Acetylation behaviour of cotton and bagasse celluloses. II. Effect of hot alkali refining

The alkali pretreatments of cotton linters, bagasse dissolving pulp, and bagasse kraft pulp increased the accessibility of the cellulose hydroxy groups to acetylating molecules. The pretreatment with hot alkali resulted in a higher degree of esterification than with cold alkali. The filterabilities of cellulose acetates obtained from alkali pretreated samples of cotton linters, dissolving pulp, and kraft pulp were better than in case of the untreated samples. Hot refining resulted in better filterability than cold refining, but resulted in stronger degradation and lower thermal stability than cold refining. The presence of hemicelluloses in the untreated pulp lowered the reactivity towards acetylation but favoured the reactivity towards xanthation. In case of cotton linters both reactivities were improved by the alkaline pretreatments. The increase in reactivity resulting from the depolymerization of the cellulose overcame the increase in inaccessibility resulting from drying after the alkaline treatment. The removal of hemicelluloses from the dissolving and kraft pulps by alkaline extraction deteriorated the reactivities towards xanthation, but had a favourable effect on the reactivity towards acetylation.     

Effect of Ultrasonic Waves on the Saccharification Processes of Lignocellulose

The pretreatment and saccharification process of lignocellulose were subjected to ultrasonic waves to enhance the saccharification rate. The morphology, structure and crystal performance of the original and treated lignocellulose samples were characterized by SEM and FTIR. Moreover, the effect of different pretreatment methods on the structure of the raw materials and the influence of ultrasonic waves on the saccharification rate, were studied. SEM photographs show that the surface conformation of the granulated raw material is not changed, because the energy of the ultrasonic vibration is too low to cause changes to its structure. A FTIR spectrum shows that the ultrasonically assisted alkali pretreatment effectively destroys the intermolecular hydrogen bonding of lignocellulose and decreases its crystallinity. The catalytic efficiency of cellulase was increased by 70 % under ultrasonic treatment. Therefore, the ultrasonically assisted alkali pretreatment can improves the degradation rate of lignin and the saccharification rate of zymohydrolysis. The mechanism of the effect of ultrasonic waves on the enzymatic catalysis process is also discussed in detail.     

选择性氧化法合成双醛纤维素硫酸酯

为了发展一个新的生物活性物质利用纤维素资源,采用高碘酸钠(NalO4)对微晶纤维素(MCC)进行选择性氧化,又与亚硫酸氢钠(NaHSO3)进行磺化反应,得到了双醛纤维素硫酸酯(OSC)。通过红外光谱(FTIR)分析手段对产品结构进行了表征。并考察了工艺参数对DAC醛基含量和OSC取代度的影响,得出了各合成阶段的关键工艺参数——时间、温度、pH值和反应物配比的最佳控制值。结果表明:当反应物配比为n(NaHSO3)∶n(DAC)=2∶1,产品合成温度为22℃,合成时间为2 h时,所得产品磺酸基取代度最高,并具有明显的表面活性。     

Microcrystalline cellulose as reactive reinforcing fillers for epoxidized soybean oil polymer composites

Microcrystalline cellulose (MCC) and its oxidized product dialdehyde cellulose (DAC) were introduced as the reinforcing filler in epoxidized soybean oil (ESO) thermosetting polymer. The composites comprising up to 25 wt % cellulose fillers were obtained via a solution casting. The reinforcing effects of the cellulose were evaluated by microstructure analysis, dynamic mechanical analysis, and tensile and thermal stability tests. The results showed that at the same filler concentration, DAC led to higher stretching strength, modulus, and break elongation than MCC. The 5 wt % DAC loading in ESO polymer exhibits the highest toughness and thermal stability due to the good dispersion and interfacial interaction between DAC and ESO polymer matrix. The increased storage modulus and glass transition temperature also indicate the cellulose fillers impart stiffness to the composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42488.     

Structural changes of regenerated cellulose dissolved in FeTNa,NaOH/thiourea,and NMMO systems

Regenerated cellulose was prepared from microcrystalline cellulose (MCC) via dissolution in three well‐known nonderivatizing systems: ferric chloride/sodium tartarate/sodium hydroxide (FeTNa), sodium hydroxide/thiourea (NaOH/thiourea), and N‐methylmorpholine‐N‐oxide (NMMO) systems. The effect of regeneration using the different systems on the supramolecular structure of the regenerated celluloses was studied using X‐ray diffraction and Fourier transform infrared (FTIR). The effect of regeneration on supermolecular structure, morphology, and thermal stability of regenerated celluloses were studied using scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The effect of regeneration systems used on the chemical reactivity of cellulose toward carboxymethylation, acetylation, and cyanoethylation reactions was briefly studied. The results showed dependence of all the aforementioned properties on the dissolution reagent used in spite of that all studied reagents cause the same change in cellulose crystalline structure (from cellulose I to cellulose II). The degree of polymerization, crystallinity, and thermal stability of the regenerated cellulose (RC) samples were in the following order: NaOH/thiourea RC > FeTNa RC > NMMO RC. SEM micrograph showed unique surface for the NMMO RC sample. The reactivity of the different regenerated cellulose samples toward carboxymethylation, cyanoethylation, and acetylation depended mainly on the reaction system and conditions used rather than on crystallinity of regenerated cellulose. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

“Dialdehyde Cellulose” Nanofibers by Electrospinning as Polyvinyl Alcohol Blends: Manufacture and Product Characterization

A nanofiber was obtained by electrospinning of “dialdehyde cellulose” (periodate-oxidized cellulose, DAC) and polyvinyl alcohol (PVA), using only water as the solvent. Celluloses of four different origins were fully oxidized with sodium periodate to water-soluble DAC. Aqueous solution of DAC showed inadequate spinnability regardless of the polymer concentration and the electrospinning conditions used. Addition of PVA improved the solution's viscoelasticity and, consequently, the solution's spinnability. We examined the effects of DAC/PVA composition and electrospinning parameters on fiber morphology. Highly homogeneous nanofibers were prepared from 1:1 up to 2:1 (weight) DAC/PVA blends while samples of lower viscosity or higher relative DAC contents resulted in continuous, beaded fiber networks. Characterization of the electrospun fabrics revealed a highly crosslinked DAC structure reinforced with PVA, strongly interacting through hemiacetal bonds and hydrogen bonding. Fluorescence labeling confirmed the presence of reactive aldehyde functionalities in the electrospun web. The versatile properties of DAC as reactive material can now be imparted on electrospun fiber and nanofiber material – which was not possible so far –further widening the application scope of this interesting cellulose derivative.     

天然纤维素蒸汽闪爆改性对其长支链酯合成影响

采用蒸汽闪爆技术对天然纤维素进行改性,并利用改性后的纤维素、乙酸酐和脂肪酸合成长支链纤维素酯。结果表明,蒸汽闪爆处理后纤维素葡萄糖环单元三个羟基的可及性及相对反应性能得到提高,同时缩短了反应周期。     

氧化纤维素的制备研究

介绍了氧化纤维素 (DAC)的制备过程 ,用正交法探讨了以NaIO4 作氧化纤维素时反应温度、溶液pH值、氧化剂浓度、反应时间以及交互作用对DAC醛基含量的影响 ,找到了影响醛基含量的主要因素为反应温度、反应温度与NaIO4 的交互作用、反应温度与溶液 pH值的交互作用。初步确定了制备氧化纤维素的反应工艺 ,使醛基含量较高时的最佳反应条件为 :反应温度 3 5℃ ,反应时间 3h ,NaIO4 质量分数 6.78% ,pH值为 2时 ,醛基含量达 68.2 0 %。     

Fast in situ copolymerization of PET/PEN blends by ultrasonically-aided extrusion

An ultrasonically-aided extrusion process was developed for fast in situ compatibilization of immiscible polymer blends. PET, PEN, and their 50/50 blend were ultrasonically extruded at various amplitudes. PET underwent homopolymerization and degradation, respectively, at ultrasonic amplitudes of 7.5 and 10 μm, while PEN underwent degradation at amplitudes of 5, 7.5, and 10 μm. MALDI-TOF mass spectrometry revealed greater amounts of hydroxyl and carboxyl terminated oligomers in ultrasonically treated PET and PEN, indicating their greater reactivity. Ultrasonic treatment at short residence time led to the enhancement of transesterification reaction in the PEN/PET blend, as shown by ¹H NMR and MALDI-TOF, indicating greater randomization with ultrasonic treatment. The latter was also observed through a shift in T_g that closely follows Gibbs-DiMarzio relation and an increase in viscosity of blend with treatment at an amplitude of 10 μm. No crystallinity was observed in the blend due to the already high level of transesterification introduced by extrusion without treatment. Accordingly, crystallinity, mechanical properties, oxygen permeability, and optical clarity of the blend were not influenced by ultrasonic treatment.     

Changes in supramolecular structure and improvement in reactivity of dissolving pulp via enzymatic pretreatment with processive endoglucanase EG1 from Volvaria volvacea

Abstract

Processive endoglucanase EG1 and its core domain, EG1(CD), were used to pretreat the commercial dissolving pulp to improve cellulose reactivity. The Fock reactivity of the pulp which was treated with EG1 and EG1 (CD) at 50?U/g enzyme loading increased from 74.3% of the control to 90.6% and 88.4%, respectively. Refining also improved the Fock reactivity of the pulp, but not as effective as EG1 or EG1(CD) treatment. Refining prior to EG1 or EG1(CD) treatment could slightly further improve the Fock reactivity, to 91.6% and 90.0%, respectively. After enzymatic treatment and (or) refining, the water retention value, differential scanning calorimetry and alkaline solubility analysis indicated that enzyme treatment, especially by EG1, significantly increased the accessibility of fibers to reaction reagents. Combined with the characteristics of soluble reducing sugar produced by EG1 treatment and the changes of degree of polymerization, it is inferred that a small fraction of cellulose crystallization regions are destroyed in the enzymatic hydrolysis process due to the processive acting ability of EG1, and some microchannels in the fiber cell wall were created, which is similar to the effect of “drilling holes”, so that the reaction reagent can reach the inside of the cell wall evenly, thus obviously improving the reactivity of the dissolved pulp.     

Radiation degradation of microcrystalline cellulose in solid status

Pulverization and degradation are important pretreatment procedures in producing bio‐ethanol from cellulose. In this study, microcrystalline cellulose (MCC), a pure α‐cellulose, was degraded by γ‐irradiation. The average degree of polymerization, content of reducing sugar, crystalline structure, and molecular structure were investigated to elucidate the radiation effect on the degradation of MCC. The results manifested that γ‐ray destroyed part of the chemical bond and hydrogen bond, leading to the degradation of cellulose and increasing of the reducing sugar content. According to the Fourier transform infrared result, radiation degradation led to the formation of reductive carbonyl group. Meanwhile, radiation had slight influence on the crystalline structures of MCC. Therefore, the radiation degradation procedure is expected to benefit the further proceedings such as ultrafine treatment and enzyme hydrolysis of cellulose. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation and characterization of composite membranes of polysulfone and microcrystalline cellulose

Physical and chemical modifications of polymeric ultrafiltration membranes are necessary to improve their hydrophilic properties, strength, and other characteristics. Microcrystalline cellulose (MCC) was prepared from cellulose pulp by acid‐catalyzed hydrolysis in the presence of ultrasonic radiation, and the properties of MCC were evaluated. Through the addition of MCC to a polysulfone (PS) membrane solution, a casting solution of a PS/MCC blend was obtained. Subsequently, the ultrafiltration membrane from the blend was further developed in a phase‐inversion process comprising immersion and deposition. The capacity for ultrafiltration was better with increasing MCC content. When the ratio of MCC to PS was 0.3, the pure water flux of the composite membrane reached 234.2 L/m²/h, and the retention of a bovine serum albumin solution (1 g/L) was as high as 93.4%. The membranes were also observed with scanning electron microscopy and atomic force microscopy to study their microstructures. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

蔗渣浆制造黏液纤维的研究

<正>在黏液纤维制造中,用蔗渣浆代替木浆作原料,常被人怀疑甚至否定其可能性,其主要根据为草类纤维的形态结构不同於木材纤维,而以天然纤维的形态结构作为对原料适合与否的判断标准。我们认为:黏液丝浆的良好制备条件均应最大限度地破坏了天然纤维的形态结构,主要是细胞壁的组织。後者的存在影响丝光化与黄酸化的反应     

纤维素的酸处理及醋酸酯化表面改性研究

分别用HCl和H2SO4处理从棉纤维中提取的纤维素,100℃下回流水解30～60 min得到微晶纤维素(MCC),并对其进行醋酸酯化表面改性.采用X-射线衍射(XRD)、热重分析(TG)、红外光谱(IR)技术研究酸处理对MCC的聚合度、结晶度和热稳定性的影响,探讨了改性方法对产物性能的影响.结果表明,纤维素微晶化后仍保持原来的晶型以及晶区和非晶区共存的微细结构,结晶度不能达到100%.扫描电子显微镜(SEM)测试结果表明,不同酸处理后所得产物的形态和热性能有所不同,MCC的最高适用温度不宜超过270℃.适宜的醋酸酯化改性条件为:硫酸和水体积比1∶8、温度60～70℃、改性处理3～5 h.改性后微晶纤维素的内部结晶区结构没有变化,在有机溶剂中的分散性得到良好的改善.     

Preparation and characterization of chitosan coatings onto regular cellulose fibers with ultrasound technique

Regenerated cellulose fibers—viscose fibers—were coated with chitosan using an ultrasound technique to improve their accessibility, reactivity and sorption properties. The main purpose of our research was to study the modification of viscose fibers and to determine the effect of the application of chitosan onto viscose fibers. Samples were obtained by treating the fibers with chitosan in a dilute acetic acid solution in an ultrasonic bath. The influences of the chitosan coating on the changes in morphology, supramolecular structure, sorption and tensile properties were studied. The spectra (FTIR analysis) of the treated viscose fibers showed changes and new absorption bands that revealed the existence of the chemical interactions with the chitosan. The scanning electron microscope images confirmed that the surface of the fibers was covered with the chitosan. A decrease in the water retention value and increase in the absorption and moisture content with an increasing concentration of chitosan was noted. Furthermore, the differences in tensile behavior were analyzed using an Instron tensile testing machine. The chitosan coating had no effect on the tensile strength of the viscose fibers, but influenced the tensile strain. Some changes, though not significant, were noted in the structure (crystallinity, orientation) of the treated viscose fibers.     

Ultrasonic‐assisted dyeing: II. Nylon fibre structure and comparative dyeing rate with reactive dyes

Comparative dyeing kinetics of nylon‐6 fibre with different reactive dyes using conventional and ultrasonic conditions are presented. The time/dye‐uptake isotherms are revealing the enhanced dye‐uptake in the second phase of dyeing (diffusion phase). The data of dyeing rate fit well with the integrated form of the first‐order rate equation and values of dyeing rate constant and half‐time of dyeing are discussed. Ultrasonic efficiency in accelerating the dyeing rate relative to conventional heating was examined for all dyes used to show that ultrasonics are most effective for a dyeing system which has difficulty in achieving high dye‐uptake. To clarify the role of fibre fine structure and whether it is affected during dyeing with ultrasonic waves, time‐dependent ultrasonic pre‐treatment of nylon‐6 fibres and its effect on the colour strength obtained is presented. X‐ray diffraction studies on nylon‐6 fibres conventionally and ultrasonically pre‐treated have shown that the percentage of fibre crystallinity has become higher in ultrasonically treated fibre in comparison with that of conventionally treated. Although the increased crystallinity of the fibre, which occurs simultaneously during the ultrasonic dyeing process, would retard dye uptake, it seems that the enhanced effect of power ultrasonic is high enough to overcome this side‐effect on the fibre. © 2003 Society of Chemical Industry     

不同结晶度纤维素的酶解历程的SEC-MALLS研究(英文)

The reactions of exo-cellulase (cellobiohydrolase, CBH) and endo-cellulase (endoglucanase, EG) were investigated by analyzing the insoluble residues of microcrystalline cellulose (MCC) and filter paper cellulose (FPC) during enzymatic hydrolysis. Molecular parameters including molecular weight and its distribution, degree of po-lymerization, and radii of gyration were measured by size exclusion chromatography coupled with multi-angle laser light scattering. No significant change in MCC chains was found during the whole reaction period, indicating that CBH digestion follows a layer-by-layer solubilization manner. This reaction mode might be the major reason for slow enzymatic hydrolysis of cellulose. On the other hand, the degree of polymerization of FPC chains decreases rapidly in the initial reaction, indicating that EG digestion follows a random scission manner, which may create new ends for CBH easily. The slopes of the conformation plots for MCC and FPC increase gradually, indicating stronger chain stiffness of cellulose during hydrolysis.     

离子液体中羟丙基纤维素的合成

使用离子液体1,3-二乙基咪唑磷酸二乙酯盐([EEIM][DEP])为反应溶剂主组分来溶解微晶纤维素进行羟丙基化衍生,微晶纤维素和醚化剂在离子液体中均可形成均相,通过碱化、醚化、酸化及洗涤等步骤制备得到不同取代度的羟丙基纤维素。考察了碱化反应温度、反应原料摩尔比、醚化反应时间及酸化剂的种类对羟丙基纤维素产品的收率和摩尔取代度的影响,并采用红外、核磁、TGA等手段对产品结构进行了表征。     

微晶纤维素的氧化及吸附性能

以微晶纤维素为原料,高碘酸钠(NaIO4)作氧化剂制备了氧化纤维素,考察了反应时间、高碘酸钠与微晶纤维素投料比、反应温度和溶液pH等条件对醛基的影响;为了减少醛基的不良反应,用明胶作包覆材料合成了包醛氧化纤维素,测定了氧化纤维素和包醛氧化纤维素的吸附性能。发现反应时间3h、m(高碘酸钠)/m(微晶纤维素)=2、反应温度35℃、pH=2和w(明胶)=1%,可获得较多醛基;吸附力随醛基的增多而提高;用明胶包覆后醛基数量虽然减少,但吸附力明显提高,其中w(明胶)=3%时吸附力最大,达到31 5mg/g,经5～12h达到吸附平衡。     

Aldehyde functionalized cellulose support for hydrogels

Activated cellulose carrying aldehyde (CHO) and acylchloride (COCl) reactive sites was created by reacting cellulose with dialdehydes, i.e., polyethylene glycol (PEG) diacylchloride and glutaraldehyde (GA), to yield Cell‐PEG‐COCl and Cell‐CHO, respectively. Cellulose fibers and microcrystalline cellulose were readily esterified by PEG diacylchloride to form Cell‐PEG‐COCl to reach as high as 0.24 to 0.37 mmol aceylchloride per gram cellulose, respectively. The generation of free COOH from PEG diacylchloride reactions was optimized at the lower COCl/OH ratio, where the tendency to half‐ester formation was more prevalent than to diesters. Reactions with 8 and 16% GA, generated 0.83 to 1.26 μmol free aldehyde per gram of cellulose, respectively. The reactivity of the aldehyde groups toward poly(vinyl alcohol) (PVA) hydroxyl was robust, generating cellulose fiber supported PVA hydrogels that could swell up to 62 times. These reactions have shown to be highly effective to create aldehyde functionalized cellulose and demonstrated a simple, yet viable way to support PVA hydrogels for superior swelling and improved mechanical stability. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010