Compounding Fiber Reinforced Polymers: Process Development, Implementation, and Observations While Investigating the Impact of Surface Treatment and Screw Design on Fiber Unbundling, Breakage, and Distribution

Abstract

This article examines how screw design and fiber type, diameter, and compatibility impact specific mechanical energy (SME) development in co-rotating twin-screw extruder compounding of glass and carbon-fiber reinforced nylon and HDPE. A data driven experimental approach to correlate process parameters and fundamental physics was developed, then run on the twin-screw extruder at industrial compounding conditions. Operating parameter comparisons include two twin-screw extruder screw configurations, specifically, one based on ZME (Zahnmischelement) tooth-based geometry and the other on kneading blocks (KB). Additional parameter comparisons are two base polymers (polar, non-polar), multiple high aspect ratio glass-fiber grades and carbon-fiber, as well as rpm, rate, and percent fiber. SME comparisons between ZME and KB based mixing sections, and among the various fiber types, diameters, and compatibilization agents are discussed and analyzed in detail. For example, processing 30% 10-μm nylon sized glass-filled nylon consumed almost 10% more downstream mixing SME than processing 13-μm nylon sized fiber. The wide range of compounded formulations produced by these runs will be used to verify a preliminary first principles fiber unbundling model based on Hamaker analysis. As this is a process study, analysis of fiber dispersion, attrition, as well as model verification review will be presented in subsequent publications.