Natural fibres, impurities

The action of alkaline scouring agent is to saponify any residual oils, to neutralise carboxylic acids, to solubilise any sizing materials and to cause dispersion of naturally occuring impurities in natural fibres. Table 4.1 summerises the removal process involved during scouring. 

Natural fibres contain oils, fats, and waxes, together with other impurities. Garments, fabrics, or yarns may contain oil and adventitious dirt collected during manufacturing. The term scouring applies to the removal of these impurities. 

Alkali treatment Mercerization or alkali treatment with strong alkali bases was developed as a method for cotton fibre modification by John Mercerin 1850 [55], It is a common method to produce high quality natural fibres, by removing the natural and artificial impurities from the fibre surface. The chemical treatment reduces the fibre diameter and thereby increases the aspect ratio [26]. Mercerization is usually performed applying aqueous solutions of sodium hydroxide (NaOH), at reaction times of 30 min up to 3 hr. 

Silver halide fibres (AgClxBri x) have the widest spectral range in the mid-IR, well into the fingerprint range. Due to their crystalline nature, they have a superior flexibility. Problematic is their tendency to decompose upon contact with UV radiation or base metals. Also sulphides will chemically destroy the fibre material. Other points against are the high intrinsic attenuation due to absorption by impurities or scattering at inclusions or micro-crystals and the non-availability of (applicable) core-clad fibres. 

The menstruum 1b now to be filtered, in order to remove the sulphite of baryta and other insoluble impurities, Tho filter employed by the patentee is a thin layer of pure gelatinous hydrate of alumina laid on cloth but the liquid may also be forced through unglazed earthen or stono ware. After the solution lias percolated either of these media, it will be found that all ligneous fibre, sillcions and earthy matters, and all particles of insoluble gum have been separated and deposited on the vessels and filter employed, and very little color will remain in the depurated solution but when a very white gum is required, the process of acidulation must be repeated. By evaporating the filtered menstruum, a colorless, tasteless, and pure gum is obtained, the natural properties of which have not been in tho least degree altered. 

The loom state cotton fabric contains about 8-12% natural impurities of total weight of the fibre. These impurities mainly consists of waxes, proteins, pectic substances and mineral matters. In addition to this, the mechanically held impurities called motes are present containing seed-coat fragments, aborted seeds and leaves etc. that clinge to the fibre. Apart from these, the loom-state fabric is also contaminated with adventiteous oils such as machine oils, tars, greases etc. 

Apart from natural impurities, jute yams or fabrics contain mineral oil/jute batching oil (JBO), which is added to facilitate spinning of jute fibre. The JBO has a delustering effect and also contributes additional yellowing on exposure to light. 

Approximately 45 million tons of fibres, of which over 50% are cotton, are consumed each year for textile purposes [33]. Although synthetic fibres do not contain any natural impurities, they produce considerable amount of pollutants during wet processing. Table 13.10 gives the characteristics of different processes wastes... 

Many endeavours have been made to specify a satisfactory test for detergent power, but none is infallible, partly because, in practice, there is so much variation in the conditions under which scouring is carried out. There are differences in the ratio of liquor to goods, the nature of the mechanical agitation, the composition of the impurities to be removed, and the resistance of different fibres to alkali and temperature which have to be taken into account in practice. 

M ht scouring operations in which these surface-active compounds are commonly used varv according to the nature of the fibre and the amount and composition of the impurities to be removed. In the case of cotton the cellulose of w hich it is composed is stable to dilute solutions of alkali at the boil. I he imphrities which must be removed are natural oils and waxes, proteins, pectic substances, natural colouring matter, and adventitious dirt. The basic principle of cotton scouring is to boil the goods for several hours at atmospheric, or under elevated, pressure with a 2 per cent solution of sodium h) droxide. 

Figure 1.3 present spectra of XLV dye solution absorbtion in the mixture of formic and trifluoro-acetic acids, solutions of dyed fibres before and after spinneret, which are practically laid on each other, showing full solution of the dye and good homogeneization of polymer melt. It should be noted that the samples of fibres, being studied, fully dissolved in solvents without formation of residues (possible products of dye and PCA interaction), which tells about inertia of components regarding each other. Blinding screen was caused mainly by impurities of mechanical nature. 

More recently basalt fibres have gained in popularity. The basic material is natural basalt stone (with a composition of at least 50% Si02) which is then treated using a pyrolytic process (similar to the carbon fibre). The main challenge during the production process is to eliminate the high quantities of iron impurities (FeO or Fe203) in the basalt mineral. Basalt fibres can be used in all types of resins (epoxy, phenol, polyester). 

Purthermore, the presence of some impurities on the surface of the okra fibre can also be seen, and the fibres are cemented in non-cellulosic compounds. In particular, the cross-sectional shape of okra fibre shows a polygonal shape that varies notably from irregular shape to reasonably circular, as depicted in Pig. 1.15. Their diameter considerably vary in the range of about 40-180 pm. Purthermore, each ultimate cell is roughly polygonal in shape, with a central hole, or lumen like other natural plant fibres, as shown in Pig. 1.15. The cell wall thickness and lumen diameter vary typically between 1-10 pm and 0.1-20 pm, respectively. As a consequence of it. 

Natural cellulose fibres (derived from wood chips processed to remove the hgnins and other soluble impurities such as resins and sugars) offer some advantages for precoat filtration, the properties of which are compared with diatomite and perlite in Table 2.20. The fibre lengths vary from about 20 pm to... 

Laser chemistry can also be used for purifying certain chemicals. The production of ultrapure silicon for the semiconductor industry and for producing solar cells is of special interest. For optical fibres the purest possible Si02 is desirable. A suitable starting material is silane gas. Arsine (ASH3) and phosphine (PH3) are typical impurities. On radiation of the natural gas mixture with an ArF excimer laser (A=193nm) the impurities are quickly dissociated. The technique has a good production potential and the cost for purification could be quite reasonable. Since the cost of the laser photons will always be an important factor it is likely that laser-induced... 

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