A rubber composition manufacturing method comprising an operation in which an intermeshing internal kneader is used to knead at least rubber, silica, and silane coupling agent, wherein the operation comprises a first step in which kneading which is accompanied by increase in kneading temperature is carried out during an initial phase of the operation; kneading is carried out during the first step while a ram is maintained in a state in which it is at a first position which is higher than a lowermost position within a range of movement of which the ram is capable; and during the first step, an effective volume when the ram is at the first position is 105% to 120% relative to a value of 100% for an effective volume when the ram is at the lowermost position.

A mixer (1) for mixing a mixing material (13) in polymer processing comprises a mixing chamber (2) and more than two rotors (6a-6d) arranged in the mixing chamber (2). In particular, the rotors (6a-6d) can be configured to interlock.

A composite article can comprise a composite body including an organic polymer and ceramic particles comprising hexagonal boron nitride (hBN) particles distributed throughout the organic polymer, wherein an amount of the hBN particles ranges from 40 vol % to 90 vol % based on a total volume of the body; and the body comprises an in plane thermal conductivity of at least 15 W/mK. The hBN particles within the composite body can have a March-Dollase Orientation parameter of at least 50%.

A method for producing a polytetrafluoroethylene composition including mixing a polytetrafluoroethylene resin and a filler using an airflow mixer to provide a polytetrafluoroethylene composition containing the polytetrafluoroethylene resin and the filler. The airflow mixer is a pulse-type airflow mixer or an airflow stirrer. Also disclosed is a polytetrafluoroethylene composition produced by the production method, a polytetrafluoroethylene composition having specific physical properties, as well as a molded article, electrically conductive tube, thermally conductive film, and substrate for CCL each obtained from the polytetrafluoroethylene composition.