High intensity compounding of mica‐filled thermoplastics

Abstract High‐speed turbine mixers have been adapted for compounding filled thermoplastics by the partial flux method. The extreme shearing forces exerted by the mixing impellors simultaneously mixes and delaminates mica fillers to form finely dispersed compounds in a granular, partially fused state which can be directly injection molded without pelletizing. In practice, one turbine mixing unit can be employed for compounding all types of resins and fillers. The partial flux method permits compounding to be accomplished at peak sensor temperatures that are considerably below the resin softening or melting transitions, frequently 50°C less than normal compounding temperatures. The short residence times and reduced energy requirements possible with partial fluxing results in substantial cost reduction without compromising quality or performance. Examples are provided for polypropylene, nylon 66, poly(butene terephthalate), poly(ethylene terephthalate) and poly(phenylene oxide) alloys. Impact modifiers derived from carboxylated polyolefin waxes may be dispersed by the intense shearing action to form highly subdivided submicron particles, which promote crazing and shear deformation during fracture testing, thereby contributing to increased composited toughness with minor sacrifice in modulus and strength. The mechanical properties of micafilled thermoplastics have also been compared with those of short glass fiber composites. In certain applications requiring stiffness and dimensional stability at elevated temperatures, mica composites prepared by intensive mixing in a turbine mixer may be economically substituted for glass fiber counterparts.