Efeito do pós-processamento por recozimento sobre as propriedades do PLA impresso com e sem adição de grafeno

Abstract

Additive Manufacturing (AM) is a set of manufacturing processes that build objects layer by layer, adding material in a controlled manner. Unlike traditional manufacturing methods, which involve material removal. The ISO/ASTM52900 standard classifies additive manufacturing in seven different principles and within the principle of material extrusion, the Fused Filament Fabrication (FFF) stands out as the most widely used, accessible and responsible for the popularization of AM. The FFF technology uses a filament of thermoplastic material that is heated, extruded and deposited in successive layers to form a three-dimensional object. Due to the weak connection produced among the deposited filament layers, the polymeric structures manufactured by the FFF process have low resistance. To overcome this problem, it has recently been shown that performing postdeposition heat treatments promotes a reduction in internal thermal stresses and improves adhesion between layers, positively affecting the printed parts mechanical properties. In this context, annealing was performed on printed samples of Polylactic Acid (PLA) with and without graphene addition at temperatures of 90, 100 and 120 °C for 60, 120 and 240 min, aiming to evaluate the role of these parameters on the evolution of the aforementioned properties. The annealed samples had their chemical characteristics evaluated by X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) techniques; their thermal characteristics investigated by Thermogravimetric (TGA) and Differential Scanning Calorimetry (DSC) techniques; its electrical properties evaluated in terms of resistance, resistivity and conductivity; and their mechanical properties determined through tensile and bending tests, notch sensitivity test, impact test and hardness measurements. Chemical characterizations show that annealing does not change the chemical composition of the materials, but generates structural alterations, producing their crystallization. Thermal characterizations confirmed the crystallization of the materials, and indicate a slight increase on its degree of thermal stability. Electrical characterization showed that crystallization does not produce any effect on the characteristics of PLA printed without graphene, but it improves the conductivity of PLA printed with graphene. Mechanical characterization indicated that annealing increased the mechanical strength, fracture resistance, impact strength, stiffness and hardness of both materials, but reduced their plasticity. Finally, the fractography of the specimens showed that annealing has no effect on the mechanical fracture mechanisms.