Influence of glycine on the kinetics of the graft copolymerization of acrylonitrile onto jute fibers initiated by ceric ion

A study of the influence of glycine on the graft copolymerization of acrylonitrile (AN) onto jute fiber using ceric ion has been made. The effect of concentrations of monomer, Ce (IV), and glycine on graft yield have been studied. In addition, the effect of time, temperature, acid, and the amount of jute fiber on graft yield has been investigated. On the basis of experimental findings, a qualitative reaction mechanism has been proposed and the optimum condition for effective grafting has been suggested.     

Grafting of acrylonitrile onto different cellulose forms by the xanthate method

Wood pulp and regenerated cellulose (viscose fibres) were grafted by the xanthate method. In some cases, the regenerated cellulose was more accessible towards grafting than wood pulp. Grafting of incompletely regenerated viscose fibres which were obtained by changing the spinning conditions in order to spare the step of partial xanthation caused more orientation of the filaments. The mechanical properties of these filaments were in general poor.     

ESR study of reactions of cellulose initiated by the ceric ion method

The ESR spectra of microcrystalline cellulose and purified cotton cellulose reacted with ceric ammonium nitrate in nitric acid were determined. The effects of the concentration of ceric ion, atmosphere, temperature, and graft copolymerization with acrylonitrile on the rates of formation and decay of radicals in the cellulose molecule were determined under both static and dynamic conditions. Under static conditions, after the desired conditions of reaction, the samples were frozen at –100 or –160°C., and then the concentration of free radicals was determined. Under dynamic conditions ceric ion solution was continuously flowed through the celluloses while these determinations were being made at 25°C. In the presence of oxygen the rate of decay of free radicals was decreased. On initiation of copolymerization reactions with acrylonitrile, there was an increase in radical concentration, then a decrease. Apparently, during graft copolymerization the radical site initially on the cellulose molecule was retained on the end of the growing polymer chain. Then additional ceric ion coordinated with the hydroxyl groups of the cellulose, leading to the formation of additional radical sites. An Arrhenius interpretation of the effect of temperature on the formation of these additional radical sites gave apparent activation energies for radical formation on cotton cellulose as 34 kcal./mole and on microcrystalline cellulose as 29 kcal./mole.     

Grafting of methyl methacrylate onto cellulose nitrate initiated by benzoyl peroxide

It has been observed that grafting of vinyl monomers onto cellulose nitrate in solution takes place using benzoyl peroxode. The graft copolymer was isolated from the unreacted backbone and homopolymer by selective solvent extraction. The effect of variables, such as the initiator concentration, the monomer concentration and the reaction time on the percent grafting and the grafting efficiency, were discussed. A probable mechanism for grafting of vinyl monomers to cellulose nitrate in solution has been proposed.     

Influence of dimethyl sulfoxide on the kinetics of the graft copolymerization of acrylonitrile onto the jute fibers initiated by ceric ion

A study of the influence of dimethyl sulfoxide (DMSO) on the graft copolymerization of acrylonitrile (AN) onto jute fiber using ceric ion has been made. The effect of concentrations of monomer, Ce(IV) and DMSO on graft yield have been studied. Besides, the effect of time, temperature, acid, and the amount of jute fiber on graft yield has been investigated. On the basis of experimental findings, a reaction mechanism has been proposed and optimum condition for effective grafting has been suggested.     

Oxidation of cellulose by ceric ion

Dissolving pulp was oxidized by ceric ammonium sulfate in sulfuric acid medium under oxygen-free argon. Initial rapid oxidation was followed by first-order consumption of ceric ion. The rate of cellulose oxidation (?R_Ce) which was taken at the beginning of the first order consumption period, levelled off with an increase in the concentration of ceric ion. It was found that the ?R_Ce was dependent on the concentration of cellulose in the second power. The rate of ceric ion consumption was a function of the available surface area of cellulose.     

Grafting of poly(triethylene glycol dimethacrylate) onto chitosan by ceric ion initiation

Grafting of poly(triethylene glycol dimethacrylate) (poly(TriEGDMA)), onto chitosan by ceric ion initiation has been investigated. The grafting conditions were optimized by studying the effect of monomer and initiator concentrations as well as time and temperature. Products with lower grafting yields (90–261%) were water and acid soluble. Those with higher grafting yields (350–868%) were insoluble, indicating a cross linked structure. Chitosan-graft- poly(TriEGDMA) products had a lower thermal stability than chitosan as revealed by DSC analysis. C-13 NMR and FTIR analyses suggested a grafting mechanism that proceeds via oxidation and chain scission of chitosan. The products are degraded by the enzymes lysozyme, lipase and α-amylase–protease.     

Preparation and characterization of hydrogels obtained by grafting of acrylonitrile onto cassava starch by ceric ion initiation

Graft starch-polyacrylonitrile copolymers have been obtained from cassava starch (yucca starch or tapioca), which was pre-heated at 65 and 95°C for different lengths of time. The copolymerization was carried out by using ceric ion as initiator at different concentrations (2.0 to 8.0 mmol/L) and also varying both the length of time of copolymerization and the ratio of monomer to starch. The composition, or grafting parameters, of all the obtained copolymers was determined by weight difference after they were extracted with dimethylformamide and hydrolyzed with an acidic solution. Samples of these copolymers were also hydrolyzed with an aqueous solution of potasium bydroxide to produce the corresponding hydrogels, and its absorbency in water was determined. © 1993 John Wiley & Sons, Inc.     

Graft copolymerization of acrylonitrile onto hemicellulose using ceric ammonium nitrate

The ability of ceric ammonium nitrate to induce graft copolymerization of acrylonitrile onto hemicellulose was investigated. The graft yield depends on monomer and initiator concentrations as well as reaction time and temperature. Chemical analysis of the reaction product of hemicellulose and acrylonitrile in the presence of ceric ammonium nitrate revealed that the ceric ammonium nitrate acted as initiator for polymerization of acrylonitrile and as oxidizing agent for hemicellulose. Proof for grafting of hemicellulose was provided through IR analysis.     

Grafting of vinyl monomers onto wood fibers initiated by peroxidation

Summary The oxidation of chemithermomechanical (aspen) pulp with ruthenium tetroxide followed by peroxidation with hydrogen peroxide was performed to study the graft copolymerization of methacrylic acid, epoxypropyl acrylate and epoxypropyl methacrylate. For epoxy monomers, lower pH (i.e. < 5) is more favorable due to the participation of the epoxy group in the grafting reaction in acidic medium. Moreover, the grafting of epoxy monomers appeared more efficient than methacrylic acid.     

Grafting of methyl methacrylate onto silk fibers initiated by tri-n-butylborane

Structural characteristics of the methyl methacrylate (MMA)-grafted silk fibers using tri-n-butylborane as an initiator were analyzed by infrared spectroscopy and differential scanning calorimetry (DSC), and their refractive index and tensile properties were measured. Graft polymerization was promoted by FeCl₃ pretreatment of the silk. The graft yield reached a maximum by the immersion in 4% FeCl₃ solution for 1 min at 25°C. The infrared spectrum of poly(MMA)-grafted silk fibers showed overlapped absorption bands of silk fibroin with the β structure and of the grafted MMA polymer. A grafted silk fiber with graft yield of more than 140% exhibited two endothermic peaks at 321°C and 396°C on the DSC curve, attributed to the thermal decomposition of silk fibroin and grafted poly(MMA) chain, respectively. Refractive index measurements suggested that the molecular orientation and the crystallinity of the silk fiber decreased with increasing graft yield. Electron photomicrographs showed that silk was coated by grafted PMMA. The tensile strength of the grafted silk decreased rapidly by the grafting even at a lower level.     

Graft copolymerization onto cellulose by ceric ion initiator system: Effects of kind of acid and irradiation with ultraviolet light

The effects of kind of acid and irradiation of ultraviolet light on the graft copolymerization of methyl methacrylate onto cellulose with adsorbed ceric ion were investigated. Irrespective of ultraviolet light irradiation, the amount of reduced ceric ion in the reaction systems was increased in the order HCl > HClO₄ > HNO₃ > H₂SO₄, and the number of grafts formed was increased in the order HClO₄ > HNO₃ > HCl > H₂SO₄. Thus, it was definitely observed that the graft copolymerization is affected by the kind of acid. Ultraviolet light remarkably accelerated the reduction of ceric ion adsorbed on cellulose in the various acid mediums, but decreased the efficiency of graft formation. The most favorable results for the formation of grafts were obtained in the system in which HClO₄ and ultraviolet irradiation was employed. A combination of H₂SO₄ and ultraviolet irradiation resulted in the lowest per cent grafting and average molecular weight of grafts. It was found that H₂SO₄ characteristically dissolves out ceric ion adsorbed into an aqueous solution and accelerates the formation of homopolymer.     

Grafting acrylonitrile on kenaf fibers using ceric ion–p-xylene redox pair

Polyacrylonitrile was grafted onto kenaf fibers in aqueous media by ceric ion–p-xylene redox system. The graft yield dependence on p-xylene concentration in the range 1.8–45.0 × 10⁻⁴M showed a minimum accompanied by an enhanced yield. This suggested the existence of two kinetically distinct grafting reactions associated with two precursor-initiating species, a p-xylyl radical and a diradical. The frequency of graft F_g and the average molecular weight of grafted polymer M_v were inversely related at varying concentrations of p-xylene with values for M_v of up to 5.18 × 10⁴. The effect of ceric ion concentration on M_v showed that the ion is nonterminating at low concentrations in the range 8.3–33.3 × 10⁻³M. The graft yield showed positive temperature dependence in the region of 30–40°C and a negative one at higher temperatures, resulting in a decrease in the initial rate of graft at 70°C by a factor of 8 compared to its value at 40°C. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1751–1755, 1999     

Grafting acrylonitrile onto wood pulp: Influence of process variables

Graft polymerization of acrylonitrile onto a never-dried bleached kraft pulp by the ceric ion process was not affected by the presence of air, nor by the use of technical-grade ceric salt and unpurified monomer. The initial polymerization rate and final degree of conversion to grafted polymer increased with monomer and pulp concentration. An increase in the catalyst concentration also increased the initial rate and final conversion up to a maximum value, after which they leveled off. The amount of catalyst required for a given degree of conversion was minimized when operating at high concentration of pulp and monomer and when the catalyst was added last. Attainable graft level decreased when the pulp was dried but could be brought back to its normal level after the dried pulp was beaten. The molecular weight of the polymer increased with monomer concentration but was independent of ceric salt concentration when the latter was low. The number of grafted sites increased with ceric salt concentration.     

Ultraviolet-radiation-induced graft copolymerization of styrene and acrylonitrile onto cotton cellulose

Photoinitiated graft copolymerization of the vinyl monomers, styrene and acrylonitrile, onto cotton cellulose was studied using uranyl nitrate and ceric ammonium nitrate as photoinitiators. Uranyl nitrate photoinitiation showed a higher level of grafting for styrene, whereas in the case of acrylonitrile ceric ammonium nitrate was found to be the better photoinitiator. Optimized conditions of grafting, when employed to cotton swollen with sodium hydroxide and zinc chloride, enhanced the graft levels for both monomers. Grafted samples were subjected to thermal analysis, as well as estimation of moisture regain and tenacity. Thermal stability increased, whereas, the moisture regain and tenacity decreased, with the increase in graft add-on in the case of both monomers. Acrylonitrile-grafted cotton showed dyeability with cationic dye that improved with the level of graft add-on. Possible explanations have been given.     

Polymerization and graft copolymerization of styrene initiated by ceric ion in acetonitrile/water solution

The polymerization of styrene initiated by a ceric ion/pinacol system and the graft copolymerization of styrene onto microcrystalline cellulose initiated by ceric ion were studied in the mixed solution composed of acetonitrile and water. Although the graft copolymer of polystyrene onto microcrystalline cellulose was not obtained in the acetonitrile solution, addition of water initiated the polymerization, and the grafting ratio was increased with increasing the water added. The rate of polymerization of styrene in the ceric ion/pinacol system increased similarly with increasing the water content in the solution. Acetonitrile is miscible with water, but the solution was separated to two phases by adding styrene into the solution containing above 20% of water; the monomer was dissolved in both acetonitrile and water phases. The polymer was undissolved in this mixed solution. The effects of water on the polymerization in the mixed solvent system are discussed from the standpoint of reaction mechanism.