Environmentally-friendly physico-chemical rapid ultrasonic recycling of fumed silica-filled poly(dimethyl siloxane) vulcanizate

Abstract

Fumed silica-filled PDMS, where quite a strong interaction exists between the filler and matrix via hydrogen bonding, was recycled by means of an extruder with high power ultrasound attachment. It was found that the reinforcing filler plays an important role in the devulcanization process. Compared to the precipitated silica-filled PDMS, higher power is consumed during the devulcanization process of fumed silica-filled PDMS due to a strong interaction between the fumed silica particles and PDMS chains. The decrease in crosslink density after the devulcanization process shows that the process is quite dependent on the concentration of fumed silica. Throughout a simulation of scission of chemical bonds during the process, the influence of the concentration of filler on the devulcanization was investigated. The scission of main chains (Si–O) and crosslinks (Si–C and C–C) concurrently occurs during the process. Crosslinks are predominantly severed in the absence of fumed silica while the main chain rupture tends to increase with the filler concentration. The main chain scission leads to the deactivation of filler which reduces gel fraction and crosslink density of the revulcanizates. The mechanical properties of the revulcanizate show that the fumed silica significantly affects the final properties of the recycled PDMS.