Cellulose-based composites natural fibres

Most of the previous research on natural fibre composites has focused on reinforcements such as flax, hemp, sisal and jute, and thermoplastic and thermoset matrices. Some of these composites have been produced using matrices made of derivatives from cellulose, starch and lactic acid to develop fully biodegradable composites or biocomposites [52]. The emerging diversity of applications of natural fibre composites has seen the production of sandwich structures based on natural fibre composite skins (see Fig. 23.10). 

It has also been found that moisture absorbance of the natural fibre-polymer composite can be prevented if the fibre-matrix adhesion is optimized [15, 24]. Indeed, whereas composites based on standard PP and cellulosic fibres displayed high water content at the interphase, due to the presence of microcavities, the encapsulation of the fibres with MAPP decreased the water sensitivity of the composites in terms of both the water uptake and its diffusion coefficient [25], as shown in Fig. 19.9. 

Another important aspect is the moisture content of natural fibres. These fibres are hydrophilic and absorb water. The moisture content can be as high as 20%, but in most cases it will be in the range of 5-10%. Lack of good interfacial adhesion with the polymer phase, due to the inherently poor compatibility and the ability of the hydrophilic cellulose fibres to disperse with the hydrophobic resins, makes the use of cellulose-based fibre-reinforced composites less attractive. During processing, the presence of water can create voids in the matrix and also lead to a poor adhesion of the fibres with the hydrophobic resin. The hydrophilic nature of natural fibres can be a problem in the finished composites as well. 

Materials such as metal, plastic, wood, paper, and leather are coated with pofymers primarily for protection and for the improvement of their properties. For this purpose, cellulose acetate (CA), cellulose acetate propionate (CAP), and cellulose acetate butyrate (CAB) are the most important classical and solvent-based cellulose esters of the coating industry [44]. Cellulose esters are widely used in composites and laminates as binder, filler, and laminate %ers. In combination with natural fibres, they can be used to some extent as composites from sustainable raw materials with good biodegradability. An additional domain of cellulose esters is their use in controlled-release systems, as well as membranes and other separation media [44, 47]. In the field of controlled-release systems, eellulose esters are used as enteric coatings, hydro-phobic matrices, and semipermeable membranes for appheations in pharmacy, agriculture, and cosmetics. 

Nogi M, Yano H (2008) Transparent nanocomposites based on cellulose produced by bacteria offer potential innovation in the electronics device industry. Adv Mater 20 1849-1852 Oksman K, Skrifvars M, Selin JF (2003) Natural fibres as reinforcement in polylactic acid (PLA) composites. Compos Sci Technol 63 1317-1324 Pandey JK, Kumar AP, Misra M, Mohanty AK, Drzal LT, Singh RP (2005) Recent advances in biodegradable nanocomposites. J Nanosci Nanotechnol 5 497-526 Panshin AJ, de Zeeuw C (1980) Textbook of wood technology stracture, identification, uses, and properties of the commercial woods of the United States, 4th edn. McGraw Hill Inc., New York... 

The use of fibres and fabrics as additives to reinforce matrix materials in structures that are often referred to as composites goes back into prehistory, as in the use of straw to reinforce clay bricks. As usual, nature developed such structures first. Examples are wood (cellulosic fibres in a lignin matrix) and bone (collagen fibres in an inorganic matrix). A composite need not be based on fibres - it is a material or product formed by intimate combination of two or more distinct physical phases, so the sh ls of crustaceans (calcium carbonate in a chitin matrix) are composite structures. However, the word composite now commonly brings to mind structures consisting of fibres embedded in a matrix of some other material, whether plastic, ceramic or metal (i.e. fibrous composites), and even tends to be used particularly for structures in which the fibres are laid out in organized fashion before the matrix material is consolidated around them. 

---