Rice Husk Ash/Silicone Rubber-Based Binary Blended Geopolymer Coating Composite: Fire Retardant, Moisture Absorption, Optimize Composition, and Microstructural Analysis

Abstract

Geopolymer coating using rice husk ash (RHA) as the aluminosilicate source has shown excellent fire retardant properties. However, incorporation of rice husk ash into the geopolymer matrix increased water absorption properties of the polymer composite. As such, silicone rubber (SiR) was introduced to improve the moisture absorption and fire retardant properties of the composite. Additionally, the less efficient one-factor-at-a-time (OFAT) approach was conventionally used in past studies on the RHA-based geopolymer composite. In understanding the optimum value and significant effect of factors on the fire retardant and moisture absorption properties of the binary blended geopolymer coating composite, the use of statistical analysis and regression coefficient model (mathematical model) was considered essential. The objectives of this study are to identify the significant effect of factors on moisture absorption and fire retardant properties, to determine the optimum composition, and to study the microstructure of the rice husk ash/silicone rubber (RHA/SiR)-based binary blended geopolymer coating composite. The RHA/AA and SiR/Ge ratios were chosen as factors, and the response surface methodology (RSM) was employed to design experiments and conduct analyses. Fire retardant and moisture absorption tests were conducted. A scanning electron microscope (SEM) was used to observe the microstructure of geopolymer samples. The RHA/alkaline activator (AA) and SiR/Ge ratios were shown to have a significant effect on the responses (temperature at equilibrium and moisture absorption). The high ratio of RHA/AA and SiR/Ge resulted in a lower temperature at equilibrium (TAE) below 200°C and at moisture absorption below 16%. The optimum formulation for the geopolymer coating composite can be achieved when the RHA/AA ratio, SiR/Ge ratio, and sodium hydroxide concentration are set at 0.85, 0.70, and 14 M, respectively. SEM micrographs of samples with good fire retardant properties showed that the char residue of the geopolymer composite coating, which is a layer of excess silicone rubber, is porous and continuous, thus providing a shielding effect for the layer of geopolymer underneath. The sample with good moisture absorption showed the formation of a thin outer layer of silicone rubber without any cracks. The unreacted SiR formed a thin layer beneath the geopolymer composite matrix providing a good moisture barrier.

Flame Retardant Coatings: Additives, Binders, and Fillers

“…Meanwhile, this carbonated fly ash exhibits up to 3 times higher penetration when compared with silicone rubber composites filled with other fillers, such as aluminum trihydroxide and magnesium hydroxide, which are commonly used fillers [ 299 ]. The carbonation process of fly ash also improves the mechanical properties of the fly ash–silicone rubber composite as well, contributing to an increase in flame retardant protection [ 300 , 301 ].…”

Reduction of Methylene Blue Using Silica Nanoparticles Obtained from Waste ZrC

“…[14][15][16][17][18][19] In recent years, rice husk and wheat husk as silica precursors with high silica content and cheap raw material costs (agricultural wastes) have been employed to manufacture SiO 2 . [1,3,20,21] Also, the silica prepared for use in the aforementioned applications must be of high purity. As a result, many methods for removing silica impurities have been reported.…”

Rice-Husk-Ash-Based Geopolymer Coating: Fire-Retardant, Optimize Composition, Microstructural, Thermal and Element Characteristics Analysis

“…Appropriate composition in making intumescent coating is crucial in producing the best performance for the intumescent system. Geopolymer has the potential as an intumescent coating [5][6][7][8].…”

“…Despite many publications on rice-husk-ash-based polymer composite reported in the literature in recent years [5,8,[24][25][26], most studies were carried out on the one-factor-a-time (OFAT) approach. The application of statistical analysis and regression coefficients (mathematical models) is required effectively identify the optimal composition of geopolymer coating with improved fire-retardant and thermal properties to increase efficiency.…”