Flow Visualization Investigations of the Addition of Carbon Black and Oil to Elastomers in an Internal Mixer

Abstract

Abstract Internal mixing is one of the most important of processing operations, being used to incorporate fillers, oils, and other compounding ingredients into elastomers and plastics. The development of internal mixers has a long history largely described in the patent literature. Published experimental studies of flow in an internal mixer have been few, and primarily involved measurements of energy consumption, temperature histories, and characteristics of dumped mixes. It is only recently that efforts have been made to directly observe the motions of elastomers in an internal mixer. Freakley and Wan Idris and Asai et al. have made flow visualization studies of the motions of silicone rubber and aqueous carboxymethyl cellulose solutions at room temperature. Freakley and his coworkers and Toki et al. have followed motions of rubber in an internal mixer using mounted pressure transducers. More recently, the present authors have developed experimental techniques to visualize the flow of commercial elastomers and plastics at processing temperatures. The first study visualized flow in the plane perpendicular to the rotor axes and contrasted the behavior of various synthetic rubbers (polybutadiene, butadiene-styrene copolymer), natural rubber, and thermoplastics. In a later study, Min has made observations of flow in the plane parallel to the rotor axes for various rotor designs. The techniques developed in the first two papers were subsequently applied by Min to investigate the blending of an elastomer and a thermoplastic. It is the purpose of the present paper to present a detailed investigation of the addition of the primary compounding ingredients of carbon black and oil to an internal mixer. Much has been theorized and written about the incorporation of carbon black and oil. However, this has largely been conjecture based upon observations of torques, power consumption, temperature profiles, and the condition of dumped compounds. We present in this paper a unique flow visualization investigation of the flow phenomena and material distribution resulting from the addition of these ingredients to elastomers in an internal mixer. This paper continues our investigations of flow visualization during rubber processing.