Potential of mucilage-based hydrogel for passive cooling technology: Mucilage extraction techniques and elucidation of thermal, mechanical and physiochemical properties of mucilage-based hydrogel

Current air-conditioning and refrigeration systems utilize active cooling technology, which consumes a lot of energy from fossil fuels, thereby increasing global warming and depletion of the ozone layer. Passive cooling is considered an alternative to active cooling because it is effective and less expensive and does not require the use of electricity, so cooling can be achieved in locations where there is no electricity. Hydrogels are flexible and soft 3-dimensional networks with high water content and evaporative and radiative cooling properties that make them suitable for use in passive cooling technology. Natural hydrogels are considered alternatives to synthetic hydrogels because they are biodegradable, biocompatible, sensitive to external environments and mostly sourced from plant-based sources. There are limited studies on the application of mucilage-based hydrogel for passive cooling, despite its excellent thermal, mechanical and physiochemical properties. Therefore, this study evaluates the properties of mucilage-based hydrogel as a plausible alternative to synthetic hydrogel for passive cooling. The possibility of using mucilage-based hydrogel in passive cooling technology depends on the mucilage biomass feedstock, mucilage extraction techniques, polymerization techniques and additives introduced into the hydrogel matrix. Different mucilage extraction techniques; mucilage percentage yield; the effects of crosslinkers, polymers and nanoparticle additives on the properties of mucilage-based hydrogel; and the potential of using mucilage-based hydrogel for passive cooling technology are examined in this review.