With the development of additive manufacturing technologies, lattice structures capable of simultaneously providing lightweight characteristics, high specific strength, and functional properties have gained increasing importance in engineering applications. In particular, the use of electrically conductive composite filaments offers new opportunities in areas such as health monitoring, piezoresistive sensing, and smart engineering systems. In such applications, structures are required to possess not only adequate electrical performance but also reliable mechanical strength. However, the anisotropic behavior resulting from the layered structure of parts produced by the Fused Deposition Modeling (FDM) process causes both mechanical and electrical properties to vary depending on the build orientation. In this study, the mechanical and electrical performances of TPMS (Triply Periodic Minimal Surface)-based Gyroid, Diamond, and Schwarz lattice structures fabricated by the FDM process using ABS matrix filaments reinforced with MWCNTs (Multi-Walled Carbon Nanotubes) were investigated. Compression tests, surface hardness measurements, and electrical resistance measurements were conducted on specimens manufactured in different build orientations (XY and Z). The analysis and characterization results demonstrated that TPMS topology, MWCNT content, and build orientation have significant effects on the performance of the structures. The highest electrical conductivity value, 0.0257 S/m, was obtained for the Gyroid specimens containing 1% MWCNT and manufactured in the Z orientation. As the MWCNT content increased to 3% and 5%, a significant decrease in conductivity values was observed, which was associated with nanotube agglomeration and the disruption of conductive network continuity at higher filler contents. Furthermore, it was determined that build orientation induced considerable anisotropy in electrical behavior, resulting in conductivity differences approaching two hundredfold between the Z and XY orientations in some specimens. When the mechanical and electrical results were evaluated together, the Gyroid geometry exhibited a more balanced and stable performance, and it was revealed that TPMS topology and build orientation are critical parameters in the design of multifunctional composite structures.
Syntactic foams based on different resins with densities ranging from 0.23 to 0.67 g/cm 3 were fabricated. Long-term thermo-oxidative aging of these materials was conducted at temperatures of 120, 150, 180, 210, 250, and 280°C for 500 hours, and the relationship between density and aging rate was established. The degradation rate increases with decreasing density. This dependence is explained by the structure of the composites. For low-density syntactic foams (below 0.3 g/cm 3 ), this effect leads to rapid aging at elevated temperatures. Accordingly, low-density syntactic foams based on more thermally resistant binders – specifically phenolic triazine and polyimide resins – were also produced. Thermo-oxidative aging of these materials was also conducted. The results demonstrate that these materials exhibit greater thermal stability than those based on epoxy resin.
It is well known that polymeric foams, as a significant class of engineering materials are of growing importance due to their unique properties. In this study the role of die geometry in shaping the microstructure of extruded HDPE/talc foams was investigated by establishing a correlation between flow dynamics and morphological evolution. The extrusion process was conducted using three dies with nozzle diameters of 1, 2, and 3 mm at die temperatures of 130, 133, and 136 degrees C, utilizing CO2 as the physical blowing agent. Results revealed that die geometry significantly modulates the melt's rheological behavior, the 2 mm die (L/D = 5) provided an optimal balance between a sufficient pressure drop rate (approximate to 25 bar/s) and an intermediate apparent viscosity (between 18,072 to 22,200 Pa.s). This configuration at 130 degrees C yielded the best structural characteristics, including a foam density of 0.420 g/cm3 an expansion ratio of 2.25 and a cell density of 1.9 & times; 105 cells/cm3. Compared to the 1 mm die, the foam density decreased by 19.23%. While the 1 mm die offered the highest pressure drop rate (approximate to 87 bar/s) its performance was limited by excessive back-pressure exceeding the gas injection threshold, which hindered gas entry and reduced solubility. Conversely the 3 mm die caused structural deterioration due to a low pressure drop rate and excessive melt viscosity. Achieving desirable foam structures requires a precise synergy between die-induced thermodynamic instability and rheological resistance. Ultimately, optimizing die geometry and temperature is crucial to ensure sufficient gas entry and maintain the melt strength necessary for superior microcellular morphology.
Polyamide 11 (PA1101) tetrakaidecahedron (TKD) lattice structures fabricated using selective laser sintering (SLS) were examined to understand the combined influence of structural density and chemical vapor smoothing (CVS) on compressive mechanical performance. Lattices with relative densities of 10-30% were fabricated and treated in a solvent system consisting of hexafluoroisopropanol (HFIP) diluted in dichloromethane (DCM). The treatment was conducted under controlled exposure time (5-15min) and temperature conditions (40-50 degrees C). The results indicate that vapor treatment alters the compressive performance of the lattice structures depending on both density and processing severity. At 10% relative density, ultimate compressive strength increased from 0.29 +/- 0.01 MPa in the as-built condition to 0.59 +/- 0.16 MPa after vapor smoothing treatment. Correspondingly, Young's modulus increased from 2.69 +/- 0.12 MPa to 4.94 +/- 1.35 MPa, while energy absorption increased from 0.16 +/- 0.01 J to 0.32 +/- 0.06 J. At 20% relative density, it exhibited moderate improvement, with compressive strength increasing from 1.29 +/- 0.03 MPa to 1.45 +/- 0.11 MPa, and Young's modulus values increasing from 11.88 +/- 0.30 MPa to 12.26 +/- 0.86 MPa. Energy absorption varied between 0.69 +/- 0.04 J and 0.79 +/- 0.15 J after vapor smoothing. For 30% relative density, compressive strength increased from 2.81 +/- 0.20 MPa to 3.40 +/- 0.38 MPa, while Young's modulus increased from 23.52 +/- 0.36 MPa to 24.97 +/- 3.54 MPa, accompanied by energy absorption values increasing from 1.64 +/- 0.21 J to 1.93 +/- 0.41 J. A particle swarm optimization (PSO) based multi-objective framework was used to determine balanced processing parameters, indicating that higher relative density, combined with moderate exposure time and controlled temperature, provides improved room-temperature compressive strength without a significant reduction in stiffness.
Polyvinyl chloride (PVC)-based composite membranes containing calcined bentonite (UCB) and organo-modified bentonite (AMB) were prepared by non-solvent-induced phase separation (NIPS) and evaluated for their porous structure and oil sorption performance. The results showed that clay modification significantly influenced membrane morphology and porosity. Increasing UCB content reduced membrane porosity from 71.2% to 61.2%, whereas AMB incorporation increased porosity up to 74.1%, indicating the formation of a more open and interconnected porous structure. These structural differences were reflected in the sorption behavior of the membranes. AMB-containing membranes exhibited the highest oil uptake, reaching 4.56 g g-1 for crude oil and 2.22 g g-1 for hydraulic oil, while maintaining low water uptake (0.19 g g-1). Mechanical and thermal characterization demonstrated that incorporating modified bentonite affected the overall performance of the PVC matrix, with composition-dependent changes in strength and thermal stability. Complementary density functional theory (DFT) calculations using simplified molecular models revealed differences in HOMO-LUMO energy gaps between PVC/UCB and PVC/AMB systems, providing qualitative support for the distinct interaction environments generated by clay modification. Overall, the results indicate that the dispersion state and surface modification of bentonite play an important role in controlling pore development and sorption behavior in PVC-based porous membranes, highlighting their potential for oil-related environmental applications.
