Materials Science Forum Vol. 1199

Abstract: This study is part of my doctoral research and investigates the sustainable recycling of aluminum waste through the development of aluminum-containing polymer hybrid materials. The study aims to understand how the type, structure, and distribution of these reinforcements influence the mechanical strength and overall behavior of the composites. The increasing demand for lightweight, high-performance, and environmentally friendly materials in various industries - such as automotive, construction, and packaging - has driven the exploration of metal-polymer composites. In this context, aluminum, due to its low density, corrosion resistance, and recyclability, presents a promising candidate for reinforcement in polymer matrices. Special attention was given to how the particle size and distribution affect the elasticity, flexibility, and structural integrity of a selected PU-foam. The study aims to contribute to the broader field of circular materials engineering by offering insights into how industrial aluminum waste can be effectively reused in high-value polymer systems.

Abstract: Mechanical recycling of high-temperature semi-aromatic polyamides remains challenging due to their high melting temperatures and limited processability. In this study, secondary glass-fiber-reinforced polyphthalamide was processed by two mechanical size-reduction routes: conventional crushing and pulverization in an industrial high-speed dual-disc pulverizer. Structural and thermal changes were evaluated by Fourier Transform infrared spectroscopy, X-ray diffraction and differential scanning calorimetry. Fourier Transform infrared spectroscopy confirms that both routes preserve the polyphthalamide backbone, while the pulverized material shows subtle changes in the N-H and C=O regions consistent with partial reorganization of the hydrogen-bonding network. X-ray diffraction shows a decrease in apparent crystallinity from ~24.2% (crushed) to ~18.4% (pulverized), accompanied by an increase in average crystallite size from ~10.3 to ~12.8 nm, suggesting lamellar-scale restructuring. Differential scanning calorimetry analysis emphasizes the first heating as a probe of the as-processed condition: the pulverized secondary glass-fiber-reinforced polyphthalamide exhibits a lower melting enthalpy (≈17 J/g versus ≈23 J/g for the crushed reference) and a distinct cold-crystallization peak near 166 °C. This feature is not observed in the crushed material and disappears after melting and controlled cooling, whereas Tg and Tm remain largely unchanged. Overall, X-ray diffraction and differential scanning calorimetry consistently show that the pulverized powder differs from the crushed reference mainly in first-heating enthalpy and the appearance of cold crystallization, while Tg and Tm remain similar. From an application perspective, pulverized secondary glass-fiber-reinforced polyphthalamide is a fine, heat-stable recycled feedstock that can be reintroduced more readily into polyamide blends and compounds, providing a simple, solvent-free route to enhance the engineering value of recycled high-temperature polyphthalamide.

Abstract: The limbs of compound bows are subjected to highly complex and intensive mechanical loads throughout the entire shooting cycle. Due to the operation of the cam system, forces acting on the limbs may exceed the applied draw force by several times, particularly near maximum draw. Extreme dynamic loads can be generated during dry firing, which may result in sudden and often fiber-directional failure of composite limbs. Local stress levels are further increased by stress concentration effects arising from geometric and material inhomogeneities. In this study, the forces acting on the cam system and the bow limbs were determined through preliminary analytical calculations. The Euler–Bernoulli beam theory was applied to estimate limb deflection analytically. The analysis was refined using the Timoshenko beam model to account for shear deformation and cross-sectional rotation. Cross-sectional second moments of area and relevant material properties were determined to ensure accurate results. The calculated deflections, although small in magnitude, were shown to have a significant influence on the stress state of the limbs. Based on the numerical results, it was concluded that compound bow limbs operate close to, or in some cases beyond, their material limit under severe loading conditions.

Abstract: Processing methods strongly influence the degradation behaviour of semi-crystalline polylactic acid (PLA) by affecting its molecular orientation, crystallinity, and micro-and macrostructural features. In our previous study, we presented the changes in the properties of the electrospun PLA fibers during in vitro degradation. Building on these findings, this study compares the degradation of PLA specimens prepared using two bulk processing methods: (i) fused filament fabrication (FFF) 3D printing and (ii) film extrusion. Specimens were incubated in phosphate-buffered saline (pH 7.4) at 37 °C for 1, 3, 7, 28, and 56 days. At each time point, degradation was assessed by tensile testing, differential scanning calorimetry, and weight retention analysis. PLA films exhibited an initial decrease in Young’s modulus, followed by a temporary increase and subsequent decline, whereas FFF specimens maintained mechanical stability for several days before a gradual deterioration. Both specimens showed reduced crystallinity over time, with FFF samples becoming fully amorphous by day 56. Minimal weight change (<1%) indicated that degradation proceeded primarily through structural and morphological changes rather than bulk erosion. Overall, 3D-printed PLA exhibited more stable mechanical properties than extruded PLA films. These findings highlight the significant impact of the processing route on PLA degradation, guiding the optimization of PLA performance in biomedical, packaging, and sustainable material applications.