Mater. Proc. 2020 , 2 , 29
7 of 8
surface created voids for the flow of the water through the coating, while the presence of fillers improved the coating coverage and density, providing better bulkiness compared to the pure natural rubber. The original rubber coating had a water contact angle of 95°, being in the hydrophobic range. The presence of kaolinite gradually increases the coating hydrophobicity, likely due to the hydrophobic properties of the fillers in combination with the creation of some additional surface roughness, seen in the microscopic images. The talc particles are hydrophilic, and their properties consequently prevail while exposed at the surface, resulting in a gradual decrease in hydrophobicity with the higher talc concentrations. The hydrophobic properties of SMI nanoparticles are beneficially exploited while added in different concentrations, rising up to a maximum water contact angle of 110°. While the water contact angle indicates the polar interactions, the diiodomethane is an apolar liquid and often shows opposite trends to the water contact angles.
Figure 5. Surface properties of natural rubber coatings on paper substrates, ( a ) static contact angles for water (blue bars) and diiodomethane (orange bars), ( b ) calculated work of adhesion Wa, ( c ) experimental adhesion force from loop test. The adhesion between coated surfaces of natural rubber composites has been studied in the frame of the tendency for self-adhesion of natural rubber materials. The work of adhesion, Wa = · L (1 + cos Ό ) with · L = liquid tension, and taking into account the contact between similar rubber coating materials, can theoretically be calculated from the water and diiodomethane contact angles. The
Made with FlippingBook Ebook Creator