Abstract
Abstract The term “structuring” used in silicone rubber describes a phenomenon of the increase in the viscosity of polydimethylsiloxane filled with silica during storage, which limits the applications of the room temperature vulcanized (RTV) silicone rubber in the field of aerospace and military. In this pursuit, the present study was envisaged to solve the problem of structuring of the RTV. A solvent-free method was used to hydrophobize the hydrophilic silica with hexamethyldisilazane. An RTV composition prepared using eight parts of hydrophobic silica with 2.91% C content exhibited a viscosity of less than 100 Pa s, with no significant change in 21 days. In contrast, eight parts of the hydrophilic fumed silica showed an initial viscosity of RTV to be greater than 2,000 Pa s. Silica samples with different adsorbed water content were used to prepare the RTV compositions. It was found that the viscosity of the RTV prepared using the sufficiently dried silica was 5.6 times lower than that of the wet silica. The “dissolution” model of the silica–silica hydrogen bonds in water was proposed. Furthermore, the change in the viscosity of the RTV compositions at different temperatures in the range of −15°C to 30°C was studied. The viscosity of RTV stored at –15°C for 34 days did not change significantly, whereas that stored at room temperature increased from 100 to 1,710 Pa s within 21 days.
Highlights
Silicone rubber is a synthetic polymer that combines the advantages of both inorganic and organic materials
We focused on the structuring behavior of HPDMS-fumed silica system and studied the influencing factors with the corresponding underlying mechanisms
We found that the water absorption content of the fumed silica exhibited a significant role in the rate of structuring, which was detrimental to the material
Summary
Silicone rubber is a synthetic polymer that combines the advantages of both inorganic and organic materials. It possesses excellent heat, chemical, and ultraviolet radiation resistance and exhibits a second-lowest surface tension after the fluorine-containing materials. Silicone rubber can withstand a wide range of temperatures from −50°C to 200°C. All these special properties lead to its diverse application in fields such as aviation, aerospace, medical, construction, and electronics. The main polymer component of silicone rubber is polydiorganosiloxane, whose backbone consists of repeated R2SiO units. The instance of RTV products includes mold making RTV, adhesives, coatings, sealants, electronic thermal conductive adhesives, etc
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