Unidirectional composites natural fibre

Bacterial cellulose-modified sisal and hemp fibres have also been used to produce unidirectional natural fibre reinforced CAB and polylactide (PLLA) model composites [9]. The mechanical properties of bacterial cellulose-coated sisal fibre reinforced polymers showed significant improvements over neat polymers (Table 6.8). The tensile strength and modulus for sisal/PLLA composites improved by as much as 68 and 49%, respectively. However, improvements were... 

Composites may be characterized according to type of anisotropy. The structural anisotropy created by appropriate distribution of fibres or inclusions should be distinguished from anisotropy of crystals or natural organic materials like bone or wood. The anisotropy of composites is generated more or less purposefully, according to design and adequate technology. At various scales composites with random, unidirectional, bi-directional (laminates) and multidirectional anisotropy are produced. 

The anisotropy, or directional nature, of unidirectional fibre composites is mentioned in Chapter 1. To improve the modulus and strength for intermediate angles (i.e. between 0° and 90°) woven fabrics or multiple constructions are used. The latter is made up of a series of unidirectional plies laid up so that there is an angle, say, 10°, 20°, 30° or 45°, etc., between successive plies. To avoid the laminate distorting it is necessary to balance the construction about the centre plane — i.e. to have as many —0 plies as +0 ones. A typical balanced laminate is [0 45 0]s-Because there are now some plies in intermediate directions the modulus and strength of the laminate in these directions is increased. The exact values for thermoelastic properties can be calculated from classical laminate theory, see Jones (1975). It is more difficult to calculate the effect on strength because of interaction between failure modes and individual plies, etc. 

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