Process Influences on Plastificate and Fiber Microstructure Formation: An LFT-D Compression Molding Parameter Study

Direct compounding of long fiber thermoplastic (LFT-D) materials in compression molding are two complex processes in series linked by the plastificate. Continuous compounding and sequential compression create a time-dependent property progression along the extrusion direction of the plastificate. Under variation of secondary parameters, extruder die temperature, and die height of the LFT-D line, samples of plastificates, flow fronts and plates are manufactured and characterized. The plastificate density progression along the extrusion direction is primarily influenced by the temperature of the die. Lofting of the plastificate is higher at high temperatures while the density difference along the extrusion direction is lower. This density difference is known to influence fiber orientations and mechanical properties. The flow front of the material filling the mold is skewed because of the density difference. We show that the skewness is mainly influenced by the die height and is lower at high die heights. The fiber content distribution in the plate is discussed and found to be influenced by the length of the plastificate which is in turn determined by the secondary parameters. These secondary parameters of the LFT-D line can play a role in process optimization once the primary parameters are selected. This work provides clues and observations of principles for such optimizations.