Thermotropic behavior of cholesterol-linked polysaccharides

Cholesterol-linked polysaccharides were prepared by reacting monocholesterylsuccinate (ChMS) with cellulose acetate [AC; degree of substitution (DS) 1.00, 1.80, and 2.33], ethyl cellulose (EC; DS 2.46), starch, and hydroxyethyl starch (HES; molar substitution, 0.05–0.07). The degree of ChMS substitution ranged from 0.27 to 1.29. The polymers were characterized by IR, NMR, DSC, and hot-stage coupled polarizing microscopy. Polymers with a higher DS of ChMS showed a thermotropic liquid crystalline behavior. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 195–201, 1998     

Carboxymethylcellulose synthesis in organic media containing ethanol and/or acetone

A study of the carboxymethylation of wood pulp cellulose and cotton linters cellulose in different organic media, namely, ethanol, acetone, and ethanol-acetone mixtures, is performed. Previously, the ethanol-acetone 1 : 1 (w/w) mixture used as reaction medium was found to give a higher degree of substitution (DS) than the pure solvents separately. In the present work, the kinetic investigation of cellulose carboxymethylation was carried out in ethanol-acetone 3 : 7 (w/w) mixture, as well as in acetone as reaction media, and the same synergistic effect of the solvents mixture was observed. The data suggested a pseudo-first-order kinetic behavior satisfactorily described by the following equation: ln(1.11 − DS) = −kt. The two reaction steps observed are related to the transformations of less ordered regions with higher reaction rate and more ordered regions with smaller reaction rates, respectively. A possible explanation for this behaviour is given, taking into account the different structural changes of cellulose crystallinity and accessibility produced by ethanol-acetone 3 : 7 (w/w) mixture, ethanol, and acetone, as revealed by X-ray diffraction and calorimetry determinations. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 481–486, 1998     

Comparison of succinylation methods for bacterial cellulose and adsorption capacities of bacterial cellulose derivatives for Cu<Superscript>2+</Superscript> ion

Bacterial cellulose (BC) was homogenously modified with succinic anhydride in N,N-dimethylacetamide/LiCl in the presence of triethylamine and heterogeneously in pyridine in the presence of 4-dimethylaminopyridine. FTIR, XRD, 13C CP MAS NMR, SEM were used to characterize BC and succinylated bacterial cellulose (SBC). For homogeneous modification, the degree of substitution (DS) of SBC differs from 0.21 to 1.45 with the variation of the adding amount of succinic anhydrate, temperature, reaction time, and the amount of triethylamine. DS and XRD profiles reveal that heterogenous reaction mainly happens on the surface of BC membrane. The adsorption capacity and mechanism of Cu²⁺ onto BC and SBC were investigated. The result shows the adsorption is affected by the morphology and the DS of adsorbents.     

Controlled heterogeneous modification of cellulose fibers with fatty acids: Effect of reaction conditions on the extent of esterification and fiber properties

The controlled heterogeneous partial modification of cellulose fibers with fatty acids, partially preserving the fiber structure, was investigated. The effect of reaction conditions, such as reaction time, fatty acid chain length, and solvent types (swelling and non swelling), on the extent of esterification and fiber properties was evaluated by elemental analysis, IR‐ATR, X‐ray diffraction, ¹³C CPMAS NMR, contact angle measurement, thermogravimetry, and scanning electron microscopy. The degree of substitution (DS) increased with reaction time and with the swelling effect of the reaction medium and decreased with the fatty acids chain length. Higher the DS, higher is the decrystallization of cellulose as a result of the heterogeneous esterification reaction. The esterification with fatty acids enhanced the hydrophobic character of the fibers, but decreased their thermal stability. These properties are not strongly affected by the DS in the range investigated, viz. up to 1.4. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1093–1102, 2006     

The preparation and properties of vinyl cellulose

The vinylation of cellulose by acetylene under alkaline conditions was optimized with respect to both DS and DP. Shortening the reaction time reduced the harmful alkaline depolymerization of cellulose during the reaction and gave products with higher DP values. Thus cellulose, activated by KOH, was vinylated for 180 min at 431K and 5.5 MPa to yield 72.1% of a product with DS 1.46 and DP _w 175. Results of vinyl cellulose analysis by new and old methods were in good agreement with each other. Trimethylsilylated vinyl cellulose was prepared for proton NMR and GPC measurements. It was found that vinyl cellulose slowly loses its vinyl groups when stored in light and air.     

Preparation of polymer brush-type cellulose β-ketoesters using LiCl/1,3-dimethyl-2-imidazolidinone as a solvent

Cellulose β-ketoesters with branched alkenyl chains were prepared using cis-9-octadecenyl ketene dimer (OKD) and LiCl/1,3-dimethyl-2-imidazolidinone (DMI) as the esterifying reagent and cellulose solvent, respectively. Relationships between degree of substitution (DS) of the cellulose/OKD β-ketoesters and reaction conditions were studied in detail. The results showed that DS values of the products were controllable up to 2.1 by selecting the reaction conditions. Solution- and solid-state ¹³C-NMR analyses revealed that cellulose backbones of the cellulose/OKD β-ketoesters with DS 2.1 behave like solid in chloroform owing to strong restriction on movement of cellulose chains by the long and branched alkenyl substituents introduced. Size-exclusion chromatographic analysis showed that little depolymerization occurred on cellulose during β-ketoesterification at room temperature, and that molecules of the cellulose/OKD β-ketoesters with DS 2.1 had semi rigid-rod conformation in tetrahydrofuran. Thus, cellulose β-ketoesters with densely substituents like polymer brushes or comb-shaped polymers were prepared in this study.     

Cellulose furoate. III. Properties and applications

Cellulose furoates synthesized by a homogeneous reaction was used to make film and fiber. Either colorless or light yellow, transparent cellulose furoate film can be made by solvent cast. Cellulose furoate film with a DS of 2.56 and 20% PEG-400 as the plasticizer displayed 5441 psi maximum tenacity and 21.5% maximum strain. The film without plasticizer has a water vapor permeability of 0.124 ng · m/m² · s · Pa. DMTA study identified the T_g of cellulose furoate with a DS of 2.77 was 225°C. As the DS decreased, the T_g shifted toward higher temperature. The success of wet-spun fibers from LiCl/DMAc solution of cellulose and cellulose furoate substantiated cellulose furoate is compatible with cellulose. Unfortunately, the wet-spun fibers lost their mechanical and surface properties, and bioresistant property against Myrothecium verrucaria, Cheatomium globosum, and Aspergillus terreus. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 253–257, 2001     

Correlation between the conditions of fabrication and structure of cotton cellulose for viscose formation

The effect of different regimes for each stage of fabrication of cotton cellulose on its supermolecular structure was evaluated by electron microscopic methods. It was shown that rigorous conditions of fabrication of cotton cellulose cause destruction and loosening of the surface and inner layers of the fibre. This indicates an increase in the reactivity of the cellulose and is promising for processing it into viscose fibres. Translated from Khimicheskie Volokna, No. 1, pp. 22–26, January–February, 1998.     

共反应剂法合成金刚烷甲酸纤维素酯

In order to develop a novel bioactive material utilizing cellulose resource, adamantane carboxylic acid esters of cellulose were synthesized through in-situ activation of the adamantane carboxylic acid using N,N-dimethylacetamide/LiCl as solvent, p-toluenesulfonyl chloride as co-reagent.The structure and properties of adamantane carboxylic acid esters of cellulose were characterized by means of IR, ¹H NMR, TG,etc.The esterification conditions were investigated in detail.The results showed that the degree of substitution was influenced by reaction temperature, reaction time and mole ratios of repeat units of cellulose/adamantane carboxylic acid/p-toluenesulfonyl chloride.Under the optimized reaction conditions, the highest degree of substitution (DS) was 1.9.TG analysis revealed that the thermal stability of cellulose esters was improved with the increase of DS due to the incorporation of adamantane carboxylic acid into chains of cellulose.The products are soluble in various organic solvents, depending on the DS.     

Effect of water on vapor phase photografting on cellulose and its derivatives

Effect of water on vapor phase photografting on cellulose was investigated at 60°C. An activated grafting of methyl methacrylate by water contained in the sample was observed in the experiment. The effect of water was commonly recorded irrespective of the type of cellulose derivatives such as cellulose acetate (degree of substitution, DS = 0.18 and 0.33), cellulose nitrate (DS = 0.35 and 0.75), and carboxymethl cellulose (DS = 0.19 and 0.74). Organic solvents can also be used in place of water, indicating that the percent grafting decreases in the order, water > methanol > acetone > cyclohexane. From ESR studies, water in the sample was found to contribute to the decay of cellulose radicals rather than to the radical formation. The decay was accelerated by organic solvents, and the magnitude of the effect was in the order, water ≈ methanol > acetone > cyclohexane. Based on the above investigation, it was presumed that water contained in the sample cannot contribute directly to the formation of cellulose radicals which may initiate grafting, but mostly promotes the penetration of monomer into cellulose fibers. Such penetration could lead cellulose radicals to an effective initiation of grafting.     

On the polarity and donor-acceptor-properties of polysaccharides

Summary Acidic parameters according to the GUTMANN's acceptor numbers (AN) of cellulose acetates and unmodified cellulose have been determined by means of the negatively solvatochromic probe dye Fe(phen)₂(CN)₂. Unmodified cellulose possesses a relatively high acceptor strength due to cooperative hydrogen bonds while increasing acetate contents in the polymer chain lower the acceptor strength. The dependence of AN on the acetate content can be used to estimate the degree of substitution (DS). Pecularities in the substitution interval (DS=0 to DS=1.5) are discussed.     

Nucleophilic displacement reactions on tosyl cellulose by chiral amines

Summary New 6-deoxy-6-amino cellulose derivatives with a degree of substitution (DS) in the range from 0.4 to 0.6 were synthesized by nucleophilic displacement (S_N) reactions of cellulose tosylates (DS_Tos 0.74 and 1.29) with R(+)-, S(−)- and racemic 1-phenylethylamine under homogeneous conditions in N,N-dimethylformamide and water. The structure of the polymers was characterized by elemental analysis, FTIR and ¹³C NMR spectroscopy. The DS values obtained as well as the optical rotation and circular dichroism measurements in dimethyl sulfoxide reveal that the initial chirality of the cellulose backbone does not have any significant influence on its reactivity with either of the two enantiomeric amines. Received: 21 September 2000/Accepted: 5 January 2001     

~(13)C-NMR法研究醋酸纤维素的取代基分布

用常规醋酸纤维素的13C-NMR法计算取代基分布难以准确。采用先将二醋酸纤维素中的剩余羟基完全丙酰化,再用13C-NMR法测定二醋酸纤维素乙酰基的取代分布的方法,其研究结果表明,完全丙酰化的二醋酸纤维素的碳谱中羰基碳区两组三重峰可较好地分开,因而可以根据它们的面积比算出其总取代度及在2,3和6位碳原子上的取代基分布。     

Experimental study on carboxymethylation of cellulose extracted from Posidonia oceanica

The production of carboxymethylcellulose (CMC) from bleached cellulose pulps obtained from Posidonia oceanica was explored. The optimal reaction conditions were studied for the carboxymethylation of cellulose in organic liquids. The carboxymethylation reaction was carried out with NaOH and monochloroacetic acid (MAC) as the reagent. Different alcohols were compared in terms of the degree of substitution (DS). The highest DS was obtained with n‐butanol. For this alcohol, the effects of the temperature, alkali concentration, and MAC concentration were studied. The reaction was also carried out in three consecutive steps. The resulting CMC had a DS of about 2.75. The functionalization of cellulose was checked using FTIR spectroscopy and ¹³C‐NMR. The X‐ray analysis showed that the crystalline structure of cellulose decreased when the DS increased and the structure was totally amorphous in high DS material. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1808–1816, 2006     

3-<Emphasis Type="Italic">O</Emphasis>-Propyl cellulose: cellulose ether with exceptionally low flocculation temperature

The synthesis of 3-O-propyl cellulose with degree of substitution (DS) ranging from 0.19 to 1.02 was carried out via 2,6-di-O-thexyldimethylsilyl cellulose. The products were characterized by means of one- and two-dimensional NMR spectroscopy after peracetylation. The dissolution behavior of 3-mono-O-propyl cellulose in water was studied and compared with propyl cellulose derivatives having different degree of substitution and distribution of functional groups. Depending on the DS, exceptionally low flocculation temperatures between 15 and 23 °C were found for 3-O-propyl celluloses.     

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.     

Electrospinning of cellulose‐based nanofibers

Cellulose derivatives of carboxymethyl cellulose sodium salt (CMC), hydroxypropyl methylcellulose (HPMC), methylcellulose (MC), and enzymatically treated cellulose have been electrospun, and the microstructure of the resulting nanofibers has been analyzed by scanning electron microscopy (SEM). Before electrospinning, the solutions were characterized by viscometry and surface tension measurements, and the results were correlated with spinnability. Four different CMC derivatives, varying in molecular weight (M_w), degree of substitution (DS), and substitution pattern, have been electrospun in mixtures with poly(ethylene oxide) (PEO), and nanofibers of various characteristics have formed. The CMC‐based nanostructures, i.e., the nonwoven sheet and individual nanofibers, proved to be independent of M_w and DS but largely dependent on the substitution pattern. The nonwoven sheets varied in homogeneity, and beads appeared on the individual fibers. Depending on the chemical nature of the CMC, the extraction of PEO resulted in pure CMC nanostructures of varying appearance, indicating that the distribution of PEO and CMC in the nanofibers also varied. Two different HPMC derivatives, varying in DS, were electrospun into nanofibers. Homogeneous nonwoven sheets based on nanofibers of similar appearance are formed, independent of the substitution content of the HPMC sample. Preliminary fibers were obtained from enzymatically treated cellulose in a solvent system based on lithium chloride dissolved in dimethyl acetamide (LiCl: DMAc). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1473–1482, 2007     

纤维素在离子液体AmimCl中的均相苯甲酰化反应

酱油渣中可以提取到纤维素等生物资源,但由于纤维素不溶于水和一般溶剂,难以进行衍生化应用,因此常常遭到浪费。而离子液体对纤维素呈现出较好的溶解性,可作为纤维素衍生化的良好溶剂。本文利用提取过油脂和半纤维素的酱油渣为原料进一步提取纤维素,并对以离子液体为溶剂,无催化剂条件下纤维素的均相苯甲酰化进行了研究。重点考察了离子液体种类对均相苯甲酰化的产率和取代率的影响,反应温度、时间、苯甲酰氯与葡萄糖单元摩尔比对均相苯甲酰化的取代率的影响。研究结果发现以离子液体AminCl（1-烯丙基-3甲基咪唑氯盐）为溶剂时有最优的产率。在最优反应条件为温度80℃、时间90min、苯甲酰氯与葡萄糖单元摩尔比4：1时,可得到最高取代率0.72。     

Aerobic biodegradation of cellulose acetate

Two separate assay systems were used to evaluate the biodegradation potential of cellulose acetate: an in vitro enrichment cultivation technique (closed batch system), and a system in which cellulose diacetate (CDA) films were suspended in a wastewater treatment system (open continuous feed system). The in vitro assay employed a stable enrichment culture, which was initiated by inoculating a basal salts medium containing cellulose acetate with 5% (v/v) activated sludge. Microscopic examination revealed extensive degradation of CDA (DS = 2.5) fibers after 2–3 weeks of incubation. Characterization of the CA fibers recovered from inoculated flasks demonstrated a lower average degree of substitution and a change in the mol wt profiles. In vitro enrichments with CDA (DS = 1.7) films were able to degrade > 80% of the films in 4–5 days. Cellulose acetate (DS = 2.5) films required 10–12 days for extensive degradation. Films prepared from cellulose triacetate remained essentially unchanged after 28 days in the in vitro assay. The wastewater treatment assay was less active than the in vitro enrichment system. For example, approximately 27 days were required for 70% degradation of CDA (DS = 1.7) films to occur while CDA (DS = 2.5) films required approximately 10 weeks before significant degradation was obtained. Supporting evidence for the biodegradation potential of cellulose acetate was obtained through the conversion of cellulose [1-¹⁴C]-acetate to ¹⁴CO₂ in the in vitro assay. The results of this work demonstrate that cellulose acetate fibers and films are potentially biodegradable and that the rate of biodegradation is highly dependent on the degree of substitution. © 1993 John Wiley & Sons, Inc.     

Solvent-free Synthesis of Cellulose Acetate by Solid Superacid Catalysis

Herein a novel process to synthesize cellulose acetate (CA) is reported in a solvent-free ball-milling reactor in the presence of solid superacid SO₄ ²⁻/ZrO₂ as green catalyst. FT-IR and H¹-NMR spectra reveal that the maximum degree of substitution (DS) of formed cellulose acetate can achieve 1.8, and the DS depends on the reaction time. This method provides a new environmental benign and simple way to synthesize cellulose acetate.