Laboratory internal mixers – also known as torque rheometers – are widely used in academic and industrial laboratories to prepare small amounts of polymer blends and compounds, to test new polymers and additives, etc. A simple engineering model relating the two experimentally accessible dependent variables, torque and temperature, to time and processing conditions, may help material engineers with limited background (and interest) in processing, to understand what is happening inside the processing chamber. Such model, an extension of existing ones but including heat transfer considerations, is developed and the required empirical geometric and and technical parameters are discussed. As example of application, a study of degradation and chain extension during processing of additivated biodegradable thermoplastic copolyester poly(butylene adipate terephthalate) (PBAT) is discussed. Change (and rate of change) of molar mass is discussed in terms of additive concentration and processing temperature.
