Issue 48

C.M.S. Vincente et alii, Frattura ed Integrità Strutturale, 48 (2019) 748-756; DOI: 10.3221/IGF-ESIS.48.68 754 can be explained by the fact that the PU coating will fill the air gaps of PLA left by the FDM process (which will reduce the roughness), helping to distribute the applied load and preventing the process of crack propagation. In fact, a similar effect was also reported on the work of Leite et al , where the application of an acrylic varnish on ABS parts fabricated by FDM, behind prevent water absorption was led to a strong increase of σ y (> 30%) for samples printed in the flat direction [23]. The benefits and simplicity of the use of protective coatings on PLA parts are a potential alternative to other chemical treatments that were proposed to sealing FDM components, but with negative consequences on some mechanical properties [26,28,35] especially when thin sections are present on parts [36]. C ONCLUSIONS his work describes the fabrication and characterization of PLA parts produced by FDM, with and without protective coatings. The relationships between processing and properties that were determined allow to provide guidelines for obtain PLA parts with tailored properties depending on the final application. The 3D printing studied parameters levels and protective coatings influence strength and ductility/toughness of PLA parts. The application of acrylic and PU based coatings reduces water absorption of PLA produced by FDM. The PU protective coating demonstrated to be the most effective, reducing the water absorption by 38%, when compared with uncoated samples. The mechanical properties of PLA parts were also improved from 8 to 24 %, when samples are coated with PU. The presented results contribute to fulfill the lack of data which users of FDM printers face when projecting with PLA, contributing to stablish a better balance between strength and ductility/toughness on FDM PLA parts and broadening the scope of application of this environment– friendly material. A CKNOWLEDGMENTS his work was supported by Fundação para a Ciência e Tecnologia (FCT), through IDMEC, under LAETA project, UID/EMS/50022/2019. The authors also gratefully acknowledge the funding of FIBR3D project, Reference SAICTPAC/0036/2015, financed by European Structural and Investment Funds (ESIFs) through the Lisbon Regional Operational Programme 2020 and by FCT national funds, POCI-01-0145-FEDER-016414. Marco Leite acknowledges the FCT funding through UNIDEMI project UID/EMS/00667/2019. Carlos M.S. Vicente acknowledge the FIBR3D project, reference SAICTPAC/0036/2015, for the post-doctoral research grant. R EFERENCES [1] Gibson, I., Rosen, D., Stucker, B. (2015).Introduction and Basic Principles. Additive Manufacturing Technologies, New York, Springer, pp. 1–18. [2] Gibson, I., Rosen, D., Stucker, B. (2015).The Impact of Low-Cost AM Systems. Additive Manufacturing Technologies, New York, Springer, pp. 293–301. [3] Ligon, S.C., Liska, R., Stampfl, J., Gurr, M., Mülhaupt, R. (2017). Polymers for 3D Printing and Customized Additive Manufacturing, Chem. Rev., 117(15), pp. 10212–10290, DOI: 10.1021/acs.chemrev.7b00074. [4] Nampoothiri, K.M., Nair, N.R., John, R.P. (2010). An overview of the recent developments in polylactide (PLA) research, Bioresour. Technol., 101(22), pp. 8493–8501, DOI: 10.1016/J.BIORTECH.2010.05.092. [5] Torres, J., Cole, M., Owji, A., DeMastry, Z., Gordon, A.P. (2016). An approach for mechanical property optimization of fused deposition modeling with polylactic acid via design of experiments, Rapid Prototyp. J., 22(2), pp. 387–404, DOI: 10.1108/RPJ-07-2014-0083. [6] Bayraktar, Ö., Uzun, G., Çakiroğlu, R., Guldas, A. (2017). Experimental study on the 3D-printed plastic parts and predicting the mechanical properties using artificial neural networks, Polym. Adv. Technol., 28(8), pp. 1044–1051, DOI: 10.1002/pat.3960. [7] Lanzotti, A., Grasso, M., Staiano, G., Martorelli, M. (2015). The impact of process parameters on mechanical properties of parts fabricated in PLA with an open-source 3-D printer, Rapid Prototyp. J., 21(5), pp. 604–617, DOI: 10.1108/RPJ-09-2014-0135. [8] Liu, X., Zhang, M., Li, S., Si, L., Peng, J., Hu, Y. (2017). Mechanical property parametric appraisal of fused deposition T T