Miguel Angel Rodriguez Perez

Nanocellular polyetherimide (PEI) exhibits enhanced toughness and impact resistance compared to the initial solid precursor, an effect usually attributed to the presence of nanometric cells within a confined glassy polymer matrix. In this work, we examine whether the CO ₂ saturation step used in gas dissolution foaming can affect the mechanical response by modifying the thermodynamic state of the glassy polymer. Thermal annealing without CO ₂ increases the yield stress and reduces ductility, whereas solid PEI saturated with CO ₂ and subsequently fully desorbed shows lower yield stress, an increase in tensile ductility, and an improved impact response. Density, gas transport, WAXS, and PALS measurements were used to further analyze this state, showing that the effect of CO ₂ leads to a subtle modification of the glassy matrix, changing the packing and gas accessible regions of the matrix. It is proposed that this matrix state, together with the nanocellular architecture, contributes to the brittle‐to‐ductile transition observed in nanocellular PEI. Our work highlights that optimization of the mechanical properties of nanocellular polymers should not only focus on the key characteristics of the final cellular morphology, but also on the conditions that define the state of the polymer matrix surrounding the pores before and during foaming.

Background: Mechanical reliability and size-dependent strength behavior remain critical concerns for CAD/CAM restorative materials. This study evaluated resin-based CAD/CAM materials, including resin composite blocks (RCBs) and nanoceramics. The influence of specimen size on flexural strength and the applicability of Weibull-based strength predictions were assessed by comparing experimental and Weibull-predicted values. Methods: Twelve CAD/CAM materials were investigated, including ten resin-based materials and two controls (lithium disilicate ceramic and polymethyl methacrylate). Rectangular specimens (1 × 4 × 14 mm and 1 × 12 × 14 mm) were tested using a three-point bending test. Flexural strength, modulus, and resilience were calculated. Reliability and size dependence were assessed using two-parameter Weibull statistics and effective-volume-based predictions. Data were analyzed using statistical tests selected according to data distribution characteristics (α = 0.05). Results: RCBs exhibited higher flexural strength, modulus, and resilience than nanoceramics (p < 0.05). Weibull analysis indicated higher reliability and limited size dependence for RCBs, whereas nanoceramics showed greater variability. The ceramic control exhibited the expected reduction in strength with increasing specimen size. In contrast, resin-based materials showed inconsistent responses to changes in specimen size. Prediction error analysis revealed variable agreement between predicted and experimental values, indicating that agreement with classical Weibull assumptions was material-dependent. Conclusions: Resin-based CAD/CAM materials demonstrated limited size-dependent behavior compared with brittle ceramics. The reduced agreement between experimental and Weibull-predicted values suggests that effective-volume scaling may have limited applicability for these contemporary materials and should be interpreted cautiously on a material-specific basis.

Achieving precise control over structural parameters is crucial for optimizing the performance of bio-based aerogels in energy-related applications. In this work, we investigate the influence of molecular weight and concentration on the development of sustainable polylactic acid (PLA)-based aerogels tailored for thermal insulation. The effects on density, porosity, crystallinity, morphology of the porous structure, mechanical strength, and thermal conductivity were systematically analyzed. It was observed that higher molecular weight PLA can reduce shrinkage during the drying step, leading to lighter aerogels. The relationship between chain mobility (governed by viscosity) and molecular weight was found to be key in governing the microstructure morphology. Sound speed measurements revealed significant variations in the structural factor (g), which are intrinsically associated with the material’s solid tortuosity, and thus in the mechanical and thermal properties. The elastic modulus and compressive strength increased by up to 170% and 63% in samples with densities of ca. 100 kg/m3 and 140 kg/m3, respectively, when the molecular weight was increased from 138 to 175 kDa. Furthermore, all aerogels maintained low thermal conductivities (~30 mW/m·K), and some of them showed values clearly below 30 mW/m·K, owing to a reduction in various heat transfer mechanisms resulting from modifications in key structural parameters, such as porosity and pore size. These findings provide a scalable strategy to engineer bio-based, low-density, and mechanically robust PLA aerogels with stable thermal properties, advancing their deployment as sustainable alternatives to fossil-based insulation materials in clean energy and environmental technologies.

Temperature-dependent performance of PLA aerogels was evaluated under representative service conditions (20-120 °C) to assess their suitability as potential bio-based thermal insulations for the construction sectors. Thermal and mechanical properties measured under elevated temperatures (up to 120 ºC) revealed that the high crystallinity (> 60%) of these materials in combination with their high porosity (over 90%) masks the temperature-driven effects within the amorphous regions. As a result, thermal conductivity measured by transient plane source method increased by only 14% over a 100 ºC temperature span. Correlation with steady-state measurements enabled reliable estimation of absolute values (37 mW/m·K at 120 °C). Furthermore, their mechanical stiffness was largely retained, with an elastic modulus of 1.1 MPa at 120 ºC.After exposure to different temperatures and reaching room temperature again, density, porosity, microstructure, thermal conductivity, and mechanical stiffness were preserved, while a slight crystallinity increase due to annealing was observed. The results confirm the capacity of PLA aerogels to withstand thermal exposure and recover their initial properties after subsequent cooling.Initial evidence toward scale-up was obtained through fabrication of a larger sample (8 x 12 x 1.2 cm), whose thermal conductivity was measured in a Hot Box setup under more representative operating conditions to real application. Finally, recyclability via redissolution-refabrication yielded aerogels with properties comparable to those of pristine samples. Overall, these results represent a significant step toward the scale-up of PLA aerogels while underscoring the remaining challenges associated with potential industrial implementation in the building sector.

Laboratory-scale cryogenic X-ray microtomography was employed for the first time to investigate the early structural evolution of polyurethane (PU) foams. This method enables ex situ studying the internal morphology of the frozen reactive mixture at various times before cell impingement. In this work, the precision of the method was evaluated by studying the early bubble formation and growth under different blowing agents and catalyst contents. It was detected that tripling the catalyst weight content doubled cell nucleation density, from 8.9 × 10⁵ to 1.8 × 10⁶ cells cm⁻³. Yet, doubling the water content has lesser impact on nucleation but leads to fast speeds of cell growth and, in turn, lower relative density at equal reaction times. Overall, it is demonstrated that laboratory cryogenic microtomography can be used to democratise the 3D investigation of the internal structure of foams which was until now only possible in synchrotron facilities. In addition, this method can help elucidate the mechanisms of nucleation and degeneration via directly measuring the density of bubbles and distance between them in the reactive mixture. Finally, this methodology could be extended to recent laboratory nanotomography systems utilizing X-ray tubes with nanometric spot sizes, thereby enabling the confident identification of nucleation events.

Current ecological and environmental concerns have led to a rapid increase in social interest in research and innovation in the field of sustainable plastics, which directly affects foamed plastic products. In this study, we present our contribution by investigating the effects of egg white protein and corn starch particles on open-cell biofoams produced from natural rubber latex in a two-step process based on an initial aeration that leads to a liquid foam precursor and its dehydration by microwave radiation. By incorporating corn starch and either replacing or maintaining the levels of egg white protein, two independent series of foams were examined. We observed how the reduction in egg white led to bigger and heterogeneous cells, although the density values were practically maintained around 100 kg/m³. In contrast, the formulations with corn starch at a fixed level of egg white protein created foams with homogeneous structures and smaller cells (≤120 µm). In addition, in terms of density, both series present values around 100 kg/m³ for the final solid foams, indicating that the addition of starch does not involve density increments. On the contrary, densities are still low, and the cellular structure homogeneity improves, confirming that starch is a very promising stabilizer bio-particle in the development of biofoams from liquids.

In the synthesis of aerogels, the influence of the drying process on the nanostructure is an issue of utmost relevance for tailoring the final properties of these materials. Among the complex parameters affecting this process, the hydrophobicity of the aerogel structure plays a key role. Thus, herein, four different silica aerogel formulations based on tetraethyl orthosilicate and trimethoxymethylsilane were employed to produce aerogels with different wettability properties (from hydrophilic samples to highly hydrophobic). The synthesized gels were dried by three methods, namely freeze-drying, high-temperature supercritical drying with ethanol, and low-temperature supercritical drying with carbon dioxide, and the influence of each procedure on bulk density, porosity, pore size, and specific surface area of the resulting aerogels was analyzed in detail. The direct correlation between the surface hydrophobicity/hydrophilicity of the silica gels and the effects of each drying technique was analyzed, providing insights into a proper selection of the drying method depending on both the water affinity of the gel and the desired textural properties and structures.

In the synthesis of aerogels, the influence of the drying process on the nanostructure is an issue of utmost relevance for tailoring the final properties of these materials. Among the complex parameters affecting this process, hydrophobicity of the aerogel structure plays a key role. Thus, herein, four different silica aerogel formulations based on tetraethyl orthosilicate and trimethoxymethylsilane have been employed to produce aerogels with different wettability properties (from hydrophilic samples to highly hydrophobic). The synthesized gels were dried by three methods: freeze-drying, high-temperature supercritical drying with ethanol and low-temperature supercritical drying with carbon dioxide, and the influence of each procedure on bulk density, porosity, pore size, and specific surface area of the resulting aerogels was analyzed in detail. A clear correlation between the surface hydrophobicity/hydrophilicity of the silica gels and the effects of each drying technique was found, providing insights into a proper selection of the drying method depending on both, the water affinity of the gel, and the desired textural properties and structures. Thus, this work promotes a step forward in the search for the optimal aerogel features through the synthesis procedure with the aim of reaching on-demand applications.

The article examines the possibility of using ophthalmic lens waste (OLW) as a filler in styrene–butadiene rubber (SBR) composites in varying proportions. It analyzes the impact of OLW on the composites’ rheological, structural, morphological, mechanical, and thermal properties. Results show that OLW addition does not significantly alter vulcanization time, leading to thermal savings during processing. The crosslink densities, determined by the swelling method in an organic solvent and the mechanical behavior of the elastomers, increased with the incorporation of OLW, suggesting a filler/polymeric matrix interaction. The Lorenz–Parks model confirmed matrix–filler interaction, although it was insufficient to substantially improve mechanical reinforcement, with OLW mainly acting as a filler. Thermogravimetric tests revealed good thermal stability, but dynamic mechanical analysis indicated reduced damping properties. Spectroscopic analysis indicated the lack of molecular bonding between the polymer and the OLW filler. The study suggests that the optimal OLW content is between 10 and 20 phr, enabling the production of a new composite. Overall, incorporating OLW into vulcanized SBR composites offers a sustainable and cost-effective approach to reusing industrial waste in polymer production, providing an environmentally friendly alternative for the polymer industry.