Not all PLA filaments are created equal: an experimental investigation

Abstract

<jats:sec> <jats:title content-type="abstract-subheading">Purpose</jats:title> <jats:p>Additive manufacturing (AM) methods such as material extrusion (ME) are becoming widely used by engineers, designers and hobbyists alike for a wide variety of applications. Successfully manufacturing objects using ME three-dimensional printers can often require numerous iterations to attain predictable performance because the exact mechanical behavior of parts fabricated via additive processes are difficult to predict. One of that factors that contributes to this difficulty is the wide variety of ME feed stock materials currently available in the marketplace. These build materials are often sold based on their base polymer material such as acrylonitrile butadiene styrene or polylactic acid (PLA), but are produced by numerous different commercial suppliers in a wide variety of colors using typically undisclosed additive feed stocks and base polymer formulations. This paper aims to present the results from an experimental study concerned with quantifying how these sources of polymer variability can affect the mechanical behavior of three-dimensional printed objects. Specifically, the set of experiments conducted in this study focused on following: several different colors of PLA filament from a single commercial supplier to explore the effect of color additives and three filaments of the same color but produced by three different suppliers to account for potential variations in polymer formulation.</jats:p> </jats:sec> <jats:sec> <jats:title content-type="abstract-subheading">Design/methodology/approach</jats:title> <jats:p>A set of five common mechanical and material characterization tests were performed on 11 commercially available PLA filaments in an effort to gain insight into the variations in mechanical response that stem from variances in filament manufacturer, feed stock polymer, additives and processing. Three black PLA filaments were purchased from three different commercial suppliers to consider the variations introduced by use of different feed stock polymers and filament processing by different manufacturers. An additional eight PLA filaments in varying colors were purchased from one of the three suppliers to focus on how color additives lead to property variations. Some tests were performed on unprocessed filament samples, while others were performed on objects three-dimensional printed from the various filaments. This study looked specifically at four mechanical properties (Young’s modulus, storage modulus, yield strength and toughness) as a function of numerous material properties (e.g. additive loading, molecular weight, molecular weight dispersity, enthalpy of melting and crystallinity).</jats:p> </jats:sec> <jats:sec> <jats:title content-type="abstract-subheading">Findings</jats:title> <jats:p>For the 11 filaments tested the following mean values and standard deviations were observed for the material properties considered: <jats:italic>p<jats:sub>a</jats:sub></jats:italic> = 1.3 ± 0.9% (percent additives), <jats:italic>M<jats:sub>w</jats:sub></jats:italic> = 98.6 ± 16.4 kDa (molecular weight), Ð = 1.33 ± 0.1 (molecular weight dispersity), <jats:italic>H<jats:sub>m</jats:sub></jats:italic> = 37.4 ± 7.2 J/g (enthalpy of melting) and = 19.6 ± 2.1% (crystallinity). The corresponding mean values and standard deviations for the resulting mechanical behaviors were: <jats:italic>E</jats:italic> = 2,790 ± 145 MPa (Young’s modulus), <jats:italic>E</jats:italic>’ = 1,050 ± 125 MPa (storage modulus), <jats:italic>S<jats:sub>y</jats:sub></jats:italic> = 49.6 ± 4.93 MPa (yield strength) and <jats:italic>U<jats:sub>t</jats:sub></jats:italic> = 1.87 ± 0.354 MJ/m^<jats:sup>3</jats:sup> (toughness). These variations were observed in filaments that were all manufactured from the same base polymer (e.g. PLA) and are only different in terms of the additives used by the manufacturers to produce different colors or different three-dimensional printing performance. Unfortunately, while the observed variations were significant, no definitive strong correlations were found between these observed variations in the mechanical behavior of the filaments studied and the considered material properties.</jats:p> </jats:sec> <jats:sec> <jats:title content-type="abstract-subheading">Research limitations/implications</jats:title> <jats:p>These variations in mechanical behavior and material properties could not be ascribed to any specific factor, but rather show that the mechanical of three-dimensional printed parts are potentially affected by variations in base polymer properties, additive usage and filament processing choices in complex ways that can be difficult to predict.</jats:p> </jats:sec> <jats:sec> <jats:title content-type="abstract-subheading">Practical implications</jats:title> <jats:p>These results emphasize the need to take processing and thereby even filament color, into account when using ME printers, they emphasize the need for designers to use AM with caution when the mechanical behavior of a printed part is critical and they highlight the need for continued research in this important area. While all filaments used were marked as PLA, the feedstock materials, additives and processing conditions created significant differences in the mechanical behavior of the printed objects evaluated, but these differences could not be accurately and reliably predicted as function of the observed material properties that were the focus of this study.</jats:p> </jats:sec> <jats:sec> <jats:title content-type="abstract-subheading">Originality/value</jats:title> <jats:p>The testing methods used in the study can be used by engineers and creators alike to better analyze the material properties of their filament printed objects, to increase success in print and mechanical design. Furthermore, the results clearly show that as AM continues to evolve and grow as a manufacturing method, standardization of feedstock processing conditions and additives would enable more reliable and repeatable printed objects and would better assist designers in effectively implementing AM methods.</jats:p> </jats:sec>

Analysis of Test Plastic Samples Printed by the Additive Method Fused Filament Fabrication

“…After a deeper analysis, a strong relationship between tensile strength and percent crystallinity of samples of different colors was proven. Other researchers [KOH 2018] [SOARES 2008] [SCHWARTZ 2020] [SPINA 2019] [VALERGA 2017] also confirm that different PLA colors lead to different quality of 3D printed products under the same process conditions. Color additive as well as the coloring process itself can cause mentioned deviations.…”

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Fused filament fabrication: comparison of methods for determining the interfacial strength of single welded tracks

“…With this, optimal operating parameters in terms of maximal interfacial strength can be defined for filaments. One should keep in mind that even for the same polymer, material properties of printed objects might vary [26]. To obtain more fundamental material insights, specimens should not be printed simultaneously to minimise the effects mentioned in the last chapter.…”

Characterization of 3d printing filaments applied in restoration of sensitive archaeological objects using rapid prototyping

“…One important drawback is that commercial filament composition is generally unknown, and for this reason, we cannot assure if those materials are reliable for archaeological restoration. Characterization of 3D printing filaments used for restoration of archaeological objects is a problem that must be investigated to ensure their reliability (Cantrell, et al, 2016;Grasso, et al, 2018;Yang, et al, 2018;Breda Soares, et al, 2018;Behzadnasab, et al, 2019;Schwartz, et al, 2020).…”