Microencapsulation of phase change material with silica from sodium silicate by spray drying process

Abstract

Phase change materials (PCMs) are substance that absorb, store, and release heat when they change state. In order to protect the PCMs from surrounding, to maintain the amount of them and their ability and to avoid the leakage of melted PCMs, the PCMs were encapsulated. Silica has many desirable properties for using as a shell material to encapsulate PCMs such as chemical inertness, high mechanical strength. Efforts have been devoted to reduce the cost of encapsulation PCMs with silica by using low cost sodium silicate as a silica source to replace the tetraethyl orthosilicate (TEOS). The encapsulated PCMs with silica as a supporting material was successfully prepared in O/W emulsion. The encapsulation efficiency and stability of the capsule depends on the emulsion preparation. In this research, the O/W emulsion for preparing the microencapsulation of PCMs with silica from sodium silicate by spray drying was studied. The microcapsules were prepared in an O/W emulsion with Tween 20 as emulsifier. The oil phase was n-Octadecane as the model of PCM. The water phase is the silica sol-gel solution which was formed via sol-gel reaction of sodium silicate solution with hydrochloric acid. Finally, the microcapsules were obtained by spray drying of an emulsion. The optimum condition for preparing microcapsule as following: the homogenizing speed 18,000 rpm homogenizing time 3 minutes phase change material 50 wt% of total solid and mole ratio of surfactant and phase change material 0.1:1. The spray dried microcapsules were smooth and nonporous spherical particle containing PCMs droplets which were embedded in the wall of the silica particles. Encapsulation efficiency and retention of phase change material in microcapsule were 7.8% and 19%, respectively. The average latent heat of microencapsulated n-Octadecane was 14.85 J/g.