Investigating 3D Printability of Polypropylene using Fused Deposition Modelling

Abstract

Polypropylene (PP) is a widely used thermoplastic due to its excellent chemical resistance, low density, and cost-effectiveness. However, its application in the additive manufacturing (AM) industry presents many challenges. This study focuses on three key challenges associated with Fused Deposition Modeling (FDM) of PP, including geometric warpage in printed parts, void formation and poor interlayer adhesion which compromises the mechanical strength of 3DP parts. The subject of this study comprised of five grades of neat PP, each with varying MFR ranging from 0.3g/10min up to 70g/10min. The supplied pellets from each grade was extruded into filaments and 3DP into tensile bars. Injection molded tensile bars and compression molded discs were also prepared. The rheological properties of PP grades were characterized through a frequency sweep test. All PP grades exhibited a shear thinning behavior with varying levels, PP1 with the highest shear thinning behavior and PP5 the lowest. The extrusion and printing nozzle temperature were then selected based on the results of the frequency sweep test.

A series of experiments were conducted to evaluate the effect of varying MFR and nozzle temperature on mechanical properties, dimensional accuracy, and interlayer adhesion and thermal degradation of printed parts. Characterization techniques include tensile testing, flexural testing, Charpy impact testing, FTIR, stereo microscope imaging of voids, and warpage measurement through Quick Scope.

The results indicate that with the increase in MFR, the voids in printed parts reduced by 195% from PP2 to PP5 and the interlayer bonding was significantly improved. In terms of structure, PP2 and PP3 printed samples exhibited the least warpage and best structural integrity. PP4 printed parts showed the highest retention in Young’s Modulus, Yield Stress, and Elongation at Break.

Date of Award	8 May 2025
Original language	American English
Supervisor	Rashid Abu Al Rub (Supervisor)