Polymer materials are increasingly widely used in high-fire-risk applications, such as aviation interior components. This study aimed to compare the tensile, thermal, and flame-retardant properties of test samples made from ultra-performance materials, polyetherimide (PEI) and polyetherketoneketone (PEKK), using the fused filament fabrication process (FFF). The tensile tests were performed for these materials at different raster angles (0, 45, and 90°). The thermomechanical tests were done in the axial, perpendicular, and through-thickness directions to the extruded filaments. The impact of printing parameters on the flame retardancy of 3D-printed samples was investigated in vertical burn tests with varying specimen thicknesses and printing directions. Experimentally, it was testified that PEKK had better isotropic behaviour than PEI for mechanical performance, thermal expansion, and fire-resistant properties, which are essential in fabricating intricately shaped products.

Glass fibers slowly dissolve and age when exposed to water molecules. This phenomenon also occurs when glass fibers are inside fiber-reinforced composites protected by the matrix. This environmental aging results in the deterioration of the mechanical properties of the composite. In structural applications, GFRPs are continuously exposed to water environments for decades (typically, the design lifetime is around 25 years or even more). During their lifetime, these materials are affected by various temperatures, pH (acidity) levels, mechanical loads, and the synergy of these factors. The rate of the degradation process depends on the nature of the glass, sizing, fiber orientation, and environmental factors such as acidity, temperature, and mechanical stress. In this work, the degradation of typical industrial-grade R-glass fibers inside an epoxy fiber-reinforced composite was studied experimentally and computationally. A Dissolving Cylinder Zero-Order Kinetic (DCZOK) model was applied and could describe the long-term dissolution of glass composites, considering the influence of fiber orientation (hoop vs. transverse), pH (1.7, 4.0, 5.7, 7.0, and 10.0), and temperature (20, 40, 60, and 80 °C). The limitations of the DCZOK model and the effects of sizing protection, the accumulation of degradation products inside the composite, and water availability were investigated. Dissolution was experimentally measured using ICP-MS. As in the case of the fibers, for GFRPs, the temperature showed an Arrhenius-type influence on the kinetics, increasing the rate of dissolution exponentially with increasing temperature. Similar to fibers, GFRPs showed a hyperbolic dependence on pH. The model was able to capture all of these effects, and the limitations were addressed. The significance of the study is the contribution to a better understanding of mass loss and dissolution modeling in GFRPs, which is linked to the deterioration of the mechanical properties of GFRPs. This link should be further investigated experimentally and computationally.

Despite the impressive properties of additively manufactured products, their inherent anisotropy is a crucial challenge for polymeric parts made via fused filament fabrication (FFF). This study compared the tensile, thermophysical, smoke density, and toxicity characteristics of Ultem 9085 (a blend of polyetherimide and polycarbonate) for samples printed in various orientations (X, Y, and Z). The results revealed that mechanical properties, such as elastic modulus and tensile strength, significantly differed from the Z printing orientation, particularly in the X and Y printing layer orientations. Thermomechanical analysis revealed that Ultem 9085 had high anisotropic effects in the coefficient of thermal expansion, indicating superior thermal properties along the printing orientation. The smoke density and toxicity test results proved that Ultem 9085 complies with aviation safety standards. Smoke density tests showed that all samples, regardless of print orientation or thickness, stayed well below the regulatory limit, making them suitable for aircraft interiors.

Glass fibers slowly dissolve and age when exposed to water molecules. Such a phenomenon also occurs when glass fibers are inside fiber-reinforced composites protected by the matrix. This en-vironmental aging results in the deterioration of the mechanical properties of the composite. In structural applications, GFRPs are continuously exposed to water environments for decades (typically design lifetime is around 25 years or even more). During their lifetime, these materials are affected by various temperatures, pH acidity levels, mechanical loads, and the synergy of these factors. The rate of the degradation process depends on the nature of glass, sizing, fiber orientation, and environmental factors such as acidity, temperature, and mechanical stress. In this work, degradation of typical industrial grade R-glass fibers, when inside an epoxy fiber-reinforced composite, is studied experimentally and computationally. A Dissolving Cylinder Zero-Order Kinetic (DCZOK) model was applied and could describe the long-term dissolution of glass composites, considering the influence of fiber orientation (hoop vs transverse), pH (1.7, 4.0, 5.7, 7.0, and 10.0), and temperature (20, 40, 60, and 80 °C). The limitations of the DCZOK model and effects of sizing protection, accumulation of degradation products inside the composite, and water availability were discussed. Experimentally dissolution was measured using ICP-MS. Like for the fibers, for GFRPs also, the temperature showed an Arrhenius-type influence on the ki-netics, increasing the rate of dissolution exponentially with increasing temperature. Similar to fibers, GFRPs showed a hyperbolic dependence on pH. The model was able to capture all of these effects, and the limitations were addressed.