Aramid-fibre-reinforced polymer

AFRP Aramid-fibre-reinforced polymer composites... 

Fibre-reinforced polymers (FRP) rebars, usually made of an epoxy matrix reinforced with carbon or aramide fibres, have also been proposed both as prestressing wires and reinforcement. Nevertheless, they are not discussed here, because these applications are still in the experimental phase and there is a lack of experience on their durability. In fact, while they are not affected by electrochemical corrosion typical of metals, they are not immune to other types of degradation. FRP are also used in the form of laminates or sheets as externally bonded reinforcement in the rehabilitation of damaged structures this application will be addressed in Chapter 19. 

Fibre reinforced polymers (FRPs) are composed of a reinforcement material (glass, aramid or carbon fibres) surrounded and retained by a (thermoplastic or thermosetting) polymer matrix (unsaturated polyester, epoxy, vinyl ester, or polyurethane). FRPs were first used in the rehahiUtation of reinforced or pre-stressed concrete, but they have also been widely used in the reinforcement of timber structures. 

Klein N, Marom G, Wachtel E, Microstructure of nylon 6,6 transcrystalline layers in earbon and aramid fibre reinforced composites. Polymer, 37(24), 5493-5498, 1996. 

Correa and co-workers [a.272] studied the thermal behaviour of short-fibre-reinforced PU composites by DSC and TG techniques and reported that the thermal resistance of aramid-fibre-reinforced composites was greater than that of carbon-fibre-reinforced composites or the pure matrix polymer. The DTG results are presented in Figure 31. 

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

To date, only one class of polymer has been found in which this problem can be overcome and highly successful reinforcement fibres produced. These are the aramld polymers, so-called because they contain both aromatic and amide groups in the molecular chain. Indeed, it is this combination which is the key to their success. Kevlar 49 is currently the most widely used aramid fibre for reinforcement of plastics, and it illustrates the point well. It consists of the polymer poly(paraphenylene terephthalamide) ... 

The chapter demonstrates that in spite of the incompatibility between hydrophilic natural fibres and hydrophobic polymeric matrices, the properties of natural fibre composites can be enhanced through chemical modifications. The chemical treatments have therefore played a key role in the increased applications of natural fibre composites in the automotive sector. Recent work has also shown that if some of the drawbacks of natural fibres can be adequately addressed, these materials can easily replace glass fibres in many applications. The chapter has also shown that there have been attempts to use natural fibre composites in structural applications, an area which has been hitherto the reserve of synthetic fibres like glass and aramid. The use of polymer nanocomposites in applications of natural fibre-reinforced composites, though at infancy, may provide means to address these efficiencies. Evidence-based life-cycle assessment of natural fibre-reinforced composites is required to build confidence in the green composites applications in automotive sector. 

There are a large number of possible fibre materials that can be used in reinforced polymers. The most common are glass, carbon, aramid, and polyethylene. 

Reinforcements, with the exception of carbon and SiC fibres, are electrical insulators, as are all polymer matrices whether thermoset or thermoplastic. Hence composites based on glass or aramid fibres can be used as insulators or in situations where transparency to electromagnetic radiation is required (e.g. D-glass). Materials based on carbon fibres may be used for electrical screening. 

As a result of their outstanding physical and mechanical properties, aromatic polyamides are attractive materials for use in high-performance structural applications 853072 833611 820253, including aircraft components or fire protection garments, as constituents of both traditional, i.e., fibre-reinforced composites 774110 762844, and molecular composites. One of these applications takes advantage of their thermal stability 881232 825031 763791 755849 and allows the manufacturing of heat-resistant materials for fire protection 713906. In a different context, aromatic polyamides (aramid fibres) have been proposed in the past few years as precursors of activated carbon materials with distinctive adsorbent properties (thermally stable molecular sieves). Aramid fibres, e.g., poly(w-phenylene isophthalamide), poly(p-phenylene terephthalamide) 709654, etc., are a class of synthetic polymers that possess excellent thermal and oxidative stability, good flame resistance, and superior mechanical and dielectric behaviour. 

Fibre reinforcement (e.g. glass, carbon and aramid) significantly increases the stiffness, rigidity and strength of the base polymer. 

Traditional fibres used as reinforcement in polymer composites are generally either polymers or ceramics the polymer aramids, glass, carbon, boron, aluminium oxide and silicon carbide. Carbon is a high-performance fibre material that is the most commonly used reinforcement in advanced polymer-matrix composites. Glass fibre is readily available and may be fabricated into a glass-reinforced plastic economically using a wide variety of composite-manufacturing techniques. 

Short fibres of glass, rayon, aramid, asbestos and cellulose as reinforcing fillers, have been broadly used in rubber industries due to their high modulus, high strength and low creep. In recent years especially, natural fibres such as jute fibre, cellulose fibre, " coir fibre," " sisal fibre," " etc. have been also widely used in NR composites because they are enviromnental friendly, cheap, abundant and renewable. However, natural fibres also have some disadvantages such as moisture absorption, quality variations, low thermal stability and poor compatibility with the hydrophobic polymer matrix. 

Aramids The term aramid is used to describe aromatic and partially aromatic polyamides, which constitute a class of materials that are analogous to the aliphatic nylons . The fully aromatic polymers in this category are linear, but not thermoplastic, as they decompose before they flow sufficiently to allow shaping. However, wet spinning of fibres is possible and such materials have many technical applications besides being used as reinforcement. 

Polymers added in the form of fibres are now replacing the asbestos reinforced Portland cement that appeared in the mid-1980s. The fibres commonly used today besides steel and glass are PP and PA. A variety of other synthetic fibres can be used including PE, PES, aramid and carbon [39]. 

---