Rheology for Wood Plastic Composite Extrusion Part 2: Process Simulation and Experimental Verification

Rheological data of wood plastic composites (WPCs) are not readily present in many of the common scientific databases. For this reason, designing the processing of WPCs, e.g., extrusion, is difficult or even impossible, and it is often necessary to conduct research on your own to obtain the proper data. In the first part of the paper, studies of WPCs' rheology have been performed in laboratory and production conditions. Tests in laboratory conditions have been conducted based on High-Pressure Capillary Rheometry (HPCR), using the Melt Flow Index (MFI). Tests in production conditions (on-line) have been performed by measuring the extrusion die pressure and extrusion throughput. The MFI's viscosity and on-line viscosity results have been assessed against those of HPCR. In the second part of the paper, the viscosity data and models have been used for extrusion process simulations. Experimental studies of the process have been performed, and the experimental results have been used for evaluating the models applied. It was found that the two-point MFI method of determining viscosity and the on-line tests may be a reasonable alternative in the absence of HPCR data. The MFI method using the power-law model is fast and easy to apply and allows for analytical solutions to many processing problems. A significant advantage of on-line tests is that they are performed under real flow conditions of the tested material rather than laboratory conditions that do not take into account the material processing history.