棉浆粨纤维素的超声波处理

氢键;结晶程度;棉浆粨纤维素的超声波处理     

超声波活化处理对微晶纤维素结构和氧化反应性能的影响

采用无污染的超声波技术预处理微晶纤维素, 研究了微晶纤维素在活化前后的超分子结构、形态结构和可及度的变化, 超声波活化对微晶纤维素选择性氧化性能的影响.     

Enzyme immobilization to ultra‐fine cellulose fibers via amphiphilic polyethylene glycol spacers

Ultra‐high specific surface cellulose fibers with an average diameter of 500 nm were generated from electrospinning and alkaline hydrolysis of cellulose acetate and used as porous supports for enzyme immobilization. The cellulose fiber surfaces were reacted with polyethylene glycol (PEG) diacylchloride to simultaneously add amphiphilic spacers and reactive end groups for coupling with a lipase enzyme. The quantity of reactive carboxylic acid on the fiber surfaces could be readily controlled by COCl/OH molar ratios and PEG lengths. The highest free acid (COOH) content of 1.0 mmol per gram of cellulose was obtained at 10 COCl/OH ratio with the 600‐Da PEG diacylchloride. Enzyme coupling on such PEG‐attached cellulose was optimal in the presence of a water‐soluble carbodiimide [1‐ethyl‐3‐(3‐dimethylaminopropyl) carbodiimide (EDC)] at a very low EDC/COOH molar ratio of 0.2 under acidic condition and at ambient temperature. Whereas the free lipase retained only 25% of its original activity, the fiber‐bound lipase possessed much superior retention of catalytic activity after exposure to cyclohexane (81%) and toluene (62%) and hexane (34%). The fiber‐bound lipase also exhibited significantly higher catalytic activity at elevated temperatures than the free form, that is, 10 times at 70 °C. The ultra‐fine, fibrous, and porous structures were retained throughout alkaline hydrolysis, activation, coupling, and activity assays. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4289–4299, 2004     

Fiber properties of eucalyptus kraft pulp with different carboxyl group contents

Fiber properties (fiber swelling ability, crystal structure of cellulose, fiber surface morphology, and etc.) of eucalyptus kraft pulp with different contents of carboxyl group in Na-form were studied. There was a direct proportional relationship between water retention value and carboxyl content of pulp. When the carboxyl content increased from 35.6 to 315.7 mmol/kg, tensile index and burst index increased by 56.1 and 117.8 %, respectively, and crystallinity of cellulose decreased by 11.8 %. Environmental scanning electron microscope showed that more fibrillation was observed on the carboxymethylated fiber surface, compared with the control sample. The results from Fourier transform infrared spectra analysis suggested that the relative intensity of the band at 1,633/cm was increased after carboxymethylation treatment, which showed that the carboxyl content increased. The increase in the carboxyl content not only could increase the fiber strength properties, but also could increase the recycling times of the fiber.     

Morphological and structural development of hardwood cellulose during mechanochemical pretreatment in solid state through pan-milling

Mechanochemical pretreatment of hardwood cellulose was conducted by our self-designed pan-mill equipment which has an unique and smart structure and can exert strong shear forces and pressure on materials in between and break them down. The structure transformations, including particle size, powder morphology, molecular structure, crystalline structure during milling were investigated by Laser Diffraction Particle Size Analyzer, SEM, FT-IR and WAXD, respectively. Compared with standard method of ball-milling, the pan-mill shows a much higher efficiency in mechanochemical pretreatment of hardwood cellulose. The average particle size reduced to 21 μm and the specific surface area increased to 0.8 m²/g after 40 milling cycles. Mechanical milling also led to collapse of hydrogen bonds and reduction of crystallinity. The crystallinity index of cellulose powder decreased from its original 65 to 22, after milling for 40 cycles. Thermal analysis and solubility testing illustrated that pan-milled cellulose has lower thermal stability and higher solubility in aqueous alkali.     

Physical and mechanical properties of polyvinyl alcohol and polypropylene composite materials reinforced with fibril aggregates isolated from regenerated cellulose fibers

Natural fibers in micro and nano scales may be a potential alternative for man-made fibers because of the comparable mechanical properties to those of glass, carbon, and aramid fibers. Cellulose fibril and fibril aggregate are generally prepared by physical treatments, e.g., high-pressure homogenizer, or chemical treatments, e.g., acid hydrolysis. In this study, fibril aggregates were generated from a regenerated cellulose fiber by a novel mechanical treatment. The geometrical characteristics of the fibers and the fibril aggregates were investigated using scanning electron microscopy (SEM) and polarized light microscopy (PLM), and its crystallinity was investigated by wide angle X-ray diffraction (WAXD). The degree of fibrillation of the fibers was indirectly evaluated by water retention value (WRV). Nano-biocomposites reinforced with fibril aggregates were prepared by film casting and compression molding and evaluated by tensile test. The morphological characteristics of the nanocomposites were investigated with SEM and PLM. As reference, commercial microfibrillated cellulose was also used to reinforce biodegradable polymer.     

富含纤维素类农作物秆与丙烯酸接枝共聚制备高倍率吸水树脂

用棉花秆、麦秆和玉米秆等富含纤维素类农作物秆与丙烯酸接枝共聚制备了高倍率的吸水树脂. 研究了不同水质(去离子水、自来水及雨水)对接枝产物吸水性能的影响. 采用棉花秆、麦秆、玉米秆与丙烯酸的接枝产物对去离子水的吸水倍率分别为930, 790和630 g/g, 对自来水的吸水倍率分别为670, 350和250 g/g, 用玉米秆/地瓜淀粉混合物制备的接枝产物对雨水的吸水倍率为540 g/g. 为棉花秆、 麦秆及玉米秆等富含纤维素的农作物秆的深加工与应用开辟了一条途径.     

Bacterial cellulose/poly(ethylene glycol) composite: characterization and first evaluation of biocompatibility

Bacterial cellulose (BC)/poly(ethylene glycol) (PEG) composite was prepared by immersing wet BC pellicle in PEG aqueous solution followed by freeze-drying process. The product looks like a foam structure. The morphology of BC/PEG composite was examined by scanning electron microscope (SEM) and compared with pristine BC. SEM images showed that PEG molecules was not only coated on the BC fibrils surface but also penetrated into BC fiber networks. It has very well interconnected porous network structure and large aspect surface. The composite was also characterized by Fourier transform infrared spectrum, X-ray diffraction, thermogravimetric analysis (TGA) and tensile test. It was found that the presence of PEG affected the preferential orientation of the (1[`1]0 1\bar{1}0 ) plane during the drying process of BC pellicle, which in turn decrease the crystallinity of dried BC. The TGA result showed that the thermal stability was improved from 263 to 293 °C, which might be associated with strong interaction between BC and PEG. Tensile test results indicate that the Young’s modulus and tensile strength tend to decrease. Biocompatibility of composite was preliminarily evaluated by cell adhesion studies using 3T3 fibroblast cells. The cells incubated with BC/PEG scaffolds for 48 h were capable of forming cell adhesion and proliferation, which showed much better biocompatibility than the pure BC. The prepared BC/PEG scaffolds can be used for wound dressing or tissue-engineering scaffolds.     

Structure and thermal properties of bamboo viscose,Tencel and conventional viscose fiber

Comparative investigations of new regenerated cellulosic fibers, bamboo viscose fiber and Tencel, together with conventional viscose fibers have been carried out to explain the similarity and difference in their molecular and fine structure. The analyses jointly using SEM, XRD and IR reveal that all the three fibers belong to cellulose II. Tencel consists of longer molecules and has a greater degree of crystallinity, while bamboo viscose fiber has a lower degree of crystallinty. TG-DTG-DSC study shows three fibers resemble in thermal behavior with a two-step decomposition mode. The first step is associated to water desorption, suggesting that bamboo viscose fiber holds better water retention and release ability, the second a depolymerization and decomposition of regenerated cellulose, indicating that Tencel is more thermally stable in this process than bamboo and conventional viscose fiber.     

致孔剂聚乙二醇对纤维素中空纤维膜结构与性能的影响

以离子液体氯代1-烯丙基-3-甲基咪唑（[AMI M]Cl）为溶剂纺制纤维素中空纤维膜,考察了聚乙二醇（PEG）分子量及其质量分数对中空纤维膜结构与性能的影响。采用场发射扫描电子显微镜（FESEM）对膜内、外表面形态结构进行了观察,测试了中空纤维膜的水通量、截留率等渗透性能以及最大拉伸强度、断裂伸长率等力学性能。结果表...     

Isolation of cellulose fibers from kenaf using electron beam

Cellulose fibers were isolated from a kenaf bast fiber using a electron beam irradiation (EBI) treatment. The methods of isolation were based on a hot water treatment after EBI and two-step bleaching processes. FT-IR spectroscopy demonstrated that the content of lignin and hemicellulose in the bleached cellulose fibers treated with various EBI doses decreased with increasing doses of EBI. Specifically, the lignin in the bleached cellulose fibers treated at 300 kGy, was almost completely removed. Moreover, XRD analyses showed that the bleached cellulose fibers treated at 300 kGy presented the highest crystallinity of all the samples treated with EBI. Finally, the morphology of the bleached fiber was characterized by SEM imagery, and the studies showed that the separated degree of bleached cellulose fibers treated with various EBI doses increased with an increase of EBI dose, and the bleached cellulose fibers obtained by EBI treatment at 300 kGy was separated more uniformly than the bleached cellulose fiber obtained by alkali cooking with non-irradiated kenaf fiber.     

Smooth model cellulose I surfaces from nanocrystal suspensions

Removal of lignin, hemicelluloses and other minor components during pulping results in a porous fibrillar structure. Interactions of cellulose fibre surfaces with wet-end additives and other materials depend both on the interfacial properties of the cellulose and on the morphology of the surface. It would be useful to be able to separate the interactions with the cellulose from those that depend on surface roughness and porosity by preparing flat cellulose surfaces. Current methods give surfaces of amorphous cellulose or of cellulose II, differing in density and crystallinity from the original cellulose I surface. We propose a new route to prepare smooth model surfaces of cellulose I, starting from colloidal dispersions of cellulose I nanocrystals. The nanometer-sized width of these rod-like colloidal particles allows a relatively flat surface to be prepared from the suspension by casting an aqueous suspension on an appropriate surface and allowing the water to evaporate. Oriented films can be prepared by spin-coating or shearing. The surface composition and morphology of the films were examined by X-ray photoelectron spectroscopy and atomic force microscopy.     

Enhanced removal of hemicelluloses from cellulosic fibers by poly(ethylene glycol) during alkali treatment

Enhancing removal of hemicelluloses from cellulosic fibers is of decisive importance for producing high-purity cellulose. In this study, poly(ethylene glycol) (PEG) was added to a cold caustic extraction (CCE) process to promote removal of hemicelluloses from a softwood sulfite dissolving pulp. The content of hemicelluloses was considerably decreased from 11.4 % in the original sample to 5.3 % in the PEG/CCE-treated sample under the studied conditions. This positive result of PEG addition can be explained by (1) improved inward penetration and diffusion of NaOH into the fiber structure and outward diffusion of hemicelluloses from the fiber structure to the bulk phase, and (2) enhanced fiber swelling due to inclusion of PEG in the fiber walls and improved NaOH diffusion. Moreover, the effects of PEG/CCE treatment on the distribution of hemicelluloses in the fiber walls and the molecular weight of the residual hemicelluloses in the resulting pulp were investigated.     

In situ modification of bacterial cellulose nanostructure by adding CMC during the growth of Gluconacetobacter xylinus

Many studies focus on bacterial cellulose (BC) functioning as multi-function bio-resource polymers, due to its fine fiber network, biocompatibility, high water holding capacity, and high mechanical strength. However, BC exhibits poor rehydration after drying due to its high crystallinity. This study added carboxymethylcellulose (CMC) to a BC producing culture medium, which interfered with the formation of BC structure in situ. This process created a modified BC called CBC, whose mechanical strength was found weaker than BC. Scanning electron microscope (SEM) images showed that the cellulose network in CBC became denser. X-ray diffraction and Fourier transform infrared spectroscopy (FTIR) analysis demonstrated that the addition of CMC reduced crystallinity. CBC also exhibited the highest rehydration ratio because of the lowest crystallinity at the 1.0% CMC addition level.     

Oxidation and sulfonation of cellulosics

Bleached hardwood (HW) kraft pulp and derived nanocellulosic structures were modified by a periodate oxidation followed by treatment with sodium bisulfite to yield the corresponding C2/3 sulfonates. The impact of this oxidative–reductive protocol on the chemical and physical properties of cellulose was evaluated by determining physical dimensions, functional groups, and their water absorbency properties. It was found that the water absorbency of cellulosic material can be enhanced by 8.0–199.0% with this oxidation/sulfonation protocol. Distinct differences were observed between sulfonated pulp fibers and nanocellulosic structures, with the latter exhibiting relatively higher water retention values (WRV).     

Utilizing cellulase as a hydrogen peroxide stabilizer to combine the biopolishing and bleaching procedures of cotton cellulose in one bath

In this research, the stabilization effect of cellulase on the decomposition of hydrogen peroxide was investigated for the first time. It was concluded that, regardless of the decomposition mechanism, the cellulase protein could contribute significantly to peroxide stability. This effect stems from the formation of molecular hydrogen bonding between peroxide and cellulase protein or direct sequestering of free metal ions by amino acids in cellulase. Furthermore, based on this stability, a combined biopolishing and peroxide bleaching protocol was developed to improve cotton quality more efficiently. Afterwards, physicochemical properties such as the weight and strength loss, water absorbency, and carbonyl and carboxyl group content of treated cotton cellulose were measured to show the feasibility of the new method. Fourier-transform infrared (FT-IR) and X-ray diffraction (XRD) analyses indicated that the crystallinity index of cotton was increased due to the preferential hydrolysis of amorphous cellulose by cellulase.     

Highly absorbable lyocell fiber spun from celluloses/hydrolyzed starch-g-PAN solution in NMMO monohydrate

To improve the absorption properties of lyocell fiber, a hydrolyzed starch-grafted-polyacrylonitrile (HSPAN) superabsorbent whose powder size was less than 100 μm was added to the cellulose solution in N-methyl morpholine N-oxide (NMMO) monohydrate. The lyocell fiber was prepared by dry jet-wet spinning of the solution. To begin with HSPAN whose water-absorbency was 325 g/g (water/fiber) was prepared by hydrolysis of the copolymer in which acrylonitrile (AN) monomer was grafted onto the starch. The introduction of HSPAN led to a notable improvement of absorbency and absorption rate of lyocell fiber for water. The maximum water-absorbency of the fibers containing HSPAN 2 and 5 wt% was as high as 4.55 and 8.21 g/g, respectively. These values are comparable with 1.94 g/g for unmodified lyocell fiber. SEM and polarizing optical microscope results confirmed that HSPAN remained within the lyocell fiber at both wet and dry states. With increasing HSPAN content, however, the mechanical properties of lyocell fibers were decreased. Thus, the optimum HSPAN content may give a good combination of absorption and mechanical properties.     

Crystal and pore structure of wheat straw cellulose fiber during recycling

The changes in crystal structure and pore size of wheat straw fiber after repeated recycling were studied by means of X-ray diffraction, Fourier transform infrared spectrophotometry, and transmission electron microscopy. The results showed that in unbleached wheat straw cellulose crystallinity increased and the water retention value decreased with increasing rounds of recycling. After five rounds, the crystallinity increased by 14.6% compared with fiber never used for papermaking. The width of the crystallite in a 002 lattice plane (L₀₀₂) increased after each round of recycling, which indicated co-crystallization during the recycling process. The pore-size distribution of wheat straw fiber consisted of numerous micropores and mesopores but few macropores. The pore volumes of pulp micropores and mesopores decreased after two rounds of recycling, but subsequent rounds scarcely affected the pore-volume distribution. The average pore size and specific surface area of the fiber decreased after recycling. In addition, after recycling and rewetting, the fiber lumen became irreversibly collapsed and distorted, with numerous pleats that changed the shapes and size of the pores.     

Properties of cellulose micro/nanofibers obtained from eucalyptus pulp fiber treated with anaerobic digestate and high shear mixing

High production costs remain the single greatest factor limiting wider use of cellulose micro/nanofibers by industry. The objective of the present study was to investigate the potential of using a low-cost bacteria-rich digestate (liquid anaerobic digestate—AD-supernatant) on milled eucalyptus fiber followed by high-shear mixing to obtain cellulose micro/nanofibers. The morphology, crystallinity, and thermal stability of micro/nanofibers obtained by this process were studied. The bacteria population in the AD-supernatant was comprised mostly of Bacteroides graminisolvens and Parabacteroides chartae. The digestate treatment partially removed amorphous components of the pulp fiber thereby decreasing micro/nanofiber diameters and enhancing the crystalline content. The treatment also increased the size of the crystalline cellulose. The morphology and crystallinity results demonstrate the effectiveness of digestate treatments coupled with high-shear mixing as a procedure for the production of micro/nanofibers.     

Single stage purification of flax,hemp, and milkweed stem and their physical and morphological properties

Agriculture biomass is an alternative possible solution for the extraction of cellulose, compared to the classical soft and hard wood. However, the valorization of cellulose is challenging for the researchers as it involves multiple steps. In the present study, the raw fibers of flax, hemp, and milkweed stem fibers were purified in single step using hydrogen peroxide in water. By this method authors successfully extracted the purified cellulose fibers without damaging the fiber length. The purified fibers were characterized to understand the thermal, functional, crystalline, and morphological properties by thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The FTIR results showed the effective removal of lignin and significant improvement in thermal stability was observed by TGA. Evidently, the SEM results showed significant improvement in the morphology compared to that of the raw fibers. XRD results showed that the treatment does not affect the crystallinity of the fibers.