Effect of wavelength region on photo-induced graft copolymerization onto cellulose

The effect of wavelength region of ultraviolet light was examined on the unsensitized photo-induced graft copolymerization of methyl methacrylate onto cellulose. When the quartz tube system was compared to the glass tube system, there was no induction period of copolymerization, the rate of reaction was a little larger, the homopolymerization of methyl methacrylate was increased causing interference with graft copolymerization, and the depolymerization of grafts and the scission reaction of cellulose chains occurred easily. The number of grafts was hardly improved by varying the reaction conditions, and the copolymers obtained generally exhibited low per cent grafting and contained grafts with lower degree of polymerization.     

Studies of the initiation mechanism of ferric ion–hydrogen peroxide systems in graft copolymerization on cellulose

The decomposition of hydrogen peroxide by ferric ion adsorbed on cellulose, the lowering of the degree of polymerization of cellulose, and the graft copolymerization in the systems containing methyl methacrylate were studied. As the amount of ferric ion adsorbed on cellulose and the concentration of hydrogen peroxide became higher, the amount of decomposition of hydrogen peroxide and the number of scissions of cellulose chains with higher rates at the initial stage of reaction were both observed to increase. It was recognized that the graft copolymerization was hardly initiated, while such initial reactions were proceeding. Assuming that the hydrogen peroxide decomposed with a higher rate was indifferent to the initiation reaction, a certain relationship was found between the amount of ferric ion adsorbed on cellulose ànd the initiation efficiency of hydrogen peroxide in graft copolymerization.     

Studies on the ability of cellulosic materials to initiate graft copolymerization

The activity to initiate graft copolymerization was investigated for various cellulose samples. Oxidation of the sample with hydrogen peroxide or sodium hypochlorite indicated a remarkable increase in the per cent grafting as well as the number of grafts. This phenomenon must be attributed to the formation of special reactive groups in cellulosic materials. However, the treatment with hot water caused a definite decrease in the per cent grafting or the number of grafts for the graft copolymerization on the sample, indicating a lower activity to initiate graft copolymerization. Accordingly, the reactive groups, once formed on the sample by oxidation, seemed to be easily decomposed by hot water. The ferric ion adsorbed on cellulose increased the per cent grafting and accelerated the formation of grafts, and the contribution of metallic ions to the initiation was recognized as one of the important factors of graft copolymerization.     

Effect of metallic ions in photo-induced graft copolymerization onto cellulose

In photo-induced graft copolymerization of methyl methacrylate onto cellulose, the effect of metallic ions as sensitizer was investigated. Some metallic ions were effective in their adsorbed states and accelerated the formation of grafts in the order Fe²⁺ > Ag⁺ > Fe³⁺. However, Cu²⁺ acted negatively, and little effect was observed for Co²⁺, Ni²⁺, Mn²⁺, Zn²⁺, and Cr³⁺. In the systems in which aqueous metallic salt solutions were added, the formation of grafts was generally depressed, but Fe³⁺ was an exception. The effect of metallic ions on the scission reaction of cellulose main chains did not necessarily agree with the effect on the formation of grafts. This is attributed to the varied interaction between cellulose and the different active species produced by irradiation, depending on the type of metallic ions used.     

Comparison of Fe2+?H2O2 and Fe3+?H2O2 initiation systems in graft copolymerization of cellulosic materials

Studies were carried out on decomposition of hydrogen peroxide by ferrous and ferric ions adsorbed on cellulosic materials (SP, SCP), scission of the cellulose chain and formation of grafts by graft copolymerization. As a result, it was found that the activity of ferrous ion is always higher than that of ferric ion, but there exists a common relation between the amount of decomposition of hydrogen peroxide and the number of grafts for all cellulose samples and kinds of metallic ions, and it was inferred that essentially, copolymerization takes place by the same mechanism irrespective of the kind of metallic ions. Consequently, it can be considered that the difference in degree of activity between ferrous ion and ferric ion is due to the difference in the decomposition mechanism of hydrogen peroxide by these metallic ions and it is assumed that the high activity of ferrous ion in graft copolymerization is due to the high hydrogen peroxide decomposition effect.     

Factors affecting the photo-induced graft copolymerization of methyl methacrylate onto fibrous polymer

The effects of sample swelling, photosensitizer, and solvent on the photo-induced graft copolymerization of methyl methacrylate onto fibrous polymers such as Vinylon, nylon 6, and polyester were examined. Each separate factor, sample swelling, or solvent, or their combination, increased activity of polymerization. Only some sensitizer were effective. Studying the ESR spectra of photo-irradiated polymers also showed that either the sample swelling, the photosensitizer, or the organic solvent is very effective for the formation of polymer radicals under irradiation.     

Photo-induced graft copolymerization of methyl methacrylate on poly(vinyl alcohol)

Photo-induced graft copolymerization of methyl methacrylate on poly(vinyl alcohol) (PVA) was examined in aqueous solutions. In unoxidized samples, only a few percent of PVA used took part in the formation of grafts, and the percent grafting was very low. However, if Fe²⁺, Fe³⁺, anthraquinone-2,7-disulfonate, or oxalic acid was used as sensitizer, the percent grafting was somewhat improved. Among them, the effect of Fe³⁺ was most remarkable. Oxidized PVA showed a higher initiating activity and was more susceptible to the sensitizing action of Fe³⁺ than unoxidized PVA. As Fe³⁺ has an ability to accelerate the photo-induced scission reaction of PVA chains for both oxidized and unoxidized PVA, it is thought to be very probable that the copolymer formed in the photo-induced systems has a block polymer-type structure like that in systems initiated by ceric ion or hydrogen peroxide.     

Ceric salt-initiated graft copolymerization of methyl methacrylate on preoxidized cellulose samples

The effects of preoxidation of cellulose samples on graft copolymerization in the presence of ceric salt (Ce⁴⁺) as an initiator were investigated. The use of Ce⁴⁺ as oxidizing agent inhibited the formation of grafts, and the number of grafts decreased as the concentration of Ce⁴⁺ in the pretreatment rose. In contrast, the samples oxidized with periodic acid (HIO)₄ or hydrogen peroxide (H₂O₂) tended to show improved initiation characteristics and gave a larger number of grafts than the unoxidized samples. The reactivity of oxidized samples toward Ce⁴⁺ was examined and the following results were obtained: The part of easy reactivity decreased in the Ce⁴⁺-oxidized samples but it increased in the HIO₄-oxidized samples; on the other hand, it did not vary greatly in the H₂O₂-oxidized samples. Cellulose is probably oxidized to different states by different oxidizing agents, and the reactivity of Ce⁴⁺ toward these oxidized samples, as one index, seems to be reflected in the graft copolymerization. It was consequently recognized that the graft copolymerization characteristics of cellulose samples could be improved significantly by proper selection of oxidiation conditions.     

Effect of lignin in graft copolymerization of methyl methacrylate on cellulose by ceric ion

The effect of lignin contained in cellulosic materials in graft copolymerization of methyl methacrylate on such materials using ceric ion as initiator was studied. It was found that the percent grafting and the average molecular weight of grafts became lower in samples having a larger lignin content but the number of grafts formed increased proportionally up to lignin content of about 2.5%. Ceric ion reacted at a faster rate with lignin than with cellulose in wood pulp, and the results indicating that the active sites formed on lignin by oxidation with ceric ion accelerate the formation of grafts and increase the number of grafts were obtained. But on the other hand, the active sites participated in the termination reaction of the growing graft polymer radicals to cause lowering of the average molecular weight of grafts.     

Decomposition of peroxide on carboxymethyl cellulose and its ability to initiate graft copolymerization

The decomposition of the peroxide group on fibrous carboxymethyl cellulose (CMC) and its ability to initiate graft copolymerization were investigated. The peroxide on CMC liberated hydrogen peroxide when the sample was heated in an aqueous medium. The decomposition of the peroxide was markedly increased by the use of ferrous salt and the irradiation with light of λ > 300 nm. The grafting of methyl methacrylate on CMC peroxide was initiated by heating or irradiating with light, where the rate of grafting and the reciprocal of the average molecular weight of grafts in general were proportional to the square root of the peroxide content of the sample. The peroxide content of the sample was related closely to the number of grafts in initiation. The number was estimated as 17 times for thermal initiation and 6 times for photoinitiation at the maximum values. The CMC peroxide showed a marked activity toward photografting of acrylamide, acrylic acid, acrylonitrile, and vinyl acetate on the substrate.     

Graft copolymerization to cellulose. Effect of sodium thiosulfate on hydrogen peroxide initiator system

The effect of sodium thiosulfate on the graft copolymerization of methyl methacrylate to cellulose in the hydrogen peroxide initiator system was investigated. The addition of sodium thiosulfate in general was effective for decreasing the per cent grafting and the average molecular weight of grafts and increasing the formation of homopolymer, and the effects became pronounced with increasing hydrogen peroxide concentration. Moreover, the addition of sodium thiosulfate slightly suppressed the formation of grafts at a hydrogen peroxide concentration of 3 mmole/l., but greatly promoted it at 20 mmole/l. Traces of metallic ions present in cellulose could not be eliminated sufficiently by treatment with 3N hydrochloric acid. Such ions were found to interact with hydrogen peroxide and thus participate directly in the initiation and termination of the polymerization reaction. EDTA, the chelating agent, was highly effective for suppressing such participation of metallic ions. In the hydrogen peroxide initiator system applied to the EDTA-treated samples, sodium thiosulfate caused an effective initiation of graft formation.     

Radical formation and graft copolymerization on photo-irradiated aldehyde cellulose

The relationship between the activity to initiate graft copolymerization under photo-irradiation and the photo-induced radicals of periodic acid-oxidized cellulose (aldehyde cellulose) was investigated. Aldehyde cellulose proved to have a high activity to initiate graft copolymerization under photo-irradiation, and the effect was profound, especially for hydrophilic vinyl monomers such as acrylic acid and acrylamide. By studying the ESR spectrum of photo-irradiated aldehyde cellulose, the formation of a radical giving a singlet spectrum with linewidth of 14–15 G and a g value of 2.001 was observed. This was assigned to an acyl radical orginating in the aldehyde group of the sample. Employing low molecular weight aldehydes, it was confirmed that an acyl radical formed on aldehyde compounds by photo-irradiation has a function sufficient to initiate the graft copolymerization of vinyl monomers. It was concluded that the high activity needed to induce the graft copolymerization of aldehyde cellulose under photo-irradiation was based on an acyl radical which originated in the aldehyde group of the sample.     

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.     

Graft copolymerization to cellulose in the presence of hydrogen peroxide with ultraviolet irradiation

The decomposition of hydrogen peroxide in the presence of cellulose with ultraviolet irradiation and graft copolymerization occurring upon addition of methyl methacrylate to this system was investigated. Graft copolymerization barely began in the hydrogen peroxide system without ultraviolet irradiation, but was markedly accelerated by ultraviolet irradiation. Ultraviolet light is capable of initiating the graft copolymerization even without addition of hydrogen peroxide, and this capability is enhanced further with the use of hydrogen peroxide. However, an increase in the hydrogen peroxide concentration was observed to exercise a zero or negative effect on the number of grafts. Such a phenomenon is absent in the ceric ion initiator system and, in the present study, is believed to be brought about by a characteristic enhancement of the stabilization of grafting sites effected by hydroxyl radicals. The number of grafts of copolymers obtained in the present initiator system is only approximately 0.085 mmole/100 g of cellulose at its maximum and is within the range of results obtained for the hydrogen peroxide initiator system in general.     

Preparation,characterization, and properties of cellulose–polyacrylamide graft copolymers

Graft copolymers of acrylamide on cellulose materials (α‐cellulose 55.8%, DP 287.3) obtained from Terminalia superba wood meal and its carboxymethylated derivative (DS 0.438) were prepared using a ceric ion initiator and batch polymerization and modified batch polymerization processes. The extent of graft polymer formation was measured in graft level, grafting efficiency, molecular weight of grafted polymer chains, frequency of grafting as a function of the polymerization medium, and initiator and monomer concentrations. It was found that the modified batch polymerization process yielded greater graft polymer formation and that graft copolymerization in aqueous alcohol medium resulted in enhanced levels of grafting and formation of many short grafted polymer chains. Viscosity measurements in aqueous solutions of carboxymethyl cellulose‐g‐polyacrylamide copolymer samples showed that interpositioning of polyacrylamide chains markedly increased the specific viscosity and resistance to biodegradation of the graft copolymers. The flocculation characteristics of the graft copolymers were determined with kaolin suspension. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 913–923, 2003     

Ability of cellulosic materials to initiate graft copolymerization by photo-irradiation

The ability of various kinds of cellulose samples to initiate graft copolymerization of methyl methacrylate by photo-irradiation was examined. Untreated samples (absorbent cotton, sulfite pulp, dissolving pulp, and semichemical pulp), extracted samples (1% sodium hydroxide, methanol, and ethanol-benzene mixture as extraction solvent), oxidized samples (periodic acid, sodium hypochlorite, hydrogen peroxide, and nitrogen dioxide), a reduced sample, an oximated sample, and a ferric ion-adsorbing sample were used for the experiments. It was found that impurities in the sample as well as the oxidized states affect the initiation reaction remarkably. It was also noted that the contribution of these factors was remarkable in an irradiation system with a light of wavelength longer than 300 nm, although in the systems using sensitizers or irradiation with a light of shorter wavelength, initiation took place almost indifferent to the cellulose characteristics.     

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.     

Characterization of products prepared by homogeneous grafting of styrene onto cellulose in a sulfur dioxide–diethylamine–dimethyl sulfoxide medium

Homogeneous graft copolymerization of styrene onto cellulose was carried out using a SO₂–DEA–DMSO cellulose solvent reaction medium and γ-ray mutual irradiation. The yield of grafted side chain polymer and the homopolymer in this reaction system proved to be polysulfone, a styrene–sulfur dioxide copolymer in which the number of sulfur atoms per polymer chain is 3–3.5. Several characterizations of the graft product were attempted. The graft products were extracted with boiling benzene for 24 hr to remove homopolymer, and then the cellulose backbones were hydrolyzed. After hydrolysis, the polysulfone residues were separated by thin-layer chromatography (TLC) into two components, i.e., attendant homopolysulfone and the true side chain polysulfone having some sugar residues at one of the polymer chain ends. The weight fraction of these components for each graft product was determined by a TLC scanner. The molecular weight of the side chain polysulfone remained constant and significantly lower than that of the homopolysulfone throughout the reaction period. By assuming that no scission of cellulose chains occurred throughout the graft reaction, the number of branches per starting cellulose molecule was assessed to be surprisingly large, ranging from 2.4 to 10.6 at a total dose of 1–8 mR of irradiation. It was also found that percent grafting increased with irradiation time because of an increase in the number of branches per cellulose chain. Furthermore, we succeeded in separating the graft product into ungrafted cellulose and the true graft copolymer containing a small amount of attendant hompolysulfone.     

纤维素非均相接枝丙烯酸制备吸水材料

研究了经过氧化氢(H2O2)处理过的纤维素与丙烯酸在非均相体系中进行的接枝共聚,主要考察了聚合温度、聚合时间、预处理温度和纤维素状态对接枝聚合物的接枝参数的影响,以及交联剂对吸水倍率的影响,发现了H2O2-Cellulose先形成氧化还原体系,再引发丙烯酸与纤维素接枝的聚合机理。     

Influence of physical relaxation on chemical stress–relaxation of natural rubber vulcanizates

Networks were prepared in the swollen and dry states to investigate the influence of physical relaxation on chemical stress–relaxation. The stress–relaxation behavior of solution-cured samples was different significantly from that of the samples crosslinked conventionally. The same result was also observed in the number of chain scission for both kinds of samples. On the other hand, the number of chain scission estimated by using the swelling method for samples crosslinked conventionally was in good agreement with that by the chemical stress–relaxation for solution-cured samples. It was found that there is little or no influence of the physical relaxation caused by entanglements, and no effect of dangling chains arising from scission in the equilibrium swelling. The relative change of network chain density determined by means of the swelling method was also consistent with that by sol fraction determination. These results indicate that the swelling method can be used as a measure of a degree of degradation on chemorheology. Taking into account the influence of physical relaxation on chemical stress–relaxation, a new relationship between the relative stress decay and the relative network chain density was experimentally proposed.