Analysis of the limitations of organic powder for high-temperature reprocessing of printed PLA parts

Abstract

Fused filament fabrication (FFF) is the most predominant additive manufacturing technology, not only in the industry but also for many hobbyists. This technology's popularity is because it is inexpensive, user-friendly, and open source. However, compared to other manufacturing processes, like injection molding, FFF products still have some limitations, particularly mechanical properties. Despite this, some post-processing techniques have been developed to improve such properties. One of these techniques involves applying heat treatments (HT). The objective of these HTs is to densify these FFF products and increase the crystallization degree of the semi-crystalline polylactic acid (PLA). This kind of post-processing is claimed to be a viable way to improve mechanical properties. The reprocessing in a powder bed is a type of HT which prevents thermal distortion by using a powder as a mold for the FFF component. The powder should be low cost and have easy access for any user. In this work, this HT was performed in flexural samples with an organic powder (corn flour) and it has improved maximum flexural strength (MFS) and flexural modulus (FM) by 18% and 14%, respectively. The color of parts, before and after HT, was also measured and a slight modification of the response was observed due to the HT. Despite the gains in mechanical properties, it was verified that corn flour produces a considerable amount of smoke during this HT. Thus, it was performed a thermogravimetric analysis (TGA) in three types of powders, namely corn flour, coffee powder, and corn starch. It was concluded that starch is the best one, however considering that all three organic powders release smoke, it is advisable not to use them for HT.