Effect of protective coatings on the water absorption and mechanical properties of 3D printed PLA

Carlos Vicente,João Fernandes,Maria Vaz,Marco Leite,Luis Reis,Augusto Deus

doi:10.3221/igf-esis.48.68

Abstract

This work aims to study the influence of protective coatings on the water absorption and mechanical properties of 3D printed poly–lactic acid (PLA) parts. The PLA parts were fabricated with different levels of the 3D printing process parameters, aiming to define samples with distinct strength and ductility/toughness characteristics. Water absorption tests following the standard ASTM D570–98 were performed on uncoated and coated PLA specimens. The effectiveness of two protective coatings based on acrylic and polyurethane varnish on reducing water absorption was evaluated. Both protective coatings have shown being effective on preventing water absorption by the PLA, with polyurethane presenting the best performance reducing water absorption by 38%. Tensile tests were carried out to determine the ultimate tensile strength, elastic modulus, yield tensile strength, fracture strain and toughness of specimens, before and after the application of protective coatings. The polyurethane protective coating also benefits the tensile properties of PLA parts, increasing the strength and ductility/toughness characteristics of specimens up to 24%.

Highlights

I n recent years the use of 3D printing technologies has increased significantly and this rapid growth it is expected to remain in a near future
As 3D printing technology spreads into more domestic users or at industrial level, poly–lactic acid (PLA) emerge as a valid sustainable thermoplastic alternative to non–biodegradable polymers, able to address the problem of residues derived from manufacturing processes, which impacts the environment of our planet
The characterization and improvement of the mechanical properties of PLA parts produced by fused deposition modelling (FDM) it is a topic of great interest, so that this material can be used on a reliable way

Summary

Introduction

I n recent years the use of 3D printing technologies has increased significantly and this rapid growth it is expected to remain in a near future. As 3D printing technology spreads into more domestic users or at industrial level, PLA emerge as a valid sustainable thermoplastic alternative to non–biodegradable polymers, able to address the problem of residues derived from manufacturing processes, which impacts the environment of our planet In this context, the characterization and improvement of the mechanical properties of PLA parts produced by FDM it is a topic of great interest, so that this material can be used on a reliable way. From the literature it’s well know that the higher strength of PLA parts produced by FDM is linked to higher extrusion temperatures [12,13,14], raster angles aligned with the direction of the applied force [7,9,15] and smaller layer thicknesses [7,8,16], while the ductility follows the inverse trend These trends of the FDM process provide guidelines for the definition of processing parameters of PLA parts regarding his application in elements of strength or ductility/toughness, depending on the project requirements.

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