Cellulose graft copolymers. I. Graft copolymerization of ethyl acrylate with γ-irradiated cellulose from methanol–water systems

Ethyl acrylate was graft-copolymerized with γ-irradiated, purified cotton cellulose from methanol–water systems. The accessibility of the free radicals in the irradiated cellulose to water, methanol, ethyl acrylate, and methanol–water solutions was determined by electron spin resonance spectroscopy. The maximum scavenging of the radicals was recorded with the irradiated cellulose was immersed in methanol–water solution which had a composition of 50/50 vol-%. When ethyl acrylate was added to methanol–water solution (50/50 vol-%), maximum grafting on the irradiated cellulose occurred at a concentration of ethyl acrylate of about 20 vol-%. As the concentration of ethyl acrylate was decreased, maximum grafting occurred in solutions containing less than 50 vol-% methanol. It was also noted that maximum grafting of ethyl acrylate in methanol–water solutions to irradiated cellulose occurred at boundry conditions, that is, conditions where the ternary mixture was still one phase, slightly different from compositions which caused the mixture to separate into two phases. From methanol solution, maximum grafting occurred at a concentration of ethyl acrylate of 80 vol-%. The extent of grafting from methanol was less that obtained from methanol–water solutions at lower concentrations of ethyl acrylate. The accelerative effects of water was considered to be due to the Trommsdorff effect.     

Cellulose graft copolymers. III. Effects of oxygen on graft copolymerization of ethyl acrylate with γ-irradiated cellulose

The effects of oxygen on graft copolymerization of ethyl acrylate from methanol–water systems with γ-irradiated fibrous cotton cellulose were investigated by electron spin resonance spectroscopy and by the formation of cellulose–poly(ethyl acrylate) copolymer. The concentrations of free radicals in cellulose irradiated dry in an atmosphere of nitrogen at 25°C decreased during postirradiation storage in nitrogen or oxygen. The concentration of free radicals in the irradiated cellulose, moisture regain of the irradiated cellulose, and formation of cellulose–poly(ethyl acrylate) copolymer decreased with increase in temperature and time of postirradiation storage and to a greater extent when stored in oxygen rather than in nitrogen. From the decrease in moisture regain of irradiated cellulose during postirradiation storage, it was concluded that increased intermolecular bonding occurred in irradiated cellulose during storage in both nitrogen and oxygen atmospheres. When irradiated celluloses which had been stored in either oxygen or nitrogen were copolymerized with ethyl acrylate at 60°C, less formation of copolymer was observed than when the copolymerization reactions were conducted at 25°C. It was concluded that there was no evidence for the formation or decomposition of cellulose peroxides during these reactions and that formation of graft copolymer depended primarily on the concentration of free radicals in the irradiated cellulose at the time of copolymerization.     

Cellulose graft copolymers. IV. Graft copolymerization of methacrylonitrile with γ-irradiated cellulose from DMSO–, acetone–, and methanol–water systems

Methacrylonitrile was graft-copolymerized from DMSO–, acetone–, and methanol–water systems with γ-irradiated, purified cotton cellulose. The relative extents of scavenging of the free radicals in the irradiated cellulose after immersion in the solvents for 3 min at 25°C, as determined by electron spin resonance spectroscopy, were: methanol (77%) > water (70%) ? acetone (5%) > DMSO (0%). After immersion of irradiated cellulose in the solvents for 60 min at 25°C, the relative extents of scavenging of the radicals were: methanol, water (80–85%) > DMSO (80%) > acetone (62%). From these data, it would appear that the overall rates of diffusion of methanol and water into the fibrous macrostructure were greater than the rates of diffusion of DMSO and acetone into the structure. The relative radiochemical yields of the graft copolymerization reactions of methacrylonitrile with irradiated cellulose in the different solvents were: water ? DMSO > methanol ? acetone. The addition of water to the systems increased the yields of the reactions.     

Electron spin resonance studies of γ-irradiated cellulose. II. Free radicals in accessible regions to water in cellulose I and cellulose II

The types of free radicals produced in the water-accessible regions of cellulose I and cellulose II fibers by γ-irradiation in nitrogen atmosphere at room temperature were studied by ESR spectroscopy. The ESR spectra of the irradiated cellulose I and II change by contacting the fibers with water, and after immersion in water the spectral shape depends on the orientation of the fiber axes to the magnetic field. These spectra are probably related to the free radicals generated in the highly ordered regions inaccessible to water in irradiated cellulosic fibers. The ESR spectrum of free radicals generated in decrystallized cellulose after irradiation consists of a singlet and a doublet. When the ESR spectra of free radicals formed in the highly ordered regions of cellulose I and II and the singlet and the doublet are combined in adequate ratio, the constructed spectra are similar to those of the radicals scavenged by water in the irradiated cellulose I and II fibers. From these facts, the spectra due to the free radicals in the water-accessible regions in irradiated cellulose I and II are considered to consist of the singlet and the doublet formed by free radicals in the typical amorphous regions and the spectra of other types of radicals generated in the semicrystalline regions.     

Effect of crystalline structure on the trapped radical spectra of irradiated cellulose

The effects of crystalline modification of cellulose and of water on the ESR spectra generated by the trapped free radicals in gamma-irradiated celluloses were investigated for cotton cellulose I, II, III, and IV, partially decrystallized cotton cellulose, ballmilled cotton cellulose, hydrocelluloses of cellulose III and IV, and ramie. On irradiation of the celluloses, free radicals were formed on the cellulose molecule, probably following dehydrogenation or chain cleavage. The free radicals located within the less ordered or amorphous regions of the cellulose reacted readily with water and were terminated. The radicals located within the more ordered regions of the celluloses could be made accessible to reaction with water by the interaction of the celluloses with solvents which caused dimensional changes in the cellulosic structure. In the highly ordered regions of the celluloses, even after long periods of time in solvents which caused large dimensional changes in the cellulosic structure, the trapped free radicals were not terminated by reaction with solvent or water. The ESR spectra of the irradiated, dried celluloses were determined at ?160°C, the single-line spectra recorded had line widths of about 18-24 gauss. On the absorption of water by the irradiated celluloses, the ESR spectra changed and were dependent on the crystalline structure of the irradiated celluloses. The effects of different arrangements of the irradiated celluloses, as shown by their trapped radical spectra, particularly after interaction with water, were discussed.     

Electron spin resonance studies of γ-irradiated cellulose. I. Free radicals in decrystallized cellulose

The types of free radicals formed in decrystallized cellulose prepared from cellulose I and II after γ-irradiation in nitrogen atmosphere at room temperature were studied by ESR spectroscopy. X-Ray diffraction revealed that decrystallized cellulose I and II have the same microstructure. The ESR spectra obtained with the γ-irradiated decrystallized samples are simple. By contacting the irradiated sample with moisture in nitrogen atmosphere, the ESR spectrum changed to a narrow singlet, which gradually decreased in intensity until the spectrum completely disappeared. It was found that the types of free radicals generated in the decrystallized cellulose by γ-irradiation consist of the overlap of singlet and doublet. The singlet spectrum is mainly attributed to alkoxyl radical formed by the rupture of glycosidic linkage at the C 1 or C 4 position, and the doublet spectrum is ascribed to radical formed by hydrogen abstraction from the C 1 position in cellulose molecule.     

ESR study of intramolecular energy transfer in the radiolysis of cellulose thenoates

The substitution of 2-thenoyl, 5-methyl-2-thenoyl, 2-thiopheneacryloyl, 5-bromo-2-thenoyl, and 5-bromo-2-thiopheneacryloyl groups on fibrous cotton cellulose increased the radiation resistance of cellulose, as indicated by the retention of the breaking strengths of the modified fibrous celluloses at high dosages of γ-radiation, as compared with that of irradiated, unmodified fibrous cellulose. The presence of electropositive or electronegative substituents on the thiophene groups did not reduce the radioprotective effects of these groups for cellulose. Crosslinking of the cellulose thenoates in 1,3-di(4-pyridyl)-propane did not significantly reduce the radiation resistance of the thenoates. Examination of the ESR spectra of irradiated cellulose and cellulose thenoates indicated that the site of the long-lived free radicals on the irradiated cellulose molecules was not changed by the chemical modification. However, the concentration of long-lived free radicals in irradiated cellulose thenoates, at a given radiation dosage, was less than that in irradiated cellulose. The localization of energy on carbon C₁ or C₄ of the cellulose molecule, which leads to depolymerization and loss in breaking strength of fibrous cellulose, was decreased. The radioprotective effects of thiophene groups for cellulose were similar to those of furan and benzenoid groups.     

ESR studies of photoirradiated cellulose on radical formation and decay

The ESR spectra of untreated samples and photosensitized samples of rayon cellulose, amorphous cellulose, and wood cellulose irradiated with ultraviolet light were studied. Generally, several kinds of spectra were established, and ferric ion photosensitizer increased the yield of free radicals in celluloses on irradiation. The observed five-line spectrum was resolved to be a superposition of single-line, two-line, and three-line spectra. The decay of free radicals of celluloses at ambient temperature was also examined for changes of the pattern and the intensities of ESR spectra. Based on the changes of spectra induced by a warm-up process, three kinds of radicals which gave three components of the five-line spectrum were identified. During the warm-up process, phenomena of radical migration and formation of new radicals synchronized with the decay of radicals were recognized on photosensitized samples of rayon cellulose and amorphous cellulose.     

Effect of water on vapor phase photografting on cellulose and its derivatives

Effect of water on vapor phase photografting on cellulose was investigated at 60°C. An activated grafting of methyl methacrylate by water contained in the sample was observed in the experiment. The effect of water was commonly recorded irrespective of the type of cellulose derivatives such as cellulose acetate (degree of substitution, DS = 0.18 and 0.33), cellulose nitrate (DS = 0.35 and 0.75), and carboxymethl cellulose (DS = 0.19 and 0.74). Organic solvents can also be used in place of water, indicating that the percent grafting decreases in the order, water > methanol > acetone > cyclohexane. From ESR studies, water in the sample was found to contribute to the decay of cellulose radicals rather than to the radical formation. The decay was accelerated by organic solvents, and the magnitude of the effect was in the order, water ≈ methanol > acetone > cyclohexane. Based on the above investigation, it was presumed that water contained in the sample cannot contribute directly to the formation of cellulose radicals which may initiate grafting, but mostly promotes the penetration of monomer into cellulose fibers. Such penetration could lead cellulose radicals to an effective initiation of grafting.     

Poly(vinyl alcohol) fiber radicals induced by photo-irradiation at room temperature

The decay behavior of radicals produced on poly(vinyl alcohol) (PVA) fiber by photo-irradiation at room temperature and the graft copolymerization of methyl methacrylate (MMA) on the irradiated PVA fiber were investigated. Two kinds of stable radicals showing singlet and triplet spectra were indicated for both unsensitized and ferric ion-sensitized samples, especially with the emphasis of triplet component radical. The decay of radicals was promoted by contact with various organic solvent-water solutions, which effects were in the order of dimethyl sulfoxide (DMSO)–water > acetone–water > water > dioxane–water > methanol–water. On the other hand, graft copolymerization of MMA on the preirradiated sample was effectively initiated with the aid of a little water or a mixed solution of organic solvent and water. Methanol and dioxane, which decay radicals milder than acetone and DMSO do, contributed to give a higher per cent grafting. As no initiation took place with the unirradiated sample, it is concluded that the ability of preirradiated samples to initiate graft copolymerization should be caused by the PVA fiber radicals, which are smoothly produced by photo-irradiation at room temperature and show a triplet spectrum.     

Radiation-induced reactions with cellulose. III. Kinetics of styrene copolymerization in methanol

The kinetics of the radiation-induced grafting of styrene to cellulose in methanol have been studied in air at dose rates of 0.007, 0.014, and 0.078 Mrad/hr. in ⁶⁰Co and spent fuel element facilities. The variables affecting rate of grafting include monomer concentration, radiation dose rate, and total dose. Grafting reaches a maximum at 60–70% by volume methanol in styrene. The results have been interpreted in terms of possible grafting mechanisms, including charge-transfer intermediates; however, a complete mathematical treatment of the data is not possible at present because of the absence of appropriate swelling data for cellulose in mixtures of styrene and methanol. Poor grafting observed in solutions of up to 10% monomer is attributed to radical scavenging (predominantly from the solvent) by the monomer leading to the formation of scavenged products including homopolymer. Rate of grafting falls off for solutions above 80–90% monomer concentration and radical scavenging by monomer radicals is again postulated to account for the observed behavior.     

ESR studies of the photodegradation of cellulose graft copolymers

Ultraviolet light induced free radicals in cellulose and cellulose graft copolymers were studied by means of ESR spectroscopy. At least six kinds of free radicals were formed in cellulose when the polymer was irradiated with ultraviolet light. Polystyrene and poly(methyl methacrylate) are more resistant to ultraviolet light than cellulose; however, the cellulose graft copolymers of polystyrene and poly(methyl methacrylate) were degraded by ultraviolet light. ESR studies revealed that photoinduced free radicals in cellulose graft copolymers were formed at the grafting branches of the copolymers rather than the cellulose backbone. The mechanisms of light stabilization and energy transfer reactions of cellulose and cellulose graft copolymers are discussed.     

ESR study of post-irradiation reactions of cellulose and acrylonitrile

An ESR study of the free-radical mechanisms of the post-irradiation reactions of cotton cellulose with acrylonitrile is reported. The effects of atmosphere, moisture content, and solutions of acrylonitrile on the yield and stability of free-radical sites in irradiated cellulose were determined. On interaction of γ-radiation from a ⁶⁰Co source with cotton cellulose, long-lived free-radical sites were found within the molecular lattice. Short-lived free-radical sites were apparently also formed on chain cleavage, gave strong singlet spectra, and were readily accessible to interaction with water. Other free-radical sites were formed within regions of the cellulosic fiber which were inaccessible to moisture or aqueous solutions even after contact times as long as three days. It was suggested that long-lived free-radical sites in cellulose I (containing regain moisture) resulted from dehydrogenation at C₅, and in cellulose II (containing regain moisture) resulted from dehydrogenation at C₅ and dehydrogenation of the OH group or dehydroxylation at C₆. When irradiated cellulose was contacted with a solution of acrylonitrile (15%) in 75% aqueous zinc chloride, the initial rate of decrease in spin concentration was higher than the rate of decrease as the time of contact increased. The ESR spectrum of the reacted cellulose, observed at ?100°C., as compared with the spectrum for the irradiated cellulose, had decreased in signal strength with increase in time of contact and changed from a three-line spectrum to an ill-defined spectrum. The free radical being observed was probably due to unreacted sites in the cellulose. The extent of the graft copolymerization reaction was directly related to the initial spin concentration in the irradiated cellulose.     

Rheological properties of elastomers based on cellulose fibers

Elastomers, based on cellulose fibers, were synthesized by grafting ethyl acrylate onto fibers preirradiated by a high-energy electron beam. The rheological properties and fine structure of the elastomers were investigated in order to determine factors in development of rubber-like elastomeric behavior. Mechanical properties of the elastomers depended on (1) degree of polymerization of irradiated cellulose molecules, (2) extent of grafting, and (3) experimental methods of evaluation, particularly in varying environmental conditions, for example, in making measurements in air, water, or ethyl acetate. Glass transition temperatures of the elastomers were dependent on the environmental conditions of evaluation; stiffnesses of the elastomers levelled off at about 0°C; and in all environments, a rubber-like plateau was observed. Poly(ethyl acrylate) separated from the elastomers was not soluble in acetone. The mean molecular weight of the separated poly(ethyl acrylate) of the elastomer was determined in ethyl acetate by the equilibrium swelling method. It was concluded that crosslinks existed in the elastomers. Electron microphotographs of cross sections of the elastomers, which exhibited rubber-like behavior, indicated that the fibrillar structure of the irradiated cellulose fibers formed a uniform network and that poly(ethyl acrylate) was uniformly distributed among the fibrils.     

Kinetic analysis of radiation-initiated copolymerization reactions of water-soluble vinyl monomers with cellulose

A kinetic analysis of the radiation-initiated copolymerization reactions of 2-hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate (HPMA), and methacrylic acid (MAA) from water, methanol (MeOH), N,N-dimethylformamide (DMF), dimethysulfoxide (DMSO), and combinations of these solvents with irradiated fibrous cellulose I and II was made. The maximum extent of copolymerization of HEMA and HPMA with irradiated cellulose occurred from water solutions. When organic solvents were added to the water solution, while the concentration of monomer was kept constant, the extent of copolymerization decreased. The maximum extent of copolymerization of MAA with irradiated cellulose occurred from mixtures of MeOH (15–30 vol-%) and water (85–70 vol-%) solutions rather than from water. After initiation of the copolymerization reactions, they were apparently diffusion controlled and exhibited second-order kinetics. The relative concentrations of grafted polymer and homopolymer formed with irradiated cellulose from aqueous solutions depended primarily on the concentration of water in the solutions. From MeOH (60 vol-% or less)–water (40 vol-% or more) solutions, about 60% of poly(MAA) formed was apparently grafted polymer; from solutions containing less water, the fraction of grafted polymer decreased to about 40%.     

Characterization of poly(dimethylsiloxane)‐poly(methyl hydrogen siloxane) composite membranes for organic water pervaporation separation

Hydrophobic composite membranes with a crosslinked poly(dimethylsiloxane)‐poly(methyl hydrogen siloxane) selective layer were prepared by using a new laboratory made catalyst agent. The pervaporation separation of five organic solvent–water mixtures was carried out with these composite membranes, together with swelling experiments in the same feed mixtures. The volatile organic compounds employed were ethanol, methanol, 1‐butanol, acetone, and ethyl acetate. The pervaporation and swelling experiments revealed that both the 1‐butanol and the ethyl acetate solutions showed the highest affinity for the composite membrane. When these components were employed as feed solutions, the membranes showed both high selectivity and high permeation. Mechanical–dynamical experiments of swollen and nonswollen composite membranes were also performed. The relaxation spectra were analyzed in terms of the interaction of the components of the different mixtures with the composite membrane, and the free volume corresponding to the each sample was obtained. Once the membranes had reached an equilibrium swelling, a decrease in the free volume was observed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 546–556, 2001     

Equilibrium Swelling Studies of Chemically Cross-Linked Highly Swollen Acrylamide-Sodium Acrylate Hydrogels in Various Water-Solvent Mixtures

Swelling behavior of acrylamide (AAm)/sodium acrylate (SA) hydrogels was investigated in water-solvent (methanol, ethanol, t-butanol and acetone) mixtures of various compositions. AAm/SA hydrogels were prepared by free radical solution polymerization in aqueous solutions of AAm with SA as comonomers and a multifunctional cross-linker such as trimethylolpropane triacrylate (TMPTA). Swelling experiments were performed in water and water-organic solvent mixtures of various compositions at 25°C, gravimetrically. The value of S_eq% of AAm/SA hydrogels are 64–152% for 60% of metanol, 84–102% for 60% of ethanol, 127–176% for 60% of t-butanol, 131–585% for 60% of acetone, while the value of S_eq% of AAm/SA hydrogels are 780–4510% for water and water-solvent mixtures. Some swelling kinetic parameters were found. Diffusion behavior of water and water-solvent mixtures was investigated. Diffusion of water and water-solvent mixtures into the hydrogels was found to be non-Fickian in character.     

ESR study of reactions of cellulose with ·OH generated by Fe+2/H2O2

It was demonstrated by ESR spectroscopy that the Fe⁺²/H₂O₂ system gave a reactive species which generated an ESR triplet spectrum or sorbitol similar to that generated by hydroxyl radicals from the Ti⁺³/H₃O₂ system. An ESR spectrum was obtained for the hydroxyl radicals generated by the latter system. However, the lifetime of hydroxyl radicals, generated by the Fe⁺²/H₂O₂ system, was apparently very short, and an ESR spectrum for the hydroxyl radicals, generated by this system, was not observed. The Fe⁺²/H₂O₂ system also generated triplet spectra with cotton cellulose I, cotton cellulose II, and microcrystalline cellulose, suggesting that a hydrogen atom had been abstracted from the hydroxyl group on carbon C₆, or possibly the hydrogen atom on carbon C₅. The ESR spectrum generated on microcrystalline cellulose was less intense than those generated on cellulose I and II. On initiation of graft polymerization of the activated cellulose with acrylonitrile, the triplet spectrum disappeared and was replaced by two strong singlet spectra. One of the singlet spectra was likely generated on carbon C₁ or C₄ on depolymerization of the cellulose molecule, and the other was probably generated on the end of the growing polyacrylonitrile molecular chain. The absence of a triplet spectrum gave direct evidence for the order in which the acrylonitrile monomer was being grafted onto the cellulose molecule. The mechanisms proposed by Haber and Weiss for the reactions generated in the Fe⁺²/H₂O₂ system were generally supported.     

Electron spin resonance studies of interactions of ammonia,copper, and cupriammonia with cellulose

The electron spin resonance spectra (ESR) of complexes of copper with fibrous cotton cellulose under various experimental conditions were determined. Cupric ions dissolved in solutions of strong bases, such as concentrated ammonium hydroxide, sodium hydroxide, and potassium hydroxide, formed complexes with fibrous cotton cellulose. These complexes had paramagnetic resonance properties and generated characteristic ESR spectra. Cupric ions dissolved in solutions of highly ionized neutral salts, such as sodium chloride, formed complexes with cellulose. These complexes also generated the same characteristic ESR spectra as the complexes formed in solutions of strong base. The reaction between cupric ions and cellulose was evidently very rapid and reversible. When the concentration of ammonia was decreased in, or ammonia was removed from, the cupric ion–ammonium hydroxide–cellulose complexes, the paramagnetic resonance properties of the complex were decreased or lost. Similar results were received when potassium hydroxide was removed from the complexes. The compositions of the complexes evidently are variable, that is, under different experimental conditions the relative intensities of the lines of the ESR spectra of the complexes varied, although the hyperfine splittings of the lines were constant. It was concluded that reactions of cupric ions to form complexes with adjacent hydroxyl groups on the cellulose molecule depended on an optimum spatial arrangement of the hydroxyl groups, that is, distance between the groups. Evidently, wetting of cotton cellulosic fibers with solutions of strong bases or neutral salt allowed rotation about the C₂–C₃ bond to yield this optimum arrangement. When the base or salt was removed, rotation occurred to give less favorable positions of the hydroxyl groups for complexing with cupric ions.     

Calculation of alcohol‐acetone‐cellulose acetate ternary phase diagram and their relevance to membrane formation

ABSTRACT Alcohol‐acetone‐cellulose acetate phase diagrams incorporated with methanol, ethanol, and isopropanol as nonsolvents are calculated according to a new form of the Flory–Huggins equation. Nonsolvent–cellulose acetate interaction parameters are measured by swelling experiments. Concentration‐dependent nonsolvent–solvent interaction parameters are obtained by vapor–liquid equilibrium and the Wilson equation. It is shown that alcohol is a week coagulant compared with water, and water > methanol > ethanol > isopropanol for cellulose acetate. The phase diagrams characteristic of acetone‐cellulose acetate combined with water, methanol, ethanol, and isopropanol as nonsolvents is different, which leads to the different morphological structure of a cellulose acetate membrane. The structure of a water coagulated membrane has large macrovoids from liquid–liquid phase separation. A methanol coagulated membrane has a honeycomb‐like structure from spinodal microphase separation. An ethanol or isopropanol coagulated membrane has a thicker, dense top layer from the delay time phase separation. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1650–1657, 2001