Wolfgang Roland

When two compatible polymer melts are brought into contact, a diffuse interphase is formed that governs the adhesion between them. The degree of interdiffusion is defined mainly by the processing conditions and the physico‐chemical properties of the materials. Despite the great industrial relevance of co‐extrusion in manufacturing multilayer structures, little research has dealt with interdiffusion under these processing conditions, where polymer‐polymer interfaces are subject to shear load. In this work, procedures for investigating interdiffusion both under static and real co‐extrusion flow conditions were developed. Using various grades of poly(methyl methacrylate) and styrene‐ co ‐acrylonitrile copolymer, we studied both theoretically and experimentally the effects of interfacial contact time, temperature, material compatibility, and interfacial shear stress on interdiffusion. Spectroscopic analysis of the interfaces using confocal Raman microscopy showed that the general relationships between interdiffusion, time (Fick's law) and temperature (Arrhenius relationship) are identical under both static and co‐extrusion conditions. However, the interdiffusion rate is significantly higher under shear influence. Since the prediction of the interdiffusion process supports material selection and process design in multilayer manufacturing, a simple analytical model was developed to quantify the effects of aforementioned material properties and processing conditions on the apparent mutual interdiffusion coefficient.

There are many industrial examples of low Reynolds number non‐Newtonian flows through rectangular ducts in polymer processing. They occur in all types of manufacturing processes in which raw polymeric materials are converted into products, ranging from screw extrusion to shaping operations in dies and molds. In addition, they are found in numerous rheological measurement systems. The literature provides various mathematical formulations for non‐Newtonian flows through rectangular ducts, but—if not simplified further—their solution usually requires use of numerical techniques. Removing the need for these time‐consuming techniques, we present novel analytical correction factors for the drag and pressure flows of power‐law fluids in rectangular flow channels. We approximated numerical results for a fully developed flow under isothermal conditions using symbolic regression based on genetic programming. The correction factors can be applied to the analytical theory that describes the flow of power‐law fluids between parallel plates to include effects of the side walls in the prediction of flow rate and viscous dissipation.

Intermeshing co‐rotating twin‐screw extruders are very versatile because their screw configurations can be tailored both to the application and to the properties of the materials used. Finding the best screw configuration is one of the main purposes of twin‐screw extrusion modeling, and requires models that accurately predict conveying and power consumption. The better the process can be predicted, the better the requirements of the final product can be met. We present novel prediction models of the conveying and power‐consumption behaviors of intermeshing co‐rotating twin‐screw extruder kneading blocks for Newtonian fluids. These are based on numerical simulations and therefore consider the complex three dimensional (3D) geometry of this element type without the need for common simplifications. Our models are thus capable of including all leakage flows and gap influences, which are usually ignored, for example, by the flat‐plate model. Since our models are derived by symbolic regression based on genetic programming, they consist of algebraic functions and are low‐threshold. They can be used to calculate various process parameters for individual kneading blocks or entire screw configurations, as illustrated by a use case.

In the co‐extrusion of plastics, pressure‐throughput behavior, layer distribution, and residence time are crucial parameters, modeling of which contributes to manufacturing high‐quality products at optimized process efficiency and significantly shortens development times for die systems. In previous work, we have presented symbolic regression models to predicting the (i) pressure‐throughput behavior, (ii) position of the interface, (iii) interfacial shear stress, (iv) ratio of volume flow rates, and (v) interfacial flow velocity for isothermal two‐layer co‐extrusion flows through rectangular ducts. These regression models are mathematically simple and capable of capturing the shear‐thinning nature of polymer melts without the need for numerical methods. Here, we present an experimental study validating the proposed models against co‐extrusion process data and comparing them to existing theories. To this end, a two‐layer co‐extrusion demonstration die instrumented with an optical coherence tomography sensor for detecting the interfacial position was used. To accurately set up and evaluate the die flows, the overall co‐extrusion process was represented by means of a digital process twin. Industrially relevant combinations of materials were tested under a wide range of processing conditions. Comparisons of pressure losses and interfacial positions to the predictions showed excellent agreement and the results outperformed the concept of representative viscosity.