NATURAL FIBRE-REINFORCED PLASTIC

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. 

The creep and fatigue behaviour for natural fibre-reinforced plastics is less weU understood than for glass fibre-reinforced plastics because of the lack of systematic and detailed information. Limited information is currently available oti the effects on the fatigue behaviour of natural fibre-reinforced plastics of different composite parameters such as fibre type, the quality of fibre-matrix adhesion and fibre properties and their content. 

Cams, M. and Gahle, C. (2008) Injection molding with natural fibres. Reinforced Plastics, April, pp. 18-25. 

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. 

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. 

Table 5.1 Properties of natural fibre reinforced synthetic plastics materials.

Ewins PD, Ham AC, The nature of compressive failure in unidirectional carbon fibre reinforced plastics. Royal Aircraft Establishment Technical Report 73057, 1973. 

Ewins PD, Potter RT, Some observations on the nature of fibre reinforced plastics and the implications for structural design, Phil Trans R Soc London, A294, 507-517, 1980. 

Natural fibres possess sufficient strength and stiffiiess but are difficult to use in load bearing applications by themselves because of their fibrous structure. Most plastics themselves are not suitable for load bearing applications due to their lack of sufficient strength, stiffness and dimensional stability [51]. In natural fibre reinforced composites, the fibres serve as reinforcement by giving strength and stiffness to the structure while the plastic matrix serve as the adhesive to hold the fibres in place so that suitable structural components can be made. The matrix for the natural fibres includes thermosets, thermoplastics and mbber. Different plant fibres and wood fibres are fotmd to be interesting reinforcements for rubber, thermoplastics and thermosets [52-58]. 

Kozlowski R, Mackiewicz Talarczyk M (2005) Inventory of world fibres and involvemtait of EAO in fibre research. Institute of Natural Fibres, Poznan, Poland Kozlowski R, Wladyka-Przybylak M (2004) Chapter 14 Uses of natural fiber reinforced plastics in book natural fibers, plastics and composites In Wallenberger FT, Weston NE (ed) KIuwct Academic Publishers, Boston... 

Wambua P, Ivens I, Verpoest I (2003) Natural fibers can they replace glass and fibre reinforced plastics Compos Sci Technol 63 1259-1264... 

P. Wambua, J. Ivens, and I. Verpoest, Natural fibres can they replace glass in fibre reinforced plastics Compos. Sci. Technol. 63,1259-1264 (2003). 

Wambua, R, Ivens, J., Verpoest, I. (2003). Natural fibres Can they replace glass in fibre reinforced plastics ., (9), 1259-1264. 

Carmakers started advanced developments on door panels, headliners, package trays, dashboards, and trunk liners, based on natural fibre composites with a thermoplastic or thermoset matrix, challenging mainly glass fibre reinforced plastic composites. 

Finally, it is noteworthy that if water (or indeed other highly polar liquids) is the environment of interest, then metallic and ceramic substrates are those which result in joints most likely to exhibit poor durability. This is a consequence, of course, of the relatively polar nature of their surfaces and their high surface free energies. Thus, ingressing water molecules are preferentially attracted to the surfaces of these substrates and will displace the physisorbed molecules of the adhesive. These comments are also reflected [5,6] in the values of Wa and Wai for joints based upon carbon-fibre-reinforced plastic (CFRP) substrates typically being of the order of 90 mJ/m and 30 mJ/m, respectively. The positive values of both of these terms indicate that the durability of adhesively bonded CFRP joints should not represent a major problem. This is indeed found to be the case, from the aspect of the stability of the interface. (Although problems may arise if (a) the... 

Various methods have been developed for the production of GRC components. These methods have mostly been adapted from the glass fibre reinforced plastics industry, with proper modifications to adjust for the special nature of the cementitious matrix. To obtain a product of an adequate quality the mix composition should be carefully controlled, to be compatible with the production process, while at the same time providing the needed physical and mechanical properties in the hardened composite. Thus, the properties of GRC composites vary over a wide range, and are a function of a complex combination of the production process and the mix composition. A detailed discussion of the design and production of GRC components is beyond the scope of this chapter. These topics are covered in various publications and guidelines [31-37] and only some essential points will be discussed in Section 8.7 and Chapter 14. 

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