Fibres in reinforcing plastics

The application of lignocellulosic fibres in reinforcing plastics has been known for a long time. As early as 1908 the first composite materials were applied for the production of large quantities of sheets, tubes and pipes for electronic purposes (paper or cotton to reinforce sheets, made of phenol or melamine formaldehyde resins). In 1896, aeroplane seats and fuel tanks were made of natural fibres with a small amount of polymeric binder [1],... 

Glass is predominantly the most important and widely used fibre in reinforced plastics. Other fibres are natural (cotton, sisal, jute), synthetic (nylon, polyester, acetate, rayon), or organic and Inorganic high-performance fibres (aramid. boron, carbon/graphite). 

COUPLING AGENTS FOR GLASS FIBRES IN REINFORCED PLASTICS... 

Sometimes fillers are used together with fibres in reinforced plastics. To obtain the highest fibre volume fraction, the particle size of the filler should be less than the average fibre diameter. 

Glass fibres dominate this field either as long continuous fibres (several centimetres long), which are hand-laid with the thermoset precursors, e.g., phenolics, epoxy, polyester, styrenics, and finally cured (often called fibre glass reinforcement plastic or polymer (FRP)). With thermoplastic polymers, e.g., PP, short fibres (less than 1 mm) are used. During processing with an extruder, these short fibres orient in the extrusion/draw direction giving anisotropic behaviour (properties perpendicular to the fibre direction are weaker). 

Maleic anhydride is used as a chemical intermediate in the synthesis of fumaric and tartaric acids, certain agricultural chemicals, resins in numerous products, dye intermediates and pharmaceuticals [2]. It is primarily used as a co-monomer for unsaturated polyester resins, which are used in the production of bonding agents for plywood manufacture and when mixed with glass fibres for reinforced plastics. Annual production of maleic anhydride is estimated to be over one million tormes [3]. 

Borosilicate glass fibres are used in reinforced plastics and as insulation in buildings. 

Thermoforming is another mass production method normally associated with unreinforced or short fibre reinforced thermoplastics, but because of recent developments in reinforced plastics technology, discussed below, there is a greater availability of thermoplastics sheet reinforced by long or continuous glass fibres, so it may become more important for these materials as well. 

Figure 2.5 Laser-based technique to check ply orientation in reinforced plastics laminates (By permission S Hill, Rapid nondestructive testing of carbon fibre reinforced plastics. Materials World, August 1996, Institute of Materials, London)...

Galvanic corrosion does not occur at all with ordinary organic plastics, because they are insulators. In reinforced plastics the phenomenon is confined to situations where carbon fibre reinforcement is situated in very close proximity to certain metals. This problem can easily be overcome by inserting some insulating material to break the electrical circuit. 

G S Springer, Moisture absorption in fibre-resin composites . Developments in Reinforced Plastics - 2, ed. G Pritchard, Applied Science, London, 1982, Chapter 3, pp 43-65. 

All polymer materials used in reinforced plastics display some viscoelastic or time-dependent properties. The origins of creep in composites stem from the behaviour of polymers under load together with local stress redistributions between fibre and matrix as a function of time. There is little creep at normal temperatures in the reinforcing fibres. The origin of the creep mechanisms is related to the nature and levels of internal bonding forces between the chains of the polymer, which are influenced by temperature and moisture. 

D2343- Tensile properties of glass fibre strands, yarns and rovings used in reinforced plastics 67... 

These are available as transparent, straw coloured to amber liquids for laminating, encapsulation and casting, and as dough moulding compounds for compression moulding. Polyesters are mainly used as liquid binders for glass fibre and other fibrous materials in reinforced plastics. Glass reinforced plastics (GRP) are based on polyesters. Applications include ... 

In the book of Exodus (Chapter 2) we read that the mother of Moses when she could no longer hide him, she took for him an ark of bullrushes and daubed it with slime and with pitch, and put the child therein and she laid it in the flags by the river s brink . Biblical commentaries indicate that slime is the same as bitumen but whether or not this is so we have here the precursor of our modem fibre-reinforced plastics boat. 

Plastics also find increasing use in vehicles for both water and air transport. Glass-fibre-reinforced plastic boats are widely used as a result of their economy in manufacture, ease of maintenance, lightness of weight and, for military purposes, antimagnetic characteristics. The non-corrosive nature of plastics also leads to their widespread use in boat fixtures and fittings. In aircraft, plastics are particularly useful on account of their low density. 

Jones, F.R., Interfacial aspects of glass fibre reinforced plastics. In Jones, F.R. (Ed.), Interfacial Phenomena in Composite Materials. Butterworths, London, 1989, pp. 25-32. Chaudhury, M.K., Gentle, T.M. and Plueddemann, E., Adhesion mechanism of poly(vinyl chloride) to silane primed metal surfaces. J. Adhes. Sci. Technol, 1(1), 29-38 (1987). Gellman, A.J., Naasz, B.M., Schmidt, R.G., Chaudhury, M.K, and Gentle, T.M., Secondary neutral mass spectrometry studies of germanium-silane coupling agent-polymer interphases. J. Adhes. Sci. Technol., 4(7), 597-601 (1990). 

One of the key factors which make plastics attractive for engineering applications is the possibility of property enhancement through fibre reinforcement. Composites produced in this way have enabled plastics to become acceptable in, for example, the demanding aerospace and automobile industries. Currently in the USA these industries utilise over 1(X),000 tonnes of reinforced plastics out of a total consumption of over one million tonnes. 

A wide variety of thermoplastics have been used as the base for reinforced plastics. These include polypropylene, nylon, styrene-based materials, thermoplastic polyesters, acetal, polycarbonate, polysulphone, etc. The choice of a reinforced thermoplastic depends on a wide range of factors which includes the nature of the application, the service environment and costs. In many cases conventional thermoplastic processing techniques can be used to produce moulded articles (see Chapter 4). Some typical properties of fibre reinforced nylon are given in Table 3.2. 

The viscoelastic nature of the matrix in many fibre reinforced plastics causes their properties to be time and temperature dependent. Under a constant stress they exhibit creep which will be more pronounced as the temperature increases. However, since fibres exhibit negligible creep, the time dependence of the properties of fibre reinforced plastics is very much less than that for the unreinforced matrix. 

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