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Natural fibre composites

In the field of composites, the fibre reinforcement of matrices was initially developed using man-made fibres such as glass, carbon and aramid for automotive applications to take advantage of their high tensile modulus. But they are considered critically because of the growing environmental consciousness. In recent years, Lignocellulosic fibres from renewable resources like jute, sisal, coir and pineapple leaf fibres have been used as reinforcements in thermoplastic matrices. The advantages of natural fibres over traditional man-made glass fibres are: • low cost, • low density, • high toughness, • acceptable specific strength properties, • enhanced energy recovery and • Biodegradability (environmental friendliness). • High strength • abundant and nonabrasive • nonhazardous and • Excellent reinforcing agent for plastics.

There is a growing interest in the use of bio-fibres (natural fibres) as reinforcing components for thermoplastics like Poly ethylene and Poly propylene. For better processability, these composite materials are often filled with short discontinuous fibres oriented in the direction of the applied load in order to take full advantage of the reinforcing property of the fibre. Natural fibre composites combine good mechanical properties with a low specific mass. Among all the natural fibres, sisal is of particular interest because its composites have high impact strength, besides having moderate tensile and flexural properties, compared with other lignocellulosic fibres. CHALLENGES:

But several technical issues have to be addressed while developing a natural fibre reinforced composites. The major challenges are: • Adhesion between the fibre and the matrix. • Moisture repellance. • Flame retardance. • Poor mechanical properties It is very well known that performance (mechanical properties) of composites depend on the properties of the individual components and Homogenization of the fibre’s properties. Cellulose fibres, one component of the investigated composites, are strongly polar due to hydroxyl groups and C-O-C linkages in their structure. This renders cellulose more compatible with polar, acidic or basic compounds, rather than with non-polar polymers. Because of this inherently poor compatibility between hydrophilic cellulose fibres and typical hydrophobic commodity thermoplastics, such as polyolefins, a pretreatment of the fibre surfaces, of the matrix polymer, or incorporation of surface modifiers is generally required. Polypropylene (PP)/SF composites prepared by melt-mixing and injection molding. However, the poor interfacial bonding affected the reinforcement of SF to the PP matrix. The approaches used to improve the interfacial characteristic between SF and polymer matrices including • chemical treatment(such as using solutions of sodium hydroxide, isocyanate, permanganate and peroxide) • heat treatment, • coupling agent coating, and • gamma-irradiation on the sisal fibre surface as well as adding compatibilizer such as maleic–anhydride-grafted-PP. The surface modification of fillers by grafting polymerization using organic monomers has been found to be an effective method to improve the interfacial bonding between filler and polymer matrix. The treated SF was subsequently used to fill PP.

AREAS OF APPLICATION:

Cellulosic fibres/polypropylene composites are presently used in the automotive industry(car interior) for • dashboards, • rear window shelves • Roof and door upholstery