Polyamide fibres

In recent years there has been considerable interest in aromatic polyamide fibres, better known as aramid fibres. These are defined by the US Federal Trade Commission as a manufactured fibre in which the fibre-forming substance is a long chain synthetic polyamide in which at least 85% of the amide linkages are attached directly to two aromatic rings. ... 

The repeat length in the triclinic polymer crystals (75.3 nm) is significantly less than for PBT (86.3 nm) and PET (99.5 nm). This has been claimed to make the crystal more spring-like in the long axis resulting in enhanced resilience and wear resistance in carpet fibres to a level approaching that of polyamide 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 two most important polyamide fibres are nylon 6.6 (171) and nylon 6 (172) whose structures are illustrated in Figure 7.10. A comparison with Figure 7.1 reveals the structural analogy between natural protein fibres such as wool and polyamide fibres. Polyamides may be dyed using acid... 

Working with a solution is needed for polymers which above their melting point would degrade (example aromatic polyamide fibres such as Kevlar and Twaron). For fibres the removal of the solvent is not too problematic. In e.g. injection moulding applications solvents caimot be used here thermotropic LCP s have to be used. Since these would degrade during processing, they are diluted by copolymerisation (example poly-hydroxy-benzoic acid - co - PETP)... 

The largest usage is in polyester and many dyestuff companies have disperse dye ranges for this purpose, some of which are also applied to polyamide fibres. The main colours are in the yellow, orange, red, pink and violet areas with coumarins, methines and perylene dominating the structural classes. 

Pyrazolines are a class of FBAs for use on cellulose acetate and more importantly commercially on polyamide fibres. For polyamide, anionic derivatives such as (3.62) are used, applied by pad-thermosol and related methods. 

Heumann S, Eberl A, Pobeheim H et al (2006) New model substrates for enzymes hydrolysing polyethyleneterephthalate and polyamide fibres. J Biochem Biophys Methods 69 89-99... 

Chromium and cobalt are the metals most commonly used in dyestuffs for polyamide fibres and leather because of their kinetic inertness and the stability of their complexes towards acid. Since the advent of fibre-reactive dyestuffs, chromium and cobalt complexes have also found application as dyestuffs for cellulosic fibres, particularly as black shades of high light-fastness. Copper complexes are of more importance as dyes for cellulosic fibres and are unsuitable for polyamide fibres because of their rather low stability towards acid treatments. 

Much more important commercially are the 2 1 chromium(III) and 2 1 cobalt(III) complexes of tridentate azo compounds, which find a wider application, particularly as dyestuffs for wool, polyamide fibres and leather. These have been the subject of reviews23 24 which discuss their dyeing properties in detail. The patent literature on metal complex dyes of these types is vast but since this relates principally to the achievement of specific, desirable technical effects by appropriate substitution of the azo compounds it will not be considered in detail here. Rather will the emphasis be placed upon those aspects of dyestuffs of this type which are of general interest in the context of their coordination chemistry and, more particularly, on those areas where uncertainties exist or conflicting results have been reported. 

Iron(II) complexes of 7-nitroso-6-hydroxyindazoIes (203) are sufficiently soluble in water to permit the dyeing of wool and polyamide fibres in green to olive shades having good fastness properties from weakly addic dyebaths. Cationic iron(H) complexes (204) have also been prepared from quatemized indazoles of this type but have found little or no commercial application. 

This wash-fastness mechanism of acid dyes on polyamide fibres may be a model for the uptake of nutritive substances, of drugs and so on by the organism or the uptake of K+ by complexes in cells too. 

The different properties of water with different bonds to organic molecules can be demonstrated also with dye diffusion measurements in polyamide fibres148,149. Acid dyes show a remarkable decrease of diffusion velocity in 6-polyamide if the humidity content is reduced. It is necessary to heat polyamide fibres in air contact at 150 °C to get similar diffusion velocities of acid dyes at 60 °C under water saturation. The diffusion coefficient of water itself in 6-polyamide depends strongly on the water content148,149 (Fig. 29). This was determined by a quartz spring balance method. 

Samples of plasticised PVC coatings backed with a thin polyamide fibre cloth used for arm and head rests of trains were analysed after both normal use in service and artificial ageing at 100 C. Two parameters were studied the effects of temperature inside the train and the influence of the polyurethane foam inside the rests. Plasticiser loss due to migration during ageing led to hardening of the... 

Afterfixing agent for improving the wet fastness properties of polyamide fibres dyed or printed with acid dyes. The light colour of this compound results in minimal effect on bright shades or white grounds of printed fabrics. Used to reserve polyamide when dyeing cotton/polyamide blends with direct dyes. 

Clear viscous aqueous solution. Highly effective size for filament polyamide yarns. SYNCOL F25 exhibits very high adhesion to polyamide fibres producing warps of high weaving efficiency at relatively low application levels. 

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