Composites reinforced with cellulose based fibres

This review article concerning natural and man-made cellulose fibre reinfor ced plastics, introduces possible applications of this material group. The physical properties of natural fibres are mainly determined by the chemical and physical composition, such as the structure of fibres, cellulose conte nt, angle of fibrils, cross-section, and by the degree of polymerization. O nly a few characteristic values, but especially the specific mechanical pro perties, can reach comparable values of traditional reinforcing fibres. Thi s physical structure can be modified by using alkali treatment and acetylat ion processes. The application of natural fibres as reinforcements in compo site materials requires, just as for glass-fibre reinforced composites, a s trong adhesion between the fibre and the matrix, regardless of whether a tr aditional polymer (thermoplastics or thermosets) matrix, a biodegradable po lymer matrix or cement is used. Further this article gives a survey about p hysical and chemical treatment methods which improve the fibre matrix adhes ion, their results and effects on the physical properties of composites. Th ese different treatments change among others the hydrophilic character of t he natural fibres, so that moisture effects in the composite are reduced. T o bring about hydrophobic properties to natural fibres, a special treatment , termed acetylation, can be used. The effectiveness of this method is stro ngly influenced by the treatment conditions used. The mechanical and other physical properties of the composite are generally dependent on the fibre c ontent, which also determines the possible amount of coupling agents in the composite. The influence of such treatments by taking into account fibre c ontent on the creep, quasi-static, cyclic dynamic and impact behaviour of n atural fibre reinforced plastics are discussed in detail. For special perfo rmance requirements, hybrid composites made of natural and conventional fib res can be prepared with desired properties. The processing conditions play , next to the mechanical properties of natural fibres, an important role fo r the industrial use of these materials. The results presented in this pape r show, that natural fibres can be processed with the already commonly appl ied methods: glass mat thermoplastic matrix (GMT), sheet moulding compound (SMC) or bulk moulding compound (BMC). For the processing of thermoplastics reinforced with natural fibres, new methods (e.g. the "EXPRESS" processing ) are of increasing importance. Natural fibres seem to have little resistan ce towards environmental influences. This can be recognized in the composit e and can be advantageously utilized for the development of biological degr adable composites with good physical properties. (C) 1999 Elsevier Science Ltd. All rights reserved.