Fusion deposition modeling (FDM), as a powerful and versatile 3D printing technique, has become more and more popular and affordable in recent years. An FDM printer melts a filament consisting of thermoplastic polymer(s) with or without reinforcements and extrudes it through a fine nozzle to build a desired shape layer by layer. During the process, the filament is heated to a high temperature, which may cause thermal degradation of the material. Since thermal degradation is a complicated process often involving free radicals, it could generate a wide range of degradation products. Unpleasant odors are often released during printing. Even worse, toxic and carcinogenic volatiles might be produced, raising health concerns of users. In this work, thermal degradations of three types of 3D printing filaments, i.e., Nylon A (Nylon 6 with 20 vol% continuous carbon fibers), Nylon B (Nylon 6 with 9.2 vol% chopped carbon fibers), and PPS (polyphenylene sulfide with 8 vol% chopped recycled carbon fibers), were investigated. TGA analyses suggested that there were 2.1% and 3.5% weight losses for the Nylon A and B filaments, respectively, before they were heated to their printing temperature of 270°C in air. The PPS filament was relatively stable. Only 0.1% weight loss was observed until it reached its operating temperature of 305°C. A solid-phase microextraction (SPME) coupled with gas chromatography-mass spectrometry (GC-MS) method was employed to collect and identify the volatile degradation products. Pyridine, butyrolactone, 2-nonanone, and nonanal were detected for both nylon filaments. Among them, pyridine presented in a large amount, which has a nauseating odor and has been confirmed as an animal carcinogen. Nylon A also released 1-(acetyloxy)-2-propanone, pentanoic acid, benzonitrile, and 2-octanone, while Nylon B produced octanal, decanal, and caprolactam. The difference between the two nylon filaments might be caused by different additives in them. The degradation products of the PPS filaments include Butyrolactone, phenol, 1-methyl-2-pyrrolidinone, acetophenone, 1-octanol, <i>p</i>-cresol, and nonanal. Many of them are toxic with unpleasant smells, and <i>p</i>-cresol is a possible human carcinogen. This study helps us understand the potential health concerns related to 3D printing.

Thermal degradation of nylon and polyphenylene sulfide 3D printing filaments under operating temperatures

ACS Spring Meeting 2021

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