Phenolic Resin Fibres

The commercial appearance of phenolic resins fibres in 1969 is, at first consideration, one of the more unlikelier developments in polymer technology. By their very nature the phenolic resins are amorphous whilst the capability of crystallisation is commonly taken as a prerequisite of an organic polymer. Crystallisability is not, however, essential with all fibres. Glass fibre, carbon fibre and even polyacrylonitrile fibres do not show conventional crystallinity. Strength is obtained via other mechanisms. In the case of phenolic resins it is obtained by cross-linking. 

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. 

It is not economical to use expensive woven material for long lines, which can be, and normally are, coated by mechanical means. For such lines the most commonly used material nowadays is a glass-fibre tissue of a nominal 0-5 mm thickness, consisting of glass fibres bonded together with a phenolic resin or starch. 

The highest mechanical strengths are usually obtained when the fibre is used in fine fabric form but for many purposes the fibres may be used in mat form, particularly glass fibre. The chemical properties of the laminates are largely determined by the nature of the polymer but capillary attraction along the fibre-resin interface can occur when some of these interfaces are exposed at a laminate surface. In such circumstances the resistance of both reinforcement and matrix must be considered when assessing the suitability of a laminate for use in chemical plant. Glass fibres are most commonly used for chemical plant, in conjunction with phenolic resins, and the latter with furane, epoxide and, sometimes, polyester resins. 

The engines of the Polimotor and Ford projects are in hybrid composites of phenolic resins/glass fibres and epoxy/glass fibres with combustion chambers, cylinders and pistons in metal. This permits the direct contact with hot combustion gases that the polymer could not support. The composite provides the rigidity of the engine. 

They are generally used in the form of prepregs 70% fibres/30% matrix of epoxy, poly-imide or phenolic resin. 

Typical systems are polyester and phenolic resins filled with glass fibres and mineral fillers. 

Integral-type monolithic structures are produced by extrusion. The extrusion mixture generally includes the following components a type of carbon or carbon precursor such as activated carbon particles, graphite, carbon fibres, etc., a blinder such as phenol resin, hydroxylcellidose, coal tar pitch etc. and extrusion aids/plasticizers such as water or polymers. Typical preparation steps are mixing, extrusion, diying/solidification and carbonization. 

Yoshida and co-workers [161] studied the relationship between the EDL properties in an organic electrolyte solution and the concentration of surface acidic groups of phenolic resins-based activated carbon fibres. The authors reported that EDL capacitors with high capacitance and low leakage current were obtained with ACF that showed an extremely low concentration of surface acidic functional groups per unit surface ar ... 

G L Hart, The Chemical Stability of Carbon Fibres and their Composites, PhD Thesis, Kingston Polytechnic, 1975. See also G L Hart and G Pritchard, Mechanisms of corrosion in carbon fibre-reinforced phenolic resins , in Developments in Composite Materials-1, ed. G S HoUster, London, Applied Science, 1977. 

The most widely used epoxy resins are reaction products of either bisphenol A or a novolac phenolic resin with epichlorhydrin. When used to manufacture corrosion-resistant structures for use in the chemical process industry, epoxy resins are generally hardened with either aromatic or cycloaliphatic amines. The hardeners for epoxy resins are, with few exceptions, added at levels varying from 20phr (parts per hundred resin) to lOOphr. This means that the hardener is actually quite a high proportion of the matrix resin and has quite a profound effect on the mechanical and corrosion properties of the cured resin. Thus the selection of the most suitable hardener is critical to the eventual success of the application. Epoxy resins have viscosities of several thousand mPas at room temperature, which makes it much more difficult to wet out glass fibre efficiently with them than with polyesters. Wet-out therefore involves heating the resin formulation to between 40°C and 60°C to reduce the viscosity to less than 1000 mPas. 

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