Sensing technologies for process monitoring in polymer extrusion: A comprehensive review on past, present and future aspects

The global plastics production has shown a rapid growth from 1.5 to 367 million metric tonnes from year 1950 to 2020, where it has been predicted that this growth rate might increase further within the next few decades. In future, there will a be huge demand for polymeric materials due to their superior properties such as high specific strength, ease of shaping/forming into intricate shapes, high resistance to environmental factors, etc. Here, polymer extrusion serves as one of the fundamental approaches of processing plastic/polymeric materials. Meanwhile, in the majority of polymer processes, materials are usually being processed inside closed and pressurized chambers and hence real-time process monitoring is vital for achieving high-quality products. In this study, a comprehensive review is made to explore the state-of-the-art of the major process monitoring techniques (melt temperature, melt pressure, mass throughput, screw torque melt viscosity) in polymer extrusion. Moreover, the previous works reported on process monitoring are discussed. Eventually, a critical discussion is made on the current challenges/limitations and future trends in terms of achieving better quality melt in polymer extrusion for making good quality products with a lower unit cost. The importance of the selection of appropriate monitoring techniques is also emphasized.