Browsing by Author "Egodage, S. M."

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Development of hydrophobic natural rubber latex film using diatomaceous earth
(4th International Research Symposium on Pure and Applied Sciences, Faculty of Science, University of Kelaniya, Sri Lanka, 2019) Ambegoda, A. L. D. V. T.; Egodage, S. M.; Maddumaarachchi, M.
Conversion of hydrophilic natural rubber latex (NRL) into superhydrophobic/hydrophobic natural rubber latex film will broaden the fields of its application greatly. Low surface energy and appropriate nano-scale surface roughness are the two main factors which govern the superhydrophobic property. The equilibrium between these two factors results the best superhydrophobic surfaces. Diatomaceous earth (DE) is fossilized diatom cells which can be obtained naturally. DE is a silica-based highly porous structure with nano scale roughness. Usage of DE to manufacture superhydrophobic/hydrophobic material is more economical when compared to conventional methods. DE was treated with silane (Hexadecyl-trimethoxysilane) and incorporated into natural rubber latex to manufacture hydrophobic NRL film. Silane modified DE showed superhydrophobic properties with 157° water contact angle (WCA). Unmodified DE is hydrophilic and it absorbs water. Silane modification increased the hydrophobic nature of the DE surface as well as reduced the surface roughness, this was confirmed by the SEM images. FTIR data confirmed that 𝑆𝑖−𝑂−𝑆𝑖 bond formation between DE surface and the silane. Modified DE was dispersed in aqueous phase to incorporate to NRL. Water contact angle of modified DE was reduced about 25% when dispersing due to the formation of new untreated surfaces with the particle size reduction process. pH value of dispersed DE was maintained around pH 10. WCA of modified DE incorporated NRL film was increased up to 115° from 8° giving hydrophobic properties to NR. SEM images confirmed that the smooth rubber film surface was modified into a rough surface after the incorporation of the modified DE. The tensile strength of the NRL film had been reduced about 90% after the incorporation of modified DE. However, the hardness was increased about 20%. Considering these properties of modified DE incorporated latex films, this method can be recommended to modify hydrophilic natural rubber latex films into hydrophobic. This modified material can be used in high hardness and hydrophobicity required applications. Also, it may be used as a surface coating on existing products
Development of robust superhydrophobic plastic sheets using diatomaceous earth
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Jayaweera, D. H. T. S.; Maddumaarachchi, M.; Egodage, S. M.
Superhydrophobicity is the ability of a surface to repel water droplets. Surfaces that exhibit a static water contact angle (WCA) exceeding 150° and a sliding angle less than 10° can be defined as superhydrophobic surfaces. The unique properties of superhydrophobicity include selfcleaning, drag reduction, anti-fouling, anti-corrosion etc. Several methods are employed in developing superhydrophobic surfaces, yet incorporating a superhydrophobic filler is a more convenient method which is utilized in this research. This study discusses a progressive development of a method to enhance the hydrophobicity of plastic substrates using Diatomaceous Earth (DE) as the superhydrophobic filler. In this study, the focus was on developing superhydrophobic plastic substrates with enhanced mechanical durability and stability since one of the primary concerns of superhydrophobic surfaces is their mechanical performance. The fundamental requirements for producing superhydrophobic substrates are nanoscale surface roughness and low surface energy. The nanoscale surface roughness was obtained through DE, whereas low surface energy was attained by treating DE with hexadecyltrimethoxysilane (HDTMS). The surface wettability and morphology were evaluated through WCA measurements and scanning electron microscopy (SEM) analysis, respectively. By using HDTMS to DE ratio of approximately 38% (w/w), superhydrophobic properties were achieved for treated DE with WCA around 160°. In the first approach, treated DE was incorporated into plastic substrates through melt mixing process to achieve the inbuilt hydrophobic property. Incorporation of treated DE into high-density polyethylene through melt mixing process resulted in hydrophobic plastic sheets possessing WCAs of around 99° with treated DE particle loading of 10%. The treated DE amount was not further increased due to the reduction of mechanical properties of the plastic sheet. The hydrophobicity did not reach the expected level. As revealed by SEM and SEM coupled with energy dispersive X-ray analysis, the DE particles had been destroyed and trapped within the plastic matrix during the melt mixing process. Compression molding technique was also employed to fabricate a thin layer of treated DE on the plastic substrates. Yet, it was observed that the adhesion between the DE layer and the plastic substrate was not satisfactory and the WCAs were drastically reduced after removing the loosely bound DE powder of the coating. By utilizing the solvent casting method and a subsequent lamination step, robust superhydrophobic coatings on poly(vinyl chloride), which can be considered as a polar plastic substrate, were successfully developed. The coating consisted of treated DE particles held together by an epoxy resin binder, ensuring both the cohesion of the coating and its robust adhesion to the substrate. The prepared coatings showed a remarkable level of superhydrophobicity, surpassing the threshold WCA of 150° and good mechanical properties.
Investigation of using diatomaceous earth variants as fillers in rubber composites: cure characteristics and tensile properties
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) De Costa, N. B. J.; Egodage, S. M.; Maddumaarachchi, M.
Diatomaceous earth (DE) generally made of fossilized diatom exoskeletons, is well-known for its high porosity and potential usage as a rubber filler alongside silica. This study characterizes various grades of DE such as amorphous, crystalline, crystalline brewery waste, and ground brewery waste to reduce the particle size, compared to silica. This research aims to identify their morphological properties and impact on the cure characteristics and tensile properties of natural rubber vulcanizates. First, rubber formulation was optimized to provide a baseline for the cure characteristic tests. The ground waste DE was thus prepared by ball-milling crystalline waste DE for 3 hours at 300 rpm in a laboratory scale ball mill. The fillers were then characterized extensively using established techniques such as Scanning Electron Microscopy (SEM), Dynamic Light Scattering (DLS), X-ray diffraction (XRD), X-ray fluorescence Spectroscopy (XRF), and Fourier-Transform Infrared Spectroscopy (FTIR). Rubber composites were formulated with 55 phr of each filler. As the next step, amorphous and crystalline waste DE was mixed with silica in proportions of 25%, 50%, and 75% of DE-based filler to silica by weight to prepare rubber composites. Cure characteristics were obtained using a Moving Die Rheometer (MDR) at 150 °C for 30 minutes, and ultimate tensile strength was measured with a Universal Testing Machine according to ASTM D412 standards (die cut-C) at a strain rate of 500 mm/min. The results revealed that ball milling was ineffective in reducing the particle size of crystalline waste DE at the given conditions. 100% Amorphous DE-filled composite showed inferior cure characteristics, with a low cure rate index and low cross-link density. Nevertheless, composites with 25% amorphous DE blended with silica demonstrated higher ultimate tensile strength compared to composites with 100% silica, explained by the positive synergistic effect from particle size and increased surface area of amorphous DE. However, loadings of more than 25% of amorphous DE to silica caused reduced tensile properties due to lower filler density. Waste DE-loaded composites showed reduced tensile properties due to both larger particle size and agglomeration. In conclusion, amorphous DE exhibited positive synergism with silica when used as a rubber filler, enhancing tensile properties due to higher cross-link density facilitated by smaller particles and increased filler-matrix interactions due to the nano-roughness of DE. Composites loaded with waste DE showed significantly reduced tensile properties due to pronounced agglomeration. The optimal loading of amorphous DE as a filler was determined to be 25% of DE with silica, providing a balance between improved tensile properties with higher reinforcement. This study emphasized the potential of using amorphous DE as a bio-based filler in rubber composites, highlighting the need for optimization of filler loading to mitigate agglomeration and optimize the material performance. These findings could contribute to innovating sustainable materials in polymer composites.