Effect of heat treatment on crystallinity and mechanical properties of flexible structures 3D printed with fused deposition modeling

Fused Deposition Modeling (FDM) is a widely used 3D printing technique, which works based on the principle of melted polymer extrusion through nozzle(s) and depositing them on a build plate layer by layer. However, products manufactured with this method lack proper mechanical strength. In this work, 2/1 twill weave fabric structures are 3D printed using poly (lactic) acid (PLA). The ultimate tensile strength in the warp and weft directions and the modulus (stiffnesses) are measured for non-heat-treated (NHT) samples. The printed samples were heat-treated (HT) to improve the strength and stiffness. The variation in ultimate tensile strength is statistically insignificant in warp direction at all temperatures; however, the tensile strength in weft direction decreased after heat treatment. The modulus in warp direction increased by 31% after heat treatment while in the weft direction it decreased after heat treatment. Differential scanning calorimetry (DSC) tests showed the highest crystallinity at 125°C. The properties of the twill fabrics were compared with a standard dog-bone (DB) specimen using uniaxial tensile tests, Differential scanning calorimetry tests, and optical microscope (OM). For dog-bone specimens, the maximum values of crystallinity, ultimate tensile strength, and modulus were found to be at 125°C. The maximum crystallinity percentages are higher than that of the NHT samples. The ultimate tensile strength of NHT DB specimen 3D printed in horizontal orientation improved after heat treatment. The ultimate tensile strength of DB samples in vertical directions increased after heat treatment as well. The stiffness increased in both directions for DB samples.