Mercerization and acid hydrolysis of bacterial cellulose

Structural changes in never- dried, disintegrated bacteria l cellulose by treatment with aqueous NaOH were examined by electron microscopy, X-ray diffractometry and acid hydrolysis behaviour and compared with those of cotton cellulose. The microfibril kept its fibrillar morphology after treatment with NaOH solutions of less than 9% (w/w), but changed into irregular aggregates when treated with NaOH above 12% (w/w), corresponding to the crystal conversion to cellulose II. The crystallinity of the resulting cellulose II was very low after a brief alkali treatment, but was increased significantly by elongated treatment (up to 10 days). In contrast, cotton cellulose was converted to cellulose II of fairly high crystallinity by alkali treatment of as little as 3 min duration, and the crystallinity did not change with longer treatments. The leveling-off degree of polymerization (LODP) of bacterial cellulose was decreased from 150 to 50 by 18% (w/w) NaOH treatment, while that of cotton linter decreased from 260 to 70. These characteristic differences between cotton linter cellulose and bacterial cellulose can be ascribed to a basic difference in microfibrillar organization in these materials: the microfibrils in cotton cellulose are in close contact with neighbouring microfibrils having opposite polarity, and in bacterial cellulose are isolated from each other and require chain folding to form the antiparallel cellulose II crystal     

Hydrogen bonding on accessible surfaces of cellulose from various sources and relationship to order within crystalline regions

Celluloses from a variety of common sources were analyzed for availabilities of O(2)H, O(3)H, and O(6)H in order to estimate the extent of hydrogen bonding on accessible fibrillar surfaces. Celluloses from flax, ramie, sisal, and wood (both cellulose I and II from wood) together with liquid NH₃-swollen cotton and NaOH-swollen cotton (cellulose II) had relative availabilities similar to those of native cotton. Celluloses from Valonia centricosa and in rayon samples stood apart from each other and from the “cotton family.” The difference between Valonia and cotton celluloses appears to result, in addition to the accepted smaller, less perfect crystallites in cotton, from an O(2)H hydrogen bond which is likely the intramolecular bond between O(2)H and O(6′)H that is present in Valonia and absent in cotton. Rayon samples also showed evidence of similar bonds involving O(2)H on accessible surfaces. Since the regenerated rayons had relative availabilities different from those of mercerized cotton and wood cellulose samples, it is proposed that chain packing arrangements are not the same in these two types of cellulose II.     

Kinetics of the reverse Diels-Alder reaction of dicyclopentadienecarboxylate groups on cotton cellulose

Cotton cellulose in the form of fabric has been esterified with dicyclopentadienecarboxylic acid to a degree of substitution of 0.44. The kinetics of the reverse Diels-Alder reactions of the dicyclopentadienyl groups of the resulting cellulose ester in the presence of trapping agents and of swelling and nonswelling liquids have been measured with the differential scanning calorimeter. Fiber width measurements indicate that the esterified cotton fibers are swollen in the presence of the trapping agents dibutyl maleate, N-phenylamaleimide, and N-phenylmaleimide in tetraglyme solution, and in the presence of the nonreactive swelling agents tetraglyme and glycerol. The activation parameters for the dissociations in the swollen fibers are: E_a = 28–33 kcal/mole and ΔS^* = ?5 to +5 e.u. These kinetic parameters are similar to those previously found for the dissociation of methyl dicyclopentadienecarboxylate in solution. Fiber width measurements indicate that the esterified cotton fibers are collapsed in the dry state and in the presence of paraffin oil, deposited Carbowax 6000, or deposited glyceryl tristearate. The activation parameters for the dissociations in the collapsed fibers are E_a = 18–24 kcal/mole and ΔS^* = ?20 to ?30 e.u. The kinetics are discussed in terms of the state of the cellulose matrix in the swollen and in the collapsed fibers.     

Investigation into the removal of an easy-care crosslinking agent from cotton and the subsequent regeneration of lyocell-type fibres

Dimethylol dihydroxyethylene urea (DMDHEU)-treated cotton fabrics were treated with alkali or alternatively acid followed by alkali for increasing time periods, and their effectiveness in removing the crosslinking agent was investigated by surface (X-ray photoelectron spectroscopy) analysis, bulk analysis, crease recovery angle performance and solubility in specific solvents. The cellulose yield after the chemical stripping processes was established and the effect of the acid and alkali treatments on the degree of polymerisation of the resultant cellulose determined. Surface and bulk analyses and solubility tests suggested that alkali alone could not remove the DMDHEU from the crease-resist-treated cotton fabric. However, a sequential acid/alkali treatment effectively removed the easy-care finish from the cotton fabric and produced a commercially viable yield of cellulose.     

Treatment in Swelling Solutions Modifying Cellulose Fiber Reactivity – Part 2: Accessibility and Reactivity

The reorganization of cellulose fibers by swelling treatments in alkali solutions results in numerous changes to fiber structure, causing changes of chemical reactivity in the fiber-solution heterogeneous system. An important part of the change in chemical reactivity is the change of fiber accessibility because it results in exclusion of chemicals such as reagents or catalysts from the fiber. In the second of a two-part series of papers, we examine the influence of changes in fiber accessibility and/or reactivity due to treatment in swelling solutions on the performance or behavior of substrates during and after chemical finishing treatments. Changes in fiber accessibility due to alkali treatments are visualized with fluorescence microscopy. The effect of alkali treatments on enzymatic hydrolysis and pad-dry-cure crosslinking treatments of cellulose substrates are discussed as representative examples to demonstrate the effects of swelling processes on fiber reactivity and accessibility. Model calculations indicate that a considerable redistribution of chemicals in substrates occurs during dry-cure operations resulting from molecule-specific exclusion effects. Pilling tests on lyocell knit-fabrics show the impact of preceding alkali processes on the final physical performance of textile fabric highlighting the importance of correct selection of alkali processes to achieve desired behavior.     

The effect of water on cellulose solutions in DMAc/LiCl

The solution state of cellulose in the system N,N-dimethylacetamide/lithium chloride (DMAc/LiCl) depends on various factors such as cellulose concentration, provenience (cotton, hardwood, softwood) and chemical history (pulping, pretreatment, bleaching) of cellulose, LiCl concentration, activation method, dissolution conditions (time, shaking), and water content. In particular the influencing of the latter has been intensively investigated in our present studies. Working in anhydrous conditions is not practicable for routine size exclusion chromatography (SEC) analysis. Especially in solutions diluted to SEC levels (0.9 wt% LiCl), an aggregation induced by water was observed. Depending on the time of dissolution and on the amount of water, changes in the solution state were observed. In some cases the amount of aggregates increases within a few minutes. This is reflected by a time-dependent increase in the scattering intensity and quantitatively proved by an increase in the aggregation peak in the calculated intensity distributions. With less soluble pulps, traces of water (lower than 0.01 M) can already suffice to induce and promote aggregation. To disturb a “good” stock solution, the concentration of water must be higher than 0.05 M. The aggregates formed correspond to the model of the fringed micelle.     

Hemicellulose in Dissolving Pulp and its Behaviour during its Processing to Viscose

The amount of “hemicellulose” in pulps varies according to wood species, and the pulping processes including their bleaching agents. Making viscose cellulosic and non-cellulosic material is removed during mercerisation which is the first processing step. Low molecular weight material is also formed during the reduction of the degree of polymerisation in order to fit the alkali cellulose for xanthation and dissolving, respectively. In this work commercially available dissolving pulps with respect to their behaviour during the preparation of viscose fibres shall be discussed. For these investigations a Eucalyptus sulphite and a Eucalyptus pre- hydrolysed sulphate pulps were selected.     

Infrared spectroscopy studies of the cyclic anhydride as the intermediate for the ester crosslinking of cotton cellulose by polycarboxylic acids. III. Molecular weight of a crosslinking agent

Polycarboxylic acids have been used as nonformaldehyde crosslinking agents for cotton fabrics to replace the traditional N-methylol reagents. In this research, we compared 1,2,3,4-butanetetracarboxylic acid (BTCA) with poly(maleic acid) (PMA) as crosslinking agents for cotton cellulose. BTCA and PMA have similar molecular structures with carboxyl groups bonded to their molecular backbones, and both form five-membered cyclic anhydride intermediates during a curing process. However, BTCA is a more effective crosslinking agent for cotton cellulose than PMA. This is mainly attributed to the differences in the mobility of the anhydride intermediates to access the cellulosic hydroxyl groups during a curing process. The mobility of the anhydride intermediate of PMA is reduced due to its molecular size and multiple bonding between a PMA molecule and cellulose. Consequently, more anhydride and less ester are detected on the cotton fabric treated with PMA than on the fabric treated with BTCA. The amount of the unreacted anhydride intermediate on the fabric treated with PMA is reduced whereas the amount of ester is increased when another hydroxyl-containing compound of low molecular weight is present. Thus, the infrared spectroscopy data show a clear link between the molecular weight of a polycarboxylic acid and its effectiveness for crosslinking cotton cellulose. © 1997 John Wiley & Sons, Inc.     

Flame retardant finishing of cotton fleece: part VII. Polycarboxylic acids with different numbers of functional group

In our previous research, multifunctional carboxylic acids have been used as flame retardants to reduce the flammability of cotton fleece so that the garment made of cotton fleece can pass the US mandatory requirement specified by the government regulation “Standard for the Flammability of Clothing Textiles” (16 CFR 1610). In this research, we studied and compared the effectiveness of the polycarboxylic acids having different numbers of carboxylic groups as the durable flame retardants for cotton fleece. The cotton fabrics were treated with 1,2,3,4-butanetetracarboxylic acid (BTCA), citric acid (CA), succinic acid (SUA) and malic acid (MLA). We compared the reactivity of those polycarboxylic acids to esterify cotton cellulose and their effectiveness to reduce the flammability of the cotton fleece. The data indicated that the polycarboxylic acids with higher functionalities (BTCA and CA) form more esterlinkages on cotton and are more durable to home launderings than that treated with their bifunctional counter parts (SUA and MLA, respectively). In addition, the cotton fabrics treated with BTCA and CA have higher dimensional stability and higher strength loss. All those differences can be attributed to the fact that only those acids with three or more carboxylic groups, i.e., BTCA and CA, are able to crosslink cotton cellulose whereas the bifunctional acids (SUA and MLA) only form single esterlinkage with cotton.     

Reaction pathway to CZTSe formation in CdI2

The thermal decomposition of cotton and hemp fibers was studied after mild alkaline treatments with tetramethyl-, tetraethyl- and tetrabutylammonium hydroxides with the goal of modeling the chemical activation during carbonization of cellulosic fibers. The thermal decomposition was studied by thermogravimetry/mass spectrometry and pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS). The treated samples decomposed in two temperature ranges during heating in the thermobalance. At lower temperature, tetraalkylammonium hydroxides (TAAH) ionically bonded to the cellulose molecules were decomposed; moreover, the alkaline agents initiated the partial decomposition of cellulose. Those fiber segments, which were not accessible for TAAH, decomposed at similar temperatures as the original cotton and hemp samples. It is known that quaternary ammonium hydroxides swell the cellulosic fibers; however, the results of this study proved that there was a chemical interaction between the alkaline swelling agents and cotton or hemp fibers at rather low temperatures (200–300 °C). The evolved products indicated that the alkaline chemicals reacted with the cellulose molecules and alkylated compounds were formed. This observation was confirmed by thermochemolysis experiments carried out by Py–GC/MS using tetramethylammonium hydroxide reagent. The thermochemolysis experiments under mild conditions resulted in the methylation of the glucoside units and levoglucosan, and no peeling reactions of the sugar units were observed as during strong alkaline conditions described in the literature.

     

Swelling and dissolution of cellulose, Part V: cellulose derivatives fibres in aqueous systems and ionic liquids

The swelling and dissolution mechanisms of several cellulose derivatives (nitrocellulose, cyanoethylcellulose and xanthate fibres) are studied in aqueous systems (N-methylmorpholine-N-oxide—water with various contents of water, hydroxide sodium—water) and in ionic liquids. The results are compared with the five modes describing the swelling and dissolution mechanisms of cotton and wood cellulose fibres. The mechanisms observed for the cellulose derivatives are similar to the ones of cotton and wood fibres. Swelling by ballooning is also seen with cellulose derivatives, showing that this phenomenon is linked to the fibre morphology, which can be kept after undergoing a heterogeneous derivatisation. Patrick Navard and Thomas Heinze—Members of the European Polysaccharide Network of Excellence (EPNOE),     

Studies on never-dried cotton

The differences in the porous and crystalline structure of cell walls in never-dried and nature-dried cottons have been examined by measurements of dye adsorption and desorption, centrifugal liquid retention, and decrystallization due to swelling in sodium hydroxide. Equilibrium dyeings of these two cottons have been carried out at 50 and 60°C with two direct dyes, Chlorazol Sky Blue FF and Chrysophenine G, and the adsorption isotherms obtained. The dye uptake at limiting saturation is found to be quite large for never-dried cotton as compared to nature-dried cotton, indicating a larger number of sites available to dye molecules in the former sample. However, dyeing parameters such as affinity and differential heat of dyeing are found to have lower values for never-dried cotton. This is attributed to the “frozen” structure of a large amount of water held by never-dried cotton, which retards the adsorption of dye molecules. Studies on retention of liquids (glycerol and water) by cotton by use of centrifugation techniques reveal a larger amount of pore volume in never-dried cotton than in nature-dried cotton. X-Ray studies on decrystallization of cotton by swelling in NaOH indicate that the phase transformation to cellulose II in never-dried cotton is complete at 25% (w/w) concentration of NaOH, whereas under identical swelling conditions about 10% residual, unconverted cellulose I is found in the case of nature-dried cotton. A somewhat similar anomaly is found in the dye desorption measurements. Under conditions when the dye can be completely stripped from nature-dried cotton, the never-dried cotton has been shown to retain about 50% to 80% of the adsorbed dye. These observations are attributed to irreversible pore closure during drying of never-dried cotton. Structural collapse occurring during drying of never-dried cotton, after subjecting it to solvent exchange with a large number of organic liquids, was studied by x-ray diffraction, optical microscopy, and centrifugal liquid retention techniques. It was demonstrated that the structural collapse is proportional to the polarity of the organic solvent employed in the final exchange of never-dried cotton, prior to drying. It is concluded that the structural collapse and the development of inaccessible zones in fiber during drying can be reduced if the water in never-dried cotton is exchanged with a nonpolar solvent.     

Controlled production of spruce cellulose gels using an environmentally “green” system

Stable spruce cellulose suspensions were generated in NaOH/urea aqueous solutions and used to make thermally induced gels with various swelling ratios and compressive strengths. Wood cellulose cannot be easily dissolved in water or any common organic solvent due to its high molecular weight, which largely limits its applications. Spruce cellulose was hydrolyzed by diluted sulfuric acid of various concentrations and hydrolysis times. The dissolution of these partially degraded samples was investigated in a NaOH/urea aqueous solution system considered environmentally “green.” The effects of acid hydrolysis on the structure and properties of subsequent thermally induced gels were examined using scanning electron microscopy, swelling and re-swelling experiments, and mechanical testing. The molecular weight of spruce cellulose was significantly reduced by acid hydrolysis, whereas its crystallinity slightly increased because of the removal of amorphous regions. All samples could be partially dissolved in the NaOH/urea aqueous solution and formed stable suspensions. Hydrolyzed cellulose samples with lower molecular weight exhibited a higher solubility. Rheological experiments showed these cellulose suspensions could form gels easily upon heating. A porous network structure was observed in which dissolved cellulose was physically crosslinked upon heating and then regenerated to form a three-dimensional network, where the dispersed swollen cellulose fibers filled spaces to reinforce the structure. The swelling behavior and mechanical properties of these ‘matrix-filler’ gels could be controlled by varying the mild acid hydrolysis conditions, which adjusts their degree of solubility. This research provides several opportunities for manufacturing wood cellulose based materials.     

Infrared spectroscopy studies of the cyclic anhydride as the intermediate for the ester crosslinking of cotton cellulose by polycarboxylic acids. II. Comparison of different polycarboxylic acids

Polycarboxylic acids have been used as crosslinking agents for cotton cellulose. In our previous research, we used Fourier transform infrared (FT-IR) spectroscopy to investigate the formation of five-membered cyclic anhydride intermediates on cotton fabric by different polycarboxylic acids. In this research, we found that those polycarboxylic acids capable of forming both five- and six-membered cyclic anhydrides form only five-membered cyclic anhydrides. We compared the effectiveness of the polycarboxylic acids with different molecular structures for esterifying cellulose. Those polycarboxylic acids, which have their carboxyl groups bonded to the adjacent carbons of their molecular backbones and are capable of forming five-membered cyclic anhydrides, are more effective for esterifying cellulose than those polycarboxylic acids having their carboxyl groups bonded to the alternative carbons. The only six-membered cyclic anhydride identified is the anhydride formed on the cotton fabric treated with poly(acrylic acid). © 1996 John Wiley & Sons, Inc.     

Effect of surface attachment on synthesis of bacterial cellulose

Gluconacetobacter spp. synthesize a pure form of hydrophilic cellulose that has several industrial specialty applications. Literature reports have concentrated on intensive investigation of static and agitated culture in liquid media containing high nutrient concentrations optimized for maximal cellulose production rates. The behavior of these bacteria on semisolid and solid surfaces has not been specifically addressed. The species Gluconacetobacter hansenii was examined for cellulose synthesis and colony morphology on a range of solid supports, including cotton linters, and on media thickened with agar, methyl cellulose, or gellan. The concentration and chemical structure of the thickening agent were found to be directly related to the formation of contiguous cellulose pellicules. Viability of the bacteria following freezer storage was improved when the bacteria were frozen in their cellulose pellicules. This article was authored by a contractor of the US government under contract no. DEAC05-00OR22725. Accordingly, the US government retains a nonexclusive, royalty-free license to publish or reproduce the published form of this contribution, or allow others to do so, for US government purposes.     

Acetylation of cellulose I and II studied by limiting viscosity and X-ray diffraction

When cellulose triacetates and some hydrolyzed acetates are boiled in 2.5N hydrochloric acid there is no residue. Under the same conditions cellulose is hydrolyzed, and a residue is obtained with a limiting viscosity that is related to the average length of the cellulose crystallites. These findings are combined to develop a method for studying the progress of acetylation through the amorphous portion of cellulose and into the crystallites, and to investigate the relative reactivities of cellulose I and cellulose II. Acetates were made from cotton and wood cellulose by a “fibrous” (heterogeneous) esterification involving sulfoacetic acid or perchloric acid catalyst in acetic acid-acetic anhydride; the final acetyl contents (10–41%) were attained by stopping the reaction at various points short of the triester (rather than by hydrolyzing a triester). When these acetates were boiled in 2.5N HCI they did not disappear completely, and the residues were cellulose I, indicating that cellulose acetate had been removed. With increasing acetyl the yield of residue decreased, and beyond about 33% acetyl the viscosity and x-ray measurements showed that the length and width of the crystallites decreased. However, when a nonsolvent such as toluene was added to the acetylation medium, the limiting viscosity did not change over the same acetyl range (up to 40%). Samples of varying acetyl values were taken during a regular acetylation of cotton linters in a mixer with sulfuric acid catalyst. X-ray studies of the residues obtained by boiling the acetates in 2.5N HCI revealed the presence of unreacted cellulose I even after 40% acetyl had been reached. This explains why the manufacture of cellulose esters from cellulose I requires complete esterification before they are hydrolyzed to the desired acetyl level. It was shown that there is a distinct difference between the acetylation reactivity of cellulose I and cellulose II. This indicates the importance of avoiding cellulose II formation during the refinement of cellulose for the manufacture of cellulose acetate in a process involving activation with acetic acid.     

The formation of “inverted” core-shell latexes

It has been found that when hydrophobic monomers are polymerized in the presence of highly hydrophilic polymer seed particles, the second-stage hydrophobic polymers form cores surrounded by the first-stage hydrophilic polymers, resulting in “inverted” core-shell latexes. The formation of core-shell morphology by this inversion process has been found to be dependent on the hydrophilicity and molecular weight of the first-stage hydrophilic polymers and the extent of phase separation between the two polymers involved. Particle morphology has been examined by electron microscopy, surface acid titration, alkali swelling of particles, and surface reactivity.     

Influence de divers types de substitutions cationiques sur les propriétés diélectriques de niobates de structure “bronzes oxygénés de tungstène quadratiques”

The value of the ferroelectric Curie temperature in compounds with the “tetragonal tungsten bronze structure” is related to the steric effect of large alkali or alkaline-earth cations in the lattice tunnels, to the covalency of the transition element-oxygen bonds, and to the introduction of Li⁺ ions, which due to their small size are able to occupy the nine coordination sites of the structure anisotropically.     

Multidentate Acyclic Neutral Ligands and Their Complexation

The properties of cyclic crown ethers are approximated by acyclic neutral ligands (popdands), which are compared and contrasted with open-chain bioionophores and acidic chelating agents in this article. Variations of the endo-polarophilicity/exo-lipophilicity balance, complex stability, ion slectivity can often be accomplished more easily, with greater versatility, and at less expense with acyclic polyethers than with their cyclic counterparts; complexation and decomplexation are generally faster in acyclic systems; and the pseudocavity usually has greater conformational flexibility. Acyclic crown ethers and open-chain cryptands stiffened by rigid “terminal groups” containing donor atoms readily form crystalline complexes of alkali and alkaline earth metals. Some oppen-chain neutral ligands form helical conformations in their crycstalin complexes. The observed coordination numbers and geometries are of theoretical interst. Attractive terminal group interactions lead to pseudocyclic species occupying a position intermediate between cyclic and acyclic ligands. It has recently proved possible to isolate crystalline complexes of alkali and alkaline earth metal ions with weakly donating oligo(ethylene glycol ethers) and with glycols; such complexes have also been obtained with sugars. Acyclic neutral ligands can serve as simple models of nigericin-type bioionophores and be used analytically in microelectrodes. The recently discoverd crystalline stoichiometric complexes formed by some acyclic neutral ligands with guest molecules such as urea, thiourea, and water provide a fresh insight into weak interactions between neutral molecules and for the development of urea receptors.     

Swelling of carboxymethylated cellulose fibres

Swelling of cotton cellulose fibres having different proportions of carboxyl groups in the H-form was studied. The carboxyl groups were introduced by carboxymethylation under different reaction conditions. By studying the swelling of modified cellulose samples (water retention value of non-dried fibre) it was shown that the concentration of sodium hydroxide was the dominant factor among the investigated reaction parameters. The number of acidic groups was found to play a significant but not determinative role in the level of improvement in swelling caused by carboxymethylation. A linear correlation was observed between swelling and iodine sorption capacity. The degree of collapse of the highly accessible structure of cellulose during drying (hornification) was larger in the case of more accessible carboxymethylated fibres than for the alkali treated sample. The degree of hornification increased with growing swellability and with growing number of carboxyl groups in the investigated interval (40–120 mmol carboxyl/mol cellulose). This type of modified cellulosic fibre could be used for enhanced entrapping and release of chemicals. This revised version was published online in August 2006 with corrections to the Cover Date.