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A continuous extrusion devulcanization process has been developed by using supercritical CO2. Experiments have been carried out on an industrial scale twin screw extruder to study the effects of processing conditions on the properties of devulcanized rubber. Using a fractional factorial design in three levels, the effects of process temperature, screw speed, and feed rate on the sol fraction, degree of devulcanization, Mooney viscosity, and tensile properties of devulcanized rubber have been investigated. The significance of the effects of the processing conditions decreases in the following order: flow rate, screw speed, and process temperature. Similar trends are noted for different responses with the exception of tensile properties. The observed relationship between the sol fraction and the degree of crosslinking in the rubber samples before and after devulcanization points to a highly selective disruption of the sulfur crosslinks in the rubber network during devulcanization rather than a random network scission. Mooney viscosity has been found to be in excellent agreement with the network structure properties, sol fraction, and degree of devulcanization.

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A novel type of nanosilica-supported ultraviolet absorber (SiO 2 -N-0) was successfully prepared by chemically grafting 2,4-dihydroxybenzophenone (UV-0) onto the surface of nanosilica (SiO 2 ) with the aid of a coupling agent via a solgel method, which was confirmed by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. SiO 2 -N-0 was then incorporated into poly(butylene adipate-co-terephthalate) (PBAT) to fabricate biodegradable composite film with a casting method. As expected, SiO 2 -N-0 was homogeneously dispersed in PBAT matrix, leading to higher mechanical strength and lower water vapor transmission of PBAT/SiO 2 -N-0 film than those of PBAT/SiO 2 /UV-0 film. More importantly, because of its low migration and volatility, SiO 2 -N-0 endowed PBAT film with excellent aging resistance under ultraviolet radiation than did the corresponding low molecular ultraviolet absorber UV-0. Taken together, these results suggest that thus prepared PBAT/SiO 2 -N-0 composite film may find many applications, especially as biodegradable agricultural mulch film.

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