Influence of material modification and fillers on the dimensional stability and warpage of polypropylene in screw-extrusion-based large area additive manufacturing

Abstract

In this work, the influence of a modification and fillers on the dimensional stability and warpage of semi-crystalline polypropylene compounds in screw-based Large Area Additive Manufacturing is investigated by material characterization and experimental testing. Polypropylene is modified by blending an amorphous polyolefin-copolymer as well as the addition of three different fillers talc, glass fibers, and hollow glass beads, resulting in eight investigated compounds. A material characterization using Differential Scanning Calorimetry, Thermogravimetric Analysis, thermal conductivity measurements, and pvT-measurements is carried out. Experimental investigations regarding dimensional stability and warpage deformation during processing are performed. By increasing the crystallization temperature and thermal conductivity from 112.3°C and 0.208 W/(m°C) to 127°C and 0.232 W/(m°C) through the use of a modification and talc, a better dimensional stability during processing is reached. Furthermore, both the modification of the base material and the introduction of talc or glass fibers lead to a significant reduction in the decrease in specific volume during cooling, as determined by pvT-measurements, thus reducing warpage. The experimentally determined warpage deformation could be reduced by 69% when using 10 wt. % talc-filler and by 78% when using 10 wt. % glass fibers, compared to the unmodified and unfilled base polypropylene.