PAN fibres production

Table 11.2 Nickel and cobalt absorption capacity and their diffusion coefficient as a function of precipitation-bath parameters during PAN-fibre production...

In this chapter, a relatively simple method is described to metallise polyacrylonitrile (PAN) fibres with a two-step process (ab/adsorption and reduction of Ni(II) in one bath solution followed by galvanisation), and making use of relatively cheap chemicals in order to offer a simple and economically feasible metallisation method and related metallised product. 

The results of this analysis are shown in Table 11.1. It is clear that absorption of nickel in all fibres is reasonably high, but the amount of metallic nickel is considerably higher in PAN fibres and, to a lesser extent, in natural silk. This indicates that the structure of the fibres (pore size and permeability as well as functional groups) plays an important role. Sodium dithionite and rongalite are known as good reducing agents, but their stability is fairly limited. One of their decomposition products (particularly in acidic solutions) is sulphide, which explains why an important fraction of... 

From the above results, it can be concluded that PAN fibres resulted in the desired conductive behaviour and will be used further in this investigation. Microscope images of the cross-section of PAN fibres treated with NiCl2 show that after thermofixation of the fibre, no swelling is obtained. Therefore thermofixation will be an important step in the production process and will also be taken into account in the following steps of this investigation. Finally, it should be pointed out that similar absorption behaviour of PAN fibres for Co and CoS was observed but, contrary to Ni, this led to much weaker electroconductive properties of the metallised fibres. 

During the production of cation-containing PAN fibres, it was found that absorption of Ni(II) in the fibre structure and adsorption at the surface of the fibre through formation of complexes with cyanide and carboxylic acid... 

Research in ACF has attracted increasing attention in the last few years in terms of their synthesis, and their suitability in different applications that include solvent recovery, molecular sieving, gas storage and catalysis. Activated carbon fibres are usually prepared from precursors of low or intermediate crystallinity such raw materials include polyacrylonitrile (PAN) fibres, cellulose fibres, phenolic resin fibres, pitch fibres, cloth or felts made from them, and viscose rayon cloth. They are first pyrolysed and then activated at a temperature of 700-1000 C in an atmosphere of steam or carbon dioxide. Both the processing costs and the properties of the fibre products are dependent on the nature of the starting material. 

Carbon fibres are obtained from different organic fibres (precursors) by pyrolysis, which consists of decomposition into smaller molecules at high temperature. The process of fabrication of carbon fibres from special PAN fibres includes two steps oxidative stabilization at low temperature and carbonization at high temperature in an inert atmosphere. Due to the high cost of raw materials (e.g. PAN fibres) and of this production process, carbon fibres are still expensive. Carbon fibres may be also produced from crude oil deposits like pitches or asphalts. Three main groups of carbon fibres are considered as possible composite materials reinforcement ... 

The exotherm which occurs in the degradation of pure PAN is an undesirable effect in carbon fibre production, since the rapid build up of heat fragments the chains. The exotherm is reduced if... 

The production of carbon fibres is based on the pyrolysis of organic fibres or precursors. The main starting materials are polyacrylonitrile (PAN) and pitch (coal tar or petroleum asphalt). They can be classified according to their mechanical performances ... 

The first high-strength carbon fibres were produced in the 1950s (see Donnet and Bansal, 1984). The early carbonized products were rayon-based, but it was soon found that the mechanical properties and the carbon yield could be improved by the use of polyacrylonitrile (PAN) as the precursor. Also, less expensive fibres of somewhat lower strength and modulus could be made from various other precursors including petroleum pitch and lignin. However, cotton and other forms of natural cellulose fibres possess discontinuous filaments and the resulting mechanical properties were consequently found to be inferior to those of the rayon-based fibres. 

Pavlov et al.98 observed that partially hydrolyzed. cellulose-PAN copolymers lend themselves to dyeing by add and direct dyes. Unfortunately, the products fail to form fibres suitable for textile industry because of their poor mechanical properties. 

Let us consider the timeline of a class of industrial products - synthetic polymers or pldstics. The first completely synthetic plastic wasBaKeiite invented in 2907 by Leo H- BaeKeland (2863- 29 ). It was a rigid, lightweight material and used to maKe everything from hairbrushes to handles of frying pans. Wallace Hume Carothers (2896 -2937) developed a new polyamide fibre which was marKeted as Nylon in 2938. 

Since PAN homopolymer is not used for the production of carbon fibres, the subject is not discussed. Similarly, stabilization in nitrogen is sparingly mentioned. 

The production process of activated carbon fibre consists of the development of amorphous carbon flbres at around 1000°C from fibre precursors, followed by physical activation either by steam at 800-1000°C or chemical activation. The organic fibre precursors include polyvinylidene chloride (PVDC) fibres (Saran), phenolic fibres (Kynol) , poly (acrylamide), polyacrylonitrile (PAN) and rayon fibres activated carbon fibres can also be made from vapour-grown fibres, nanotubes and... 

Their method of production is summarized in Fig. 28.28c in which atom X represents an arbitrary N content. Processing conditions (heat treatment in particular) determine the mechanical properties of the carbon fibres. Both pitch- and PAN-based carbon fibres (Fig. 28.29) are stronger and have a higher modulus of elasticity (Young s modulus) than those derived from rayon. They therefore have wider applications. Carbon fibres usually require a protective coating to provide resistance to reaction with other elements at elevated temperature. 

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