Fibre composites -processing techniques

Some of the main constituents nsed in these materials are discussed under Fibre composites - matrices and fibres and practical aspects are considered under Fibre composites - joining and Fibre composites - processing techniques. 

Fibre composites - processing techniques B C COPE Comparison of processing methods... 

This process has been described in a previous chapter as a means to process unreinforced resins. Fibre-reinforced composites can be fabricated in a similar way. The resin and fibre can be combined by usual hand lay-up or spray-up techniques. Glass fibre content up to 70 wt% or 50 vol% can be achieved for fibre composites processed by this technique. Press moulding offers obvious advantages like fast cycle time, good finish, structural integrity and high reinforcement content. 

A method is proposed for using chrome tanned leather wastes produced by the footwear and clothing industry as fillers in polymer matrices. A technique for processing the composite obtained by continuous extrusion is also demonstrated. In order to evaluate the technique, a series of PVC-leather fibre composites was prepared and extruded through a flat die to produce sheets. The process produced a leather-like sheet that could be used in several applications. The influence of the filler content on the processability and final properties of the composite sheets was evaluated. The tests revealed that the sheets were flexible and exhibited suitable water absorption levels for several applications in the footwear and clothing industry. Finally, the tests showed that this composite could be formulated and processed at high productivity levels and at a low cost. 28 refs. 

To cater for the variety of composite fabrication techniques, fibres may be formed into woven rovings, knitted preforms or continuous random mats (CRM) or chopped into lengths of >20 mm to <5 mm for use in moulding compounds or assembling into chopped strand mat (CSM). For these textile processes, the polymeric component of the size is required to maintain strand integrity and filament strength. The random continuous and chopped strand mats require additional polymeric binders. 

A selection of these techniques is also applicable to polymer composites (see Fibre composites - joining). However, since composites gain their superior properties from the reinforcement, the weld is inevitably the weak point in the system as the fibre will be discontinuous across the joint interface. All the welding processes are governed by the parameters time, temperature and pressure. In order to achieve high-quality welds, careful optimization of the welding parameters is required for each application. 

Bledski, A.K., Jaskiewicz, A., Murr, M., Sperber, V.E., Liilzendorf, R., and ReuPmann, T. (2008) Processing techniques for natural- and wood-fibre composites. Chapter 4, in Properties and Performance of Natural-Fibre Composites (ed. KL. Pickering),... 

Short fibre reinforced thermoplastic composites can be processed by most of the classical thermoplastic processing techniques, such as, extrusion and injection moulding. A detailed discussion is provided for these classical thermoplastic processing techniques in Section 9.1. 

In the earlier Nestehous , Concept House of Neste, Finland, the development of new on-site processing techniques were aimed at. Concrete casting moulds that stayed on the construction site were prepared from GFRP composites of polyester and they were used to prepare concrete rebars (prepared with concrete and PP fibres) used as the main load bearing material in the house. 

The properties of composites determine the processing techniques used, and these can be very different indeed. The two poles of the spectrum of composites are represented on the one hand by materials suitable for high speed conversion processes, such as injection-mouldable reinforced nylon, and on the other hand by materials used for high strength structures in very small numbers, like glass reinforced polyester for the hull of a minesweeper or carbon fibre reinforced epoxy for an airframe. 

Fig. 3 Consolidation of a self-reinforced polymer composite from a stacked arrangement of fibres dark grey reinforcement phase) and polymer films light grey matrix phase). The fibres are shown normal to the plane of the page, and many layers can be stacked with a suitable number of film plies between layers a). On the application of heat and pressure the polymer films soften and flow between the fibres. Upon cooling, these films become the matrix phase of the composite, while the fibres withstand processing without significant degradation of mechanical properties, and so remain as the reinforcement phase of the composite b). The technique is equally applicable to any planar arrangement of fibres such as woven fabrics and random fibre mats...

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