Effect of recycling on the mechanical behavior and structure of additively manufactured acrylonitrile butadiene styrene (ABS)

Fused deposition modeling (FDM) is the most common additive manufacturing system that is increasingly used for industrial and consumer applications. These systems selectively extrude/deposit polymers to manufacture parts directly from computational designs. Therefore, FDM enables conversion of recycled thermoplastic polymers to higher quality products. However, FDM induces porosity, which reduces mechanical performance and causes variations in mechanical properties of fused deposition modeled (FDMed) polymers. A safe and reliable use of FDMed-recycled polymers demands a better understanding of the effect of recycling on the mechanical properties. In this study, we investigated the effect of three rounds of recycling on the stochastic mechanical properties of FDMed ABS. A total of 337 tensile tests were performed on FDMed virgin and recycled ABS. Recycling increased the porosity of FDMed ABS from similar to 11 vol% to similar to 17 vol %. The tensile and fracture strength decreased by similar to 10%. The strain at break decreased by 25% from 5.2% to 3.9%, causing a decrease in toughness by 37%. We observed significant variations in the mechanical properties, which were analyzed using Weibull statistics. An S-type deviation from Weibull distribution was observed for strength variations that was related to porosity. Minimal degradation in ABS molecular structure was observed via gel permeation chromatography, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. X-ray fluorescence spectroscopy revealed an increase in elemental iron with recycling. (c) 2020 Elsevier Ltd. All rights reserved.