Polyamides with Natural Fibres

Reprinted from [a.287] with permission from Elsevier 

This result suggested that cotton fibres in this blend accelerated the thermal degradation of aromatic polyamide fibres. On the other hand, compared to the calculated activation energies, an important decrease took place during the thermal degradation process, showing the formation of intermediate degradation structures with lower thermal stability. 

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Polymers with a certain degree of crystallinity in the drawn state to this group belong the important synthetic fibres like polyesters and polyamides with natural draw ratios of about 4—5... 

Granular soil with fibre reinforcement is a material composed of granular natural soil (i.e. sand) and thin continuous fibres distributed in the material volume with or without cement or any other binding agent. The synthetic (polyester, polypropylene or polyamide) fibres are very thin and their volume fraction is low starting from 0.1% or 0.3% also natural fibres may be used (e.g. sisal, coir). The fibres are distributed in a uniform and isotropic way (3D) or are parallel to a selected plane (2D). The main influence of the reinforcement is the cohesion of sand, which is enhanced with the fibre content, while the angle of the internal friction remains constant. 

Nonwoven geotextHes are permeable geosynthetics made of nonwoven materials used with soil, rock, or other geotechnical-related material as an integral part of a civil engineering project, structure, or system. They are frequently made from synthetic polymers such as polypropylene, polyethylene, polyamide, and polyester, as well as natural fibres such as jute, sisal, and coir. The European standards (EN) for the specifications and performance requirements of geotextiles in 11 application areas (roads and other... 

The heat deflection temperature (or heat distortion temperature) is an important material property mostly used to determine a material s useful temperature operating range. It refers to the temperature below which a moulded object can hold its own shape. It can be determined using a dynamic mechanical analyser set to apply a constant force. The HDT was determined for blends of plasticized soy flour (52% protein) and polyamide (nylon) as 45 °C when plasticized with 20 wt% sorbital, 35 °C when plasticized with 20 wt% glycerol, and 39 °C when plasticized with 10 wt% of each." When such a blend is used to make composites with natural flbres, increasing content of natural fibres also increased the HDT. 

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... 

Table 6.30 shows the properties of the same thermoplastic (short fibre reinforced polyamide) reinforced with the same level of the three main reinforcement fibres, illustrating the effect of the fibre nature. 

The wide range of natural and man-made fibres provides many combinations to create new effects with desirable properties. Strength, wearibility and crease recovery are the main properties responsible for synthetic fibres becoming established for blends with cotton, viscose and wool. The acrylics are also in much demand for such blends, while polyamide fibres and triacetates are of secondary importance. 

Polyamides can, as a rule, be brightened with those products suitable fi protein fibres. They have, however, an affinity for insoluble dispersions ( organic compounds and, because of their hydrophobic nature, it is on derivatives of this type that can be applied to polyesters. Water-insolub fluorescent brightening agents, in the form of dispersions, are based, one example, on compounds derived from (12) which are favoured becau of their comparatively good light-fastness ... 

The group includes many natural and synthetic dyes, the latter usually being obtained from anthracene. They have no natural affinity for textiles but are applied to cellulosic or protein fibres which have been mordanted previously with a metallic oxide. The acid mordant dyes are a special class of dyes applied to wool or polyamide fibres as if the were acid dyes, and then given very high wet-fastness by subsequent mordanting. 

If it is not possible to select dyestuffs which will give a solid result on both fibres, it is necessary to dye in the presence of 4 to 8 per cent of carrier until the polyester is on shade. The polyamide is then stripped with sodium hydrosulphite or zinc formaldehyde-sulphoxylate and acetic acid at the boil, leaving the other fibre unaffected because, on account of its hydro-phobic nature, the entry of the hydrosulphite into the polyester is extremely slow. It is, of course, important to select dyestuffs which will reduce easily to colourless compounds. The nylon can then be dyed to... 

Each fabric has its own particular characteristic vtiiich can be used to advantage in the filtration process. Thus the smooth-surfaced mono- and multifilament (high-twist) cloths are particularly suited to the liquid environment, in the separation of sticky, clogging substances such as sludges or colloids. Retention of such small material depends on a rapidly formed surfece layer of particulates in the reported use of monofilament polyamides for effluent treatment plants [Grove Daveloose, 1982]. Apparently in this application, change firom q>un fibre to woven cloth increased the cloth lifetime from 3 months to 2.5 years The adhesive nature of such solids may be modified by treatment with polyelectrolytes. Quite opposite results can also be experienced, however, where the three-dimensional capture characteristics of staple fibre material is the best option. 

As indicated earlier in this chapter, although diisocyanates are the intermediates responsible for chain extension and the formation of urethane links or a variety of crosslinks by further reaction, much of the ultimate polymer structure is dependent upon the nature of the components carrying the groups with which the isocyanates react initially. Such components can be simple acu-diols, such as were employed in early work on linear polyurethanes, giving polymers linked only by —NHCOO—. Examples of such polymers are listed in Table 1.2. Linear polyurethanes of this type are crystalline, fibre-forming polymers but are lower melting than the corresponding polyamides, and none has become of real importance either as a synthetic fibre or as a thermoplastic material. 

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