Thermal properties of 3D printed products from the most common polymers

This research focuses on four thermal characteristics of 3D products printed from the fourteen most common filaments. The softening temperature, coefficient of linear thermal expansion (CLTE), irreversible thermal strain, and thermal conductivity of the 3D printed samples at various measurement directions were evaluated, systematised, and analysed. Semi-crystalline and amorphous, electrically conductive and thermochromic polymer filaments were investigated. Four sets of samples were printed by the Ultimaker S5 3D printer. Printer settings provided the unidirectional orientation of all filament fibres in all specimens and uniform within any specimen’s cross section to investigate the anisotropy of their properties. For investigation of the thermal characteristic of the 3D printed samples, thermomechanical analysis (TMA), differential scanning calorimetry (DSC) methods, and method for measurement of the thermal conductivity (Hot-Disk) were used. The penetration test showed that polyetherimide samples had the highest heat resistance, while the samples from polylactic acid (PLA) had the lowest one. The results of TMA demonstrated that the samples of polypropylene (PP), thermoplastic polyurethane (TPU), and Polyamide had the highest CLTE. In general, semi-crystalline polymers had a higher coefficient of thermal expansion than amorphous ones. During the TMA, almost all samples showed an irreversible thermal strain. PLA Red and Co-polyester showed significant shrinkage of 6–9% in the print direction and expansion in the build direction compared to other samples. Samples of PLA LAVA, acrylonitrile butadiene styrene, polycarbonate, PP, and TPU filaments demonstrated more stable thermal behaviour. The thermal conductivity analysis showed that almost all specimens had a certain degree of anisotropy. The highest thermal conductivity value was obtained for print direction for materials with pronounced anisotropic behaviour, except for polyamide samples. DSC study of post-printing relaxation of the structure of printed samples showed that rapidly cooled samples of semi-crystalline PLA material had a non-equilibrium structure with a low degree of crystallinity. Such structures changed with the time up to 400 h after printing, which also affected their stiffness and strength. The annealing of printed samples at temperatures of cold crystallisation allowed a significant increase in their crystallinity degree, thus approaching the upper limit of this degree for semi-crystalline PLA.