The Effect of Heat Treatment on a 3D-Printed PLA Polymer’s Mechanical Properties

Abstract

Three-dimensional printing is a useful and common process in additive manufacturing nowadays. The advantage of additive polymer technology is its rapidity and design freedom. Polymer materials’ mechanical properties depend on the process parameters and the chemical composition of the polymer used. Mechanical properties are very important in product applicability. The mechanical properties of polymers can be enhanced by heat treatment. Additive-manufactured PLA’s mechanical properties and structure can be modified via heat treatment after the 3D printing process. The goal of this research was to test the effect of heat treatment on the mechanical and structural parameters of additive-manufactured PLA. This was achieved via the FDM processing of standard PLA tensile test specimens with longitudinal and vertical printing orientations. After printing, the test specimens were heat-treated at 55 °C, 65 °C and 80 °C for 5 h and after being held at 20 °C for 15 h. The printed and heat-treated specimens were tested using tensile tests and microscopy. Based on the test results, we can conclude that the optimal heat treatment process temperature was 65 °C for 5 h. Under the heat treatment, the test specimens did not show any deformation, the tensile strength increased by 35% and the porosity of the PLA structure decreased.

Experimental Study of In-Process Heat Treatment on the Mechanical Properties of 3D Printed Thermoplastic Polymer PLA

“…Following the variation graphs shown above, it can be considered that the values obtained for hardness are opposite to those for tensile strength. Comparing the results obtained with those found in the literature, it is found that they fall within the range of 79–84 HD, values also obtained by other researchers [ 26 , 31 ], raising the degree of confidence in the accuracy of the values obtained in this study.…”

“…The experimental values and trends are in agreement with the results obtained by other researchers in the literature [ 18 , 31 , 32 , 47 , 48 ]. This convergence of results from multiple sources significantly bolsters the confidence level associated with the outcomes presented in this paper, further confirms the possibility of applying in-process annealing during additive manufacturing, and also strengthens the reliability and significance of the multiple research studies from the literature.…”

“…Regarding the surface hardness of additively manufactured parts, the literature presents several investigations for different types of materials used in the MEX process [ 24 , 25 , 26 , 27 ], including Martens-type micro-hardness [ 28 , 29 , 30 ]. Several research studies have been carried out on the influence of heat treatment on the hardness of PLA additively manufactured parts [ 31 , 32 ]. Following the experimental determinations in [ 31 ], the results obtained by the authors showed that by applying heat treatment, the tensile strength increased considerably, by up to 35%, while the hardness of the parts subjected to heat treatment decreased, with the values fluctuating depending on the printing direction of the specimens.…”

4D printing and annealing of PETG composites reinforced with short carbon fibers

“…The other solution to improve the quality of the mechanical properties of the FDM components is annealing [27][28][29]. This is a post-process that includes heating the material to a high temperature above its glass transition temperature to enhance the chains' molecular mobility in the structure and keeping it at this temperature for a specific time resulting in amplifying interlayer bonding [30].…”

“…Shbanah et al studied the effect of heat treatment (annealing) on the mechanical properties and structure of PLA. They heat-treated the printed specimens at 55 °C, 65 °C and 80 °C for 5 h and then keeping them at 20 °C for 15 h. The results of their work show that the optimal heat treatment was 65 °C for 5 h and also presented a 35% increase in the tensile strength of the material and a decrease in the amount of porosity in the structure [27].…”