Importance of Polymer Rheology on Material Extrusion Additive Manufacturing: Correlating Process Physics to Print Properties

Abstract

Recent advances in the field of additive manufacturing (AM) or 3D printing, have garnered serious interest for its potential to substitute time-consuming and costly subtractive and formative manufacturing techniques. Material extrusion (MatEx), employing filament and pelletbased feedstocks, is an AM technique for fabricating three-dimensional objects dictated by a computer-aided design (CAD) file in a layer-by-layer manner. Being inherently a "melt-and-form" technique, the physics of MatEx is strongly dependent on the melt flow behavior of the polymers and hence on their rheology. The focus of this review article is to analyze the current progress in rheological characterizations of filament and pellet-based polymeric feedstocks for application in MatEx. The importance of shear and temperature-dependent viscosities in relation to consistent extrusion through the print nozzle and in the standoff region between nozzle and bed will be highlighted. The importance of shear and/or extensional viscosities and extent of die swell (upon exit from the nozzle) experienced by the polymers under processing parameters relevant to MatEx will be investigated. Postextrusion from the nozzle, the rheological characteristics of the viscous polymer melt as it cools once deposited on the print bed governs the degree of interlayer welding, that impacts the mechanical performance of the printed parts. Controlling and monitoring rheological properties such as zero-shear viscosities and shear moduli of the melt is of significant importance in this region in order to ensure proper mechanical robustness and shape integrity of the deposited layers. Both experimental and theoretical approaches based on polymer chain reptation mechanisms will be reviewed in detail and suggestions to address the existing limitations associated with the process will be provided. Fundamental understanding of the correlation between the classical theories and current understanding based on recent experimentation and analysis is expected to assist the design and development of the next generation of polymer feedstocks and machine designs for MatEx-based AM.

Rheological investigation of nylon‐carbon fiber composites fabricated using material extrusion‐based additive manufacturing

“…The relative increase in the value of n with temperature for the CF-PA6 composite is less than that of PA6, which may be due to the fiber alignment occurring at the high shear rates, which hinders the propensity of the polymer chains to flow at higher temperatures. [28] The shear rate experienced by the polymer melt during extrusion through the nozzle can be calculated using the following equations [29,30] :…”

Current Trends on Protein Driven Bioinks for 3D Printing

“…The extraction and purification methodologies can degrade the protein which will critically affect the molecular weight (MW) of proteins, which is intrinsically connected to its rheological properties. Above a critical MW, viscosity is proportional to MW 3.4 due to entanglement of the polymer molecules [ 82 , 83 ].…”

Analysis of PLA Composite Filaments Reinforced with Lignin and Polymerised-Lignin-Treated NFC

“…Three-dimensional (3D) printing technology (also known as additive manufacturing (AM)) is constantly expanding, mainly due to the advantages in the rapid and cost-effective production of complex, tailored-shape products [ 1 , 2 ]. In order to meet the demands of an increasingly challenging market (automotive, aerospace, biomedical products, architectural and ornamental products, and other fields of application) [ 2 ], different materials have been used; e.g., polymers, metals, resins, ceramic, sand, wax, etc.…”

“…Three-dimensional (3D) printing technology (also known as additive manufacturing (AM)) is constantly expanding, mainly due to the advantages in the rapid and cost-effective production of complex, tailored-shape products [ 1 , 2 ]. In order to meet the demands of an increasingly challenging market (automotive, aerospace, biomedical products, architectural and ornamental products, and other fields of application) [ 2 ], different materials have been used; e.g., polymers, metals, resins, ceramic, sand, wax, etc. The most commonly used polymers for 3D printing are poly(lactide) (PLA), acrylonitrile butadiene styrene (ABS), polyamide (PA), and polycarbonate (PC) [ 3 , 4 , 5 ]; however, in recent years, more sustainable and environmentally friendly materials have been sought and gradually introduced, such as collagen, alginate, chitosan, and cellulose and its derivatives (hemicellulose, lignin, etc.)…”