Grafting onto wool

Summary In order to study the role of -SH group of wool in graft copolymerization, an attempt has been made to study grafting of acrylic acid (AAc) onto reduced wool in aqueous medium using ceric ammonium nitrate (CAN) as redox initiator. HNO₃ was found to catalyze the graft copolymerization. Reduction of wool was effected with thioglycolic acid (TGA) in aqueous medium. Percentage of grafting was determined as a function of concentration of (i) CAN, (ii) vinyl monomer (AAc), (iii) nitric acid, (iv) time and (v) temperature. Under optimum conditions, poly-(acrylic acid) was grafted to the reduced wool to the extent of 9.14%, the unreduced wool under optimum conditions afforded maximum grafting of poly(AAc) to the extent of 12.24%. Reduction of wool does not promote grafting of AAc in the presence of CAN.     

Grafting onto wool. XXVIII. Effects of acids on gamma-radiation induced graft copolymerization of ethylmethacrylate onto wool fiber

Graft copolymerization of ethylmethacrylate (EMA) onto Himachali wool fiber has been investigated in aqueous medium by mutual gamma irradiation from a Co⁶⁰ source in air and in nitrogen atmosphere. Percentage of grafting has been evaluated as a function of (i) total dose, (ii) concentration of monomer, and (iii) effect of concentration of different acids such as hydrochloric acid, sulfuric acid, nitric acid, perchloric acid, and acetic acid. Maximum percentage of grafting has been obtained in the presence of sulfuric acid. Following reactivity order of different acids towards grafting has been observed: H₂SO₄ > HCI > HNO₃ > HCIO₄ > CH₃COOH. A plausible mechanism to explain the effect of acids on percentage of grafting of EMA has been suggested.     

Grafting vinyl monomers onto wool fibers: Graft copolymerization of methyl methacrylate onto wool fibers using vanadyl acetyl acetonate complex

The graft copolymerization of methyl methacrylate (MMA) onto native and reduced Indian Chokla wool fibers was studied in aqueous solution using the acetylacetonate oxovanadium (IV) complex. The rate of grafting was investigated by varying the concentration of the monomer and the complex, acidity of the medium, and the solvent composition of the reaction medium. The graft yield increases with increasing concentration of the initiator up to 8.75 × 10^?5 mol/L, of the monomer up to 0.5634 mol/L, and thereafter it decreases. MMA was found to be the most active monomer when compared to other vinyl monomers. Grafting increases with increasing concentration of HClO₄ and with increasing temperature. Reduced and oxidized wools were found to be better substrates than untreated, esterified, crosslinked, and trinitrophenylated wools. The extent of grafting was mostly dependent upon the concentration of ? SH groups in case of reduced wool. A suitable reaction scheme has been proposed and the activation energy was calculated from Arrhenius plot.     

Grafting vinyl monomers onto wool fibers,IX. Graft copolymerization of methyl methacrylate onto wool using peroxydiphosphate-cysteine redox system

The graft copolymerization of methyl methacrylate onto wool was studied at 50°C using peroxydiphosphate-cysteine redox system as initiator. The rate of grafting was determined by varying monomer, initiator, cysteine, acid and temperature. The grafting is considerably influenced by chemical modification prior to grafting. A suitable kinetic path has been pictured and a rate expression has been derived.     

Grafting vinyl monomers onto wool fibers. V. Graft copolymerization of methyl methacrylate onto wool using peroxydiphosphate as initiator

Graft copolymerization of methyl methacrylate onto wool was investigated in aqueous solution using potassium peroxydiphosphate as initiator. The rate of grafting was determined by varying monomer, peroxydiphosphate ion, temperature, solvent, and nature of wool. The graft yield increases with increase in monomer concentration. The graft yield increases significantly by increasing peroxydiphosphate ion up to 80 × 10^?4mole/l.; with further increase of peroxydiphosphate ion the graft yield decreases. The rate of grafting increases with increase in temperature. The effect of acid-and water-soluble solvents on the rate of grafting was investigated and a suitable rate expression has been derived.     

Grafting vinyl monomers onto wool fibers IV. Graft copolymerization of methyl methacrylate onto wool using peroxydisulfate catalysed by silver ions

Graft copolymerization of methyl methacrylate onto wool was investigated in aqueous solution using peroxydisulfate catalysed by silver ions. The rate of grafting was determined by varying the concentration of monomer, peroxydisulfate ion, thiourea, the temperature and the solvent. The graft yield increased with increasing monomer concentration, peroxydisulfate concentration, thiourea concentration, and temperature in all cases to a certain value, beyond of which a decrease in graft yield was observed. The effect of certain inorganic salts and water soluble solvents on the rate of grafting was investigated. The alkali solubility of the grafted fiber was studied.     

Grafting onto wool. III. Relationship between alpha- and beta-forms in wool keratin of grafted fibers

A quantitative study of the change in the x-ray intensity diffracted from the α- and β-crystalline phases of grafted fibers was carried out. It was demonstrated that a part of the α-helical sections is disrupted by the deposition of polymer and that during extension processes a marked stabilization for the remainder results from the interaction between the residues on the α-helix and the rigid polymer chain. It was also considered that the disrupted sections are identical to the portions which would be easily deformed by stretching. The results on fibers containing hydrophilic polymer suggested little possibility that the β-chain crystal is produced from the disrupted chains of α-crystallites. The mechanism of the so-called α–β transformation was proposed as ? α M, M^* ? β.     

Grafting onto wool fibers: Graft copolymerization of methyl methacrylate onto wool fibers initiated by KHSO5/Fe(III) couple

Graft copolymerization of methyl methacrylate (MMA) onto wool fibers has been carried out in an aqueous medium under deaerated condition initiated by potassium monopersulphate (KHSO₅/Fe(III) system, at varying concentration of the reactants and temperature. The effect of various salts and organic solvents on the extent of grafting has also been studied. Maximum graft percentage of 210.8% was obtained in 4 h at 40°C with the concentration of MMA (0.46 M), KHSO₅ (0.0195 M), Fe(III) (1.25 × 10^?4 M) in the presence of 50% formic acid. Various improved properties of the grafts have been studied and compared with the parent fiber.     

Grafting vinyl monomers onto wool fibers. VIII. Graft copolymerization of methyl methacrylate onto wool using peroxydiphosphate–fructose redox system

The graft copolymerization of methyl methacrylate onto wool fibers was investigated in aqueous solution using the peroxydiphosphate–fructose redox system. The rate of grafting was determined by varying monomer, acidity of the medium, temperature, nature of wool, and reaction medium. The graft yield increases with increase in peroxydiphosphate concentration. With increase in concentration of fructose up to 7.5 × 10^?4 mole/l., there is a significant increase in graft yield; and with further increase in concentration of fructose the graft yield decreases. The graft yield increases with increase in monomer concentration up to 65.72 × 10^?2 mole/l. and decreases thereafter. The grafting is considerably influenced by chemical modification prior to grafting. The effect of acid, temperature, and solvent on the rate of grafting has been investigated and a suitable rate expression has been derived.     

Grafting vinyl monomers onto wool fibers. I. Graft copolymerization of methyl methacrylate onto wool using V5+–thiourea redox system

The graft copolymerization of methyl methacrylate in wool fibers was investigated in aqueous solution using V⁵⁺—thiourea redox system. The rate of grafting was determined by varying monomer, thiourea, acidity of the medium, temperature, nature of wool, different acrylic monomers, and reaction medium. The graft yield increases significantly by increasing reaction time in the initial stages of the reaction but it does slow down on prolonging the duration of grafting. The effect of increasing monomer concentration brings about a significant enhancement in the graft yield. The graft yield increases with increasing thiourea concentration, but beyond 0.0075M, the percentage graft yield decreases. The graft yields are considerably influenced by chemical modification prior to grafting. Wool reduced with thioglycolic acid is more susceptible to grafting than untreated wool; the opposite effect is noted in the case of trinitrophenylated and esterified wools. A suitable kinetic scheme has been proposed and the rate equation has been evaluated.     

Grafting onto wool: 8. Amino-acid compositions of various fractions of wool graft copolymers synthesised by methanol-benzoyl peroxide system

The amino-acid composition of the mother protein in the graft copolymer synthesised by the methanol—benzoyl peroxide initiating system was investigated. True graft copolymers were successfully separated from the grafted fibres by applying a fractional precipitation method. Analyses showed that the mother protein contains less cystine, threonine, serine, proline but more lysine, aspartic acid, glutamic acid, alanine and leucine than wool. The amino-acid compositions of any of the fractions obtained were almost identical to that of the low-sulphur S-carboxymethylkerateine protein which is considered to originate in crystalline microfibrils. On the formation of grafting centres in the protein chains in the complex structure of wool, such a selectivity has also been observed for the case of lithium bromide and peroxydisulphate redox initiating system. It was suggested, however, that there are two different types of molecule in the low sulphur protein components involved in these two graft copolymers.     

Grafting onto polyformaldehyde fibers

Acrylic acid (AA), acrylonitrile (AN), and acrylamide (AM) were grafted onto polyformaldehyde (PF) fibers employing γ-ray irradiation as well as benzoyl peroxide initiation. The nature of the graft copolymer obtained from a given monomer was dependent on the type of method used for the grafting reactions. This was reflected in the various characteristics of the grafted PF fibers such as moisture regain and dyeability to disperse, direct, basic, and acid dyes. The extent of grafting was dependent on time, concentration of the initiator, concentration of monomer, and irradiation dose. The grafting reaction with all the three monomers and both methods of grafting studied followed first-order kinetics. The rate constant values for grafting with AA, AN, and AM were 0.493, 0.576, and 0.420 hr^?1, respectively for the irradiation method and 0.385, 0.385, and 0.346 hr^?1, respectively, for the benzoyl peroxide initiation technique. The increase in the moisture regain was directly proportional to the amount of graft in the fiber. Acrylic acid grafted PF fibers were rendered hydrophilic to the highest extent (7.9% M.R. for 42% graft), while AM-grafted fibers were rendered so to the lowest extent (7.23% M.R. for 76.5% graft). Considerable improvement in dyeability of PF fibers was observed as a result of grafting. In general, dyeability was proportional to the amount of graft introduced in the fibers. The AA-grafted PF fibers gave a six-to sevenfold increase in disperse dye content when the irradiation method was followed and a four-to fivefold improvement when the chemical method was used during the grafting reaction. The AA-grafted and AM-grafted PF fibers show considerable affinity toward direct cotton dyes. The two substrates could also be dyed with fiber-reactive dyes in deep fast shades, the AM-grafted PF fibers giving deeper shades as a result of higher reactivity imparted to the substrate by the NH₂ group of the graft copolymer. The AA- and AN-grafted PF fibers could be dyed in intense deep shades with cationic dyes. Similarly, AM-grafted substrates gave bright deep shades with acid dyes. Infrared studies, used to analyze the grafted PF fibers, indicated the presence of ? COOH, ? CN, and ? NH₂ groups introduced in the fiber structure as a result of grafting with AA, AN, and AM.     

Redox-initiated graft copolymerization onto wool with thiourea as reductant. IV. Grafting of vinyl sulfone dyes onto wool using thiourea–H2O2 redox system

Wool samples were dyed with a vinyl sulfone dye in the presence of thiourea and H₂O₂ under a variety of conditions. Increasing the H₂O₂ concentration from 2.5 mmole/l. to 20 mmole/l. caused a significant enhancement in the rate of the dyeing, whereas increasing the thiourea concentration from 1.25 mmole/l. to 10 mmole/l. brought about an increase in the rate of dyeing. Further increase in the thiourea concentration (i.e., up to 15 mmole/l.) caused a significant decrease in the rate of dyeing. Raising the dyeing bath temperature from 30°C to 70°C accelerated appreciably the rate of dye uptake. With respect to dye concentration, complete exhaustion occurred at dye concentrations of 0.5% and 1% (owf) when dyeing was performed at 70°C and pH 6 over a duration of 2 hr. This contrasts with 90% and 55% exhaustion for dye concentrations of 3% and 5% (owf), respectively. The rate of dyeing obtained at different pH's follows the order pH 2 < pH 4 < pH 6 < pH 8. A dye fixation of approximately 68%, 64%, and 50% could be achieved at pH 4, 6, and 8, respectively, if dyeing was performed at 70°C for 2 hr in a bath containing a dye concentration of 3% (owf) in the presence of thiourea (10 mmole/l.) and H₂O₂ (15 mmole/l.). The mechanism of dyeing is believed to be grafting by vinyl addition to wool radical formed under the influence of the decomposition products of thiourea and H₂O₂. Evidence of this mechanism is presented.     

Radiation-induced graft copolymerization of methyl methacrylate onto natural and modified wool. I. Grafting and characterization

The radiation-induced graft copolymerization of methyl methacrylate onto wool fibers and chemically modified (oxidized, methylated, reduced, and crosslinked) wool fibers was investigated in dimethylformamide at room temperature. The homopolymer was separated from the graft copolymer by Soxhlet extraction. The grafting increased with increase in radiation dosage from 0.5 to 1.5 Mrads. The % graft-on depended on the nature of the wool fibers and decreased in the following order: methylated wool, reduced wool, oxidized wool, natural wool, and crosslinked wool. The molecular weights of the grafted copolymer (after separation from the wool fibers) and homopolymers were determined viscometrically. An increase in the radiation dosage reduced the molecular weights of the polymers.     

Grafting biodegradable polyesters onto cellulose

To increase the compatibility between cellulose fibers and polyester matrix an original method for grafting hydrophobic oligoesters onto cellulose was proposed. Two kinds of cellulose substrates were employed as cellulose films and microcrystalline cellulose powder. Different oligoesters containing reactive end groups based on poly(DL ‐lactic acid) PDL‐LA, poly(ε‐caprolactone) PCL and poly(3‐hydroxyalkanoate)s PHA were first prepared and characterized by size exclusion chromatography (SEC), nuclear magnetic resonance (NMR), and differential scanning calorimetry (DSC). The carboxylic end groups of the polyesters were activated using thionyl chloride (SOCl₂) to increase the esterification reaction with the hydroxyl groups of the cellulose. The esterification was realized in a heterogenous medium without any catalyst by deposition of chloride oligoesters in solution (2–100 g L⁻¹) onto cellulose film at different temperatures (25–105°C) during 1–12 h. The successful grafting on the various substrates was confirmed on the basis of FTIR spectroscopy, contact angle measurement, X‐ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). In particular, it is shown that a small quantity of grafted oligoesters led to a significant increase of the hydrophobic character of the cellulose with a contact angle near 130°. The increase of hydrophobicity of cellulose is independent of the nature and length of grafting oligoesters. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Grafting onto wool. VII. Ceric ion-initiated graft copolymerization of vinyl monomers. Comparison of monomer reactivities

In an attempt to compare relative reactivities of vinyl monomers toward grafting, methyl methacrylate (MMA) and acrylic acid (AAc) were grafted separately to Himachali wool in aqueous medium by using ceric ammonium nitrate (CAN) as redox initiator. Nitric acid was found to catalyze the reaction. Percent grafting was determined as a function of concentration of nitric acid, concentration of CAN, concentration of monomer, time, and temperature. Optimum conditions for maximum grafting were evaluated for each monomer and were found to depend upon the nature of the monomer. Reactivities of MMA and AAc toward grafting were compared with those of methyl acrylate (MA), ethyl acrylate (EA), and vinyl acetate (VAc) reported earlier from this laboratory and were found to follow the order MA > EA > MMA > VAc > AAc. An explanation for the observed order of reactivity of different vinyl monomers is presented.     

Grafting onto wool. VI. Effect of amines in ceric ion-initiated grafting of poly(vinyl acetate)

Poly(vinyl acetate) has been graft copolymerized onto Himachali wool in the presence of ceric ammonium nitrate alone and in presence of amines in aqueous medium under a wide variety of reaction conditions. Nitric acid was found to catalyze the graft copolymerization. Maximum grafting under optimum conditions has been determined. Several grafting experiments were carried out in presence of triethylamine and triethanolamine. Both amines were found to reduce the extent of grafting. The decrease in the percent grafting in presence of amines has been explained in terms of a chain-transfer mechanism.     

Methylmethacrylate Grafting onto Cotton Stalk Pulp

Grafting of cotton stalk pulp with methylmethacrylate monomer using a ceric salt redox system is carried out. The effect of different variables—for example, monomer dose, reaction time, reaction temperature, acid concentration, initiator concentration, and liquor ratio—are studied. The effect of the presence of different amounts of residual lignin in cotton stalks pulp on the grafting process is demonstrated. Residual lignin percentage in the pulp plays an important role in determining the grafting rate. A sharp decrease in the grafting rate is observed by increasing the residual lignin percent in pulp from 1.64% to 4.96%. As the residual lignin percentage in the pulp is increased to 12% in pulp, the grafting reaction is nearly stopped. Optimization of the grafting conditions is clarified.