Fibre for reinforcement

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]. 

This chapter first gives an overview of cellulose raw materials and their molecular and supermolecular structures. The principles of shaping cellulose into fibres, films, and nonwovens by means of solution techniques are then outlined followed by a section on properties and market applications of these materials. Derivatives of cellulose are presented with special emphasis on thermoplastic cellulose esters, typical plasticizers, and promising reinforcing materials. Finally, recent developments and future prospects of cellulose materials are reviewed as far as the above applications are concerned. This book does not cover the important applications of cellulose and ligno cellulose fibres for reinforcing thermoplastics, like wood plastic composites (WPC) and natural fibre reinforced plastics (NFRP), since in these cases cellulose does not substitute a thermoplastic. 

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 polymeric composite consists of fibres for reinforcement on the one hand and of the matrix on the other hand. One of the main problems encountered here is the contact or adhesion between the fibres and the polymeric matrix, the so-called interphase problem. The adhesion between fibre surface and polymeric matrix depends... 

Hill, P. S., Smith, S. and Barnes, F. J. (1999), Use of high modulus carbon fibres for reinforcement of cast iron compression struts within London Underground project details , Conference on Composites and Plastics in Construction, November 1999, BRE, Watford, UK. RAPRA Technology, Shawbury, Shrewsbury, UK, paper 16 1-6. 

Table 5.3 Examples of steel fibres for reinforcement of cement-based matrices... 

Fig.14 Stress-strain behaviour of fibres for reinforcement of polymers...

Hughes, J.D.H. (1986) Fibres for reinforcement. Metals and Materials June 1986, 365-8. 

It can be seen that soluble pigments (the white dots in the figure) have leached into seawater from the upper part of the coating forming a so-called pigment-leached layer with porosity. The thickness of the leached layer can be measured. Long fibres, for reinforcement, are also visible in the coating. 

Tensile drawing Centrifugal drawing (or spraying) Optical fibre (using a preform), fibres for reinforcement Fibrous glass for thermal insulation, acoustical insulation, air filtration... 

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 mechanical properties of pure polymeric materials are often inadequate for particular applications, and to overcome this problem these materials may be reinforced in some way. The most common method is to include a substantial amount of a rigid filler or fillers, generally as finely divided powder, or as rods or fibres. For certain materials, elastomeric particles may be used, and these have the effect of reducing brittleness. 

A natural fibre which has been superseded by the various synthetic fibres for use as reinforcement in mbber articles. 

A large variety of hose constructions are produced by the rubber industry for a wide range of applications. To contain transported liquids, usually under pressure, it is necessary to reinforce the hose construction with fabric, yam or short fibres to constrain expansion of the rubber. Although hand-built construction using fabric still represents a proportion of the production, it is also very common to use yams either braided or knitted directly onto the hose liner. For heavy duty purposes it is also necessary to use wire, in a braided form, to either reinforce or protect the hose from external damage. Use of short fibres as reinforcement represents a small proportion of hose production and requires specialised dies for extrusion to orientate the fibres circumferentially. 

Reinforcement with carbon and glass fibres moderately improves moduli, as shown in Figure 4.89(b). Note that the load is 14 MPa for reinforced grades and 7 MPa for the neat grade. 

Figure 4.111 displays examples of SN or Wohler s curves for three given grades of neat and glass (GF) or carbon fibre (CF) reinforced PEI. 

Glass fibres are the most commonly used reinforcements, accounting for 95% of the consumption of fibres for plastic reinforcement. 

Many researchers have used glass and glass-ceramic matrices for reinforcing with high-modulus graphite fibres [1, 2], silicon carbide fibres and silicon carbide mono-filaments [3-7], Very strong, tough and refractory composites were obtained from these efforts. 

So far, it would seem that only thermosetting resins are suitable for reinforcement with continuous fibres. Historically, this is a logical situation, since impregnating is easiest with a not too highly viscous liquid, such as a resin, which is still a low-molecular substance during impregnation. Molten thermoplastics, on the contrary,... 

Vegetable fibres (including wood fibres) represent a good replacement solution for glass and carbon fibres for the reinforcement of composites based on a thermoplastic matrix. The advantages of vegetable fibres are economically and ecologically important ... 

The most important polymeric matrices are linear and cross-linked polyesters, epoxy resins and linear and cross-linked polyimides the most important reinforcements are high-performance polymeric fibres and filaments (for polymeric composites), filaments of refractory metals and inorganic materials (E-glass, A12C>3, B, BN, SiC and Carbon) and whiskers (fibrillar single crystals of A1203, B4C, WC, SiC and C, exclusively for reinforcement of metals). 

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