Factors affecting vapor phase photografting of vinyl monomers on cellulose

Effects of water contained in the sample, the type of sensitizer, and the nature of vinyl monomer on vapor phase photografting on cellulose were investigated at 60°C. The grafting was enhanced by the water contained in the cellulose sample, resulting in an increased percent grafting with increasing the quantity of water. The use of sensitizers such as ferric chloride, ferrous sulfate, ceric ammonium nitrate, hydrogen peroxide, benzophenone, and sodium anthraquinone-2,7-disulfonate led to accelerated graftings. However, the maximum grafting was observed at an optimum quantity of sensitizer for each sensitized system, and the formation of grafted polymer was restricted by the use of sensitizer beyond the quantity. Ferric chloride and hydrogen peroxide exhibited higher activities among the sensitizers. With respect to the nature of monomer, methyl methacrylate, acrylic acid, methacrylic acid, and acrylonitrile were observed to be introduced into cellulose substrate by the vapor phase photografting, though no initiation was recorded for styrene and N-vinylpyrrolidone. However, the latter monomers were introduced by using monomer mixtures with acrylonitrile, affording a maximum percent grafting at a certain monomer composition.     

Liquid-crystalline state of cellulose and its derivatives

Conclusions Literature material on the liquid-crystalline state of solutions and melts of cellulose and its derivatives has been analyzed.Translated from Khimicheskie Volokna, No. 3, pp. 8–12, May–June, 1983.     

Effect of water in vapor-phase photografting of vinyl monomers on polymer films

The effect of water added to monomer being supplied in the vapor phase was investigated in photografting on sensitizer-coated polymer films at 60°C. A pertinent quantity of water accelerated sharply the photografting irrespective of the nature of monomer (acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, and acrylonitrile), film substrate (low-density and high-density polyethylenes, polypropyrene, nylon 6, and polyester), and sensitizer (benzophenone and anthraquinone). Water was found to increase the molecular weight of the grafts, which was studied on acrylonitrile-grafted nylon 6 film. It was confirmed that water exhibited an accelerating action on photoinduced solution polymerizations of acrylic acid and methyl methacrylate, resulting in an increased molecular weight of the both polymers. These results suggest that the accelerating action of water may result from the restriction of chain termination.     

Reactivity of glycidyl-methacrylate-grafted cellulose prepared by means of photografting

Photografting was applied to functionalize cellulose, that is, epoxy groups were introduced into the cellulose substrate by photografting of glycidyl methacrylate (GMA) using hydrogen peroxide as a photoinitiator. Dissolving pulp from softwoods was used as the cellulose sample. The GMA-grafted cellulose (G-Cell) was subjected to the following examinations in comparision with epoxy-activated cellulose (E-Cell) prepared by reaction with epichlorohydrin: (1) reactivity of G-Cell towards amines such as ethylenediamine, tetramethylenediamine, hexamethylenediamine, diethylenetriamine, and triethylenetetramine; (2) ability of the aminated celluloses obtained by examination (1) to adsorb cupric ion; and (3) catalytic activity of the aminated cellulose–cupric ion complexes prepared by examination (2) for decomposition of hydrogen peroxide. The amount of amine residue introduced into the substrate was higher for E-Cell than G-Cell, showing the existence of epoxy groups in G-Cell which cannot contribute to the reaction. The ability of the aminated celluloses to adsorb cupric ion was nearly equal for G-Cell and E-Cell though tetramethylenediamine and hexamethylenediamine-introduced samples did not show the ability. It was found that all complexes prepared by reaction of the aminated cellulose with cupric ion exhibited catalytic activity for decomposition of hydrogen peroxide. © 1995 John Wiley & Sons, Inc.     

Effect of vapor phase pressure in synthesis of polyamide-6 on its indexes

An algorithm for calculating the vapor-liquid state of the polycaproamide (PCA)-low-molecular-weight compound (LMC)-H₂O system was developed based on published data, and it can be used to optimize the technology for synthesis of PCA with defined properties. The validity of the algorithm was tested experimentally on a pilot installation with an output of 2–3 tons/day.All-Russian Scientific-Research Institute of Synthetic Fibres. Tver'. Translated from Khimicheskie Volokna, No. 2, pp. 23–24, March–April, 1996.     

Effect of vapor phase ethylenediamine crosslinking of matrimid on alcohol vapor sorption and diffusion

This work examines the sorption, diffusion, and polymer relaxation behavior for water and C1‐C7 alcohol vapors at 30 °C in ethylenediamine vapor‐phase crosslinked Matrimid. Ethylenediamine is sufficiently volatile that crosslinking can occur by exposing the polymeric film to saturated vapor, in contrast to more conventional means of dissolving the crosslinker in a solvent and immersing the polymeric film in the solution. The vapor‐phase exposure method avoids the use of additional solvent and undesired solvent‐induced swelling. Sorption isotherms demonstrate that water and C1‐C5 alcohols do not appreciably differ for unmodified and crosslinked Matrimid; however, an approximate 90% reduction in sorption was determined for hexanol and heptanol. A minor impact on diffusion coefficients for water, methanol, and ethanol was observed, while those of propanol and butanol were reduced over an order of magnitude. Relaxation kinetics were similarly unchanged for water and C1‐C3 alcohols, while being significantly reduced for butanol and higher alcohols. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44771.     

Water-absorbing characteristics of acrylic acid-grafted carboxymethyl cellulose synthesized by photografting

Cellulosic absorbents for water were synthesized by photografting (λ > 300 nm) acrylic acid (AA) onto fiberous carboxymethyl cellulose (CMC, degree of substitution [DS] = 0.1–0.4) at 30°C in the presence of N,N′-methylenebisacrylamide as a crosslinker. The CMC sample was pretreated with hydrogen peroxide in the presence of sulfuric acid to prepare CMC peroxides with a peracid type as a polymeric photoinitiator. The peroxides were active for the photografting and AA could be grafted onto CMC with percent graftings higher than 150% by photoirradiation of 10 min at 30°C. The amount of water absorbed increased with increasing percent grafting of AA and DS of CMC. The amount was reduced considerably when the absorbents were prepared by the photografting of AA onto crosslinked CMC in the absence of the crosslinker. Graft copolymers which display a decreasing water absorbency as a function of temperature were prepared by two methods: In the first synthesis method, AA and N-isopropylacrylamide (NIPAAm) binary monomers were graft-copoly-merized onto CMC samples using photoinitiation. In the second method, photografting of AA was followed by a second-step photografting of NIPAAm to produce a terpolymer with two types of side chains of differing repeat unit composition on the CMC substrate. Graft copolymers formed by both methods showed decreasing water absorbency as temperature increased with losses in water absorbency of up to about 60% as the temperature was increased above 30°C. Effects of NIPAAm composition and corsslinker content in the graft copolymers on the decreasing water absorbency as a function of temperature were also examined. © 1996 John Wiley & Sons, Inc.     

Dielectric studies of cellulose and its derivatives: 1. Acetylation of cellulose

Dielectric conductivity (dc) and water absorption measurements are reported on a series of cellulose linter samples acetylated to varying degrees. The data illustrates the effects of the original structure of the cellulose linters both on the ease of acetylation and also on the subsequent dynamic characteristics of the polymer. It is only in the most forcing conditions that the primary fibrillar structure is destroyed. A change in properties is observed to occur at 40% acetylation of the hydroxyl groups, this coincides with the concentration of accessible groups as determined by deuterium exchange. A correlation is observed between the absorption and electrical observations on these systems.     

Dielectric studies of cellulose and its derivatives: 3. Glycerol in cellulose acetate

Dielectric studies are reported on cellulose acetate doped with glycerol. The addition of glycerol initially leads to the generation of a strongly interacting layer manifest by an increase in the amplitude of the side chain motion of the cellulose acetate and also the appearance of a higher temperature relaxation. Further addition of glycerol allows development of a multilayer situation which has relaxation properties similar to that of pure glycerol and is essentially independent of the cellulose acetate matrix. The high temperature conductivity of the samples investigated is critically dependent on the concentration of the dopant, increasing markedly for concentrations above 2–3%. This change in behaviour appears to correlate with the fibrillar surface area and is associated with the generation of proton conduction in the system. The general characteristics of this behaviour are similar to those previously reported¹ for the addition of water to cellulose derivatives.     

Permeation of water vapor through cellulose triacetate membranes in hollow fiber form

A modification of the carrier gas method for measuring permeability of a hollow fiber to a vapor is described with particular application to water vapor permeation through asymmetric cellulose triacetate in hollow fiber from. Conventional methods are inadequate because the high flux of permeation vapor combined with its low pressure on the permeate side and the small diameter of the fiber lead to an excessive buildup of pressure in the permeate stream—in some cases so great as to render much of the fiber length ineffective. The method described in this paper involves the permeation from the outside to the inside of the fiber of a binary mixture consisting of the water vapor and a fairly highly permeable carrier (helium). There is a significant pressure drop along the fiber, but a theoretical treatment is presented to take this into account and to permit a determination of the vapor permeability. Experiments at 35°C over a range of water vapor pressures up to 1.7 cm Hg gave a water flux of 9 × 10^?3 cc(S.T.P.)/cm²-sec-cm Hg, with an apparent slight decrease with increasing pressure. Over the same range of water vapor pressure the helium flux decreased from 2.3 × 10^?4 to 1.85 × 10^?4 cc(S.T.P.)/cm²-sec-cm Hg.     

Vapor phase photografting on low-density polyethylene film in binary monomer systems

Vapor phase photografting of monomer mixtures on low-density polyethylene film, on which benzoyl peroxide is coated, was investigated at 60°C using various vinyl, allyl, and solid monomers. Styrene (St) itself was difficult to graft on the film substrate, but the combinations of St with vinyl monomers such as acrylonitrile (AN), glycidyl methacrylate (GMA), acrylic acid, and methacrylic acid led to the accelerated grafting, affording a maximum percent grafting at an certain monomer ratio. The same combination effect was observed for AN–N-vinyl pyrrolidone and –GMA monomer mixtures. The monomer combinations such as allyl aldehyde–St and allyl alcohol–maleic anhydride were useful for performing the grafting of allyl monomers effectively. Maleic anhydride and maleimide as solid monomers were also possible to introduce into the film substrate by means of the monomer combination, where St, N-vinyl pyrrolidone, vinyl ethers, and benzyl methacrylate were available as comonomers. Thus, the monomer combinations affording an accelerating effect on grafting may be monomer pairs rich in an alternative copolymerizability, suggesting that monomer reactivity ratio controls a major factor for the combination effect. It was confirmed from IR study on grafted films that both monomer components are introduced in the film substrate as the grafted chain component.     

NMR and calorimetric investigation of water in a superabsorbing crosslinked network based on cellulose derivatives

In this study we have investigated the state of water in a superabsorbing network based on hydroxyethylcellulose (HEC) and carboxymethylcellulose sodium salt (CMCNa) crosslinked with divinylsulfone (DVS).This type of network, at low degree of crosslinking, when exposed to distilled water is able to form a stable hydrogel containing an amount of water as high as 1000 times its own weight.De-hydrated/re-hydrated networks, containing different amounts of absorbed water, have been studied using differential scanning calorimetry (DSC) and NMR relaxometric methods. DSC analysis allowed the evaluation of freezable and non-freezable fractions of absorbed water showing also the presence of two types of freezable water. On the other hand, NMR relaxometry evidenced the presence of two hydration shells, characterized by a different mobility, which in both cases is lower than that of bulk water.An excellent quantitative agreement was found in the determination of the amount of freezable water using the two techniques.A comparison of the state of water in the crosslinked network and in the corresponding uncrosslinked mechanical mixture shows that in the last case micro-heterogeneity arises.     

Formation of peroxides on cellulose derivatives

Formation of peroxides on cellulose derivatives such as fibrous carboxymethyl cellulose, acrylic acid-grafted cellulose, and aldehyde cellulose with the use of hydrogen peroxide was investigated. Formation of peroxides was observed for each cellulose derivative with the reaction at 25°C and the amount of formation was related closely to the carboxyl or carbonyl contents in the samples. The peroxides were fairly stable in wet samples at low temperatures, but almost all peroxides were decomposed at 60°C. When the cellulose peroxides were warmed with water, hydrogen peroxide separated from the cellulose peroxides into an aqueous medium. The structure of the peroxides formed on the cellulose derivatives is discussed on the basis of the experimental results.     

Influence of water on phase transition and rheological behavior of cellulose/ionic liquid/water ternary systems

The influence of water content on liquid crystalline (LC) gel formation and the rheological behavior of a ternary microcrystalline cellulose (MCC)/1‐ehtyl‐3‐methylimidazolium acetate (EmimAc)/water system was investigated using polarized optical microscopy (POM) and rheometry. POM indicated that the distinct water content range for forming a fully anisotropic LC gel with 14 wt % MCC was 4–10 wt %. Adding water to the MCC/EmimAc system resulted in enhanced complex viscosity and storage and loss moduli, and ultimately LC gel formation. Comparison of creep compliance vs. time revealed that the system without water showed representative viscoelastic behavior, while the time dependence of creep compliance disappeared as the water content increased, suggesting elastic‐solid behavior. Additionally, hydrogen bonding between cellulose and EmimAc weakened as water content increased, whereas the intra‐ and intermolecular hydrogen bonds of cellulose became stronger because of strong self‐association. This strong bonding caused aggregation, chain entanglement, and self‐supporting LC gel network formation. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44658.     

Effect of selective localization of cellulose nanowhiskers on viscoelastic phase separation

Viscoelastic phase separation (VPS) is a fundamental physical phenomenon that creates percolated network structure in dynamically asymmetric mixtures. The object of this study was to investigate the effect of rod shape nanoparticles with different surface chemistries on VPS in the polystyrene/poly(vinyl methyl ether), PS/PVME, blend. For this purpose, hydrophilic (CNWs) and hydrophobic (M‐CNWs) cellulose nanowhiskers (CNWs) were prepared to be used as nanorods. Rheological measurments were employed to investigate the effect of nanowhiskers on phase separation temperature, kinetics of phase separation, and dynamic asymmetry. The evolution of morphology during the phase separation at a fixed quench depth was assessed using polarized optical microscopy. The nanowhiskers were effective in decreasing the correlation length, which slowed down the phase separation. CNWs self‐assembled into the PVME‐rich phase during the phase separation, which led to a decrease in the dynamic asymmetry and beyond a critical volume fraction of CNWs, the VPS mechanism changed to spinodal decomposition (SD). However, in the presence of M‐CNW, the localization of M‐CNWs into the PS‐rich phase enhanced the dynamic asymmetry and at 2 vol% M‐CNWs, the induced PS‐rich network by VPS was arrested. The linear and non‐linear viscoelastic behavior of the samples were studied as well. POLYM. ENG. SCI., 58:928–942, 2018. © 2017 Society of Plastics Engineers     

Surface photografting initiated by benzophenone in water and mixed solvents containing water and ethanol

Photografting reactions are usually carried out in organic solvents due to the water insoluble nature of photoinitiators such as benzophenone (BP). This work reports the effect of water and mixed solvents containing water and ethanol on the surface photografting of methacrylic acid (MAA) onto polyethylene initiated by BP. The percent grafting increased with the increase of water volume ratio in the mixed solvent, and BP showed the highest photoinitiation efficiency when dissolved in pure water solvent. Effects of BP concentration, monomer concentration, and monomer type on photografting were studied. The percent grafting showed the maximum at a lower BP concentration (0.20 mol/mol %) in pure water solvent than that (0.60 mol/mol %) in the mixed solvent with 90 v/v % water. The percent grafting first increased with the increase of monomer concentration till 3 mol L^?1 and then decreased. Acrylic acid (AA) could also be photografted onto polyethylene by BP in the mixed solvents. UV–visible spectroscopic examinations revealed that the λ_max of π–π* transitions of BP red shifted as the increase of the water volume ratio, i.e., the polarity of the solvent. The excitation of BP in solvents with a higher polarity under UV irradiation requires less energy, so the photografting initiated by BP is easier to occur. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Dielectric studies of proton migration and relaxation in wet cellulose and its derivatives

Dielectric relaxation data are reported over a frequency range 400 Hz to 12 kHz and over a temperature range 193 to 323K on cellulose, cellulose acetate and ethyl cellulose with various water contents. A relaxation peak shifted to the low temperature side of the beta process was observed for cellulose acetate with less than 4% water. The effect of water addition in the case of cellulose and ethyl cellulose was initially to increase the amplitude of the loss associated with side group motion. Above 4% water content, the low temperature relaxation in cellulose acetate moves to lower temperatures and an increase in the loss is observed at high temperatures. Similar behaviour was observed in cellulose and ethyl cellulose. A transformation of the frequency dependent conductivity data allowed identification of a hopping conduction process at high temperature. The lowest temperature processes are analyzed in terms of dipole relaxation and the higher temperature features in terms of proton migration.     

水蒸气对煤粉再燃还原NO的影响

在兖州烟煤煤粉再燃还原NO的固定床反应器试验中加入不同量的水蒸汽,研究了水蒸汽对煤粉再燃还原NO的影响。结果表明,水蒸汽的加入加快了煤粉再燃还原NO的速度,但单位质量煤粉的还原效果随水蒸汽量的增加而降低,原因是水蒸汽同时也加速了煤粉的燃尽。水蒸汽加快了CO和CO2生成速度以及O2消耗速度,在挥发分为主的反应阶段促进CO2的生成更明显,而在焦炭为主的反应阶段促进CO的生成更明显,但单位质量煤粉的CO2生成量和O2消耗量均降低、CO生成量增加。煤粉再燃的燃尽时间随水蒸汽量的增加而缩短,比如当水蒸汽量为2%时,燃尽时间缩短了25.9%,当水蒸汽量为4%时,燃尽时间缩短了47.8%。在再燃区加入一定量的水蒸汽,既能改善煤粉对NO的还原效果,又能提高煤粉的燃尽率。工程应用要根据煤质特点、主燃区NO浓度、再燃煤粉比例、再燃区过量空气系数、经济性评价等因素进行试验确定最佳水蒸汽量。