Hydrophobic properties and chemical characterisation of natural water repellent materials in Australian sands

Water-repellency in non-wetting sands is due to hydrophobic waxes present o n the surface of sand grains and contained in particulate organic matter pr esent in these sands. This study investigates the physico-chemical characte ristics of these natural waxes and compares them to waxes extracted from po tential original source materials. Non-polar and polar hydrophobic wax extracts were obtained from whole non-w etting sand, and its individual constituents, and associated organic matter . These included the sand fraction, the intrinsic particulate organic matte r, tree litter, eucalyptus leaves, balk, lucerne and lupin plants, and fung i and actinomycetes isolated from these sands. Waxes were characterised for their hydrophobic properties and composition of their chemical constituent s. The hydrophobicities of the waxes were assessed by measuring the water-r epellency induced after treating acid washed sand with wax extracts. Non-polar and polar wax extracts of the tree litter displayed hydrophobic p roperties that were similar to the corresponding waxes isolated from non-we tting sand and intrinsic particulate organic matter. Unlike these plant-der ived waxes, the microbial wax extracts possessed different hydrophobic prop erties. Characterisation of the components of the extracted waxes by gas chromatogr aphy-mass spectroscopy (GC-MS) analysis revealed a strong similarity in the composition of waxes isolated from non-wetting sand, tree litter and other plant material. The major components found were unbranched and blanched C- 16 to C-36 fatty acids and their eaters, alkanes, phytanols, phytanes, and sterols. Some of these components were not detected in the: microbial waxes . Unextracted samples, as well as wax extracts of non-wetting sand, intrinsic particulate organic matter, tree litter and fresh plant material were furt her analysed by solution and solid stare Nuclear Magnetic Resonance spectro scopy which revealed the relative content of the different chemical species present. (C) 2000 Elsevier Science B.V. All rights reserved.