Natural cellulose fibres

The distinction between long, thin cylinders and fibres is quantitative, rather than qualitative. Nevertheless we Shall make the distinction because there is great technical relevance natural fibres (cellulose), synthetic ones (nylon), non-woven fabrics, etc., are materials belonging to this group. The wettability of bundles or mats of fibres and woven fabrics is of prime importance for clothing, tents and several other industrial products. 

Processed natural fibre cellulose Wet-laid (paper, filter sheets)... 

We know that cellulose (chief component of the cell walls of a plant), proteins essential constituents of living cells, rubber, leather and natural fibres like silk, wool, etc. are all polymers and these are known as natural polymers. 

Much of our technology has been developed by observing and imitating the natural world. Synthetic polymers, such as those you just encountered, were developed by imitating natural polymers. For example, the natural polymer cellulose provides most of the structure of plants. Wood, paper, cotton, and flax, are all composed of cellulose fibres. Figure 2.15 shows part of a cellulose polymer. 

The first successful experiments were reported by Schwab [16] Cu, Ni and Pt on quartz HI were used to dehydrogenate racemic 2-butanol 23. At low conversions, a measurable optical rotation of the reaction solution indicated that one enantiomer of 23 had reacted preferentially (eeright-handed quartz gave the opposite optical rotation it was deduced that the chiral arrangement of the crystal was indeed responsible for this kinetic resolution (for a review see [8]). Later, natural fibres like silk fibroin H5 (Akabori [21]), polysaccharides H8 (Balandin [23]) and cellulose H12 (Harada [29]) were employed as chiral carriers or as protective polymer for several metals. With the exception of Pd/silk fibroin HS, where ee s up to 66% were reported, the optical yields observed for catalysts from natural or synthetic (H8, Hll. H13) chiral supports were very low and it was later found that the results observed with HS were not reproducible [4],... 

Hemicelluloses are constituted of different hexoses and pentoses glucose, mannose, xylose, etc. Since these heteropolysaccharides are often branched polymers, they cannot constitute crystalline structures. However, their function in the constitution of natural fibres is crucial. Together with lignin, they constitute the bonding matrix of the cellulose microfibres. 

Although jute is a natural fibre like cotton, it differs in chemical composition. Unlike cotton jute contains a high percentage of non-cellulosic matter (about 40%) and the pre-treatment processes of jute are somewhat different from that of cotton. Scouring of jute with caustic soda under pressure cannot be carried out like cotton because of removal of hemi-cellulose which results in high losses of tensile strength (10-15%) and weight (6-8%). 

As a result of these investigations it is generally agreed that naturally-occurring cellulosic fibres contain of the order of 60 to 70 per cent of molecules orientated in crystalline structure. The regenerated celluloses contain 30 to 40 per cent, Terylene 50 per cent, and nylon between 50 and 60 per cent. 

The value of cellulose as a natural fibre lies in just this fact of... 

In this chapter, packaging materials based on cellulose or natural fibres will be discussed. They provide a major contribution to the packaging of pharmaceuticals, the size and nature of which can readily be overlooked since the number of applications is far more diverse and more paper and board is used than glass, metal or plastics. 

Natural Fibres.—The photolysis of cellulose and related compounds at... 

Mechanical separation of cellulose fibrils from natural fibre resources may involve the process of grinding to apply shear stress to the longitudinal axis of the fibres, so that the fibrillated fibres will have diameters ranging 20—90 nm (Taniguchi and Okamura, 1998). Ultrasonic extraction is another approach to disrupt the adhesion among the fibrils so as to extract nanofibrils from both cellulosic and protein fibre sources... 

The starting point in the textile supply chain is the raw material preparation. Textile fibres are obtained from two main sources natural (cellulose or animal) fibres or synthetic fibres. Natural cellulosic fibres include conventional and organic cottons, rayon, linen, hemp, jute, ramie and sisal. Cotton is used to produce 40% of world textile products (Saicheua et al., 2012). The major environmental concern in cellulosic fibre production, especially for cotton fibre, is the chemical fertilizers and pesticides used during cultivation. The second concern is the high level of water consumption (Dave and Aspegren, 2010 Muthu, 2014). Cotton is one of the most popular natural fibres used in the world. Three percent of the world s cultivated land is used for cotton production and 16% of the world s insecticides are used on this crop alone (Saicheua et al., 2012 Muthu, 2014). Moreover, the use of chemical fertilizers, pesticides, machinery and electricity causes some human health and environmental problems. Also cotton growing requires 7—29 tonnes of water per kg of raw cotton fibres (KaUiala and Nousiainen, 1999). Other types of cellulosic fibres are hemp and flax, which can be considered to be the most significant sustainable fibres in the non cotton natural fibre sector (Werf, 2004 Muthu, 2014). 

Kontturi, E.J. Surface Chemistry of Cellulose From Natural Fibres to Model Surfaces. Technische Universiteit Eindhoven, Germany (2005)... 

The possible uses of cellulose of various forms is manifold (fibres, cellulose derivatives as well as new products such as cellulose aero gels), however a chemical synthesis of cellulose, as demonstrated by nature, has not yet been realized.In order to meet the high requirements for products made of cellulose, it is usually necessary to obtain cellulose from plant material by selective removal of non-cellulose components. In the case of... 

The classical two-phase model assuming a composite arrangement of distinct crystalline and extended amorphous regions to describe the superstructure of natural fibres apparently has to be revised. Concepts like crystallinity and amorphicity are well adapted to describe homogeneous states of matter. They are, however, rather ill-defined when it comes to treating dense composite materials like cellulose, or proteins, given that intermolecular correlations do not build up or die off abruptly at some fictitious interfaces. 

The mechanical characteristics of the fibres well reflect the complexity of their structures. While wool shows a decrease of E-modulus and an increase of elongation at a break in the wet stage compared to the dry one, cellulosic fibres behave inversely. A summary of the mechanical properties of natural fibres is given in Table 9.6.5. 

Natural fibres can be subdivided into plant, animal, and mineral fibres. All plant fibres (cotton, jute, flax, hemp, etc.) are made of cellulose animal fibres are made of protein (wool, silk, hair). Based upon their origin, plant fibres are subdivided into bast and hard fibres. Bast fibres are derived fix)m the stems or stalks of plants hemp, jute, ramie, and flax, for example, belong to this category. Hard fibres, on the other hand, are derived from leaves, leaf sheaths, or fruit sisal and coconut belong to this category ... 

This chapter first gives an overview of cellulose raw materials and their molecular and supermolecular structures. The principles of shaping cellulose into fibres, films, and nonwovens by means of solution techniques are then outlined followed by a section on properties and market applications of these materials. Derivatives of cellulose are presented with special emphasis on thermoplastic cellulose esters, typical plasticizers, and promising reinforcing materials. Finally, recent developments and future prospects of cellulose materials are reviewed as far as the above applications are concerned. This book does not cover the important applications of cellulose and ligno cellulose fibres for reinforcing thermoplastics, like wood plastic composites (WPC) and natural fibre reinforced plastics (NFRP), since in these cases cellulose does not substitute a thermoplastic. 

Natural fibres show many advantages over glass fibres when used as reinforcement of synthetic polymers (see Table 5.1) the relatively high density of glass fibres 2.5 g/cm ) compared to cellulose or ligno-cellulose fibres of 1.5 g/cm makes lightweight applications possible. 

Commonly used natural fibres are cotton and silk, but also included are the regenerated cellulosic fibres (viscose rayon) these are widely used in non-implantable materials and healthcare/hygiene products. A wide variety of products and specific applications utilise the unique characteristics that synthetic fibres exhibit. Commonly used synthetic materials include polyester, polyamide, polytetrafluoroethylene (PTFE), polypropylene, carbon, glass, and so on. 

Njuguna J, Wambua P, Piehchowski K, Kayvantash K. Natural fibre-reinforced polymer composites and nanocomposites for automotive applications, cellulose fibers bio- and nano-polymer composites. In Kaha S, Kaith BS, Kaur 1, editors. Cellulose fibres bio- and nano-polymer composites. Berlin, Heidelberg Springer 2011. 

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