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

Siti Hasnah Kamarudin,Intan Syafinaz Mohamed Amin Tawakkal,Tee Hui Yek,Nurul Ain Maidin,Mohd Hidayat Ab Rahman,Norkhairunnisa Mazlan,Mohd Salahuddin Mohd Basri,Rosnita A Talib

doi:10.3390/polym13060985

Siti Hasnah Kamarudin, Intan Syafinaz Mohamed Amin Tawakkal + Show 6 more

Open Access

https://doi.org/10.3390/polym13060985

Copy DOI

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.

Highlights

Rice is mostly produced in Asia and Asians consume more than 80% of the world’s rice.The volume of rice production is estimated to be 156 million tons per year, generating a massive amount of solid waste [1]
A low temperature at equilibrium (TAE) indicates that the sample possesses good fire retardant properties and vice versa
A higher V1 and V2 resulted in a lower TAE below 200 ◦ C and lower moisture absorption below 16%

Summary

Introduction

The volume of rice production is estimated to be 156 million tons per year, generating a massive amount of solid waste [1]. Rice husk ash (RHA) is obtained by burning the rice husks at 600◦ C for 6 h and grinding it using a jet mill to reduce the particle size [2]. The rice husk comprises 50% of cellulose, 25–30% of lignin, 15–20% of silicate, and 10–15% moisture content [3]. It is simultaneously an environmentally friendly and low cost source compared to conventional materials for improving mechanical, thermal, and physicochemical properties of polymer composites [4]

Objectives

Methods

Results

Conclusion