Low molecular weight water‐soluble chitosans: Preparation with the aid of cellulase,characterization, and solubility

Preparation of water‐soluble chitosan (WSC) was made by treating partially N‐deacetylated chitosan with acetic anhydride in aqueous acetic acid. The optimal conditions of preparing WSC were determined on the basis of orthogonal tests. Low molecular weight WSC with broad molecular weight (600–1.5 kDa) were obtained by the depolymerization of WSC using cellulase at optimum condition of pH 4.5 and 60°C. The solubility of WSC in water and aqueous organic solvents was investigated in detail. Weight–average molecular weight (M_w) and molecular weight distribution (M_w/M_n) of samples were measured by gel permeation chromatography. The structure of WSC and its degraded products were characterized by XRD, FTIR, and MALDI‐TOF MS. The decrease of molecular weight led to transformation of crystal structure and the increase of solubility, but the chemical structures of residues were not modified compared to WSC, which was not hydrolyzed. The solubility of the WSC in water and aqueous organic solvents increased with the decrease of molecular weight. The solubility of the WSC with low molecular weight was rather high even in aqueous dimethylacetamide and dimethylsulfoxide. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1098–1105, 2006     

Acetylation of sugarcane bagasse hemicelluloses under mild reaction conditions by using NBS as a catalyst

Sugarcane bagasse hemicelluloses were partially acetylated with acetic anhydride using N‐bromosuccinimide (NBS) as a catalyst under mild conditions in an almost solvent‐free system. The overall yield and degree of substitution (DS) were varied from 66.2 and 83.5% and between 0.27 and 1.15, respectively, by changing the reaction temperature and duration. It was found that the yield and DS increased with reaction temperature from 18 to 80°C and reaction time between 0.5 and 5.0 h. The results showed that treatment of the native hemicelluloses with acetic anhydride using NBS as a catalyst conveniently provided the corresponding biopolymer esters. The products were characterized by FTIR, ¹³C‐NMR spectroscopy, and thermal analysis. The new biopolymer acetates were thermally stable to over 200°C but underwent significant and rapid thermal degradation when heated above the onset of thermal degradation. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 53–61, 2004     

Acetylation of wheat straw using simplified procedure and ultrasonic irradiation

An investigation of the acetylation of wheat straw with acetic anhydride using a simplified procedure and with or without ultrasonic irradiation was undertaken. The new procedure greatly shortened the reaction time and simplified the chemical recovery. Acetylation weight gains of 15.8% can be achieved in 1 h at 120°C without ultrasound assistance. At the same reaction conditions but with ultrasound assistance at 60°C for 5 min, a weight percent gain (WPG) value of 15.0% was obtained, indicating a slightly negative effect of ultrasonic irradiation on the rate of acetylation without solvents or catalysts. However, a positive sonication effect on the solubility of low molecular materials, mainly extractives, was found in all the cases of the reactions. The characterization of acetylated wheat straw was performed by FTIR, solid‐state ¹³C‐NMR, and thermal studies, which provided evidence for acetylation. The thermal stability of acetylated straw was found to be higher than that of unmodified wheat straw. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1277–1284, 2003     

Vapor Phase Acetylation of Southern Pine,Douglas-Fir,and Aspen Wood Flakes

Abstract

Southern pine, Douglas-fir, and aspen wood flakes were acetylated with acetic anhydride vapor and compared with flakes acetylated with liquid acetic anhydride diluted with xylene. The rate of acetylation was much lower for the vapor than for the liquid phase reaction. Acetylation weight percent gains above 20 were achieved by both methods. Flakeboards made from both types of flakes absorbed much less water, both in water soaking tests and when subjected to humid air, and swelled at a lower rate and to a lower extent than did control boards. At low weight gains of vapor phase acetylation, the rate and extent of swelling were higher than those found for the controls.

Hygroscopicity of the resulting flakeboards decreased with increased level of wood acetylation. The equilibrium moisture content for flakeboards made from liquid phase acetylated flakes was the lowest at each relative humidity tested as compared to control boards, and boards made from vapor acetylated flakes at the same weight gain.     

N‐acyl chitosan and its fiber with excellent moisture absorbability and retentivity: Preparation in a novel [Gly]Cl/water homogeneous system

N‐acyl chitosans (such as N‐acetylated, N‐maleyl, and N‐succinyl chitosan), which were synthesized in glycine chloride ([Gly]Cl)/water homogeneous system, were of better moisture‐absorption and moisture‐retention abilities than those from the traditional methods, even better than hyaluronic acid. Moreover, the new method overcame many shortcomings, such as long reaction time, gel formed during the process of reaction, and complex workup procedure. In addition, the new [Gly]Cl solvent system was of the low volatility and no corrosion compared with organic solvent, especially, could be repeatedly used. Therefore, an environmental friendly approach for the synthesis of N‐acyl chitosan was provided. At the same time, the N‐acetylated chitosan fibers by wet‐spinning using N‐acetylated chitosan‐[Gly]Cl as spinning dope solution were firstly reported, and the fibers had smooth surface as well as round and compact structure. More to the point, the N‐acetylated chitosan fibers directly prepared in this study were of excellent mechanical properties. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

The preparation and characterization of chitosan wound dressings with different degrees of acetylation

Chitosan fibers have in recent years found applications in various fields such as antimicrobial textiles and wound dressings. In this study, chitosan fibers with different degrees of acetylation were prepared by controlling the ratio between the amount of acetic anhydride and the weight of the fibers during the acetylation process. The absorption and antimicrobial properties, as well as the dry and wet strength of nonwoven chitosan wound dressings with different degrees of acetylation were studied. Results showed that the partially acetylated chitosan wound dressing had a much higher absorption capacity than the original untreated chitosan samples, while there was a reduction in the wet strength and antimicrobial property for the partially acetylated chitosan nonwoven dressing. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

不同脱乙酰度壳聚糖的制备及其聚集行为研究

壳聚糖的脱乙酰度直接影响壳聚糖的物理化学和生物特性。在乙酸-水-甲醇体系中研究壳聚糖的乙酰化反应工艺,考察了反应时间、壳聚糖质量浓度对乙酰化反应的影响,优化了反应条件。研究表明,反应时间为6h时,壳聚糖乙酰化反应基本完全,乙酰化反应后,相对重均分子质量基本不变,壳聚糖相对分子质量分布变宽。在优化后的反应条件下,改变乙酸酐加入量分别制备了脱乙酰度为76%,64%和54%的不同脱乙酰度的壳聚糖。芘荧光光谱研究表明,壳聚糖的临界聚集浓度(CSC)随脱乙酰度的降低而增加。     

Syntheses of novel chitosan derivative with excellent solubility,anticoagulation, and antibacterial property by chemical modification

The soluble and antibacterial chitosan derivative was prepared on the basis of the regioselective chemical modification. The N‐(2‐phthaloylation) chitosan was obtained via the reaction of chitosan with phthalic anhydride in N,N‐dimethylformamide (DMF) at 130°C, and O‐(3,6‐hydroxyethyl) chitosan was produced using chlorohydrins as grafting agent and hydrazine hydrate as reductant. The structure of hydroxyethyl chitosan (HC) was characterized by X‐ray diffraction (XRD), Fourier Transform infrared spectroscopy (FTIR), and gel permeation chromatography (GPC) respectively. The solubility, anticoagulation, and antibacterial property were assessed separately. The result shows that amine I of chitosan is replaced and the amide II disappears during chemical modification, and the functional groups of C6‐OH and ‐NH2 are also reacted. The water‐solubility of the novel chitosan derivative was enhanced relatively; it could even slightly soluble in methanol. The results of platelet adhesion and the activated partial thromboplastin times (APTTs) indicate that grafting hydroxyethyl could improve anticoagulation of chitosan. The antibacterial activity of HC against Enterococcus and E. coli had been much better owing to enhancing the degree of protonation. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Studies of acetylation of jute using simplified procedure and its characterization

Dried and defatted jute fibers were acetylated for different time and temperature in the absence of catalyst and solvent. Extent of acetylation were measured by weight percent gain (WPG). These values were compared with the standard method of acetylation using a cosolvent (pyridine) system. The characterization of acetylated fibers was performed by FTIR, DSC, TGA, and SEM studies. The maximum WPG was 18.0 for an acetic anhydride-pyridine system at 120°C for 4 h whereas using only acetic anhydride WPG was 12.3 at the same reaction condition. Thermal stability of acetylated jute was found to be higher than the untreated jute. SEM studies were carried out to investigate the fiber surface morphology. FTIR studies also produced evidence for acetylation. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1517–1523, 1997     

Effect of reactivity of different types of hydroxyl groups of HTPB on mechanical properties of the cured product

The amount of three types of hydroxyl functional groups (G_OH, H_OH, and V_OH) in hydroxyl terminated polybutadiene (HTPB), remaining in samples acetylated to the same extent under two different conditions, viz., fast acetylation using acetyl chloride in presence of N-methyl imidazole catalyst and slow acetylation by acetic anhydride, differed significantly. For the fast acetylation there is a uniform reduction in all the three types of hydroxyls, probably because the reaction becomes random at rapid rates and the reactivity of the different types of hydroxyls does not play a major role. However, in the slow reaction, the reduction of G-type hydroxyls was 30% more than the expected value and there was a corresponding increase in the amount of V-type hydroxyls remaining in the acetylated product, showing reactivity of OH in the order of G > H > V. When the reaction is slow, it becomes selective and the change in reactivity of the three types of OH groups is reflected in the extent of conversion. The mechanical properties and the crosslink density data show a reduction in the samples containing lesser amounts of G_OH, confirming the branching nature of G_OH, which is involved in the crosslinking reaction. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1313–1320, 1997     

Solvent‐free acetylation of lignocellulosic fibers at room temperature: Effect on fiber structure and surface properties

Acetylation is one of the most interesting chemical treatments to improve the affinity of lignocellulosic fibers with polymeric matrices for the elaboration of several types of composites. In this paper, the acetylation of flax and wood pulp (bleached softwood Kraft pulp and thermomechanical pulp) fibers was carried out at room temperature in a solvent‐free system with acetic anhydride in the presence of sulfuric acid as catalyst. The effect of acetylation on the fine structure of fibers was investigated by spectroscopic methods, while the extent of acetylation was quantified by weight percent gain. The effect of reaction time on fiber morphology was studied at macro‐ and microscale using scanning electron microscopy, optical microscopy, and fiber quality analysis. The evolution of the hydrophobic/hydrophilic character of fibers was determined by contact angle measurements. The wettability of fibers by liquid epoxy resin was also evaluated to confirm the improvement of the affinity of acetylated fibers with the epoxy matrix. It was found that the hydrophilic character of fibers decrease with increasing reaction time, whereas the trend was less pronounced beyond specific reaction times. Acetylated fibers can therefore be potential candidates for replacing nonbiodegradable reinforcing materials in composite applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42247.     

Tensile strength and toughness of acetylated pine and lime flakes

Thin strips of pine, Pinus sylvestris, and lime, Tilia vulgaris, were acetylated with acetic anhydride to various levels of acetyl weight gains. Increase in thickness, due to the bulking effect of acetylation, and increase in equilibrium moisture content at 65% relative humidity were determined. Equilibrium moisture content decreased as the degree of acetylation increased for both pine and lime. Finite span tensile strength was determined on thin control and acetylated pine and lime strips. No significant loss of tensile strength was found in either species due to acetylation. Total work expended in fracturing the specimens (work-to-failure) was slightly decreased for acetylated pine but remained essentially unchanged for acetylated lime as compared to controls. This indicates that the toughness of the material is only slightly reduced by the acetylation process.     

H3PW12O40·4H2O as an efficient catalyst for the conversion of cellulose into partially substituted cellulose acetate

The preparation of partial acetylation of cellulose derived from rice straw was catalyzed by phosphotungstic acid with various numbers of crystal water, and H₃PW₁₂O₄₀·4H₂O was found to be as effective catalyst. The yield of the cellulose acetate was significantly enhanced by converting cellulose directly isolated from rice straw into microcrystalline cellulose before acetylation. The optimization of the acetylation was investigated by varying the amount of catalyst and acetic anhydride as well as reaction conditions including reaction time and medium, and a degree of substitution (DS) value of 2.29 and yield of 62.9% were obtained under the optimized conditions. The structure and the formation of the acetylated product were confirmed by Fourier transform infrared spectroscopy (FTIR) and powder X‐ray diffraction (XRD) technique, the thermal properties were determined by thermal analysis including thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC), and the morphology was observed by scanning electron microscope (SEM). © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41212.     

Free radical scavenging activity of cellulase‐treated chitosan

Partially N‐acetylated chitosan was hydrolyzed by the cheap, commercially available, and efficient cellulase. The products, with different molecular weight, were comparatively investigated by GPC, FT‐IR, XRD, and NMR. The results show that the decrease of molecular weight led to transformation of crystal structure and increase of water‐solubility, but the chemical structures of residues were not modified. Superoxide anion radical and hydroxyl radical quenching assay were used for the evaluation of free radical scavenging activity of cellulase‐treated chitosan in vitro. Low molecular weight chitosan (LMWC3, M_w 1.7 × 10³) exhibited high scavenging activity against free radical. It scavenged 79.3% superoxide radical at 0.1 mg mL^?1. At 2.0 mg mL^?1, scavenging percentage of initial chitiosan, LMWC1 (M_w 27.3 × 10³), LMWC2 (M_w 5.9 × 10³), and LMWC3 (M_w 1.7 × 10³) against hydroxyl radical was 14.3%, 33.1%, 47.4%, and 65.9%, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Atom transfer radical polymerization of acrylonitrile

Iron(II) chloride coordinated by succinic acid was first used as the catalyst in 2‐chloropropionitrile‐initiated atom transfer radical polymerization (ATRP) of acrylonitrile. N,N‐dimethylformamide was used as a solvent to improve the solubility of the ligand. An iron(II) chloride to succinic acid ratio of 0.5 not only gives the best control of molecular weight and its distribution but also provides rather rapid reaction rate. Effects of solvent on polymerization of acrylonitrile were also investigated. The induction period is shorter in N,N‐dimethylformamide than in propylene carbonate and toluene and the rate of the polymerization in N,N‐dimethylformamide is fastest. The molecular weight of polyacrylonitrile agrees reasonably well with the theoretical molecular weight of N,N‐dimethylformamide. The rate of polymerization increases and the induction period becomes shorter with increasing polymerization temperature, and the apparent activation energy was calculated to be 56.5 kJ mol^?1. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1050–1054, 2006     

Synthesis and characterization of a novel hyperbranched polyether

A hyperbranched polyether has been synthesized by a single‐step nucleophilic displacement polymerization technique between cyanuric chloride and the sodium salt of bisphenol‐A. The effects of various reaction parameters on the yield, and molecular weight, as measured by the intrinsic viscosity of the polymer, have been studied. The synthesized polymer has been characterized by FT‐IR, UV and ¹H NMR spectroscopies, elemental analysis, solubility and viscosity measurements. The polymer is soluble in highly polar solvents such as N,N‐dimethylacetamide, N,N‐dimethylformamide and dimethyl sulfoxide, partially soluble in dilute aqueous NaOH solution, methanol, ethanol, chloroform, etc., but insoluble in water and non‐polar hydrocarbon solvents. The solubility parameter of the hyperbranched polymer has also been measured experimentally. Copyright © 2004 Society of Chemical Industry     

N-Alkylation of chitin and some characteristics of the novel derivatives

Summary Introduction of simple alkyl groups at the C-2 nitrogen of chitin and some properties of the resulting N-alkyl-chitins have been examined. Chitosan was fully deacetylated and treated with three kinds of aldehydes, formaldehyde, acetaldehyde, and pentanal. The Schiff bases of chitosan, whose extents of substitution were dependent on the amount of aldehydes, were reduced with sodium cyanoborohydride to N-alkylated chitosans. The N-alkyl-chitosans were then transformed into the corresponding N-alkyl-chitins by acetylation with acetic anhydride followed by transesterification to remove partly formed O-acetyl groups. The resulting N-methyl-, ethyl-, and pentyl-chitins were amorphous and showed improved affinity for organic solvents. Received: 13 December 2001/Revised version: 11 January 2002/Accepted: 17 January 2002     

Erratum

Abstract

Southern pine and aspen flakes were acetylated with acetic anhydride alone without cosolvent or catalyst by a simple dip procedure. The new procedure greatly shortens reaction time and simplifies chemical recovery. Acetylation weight gains of 15% to 20% can be achieved in 1 to 3 hours with southern pine flakes and in 2 to 4 hours with aspen flakes.

Flakeboards made from acetylated southern pine or aspen flakes absorbed much less water, both in water-soaking tests and when subjected to humid air, and swelled at a lower rate and to a lower extent than did control boards.

Hygroscopicity of the resulting flakeboards decreased with increased level of wood acetylation. The equilibrium moisture content (EMC) for flakeboards made from acetylated flakes was lower at each relative humidity tested than that of control boards.     

A new approach for the preparation of chitosan from γ‐irradiation of prawn shell: effects of radiation on the characteristics of chitosan

Chitosan is a biodegradable polymer composed of randomly distributed β‐(1,4)‐linked D ‐glucosamine (deacetylated unit) and N‐acetyl‐D ‐glucosamine (acetylated unit). It is produced commercially by deacetylation of chitin, which is the structural element in the exoskeleton of crustaceans (such as crabs and shrimps) and the cell walls of fungi. In the work reported, we developed a facile technique for the preparation of chitosan by irradiating prawn shell at various intensities from 2 to 50 kGy. It was observed that γ‐irradiation of prawn shell increased the degree of deacetylation (DD) of chitin at a relatively low alkali concentration during the deacetylation process. Among the various irradiation doses applied to prawn shell, a dose of 50 kGy and 4 h heating in 50% NaOH solution yielded 84.56% DD while the chitosan obtained from non‐irradiated prawn shell with the same reaction conditions had only 74.70% DD. In order to evaluate the effect of γ‐irradiation on the various physicochemical, thermomechanical and morphological properties, the chitosan samples were again irradiated (2–100 kGy) with γ‐radiation. Molecular weight, DD, thermal properties with differential scanning calorimetry and thermogravimetric analysis, particle morphology by scanning electron microscopy, water binding capacity (WBC), fat binding capacity (FBC) and antimicrobial activity were determined and the effects of various γ‐radiation doses were assessed. The DD, WBC, FBC and antimicrobial activity of the chitosan were found to improve on irradiation. It was obvious that irradiation caused a decrease of molecular weight from 187 128 to 64 972 g mol^?1 after applying a radiation dose of 100 kGy which occurred due to the chain scission of chitosan molecules at glycosidic linkages. The decrease of molecular weight increased the water solubility of the chitosan, the extent of which was explored for biomedical applications. Copyright © 2012 Society of Chemical Industry     

Synthesis and properties of new poly(amide imide)s containing trimellitic rings and hydantoin moieties in the main chain under microwave irradiation

Trimellitic anhydride was reacted with 4,4′‐diaminodiphenyl ether in a mixture of acetic acid and pyridine (3 : 2) at room temperature and was refluxed at 90–100°C, and N,N′‐(4,4′‐diphenylether) bistrimellitimide (3) was obtained in a quantitative yield. 3 was converted into N,N′‐(4,4′‐diphenylether) bistrimellitimide diacid chloride (4) by a reaction with thionyl chloride. Then, six new poly(amide imide)s were synthesized under microwave irradiation with a domestic microwave oven through the polycondensation reactions of 4 with six different derivatives of 5,5‐disubstituted hydantoin in the presence of a small amount of a polar organic medium such as o‐cresol. The polycondensation proceeded rapidly and was completed within 7–10 min, producing a series of new poly(amide imide)s in high yields with inherent viscosities of 0.27–0.66 dL/g. The resulting poly(amide imide)s were characterized by elemental analysis, viscosity measurements, differential scanning calorimetry, thermogravimetric analysis, derivative thermogravimetry, solubility testing, and Fourier transform infrared spectroscopy. All the polymers were soluble at room temperature in polar solvents such as N,N‐dimethylacetamide, N,N‐dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, and N‐methyl‐2‐pyrrolidone. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3447–3453, 2004