Applications of power ultrasound to compatibilization of polypropylene/rubber blends and devulcanization of tire and butadiene rubbers

This is a study of the continuous ultrasonic process for the compatibilization of polypropylene (PP)/ground tire rubber (GRT) and PP/natural rubber (NR) blends using a newly developed ultrasonic reactor based on plastic extruder with a slit die attachment and devulcanization of GRT and unfilled butadiene rubber (BR) using barrel and grooved barrel reactors.; Mechanical properties, rheology and morphology of the ultrasonically treated plastic/rubber blends were investigated. Under optimal conditions of ultrasonic treatment, the mechanical properties of the blends were improved in comparison with the untreated blends. In PP/NR blends, AFM studies revealed the development of interfacial layers, interfacial roughening and improved interfacial adhesion between PP and NR phases due to the formation of in-situ copolymer at the interfaces leading to the improved properties of PP/NR blends.; A unique correlation between gel fraction and crosslink density for devulcanized GRT and BR was obtained. A comparison of the results for devulcanized GRT obtained in the coaxial reactor, developed earlier, with the present reactors indicated that additional shearing in the devulcanization zone due to screw rotation had a positive influence on improving the efficiency of devulcanization. Also, the physical properties of revulcanized GRT and the output using the present reactors were higher than those of the coaxial reactor.; Ultrasonic devulcanization of BR vulcanizates was found to occur within a narrow window of processing conditions. The mechanical properties of vulcanizates prepared from devulcanized BR were inferior to those of the virgin vulcanizates. However, vulcanizates of the blends of virgin and devulcanized BR showed a considerable enhancement of the mechanical properties. Ultrasonic treatment of BR gum was also performed indicating competing reactions of gel formation, branching, and degradation leading to changes in physical properties. Molecular characterizations of devulcanized BR and treated gum performed using NMR spectroscopy and gel permeation chromatography indicated broadening of molecular weight distribution during devulcanization of BR vulcanizates and an isomerization reaction during ultrasonic treatment of BR gum. The application of Dobson-Gordon theory to devulcanization process indicated that the rate of crosslink rupture in BR rubber was higher than that of main chain.