Influence of natural fibres on the mechanical properties of biodegradable polymers

Fibre reinforced plastics are used whenever there is the need for very high mechanical properties combined with low weight. In that respect natural fibres are of basic interest since they not only have the functional capability to substitute the widely used glass fibres but they also have advantages from the point of view of weight and fibre-matrix adhesion, specifically with polar matrix materials. They have good possibilities in waste management due to their biodegradability on the one hand and their much lower production of ash during incineration on the other. The influence of plant fibres such as flax, jute, ramie, oil palm fibres and fibres made from regenerated cellulose on the mechanical properties of biodegradable polymers was investigated using thermoplasts like polyesters, polysaccharides and blends of thermoplastic starch. The composites were produced by extrusion compounding with a co-rotating twin screw extruder. The pellets obtained were further processed into tensile test bars by injection moulding. Depending on the kind of polymer, a fibre content of 20-35% could be achieved. Generally a considerable tensile strength improvement of polyesters could not be observed. However the chemical similarity of polysaccharides and plant fibres, which consist mainly of cellulose, resulted in an increased tensile strength of the reinforced polymers. For reinforced thermoplastic wheat starch, it was four times better (37 N/mm(2)) than without fibres. The reinforcement of cellulose diacetate and starch blends caused a stress increase of 52% (55 N/mm(2)) and 64% (25 N/mm(2)), respectively. (C) 1998 Elsevier Science B.V. All rights reserved.