ESR studies on the effect of lignin and gases on UV photodegradation of cellulose

Aspen wood pulp and aspen dioxane-lignin were irradiated by ultraviolet light under vacuum employing a special technique for uniform irradiation of the powdered samples. Examination of the effect of various gases and lignin contents of the pulps on the ESR spectra showed that the spin concentration was reduced by oxygen and lignin content, while atomic hydrogen reduced it to zero. The width and shape of the line were unaffected by oxygen, while lignin content reduced the width. A resolution for the hyperfine component of the spectrum yields an average distance of 1.3 Å between the free spin at C-5 and the protons at C-6 of the cellulose.     

ESR studies of free radicals in photo-initiated graft polymerization reactions with cotton cellulose

Electron spin resonance (ESR) spectra of free-radical intermediates formed during photo-initiated graft polymerization reactions of acrylamide, methacrylamide, and diacetone acrylamide onto purified cotton cellulose were recorded. Purified cellulose was saturated with aqueous solutions of the vinyl monomers (0.5M) and then photolyzed under nitrogen by near-ultraviolet light (3100–4100 Å, peak near 3500 Å) at ?196° and 40°C. Other samples of cellulose were saturated with aqueous solutions of the monomers, dried, and then photolyzed at 40°C. In the absence of cellulose, either poorly resolved or no free-radical spectra were generated on photolysis of the monomers. Photolysis of dried cellulose at 40°C and wet cellulose at ?196°C initiated formation of a cellulosic radical that generated a singlet spectrum. Photolysis of wet cellulose at 40°C generated no ESR detectable radical; however, photolysis of wet cellulose that contained monomer at 40°C generated poorly resolved spectra. The ESR spectra of the propagating copolymer radicals recorded were poly(acrylamide), three lines; poly(methacrylamide), five lines; and poly(diacetone acrylamide), two lines (doublet).     

Biodegradation studies of cellulose and its vinylic graft copolymers by thermal analysis and mechanical spectroscopy

Cotton cellulose with different % NaOH treatments and graft copolymers of cellulose prepared with vinyl acetate (AV) and methyl acrylate (MA), and Ce(IV) ion as an initiator were submitted to biodegradation conditions. Cellulose is a biopolymer consisting solely of glucose units, and, consequently, is also easily biodegradable. Nevertheless, modified cellulose, for example, by graft copolymerization, shows an increased resistance to biodegradation. The aim of this work was to study by calorimetric and dynamic‐mechanical analysis how the chemical modification of cellulose affects its biodegradability. From the obtained results some information has also been deduced about the composition and mechanical behavior of the vinylic grafted chains. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 326–335, 2000     

An investigation of the thermal properties of cellulose tricarbanilate-polystyrene graft copolymers

The thermal properties of a cellulose tricarbanilate-polystyrene graft copolymer and also unirradiated and irradiated cellulose, converted to the tricarbanilate, have been studied. Samples heated to specified temperatures have been examined by scanning electron microscopy. Simultaneous heating and visual appraisal have provided an understanding of the physical changes which take place on heating the samples. Data relating to the decomposition of the samples are presented which indicate that the grafted polystyrene has a marked influence on the thermal stability of cellulose tricarbanilate. Heating produces significant differences in the surface characteristics of the samples studied. Evidence is presented which shows that irradiation of cellulose produces changes in chemical reactivity which have an influence on subsequent chemical modification.     

Competitive removal of heavy metal ions by cellulose graft copolymers

The effect of composition of graft chains of four types cellulose graft copolymers on the competitive removal of Pb²⁺, Cu²⁺, and Cd²⁺ ions from aqueous solution was investigated. The copolymers used were (1) cellulose‐g‐polyacrylic acid (cellulose‐g‐pAA) with grafting percentages of 7, 18, and 30%; (2) cellulose‐g‐p(AA–NMBA) prepared by grafting of AA onto cellulose in the presence of crosslinking agent of N,N′‐methylene bisacrylamide (NMBA); (3) cellulose‐g‐p(AA–AASO₃H) prepared by grafting of a monomer mixture of acrylic acid (AA) and 2‐acrylamido‐2‐methyl propane sulphonic acid (AASO₃H) containing 10% (in mole) AASO₃H; and (4) cellulose‐g‐pAASO₃H obtained by grafting of AASO₃H onto cellulose. The concentrations of ions which were kept constant at 4 mmol/L in an aqueous solution of pH 4.5 were equal. Metal ion removal capacities and removal percentages of the copolymers was determined. Metal ion removal capacity of cellulose‐g‐pAA did not change with the increase in grafting percentages of the copolymer and determined to be 0.27 mmol metal ion/g_copolymer. Although the metal removal rate of cellulose‐g‐p(AA–NMBA) copolymer was lower than that of cellulose‐g‐pAA, removal capacities of both copolymers were the same which was equal to 0.24 mmol metal ion/g_copolymer. Cellulose did not remove any ion under the same conditions. In addition, cellulose‐g‐pAASO₃H removed practically no ion from the aqueous solution (0.02 mmol metal ion/g_copolymer). The presence of AASO₃H in the graft chains of cellulose‐g‐p(AA–AASO₃H) created a synergistic effect with respect to metal removal and led to a slight increase in metal ion adsorption capability in comparison to that of cellulose‐g‐pAA. All types of cellulose copolymers were found to be selective for the removal of Pb²⁺ over Cu²⁺ and Cd²⁺. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2034–2039, 2003     

Adsorption behavior of heavy metal ions on cellulose graft copolymers

The adsorption behavior of cadmium, copper and lead ions on holocellulosic materials containing various levels of polyacrylonitrile and poly(acrylic acid) grafts was examined. The amount of metal ions adsorbed per gram of the modified cellulosic substrate depended on the metal ion type, the nature and level of the incorporated graft polymer. In all cases grafting increased the metal ion-binding capacity of the cellulosic materials (by up to 50% for Cu (II) ions). The influence of temperature and initial metal ions concentration on the sorption behavior of the metal ions on the composite materials was investigated.     

Thermal behavior of graft copolymers of cotton cellulose and acrylate monomers

Cotton cellulose yarn was grafted with methyl acrylate, ethyl acrylate, n-butyl acrylate, and methyl methacrylate at various percentages of grafting. The effects of concentration of the initiator, concentration of the acid, and of temperature on grafting was studied and the mechanism discussed. The effect of reactivity of the monomer on the percentage graft-on is pointed out. Thermal behavior of natural and grafted cotton yarn was studied using dynamic thermogravimetry in air at a heating rate of 6°C/min up to a temperature of 500°C. The thermal stabilities of the samples grafted with various acrylate monomers to various percentages of grafting were computed from their primary thermograms by calculating the values of IDT, IPDT, and E^*. The results show that the thermal stability increases with increase in graft-on per cent, and the thermal stabilities of natural cotton and cotton grafted with different monomers are in the order ethyl > methyl > natural cellulose > methyl methacrylate > n-butyl acrylate.     

Flocculation of metal-bearing waste waters using cellulose and its graft copolymers

Several types of cellulose (wood pulp) and their graft copolymers with water-soluble monomers were tested for their activity as flocculation aids. They were employed as additives to lime in flocculation experiments involving a simulated mine water containing iron, zinc, and copper salts. The results show that all the cellulosic products had a beneficial effect on the removal of iron, and to a lesser extent on the removal of zinc. The final concentration of ferric ions after 30 min was comparable with that produced by commercial flocculants (Magnifloc, Aquafloc). No improvement of flocculation activity was obtained upon grafting various polar monomers and their mixtures onto dissolving pulp.     

Structure and properties of cellulose graft copolymers. II. Cellulose–styrene graft copolymers synthesized by the ceric ion method

Styrene was graft-copolymerized onto wood cellulose by the ceric ion method of Mino and Kaizerman. The grafting reaction was found to depend strongly on the concentration of ceric ion in the grafting system and maximum grafting occurred in a narrow range of concentration of initiator, 1.0 × 10^?3-1.8 × 10^?3 mol/l, at 58 ± 1°C. A pretreatment technique, developed to enhance the monomer diffusion into cellulose, was found to increase the grafting considerably. The structures of the cellulose-styrene graft copolymers were studied by hydrolyzing away the cellulose backbone to isolate the grafted polystyrene branches. The molecular weight and the molecular weight distributions of the grafted polystyrene were determined using gel permeation chromatography. The number-average molecular weight (M?_n) ranged from 23,000 to 453,000 and the polydispersity ratios (M?_w/M?_n) varied from 2.5 to 8.0. The grafting frequencies calculated from the per cent grafting and molecular weight data were of the order of 0.05–0.4 polystyrene branches per cellulose chain.     

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.     

Fabrication of enzyme-containing cellulose fibre materials from graft copolymers containing sulfo groups

An analysis of the experimental data and their comparison with previously published [3] results led to the following conclusions: the rate of interpolymer reactions (IPR) involving lysozyme (LYS) and cellulose graft copolymer containing strongly acid groups (sulfo groups) is much lower than the rate of the reaction between LYS and a weak polyanion grafted to cellulose (graft copolymer of cellulose and polyacrylic acid (PAA) sodium salt); the relative activity (RA) of immobilized LYS decreases with an increase in the duration of the reaction, which could be due to the formation of additional bonds in polyelectrolyte complexes (PEC); with all other conditions being equal, in the case of addition to C-gr-PSSA, the RA of immobilized LYS is lower than in addition to C-gr-PAA; this confirms the opinion advanced above that in the reaction with graft chains of PSSA, the conformation of the macromolecules of the enzyme is twisted to a greater degree than in addition to PAA. Translated from Khimicheskie Volokna, No. 1, pp. 10–13, January–February, 1997.     

ESR studies of polymer transitions. IV. Spin-probe studies of styrene block copolymers

ESR spin-probe values of glass temperatures are reported for a series of di-, tri-, and radial block copolymers. With one exception, in which the hard phase is poly(t-butylstyrene), the hard component is polystyrene (PS); the soft components include polybutadiene (PBD), polyisoprene (PI), hydrogenated PBD, hydrogenated PI, and poly(dimethyl siloxane) (PDMS). T_g's of the soft phase are in general agreement with those of the respective high molecular weight homopolymers; T_g's of the hard phase generally deviate widely from those of corresponding high molecular weight homopolymers. This deviation is interpreted in teens of a number of factors, including, the molecular weight of the hard phase, differences in solubility parameters for the two phases, percent of the hard phase present, and the presence of crystallinity. Comparison of T_g's determined by ESR with T_g's from dynamic mechanical methods on S-B-S triblocks of similar composition demonstrates that the ESR method is measuring the T_g of the interpliase and hence, in principle, its composition.     

Porous structure and rheological properties of hydrogels of highly water-absorptive cellulose graft copolymers

The porous structures of the highly swollen hydrogels of cellulose—acrylamide graft copolymers were studied by the solute exclusion technique. For these hydrogels, the cumulative volume of pores up to 560 Å in pore width was between 450 and 850 mL/g, and was between 20 and 30% of the total pore volume. With an increasing in the amount of crosslinker added in the grafting procedure, the cumulative pore volume up to 560 Å decreased. Furthermore, larger pores shrunk preferentially. In the range of concentration from 0.003 to 0.3%, the viscosity of the hydrogels increased remarkably with an increase in concentration. The concentration dependence of the viscosity showed a transition at about 0.03%, which corresponded to the reciprocal of the water retention values for each copolymer. At concentrations over 3%, fluidity of the hydrogels was lost and the water swollen copolymers became viscoelastic. This dynamic viscoelasticity remained essentially unchanged in the temperature range of 20 to 80°C. The dynamic viscoelasticity was dependent on the concentration, but the concentration dependence was smaller than that of the viscosity. The larger the amount of the crosslinker added, the larger the value of dynamic modulus became.     

Structure and properties of cellulose graft copolymers. I. Radiation-induced rayon–styrene graft copolymer

Rayon–styrene graft copolymers were prepared by the direct radiation method, with the use of the preswelling technique, by irradiation with γ-rays from ⁶⁰Co. The grafting was carried out in bulk styrene and in styrene–solvent mixtures, such as styrene–methanol and styrene–acetone, to study their effect on the graft copolymerization reaction and the structure of the resulting graft copolymer. The effects of carbon tetrachloride, a chain-transfer agent, was also investigated. Three different types of rayon yarn were used; Fortisan, a modifier-type high wet-modulus rayon, and a high-tenacity tire yarn, in order to study the effect of rayon microstructure on the grafting reaction. The molecular structure of the rayon–styrene graft copolymers was studied by hydrolyzing away the cellulose backbone and measuring the molecular weights of the grafted polystyrene branches. For grafting in bulk styrene, the molecular weights of the grafted polystyrene ranged from 400,000 to 1,000,000, while those of the polystyrene homopolymer formed in the outside solution were of the order of 30,000–50,000. The molecular weights of the grafted polystyrene branches tended to increase with per cent grafting in the graft copolymer. For grafting in styrene–methanol and styrene–acetone mixtures, the molecular weights of the polystyrene branches decreased with increasing solvent content. The addition of carbon tetrachloride to bulk styrene resulted in a sharp decrease in the molecular weights of the grafted branches. The grafting frequency or number of polystyrene branches per cellulose chain was calculated from the per cent grafting and the molecular weights of the polystyrene branches. The morphology of the rayon–styrene graft copolymers and some of their physical properties are discussed.     

Behavior of cellulose graft copolymer towards persulphate oxidation. III. Poly(acrylonitrile) graft copolymers

Cotton cellulose was graft copolymerized with poly(acrylonitrile) to different levels. The copolymers so obtained together with the nongrafted cellulose were oxidized at different pH's (4–10) and temperatures (50–70°C) with potassium persulphate. The oxidation reaction was studied with respect to oxygen consumption, mass loss, and changes in copper number and carboxyl content of the cellulosic materials. It was found that the rates of oxidation at pH 4 for the copolymers are substantially higher than that of the nongrafted cellulose and the rate of oxidation is higher the higher the level of grafting. The reverse is the case at pH 10. The mass loss increases as the oxygen consumption increases irrespective of the substrate used and the pH employed. The magnitude of the mass loss is substantially lower in the case of grafted cellulose than in the case of nongrafted cellulose. The cellulosic copolymers with higher graft levels show lower mass loss than those having lower graft levels. However, the copper number and carboxyl content of the oxidized grafted cellulose are higher than those of the nongrafted cellulose at the same oxygen consumption. It is believed that the presence of poly(acrylonitrile) graft in the molecular structure of cellulose impedes cellulosic chain scission without necessarily preventing oxidation of cellulose hydroxyls.     

ATRP法均相制备纤维素/甲基丙烯酸丁酯接枝聚合物

在纤维素LiCl/DMAc均相溶液中,通过氯乙酰氯（ClC₂OCl）与纤维素的均相酰化反应制得纤维素氯乙酸酯（Cellulose-ClAc）后,将其溶解在DMAc中,在FeCl₂/4-二甲氨基吡啶（DMAP）的催化作用下,引发甲基丙烯酸丁酯（BMA）的均相ATRP 聚合反应,制备了纤维素/BMA接枝共聚物（Cellulose-g-PBMA）,考察了反应时间、反应温度、反应物配比等对酰化及接枝聚合反应的影响,并通过测试Cellulose-g-PBMA薄膜的接触角,对最终产物的疏水性能进行了研究;采用FTIR、NMR、SEM、TEM、AFM等分析手段对Cellulose-ClAc及Cellulose-g-PBMA的结构进行了表征;利用GPC分析了接枝聚合反应的活性特征。     

Preparation of cellulose graft copolymers having polypeptide side chains and their blood compatibility

Blood compatibility of cellulose graft copolymers with poly(γ-benzyl-L -glutamate) and poly(N⁵-2-hydroxyethyl-L -glutamine) (Cell-g-PBLG and Cell-g-PHEG) was examined in vivo blood tests. For this purpose, Cell-g-PBLG graft copolymers with PBLG contents ranging from 7 to 60 mol % were prepared by polymerizing N-carboxy-γ-benzyl-L-glutamate(γ-BLG NCA) using aminoethyl cellulose (AE-Cell) with degree of substitution of 0.05 as macroinitiator. Graft copolymerization was carried out under a variety of conditions at 20°C in dimethyl-sulfoxide. Monomer conversion higher than 60% were obtained for all the polymerization runs. The solubility tests revealed that all of the AE-Cell and the polypeptides formed were grafted. The Cell-g-PHEG graft copolymers were prepared by treating Cell-g-PBLG graft copolymers with 2-amino-1-ethanol. Characterization of these graft copolymers were carried out by IR spectroscopy, DSC, and water content measurement. Tests for blood compatibility, in vivo, were made by a method of peripheral vein indwelling suture which was developed by one of the authors. The coating of graft copolymers on the polyester suture was made by casting either from formic acid solution of LiCl/dimethylacetamide solutions using water as the regenerating medium, and the polymer-coated sutures were implanted into a jugular and femoral vein of a dog. The results showed that the graft copolymers examined have excellent antithrombogenic properties.