Properties of natural cellulose fibers from hop stems

This paper reports the development of natural cellulose fibers from hop stems with properties similar to that of hemp. Hop stems are currently considered as byproducts and have limited applications. Since hop belongs to the genus cannabis that also includes hemp, it should be possible to obtain natural cellulose fibers from the stems of hop plants with properties similar to that of hemp. A simple alkaline extraction was used to obtain fibers from the bark of hop stems. Fibers obtained have high cellulose content, low% crystallinity but show good orientation of the cellulose crystals to the fiber axis. The strength and modulus of the fibers are lower but elongation is higher than that of hemp. Based on the properties of the fibers, we expect that the hop stem fibers will be suitable for use in textiles and composites similar to the common cellulose fibers currently in use.     

A Comparative Analysis of in vitro cellulose synthesis from cell-free extracts of mung bean (Vigna radiata,Fabaceae) And Cotton (Gossypium hirsutum,Malvaceae)

A comparison of cellulose synthesized in vitro from primary walls of etiolated mung bean (Vigna radiata) seedlings and secondary walls of cotton fibers (Gossypium hirsutum) was made by applying conditions found to be essential for in vitro cellulose I assembly from cotton (Kudlicka et al., 1995, Plant Physiology, vol. 107, pp. 111–123). Mung bean fractions including the plasma membrane (PM), the first solubilized fraction (SE₁), and the second solubilized fraction (SE₂), incorporated more radioactive UDP-Glc into the total product than the same fractions from secondary walls. A significant difference was found with the mild digitonin solubilized fraction (SE₁), which produced eight times more total product than the SE₁ fraction of cotton. However, the SE₁ fraction from cotton produced a larger quantity of cellulose (32.1%) than from mung bean (6.9%). Treatment of the in vitro product by acetic/nitric acid reagent (AN) for varying periods of time demonstrated that cellulose synthesized in vitro from mung bean was more easily degraded than cellulose from cotton fibers. This would suggest that cellulose I produced in vitro from the cotton SE₁ fraction may have a higher crystallinity and DP than cellulose I produced in vitro from mung bean. The fibrils of cellulose produced by the SE, fraction of mung bean were loosely associated and not arranged into a compact bundle as in case of cellulose I synthesized by the cotton SE₁ fraction. The electron diffraction patterns (ED) of both products show reflections characteristic for cellulose I. Products from the SE₂ fraction of mung bean and cotton reveal similarities with the cellulose II allomorph synthesized, as well as abundant β-1,3-glucan.     

Surface modification of natural fibers using bacteria: depositing bacterial cellulose onto natural fibers to create hierarchical fiber reinforced nanocomposites

Triggered biodegradable composites made entirely from renewable resources are urgently sought after to improve material recyclability or be able to divert materials from waste streams. Many biobased polymers and natural fibers usually display poor interfacial adhesion when combined in a composite material. Here we propose a way to modify the surfaces of natural fibers by utilizing bacteria ( Acetobacter xylinum) to deposit nanosized bacterial cellulose around natural fibers, which enhances their adhesion to renewable polymers. This paper describes the process of modifying large quantities of natural fibers with bacterial cellulose through their use as substrates for bacteria during fermentation. The modified fibers were characterized by scanning electron microscopy, single fiber tensile tests, X-ray photoelectron spectroscopy, and inverse gas chromatography to determine their surface and mechanical properties. The practical adhesion between the modified fibers and the renewable polymers cellulose acetate butyrate and poly(L-lactic acid) was quantified using the single fiber pullout test.     

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.     

Recent developments in the production and applications of bacterial cellulose fibers and nanocrystals

Cellulosic nanomaterials provide a novel and sustainable platform for the production of high performance materials enabled by nanotechnology. Bacterial cellulose (BC) is a highly crystalline material and contains pure cellulose without lignin and hemicellulose. BC offers an opportunity to provide control of the products’ properties in-situ, via specific BC production methods and culture conditions. The BC potential in advanced material applications are hindered by a limited knowledge of optimal BC production conditions, efficient process scale-up, separation methods, and purification methods. There is a growing body of work on the production of bacterial cellulose nanocrystals (BCNs) from BC fibers. However, there is limited information regarding the effect of BC fibers’ characteristics on the production of nanocrystals. This review describes developments in BC and BCNs production methods and factors affecting their yield and physical characteristics.     

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。     

Biosynthèse de cellulose bactérienne à pertir de glycérol sélectivement deutérié en position 1, 2, ou 3: Etude par résonance magnétique nucléaire

Glycerol specifically deuterated at C-1, C-2, or C-3 was prepared and used for the biosynthesis of bacterial cellulose with Acetobacter xylinum.The material obtained were converted into glucitol hexaacetate and analyzed by 250-MHz nuclear magnetic resonance and mass spectrometry. The spectra indicated that the protons of the C-3 position of the starting glycerol were incorporated as substituents of the C-6 and C-1 positions of the cellulose. Similarly, protons of the C-2 and C-5 positions of the cellulose came essentially from water and the protons bonded at the C-3 and C-4 positions of the cellulose from protons bonded to C-1 of the starting glycerol.     

Prevention of fungal colonization and digestion of cellulose by the addition of methylcellulose

When the attachment of cellulolytic rumen fungi to cellulose is blocked by the addition of methylcellulose, cellulose digestion is entirely inhibited. Even after these fungi have colonized and penetrated the cellulosic fibers of filter paper, the addition of methylcellulose effectively halts cellulose digestion. This effect of methylcellulose is accompanied by the complete inhibition of fungal attachment to cellulose fibers; the addition of methylcellulose does not affect the growth of these organisms on soluble substrates. We conclude that fungal cellulose digestion, like bacterial cellulose digestion, requires the spatial juxtaposition of the cellulolytic organism and its insoluble substrate. The simultaneous inhibition of both attachment and digestion by the same inhibitor suggests that these two processes are functionally linked in the fungi.     

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.     

Analysis of cell-wall polymers during cotton fiber development

Although the fibers of cotton (Gossypium hirsutum L.) are single cells with a secondary wall composed primarily of cellulose, the cell-wall polymers of the fibers are technically difficult to characterize with respect to molecular weights. This limitation hinders understanding how the fiber wall composition changes during development, particularly with respect to genotypic variations, and how the molecular composition is related to physical properties. We analyzed cell-wall polymers from cotton fibers (cultivar, Texas Marker-1) at several developmental stages (8–60 days post-anthesis; DPA) by gel-permeation chromatography of components soluble in dimethyl acetamide and lithium chloride. This procedure solubilizes fiber cell-wall components directly without prior extraction or derivatization, processes that could lead to degradation of high-molecular-weight components. Cellwall polymers from fibers at primary cell-wall stages had lower molecular weights than the cellulose from fibers at the secondary wall stages; however, the high-molecularweight cellulose characteristic of mature cotton was detected as early as 8 DPA. High-molecular-weight material decreased during the period of 10–18 DPA with concomitant increase in lower-molecular-weight wall components, possibly indicating hydrolysis during the later stages of elongation.Abbreviations DMAC dimethyl acetamide - DP degree of polymerization - DPA days post anthesis - GPC gel-permeation chromatography - MW molecular weight - MWD molecular-weight distribution - TM-1 Texas Marker 1     

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.     

Performance of improved bacterial cellulose application in the production of functional paper

Aim: The purpose of this work was to study the feasibility of producing economic flame retardant bacterial cellulose (BC) and evaluating its behaviour in paper production. Methods and Results: This type of BC was prepared by Gluconacetobacter subsp. xylinus and substituting the glucose in the cultivation medium by glucose phosphate as a carbon source; as well as using corn steep liquor as a nitrogen source. The investigated processing technique did not dispose any toxic chemicals that pollute the surroundings or cause unacceptable effluents, making the process environmentally safe. The fire retardant behaviour of the investigated BC has been studied by non‐isothermal thermogravimetric analysis (TGA & DTGA). The activation energy of each degradation stage and the order of degradation were estimated using the Coats–Redfern equation and the least square method. Strength, optical properties, and thermogravimetric analysis of BC‐phosphate added paper sheets were also tested. Conclusions: The study confirmed that the use of glucose phosphate along with glucose was significant in the high yield production of phosphate containing bacterial cellulose (PCBC1); more so than the use of glucose phosphate alone (PCBC2). Incorporating 5% of the PCBC with wood pulp during paper sheet formation was found to significantly improve kaolin retention, strength, and fire resistance properties as compared to paper sheets produced from incorporating bacterial cellulose (BC). Significance and Impact of the Study: This modified BC is a valuable product for the preparation of specialized paper, in addition to its function as a fillers aid.     

The Use of Cellocandin, an Enzymatic Preparation from Geotrichum candidum 3C-106, for Defibring Waste Paper and Desiccation of Cellulose Suspension

The effect of cellocandin, an enzymatic preparation from Geotrichum candidum 3C-106 with cellulolytic and xylanolytic activities, on defibring of waste paper and acceleration of desiccation of paper pulp was studied. It was shown that cellocandin accelerated defibring of waste paper to cellulose fibers and desiccation of cellulose suspension.     

Screening of the common culture conditions affecting crystallinity of bacterial cellulose

By analyzing with X-ray diffraction and FT-IR spectroscopy, the main effective factors among common culture conditions on crystallinity index and I _α fraction of cellulose produced by Gluconacetobacter xylinus were examined with Plackett–Burman design experiment. Varying pH value in the medium by adjusting the composition of citrate buffer or by adding HCl/NaOH solution indicates it is the content of citrate buffer rather than its function of pH buffering that gives the influence on crystallinity. Further experiment reveals that Na⁺ concentration of 0.174 mol/l in medium with citrate buffer added would decrease the crystallinity index significantly. Comparison of carbon sources shows that fructose leads to a higher crystallinity index than glucose, which suggests a relationship between crystallinity and production speed of bacterial cellulose affected by carbon sources. An interesting phenomenon was that a longer period of cultivation would decrease the crystallinity of bacterial cellulose. The reason is assumed to be the dense network of cellulose formed by bacterial cells that restrict the motion of themselves as the incubation period extends. Though the effect of inoculum age is still unclear, the influence on crystallinity of bacterial cellulose caused by variation of some ordinary culture conditions can be drawn out from data of this work.     

Incorporation of UDPGlucose into Cell Wall Glucans and Lipids by Intact Cotton Fibers

The [¹⁴C] moiety from [³H]UDP[¹⁴C]glucose was incorporated by intact cotton fibers into hot water soluble, acetic-nitric reagent soluble and insoluble components, and chloroform-methanol soluble lipids; the [³H] UDP moiety was not incorporated. The ³H-label can be exchanged rapidly with unlabeled substrate in a chase experiment. The cell wall apparent free space of cotton fibers was in the order of 30 picomoles per milligram of dry fibers; 25 picomoles per milligram easily exchanged and about 5 picomoles per milligram more tightly adsorbed. At 50 micromolar UDPglucose, 70% of the [¹⁴C]glucose was found in the lipid fraction after both a short labeling period and chase. The percent of [¹⁴C]glucose incorporated into total glucan increased slightly with chase, but the fraction of total glucans incorporated into insoluble acetic-nitric reagent (cellulose) did increase within a 30-minute chase period. The data supports the concept that glucan synthesis, including cellulose, as well as the synthesis of steryl glucosides, acetylated steryl glucosides, and glucosyl-phosphoryl-polyprenol from externally supplied UDPglucose occurs at the plasma membrane-cell wall interface. The synthase enzymes for such synthesis must be part of this interfacial membrane system.     

Viability and cellulose synthesizing ability of Gluconacetobacter xylinus cells under high-hydrostatic pressure

The effect of pressure on viability and the synthesis of bacterial cellulose (BC) by Gluconacetobacter xylinus ATCC53582 were investigated. G. xylinus was statically cultivated in a pressurized vessel under 0.1, 30, 60, and 100 MPa at 25°C for 6 days. G. xylinus cells remained viable and retained cellulose producing ability under all the conditions tested, though the production of cellulose decreased with increasing the pressure. The BCs produced at each pressure condition were analyzed by field emission scanning electron microscopy (FE-SEM) and Fourier Transform Infrared (FT-IR). FE-SEM revealed that the widths of BC fibers produced under high pressure decreased as compared with those produced under the atmospheric pressure. By FT-IR, all the BCs were found to be of Cellulose type I, as the same as typical native cellulose. Our findings evidently showed that G. xylinus possessed a piezotolerant (barotolerant) feature adapting to 100 MPa without losing its BC producing ability. This was the first attempt in synthesizing BC with G. xylinus under elevated pressure of 100 MPa, which corresponded to the deep sea at 10,000 m.     

Characteristics of antimicrobial fibers prepared with wood periodate oxycellulose

A kind of antimicrobial fibers, a composite of Chitosan-Dialdehyde Cellulose (C-DAC) fibers, was prepared by using commercially elemental chlorine-free (ECF) bleached kraft softwood cellulose fibers oxidized by periodate and then further grafted by chitosan with different molecular weights. The characteristics of the C-DAC fibers and physical properties as well as antimicrobial activities of the handsheet made of C-DAC fibers were measured. The results show that the dry and rewet tensile indices, antimicrobial activity against Staphylococcus aureus and Escherichia coli, can be improved significantly as the molecular weight of grafted chitosan on the dialdehyde cellulose fibers decreases.     

Increased production of bacterial cellulose as starting point for scaled-up applications

Bacterial cellulose is composed of an ultrafine nanofiber network and well-ordered structure; therefore, it offers several advantages when used as native polymer or in composite systems.

In this study, a pool of 34 acetic acid bacteria strains belonging to Komagataeibacter xylinus were screened for their ability to produce bacterial cellulose. Bacterial cellulose layers of different thickness were observed for all the culture strains. A high-producing strain, which secreted more than 23 g/L of bacterial cellulose on the isolation broth during 10 days of static cultivation, was selected and tested in optimized culture conditions. In static conditions, the increase of cellulose yield and the reduction of by-products such as gluconic acid were observed. Dried bacterial cellulose obtained in the optimized broth was characterized to determine its microstructural, thermal, and mechanical properties. All the findings of this study support the use of bacterial cellulose produced by the selected strain for biomedical and food applications.

     

Functional characterization of a bacterial expansin from Bacillus subtilis for enhanced enzymatic hydrolysis of cellulose

Expansin is a plant protein family that induces plant cell wall‐loosening and cellulose disruption without exerting cellulose‐hydrolytic activity. Expansin‐like proteins have also been found in other eukaryotes such as nematodes and fungi. While searching for an expansin produced by bacteria, we found that the BsEXLX1 protein from Bacillus subtilis had a structure that was similar to that of a β‐expansin produced by maize. Therefore, we cloned the BsEXLX1 gene and expressed it in Escherichia coli to evaluate its function. When incubated with filter paper as a cellulose substrate, the recombinant protein exhibited both cellulose‐binding and cellulose‐weakening activities, which are known functions of plant expansins. In addition, evaluation of the enzymatic hydrolysis of filter paper revealed that the recombinant protein also displayed a significant synergism when mixed with cellulase. By comparing the activity of a mixture of cellulase and the bacterial expansin to the additive activity of the individual proteins, the synergistic activity was found to be as high as 240% when filter paper was incubated with cellulase and BsEXLX1, which was 5.7‐fold greater than the activity of cellulase alone. However, this synergistic effect was observed when only a low dosage of cellulase was used. This is the first study to characterize the function of an expansin produced by a non‐eukaryotic source. Biotechnol. Bioeng. 2009;102: 1342–1353. © 2008 Wiley Periodicals, Inc.     

Carbon partitioning to cellulose synthesis

This article discusses the importance and implications of regulating carbon partitioning to cellulose synthesis, the characteristics of cells that serve as major sinks for cellulose deposition, and enzymes that participate in the conversion of supplied carbon to cellulose. Cotton fibers, which deposit almost pure cellulose into their secondary cell walls, are referred to as a primary model system. For sucrose synthase, we discuss its proposed role in channeling UDP-Glc to cellulose synthase during secondary wall deposition, its gene family, its manipulation in transgenic plants, and mechanisms that may regulate its association with sites of polysaccharide synthesis. For cellulose synthase, we discuss the organization of the gene family and how protein diversity could relate to control of carbon partitioning to cellulose synthesis. Other enzymes emphasized include UDP-Glc pyrophosphorylase and sucrose phosphate synthase. New data are included on phosphorylation of cotton fiber sucrose synthase, possible regulation by Ca²⁺ of sucrose synthase localization, electron microscopic immunolocalization of sucrose synthase in cotton fibers, and phylogenetic relationships between cellulose synthase proteins, including three new ones identified in differentiating tracheary elements of Zinnia elegans. We develop a model for metabolism related to cellulose synthesis that implicates the changing intracellular localization of sucrose synthase as a molecular switch between survival metabolism and growth and/or differentiation processes involving cellulose synthesis. Abbreviations: CesA, cellulose synthase; Csl, cellulose-like synthase (genes); DCB, dichlobenil; DPA, days after anthesis; SPS, sucrose phosphate synthase; SuSy, sucrose synthase; P-SuSy, particulate SuSy; S-SuSy, soluble SuSy