Fibre reinforcement, various forms

Aramid fibres in various forms are used for polymer reinforcement ... 

Glass fibres are used in various forms for the reinforcement of polymers ... 

Table 6.13 displays the strength and modulus of a 60% glass fibre reinforced resin for various fibre forms. The properties are roughly ... 

Over the last decade, considerable efforts have been committed to the toughening of sialons and substantial progress has been achieved using various reinforcements. According to the form of reinforcement, sialon composites can be classified as either particle reinforced, discontinuous fibre (whiskers/ short fibres) reinforced, or continuous fibre reinforced. 

Fibre reinforcements are available in many different forms, designed for various fabrication procedures, as described below. 

A new approach to render fibre-reinforced rigid composite materials flame retardant is undertaken by the utilisation of complex fibrous-intumescent chars. The use of flame retarded cellulosics fabric, surface coated with an interactive intumescent as an additional reinforcement in an otherwise conventional structure has been studied. Thermal analysis has shown that when heated, all components decompose by chemically interactive mechanisms leading to a char-bonded stmcture and the residual mass of char formed is higher than expected above 450 °C, even in the case where polyester resins are present. Not only are greater fiactions of char formed above 450 °C but the chars formed are more resistant to oxidation than the respective components (resin, traditional fabric and coated cellulose). Thus composites comprising these various components will have significantly improved fire performance. 

Although composite forms of pipe may not have reached the same level of growth and widespread application as the commodity thermoplastic pipes, they have penetrated important market sectors and often attain a premium value. Composites can offer high performance for specific requirements. In the case of high pressure applications they are an alternative to steel pipe, especially where corrosion resistance and weight reduction are required. The chemical engineering construction industry with its need for conveyance of various fluids and applications in demanding environments, is a major consumer of composites, particularly fibre reinforced pressure pipes. 

The reinforcement also may have various forms stiff and tough layers, fibres and fabrics grains of hard materials are also used as reinforcement. 

The efficiency of fibre reinforcement is dependent very much upon distribution and orientation of fibres in the matrix. The fibres form an internal structure and various kinds of these structures are described in Section 6.6. 

The fibre surface has a considerable influence on the composition of the transition zone. For highly corrosion resistant glass fibres with specially coated surface, like CemFILl, this zone is very porous. This is in contrast to the strong interface formed around steel and asbestos fibres. In various composites with different kinds of fibres and matrices, the transition zone is formed as a result of chemical affinity, quality of the fibre surface and the penetration of the cement paste into the bundles of fibres. Furthermore, the ITZ may be different above and below a fibre due to bleeding and water lenses below fibres. Higher porosity of the ITZ around steel galvanized reinforcements than around ordinary steel rebars was observed by Belaid et al. (2001). 

More recently, cellulose fibres have been investigated as potential precursors for self-reinforced polymer composites, as well summarised in a review by Eichhom et al. [191]. Numerous authors have reported the use of cellulose fibres from various sources, including wood pulp fibres [192, 193], filter and Kraft paper [194-197], microcrystalline cellulose fibres [198-202], sisal fibres [203, 204], ramie fibres [205], cotton fibres [206], regenerated cellulose (Lyocell) and cellulose fibres spun from an anisotropic phosphoric acid solution (Bocell) [207], and fibres from bacterial cellulose [208]. Two main technologies have been presented to produce these so-called self-reinforced cellulose or all-cellulose composites, and these are, first, the conventional impregnation of cellulose matrix into cellulose fibres and, second, a novel selective dissolution method in which the cellulose fibre surfaces are partially dissolved to form a matrix phase that bonds fibres together. 

Figure 8.1 Various forms of glass fibre reinforcement (a) continuous roving (b) Woven mat.

Boron itself has been used for over two decades in filament form in various composites BO3/H2 is reacted at 1300° on the surface of a continuously moving tungsten fibre 12/tm in diameter. US production capacity is about 20 tonnes pa and the price in about 80(. The primary use so far has been in military aircraft and space shuttles, but boron fibre composites are also being studied as reinforcement materials for commercial aircraft. At the domestic level they are finding increasing application in golf shafts, tennis rackets and bicycle frames. 

Reinforcements are available in various physical forms - filament bundles, short chopped fibres, woven fabrics, three-dimensional fabrics, resin-impregnated filaments, and so on. There is often a surface treatment applied, which fulfils several purposes, such as to protect against abrasion and promote adhesion to the matrix. 

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