Fibre surface

The above paragraphs indicate some of the major uses of plastics materials, but these materials also find applications in a variety of other areas. In addition, closely related materials such as rubbers, fibres, surface coatings and adhesives are of considerable importance. 

In addition to plastics materials, many fibres, surface coatings and rubbers are also basically high polymers, whilst in nature itself there is an abundance of polymeric material. Proteins, cellulose, starch, lignin and natural rubber are high polymers. The detailed structures of these materials are complex and highly sophisticated in comparison the synthetic polymers produced by man are crude in the quality of their molecular architecture. 

Reaction of polyhydroxy compounds with polybasic acids gives rise to condensation polymers containing ester (—COO—) groups. Because of the presence of these groups such polycondensates are known as polyesters and find use in such diverse applications as fibres, surface coatings, plasticisers, rubbers and laminating resins. These materials are discussed in detail in Chapter 25. 

Fubini, B., Bolis, V., Giamello, E. and Volante, M. (1991). Chemical functionalities at the broken fibre surface relatable to free radicals production. In Mechanisms in Fibre Carcinogenesis (eds. R.C. Brown, J.A. Hoskins and N.F. Johnson) pp. 415-432. Plenum, New York. 

It should be understood that the reported practices of polymer/additive analysis, being the focus of this book, equally well apply to additive analysis of rubbers, textile fibres, surface coatings, paints, resins, adhesives, paper and food, but specific product knowledge gives the edge. Both fresh and aged materials may be analysed, as well as those of both industrial and forensic origin. 

Manufactured aramid fibres are usually treated by a binder such as oils and surfactants to protect the fibre surface and improve the ability to handle. In order to remove the binder the knitted fabric is immersed in... 

Cationic accelerants vary in their efficacy [161]. Other types of accelerant have also been evaluated. In one study [162], comparisons were made between tetra-ethylammonium bromide, benzyltriethylammonium chloride, polyfdiallyldimethylammonium chloride) and the diethyldimethylammonium derivative of a benzenesulphonate polyglycol ester. It was found that the cationic polymers had a greater effect than the simple quaternary ammonium compounds of lower molecular mass. This effect was attributed to the capability of the polymers to enter into hydrophobic interaction with the fibre surface. Ethylenediamine has also been found to accelerate the alkaline hydrolysis of polyester [163]. 

Desizing by chemical decomposition is applicable to starch-based sizes. Since starch and its hydrophilic derivatives are soluble in water, it might be assumed that a simple alkaline rinse with surfactant would be sufficient to effect removal from the fibre. As is also the case with some other size polymers, however, once the starch solution has dried to a film on the fibre surface it is much more difficult to effect rehydration and dissolution. Thus controlled chemical degradation is required to disintegrate and solubilise the size film without damaging the cellulosic fibre. Enzymatic, oxidative and hydrolytic degradation methods can be used. 

The many technical factors involved in desizing and the need for economy and environmental accountability emphasise the importance of monitoring and analysis. However, only a brief outline can be given here. A review of analytical procedures and simple laboratory methods for size determination is available [193]. Methods are given for size determination directly on the fibre surface, for the extraction of components of low molecular mass and for their subsequent estimation in solution. 

Corona discharge, bombardment of the wool fibre surface with electrons of sufficient energy to break covalent bonds, has also been applied to the improvement of shrink... 

The sulphite aftertreatment is particularly important with permonosulphuric acid treatment. Evidence for the underlying mechanism is available from analysis of sulphur oxidation products formed in the various processes (Table 10.34). It is evident from these results that the concentration of RSS()5 anionic groups necessary to change the hydration of the fibre surface is achieved by the reaction of bisulphite with cystine monoxide residues to give the required cysteine-S-sulphonate groups [311]. 

Figure 10.67 indicates the probable distribution of a silicone containing the optimum content of aminoethyliminopropyl groups when applied to a polyester fibre surface. In this case the attachment is through hydrophobic polymer-fibre interaction and the mobility of the silicone chain segments is increased by electrostatic repulsion between neighbouring cationic groups. Dependence of softness of the treated polyester fabric on the proportion of... 

Liquid Surface tension (mN/m) at 20 °C Textile fibre Surface energy (mN/m) at 20 °C... 

Since ideally, a biosensor should be reagentless, that is, should be able to specifically measure the concentration of an analyte without a supply of reactants, attempts to develop such bioluminescence-based optical fibre biosensors were made for the measurements of NADH28 30. For this purpose, the coreactants, FMN and decanal, were entrapped either separately or together in a polymeric matrix placed between the optical fibre surface and the bacterial oxidoreductase-luciferase membrane. In the best configuration, the period of autonomy was 1.5 h during which about twenty reliable assays could be performed. 

Such sol-gel derived and ultraviolet (UV)-curable hybrids afford enhanced corrosion and mechanical protection of fibres compared to standard polymer coatings used by the fibre optics industry. These coatings are hard, transparent and impossible to strip since they become intimately bonded to the fibre surface during curing. 

Measurements of the surface tension of aqueous solutions of various sulphonated and unsulphonated phenylazonaphthol dyes showed that the degree of surface activity (that is, the lowering of surface tension) tended to increase progressively with the degree of alkyl substitution in the series of dyes [7]. The surface-active behaviour of such alkylated dye ions ensures that they become more concentrated at the interface between the dyebath and the fibre surface, just as they do at the air-water interface of the dye solution. Foaming of dyebaths can be a serious practical problem with relatively hydrophobic dye structures solubilised by means of a single ionised group. 

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