Semi-synthetic fibres

The three most important types of synthetic fibres used commonly as textiles are polyester, polyamides (nylon) and acrylic fibres. Polyester and the semi-synthetic fibre cellulose acetate are dyed almost exclusively with the use of disperse dyes. Polyamide fibres may be coloured using either acid dyes, the principles of which have been discussed in the section on protein fibres, or with disperse dyes. Acrylic fibres are dyed mainly using basic (cationic) dyes. 

The chemical industry s interest in polymers dates back to the 19th century. In those days it was a case of synthetically modifying natural polymers with chemical reagents to either improve their properties or produce new materials with desirable characteristics. Notable examples were nitration of cellulose giving the explosive nitrocellulose, production of regenerated cellulose (rayon or artificial silk) via its xanthate derivative, and vulcanization of rubber by heating with sulphur. Manufacture of acetylated cellulose (cellulose acetate or acetate rayon) developed rapidly from 1914 onwards with its use both as a semi-synthetic fibre and as a thermoplastic material for extrusion as a film. 

Excellent softener for synthetic fibres. If applied to acrylics at temperatures above 80C the very soft bulky handle is very resistant to repeated washing or dry cleaning. Applicable for boiling basic dyebaths. On other synthetic fibres it gives a semi-durable finish. Good non-yellowing properties. 

At the International Exhibition of 1862, Alexander Parkes [2] first introduced an organic derivative of cellulose that could be moulded when heated and retain that shape when cooled. He invented the treatment of cellulose fibres with nitric acid forming cellulose nitrate that was the first semi-synthetic plastic material. He used this to make decorative brooches, trinkets and knife handles. He claimed that it could do anything that rubber could do but could be produced at a lower price. He formed a company making a... 

Preparation of semi-synthetic polymers. Cellulose plastics, particularly cellulose nitrate and acetates, were the most commercially-important semi-synthetics, and have been used to prepare photographic films, textile fibres and lacquers. 

In the mid twenties several circumstances permitted a revised orientation of both content and style of areas of research at the Central Research Laboratory. In 1925 the Technical Committee (TEA) of I.G. Farben discussed the possibilities for producing artificial fibres. At this time, I.G. Farben was the second largest producer of artificial fibres in Germany. Therefore polymer chemistry became more important for the company at the same time as dyestuffs chemistry lost its former position. However, the science of synthetic, semi-synthetic and natural polymers was not yet established in the same way as structural chemistry was for organic dyestuffs, pharmaceuticals, and intermediates. Colloid chemists regarded substances such as cellulose, silk, and wool as... 

Plastics are semi-synthetic or synthetic materials which can be manipulated to form films, fibres, foams or three-dimensional olgects. Natural polymers from plants, insects and animals are not discussed in this book. Synthetic paints, synthetic textiles and photographic film contain plastics but will not be discussed in this book because their conservation is the focus of specialist publications (Chiantore and Rava, 2005 Learner, 2005 Timar-Balazsy and Eastop, 1998 Lavedrine et al., 2003). Plastics are based on polymers, also known as macromolecules, which are large molecules made by joining together many smaller ones. The chemical and physical properties of liquid polymers are modified with additives and shaped to convert them into solids with dimensionally stable forms. 

Cellulose-based plastics, particularly cellulose nitrate and acetates, were the most commercially important semi-synthetics up to the 1940s and were used as the base for photographic film, textile fibres, moulded goods and in lacquers. Naturally occurring polymer cellulose in the form of cotton linters or wood pulp is chemically treated to increase its solubility. Cellulose has a high molecular weight of between 100000 and 500000 and an empirical formula C0H1OO5. Casein-formaldehyde is the only protein-based moulded plastic that achieved commercial success. It is based on cow s milk and is still produced in very small quantities for specialist items such as hand-coloured buttons. 

The first plastic material to be made from non-plastic precursors was cellulose nitrate. This was obtained by Alexander Parkes (1813-1890) by treating cellulose fibres with nitric acid, and was first displayed at the Great International Exhibition in Ijondon in 1862 under the name Parkesine. Parkes moulded his new material into small decorative articles, as well as utilitarian objects such as knife handles. Parkesine was the first semi-synthetic plastic, so called because one of the starting materials was polymeric. The applications of cellulose nitrate were much extended by J. W. Hyatt (1837-1920) in the United States, who found that camphor was effective as a plasticiser, and the resulting mixture was known as celluloid. Another semi-synthetic plastic, cellulose acetate, was introduced around the end of the nineteenth century, and had the advantage over cellulose nitrate of being less flammable. 

Nylons were the first synthetic semi-crystalline plastics, the first synthetic fibres and the first engineering plastics. Today, polyamides are used for various different applications an overview of the most important ones is given in Figure 9.3. 

Tencel Lyocell, to give it its full name, is produced exclusively from the wood pulp of Eucalyptus trees certified by the Forestry Stewardship Council (FSC), and the fibre carries the Pan-European Forest Council (PEFC) quality seal. Eucalyptus is woody and therefore needs energy input to convert it into a soft fibre, suitable for clothing. The Eucalyptus is reduced down then reformed into a spin-able fibre. This is done in a process with similar principles as other semi-synthetic natural fibres, such as Viscous bamboo fabric, but importandy the Lyocell process used to make Eucalyptus is much more benign and eco-friendly. It is simply the most environmentally friendly man made cellulosic fibre available today. 

The third main class of separation methods, the use of micro-porous and non-porous membranes as semi-permeable barriers (see Figure 2c) is rapidly gaining popularity in industrial separation processes for application to difficult and highly selective separations. Membranes are usually fabricated from natural fibres, synthetic polymers, ceramics or metals, but they may also consist of liquid films. Solid membranes are fabricated into flat sheets, tubes, hollow fibres or spiral-wound sheets. For the micro-porous membranes, separation is effected by differing rates of diffusion through the pores, while for non-porous membranes, separation occurs because of differences in both the solubility in the membrane and the rate of diffusion through the membrane. Table 2 is a compilation of the more common industrial separation operations based on the use of a barrier. A more comprehensive table is given by Seader and Henley.1... 

Solid or semi-solid organic polymeric products of high molecular weight, natural or synthetic origin with no definite melting points, which as a matrix binds together the reinforcement fibres. 

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