Manufacturing Of Robust Natural Fiber Preforms Utilizing Bacterial Cellulose as Binder

A novel method of manufacturing rigid and robust natural fiber preforms is presented here. This method is based on a papermaking process, whereby loose and short sisal fibers are dispersed into a water suspension containing bacterial cellulose. The fiber and nanocellulose suspension is then filtered (using vacuum or gravity) and the wet filter cake pressed to squeeze out any excess water, followed by a drying step. This will result in the hornification of the bacterial cellulose network, holding the loose natural fibers together.Our method is specially suited for the manufacturing of rigid and robust preforms of hydrophilic fibers. The porous and hydrophilic nature of such fibers results in significant water uptake, drawing in the bacterial cellulose dispersed in the suspension. The bacterial cellulose will then be filtered against the surface of these fibers, forming a bacterial cellulose coating. When the loose fiber-bacterial cellulose suspension is filtered and dried, the adjacent bacterial cellulose forms a network and hornified to hold the otherwise loose fibers together.The introduction of bacterial cellulose into the preform resulted in a significant increase of the mechanical properties of the fiber preforms. This can be attributed to the high stiffness and strength of the bacterial cellulose network. With this preform, renewable high performance hierarchical composites can also be manufactured by using conventional composite production methods, such as resin film infusion (RFI) or resin transfer molding (RTM). Here, we also describe the manufacturing of renewable hierarchical composites using double bag vacuum assisted resin infusion.     

Isolation and Structure Elucidation of α Substance-IB,a Hexapeptide Inducing Sexual Agglutination in Saccharomyces cerevisiae

Cellulose triacetate prepared from bacterial cellulose of Acetobacter xylinum subsp. sucrofermentans BPR3001A showed a higher degree of polymerization and higher mechanical strength than that from the cotton linter. The fine fibrils of bacterial cellulose required only a short time for acetylation which preserved the high degree of polymerization.     

Bacterial cellulose nanocrystals exhibiting high thermal stability and their polymer nanocomposites

Nanocrystals prepared from bacterial cellulose are considered as 'green nanomaterials' depending on their renewable nature and ease of production without the involvement of hazardous chemical treatments. In this investigation, a top down approach was followed for the preparation of bacterial cellulose nanocrystals (BCNC) using a commercially available cellulase enzyme so as to retain native properties of bacterial cellulose even in its nanodimensional form. The morphological and dimensional parameters of BCNC were studied using atomic force microscope (AFM) and transmission electron microscope (TEM). Thermal properties of BCNC produced using the novel enzyme treatment and conventional sulfuric acid hydrolysis were compared. The thermal stability of enzyme processed BCNC was almost two fold higher than sulfuric acid processed ones. Further, the activation energy required for decomposition of enzyme processed BCNC was much higher than the other. Using this enzyme processed BCNC, Polyvinylalcohol (PVA) nanocomposite films were prepared and characterized. Incorporation of these nanocrystals in polymer matrix resulted in a remarkable improvement in the thermal stability as well as mechanical properties of nanocomposite films. These nanocomposites exhibited higher melting temperature (Tm) and enthalpy of melting (ΔHm) than those of pure PVA, suggesting that the addition of nanocrystals modified the thermal properties of PVA. The effective load transfer from polymer chains to the BCNC resulted in an improved tensile strength from 62.5 MPa to 128 MPa, by the addition of just 4 wt% of BCNC. Furthermore, the elastic modulus was found to increase from 2 GPa to 3.4 GPa. The BCNC obtained through cellulose treatment under controlled conditions were associated with several desirable properties and appear to be superior over the conventional methods of nanocrystals production. The enzymatic method followed in this study is expected to contribute the fabrication of high performance polymer nanocomposites in a much greener and innovative manner.     

Production of bacterial cellulose by<Emphasis Type="Italic">Gluconacetobacter hansenii</Emphasis> PJK isolated from rotten apple

A cellulose-producing strain isolated from rotten apples was identified asGluconace-tobacter hansenii based on its physiological properties and the 16S rDNA complete sequencing method, and specifically namedGluconacetobacter hansenii PJK. The amount of bacterial cellulose (BC) produced byG. hansenii PJK in a shaking incubator was 1.5 times higher than that produced in a static culture. The addition of ethanol to the medium during cultivation enhanced the productivity of bacterial cellulose, plus the supplementation of 1% ethanol into the culture medium made the produced BC aggregate into a big lump and thus protected the bacterial-cellulose-producingG. hansenii PJK cells in the shear stress field from being converted into noncellulose-producing (Cel) mutants. Cells subcultured three times in a medium containing ethanol retained their ability to produce BC without any loss in the production yield.     

Review of recent research into cellulosic whiskers, their properties and their application in nanocomposite field

There are numerous examples where animals or plants synthesize extracellular high-performance skeletal biocomposites consisting of a matrix reinforced by fibrous biopolymers. Cellulose, the world's most abundant natural, renewable, biodegradable polymer, is a classical example of these reinforcing elements, which occur as whisker-like microfibrils that are biosynthesized and deposited in a continuous fashion. In many cases, this mode of biogenesis leads to crystalline microfibrils that are almost defect-free, with the consequence of axial physical properties approaching those of perfect crystals. This quite "primitive" polymer can be used to create high performance nanocomposites presenting outstanding properties. This reinforcing capability results from the intrinsic chemical nature of cellulose and from its hierarchical structure. Aqueous suspensions of cellulose crystallites can be prepared by acid hydrolysis of cellulose. The object of this treatment is to dissolve away regions of low lateral order so that the water-insoluble, highly crystalline residue may be converted into a stable suspension by subsequent vigorous mechanical shearing action. During the past decade, many works have been devoted to mimic biocomposites by blending cellulose whiskers from different sources with polymer matrixes.     

细菌纤维素合酶的基本特性及作用机理

细菌纤维素是一种天然的生物质高分子聚合物。相较于植物纤维素,其具有更高的纯度和优异的力学性能。有望作为一种绿色的新型高分子材料被广泛应用。细菌纤维素合酶作为合成细菌纤维素的关键酶,其主导细菌纤维素的合成过程。因此,对其合成机理的探索有助于实现细菌纤维素大量生产和广泛应用。本文从细菌纤维素合酶的基本特性出发,综述了菌种筛选、提升产量和合酶的细胞定位等内容;围绕纤维素合酶的作用机理阐述了体外合成方法的影响因素,以及利用该方法探究各亚基相关作用的现状。以此探究细菌纤维素合酶的合成机制,并提出了当前研究中存在的问题。同时,展望了该领域未来的研究方向,以期通过对合成机理的探讨为细菌纤维素的大规模应用提供理论基础。     

Preparation and characterization on mechanical and antibacterial properties of chitsoan/cellulose blends

Polysaccharides-based membranes of chitosan and cellulose blends were prepared using trifluoroacetic acid as a co-solvent. Morphology and mechanical property of prepared membranes were studied by Instron and dynamic mechanical thermal analysis. The mechanical and dynamic mechanical thermal properties of the cellulose/chitosan blends appear to be dominated by cellulose, suggests that cellulose/chitosan blends were not well miscible. It is believed that the intermolecular hydrogen bonding of cellulose is supposed to be break down to form cellulose–chitosan hydrogen bonding; however, the intra-molecular and intra-strand hydrogen bonds hold the network flat. The reduced water vapor transpiration rate through the chitosan/cellulose membranes indicates that the membranes used as a wound dressing may prevent wound from excessive dehydration. The chitosan/cellulose blend membranes demonstrate effective antimicrobial capability against Escherichia coli and Staphylococcus aureus, as examined by the antimicrobial test. These results indicate that the chitosan/cellulose blend membranes may be suitable to be used as a wound dressing with antibacterial properties.     

Improvement of bacterial cellulose production by manipulating the metabolic pathways in which ethanol and sodium citrate involved

Nowadays, bacterial cellulose has played more and more important role as new biological material for food industry and medical and industrial products based on its unique properties. However, it is still a difficult task to improve the production of bacterial cellulose, especially a large number of byproducts are produced in the metabolic biosynthesis processes. To improve bacterial cellulose production, ethanol and sodium citrate are added into the medium during the fermentation, and the activities of key enzymes and concentration of extracellular metabolites are measured to assess the changes of the metabolic flux of the hexose monophosphate pathway (HMP), the Embden–Meyerhof–Parnas pathway (EMP), and the tricarboxylic acid cycle (TCA). Our results indicate that ethanol functions as energy source for ATP generation at the early stage of the fermentation in the HMP pathway and the supplementation of ethanol significantly reduces glycerol generation (a major byproduct). While in the EMP pathway, sodium citrate plays a key role, and its supplementation results in the byproducts (mainly acetic acid and pyruvic acid) entering the gluconeogenesis pathway for cellulose synthesis. Furthermore, by adding ethanol and sodium citrate, the main byproduct citric acid in the TCA cycle is also reduced significantly. It is concluded that bacterial cellulose production can be improved by increasing energy metabolism and reducing the formation of metabolic byproducts through the metabolic regulations of the bypasses.     

Preparation and UV-protective properties of functional cellulose fabrics based on reactive azobenzene Schiff base derivative

Azobenzene Schiff base possesses excellent photochromic or thermochromic properties based on intermolecular proton transfer or cis-trans isomerization. The azobenzene Schiff base containing two reactive groups, N, N-bis{p-[(2′-sulphatoethyl)sulphonyl phenylazo] salicylidene}-1,2-ethylenediamine (BSPEA), was applied to modify cellulose materials. The functional cellulose fabrics containing azobenzene Schiff base groups were prepared. The chemical and morphological structures of functional cellulose fabrics were characterized by element analysis, FT-IR spectrum, and scanning electron microscopy (SEM). The UV-protection properties of the fabrics were investigated by the ultraviolet transmittance spectra and ultraviolet protection factor (UPF). The results show that the functional cellulose fabrics had excellent UV-protection properties with higher UPF value (UPF value reached 31.7) and lower ultraviolet transmittance (less than 5%). The modified cellulose fabrics had not significant influence on the physical properties. The functional cellulose fabrics based on reactive azobenzene Schiff base would have potential application in textile and functional materials.     

Viscoelastic properties and antimicrobial activity of cellulose fiber sheets impregnated with Ag nanoparticles

A silver nanoparticle colloid was prepared by a modified Tollens method using d-glucose as the reduction agent. The obtained nanoparticles were used for the modification of pine, linter and recycled cellulose fibers. Although the silver contents were relatively low (0.05-0.13wt.%), the cellulose-sheets prepared from the modified fibers show improved mechanical and viscoelastic properties. The tensile index (strength) increased with up to 30% in comparison to the index of the sheets obtained from the untreated fibers. The influence of the nanoparticles on the viscoelastic properties of the cellulose sheets was investigated by dynamic mechanical analysis (DMA) in the temperature range from -120 to 20°C and with a force frequency of 100Hz. A broad relaxation transition positioned at -80°C was observed in the loss modulus spectrum of all the cellulose sheets, while the Ag-modified sheets exhibited higher storage moduli values in the whole temperature range. The antimicrobial activity tests show that the pine, silver and recycled cellulose fiber sheets with silver nanoparticles can be successfully employed to prevent the viability and growth of the common pathogens Staphylococcus aureus, Escherichia coli and Candida albicans.     

Characterization of chemically treated bacterial (Acetobacter xylinum) biopolymer: some thermo-mechanical properties

Bacterial cellulose prepared from pellicles of Acetobacter xylinum (Gluconacetobacter xylinus) is a unique biopolymer in terms of its molecular structure, mechanical strength and chemical stability. The biochemical analysis revealed that various alkali treatment methods were effective in removing proteins and nucleic acids from native membrane resulting in pure cellulose membrane. The effect of various treatment regimens on thermo-mechanical properties of the material was investigated. The cellulose in the form of purified cellulose membranes was characterized by differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA) and dynamic mechanical thermal analysis (DMTA). The glass transition temperature (T(g)) of the native cellulose (untreated, compressed and dried pellicle) was found to be 13.94 degrees C, in contrast, the chemically treated cellulose membranes has higher T(g) values, ranging from 41.41 degrees C to 48.82 degrees C. Investigations on isothermal crystallization were carried out to study the bulk crystallization kinetics. Thermal decomposition pattern of the native as well as alkali treated cellulose was determined by obtaining thermo-gravimetric curves. At higher temperatures (>300 degrees C), the biopolymer was found to degrade. Nevertheless, the alkaline treated cellulose membrane was more stable (between 343.27 degrees C and 370.05 degrees C) in comparison to the native cellulose (298.07 degrees C). Further, the percentage weight loss in case of native cellulose was found to be 26.57%, in comparison to 6.45% for the treated material, at 300 degrees C. The DMTA revealed complex dynamic modulus of the material, at different temperatures and fixed shear stress, applied at a frequency of 5 Hz. The study delineated the effect of alkali treatment regimens, on the thermo-mechanical properties of bacterial cellulose for its application over a wide range of temperatures.     

Effect of reaction conditions on the properties and behavior of wood cellulose nanocrystal suspensions

Sulfuric acid hydrolysis of native cellulose fibers produces stable suspensions of cellulose nanocrystals. Above a critical concentration, the suspensions spontaneously form an anisotropic chiral nematic liquid crystal phase. We have examined the effect of reaction time and acid-to-pulp ratio on nanocrystal and suspension properties for hydrolyzed black spruce acid sulfite pulp. Longer hydrolysis times produced shorter, less polydisperse black spruce cellulose nanocrystals and slightly increased the critical concentration for anisotropic phase formation. Increased acid-to-pulp ratio reduced the dimensions of the nanocrystals thus produced; the critical concentration was increased and the biphasic range became narrower. A suspension made from a bleached kraft eucalyptus pulp gave very similar properties to the softwood nanocrystal suspension when prepared under similar hydrolysis conditions.     

Micromechanical understanding of the cell-wall structure

For improving properties of pulp fibres, a better understanding of the relationships between its macroscopic mechanical properties, fibre ultrastructure, and properties of the wood polymers is important. This paper discusses such relations between elastic properties of fibres, their matrix structure and the wood polymer elastic constants. It is argued that an orientation of all of the wood polymers in the direction of the cellulose microfibrils is most likely. The elastic longitudinal modulus of cellulose is well described by the value of 134 GPa dominating the longitudinal fibre properties. In the transverse direction the amorphous polymers play a more important role.     

Hydrothermal and pulp processing of Eucalyptus

Hydrothermal processing of Eucalyptus wood was performed at operation temperature of 181 degrees C, processing time or 37.5 min and solid water ratio of 1/6 to ensure a maximum loss of xylan recuperation with minimum cellulose fibre degradation. Under those conditions, the loss of xylan was 22% less than that achieved with the conditions 196 degrees C, 50.6 min and 1/8 (solid/water). IN In addition, an experimental design was used to study the influence of process variables: temperature (145-175 degrees C), pulping time (40-120 min) and ethanol concentration (40-70% weight concentration), on the properties of pulps (yield, kappa number, viscosity, cellulose, xylan, lignin acetyl groups contents and brightness) and paper sheets (stretch index, burst index and tear index) obtained from the solid fraction after hydrothermal treatment of Eucalyptus globulus. Pulps with acceptably high physical and chemical properties can be obtained operating at 175 degrees C for 90 min with 55% ethanol concentration.     

Green composite films prepared from cellulose,starch and lignin in room-temperature ionic liquid

A series of novel biobased composite films derived from cellulose, starch and lignin were prepared from an ionic liquid (IL), 1-allyl-3-methylimidazolium chloride (AmimCl) by coagulating in a nonsolvent condition. The ionic liquid can be recycled with a high yield and purity after the green film was prepared. The uniform design method was applied to investigate mechanical properties of the biobased composite films. The effect of each component and their associated interactive effects were investigated. The experimental results showed that contents of cellulose, lignin and starch had a significant influence on the mechanical properties of composite films. The composite films showed relatively excellent mechanical properties in dry and wet states owing to the mutual property supplement of different components. The composite films were characterized via FT-IR, X-ray diffraction (XRD) and scanning electron microscope (SEM). Their thermal stability and gas permeability were also investigated, and the results showed that the composite films had good thermal stability and high gas barrier capacity and give a CO₂:O₂ permeability ratio close to 1.     

Characteristics of the toxic action of a highly disperse copper powder on the energy processes in Escherichia coli B

The role of changes in incubation medium, connected with electrochemical dissolution of fine copper powder (FCP), in efficiency of copper inhibition of energy-dependent proton efflux from E. coli was studied. In conditions of aeration of bacterial suspension in water, toxic properties of FCP can be modelled by dispersed hydrogen peroxide. Addition of hydrogen peroxide to bacteria does not influence their sensitivity to copper chloride. Transfer of the bacteria to anaerobic conditions leads to complete inhibition of energy-dependent proton efflux from E. coli by various copper-containing compounds. The data obtained suggest that the higher efficiency of FCP action on energy processes in E. coli as compared to copper chloride is determined by alkalinization of medium and oxygen absorption in the process of electrochemical dissolution of the metal.     

Bacterial cellulose–alginate composite sponge as a yeast cell carrier for ethanol production

A bacterial cellulose–alginate (BCA) sponge, fabricated by a freeze-drying process, was successfully used as a yeast cell carrier for ethanol fermentation. The BCA sponge exhibited several advantageous properties, such as high porosity, appropriate pore size, strong hydrophilicity and high mechanical, chemical and thermal stabilities. BCA has an asymmetric structure, with a thin, dense outer layer covering an interior of interconnected macropores that are distributed throughout the sponge, which is effective for yeast immobilization. At 48 h of the fermentation, the maximum ethanol concentration produced by the immobilized culture (IC) in the BCA carrier was about 100 g/L, which was approximately 13% and 45% higher than that from the suspended culture (SC) and from IC in Ca-alginate matrix, respectively. Repeated-batch ethanol productions using IC in BCA carriers were also more stable than those using SC or IC in Ca-alginate matrix. The results of a 15 cycle repeated batch operation demonstrated that the system with IC in BCA exhibited superior long-term stability for ethanol fermentation with the average ethanol productivity at 1.9 g/L h and the immobilized yield at 86%. The improved ethanol fermentation performance was mainly due to the water uptake ability and properly interconnected pore structure, which help to overcome limiting mass transfer.     

The influence of fermentation conditions and post-treatment methods on porosity of bacterial cellulose membrane

Bacterial cellulose has been found to be attractive as a novel scaffold material due to its unique material properties. Porosity is the most important morphological parameter in the design of scaffolds for tissue engineering. The effects of fermentation conditions (cultivation time and inoculation volume) and post-treatment methods (alkali treatment and drying methods) on the porosities of bacterial cellulose membranes were investigated. With extended cultivation time and increased inoculation volume, more micro-fibrils were secreted by bacteria, which resulted in a more compact structure and diminished porosity. The porosities of alkali-treated bacterial cellulose membranes was in the order of K₂CO₃ > Na₂CO₃ > KOH > NaOH. Freeze-dried membranes had much higher porosity (92%) than the hot air-dried ones (65%). The experimental results suggested that bacterial cellulose with controlled porosities could be prepared by varying fermentation conditions and post-treatment methods. The resulting bacterial cellulose is regarded as a scaffold material of great potentialities.     

Preparation and properties of HDPE/sugarcane bagasse cellulose composites obtained for thermokinetic mixer

The use of natural fibers as reinforcement for thermoplastics has generated much interest due to their low cost, possibility of environmental protection and use of locally available renewable resources. In this work the mechanical and morphological properties of high density polyethylene/pre-treated and modified residues from sugarcane bagasse cellulose composites were analyzed. Composites were produced by a thermokinetic mixer. The microstructural analyses of fracture surface from composites can be easily evaluated by microscopic techniques. Results showed that the modification of sugarcane bagasse cellulose with zirconium oxychloride was successfully accomplished and that this reinforcement material with high density polyethylene showed tensile strength higher than non-modified sugarcane bagasse cellulose. Modification in the sugarcane bagasse cellulose influenced directly in mechanical properties of the composite material. This can be observed by the fracture surface, which showed that modified cellulose sugarcane bagasse improved interfacial adhesion between fiber and matrix.     

Factors affecting the yield and properties of bacterial cellulose

Acetobacter xylinum E₂₅ has been applied in our studies in order to find optimal culture conditions for effective bacterial cellulose (BC) production. The strain displays significantly higher stability in BC production under stationary culture conditions. In contrast, intensive agitation and aeration appear to drastically reduce cellulose synthesis since such conditions induced formation of spontaneous cellulose nonproducing mutants (Cel−), which dominated in the culture. Mutation frequency strictly depends on the medium composition in agitated cultures. Enrichment of the standard SH and Yamanaka media with 1% ethanol significantly enhanced BC production in stationary cultures. Horizontal fermentors equipped with rotating discs or rollers were successfully applied in order to improve culture conditions. Relatively slow rotation velocity (4 rpm) and large surface area enabling effective cell attachment are optimal parameters for cellulose production. Physical properties of BC samples synthesized either in stationary cultures or in a horizontal fermentor revealed that cellulose from stationary cultures demonstrated a much higher value of Young's modulus, but a much lower value of water-holding capacity. Journal of Industrial Microbiology & Biotechnology (2002) 29, 189–195 doi:10.1038/sj.jim.7000303 Received 01 March 2002/ Accepted in revised form 18 July 2002