Bacterial cellulose chemical structure

Fig. 13. C-CPMAS spectrum of bacterial cellulose containing mainly the la and a minor amount of the Ip polymorphs. Below the calculated chemical shift values according to the chemical shift crystal structure refinement are shown.

There is a wealth of data, both in the scientific and patent literature, on the chemical modification of plant cellulose. All of these methods are equally applicable to bacterial cellulose given that the two types of cellulose are chemically identical. However, it is the physical structure of bacterial cellulose membranes that make them a potential material for PEM fuel cells. Therefore, the aim is to modify bacterial cellulose pellicules in a manner that retains the structure of the cellulose and does not... 

The crystalline component of ramie and cotton differs In chemical shift and line splittings from that of valonia and bacterial cellulose. This suggests that there Is some difference in crystal structure among these samples, although the crystalline form Is generally assumed to be cellulose I for all these materials. 

Cellulose, like the polysaccharides above, has certain drawbacks. These include poor solubility in common solvents, poor crease resistance, poor dimensional stability, lack of thermoplasticity, high hydrophilicity, and lack of antimicrobial properties. To overcome such drawbacks, the controlled physical and/or chemical modification of the cellulose structure is essential [160]. Introduction of functional groups into cellulose can alleviate these problems while maintaining the desirable intrinsic properties of cellulose. Apart from the conventional plant source, cellulose is also obtained from bacteria, termed bacterial cellulose. 

The hydrogen bonds between these fibrillar units stabilize the whole structure and confer its high mechanical strength. Moreover, and different to wood and plant cellulose sources, the high chemical purity of bacterial cellulose avoids the need of chemical treatments devoted to the removal of hemicellulose and lignin, which would imply extra isolation costs. 

Although the chemical structure of bacterial cellulose is identical to that of any other vegetable-based counterpart, its fibrous morphology (Fig. 1.20), as obtained directly in its biotechnological production, is unique and consequently the properties associated with this original material are also peculiar and promise very interesting applications. Details about this futuristic biopolymer are given in Chapter 17. 

The cellulose bios5mthesized by G. xylinus is identical to that produced by plants, regarding its molecular formula and polymeric structure, but presents a higher crystallinity. The other fundamental difference between bacterial cellulose and its widespread plant-based counterpart stems from the fact that the former is chemically pure, free of lignin, hemicelluloses and the other natural components usually associated with the latter (Fig. 17.1). 

Although bacterial cellulose has the same chemical composition but different structures and physical properties, it is preferred over the plant cellulose as it can be obtained in higher purity and exhibits a higher degree of polymerization and crystallinity index. Its fibrils are about 100 times thinner, have higher tensile strength and better water holding capacity than those of plant cellulose. ... 

Within the medicinal field, bacterial cellulose alone was shown to be a versatile material for the construction of artificial blood vessels, an application which clearly benefits from the structural features of cellulose in combination with its chemical stability under physiological conditions [52], Other applications use cellulose for the production of implantable capsules [53], and even sensors [54], Another interesting biomedical application is the use of cellulose in films supporting wound healing, due to the hydrating characteristics of these cellulose-containing films [55], Besides, cellulose and cellulose derivatives are used as haemostatic agents [56], The latter two fields of application for cellulose have just recently been reviewed in the cited literatiu-e, and are thus not discussed in detail here. 

Bacterial cellulose (BC) is biodegradable polyester produced by specific genera of bacteria Acetobacter, Rhizobium, Agrobacterium) and certain algae [33,34]. The chemical structure of BC is similar to that of plant cellulose, but BC possesses considerably superior physical, mechanical, and biological properties when compared to plant cellulose [35]. BC is chemically pure and does not contain any impurities such as lignin and hemicelluloses that are associated with plant cellulose. It exhibits a fibrous network... 

Figure 15.3 Chemical structure (a) and morphology of bacterial cellulose.

Wang Z, Zhou J, Wang X, Zhang N, Sun X, Ma Z (2014) The effects of ultrasonic/microwave assisted treatment on the water vapor barrier properties of soybean protein isolate-based oleic acid/stearic acid blend edible films. Food Hydrocolloids 35 51-58 Wihodo M, Moraru Cl (2013) Physical and chemical methods used to enhance the structure and mechanical properties of protein films a review. J Food Eng 114(3) 292-302 Woehl MA, Canestraro CD, Mikowski A, Sierakowski MR (2010) Bionanocomposites of thermoplastic starch reinforced with bacterial cellulose nanofibers effect of enzymatic treatment on mechanical properties. Carbohydr Polym 80 866-873 Xu YX, Kim KM, Hanna MA, Nag D (2005) Chitosan-starch composite film preparation and characterization. Ind Crops Prod 21 185-192... 

The numerous examples of regular complex copolysaccharides often involve familiar-looking material for cellulose chemists. Figure 10 shows two pneumococcal polysaccharides. Types III and VIII, also known as "specific soluble substance", which in the 1920 s and early 1930 s were shown to be antigenic although they were free of nitrogen and did not possess any of the properties of peptides. The knowledge achieved by the extensive studies on cellulose and carbohydrates in the first decades of this century was responsible for the early establishment of the chemical structures of Types III and VIII. The revolutionary work on bacterial transformation, in which Avery, MacLeod and McCarty in 1944 identified DNA as the... 

Another purpose of adding chemicals to the culture medium is the chemical modification of the structural and physical properties of bacterial cellulose, allowing the preparation of composites directly during biosynthesis and broadening the applications of cellulose [18], as will be discussed latter. 

Chemical reactions in general can be accelerated to go in a forward direction using catalysts which do not participate directly in the reaction. Ihe type of catalyst used depends on the nature of reactants in the reaction and the different materials used are Pd, Pt, Ag, Ni, TiO, ZnO and Fe-Oxides. The inherent catalytic property of these materials can be further enhanced by increasing their specific surface area available for reactions, i.e., by reducing the particle size to nanodimensions. However, agglomeration of the nanoscale materials in their innate state is a serious limitation which reduces the effective surface area available for reaction. The aggregates are easy to recover and recycle. These limitations can be overcome mainly in two separate ways (i) immobilization of the nanoparticles in a porous support or carrier, and (ii) synthesis of the catalytic material as a nanoporous network-like structiu e using different types of templates. Bacterial cellulose has been used extensively as a support material to host the catalytic nanoparticles, while in some cases it has also been used as a template to synthesize catalyst network structure. Some typical studies wherein BC has been used as a support to hold PdCu, Pd, TiO and CdS nanoparticles are discussed first, followed by template structure based composites. 

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