acrylonitrile-co-butylacrylate) copolymer grafted cellulose was less than cellulose grafted with poly(acrylonitrile-co-ethylacrylate) or with poly(acrylonitrile-co-methyl methacrylate) copolymers. The cellulose grafted with acrylonitrile-butylacrylate comonomers has shown lowest dye uptake capacity than grafted with other comonomer system used for graft copolymerization. The presence of comonomer in the studied system has improved the extent of grafting in comparison to single monomer. The composition of the grafted chains could be controlled by controlling the conditions of the graft copolymerization. The thermal and dye uptake capacities have shown substantial improvements on graft copolymerization of selectedmonomers from their mixture in the solution.