Plasma-assisted fabrication of hydrophobic siloxane based sol–gel-coated coir fibres

This work focuses on a novel technique based on the spray–dry–cure method to establish a hydrophobic sol–gel coating on a lignocellulosic coir fibre surface. The fibres were first activated with oxygen plasma to ensure spreading of the droplets and thus coating uniformity. The efficiency of this method was highlighted by the high content of fluorine (52.1%) coming from the sol–gel-coated coir fibre revealed by X-ray photoelectron spectroscopy analysis. Scanning electron microscopy showed that the sol–gel coating was uniformly deposited. This had a drastic effect on the coir fibre surface and mechanical properties. The contact angle measurements show that the coir fibre surface becomes extremely hydrophobic after application of the sol–gel coating. The work of adhesion changed from 121.7 to 46 mJ/m 2 . Besides this drastic change into a hydrophobic surface, this study also highlighted the higher average breaking force (from 6.4 to 9.8 N), breaking strength (from 108.1 to 148.3 MPa), modulus (from 1819.1 to 2004.6 MPa) and elongation at break (from 45.9 to 60.4%) when coir fibres are plasma treated and sol–gel coated. This work shows that by using this sol–gel coating treatment, the authors have been able to overcome the major drawbacks of coir fibres, such as moisture absorbency, for their use in industry.