Native cellulose microfibrils

Electron-diffraction measurements on cellulose microfibrils from Valonia show that the reciprocal-lattice points can be indexed, not by a Meyer-Misch unit cell, but by a unit cell having a and c periods twice as long. - This finding has been confirmed, and it is suggested that, although bacterial cellulose probably has the same unit cell, other native celluloses might differ. 

In electron micrographs, the native cellulose microfibrils are usually seen as bundles of lamellae containing an indefinite number of fibrillar units. A schematic representation of the cross section of a small lamellae of microfibrils is shown in Figure 3 (14). Two structural features should be pointed out. The cellulose lattice extends through the whole cross section of the microfibrils but the surface layers are supposed to be disordered to some extent because they represent a discontinuity. The microfibrils show a preferred orientation with their lattice planes 101 well aligned parallel with the flat surface of the lamellae—i.e., the tan-... 

Manley, R., 1964. Fine structure of native cellulose microfibrils. Nature 204 (4964), 1155-1157. 

Both native and regenerated cellulose can be used for the preparation of cellulose aerogels. Cellulose in native form, generally nanofibrillar such as bacterial cellulose and microfibrillated cellulose, has been proposed for the preparation of aerocellulose [77, 266]. Aerogels based on NFC can offer advantages from an environmental point of view, because NFC is obtained from renewable resources and no harmful solvents are required during the processing. 

Hemicellulose is the other major constituent of plant-based namral fibres and it is made up of a combination of 5- and 6-ring carbon polysaccharides [22], It is a branched polymer and has much shorter polymer chains (degree of polymerisation of between 50 and 300) compared to native cellulose. In addition to this, hemicellulose is very hydrophilic in nature [35], easily hydrolysed by acids and soluble in alkali. The role of hemicellulose in natural fibres is to form the supporting matrix for cellulose microfibrils. 

For native fibers the spiral angle between cellulose microfibrils (crystallites) and fiber axis is filed. The degree of uniaxial orientation of crystallites is given for regenerated... 

In order to improve the accessibility of crystalline cellulose [24], the swelling of cellulose in ammonia or in molecules such as amines is a simple and classical way. This procedure leads to cellulose IIIi from cellulose I (native cellulose) and has been frequently used to improve the reactivity of crystalline cellulose for the preparation of derivatives in better yields [25-26], Indeed, this conversion carried out essentially at a solid-state process that keeps the integrity of the cellulose microfibrils while achieving a substantial decrystallization and a reorganization of the intra-crystalline hydrogen bond pattern of cellulose [27-28],... 

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