Lignocellulosic fibers lignin

Fibers for commercial and domestic use are broadly classified as natural or synthetic. The natural fibers are vegetable, animal, or mineral ia origin. Vegetable fibers, as the name implies, are derived from plants. The principal chemical component ia plants is cellulose, and therefore they are also referred to as ceUulosic fibers. The fibers are usually bound by a natural phenoHc polymer, lignin, which also is frequentiy present ia the cell wall of the fiber thus vegetable fibers are also often referred to as lignocellulosic fibers, except for cotton which does not contain lignin. 

Mansour, O.Y., Nagaty, A. and Beshay, A-F. (1982). Grafting of some vinyl monomers onto ligno-cellulose and cellulose in the presence of lignin. In Graft Polymerisation of Lignocellulosic Fibers, Hon, D.N.S. (Ed.). ACS Symposium, 187, pp. 253-268. 

Crestini C, Crucianelli M, Orlandi M, Saladino R (2010) Oxidative strategies in lignin chemistry a new environmental friendly approach for the functionalisation of lignin and lignocellulosic fibers. Catal Today 156 8... 

The cellulose microfibril constitutes the basic structural unit of the plant cell wall each microfibril can be considered as a string of cellulose crystallites, linked along the chain axis by amorphous domains (Fig. 7.1). Their structure consists of a predominantly crystalline ceUulosic core which is covered with a sheath of paracrystalUne polyglucosan material surrounded by hemicelluloses (Whistler and Richards 1970). These microfibrils are conjoined by other polymers like lignin and hemicelluloses and aggregate further to form lignocellulosic fibers. As they are almost defect free, the modulus of these sub-entities is close to the theoretical limit for cellulose. 

It is important to mention that the chemical composition of each type of fibers and the orientation of microfibrils about the fiber axis, called microfibrillar angle (Table 8.1), may significantly differ. Similarly, depending on the cellulose and lignin contents, crystallinity index of each type of fiber differs. In view of these, when lignocellulosic fibers are tested for their tensile properties, their fracture mode differs, which may be intercellular or intracellular or mixed modes of fracture. Accordingly, the tensile properties and fractographs are different for each type of fiber. These are also listed for some fibers in Table 8.1 and Fig. 8.3, respectively. 

Like all the lignocellulosic fibers, the physical and chemical properties of jute fiber is also dependent on the three chemical components, viz., cellulose, hemicellulose and lignin. The chemical composition and structural parameters of jute fibers are represented in Table 20.3. 

Acrylic acid-modified Ficus carica lignocellulosic fiber was used as adsorbent. And the removal of Cr(VI) was evaluated in the presence of various metal ions aqueous solutions [87]. The F. carica fibers were washed, dried at 50°C for 24 h, and soxhlet extracted with acetone for 12 h in order to remove waxes and lignin. Then it was dried at 50°C for 5h and then cut into pieces of 1.0-1.5mm-size. The F. carica fibers were immersed in 100 ml of double distilled water for 24 h in order to activate the reactive sites. A known amount of ceric ammonium nitrate, concentrated nitric acid, and acrylic acid was added to the flask containing the fiber. The mixture was heated to constant temperature for a definite time. The modified F carica fibers were washed with ethanol and dried at 50°C to a constant weight. The maximum adsorption capacity of Cr(VI) onto adsorbent was found to be 28.90 mg g". ... 

Plants are very attractive and potential sources of cellulose primarily because they are abundant and relatively cheap to harvest. Cellulose can be extracted from lignocellulosic fibers, which are available aU over the world. A wide variety of plant materials like cotton, ramie, sisal, flax, wheat straw, tubers, sugar beet, soya bean, etc., are known for cellulose microfibril production. Wood is another main important source of extracting cellulose fibrils, where cellulose microfibrils were reinforced by intracellular amorphous materials made of hemicelluloses, lignin, resin, etc. Extraction of pure cellulose microfibrils from these lignocelluloseic materials involves chemical treatments such as alkali extraction and bleaching. 

The initial starting moisture content of wood flour should be 5% to 8% or less. Lignocellulosic fibers have chemical compositions of 6% water (3% of residual water), 55% cellulose, 8% hemi cellulose, 28% lignin and 3% minerals and they are thermally stable up to 200 °C [ 125). 

Natural fibers can be classified according to their source vegetable, animal or mineral. In particular, vegetable fibers consist basically of cellulose, hemicellulose, lignin, and other amorphous constituents, in smaller amounts, and due to their chemical composition they are also known as lignocellulosic fibers [21],... 

The chemical composition and cellular structure of lignocellulosic fibers are complex and heterogeneous, each fiber is considered to be a natural composite formed by rigid cellulose microfibrils wrapped in an amorphous polymeric matrix, basically formed by hemicellulose and lignin [21,22]. 

Holzfaser, /. wood fiber, ligneous fiber wood pulp = Holzfaserstoff. -papier, n. wood-pulp paper, -stoff, m. lignin cellulose lignocellulose. 

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