Reinforcing fibres

The reinforcing filler usually takes the form of fibres but particles (for example glass spheres) are also used. A wide range of amorphous and crystalline materials can be used as reinforcing fibres. These include glass, carbon, boron, and silica. In recent years, fibres have been produced from synthetic polymers-for example, Kevlar fibres (from aromatic polyamides) and PET fibres. The stress-strain behaviour of some typical fibres is shown in Fig. 3.2. 

Reinforcing fibres have diameters varying from 7 /im to 1(X) /im. They may be continuous or in the form of chopped strands (lengths 3 mm-50 mm). When chopped strands are used, the length to diameter ratio is called the Aspect Ratio. The properties of a short-fibre composite are very dependent on the aspect ratio - the greater the aspect ratio the greater will be the strength and stiffness of the composite. 

Table 3.3 indicates the extent to which the properties of plastics are influenced by the level of fibre content. Full details of the forms in which reinforcing fibres are available for inclusion in plastics are given in Chapter 4. 

An inherent problem with all of the above moulding methods is that they must, by their nature, use short fibres (typically 0.2-0.4 mm long). As a result the full potential of the reinforcing fibres is not realised (see Section 2.8.5). In recent years therefore, there have been a number of developments in reinforced... 

Thermal decomposition of the matrix material offers a simple way of recovering the relatively expensive reinforcing fibres from a fibre-reinforced laminate. The epoxy resin matrix was made to decompose by thermal treatment in air or nitrogen, this treatment allowing the carbon fibres to be recovered without damage. 

Kevlar has the highest tensile strength and is often used as a reinforcing fibre in composites with, e.g., epoxy, PEEK. The thermotropic liquid crystal polymer Vectran is made by melt polymerisation of p-acetoxybenzoic acid and 6-acetoxy-2-naphthoic acid, (the corresponding hydroxy acids decompose on melting). Because of its liquid crystal properties the polymer can be spun into fibres from the melt. Kevlar is spun from a solution in concentrated sulfuric acid, and can be melt drawn to give a high modulus (stiff) polymer. Vectran ... 

Currently, glass fibres are the most widely used, accounting for 95% of the reinforcement fibres consumed by plastics. Aramid and carbon fibres account for nearly all the remaining 5%. 

ISO 1889 1997 Reinforcement yarns - Determination of linear density ISO 1890 1997 Reinforcement yarns - Determination of twist ISO 2113 1996 Reinforcement fibres - Woven fabrics - Basis for a specification ISO 2113 1996/Cor 1 2003... 

ISO 10122 1995 Reinforcement materials -Tubular braided sleeves - Basis for a specification ISO 10371 1993 Reinforcement materials - Braided tapes - Basis for a specification ISO 12215-1 2000 Small craft - Hull construction and scantlings - Part 1 Materials Thermosetting resins, glass-fibre reinforcement, reference laminate ISO 15100 2000 Plastics - Reinforcement fibres - Chopped strands - Determination of bulk density... 

E-glass the general-purpose grade that represents more than 90% of the reinforcement fibres. 

Market share of the reinforcement fibres 90 Sports leisure Antiballistic <10 windows Printed circuit boards <10... 

EMS hybrid yarns or Schappe s preimpregnated yarns are a combination of reinforcing fibres (glass, aramid or carbon) and polyamide 12. 

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. 

In this category, not all the reinforcement fibres are truly continuous (certain GMT, for example) but they all have a longer length than in the LFRT. 

Certain polyquinoxalines are thermo-stable with high glass transition temperatures up to 435°C,high decomposition temperatures (510-560°C) and notable oxidative resistance in air, but, on the other hand, they form highly viscous solutions that don t wet reinforcing fibres easily. 

The production of modern car tyres uses more than 100 raw materials, most of which are based on petroleum products. Tyres consist of natural and synthetic mbber, typically styrene-butadiene (SBR) reinforcing fillers (e.g., carbon black, silica, clay, calcium carbonate) reinforcing fibres... 

Schweitzer RA,Winterman AW (1989) Reinforcing fibres and fillers. In Lutz JT Jr (ed) Thermoplastic polymer additives. Marcel Dekker, New York, p417... 

There has been much interest in flow and flow orientation effects with polymer melts containing anisometric particles which may be plate-like or fibrous. Flow-induced orientation of short reinforcing fibres is an area of considerable commercial importance, which is beyond the scope of the review [30]. 

Polyether ether ketone (PEEK) and Polyether sulphone (PES) belong to the most recent developments in the field of technical high-performance polymers. Both possess very good thermal and mechanical properties, which can be further improved by reinforcing fibres. Their application is mainly in aircraft and space vehicles. 

The large effect on crystalline polymers is, on the one hand, trivial and self-evident on the other hand it appears that reinforcing fibres bring about such an increase in the stiffness at increasing temperatures that the temperature region of application is substantially widened. 

Janes, Neumann and Sethna ° reviewed the general subject of solid lubricant composites in polymers and metals. They pointed out that the reduction in mechanical properties with higher concentrations of solid lubricant can be offset by the use of fibre reinforcement. Glass fibre is probably the most commonly used reinforcing fibre, with carbon fibre as a second choice. Metal and ceramic fibres have been used experimentally to reinforce polymers, but have not apparently been used commercially. To some extent powders such as bronze, lead, silica, alumina, titanium oxide or calcium carbonate can be used to improve compressive modulus, hardness and wear rate. 

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