Search Results (1,826)

Rigid PU foams have wide practical applications, and their mathematical modelling would benefit from deeper knowledge about the variants of independent elastic constants of symmetric PU foams. Therefore, in this study, various symmetry elements of rigid PU foams were analysed in relation to the characteristics of production moulds and technologies. The generalised Hooke’s law was considered together with additional relationships valid for certain types of symmetry. Variants of independent elastic constants were determined for orthotropic, orthotropic with a rotational symmetry, and isotropic PU foams. For transtropic PU foams, nine variants of independent elastic constants were identified and corresponding equations for the components of response strain tensor were derived. Then, in order to investigate the results provided by the 9 variants, 12 elastic constants were determined experimentally in compression and shear for free-rise, rigid, and quasi-transtropic PU foams with average densities of 34 kg/m³, 55 kg/m³, and 75 kg/m³. Based on the analysis of (a) measurement uncertainties and (b) satisfying of the transtropy equations, an assessment was made of the correspondence of the experimentally determined elastic constants to the constants of a perfectly transtropic material. This made it possible to identify variants of independent constants that ensure the best correspondence between the calculated strains and the set of average strains. Full article

Sandwich panels, widely used in factory and warehouse construction, are highly susceptible to fire due to their fragile surfaces and polyurethane-insulated cores. Such structures facilitate rapid fire spread, significantly increasing the risk of extensive thermal damage. Although conventional measures, such as surface pre-wetting, are commonly utilized, their effectiveness is limited due to rapid evaporation. To address this issue, the current study evaluates the effectiveness of compressed air foam (CAF) applied as a pre-application treatment for delaying fire spread. Full-scale fire experiments were conducted to measure temperature variations across sandwich panel surfaces treated under three different conditions: untreated, water-treated, and CAF-treated. Experimental results indicated that CAF effectively formed a stable insulating barrier, maintaining temperatures well below critical thresholds, compared to untreated and water-treated panels. CAF application demonstrated superior thermal protection, reducing internal temperatures by up to 78% compared to untreated conditions and by 67.5% compared to water-treated conditions. These findings underscore the practical importance of adopting CAF pre-application as a proactive fire mitigation strategy, significantly enhancing fire safety standards in industrial and storage facilities constructed with sandwich panels. Full article

The intensifying freshwater crisis underscores the critical need for all-weather, low-energy atmospheric water harvesting technologies. Inspired by the scale-like protrusions and interconnected channels of Tillandsia leaves that enable efficient water capture and release, a polyvinyl alcohol-based foam featuring a three-dimensional porous structure is fabricated using the supercritical carbon dioxide foaming technology. Compared to the traditional freeze-drying method, this approach significantly reduces preparation energy consumption and shortens the production cycle. Lithium chloride integration endows the foam with exceptional moisture absorption capacity, reaching 300% of its weight. Leveraging graphene’s outstanding photothermal conversion properties, the foam achieves a photothermal dehydration rate of 80.7% within 80 min under 1 Sun irradiation, demonstrating a rapid water release capacity. Furthermore, the polyvinyl alcohol-based foam exhibits no performance degradation after 60 cycles, indicating remarkable stability. This technology provides a scalable, low-cost, and all-climate-applicable solution for water-scarce regions. Full article

Lightweight Aggregate Reinforced Concrete (LWARC) is increasingly used in structural systems to reduce dead load, especially in flat slabs. This study focuses on LWARC-incorporating polystyrene foam as a partial aggregate replacement, achieving a dry unit weight reduction from 23.0 kN/m³ to 19.0 kN/m³. While beneficial for lowering dead loads, this substitution exacerbates punching shear vulnerability, necessitating innovative strengthening solutions. Fiber-Reinforced Polymers (FRPs), recognized for their high strength-to-weight ratio, corrosion resistance, and adaptability, are employed to address these limitations. This paper evaluates the punching shear strengthening of LWARC flat slabs using externally bonded carbon fiber-reinforced polymer (CFRP) sheets, embedded through-section (ETS) steel bars, and ETS glass fiber-reinforced polymer (GFRP) bars. Ten specimens were tested under concentric loading, including an unstrengthened control slab. Experimental results were compared with predictions from ECP 203-2023, ACI 318-19, and BS 8110 to assess code applicability. Strengthened specimens demonstrated significant improvements in punching capacity and ductility. The ETS steel bar technique increased punching strength by 41% compared to the control, while inclined reinforcement configurations outperformed vertical layouts by 24% due to optimized shear transfer. Full article

Practical applications such as solar power energy systems, electronic cooling, and the convective drying of vented enclosures require continuous developments to enhance fluid and heat flow. Numerous studies have investigated the enhancement of heat transfer in L-formed vented cavities by inserting heat-generating components, filling the cavity with nanofluids, providing an inner rotating cylinder and a phase-change packed system, etc. Contemporary work has examined the thermal performance of L-shaped porous vented enclosures, which can be augmented by using metal foam, using nanofluids as a saturated fluid, and increasing the wall surface area by corrugating the cavity’s heating wall. These features are not discussed in published articles, and their exploration can be considered a novelty point in this work. In this study, a vented cavity was occupied by a copper metal foam with $PPI=10$ and saturated with a copper–water nanofluid. The cavity walls were well insulated except for the left wall, which was kept at a hot isothermal temperature and was either non-corrugated or corrugated with rectangular waves. The Darcy–Brinkman–Forchheimer model and local thermal non-equilibrium models were adopted in momentum and energy-governing equations and solved numerically by utilizing commercial software. The influences of various effective parameters, including the Reynolds number ($20\le Re\le 1000$), the nanoparticle volume fraction ($0\%\le \phi \le 20\%$), the inflow and outflow vent aspect ratios ($0.1\le D/H\le 0.4$), the rectangular wave corrugation number ($N=5$ and $N=10$), and the corrugation dimension ratio ($CR=1$ and $CR=0.5$) were determined. The results indicate that the flow field and heat transfer were affected mainly by variations in $Re$, $D/H$, and $\phi$ for a non-corrugated left wall; they were additionally influenced by $N$ and $CR$ when the wall was corrugated. The fluid- and solid-phase temperatures of the metal foam increased with an increase in $Re$ and $D/H$. The fluid-phase Nusselt number near the hot left sidewall increased with an increase in $\phi$ by $\left(25–60\right)\%$, while the solid-phase Nusselt number decreased by $\left(10–30\right)\%$, and these numbers rose by around $3.5$ times when the Reynolds number increased from $20$ to $1000$. For the corrugated hot wall, the Nusselt numbers of the two metal foam phases increased with an increase in $Re$ and decreased with an increase in $D/H$, $CR$, or $N$ by $10\%$, $19\%$, and $37\%$. The original aspect of this study is its use of a thermal, non-equilibrium, nanofluid-saturated metal foam in a corrugated L-shaped vented cavity. We aimed to investigate the thermal performance of this system in order to reinforce the viability of applying this material in thermal engineering systems. Full article

This study investigates the feasibility of incorporating chemically recycled polyol (glycolysate), derived from semi-rigid polyurethane waste from the building industry, into rigid PUF formulations intended for thermal insulation applications. Glycolysis was performed using a diethylene glycol–glycerol mixture (4:1) at 185 °C in the presence of a dibutyltin dilaurate (DBTDL) catalyst. The resulting glycolysate was characterized by a hydroxyl number of 590 mg KOH/g. Foams containing 5–50% recycled polyol were prepared and described in terms of foaming kinetics, cellular structure, thermal conductivity, apparent density, mechanical performance, dimensional stability, flammability, and volatile organic compound (VOC) emissions. The incorporation of glycolysate accelerated the foaming process, with the gel time reduced from 44 s to 16 s in the sample containing 40% recycled polyol, enabling a reduction in catalyst content. The substitution of up to 40% virgin polyol with recycled polyol maintained a high closed-cell content (up to 87.7%), low thermal conductivity (λ₁₀ = 26.3 mW/(m·K)), and dimensional stability below 1%. Additionally, compressive strength improvements of up to 30% were observed compared to the reference foam (294 kPa versus 208 kPa for the reference sample). Flammability testing confirmed compliance with the B2 classification (DIN 4102), while preliminary qualitative VOC screening indicated no formation of additional harmful volatile compounds in glycolysate-containing samples compared to the reference. The results demonstrate that glycolysate can be effectively utilized in high-performance insulation materials, contributing to improved resource efficiency and a reduced carbon footprint. Full article

Lightweight PLA (LW-PLA) filaments enable material-saving designs in fused filament fabrication (FFF), yet optimizing their mechanical performance remains challenging due to temperature-sensitive foaming behavior. This study aims to enhance the structural strength and material efficiency of LW-PLA parts using a multi-objective statistical approach. Four key process parameters—infill density (Id), material flow rate (Mf), wall line count (Wlc), and infill pattern (Ip)—were systematically varied using a Taguchi L₁₆ orthogonal array. Tensile strength (Ts), flexural strength (Fs), and material consumption (Mc) were selected as the critical response metrics. Grey Relational Analysis (GRA) was used to aggregate these responses into a single performance index, and ANOVA determined each factor’s contribution. The optimal combination of 60% infill density, 70% material flow, 4 wall lines, and line infill pattern yielded a 9.02% improvement in the overall performance index compared to the baseline, with corresponding Ts and Fs values of 13.58 MPa and 20.51 MPa. Mf and Wlc were the most influential parameters on mechanical behavior, while Id mainly affected Mc. These findings confirm that integrating Taguchi and GRA enables effective parameter tuning for LW-PLA, balancing strength and efficiency. This work contributes to the development of lightweight, high-performance parts suitable for functional applications such as UAVs and prototyping. Full article

Waste glass recycling generates waste streams such as fine glass fraction, waste ceramics containing fine glass, and waste polyethylene plastics. All of the aforementioned streams contain contaminants of organic and inorganic origin that are difficult to remove. This research was conducted to determine technological processes aimed at achieving a circular economy (CE) in the recycling of waste glass. Foam glass was made from the fine-grained, multicolored fraction of contaminated glass, an effective method for recycling glass waste at a low cost. A frothing system based on manganese oxide (MnO₂) and silicon carbide (SiC) was proposed, and an optimum weight ratio of MnO₂/SiC equal to 1.0 was determined. The possibility of controlling the process to achieve the desired foam glass densities was demonstrated. Statistical analysis was used to determine the effect of the MnO₂/SiC ratio and MnO₂ content on the density of the resulting foam glass products. Waste ceramics contaminated with different-colored glass were transformed into ceramic–glass granules. The characteristic temperature curve of the technological process was determined. The metal content in water extracts from ceramic–glass granules and pH value indicate their potential use for alkalizing areas degraded by industry and agriculture. Waste polyethylene-based plastics were converted into polyethylene waxes by thermal treatment carried out in two temperature ranges: low temperature (155–175 °C) and high temperature (optimum in 395 °C). The melting temperature range of the obtained waxes (95–105 °C) and their FTIR spectral characteristics indicate the potential application of these materials in the plastics and rubber industries. The integrated management of all material streams generated in the glass recycling process allowed for the development of a CE model for the glass recycling plant. Full article

Hierarchically porous polymers can unite macro-scale architected voids with micro-scale pores, enabling unique combinations of low density, high surface area, and controlled transport properties that are difficult to achieve with traditional methods. This review outlines the current advancements in creating such multiscale architectures using fused filament fabrication (FFF), the most widely used polymer additive manufacturing technique. Unlike earlier reviews that consider lattice architectures and foaming chemistries separately, this work integrates both within a single analysis. It begins with an overview of FFF fundamentals and how process parameters affect macropore formation. Design strategies for achieving macroporosity (≳100 µm) with a single thermoplastic are presented and categorized: 2D infill patterns, strut-based lattices, triply periodic minimal surfaces (TPMS), and Voronoi structures, along with functionally graded approaches. The discussion then shifts to functional filaments incorporating chemical or physical blowing agents, thermally expandable or hollow microspheres, and sacrificial porogens, which create microporosity (≲100 µm) either in situ or through post-processing. Each material approach is connected to case studies that demonstrate its application. A comparative analysis highlights the advantages of each method. Key challenges such as viscosity control, thermal gradient management, dimensional instability during foaming, environmental concerns, and the absence of standardized porosity measurement techniques are addressed. Finally, emerging solutions and future directions are explored. Overall, this review provides a comprehensive perspective on strategies that enhance FFF’s capability to fabricate hierarchically porous polymer structures. Full article

Numerous thermal practical applications utilize shell and tube heat exchanger appliances to transfer heat energy between hot and cold working fluids. Incorporating metal foam to the outer periphery of inner tube improves the heat transfer process from hot water in the tube side to cold water in the shell side and consequently improves heat exchanger performance. In this study, the integration of use of a porous material together with designing a robust adaptive controller could efficiently regulate the outlet cold water temperature to the desired value. This is achieved with respect to the time required for cold water to reach the desired temperature (settling time) and the amount of hot water volume flow during a certain time span. A barrier function-based adaptive sliding mode controller (BF-based adaptive SMC) is proposed, which requires only the information of temperature measurement of cold water. The stability of BF-based adaptive SMC is proved utilizing Lyapunov function analysis. The effectiveness of proposed controller is verified via numerical results, which showed that the proposed controller could achieve considerable accuracy of cold water temperature using suitable design parameters. In addition, the robustness of controller against variation in inlet temperature is also verified. Another improvement to performance of heat exchanger system is achieved by adding the metal foam of aluminum material on inner pipe perimeter with wide range of metal foam to outer inner pipe diameters ratio ($1\le s\le 1.8$). The results showed that the settling time is significantly reduced which enables outlet cold water to reach the required temperature faster. With respect of the case of non-adding metal foam on inner pipe outer circumference, when $s=1.2$, the settling time and hot water temperature are reduced by $1/2$ and $17.3\%$, respectively, while for $s=1.8$, they are decreased by $\le 1/20$ and $35.3\%$ correspondingly. Accordingly, the required volume flow for hot water is reduced considerably. Full article

Foams, as a type of porous materials, have found broad functional and structural application in heat and sound insulation, the mitigation of mechanical vibrations and impacts, packaging, etc. This paper aims to comprehensively review recently developed biobased foams (BBFs) with a comparison with their counterparts—namely, synthetic polymer foams—in terms of their foaming methods, physical and mechanical properties, and broad applications. A brief introduction to general foams, polymeric foams, and BBFs is provided, followed by a comparison of the related foaming methods; physical, mechanical, and chemical properties; and current and prospective applications. Several main polymer foaming methods (e.g., physical, chemical, and mechanical foaming) and their unique features are further examined in detail. The structure-related properties of polymeric foams (e.g., mass density, thermal conductivity, and rate effects in mechanical responses) are discussed, and the fundamental linearly viscoelastic models are summarized to account for the simple rate effect in the mechanical moduli of polymeric foams under varying loading rates. Furthermore, specific focus is placed on the foaming processes and material properties of sustainable BBFs (e.g., soybean-based, corn-based, and starch-based foams) and their potential to substitute conventional synthetic polymer foams. The technical challenges in processing BBFs are discussed, and the most promising applications of BBFs are then considered. Full article

Cellulose aerogel is a promising thermal insulation material with terrific thermal insulation and environmental friendliness. However, the intrinsic flammability of polysaccharide molecules and dependence on freeze-drying have limited its application in flame-retardant and thermal management systems. Here, we develop a flame-retardant biomass aerogel based on a dual-network matrix of bacterial cellulose and sodium alginate. This innovative material enables high-efficiency and low-cost preparation via ambient pressure drying technology (only ~3.5% volume shrinkage), while achieving flame retardancy by introducing an inorganic nanosheet microstructure within a polymer matrix. The resulting dual-network flame-retardant cellulose aerogel demonstrates thermal performance superior to that of most polymer foams and conventional cellulose aerogels, featuring an ultra-low thermal conductivity of ~0.04 W m⁻¹ K⁻¹ and a high limiting oxygen index (LOI) of ~69%. This research provides a novel strategy for simultaneous flame-retardant modification and energy-efficient manufacturing of biomass-derived aerogels. Full article

This study aims to screen out high-yield protease lactic acid bacteria (LAB) from cheese and analyze the flavor and functional characteristics of their fermentation of corn protein hydrolysate (CPH). Lacticaseibacillus rhamnosus ZYN-71 and Limosilactobacillus fermentum ZYN-76 were isolated and screened by traditional biological methods. Then, the two strains synergistically fermented CPH, and it was found that the scavenging rate of DPPH, ·OH, and O²⁻· and the chelating ability of Fe²⁺ of the fermented CPH increased by 22.85%, 3.82%, 63.37%, and 43.27%, respectively. Meanwhile, the solubility, water-holding capacity, oil-holding capacity, foaming property, foam stability, emulsification property, and emulsification stability had also been improved to varying degrees. The aroma of the CPH after fermentation mainly consisted of aldehydes (20.2%) and nitrogen heterocyclic compounds (19.4%), and the content of off-flavor components was reduced. LAB fermentation effectively improves the practical problems existing in the current application of corn proteolytic products. This research can provide a research basis for corn protein-related products. Full article

This article discusses the current requirements for laboratory testing of the fire properties of seating in railway vehicles and the criteria for their assessment. The results of flammability and smoke tests performed on selected passenger seats and samples of the upholstery systems used in their construction are presented in order to find connections between them. It was demonstrated that the composition of the upholstery fabric has a significant impact on the burning behavior of the seats and the upholstery systems themselves, assuming that the same foam was used in their construction. Based on the conducted research, material composition analysis, and results, a lack of correlation was also found between the results of tests using a cone calorimeter and a furniture calorimeter. This confirms that the fire properties of upholstered products depend on many factors, including composition, shape, materials used, type of upholstery, and the design solutions of the finished seats. The tested upholstered products intended for railway applications are characterized by stochastic variability resulting from their specific applications and functional and operational properties. Full article

This study systematically analyzes the influencing factors and optimization strategies of foam stability and performance for CO₂-soluble foaming agents in high-temperature and high-pressure (HTHP) complex reservoir environments. By constructing a HTHP experimental system and utilizing dynamic foam testing, interfacial tension analysis, and microscopic observation of liquid films, the effects of chemical factors (e.g., pH, foaming agent concentration, stabilizer synergy) and physical factors (e.g., temperature, pressure) on foam behavior are investigated. The results show that the nonionic surfactant E-1312 exhibits optimal foam performance in neutral to mildly alkaline environments. The foam performance tends to saturate at around 0.5% concentration. High pressure enhances the foam stability, whereas elevated temperature significantly reduces the foam lifetime. Moreover, the addition of nano-sized foam stabilizers such as silica (SiO₂) can significantly delay liquid film drainage and strengthen interfacial mechanical properties, thereby improving foam durability. This study further reveals the key mechanisms of CO₂-soluble foaming agents in terms of interfacial behavior, liquid film evolution, and foam formation in porous media, providing theoretical guidance and optimization pathways for the molecular design and field application of CO₂ foam flooding technology. Full article