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°C, utilizing CO 2 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 (≈25 bar/s) and an intermediate apparent viscosity (between 18,072 to 22,200 Pa.s). This configuration at 130°C yielded the best structural characteristics, including a foam density of 0.420 g/cm 3 an expansion ratio of 2.25 and a cell density of 1.9 × 10 5 cells/cm 3 . Compared to the 1 mm die, the foam density decreased by 19.23%. While the 1 mm die offered the highest pressure drop rate (≈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°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.
Polyurethane foams (PUFs) are extensively used in acoustic applications due to their porous structure and high sound energy dissipation, making them ideal for noise control. In this context, this study presents an experimental and numerical analysis of homogeneous and multilayer open-cell PUF systems, evaluating their acoustic performance over a wide frequency range. Three modelling approaches were assessed: the empirical Delany-Bazley (DB) model, the modified DB-Miki model and the semi-phenomenological Johnson-Champoux-Allard (JCA) model. To complement these models, an inverse parameter identification procedure in MATLAB was employed to extract key non-acoustic parameters: porosity, tortuosity, airflow resistivity, and viscous characteristic length, directly from measured sound absorption data, enabling a more physically meaningful characterization. Results indicate that DB and DB-Miki models provide reasonable predictions at mid-range frequencies but show limitations at low frequencies. Conversely, the JCA model achieves higher predictive accuracy across the full spectrum, effectively capturing complex dissipation phenomena in multilayer structures. These findings highlight the value of combining inverse parameter estimation with suitable acoustic models to reliably characterize porous materials, offering a robust approach for designing PUF-based acoustic solutions.
