State of cure in silicone/clay nanocomposite coatings: The puzzle and the solution

Abstract

Properties of a rubber/clay nanocomposite coating depend on rubber network formed in the presence of clay platelets. Not surprisingly, however, a few is known about the state of cure in silicone nanocomposites. In this work, nanoclay flakes are modified with trifunctional silane, fully characterized, and then added to silicone coatings. The resulting nanocomposites are underwent nonisothermal differential scanning calorimetry (DSC) varying heating regime. Fourier-transform infrared spectrophotometry, X-ray diffractometry, and thermogravimetric analysis (TGA) techniques were employed to quantify grafting reaction efficiency and thermal stability of modified nanoclay. Cure characteristics of nanocomposites (exothermal peak temperature as well as cure enthalpy) containing pristine and silane-modified nanoclays were discussed in terms of clay content under different DSC heating rates. The mysterious state of cure in silicone/clay nanocomposite coatings was unraveled and then explained by solving curing puzzle for silicone/clay systems through comparison between newly defined T* and ΔH* dimensionless indexes dedicated to the crosslinked nanocomposite networks with respect to blank silicone coating. The progressive/diffusional crosslinking and complete/partial/imperfect curing were respectively evaluated by analyzing fluctuations in T* and ΔH* values, where the effects of clay content and surface chemistry were satisfactorily quantified.