Effect of humidity on moisture absorption of sodium percarbonate and its thermal hazard

Abstract

Sodium percarbonate (SPC), also known as sodium carbonate–hydrogen peroxide, is a bleaching. The thermal decomposition of SPC produces oxygen, which slightly increases its bleaching ability. Nevertheless, the heat and oxygen produced pose a fire risk, potentially leading to spontaneous combustion when the SPC is stored alongside flammable materials. Previous studies have noted that water vapour affects SPC decomposition; However, the moisture absorption of SPC and the particular details of the effect have not been reported. In this study, the moisture absorption test revealed the deliquescence of SPC above 75% relative humidity (RH) and its hygroscopicity above 60% RH. Deliquescence occurred at 30 °C and 84% RH for 192 h, and the absorbed water caused its decomposition. Adiabatic calorimetry revealed only 30 wt% water, which was similar to that absorbed by SPC stored for 24 h at 30 °C and 97% RH, decreasing the thermal stability of SPC. These results indicate that the humidity surrounding the SPC is an extremely important parameter for estimating thermal hazards during the storage and manufacturing of SPC.