Rapid, efficient and controllable photo-assisted polysulfide sealing over MnO2

Abstract

MnO₂ is widely utilized as a vulcanizing agent for polysulfide (PS) sealing; however, it is difficult to flexibly adjust the vulcanizing process while keeping costs low. Herein, we successfully prepared α-MnO₂, γ-MnO₂ and δ-MnO₂, as characterized by X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy mapping and X-ray photoelectron spectroscopy, and found for the first time that the photogenerated carriers on MnO₂ can trigger the free radical attack of –SH under visible light, leading to rapid, efficient and controllable PS sealing. Furthermore, the effect of different treatment conditions, crystalline form, and light power density on the curing rate was investigated. δ-MnO₂ showed better PS sealing performance under irradiation of 1140 mW cm⁻² than under natural light and dark conditions, and δ-MnO₂ showed a higher curing rate than those of α-MnO₂ and γ-MnO₂. Moreover, the curing rate increased with an increase in the light power density. The induction time and curing rate can be flexibly controlled by adjusting the optical power density and turning the light on/off. Furthermore, the effect of illumination uniformity on rubber surface shape was investigated, and a sample with a flat surface was obtained under uniform illumination. In addition, two pathways of photocatalytic initiation and the traditional PS oxidation radical mechanism for polysulfide sealing over δ-MnO₂via photo-assistance were proposed. This study details a novel, facile and general strategy to achieve rapid, efficient and controllable PS sealing in industrial settings.