JOURNAL OF MATERIALS SCIENCE 16 (1981) 1 548-1 556 Copper coating on coir fibres C. PAVITHRAN, K. GOPAKUMAR, S. V. PRASAD, P. K. ROHATGI Regional Research Laboratory (CSIR), Trivandrum-695019, India Conditions for obtaining continuous coatings of copper (thickness range 1.5 to 5/am) on coir fibres have been reported. Activation of the surface of coir fibres was achieved by treating the surface of the fibres with NaOH-HCHO/ammoniacal AgNO3 solut'ion. Copper was deposited on the activated surface of coir fibres from Fehling-formaldehyde solution. The effects of variation in formaldehyde and sodium hydroxide concentrations and pressures inside the coating vessel on deposition rates were determined. The minimum concentrations of NaOH and HCHO required for maintaining a maximum rate of depo- sition of copper from a solution contaning 10g 1-1 copper sulphate were found to be 6.6 g 1-1 and 2.5 to 3.5 g 1-1, respectively. Optical and scanning electron microscope studies show that relatively more uniform and non-porous copper coatings were obtained when deposition was carried out under reduced pressures. A 5/am thick copper coating on coir fibre prevents the propagation of flame as was shown by flammability tests. Copper coating on coir fibre decreases its electrical resistivity from 2.55 x 10 6 ~cm to 4.68 • 10-3~cm with 1.5/am thick coating and 3.76 • 10-s ~cm with 5/am thick coating. Reinforcement of polyester with copper-coated coir fibre leads to an increase of about 25% in tensile strength and flexural strength as compared to polyester reinforced with plain coir fibre. 1. Introduction Coir fibre comes from coconut palm and is avail- able in very large quantities, of the order of 5 million tons year-~, world-wide. Coir consists of cellulose fibres with hemicellulose and lignin as the bonding material for the fibres. The coir fibre is therefore in a sense a fibrous composite material (Fig. la). Natural fibres have been one of the cheap and renewable resources of materials and they are receiving increasing attention as reinforcements in polymeric materials in composites due to the shortage of non-renewable resources [1, 2]. How- ever, low and variable strength, poor resistance to weathering and lack of wettability with various polymeric matrix materials make natural fibres less desirable compared to synthetic fibres as rein- forcements. To overcome some of these drawbacks we have explored the possibility of coating the coir fibres with metals, specifically copper. As a result of metal coatings, the fibres can also become electrically and thermally conductive, and the polymer composites made out of these fibres can find uses in electromagnetic interference (EMI) shielding, electrical heating and discharging static electricity like metal-polymer composites [3-51. In this paper we report optimum conditions for coating coir fibre with copper using an electro- -tess technique. Flammability, mechanical and electrical properties of coated fibres are compared with those of uncoated fibres. Mechanical and electrical properties of polyester composites con- taining both uncoated and copper-coated fibres are also reported. 2. Experimental procedure Retted coir fibres supplied by a local manufac- turing unit were graded and trimmed according to thickness and uniformity. The length of the trimmed fibres varied from 7 to 15 cm. The thick- ness of the fibres selected for coating was in the range 0.15 to 0.30 mm. The fibres were thoroughly washed with water to remove dirt and salt adhering to the surface. 1548 0022-2461/81/061548-09502.90/0 9 Chapmanand HaIl Ltd.