Enhancement of hydrophobicity in natural rubber vulcanizates using diatomaceous earth

This study discusses an approach that gives the Natural Rubber (NR) vulcanizates an elevated hydrophobic character. The method used a chemically treated filler called diatomaceous earth (DE) to deliver the hydrophobic characteristics to NR. DE has a nanoscale roughness. It was chemically treated with hexadecyltrimethoxy silane to obtain low surface energy. The combination of nanoscale roughness and low surface energy gave superhydrophobic properties to DE. A series of treated-DE was made with varying silane percentages to find an optimum silane to DE ratio to get the maximum possible hydrophobicity. The optimum ratio was recorded as 38% w/w, and the treated DE displayed a superhydrophobic water contact angle (WCA) of 152°. The treated-DE was added to the rubber as a filler during the compounding process. The filler was added in varying amounts of 5 phr, 10 phr, 15 phr, and 20 phr to observe the changes in the hydrophobic property. The wettability and morphology of developed vulcanizates were measured using WCA measurements and scanning electron microscope (SEM) analysis, respectively. NR compounded with 20 phr filler exhibited an enhanced WCA of 136°, compared to the WCA of 92° of the NR vulcanizate with no treated-DE, and displayed improved tensile, and tear properties.