Optimized Dimensional Stability of Polypropylene Composites for Screw‐Extrusion Additive Manufacturing via Tuning Crystallinity and Melt Strength

The high crystallinity and fast crystallization of polypropylene (PP) severely restrict its additive manufacturing (AM) applications. To tackle this issue, this research created polypropylene/glass fiber composite for screw‐extrusion additive manufacturing (SEAM) by tuning PP's crystallization and rheological properties. To tune the crystallinity and melt strength of PP, low‐viscosity random copolymer PP (CL‐PP1) was adopted as matrix, blended with another high‐viscosity random copolymer PP (CL‐PP2) with low crystallinity (only 9.68%), with the incorporation of calcium carbonate masterbatch (Ca) and glass fiber (GF), which disrupted PP molecular chain regularity, synergistically reducing PP crystallinity from 24.79% to 9.47%, which drastically reduced print warpage ratio (WR, from 127.3% to 1.9%) and increased first layer adhesion (peel force: from 0 to 205 N/m). Rheological analyses showed CL‐PP2 enhanced the composites' complex viscosity and melt strength, enabling 60° overhang printing with negligible distortion at a CL‐PP1/CL‐PP2 blend ratio of 50/50. Mechanical property tests indicated the 50/50 composite retained a tensile strength of 16.2 MPa while exhibiting 312.4% elongation at break and 20.4 kJ/m 2 notched impact strength, attributed to great CL‐PP1/CL‐PP2 interfacial compatibility and plastic deformation of amorphous regions. This printability‐mechanical property balance provides a new method for large‐scale SEAM application of GF‐PP composites.