Dissertação
Efeito do pós-processamento por recozimento sobre as propriedades do PLA impresso com e sem adição de grafeno
Fecha
2023-05-26Autor
Liesenfeld, Janaina
Institución
Resumen
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.