Preparation of cellulose films from solution of bacterial cellulose in NMMO

Bacterial cellulose (BC) was dissolved in N-methylmorpholine N-oxide (NMMO) to prepare regenerated BC films (RBC) with phase inversion. The solubility of BC, supermolecule on structure, morphology, thermal and physical properties of the films were investigated by Fourier transform infrared spectroscopy (FT-IR), solid-state cross polarization/magic angle spinning ¹³C nuclear magnetic resonance (CP/MAS ¹³C NMR), wide-angle X-ray diffraction (WAXD), scanning electron microscope (SEM), and thermogravimetric analysis (TGA). The investigation suggested BC was dissolved completely in NMMO. From the C₆ signal shifts to the amorphous area, the crystallinity of materials decreased from 79.20% to 38.17%, and the transformation from cellulose I to II occurred. It was also found that the banded structure of the native materials was replaced by homogeneous and densified sections, so RBC films had better mechanical and barrier properties, and do thermal stability was similar to that of the native BC.     

Kinetic study on enzymatic hydrolysis of cellulose by cellulose from Trichoderma viride

Pure cellulose (Avicel) was hydrolyzed batchwise at 50 degrees C and pH 4.8 by cellulase from Trichoderma viride (Meicelase CEP). Then the effects of the crystallinity of cellulose as well as the thermal deactivation and product (cellubiose and glucose) inhibition to cellulose on the hydrolysis rate were quantitatively investigated. While these factor had evidently retarded the enzymatic hydrolysis of cellulose to a significant extent, the hydrolysis rates observed could not be explained. For practical purposes, an empirical, simple rate expression was developed which included only one parameter: a overall rate retardation constant. This empirical rate expression held for the hydrolysis of at least two kind of cellulosic materials: Avicel and tissue paper.     

Natural cellulose fibers from soybean straw

This paper reports the development of natural cellulose technical fibers from soybean straw with properties similar to the natural cellulose fibers in current use. About 220 million tons of soybean straw available in the world every year could complement the byproducts of other major food crops as inexpensive, abundant and annually renewable sources for natural cellulose fibers. Using the agricultural byproducts as sources for fibers could help to address the concerns on the future price and availability of both the natural and synthetic fibers in current use and also help to add value to the food crops. A simple alkaline extraction was used to obtain technical fibers from soybean straw and the composition, structure and properties of the fibers was studied. Technical fibers obtained from soybean straw have high cellulose content (85%) but low% crystallinity (47%). The technical fibers have breaking tenacity (2.7 g/den) and breaking elongation (3.9%) higher than those of fibers obtained from wheat straw and sorghum stalk and leaves but lower than that of cotton. Overall, the structure and properties of the technical fibers obtained from soybean straw indicates that the fibers could be suitable for use in textile, composite and other industrial applications.     

Enzymatic production of ethanol from cellulose using soluble cellulose acetate as an intermediate

A two-stage process for the enzymatic conversion of cellulose to ethanol is proposed as an alternative to currently incomplete and relatively slow enzymatic conversion processes employing natural insoluble cellulose. This alternative approach is designed to promote faster and more complete conversion of cellulose to fermentable sugars through the use of a homogeneous enzymatic hydrolysis reaction. Cellulose is chemically dissolved in the first stage to form water-soluble cellulose acetate (WSCA). The WSCA is then converted to ethanol in a simultaneous saccharification-fermentation with Pestal-otiopsis westerdijkii enzymes (containing cellulolytic and acetyl esterase components) and yeast.Water-soluble cellulose acetate was successfully prepared from purified wood cellulose (Solka Floe) and chemical reagents. Enzyme pretreatment of WSCAto form metabolizable sugars was a necessary step in achieving practical conversion of WSCA to ethanol using yeast. The results showed that WSCA has a low enzyme requirement and a high convertibility to reducing sugars with enzymes from P. westerdijkii fungus. Pestalotiopsis westerdijkii enzymes were found to be superior to enzymes from Trichoderma viride in producing metabolizable glucose from WSCA. The yeast utilized 55-70% of the hydrolyzate sugars that were produced by P. westerrlijkii enzymes on WSCA and produced ethanol. The acetate that was liberated into solution by the action of acetyl esterase enzymes on WSCA was found to have a stimulatory effect on ethanol production in yeast. This is an important feature that can be used to advantage in manipulating the conversion to maximize the production of ethanol. Hence, the simultaneous saccharification-fermentation of WSCA to ethanol using P. westerdijkii enzymes and yeast has features that are highly desirable for developing an economical cellulose conversion process.     

Bulk cellulose plastic materials from processing cellulose powder using back pressure-equal channel angular pressing

Bulk cellulose plastic materials with a continuous morphology were successfully processed from cellulose powder through back pressure-equal channel angular pressing (BP-ECAP) at 150 °C without using any additives. The strong shear deformation during the process caused an efficient deformation of cellulose granular and crystalline structures, resulting in effective chain penetration and strong intermolecular interactions throughout the whole material. The mechanical behaviour of the cellulose plastics was comparable to those of polymer/cellulose composites. Ball milling the cellulose powder prior to processing disrupted the crystalline structures thus resulting in more significant modifications of the molecular motions of the cellulose. The outcome of this research provides a potential methodology for manufacturing renewable and biodegradable bulk materials from cellulose-based agricultural waste.     

Ethanol formation from cellulose by thermophilic bacteria

Summary A wild coculture of obligately thermophilic bacteria, including only a single cellulolytic species Clostridium, ferments 2% crystalline cellulose and produces 4.6–5.1 g·l^–1 of ethanol at 55°–60° C; that is, 0.96–1.1 moles of ethanol from 1 mole of glucose equivalent of cellulose degraded. However, the ethanol yield decreases with increasing cellulose concentration. Ethanolacetic acid ratio varies around 1 and cannot be influenced by substrate concentration. However, this ratio can be influenced by changing pH and temperature. For the ethanol production from cellulose, neutral and weekly alkaline media with a pH of 7.0–8.0 and a temperature of 55° C are optimal. Experiments in which the coculture was subjected to high ethanol concentrations showed that higher concentrations of added ethanol (up to 20 g·l^–1) suppress cellulose degradation by 50% and inhibit the actual production of ethanol.     

Biodegradable and biocompatible polyampholyte microgels derived from chitosan, carboxymethyl cellulose and modified methyl cellulose

Two biocompatible and biodegradable polyampholyte microgels, namely chitosan-carboxymethyl cellulose (CS-CMC) and chitosan-modified methyl cellulose (CS-ModMC) were synthesized by an inverse microemulsion technique. The CS-CMC microgel system was pH-responsive while the CS-ModMC system possessed both pH and thermo-responsive properties. For CS-CMC system, the number of -OCH₂COOH and -NH₂ groups was determined to be 1.5 and 1.1 meq/g of microgel, respectively. In the pH range of 4-9, the zeta potential values varied from +10 to −40 mV, while the hydrodynamic radius varied from 160 nm in the swollen state (acidic and basic pH) to 110 nm in the “collapse” state (neutral pH). Furthermore, TEM micrographs confirmed the swelling/deswelling behaviour of CS-CMC microgel particles at acidic, neutral and basic conditions. For CS-ModMC system, the number of -OCH₂COOH and -NH₂ groups was determined to be 0.8 and 0.6 meq/g microgel, respectively. In the pH range of 4-9, the surface charge on the microgels varied from +25 to −60 mV and the hydrodynamic radii were 190 nm at low pH, 80 nm at neutral pH, to 120 nm at a high pH. In vitro drug release studies confirmed that CS-CMC microgels could encapsulate and release a model drug, thus they could potentially be used as biocompatible and biodegradable drug carriers.     

Nonleaching antimicrobial films prepared from surface-modified microfibrillated cellulose

We have prepared potentially permanent antimicrobial films based on surface-modified microfibrillated cellulose (MFC). MFC, obtained by disintegration of bleached softwood sulfite pulp in a homogenizer, was grafted with the quaternary ammonium compound octadecyldimethyl(3-trimethoxysilylpropyl)ammonium chloride (ODDMAC) by a simple adsorption-curing process. Films prepared from the ODDMAC-modified MFC were characterized by Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) and tested for antibacterial activity against the Gram-positive bacterium Staphylococcus aureus and the Gram-negative bacteria Escherichia coli and Pseudomonas aeruginosa. The films showed substantial antibacterial capacity even at very low concentrations of antimicrobial agent immobilized on the surface. A zone of inhibition test demonstrated that no ODDMAC diffused into the surroundings, verifying that the films were indeed of the nonleaching type.     

Homogenous reactions of cellulose from different natural sources

Two different homogenous reactions on bacterial cellulose (BC), kenaf fiber (KF) and microcrystalline cellulose (MC) were performed to monitor their chemical reactivity. The first reaction was selective oxidation of the primary hydroxyl group with sodium chlorite in the presence of catalytic amount of sodium chloride. While, the second was the formation of triester hypoiodous cellulose using potassium iodate and potassium iodide. The chemical structures of these derivatives were investigated using FT-IR and solid state ¹³C NMR spectroscopies. The BC fibrils required the shortest time among these cellulose samples for both reactions, whereas the viscosity values of BC after iodination and oxidation have the best values compared to KF and MC. FT-IR results show the absence of the hydroxy group of BC and a weak absorption band in both KF and MC. On the other hand, the crystallinity index (CI) of BC is higher than those of both KF and MC. FT-IR spectra of the oxidized different cellulose samples, confirmed the presence of a strong absorption band at around 1590 cm⁻¹ that attributed to vibration band of carbonyl group of carboxylic moiety. Moreover, in the ¹³C NMR spectrum of oxidized cellulose, the lack of signal at 62 ppm and the appearance of signal at 171 ppm indicated that the primary alcohol group is completely oxidized to carboxylic acid. These results showed that BC had a higher reactivity than other samples due to its great purity and low degree of polymerization.     

Production of cellulose from glucose by Acetobacter xylinum

Acetobacter xylinum 1FO 13693 was selected as the best cellulose-producing bacterium among 41 strains belonging to the genus Acetobacter and Agrobacterium. Cellulose was found to be produced at the liquid surface in static liquid cultivation. The rate of cellulose production depended proportionally on the surface-area of the culture medium and was unaffected by the depth and volume of the medium. The optimum pH for cellulose production was 4.0 to 6.0. Glucose, fructose and glycerol were preferred carbon sources for cellulose production. The yield of cellulose, relative to the glucose consumed, decreased with an increase in initial glucose concentration, and gluconic acid accumulated at a high initial glucose concentration. The decrease in cellulose yield could be due to some glucose being metabolized to gluconic acid. However, the accumulated gluconic acid did not affect cellulose production. The culture conditions of the bacterium for cellulose production were optimized. The maximum production rate of cellulose was 36 g/d·m², with a yield of 100% for added glucose under the optimal conditions.     

Conformational features of crystal-surface cellulose from higher plants

Native cellulose in higher plants forms crystalline fibrils a few nm across, with a substantial fraction of their glucan chains at the surface. The accepted crystal structures feature a flat-ribbon 21 helical chain conformation with every glucose residue locked to the next by hydrogen bonds from O-3' to O-5 and from O-2 to O-6'. Using solid-state NMR spectroscopy we show that the surface chains have a different C-6 conformation so that O-6 is not in the correct position for the hydrogen bond from O-2. We also present evidence consistent with a model in which alternate glucosyl residues are transiently or permanently twisted away from the flat-ribbon conformation of the chain, weakening the O-3' - 0-5 hydrogen bond. Previous molecular modelling and the modelling studies reported here indicate that this 'translational' chain conformation is energetically feasible and does not preclude binding of the surface chains to the interior chains, because the surface chains share the axial repeat distance of the 21 helix. Reduced intramolecular hydrogen bonding allows the surface chains to form more hydrogen bonds to external molecules in textiles, wood, paper and the living plant.     

Determination of cellulose crystallinity from powder diffraction diagrams

One‐dimensional (1D) (spherically averaged) powder diffraction diagrams are commonly used to determine the degree of cellulose crystallinity in biomass samples. Here, it is shown using molecular modeling how disorder in cellulose fibrils can lead to considerable uncertainty in conclusions drawn concerning crystallinity based on 1D powder diffraction data alone. For example, cellulose microfibrils that contain both crystalline and noncrystalline segments can lead to powder diffraction diagrams lacking identifiable peaks, while microfibrils without any crystalline segments can lead to such peaks. This leads to false positives, that is, assigning disordered cellulose as crystalline, and false negatives, that is, categorizing fibrils with crystalline segments as amorphous. The reliable determination of the fraction of crystallinity in any given biomass sample will require a more sophisticated approach combining detailed experiment and simulation. © 2014 Wiley Periodicals, Inc. Biopolymers 103: 67–73, 2015.     

Towards electronic paper displays made from microbial cellulose

Cellulose (in the form of printed paper) has always been the prime medium for displaying information in our society and is far better than the various existing display technologies. This is because of its high reflectivity, contrast, low cost and flexibility. There is a major initiative to push for a dynamic display technology that emulates paper (popularly known as electronic paper). We have successfully demonstrated the proof of the concept of developing a dynamic display on cellulose. To the best of our knowledge, this is the first significant effort to achieve an electronic display using bacterial cellulose. First, bacterial cellulose is synthesized in a culture of Acetobacter xylinum in standard glucose-rich medium. The bacterial cellulose membrane thus formed (not pulp) is dimensionally stable, has a paper-like appearance and has a unique microfibrillar nanostructure. The technique then involves first making the cellulose an electrically conducting (or semi-conducting) sheet by depositing ions around the microfibrils to provide conducting pathways and then immobilizing electrochromic dyes within the microstructure. The whole system is then cased between transparent electrodes, and upon application of switching potentials (2–5 V) a reversible color change can be demonstrated down to a standard pixel-sized area (ca. 100 m²). Using a standard back-plane or in-plane drive circuit, a high-resolution dynamic display device using cellulose as substrate can be constructed. The major advantages of such a device are its high paper-like reflectivity, flexibility, contrast and biodegradability. The device has the potential to be extended to various applications, such as e-book tablets, e-newspapers, dynamic wall papers, rewritable maps and learning tools.     

Laccase from Melanocarpus albomyces binds effectively to cellulose

A laccase from the thermophilic fungus Melanocarpus albomyces was shown to bind to softwood and pure microcrystalline cellulose. The binding isotherm fitted well the Langmuir type one-site binding model. The adsorption parameters indicated that M. albomyces laccase binds with high affinity to cellulose with a relatively low maximum binding capacity, as compared to the values for various cellulases. The binding was shown to be reversible and not influenced by non-specific protein or 0.1-0.5 M Na2SO4. No binding was detected with laccases from Trametes hirsuta or Mauginiella sp., which suggests that binding to cellulose is typical for only some laccases.     

Comb polymers prepared by ATRP from hydroxypropyl cellulose

Hydroxypropyl cellulose (HPC) was used as a core molecule for controlled grafting of monomers by ATRP, the aim being to produce densely grafted comb polymers. HPC was either allowed to react with an ATRP initiator or the first generation initiator-functionalized 2,2-bis(methylol)propionic acid dendron to create macroinitiators having high degrees of functionality. The macroinitiators were then "grafted from" using ATRP of methyl methacrylate (MMA) or hexadecyl methacrylate. Block copolymers were obtained by chain extending PMMA-grafted HPCs via the ATRP of tert-butyl acrylate. Subsequent selective acidolysis of the tert-butyl ester moieties was performed to form a block of poly(acrylic acid) resulting in amphiphilic block copolymer grafts. The graft copolymers were characterized by 1H NMR and FT-IR spectroscopies, DSC, TGA, rheological measurements, DLS, and tapping mode AFM on samples spin coated upon mica. It was found that the comb (co)polymers were in the nanometer size range and that the dendronization had an interesting effect on the rheological properties.     

纸浆废料生物炼制细菌纤维素的研究

细菌纤维素(bacterial cellulose,BC)是一种由微生物产生的具有纳米结构的纤维素材料。BC生产的培养基成本偏高,限制了其规模化工业生产和商业应用。为开发新的BC生产原料,通过Cellic CTec 2纤维素酶直接水解硫酸盐和亚硫酸盐两种纸浆废料获得可发酵糖,以其成功制备出BC并研究比较了两种酶解液对BC产量和结构的差异。结果表明,硫酸盐纸浆废料获得的BC产量最高,达9.0 g/L,比亚硫酸盐纸浆废料的7.7 g/L高了17%。两种原料制备的BC膜的结晶度分别为61%和66%,比葡萄糖制备的(78%)低。红外光谱分析表明,不同碳源制备的BC膜的成分没有明显差异。