Continuous mixing and compounding of polymer/filler and polymer/polymer mixtures with the aid of ultrasound

High power ultrasound is applied to break down silica agglomerates in EPDM/silica mixtures and to compatibilize plastic/rubber and rubber/rubber blends during extrusion process. Ultrasonically treated EPDM/silica mixtures without silane treatment of silica indicated significantly reduced sizes of silica agglomerates in comparison with those obtained by an internal mixer and lower than the EPDM/silica mixtures treated by the silane. The viscosity of the ultrasonically treated mixtures was found to be higher than that of the silane treated mixtures, while the extrudate swells of both mixtures were close to each other. Ultrasonically treated plastic/rubber and rubber/rubber blends indicated in-situ copolymer formation and compatibilization in the melt state leading to significant enhancement of the mechanical properties of the blends. An idea is put forward about the possibility of in-situ copolymer formation at the interfaces and their vicinities in the ultrasonically treated blends during extrusion. Data obtained by a solvent extraction indicating reduction in the amount of the extractable component, gel permeation chromatography indicating formation of the high molecular weight tail, atomic force microscopy indicating smooth interfacial region and scanning electron microscopy indicating stabilization of the phase morphology in the melt state of the ultrasonically treated blends point towards the occurrence of in-situ copolymer formation. The discovery creates a new field of the study of ultrasonic-assisted mixing of rubber with filler and compatibilization of immiscible polymer blends during extrusion.