Bacterial cellulose additives

Reticulated bacterial cellulose may be used in place of a conventional gellant or in combination with conventional gellants to provide enhanced drilling muds [1837]. The addition of relatively small quantities of reticulated bacterial cellulose to wellbore drilling muds enhances their rheologic properties. 

Reticulated Bacterial Cellulose. A cellulose with an intertwined reticulated structure, produced from bacteria, has unique properties and functionalities unlike other conventional celluloses. When added to aqueous systems, reticulated bacterial cellulose improves the fluid rheology and the particle suspension over a wide range of conditions [1836]. Test results showed advantages in fluid performance and significant economic benefits by the addition of reticulated bacterial cellulose. 

Work with electron microscopes showed that there is preferential enzymatic activity at only one end of the native microfibrils. This indicates that the reducing ends are all at one end of the microfibril and thus the chains are parallel, not antiparallel [240]. Electron microscopy and diffraction work on algal and bacterial cellulose confirmed the parallel-up nature of the chain orientation in the unit cell and the addition of new glucose residues to the cellulose chain at the nonreducing end [241]. Similar attempts with ramie fibers were not successful. 

Bacterial cellulose has several unique properties that potentially make it a valuable material for the development of PEM fuel cells (Reference 1) (1) it is an inexpensive and non-toxic natural resource (2) it has good chemical and mechanical stability (3) it is very hydrophilic and (4) it doesn t re-swell after drying. Additionally, its thermal stability and gas crossover characteristics are superior to Nation 117 , a material currently widely used as a proton conductive membrane in PEM fuel cells. 

This study showed that the bacterial cellulose derived fix)m coconut and pineapple juices can be converted efficiently to bacterial cellulose by the supplementation of yeast extract and ethanol under static fermentation conditions at 30 °C. Bacterial celluloses produced from all strains are growth associated products. Coconut juice seems to be a better substrate than pineapple juice. In view of energy consumption, the productivity of BC on this medium is high, which makes the production costs lower than expected. It is also clear that different A. xylinum strains produce different BC content levels under the same inoculation volumes and under static cultivation conditions. These results suggest that bacterial cellulose pellicles of all strains appear to be easily applied to use in many applications such as food, paper, and textile industries, without requiring additional steps of decolorization and purification. Furthermore, the properties of cellulose, in tenns of crystallinity, high water-absorption capacity, and mechanical strength of the reported strains, have additional applications in cosmetics and medicine. 

Nitrogen is a main component of proteins necessary in cell metabolism, and comprises 8-14 % of the dry cell mass of bacteria. The effect of various nitrogen sources on the production of bacterial cellulose has been reported casein hydro-lyzate gave yield of 5 g/L, and peptone gave yield of 4.8 g/L of cellulose in A. xylinum [13]. The addition of extra nitrogen favours the biomass production, but diminishes cellulose pr oduction. 

Seifert, M., Hesse, S., Kabrelian, V., Klemm, D. Controlling the water content of never dried and reswollen bacterial cellulose by the addition of water-soluble polymers to the culture medium. J. Polym. Sci. Part A Polym. Chem. 42(3), 463-470 (2004)... 

The specific properties of bacterial cellulose make it interesting for important applications, such as a nutritional component (additive of low caloric contents, stabilizer, texture modifier, nata de coco), a pharmacological agent (temporary dressing, excipient, cosmetics, drug carriers), as well in telecommunications and papermaking, as summarized in Table 17.2. 

As shown in Fig. 17.11, a bacterial cellulose dry membrane can be heated up to 325°C before it starts to bum, which is at least 75 °C above the burning temperature of conventional office paper. This higher thermal resistance can is attributed to the absence of additives in its composition, which are common in papermaking. 

PVA-C composites are prepared by the additimi of fillers into the PVA solution before the freeze-thaw process. The main purposes of filler addition are for improving mechanical properties and for controlled release and delivery. A wide variety of filler materials that vary in dimensimis from micro- to nanometers have been reported, but here we focus on two widely studied filler materials for their relevance in biomedical applications bacterial cellulose and chitosan. 

Fig. 10 Effect of addition of bacterial cellulose (BC) on the compression elastic modulus of the PVA-BC nanocomposite as a function of the number of ETCs at 45 % strain and 100 %/s strain rate. Reprinted from [45] with permission. Copyright 2009 Wiley Periodicals...

The properties of PVA-C summarized and reviewed thus far demonstrate many of the desirable properties that make it the material of choice for a broad range of biomedical applications. Using the fi eeze-thaw cycling procedure, PVA-C can be prepared with both tunable mechanical properties and diffusion properties. With the addition of biocompatible nanofillers such as bacterial cellulose and chitosan, the range of these properties can be further broadened. The diffusion properties and some applications of PVA-C for controlled release and delivery have already been covered (see Sect. 3.2). The focus of this section will be on the use of PVA-C as a material for medical devices. 

Yamamoto H, Horn F. (1994). In sim crystallization of bacterial cellulose I. Influences of polymeric additives, stirring and temperature on the formation celluloses I a and I 3 as revealed by cross polarization/magic angle spinning (CP/MAS) 13 C NMR spectroscopy. Cellulose, 1, 57-66. 

In addition to plant-derived cellulose, cellulose can also be synthesised by bacteria such as from the Acetobacter species. By culturing cellulose-producing bacteria in the presence of natural fibres in an appropriate culture medium, bacterial cellulose is preferentially deposited in situ onto the surface of natural fibres. The introduction of bacterial cellulose onto natural fibres provides new means of controlling the interaction between natural fibres and polymer matrices. Coating of natural fibres with bacterial cellulose not only facilitates good distribution of bacterial cellulose within the matrix, but also results in an improved interfacial adhesion between the fibres and the matrix. This enhances the interaction between the natural fibres and the polymer matrix through mechanical interlocking. 

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