Melt-Based Additive Manufacturing of Polyolefins Using Material Extrusion and Powder Bed Fusion

Polyolefin-based thermoplastics such as polyethylene and polypropylene constitute a major fraction of the polymers employed in commodity applications due to their ease of processability, durability, and economic viability. Additive manufacturing (AM) of polyolefins offers both a viable path toward functional prototyping of design concepts and direct manufacturing of end-use parts. Melt-based AM of polyolefins is more challenging than other semicrystalline polymers (polyamides) due to the relatively high levels of volumetric shrinkage encountered during crystallization of such polymers that lead to significant issues related to warpage and interlayer adhesion. The focus of this review is to evaluate the latest state-of-the-art for processing polyolefins by powder bed fusion (PBF) and material extrusion (MatEx) AM modalities. Recent progress in processing neat, filled, and blends of polyolefins using PBF and MatEx are discussed to highlight the importance of the rheological and morphological characteristics of the polymer melt on the printed parts performance. The existing challenges to AM of polyolefins are emphasized and strategies to address the limitations are recommended through a better understanding of the associated process-structure-property relationships. A holistic approach spanning synthetic modifications for feedstock development, improved system design, and physics-guided process parameter selection is required to broadly adopt melt-based AM of polyolefins.