Fast pyrolysis of silicones at low temperatures catalyzed by anatase titanium dioxide

Abstract

Silicones are widely used in medical and engineering field for their remarkable properties. The resulting waste is an increasing economic and environmental problem. Pyrolysis can be a feasible way to recycle silicone waste. Since its high thermal stability, looking for an efficient catalyst becomes necessary. In this work, anatase titanium dioxide was found to be very efficient in catalyzing the pyrolysis of silicones even at extremely low temperatures. The pyrolysis rate, pyrolysis products, the catalytic mechanism of silicones and the reusability of catalyst were investigated in detail via thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), wide-angle X-ray diffractometer (wide angle XRD), thermogravimetric analysis-Fourier transform infrared spectroscopy (TG-FTIR), and pyrolysis-gas chromatography/mass spectroscopy (Py-GC/MS). During pyrolysis, polysiloxane chain undergoes catalyzed unzipping depolymerization. The catalytic mechanism is believed to be the nucleophilic attack of silicon in the main chain by the hydroxyl group on anatase titanium dioxide. This is the first report on pyrolysis of silicones catalyzed by anatase titanium dioxide. The blending of anatase titanium dioxide with polysiloxane may become a promising technology for inexpensive, high efficient and sustainable feature in feedstock recycling of silicones. In addition, this new discovery also offers guidance that fillers with such high active hydroxyl groups should be avoided in polysixoane composites.