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.     

天然竹纤维的固态核磁共振谱表征

利用固态核磁共振碳谱分析研究了天然竹纤维的结晶结构,并与常规的天然纤维素纤维苎麻、亚麻和棉纤维进行了比较。研究表明竹纤维的结晶度、晶粒尺寸与苎麻相似,大于棉纤维和亚麻纤维。利用13C NMR分析计算出了竹纤维中纤维素的晶型含量,结果显示,竹纤维的晶型与棉纤维、苎麻和亚麻相似,纤维素Ⅰβ占优势。利用核磁共振谱计算的几种纤维素纤维的结晶度和晶粒尺寸小于利用X射线衍射计算的结果,只有对于高结晶度的纤维如竹纤维和苎麻偏差才比较小,主要原因在于NMR分析对小范围的有序更为敏感,只有晶区内的材料才能看作结晶区。     

Irradiation of cotton celluloses I and II in presence of organic solvents

The infrared spectra and dielectric properties of cotton celluloses I and II, γ-irradiated in the presence of organic solvents have been investigated. The obtained data showed that irradiation of cotton celluloses I and II in organic solvents helps in oxidation of these celluloses and increases their dielectric constant. Examination of the infrared spectra and X-ray diffraction (XRD) patterns revealed that irradiation of cotton celluloses I and II in organic solvents produces considerable changes in their crystallinity. It was found that the highest values of crystallinity and dielectric constant are obtained when the samples are irradiated in chloroform whereas the lowest values are obtained when the samples are irradiated in toluene.     

Cellulose crystallite sizes in diploid and tetraploid native cotton

Cellulose crystallite sizes in directions perpendicular to (101), (101 ), and (002) planes, have been estimated from X-ray powder diffraction patterns. The diffraction peaks were resolved using the FIT X-ray diffraction data analysis program (written by SOCABIM, Siemens DIFFRAC AT Software System, Siemens, Germany). The complete data for all the three equatorial planes was analyzed for 2θ, d values, full width at half-maximum (FWHM), and the normalized area under the three diffraction peaks, for seven cotton cultivars grown at four different locations in India in different crop years. The mean crystallite sizes were determined using the Scherrer equation. The reference standard included degummed and purified ramie fibers for relative crystallinity estimation in cotton cultivars. It has been observed that, though the computed crystallite sizes corresponding to (101), (101 ), and (002) planes vary within individual varieties with location and year of growth, the combined average crystallite size corresponding to (101) and (101 ) planes taken together for individual varieties from all locations and crop years is close to the combined average crystallite size corresponding to the (002) planes, irrespective of the species of cotton. The values of the average relative crystallinity with respect to highly oriented degummed and purified ramie fibers of individual varieties from all locations and crop years do not significantly vary between varieties and species of cotton. It is visualized that variations in crystallite sizes arise as a result of the differences in the amount of cellulose synthesized within fibers of individual varieties and their disposition within the matrix of their developing fibers. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 2107–2112, 1998     

Mercerization of cellulose. I. X-ray diffraction evidence for intermediate structures

A study of the mercerization of ramie cellulose was begun using x-ray diffraction, in order to determine the types of alkali–cellulose structures that occur as intermediates during the conversion of cellulose I to cellulose II. A total of five unique alkali–celluloses (Na–celluloses) could be generated reproducibly, depending only on the alkali concentration used. The reproducibility was enhanced by slowing down the mercerization process, by laterally compressing the fibers in capillary tubes. The five structures, named Na–celluloses I, IIA, IIB, III, and IV, were of two types based on their crystallographic fiber repeats. The first type was represented by Na–celluloses I, III, and IV, all exhibiting a ca. 10 Å repeat. The second type was represented by Na–celluloses IIA and IIB, with a ca. 15 Å repeat. The latter structures are possibly based on a threefold helical chain conformation, which has not been seen in crystalline celluloses. All Na–cellulose structures exhibited a reasonable degree of crystallinity and high degree of fibrous orientation. They formed a definite interconversion scheme, marked by crystalline-to-crystalline phase transformations.     

Evaluation of microcrystalline cellulose. I. Changes in ultrastructural characteristics during preliminary acid hydrolysis

Several microcrystalline celluloses prepared from viscose staple, bagasse, ramie, and cotton were evaluated by viscosimetry, X-ray diffraction and scanning and transmission electron microscopies. The changes in crystallinity, size of crystallites, grain-size distribution, morphological features, and degree of polymerization were found to be dependent on and greatly limited by the polymorphic conformations of cellulose. These changes were more conspicuous in cellulose II than in cellulose I. The coexistence of a two-phase system still remains in all the specimens of microcrystalline cellulose powders. Combining the findings with respect to the extent of the changes in the size of crystallites, it appears inevitable that recrystallization in some of the defective crystallites and degradation in the disordered areas of cellulose occurs simultaneously in the preliminary hydrolysis process during the production of microcrystalline cellulose. © 1996 John Wiley & Sons, Inc.     

Cerium-initiated grafting of acrylonitrile onto cellulosic materials

Grafting of acrylonitrile onto native cotton, swollen cotton, viscose, ramie, and hydrocellulose was studied with tetravalent cerium as initiator. The effect of temperature on the graft yields is examined. With ceric ammonium nitrate the grafting yields are found to be higher at 20 and 40 than at 60°C. Ceric ammonium sulfate, on the other hand, produces more grafting at 60 than at 20 and 40°C. The consumption of ceric ions is less, whereas the per cent graft yields are higher for the swollen cottons and viscose than for native cotton. Graft yields are shown to be related to substrate accessibility if the grafting reaction is carried out under conditions that suppress homopolymerization. Oxidation of these celluloses with Ce^IV has also been studied. It is found that more Ce^IV is consumed during grafting than during oxidation of cellulose under identical reaction conditions. Excess Ce^IV consumed in the grafting reaction has been shown to be directly related to extent of homopolymerization, which accompanies grafting. Some data on the storage stability of the free-radical activity produced by oxidation of cellulose with Ce^IV are also reported. It is observed that the cerium-oxidized samples can initiate graft poly merization even after 4–5 hr. if stored in nitrogen.     

On the degree of crystallinity in jute and mesta fibers in different states of purifications and moisture conditions

The degree of crystallinity (DC) in different moisture conditions was studied for jute and mesta holo- and α-celluloses. As in the case of raw fibers the DC was found to decrease as humidity increased, but the rate of change was diminished in the present case. The lower rate is explained on the supposition that some of the regions previously accessible to water have, after removal of lignin and hemicelluloses, assumed more ordered states and are less accessible. The DC increased as lignin and hemicelluloses were removed and tended to approach that of ramie or cotton. The crystalline structure of jute α-celluloses was also found to be similar to that of ramie or cotton.     

Disorder in cellulosic fibers

Ruland's concept of an isotropic disorder function is applied to estimate the disorder parameter and the degree of crystallinity in a few cellulosic fibers: two cottons, native ramie, and a high-tenacity rayon. The results indicate an increase in disorder without any change in crystallinity on mercerization of native celluloses. On hydrolysis, with or without a pretreatment of mercerization, the samples exhibit a higher crystallinity, disorder remaining the same as for native celluloses. A ball-milled sample of “amorphous” cellulose is still found to be fairly crystalline with the lowest disorder. On being wetted in water and oven-dried, a distorted form of cellulose II with higher crystallinity and disorder was obtained. The polynosic fiber, Tufcel, has low values for the degree of crystallinity, disorder parameter, as well as crystallite dimension. A strong dependence of the degree of crystallinity on the crystallite size, particularly the lateral, is observed.     

Effect of mercerisation and crosslinking on the dyeing properties of ramie fabric

The dyeing of ramie fabrics crosslinked with 1,2,3,4-butanetetracarboxylic acid has been studied using a typical direct dye CI Direct Red 81. Adsorption time curves from finite baths of untreated ramie, tension-mercerised ramie, slack-mercerised ramie and cotton fabrics have been compared. It has been found that mercerisation improved the equilibrium adsorption and dyeing rate, while it reduced the maximum dye adsorption and equilibrium constant on ramie fabric. Crosslinking with butanetetracarboxylic acid decreased most of these parameters related to the dyeing profile, although the activation energy of dyeing was increased. A pore model approach has been used to explain the changes in dyeing properties arising from the crosslinking of ramie using butanetetracarboxylic acid.     

Graft copolymerization of vinyl monomers onto modified cotton. IX. Hydrogen peroxide–thiourea dioxide redox system induced grafting of 2-methyl-5-vinylpyridine onto oxidized celluloses

Cotton cellulose was independently oxidized with potassium periodate, potassium dichromate-sulfuric acid, and potassium dichromate–oxalic acid, and the resulting oxidized celluloses were further modified by treatment with chlorous acid or sodium borohydride. The various modified celluloses so obtained were grafted with 2-methyl-5-vinylpyridine using a thiourea–dioxide–H₂O₂ redox system. It was found that the initiation characteristics of the cellulose samples vary widely with the oxidizing agent used. Further modification of the oxidized celluloses by treating them with chlorous acid enhances considerably their susceptibility toward grafting. The opposite holds true when these oxidized celluloses were modified by sodium borohydride treatment. Excluding thiourea dioxide from the polymerization system offsets grafting onto cotton cellulose while considerable grafting takes place on the various oxidized celluloses and their further modified samples. The work was also extended to study the factors which affect the graft uptake, homopolymer formation, and total conversion. In addition, the reactions involved in initiation of grafting were elucidated.     

Dyeing of chemically modified cellulose. IV. Dyeing of oxidized celluloses with some reactive and direct dyes

Oxidation of cotton cellulose with potassium periodate, potassium dichromate-sulfuric acid, and potassium dichromate-oxalic acid results in creation of variable amounts of acidic and reducing groups along the cellulose molecule, being dependent upon the type of oxidizing agent used. Such groups were found to have a profound effect on the acceptability of cellulose for reactive and direct dyes. The rate and extent of dye uptake for the oxidized celluloses were significantly lower than those of the unoxidized cellulose. While presence of the acidic groups in cellulose molecules induces a negative environment thereby making approach of the dye anions to the cellulose difficult, presence of the reducing groups lowers the magnitude of cellulose reactivity as well as decreasing its adsorptive power. Further modification of the oxidized celluloses via either borohydride or chlorous acid treatment brought about modified celluloses the dyeability of which confirms the inhibiting effect of the acidic and reducing groups of those oxidized celluloses on the rate and extent of dyeing with reactive and direct dyes.     

苎麻/棉混纺毛巾染整工艺探讨

苎麻／棉混纺毛巾经一浴法煮漂后，进行抛光酶处理，用活性染料染色，再进行柔软整理。给出了溢流染整加工工艺的技术条件。     

Cellulose membranes for reverse osmosis Part I. RO cellulose acetate membranes including a composite with polypropylene

With the aim of obtaining RO membranes for brackish water desalination from purified celluloses (cotton linters and bleached bagasse pulp), two reactions (heterogeneous and homogeneous) were applied for the synthesis of cellulose acetate (CA). The efficiency of the membranes was measured and compared with those prepared from purchased CA and prepared CA by acetylation of imported high-grade viscose wood pulp. The effect of blending CA with polypropylene (PP), on the efficiency of the prepared RO membranes was also studied. Results showed that the method of preparation of CA plays a profound effect on the salt rejection and water flux of the RO membranes. The efficiencies of RO membranes formed from heterogeneously acetylated celluloses are higher than those prepared from homogeneous ones. Blending the acetylated cellulose with 9% PP wastes improves the efficiency of membranes prepared from the homogeneously acetylated celluloses.     

Modification of the surface characteristics of cotton by the introduction of anionic groups,and the mechanism of ion binding

The introduction of carboxymethyl, phosphate and sulfate groups into cotton cellulose considerably modifies the capacity of the cellulose to bind cationic systems. The ion-binding characteristics of these anionic derivatives have been quantitatively studied using the cationic dye methylene blue. Diffuse reflectance spectral measurements demonstrate that two types of sulfated and phosphorylated celluloses can be produced, which differ considerably in the interaction of their anionic groups with the dye. Anionic systems are, in contrast, repelled by the anionic substituents. In this way the resistance of the cotton cellulose to wet soiling can be considerably increased. The mechanism of ion binding to anionic celluloses has been examined and the information utilized to predict methods of modifying the surface characteristics of cotton cellulosee. One of eight papers being published from the Symposium “Surface Active Agents in the Textile Industry, presented at the AOCS Meeting, New Orleans, April 1970.     

X‐ray diffraction methods in the study of the effect of microwave heating on the transformation of cellulose I into cellulose II during mercerization

X‐ray diffraction (XRD) techniques were used in the study of the effect of microwave (MW) heating on the structural properties of cotton celluloses I and II and on the mercerization mechanism of cotton fibers. Samples of celluloses I and II were MW heated at 900 W for different times ranging from 10 to 40 min. The obtained data revealed that MW heating of cellulose II in opened glass tubes produces no significant effects on the resolution of its XRD patterns, whereas the most evident effects occur when cotton fibers (cellulose I) are heated in opened tubes at 900 W for 10 and 20 min. Also, mixtures of cotton fibers and aqueous solution of NaOH with different concentrations were exposed to MW radiation for different times and different powers. It was found that MW heating has no considerable effects on the mechanism of transformation of cellulose I into cellulose II during mercerization. On the other hand, MW heating of cotton fibers during mercerization reduces the values of concentration of NaOH in the aqueous solution and the time of treatment that are needed for the complete transformation of cellulose lattice type I into cellulose lattice type II without any heating. Also it was found that the magnitude of reductions depends on the applied power. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Modification of the fine structure of cellulose by halogen and heat treatments

Treatment of various celluloses such as cotton, sulphite, and sulphate pulp with bromine water brings about profound changes in the fine structure of the fiber. Depending on the conditions of the treatment and on the nature of the cellulose, increases or decreases in the accessibility of the cellulose are observed, indicating crystallization and decrystallization processes. In the case of bleached sulphate pulp, similarly to rayon previously studied, an initial decrystallization proceeds the crystallization step. These changes were determined by the IR method, which was correlated previously to the bromine accessibility method. They are accompanied by highly significant changes in moisture absorption. The crystallization proceeds according to first-order kinetics with respect to the concentration of the less-ordered regions (LOR) of the cellulose. The rates of crystallization for the various celluloses varied in a range of 4 orders of magnitude. The activation energies of the bromide induced crystallization were found for all celluloses to be in the range of 10–15 kcal/mol, as compared to 30–40 kcal/mol obtained upon crystallizing the same celluloses by heating in the temperature range of 180–200°C. These values correspond to those of solvent and thermal crystallizations of poly(ethylene terephthalate), indicating the similarity between the crystallization mechanisms of the two polymers.     

Electron diffraction technique for the determination of cellulose crystallinity

An electron-microscopic diffraction technique has been described to record with ease diffraction patterns of cotton cellulose with 3–5 sec exposure time, which is suited to determined the crystallinity of cellulose. The % crystallinity index for cotton and ramie determined by this technique amounted to 81% and 85%, respectively.     

Enzymatic hydrolysis of cotton wastes. Effect of γ-ray pretreatments

Textile cotton wastes were irradiated with γ-rays at different doses and solubilized with 10% NaOH solutions. The regenerated products underwent enzymatic hydrolysis and their degradation pattern was compared with that of the cotton celluloses untreated or treated only with γ-rays. The different samples were characterized by measurements of X-ray diffraction, degree of polymerization, moisture regain and water retention. The structural and morphological modifications induced by the pretreatments were correlated with the variations of kinetic parameters, particularly the V_max/K_m ratio, defined as specificity constant. Only the combination of irradiation with dissolution pretreatments gave a considerable increase of hydrolysis reaction effectiveness.     

Photodegradation of oxidized cotton cellulose

Different functional groups were systematically introduced into cotton cellulose and their effect on the stability of cotton toward photochemical degradation was examined. First, the cotton was progressively oxidized with sodium metaperiodate up to an oxygen consumption of 2.45 atom per 100 anhydroglucose units (agu) to form 2,3-dialdehyde cellulose. These products were reduced with potassium borohydride to obtain 2,3-dialcohol cellulose or were oxidized with sodium chlorite to obtain 2,3-dicarboxyl cellulose. The chemical modifications of the cellulose structure caused a drop in tensile strength of 34% for the dialdehyde of 2.45 oxygen consumption per 100 agu compared to 27% and 37% in the case of the dialcohol and the dicarboxyl celluloses, respectively. Upon irradiation with UV light, the breaking strengths of the dialcohol and the dicarboxyl celluloses were generally higher up to an oxygen consumption of 0.63 per 100 agu when compared to the dialdehyde and then fell more drastically. The tensile data of the exposed oxycelluloses correlated well with the reciprocal of their intrinsic viscosities (R² = 0.89). The primary alcohol groups appeared to accelerate the progress of the photochemical degradation. The photochemical effects of the carboxyl groups could not be differentiated from the autohydrolysis to which dicarboxyl cellulose is susceptible. No indication of a change in morphology was detected for any of the treatment types. © 1993 John Wiley & Sons, Inc.