Natural fibre-polylactide PLA composites

PLA is attractive eommercially because it is biodegradable, can be produced from renewable resources and resembles polystyrene in some of its properties. 

4 Polymerisation of L-lactic acid to L- PLA by direct condensation or by ringopening via the L-lactide. 

As with other biopolymers, PLA remains relatively costly when compared with commodity thermoplastics such as polyethylene and polypropylene but a cost level competitive with polyethylene terephthalate (PET) is considered feasible. Possibly because the polymer has only recently been available in bulk to any great degree, there has so far been relatively little research on PLA as a matrix in natural fibre biocomposites. 

5 Tensile strength of compression-moulded jute-PLA composites showing the enhanced strength and brittleness of the composites processed at 190 C or 210°C as compared with the unreinforced polymer processed at 190 C (source Plackett ef a/., 2003). 

A commercial paper-like sheet of kenaf fibre was converted to a composite material by impregnation with a solution of a commercial L-PLA in dioxane solution (Nishino et al, 2002). Following this procedure, a composite material with 70% v/v fibre content was obtained. Tensile tests showed that a maximum tensile stress of about 60 MPa was found for the best composite material, comparing with a value of about 20 MPa for the unreinforced polymer processed in the same way. Similarly, a tensile modulus of about 6 GPa for the kenaf-PLA composite compared with a value of just over 1 GPa for the unreinforced polymer. The authors concluded that good stress transfer fi om the resin to the matrix had been obtained. In research by Shibata et al (2003), a flexural modulus of 5.5 GPa was achieved at 20% w/w abaca fibre content in a PLA composite. This result compares with a flexural modulus of 3.5 GPa for the unreinforced pol3mier. A further increase in flexural modulus was obtained when 

---