Alkalization mechanism of cellulose in hydroxypropylcellulose preparation process

The role of alkali treatment of cellulose in hydroxypropylcelluloe (HPC) preparation has been studied from the viewpoint of the selective distribution of sodium hydroxide between HPC and cellulose phases. Generally it is considered to be important to prepare uniform alkali cellulose, whose calculated value of composition is C₆H₁₀O₅NaOH. x H₂O, prior to etherification of cellulose. Therefore, enough alkali to obtain alkali cellulose is used by major manufacturers of cellulose ethers. However, HPC having good solution qualities and performance properties can be prepared even from partially alkalized cellulose by using 0.2–0.4 molar sodium hydroxide per anhydroglucose unit. The results obtained from a series of experiments indicate the following mechanism for the formation of HPC. Hydroxypropylation is initiated in the alkalized portion of cellulose if such portion and propylene oxide are present together. As the hydroxypropylation proceeds, the liberated sodium hydroxide in HPC phase migrates into the cellulose phase due to the shift of distribution equilibrium of sodium hydroxide; the above tendency is enhanced by byproducts such as propyleneglycol. Some newly alkalized portions are present and hydroxypropylation follows. These processes are repeated, and then all portions of cellulose are alkalized and hydroxypropylated.     

Graft polymerization of some vinyl monomers onto alkali-treated cellulose

Treatment of cellulose by different concentrations of alkali, namely, 5–30% NaOH, changed its fine structure and transferred cellulose I into cellulose II. The decreased crystallinity due to alkali treatment and the transformation of cellulose I into cellulose II lowered the reactivity of cellulose toward the grafting polymerization reactions. Compactness of the structure as a result of the treatment of cellulose with 5% sodium hydroxide concentration decreased the rate of the grafting reaction and the grafting yield. On the other hand, such treatment of cellulose with different concentrations of alkali increased the rate of ceric consumption, i.e., increased the rate of oxidation of cellulose. Thus, the termination reaction of the grafting polymerization process may occur as a result of such oxidation and because of the increase of the active sites onto cellulose, leading to a decrease of the grafting yields and rate of grafting polymerization reaction by using the free-radical grafting process. The use of the ionic-xanthate method of grafting polyvinyl- and polyallyl-on alkali-treated cellulose shows an increase of grafting efficiency and grafting yields. Maximum grafting efficiency and yields were achieved when cellulose was treated with sodium hydroxide concentration below 15%, and maximum crystallinity indices were obtained. Using 15–25% sodium hydroxide lowered the indices of crystallinity, and lower grafting yields and grafting efficiency were achieved. Thus, transformation of cellulose I into cellulose II decreased the reactivity of these treated celluloses toward graft polymerization reactions by the use of the ionic-xanthate method. In our opinion, termination reactions may also occur and affect the results.     

Simultaneous SAXS and WAXS investigations of changes in native cellulose fiber microstructure on swelling in aqueous sodium hydroxide

Simultaneous small‐ and wide‐angle X‐ray scattering was used to follow changes in the microstructure of native cellulose (cellulose I) fibers during conversion to sodium cellulose I (Na‐cellulose I) by aqueous sodium hydroxide. Wide‐angle X‐ray scattering was used to monitor the extent of conversion, while small‐angle X‐ray scattering was used to explore what occurs at the higher structural levels of the elementary fibrils, microfibrils, and interfibrillar voids. Native cellulose fibers, swollen in either water or aqueous sodium hydroxide, exhibited an increase in the void volume fraction and a decrease in the void cross‐section size, as the swelling agent separated elementary fibrils, opening up the structure, and creating many small voids. After conversion of swollen native cellulose to sodium cellulose I, the void volume fraction and average void cross‐section dimensions both increased. During conversion from dry cellulose I fibers to swollen Na‐cellulose I fibers, the void cross‐section dimensions went through a minimum, suggesting that the void structure may go via an intermediate similar to the water swollen structure of cellulose I. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1209–1218, 2002     

Mercerization of cellulose. II. Alkali–cellulose intermediates and a possible mercerization mechanism

Continued study of the five crystalline Na–celluloses, previously shown to occur as intermediates during the mercerization of cellulose and exhibiting two types of crystallographic fiber repeats, further indicates that they fall into three classes based on their unit cells and NaOH contents. In one class are Na–celluloses I and III, both containing up to 34% NaOH; in the second class are Na–celluloses IIA and IIB, marked by ca.15 Å fiber repeat and containing up to 65% NaOH; and in the third class is Na–cellulose IV which is likely to be a hydrated form of cellulose II. Na–cellulose I was found to be the common first alkali–cellulose structure produced in the NaOH treatment of both cellulose I and cellulose II. Further study of this conversion step suggested a mercerization mechanism in which the alkali begins the conversion of cellulose to Na–cellulose I in the amorphous parts of the fiber. The conversion of the parallel-chain cellulose I structure to an antiparallel one is likely to occur already in this first step.     

The effect of crosslinking on the swelling of cotton in solutions of sodium hydroxide and cadoxen

This paper describes the effects of prior crosslinking in dimethylol ethyleneurea (DMEU) on the swelling of cotton fiber in aqueous solutions of sodium hydroxide and in cadoxen solutions (solutions of cadmium oxide in mixtures of ethylenediamine and water). The degree of swelling in the weaker swelling solutions is markedly reduced by the crosslinking, but in the stronger solutions (particularly in concentrated sodium hydroxide) the effect of prior crosslinking is only small; this is accounted for in terms of a fibril-tearing mechanism in these stronger solutions. Crosslinking cotton reduces the mercerizing effect of strong alkali solutions (i.e., the disordering and the cellulose I → II lattice change), and also reduces the solubility of the fiber in solutions of cadoxen and cuprammonium hydroxide.     

NaOH/urea aqueous solutions improving properties of regenerated‐cellulosic fabrics

The application of sodium hydroxide and sodium hydroxide containing urea solutions has been utilized for regenerated‐cellulosic material activation. The treatments resulted in the reorganization of cellulose fibers, hence accessibility and reactivity. In this study, sodium hydroxide–urea solutions were applied to lyocell and viscose‐knitted fabrics as finishing treatment to improve the accessibility and physical properties of textiles. Besides the mixtures, different concentrations of sole sodium hydroxide and sole urea treatment were applied. The different concentrations of urea, sodium hydroxide, and sodium hydroxide–urea mixtures were used with small increment to detect suitable concentrations and mixture ratios applied for fabrics modification. The results showed the effectiveness of applying the mixture solutions of alkali–urea particularly to CV‐knitted fabrics for improving pilling behavior, whereas for CLY fabrics, the standard alkali solutions showed the best pilling performance. The utilization of urea and sodium hydroxide–urea mixture played an important role for regenerated‐cellulosic fabrics where high alkali concentrations is not preferred to avoid fabric damages and where a mixture system could inhibit some of these aspects. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Flow birefringence and viscosity of cellulose solutions in semi-dilute regime

An attempt was made to study the flow birefringence and the viscosity of the systems of cellulose in aqueous sodium hydroxide and cadoxen solutions. For this purpose alkali-soluble cellulose samples with crystal form I (simply denoted as cellulose I sample), prepared from conifer wood pulp by the steam-explosion method, and alkali-soluble cellulose samples with crystal form of cellulose II (cellulose II sample), regenerated from cuprammonium cellulose solution under specific conditions, were used. The extinction angle χ of aqueous alkali solutions of the cellulose I sample is significantly less shear rate (γ) dependent as compared with that of the cellulose II sample. In the latter system the χ versus γ relations for a given cellulose sample shifted to the higher γ side with decrease in the average molecular weight. The viscosity of the cellulose II sample in aqueous sodium hydroxide solutions is approximately twice that of the cellulose I sample in the same solvent if compared at the same molecular weight, same concentration, and same temperature. The latter solution showed a non-Newtonian property at relatively smaller γ than the former solution did. Spin-lattice relaxation time T₁ (by ¹³C-NMR) of cellulose in cadoxen solution was smaller in cellulose I, suggesting the existence of intra- and intermolecular hydrogen bondings at the C₆ position of cellulose molecules in cellulose I solution. A dynamic light scattering study on cellulose in cadoxen showed that in a 5 wt % solution of cellulose I cellulose particles are dispersed with time into smaller particles and the larger particles could be excluded by ultracentrifuge and in cellulose II solutions the cellulose particles had almost the same size during storage. The above findings indicate that in 5 wt% cellulose I solutions in aqueous alkali or in cadoxen, cellulose I is not dissolved molecularly, but a supra-molecular structure of the solid is at least partly reserved in the above solutions.     

毛竹笋壳制备羧甲基纤维素

以废弃毛竹笋壳为原料,经过4次加碱法制备出了羧甲基纤维素,并通过FTIR、XRD、TGA、SEM手段对原料与产品进行了表征。实验结果表明,制备羧甲基纤维素的最佳工艺条件为精制竹笋壳5 g,氢氧化钠5 g,氯乙酸6 g,85%乙醇溶液为溶剂,第1次碱化温度和时间分别为30 ℃和90 min,加入氢氧化钠总质量的80%,后3次碱化是在醚化过程中平均加入剩余20%的碱,醚化最终温度为70 ℃,醚化总时间为3 h。在此工艺条件下,所得到的羧甲基纤维素的取代度为0.9341,黏度为35 mPa?s。     

Changes in the structure of flax cellulose induced by solutions of lithium,sodium, and potassium hydroxides

In the reaction of cellulose-containing flax material with aqueous solutions of LiOH, NaOH, and KOH, the degree of swelling, sorption of water and alkali, parameters of the crystal lattice formed by alkali cellulose, degree of removal of lignin, and change in the degree of polymerization are a function of the type of cation. For the sorption characteristics and crystal lattice parameters of alkali cellulose, this dependence is determined by the change in the structure of the first and second hydrate shells of the cations. Despite the important differences in the degree of swelling, crystal lattice parameters of alkali cellulose, and degree of removal of lignin, the changes in the crystal structure of the cellulose related to the transition from crystalline modification I to modification II under the effect of the three different bases are similar and take place in approximately the same concentration region.Translated from Khimicheskie Volokna, No. 6, pp. 15–19, November–December, 2004.     

Swelling of cotton fibers in ethylenediamine–morpholine mixtures

Cotton fibers were treated with anhydrous mixtures of ethylenediamine and morpholine of varying proportions to study the changes in accessibility (X-ray crystallinity index, swelling by propanol-2 retention, formylaiton, and dyeability) as well as lattice conversions from cellulose I to cellulose II and cellulose III. Positive synergistic influence of the highest order was noticed at 70:30 (molar proportion 3:1) ethylenediamine–morpholine mixture as judged from accessibility and lattice conversion from cellulose I to cellulose II. The same critical proportion was found to give the highest order of negative synergistic effect in the lattice conversion of cellulose I into cellulose III. These opposing trends have been explained on the basis of the different mechanisms associated with the lattice conversions of cellulose I into cellulose II and cellulose III.     

Variables affecting the methylation reactions of cellulose

Solubility of methyl cellulose (MC) depends on the degree of substitution (DS), the average degree of polymerization (DP), and the distribution of methoxyl groups. Of these, the DS appears to be the most important. The DS of the MC depends on the conditions of preparation. The conditions studied in this work revealed that the DS of the MC increased as the concentration of sodium hydroxide increased from 10 to 50%. This result is attributed to the increase in the extent of formation of alkali cellulose II as a result of the increase in the alkali concentration and hence the increase of the DS of the MC. Decreasing both the ratio of dimethyl sulfate: cellulose and the liquor ratio increased the DS. High DS was achieved within a period of 2 and 3 h. However, the DS increased as the time increased. The decrease of the DS as the liquor ratio increased may be attributed to the sol–gel transition due to the interaction of the hydrophobic methoxyl groups within the polymer chains. To reveal the effect of the thermal sol–gel transition, the reaction was carried out in nonaqueous medium and the results obtained showed an increase of the DS with the increase of the solvent ratio until a maximum. This result may be contributed to the breakdown of the hydrogen bonding in the presence of solvents that transfer the reaction medium to the sol-form and hence more methylating reaction takes place. The degree of the solvation of the methyl groups into the solvents also plays a role. © 1994 John Wiley & Sons, Inc.     

Enhancement of thermal stability associated with the chemical treatment of bacterial (Gluconacetobacter xylinus) cellulose

Bacterial cellulose produced by Gluconacetobacter xylinus was treated with sodium carbonate (Na₂CO₃) and sodium hydroxide (NaOH) to remove entrapped noncellulosic materials. Fourier transform infrared (FTIR) spectroscopy has been used to investigate the effect of alkali on the chemical structure of bacterial cellulose. The changes in the crystalline nature of these membranes were analyzed using X‐ray diffraction (XRD) technique. The morphology and the removal of noncellulosic impurities followed by alkali treatment were studied using scanning electron microscopy (SEM) and energy dispersive X‐ray spectrometry (EDS). The enhanced thermal stability of bacterial cellulose was evident from thermogravimetric analysis (TGA). Further, the alkali treatments resulted in relatively pure form of cellulose, which finds application in various spheres. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Reversible crosslinking in cellulose. VI. Formation of sulfonium derivatives by the reaction of cellulose β-mercaptoethylaminocarboxylate with methyl iodide

The reaction of methyl iodide with cellulose β-mercaptoethylaminocarboxylate (RDTC) made from cotton was investigated. The product was found to contain dimethyl sulfonium groups in addition to S-methyl groups, with accompanying hydrolytic cleavage of some of urethane linkages. The iodide counterions could be easily exchanged with hydroxide and chloride ions. The dyeabilty of RDTC and its sulfonium derivatives toward Direct Sky Blue A was studied. The equilibrium uptake of the dye by RDTC decreased with increasing sulfur content, while the uptake by the sulfonium derivatives was higher than that of control cotton and increased with increasing sulfonium content. The counterions did not affect the dyeability. The dye adsorbed onto the sulfonium derivatives was very fast against solvent extraction, and could be extracted only with Cadoxen containing 0.5% sodium hydroxide. The equilibrium uptake of the dye was much more than the amount calculated on basis of the 1 : 1 ionic bonding between the sulfonic acid group in the dye molecule and the sulfonium group in the modified cotton. The spatial effect in the dye–sulfonium bonding is discussed.     

Effect of the Loosening of Wood Texture on the Mercerization of Cellulose in Wood

When wood was treated with 23% aqueous sodium hydroxide followed by washing with water and drying, no lattice conversion of cellulose was observed under the experimental conditions employed. On the other hand, wood subjected to a pretreatment that results in the loosening of its morphological texture, upon mercerization, showed a varying degree of lattice conversion. The explosion process and the TFA (trifluoroacetic acid) treatment were used to achieve the loosening of wood texture. The lattice conversion of cellulose was studied by X-ray diffractograms. The extent of lattice conversion was found to depend on the conditions of the pretreatment used to achieve the loosening of wood texture. The extent of lattice conversion increased with an increase in the explosion temperature and the time at temperature, within the range of these experiments. Increased duration of TFA pretreatment, at a particular temperature, resulted in a higher degree of lattice conversion. These observed facts have been ascribed to the extent of loosening of the morphological texture of wood, which allows comparatively free swelling of cellulose in alkali.     

Mercerization of cellulose. IV. Mechanism of mercerization and crystallite sizes

Using the Guinier plot, the 200 reflection profile of ramie cellulose I was resolved into two components. One component represented a crystallite size of ～ 20 Å, and the other component represented a crystallite size of ～ 61 Å. These components were followed during the conversion of cellulose I to Na–cellulose I, in order to estimate the contribution of the smaller crystallites to the early rapid stage of conversion. From the intensity ratio of the two components, it appears that during the first ～ 20% conversion the formation of Na–cellulose I occurs mainly in the oriented amorphous regions of the fiber. Following this, up to ～ 65% conversion the destruction and transformation of small crystallites takes place. The small average size of the ～ 20 Å crystallites, as well as their relatively high reactivity to alkali, appear to facilitate the conversion of the parallel-chain cellulose I structure to an antiparallel one.     

相转移催化法纤维素羧甲基化工艺研究

研究了以棉短绒（精制棉）为原料、氯乙酸为醚化剂,合成羧甲基纤维素钠。探索了纤维素在碱化、醚化阶段的反应机理。考察了渗透剂、氢氧化钠溶液浓度及其用量、醚化时间4种因素对所合成羧甲基纤维素钠的水溶液粘度的影响。通过检测醚化后羧甲基纤维素钠的取代度和2%水溶液的粘度,确定了最佳工艺条件：碱化温度为30~35℃,碱化时间为50 min,醚化温度为70~75℃,醚化时间为70 min,碱溶液浓度为25%,渗透剂添加量为3%。此条件下制备的羧甲基纤维素钠,水溶液浓度为2%时,粘度达到600~650 MPa.s,取代度为0.530~0.560。     

Preparation and application of acrylonitrile‐grafted cyanoethyl cellulose for the removal of copper (II) ions

Cyanoethyl cellulose (CE‐Cell) with two different degrees of substitution of 0.37 and 0.60 were prepared from cotton linter. The ionic‐xanthate method was used to graft the acrylonitrile onto CE‐Cell to form acrylonitrile‐grafted cyanoethyl cellulose (GCE‐Cell). The conditions of grafting such as sodium hydroxide concentration, grafting time, monomer concentration, and temperature were optimized. The hydrolyzed CE‐Cell and GCE‐Cell were applied for the adsorption of copper (II) ions from aqueous solution. IR spectroscopy was also used for further evaluation of CE‐Cell and GCE‐Cell. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 329–334, 2006     

Fractional turbidimetric analysis of the molar substitution of hydroxyethyl cellulose

High quality packaging films from hydroxyethyl cellulose of low degree of substitution (DS) are being produced commercially in this country and abroad. Increasing demand for this and a variety of other applications requires a rapid and simple production control method for determining hydroxyethyl substitution of cellulose. None of the known analytical methods fulfills these requirements. The present paper describes a method which is based on the relationship between the solubility and the molar hydroxyethyl substitution of hydroxyethyl cellulose. A washed and dried sample of hydroxyethyl cellulose is dissolved in 7% aqueous sodium hydroxide. Methyl alcohol, a nonsolvent, is used to precipitate a fraction of the sample. The turbidity of the equilibrium system is determined and optical density readings are related to molar substitution. The method is most useful in low DS ranges of 2–8% EtO but is susceptile to broader application through adjustment of the composition of the solvent–nonsolvent mixture. Relatively large variations in DP can be tolerated. The molar substitution level of an hydroxyethyl cellulose sample can be obtained in 40 min. by this method, making it a practical production control technique.     

Preparation and properties of chemical cellulose from ascidian tunic and their regenerated cellulose fibers

Chemical cellulose (dissolving pulp) was prepared from ascidian tunic by modified paper‐pulp process (prehydrolysis with acidic aqueous solution of H₂SO₄, digestion with alkali aqueous solution of NaOH/Na₂S, bleaching with aqueous NaOCl solution, and washing with acetone/water). The α‐ cellulose content and the degree of polymerization (DPw) of the chemical cellulose was about 98 wt % and 918, respectively. The Japanese Industrial Standard (JIS) whiteness of the chemical cellulose was about 98%. From the X‐ray diffraction patterns and ¹³C‐NMR spectrum, it was found that the chemical cellulose obtained here has cellulose Iβ crystal structure. A new regenerated cellulose fiber was prepared from the chemical cellulose by dry–wet spinning using N‐methylmorpholine‐ N‐oxide (NMMO)/water (87/13 wt %) as solvent. The new regenerated cellulose fiber prepared in this study has a higher ratio of wet‐to‐dry strength (<0.97) than commercially regenerated cellulose fibers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1634–1643, 2002.     

Effects of mercerization of bamboo strips on mechanical properties of unidirectional bamboo–novolac composites

Bamboo strip reinforced novolac resin composites were fabricated using bamboo strips that were treated with varying concentrations of sodium hydroxide solution at a constant filler loading (25%). The mechanical properties of various composites (flexural modulus, toughness, tensile strength, and elastic modulus) were determined. The physical characteristics, such as the wetting ability of the alkali treated reinforcements, were increased because of alkali treatment. With increasing concentrations of alkali, a higher percent loss in weight occurred. The mechanical properties were increased with increasing mercerizing strength. Maximum improvement in properties was achieved with 16–20% of caustic treated reinforcements. An FTIR study indicated aryl alkyl ether formation with ? OH groups of cellulose and methylol groups of novolac resin. Beyond 20% there was degradation in all strength properties because of the failure in the mechanical properties of the reinforcements. A correlation was found to exist between the mechanical properties and the developed morphology. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100:238–244, 2006