Search Results (292)

Conventional cement-based grouts used to stabilize fractured rock slopes and fill large cavities are heavy, carbon-intensive, and can impose excessive dead load on weakened rock masses. This study addresses these limitations by integrating bio-based rigid polyurethane—particularly castor oil-based polyurethane—into a slag-based geopolymer mortar, producing a lightweight, low-permeability, rock-adherent alternative grouting system. Three formulations were evaluated: unmodified geopolymer grout (GG), geopolymer grout modified with petroleum-based polyurethane (G-PUG), and geopolymer grout modified with castor oil-based polyurethane (GCO-PUG). Materials were characterized using infrared spectroscopy, thermogravimetric analysis (TGA), X-ray diffraction, and scanning electron microscopy with energy-dispersive X-ray spectroscopy, and tested for apparent density, permeability, unconfined compressive strength, and direct shear behavior—including at the grout–limestone interface using rock sourced from El-Mokattam plateau, Cairo. Polyurethane incorporation reduced apparent density by up to 24% (from 22.15 to 16.89 kN/m³) and permeability to as low as 2.3 × 10⁻⁸ m/s, at the cost of a substantial reduction in compressive strength (from 5564 to 139 kN/m²). The castor oil-based grout also showed improved rock adhesion, with interfacial cohesion increasing by 67% relative to its standalone state. Accordingly, unmodified GG is recommended for high-load structural applications, whereas GCO-PUG provides a lightweight, low-permeability, and strongly rock-adherent alternative for filling large cavities and stabilizing slopes under moisture-sensitive and weight-critical conditions, where reducing self-weight and limiting water ingress are more important than achieving maximum compressive strength. Full article

Contact-surface construction affects pressure distribution, physiological response, and perceived comfort in body-contact furniture. This study compared five contact interfaces for classroom nap chairs: rigid polypropylene (PP), a thermoplastic polyurethane (TPU)-surfaced PP laminate, woven mesh, closed-cell ethylene-vinyl acetate (EVA) foam, and flexible polyurethane (PU) foam. Twenty-six participants, including 13 females and 13 males, were tested in a 95° study posture and a 135° nap posture at the head–neck, waist–back, and hip–thigh regions. Four participant-level pressure indicators were direction-corrected and combined using an equal-weight geometric mean. The pressure index was integrated with electrodermal activity (EDA) at the participant level and subsequently combined across postures with weak subjective calibration. Under the 95° posture, EVA foam ranked highest at the hip–thigh region, while PU foam ranked highest at the waist–back and head–neck regions. Under the 135° posture, woven mesh ranked highest at the hip–thigh and head–neck regions, while PU foam remained highest at the waist–back region. Final integrated suitability differed significantly among materials in all three body regions (Friedman χ² (4) = 90.246–96.769, all p < 0.001). M4 had the highest mean in the head–neck region (0.648), but did not differ significantly from M5 (0.634; Holm-adjusted p = 0.075). M5 had the highest mean in the waist–back region (0.821), and M3 in the hip–thigh region (0.679); both were significantly higher than the corresponding second-ranked interfaces (Holm-adjusted p < 0.001). Exploratory stiffness models indicated peak locations near 130 kPa for the head–neck region and 140 kPa for the hip–thigh region, whereas the waist–back response was highest at the lower measured boundary of 70 kPa. These findings support region-specific interface design rather than a uniform contact surface for the entire chair. Full article

Rigid polyurethane foams (RPUFs) are widely used as lightweight thermal insulation materials. Their properties can be improved by incorporating inorganic fillers. However, the effect of filler particle size has not been sufficiently investigated. This study examines the influence of aluminosilicate microsphere diameter (80, 150, 300, and 500 μm) on the properties of RPUFs. Foams containing 10 wt.% microspheres (M) were prepared by the free-rise method. Their cellular structure, apparent density, mechanical, acoustic, thermal, and thermomechanical properties were evaluated. The addition of microspheres reduced the average cell diameter from 184 ± 29 μm for PU_0 to 147–174 μm, depending on microsphere size, and increased the apparent density from 31.3 to approximately 37 kg·m⁻³. The compressive strength decreased from 186 ± 6 kPa for PU_0 to 159 ± 2 kPa for PU_500M, whereas the tensile strength increased from 257 ± 14 kPa for PU_0 to 323 ± 14 kPa for PU_500M. The highest average sound absorption coefficient (0.14) was obtained for PU_300M, representing a 75% improvement over PU_0 (0.08). The composites also showed improved thermal stability and storage modulus. Among the investigated composites, PU_300M exhibited the most balanced combination of mechanical and acoustic properties. Full article

Rigid polyurethane foams are used in impact-attenuation systems due to their tunable cellular structure and energy dissipation capacity. However, expanded polystyrene (EPS), commonly used for impact protection, presents limitations related to impact attenuation performance and limited design flexibility. This study evaluates the impact performance of rigid polyurethane foams modified with diethanolamine and assesses formulation efficiency using Data Envelopment Analysis (DEA). Rigid PU foam formulations containing 0–3 wt% DEOA were synthesized and characterized by impact testing, apparent density measurements, Scanning Electron Microscopy, Fourier Transform Infrared Spectroscopy, and Thermogravimetric Analysis/Derivative Thermogravimetry. DEA was applied to correlate diethanolamine content with impact absorption efficiency. Excessive crosslinking and reduced energy dissipation were observed above 2 wt%, while concentrations below 0.5 wt% resulted in poorly structured foams. The formulation containing 1 wt% DEOA was identified as the most efficient among the investigated formulations, exhibiting the best overall performance, reducing transmitted peak acceleration by 13.8% compared with neat PU foam, while exhibiting an approximately 48% increase in apparent density, more complete consumption of NCO groups, a more uniform cellular structure, and only modest changes in thermal degradation behavior. These findings indicate that the improved impact performance is associated with the combined effects of increased apparent density, modified cellular morphology, and changes in the polyurethane network promoted by DEOA, underscore the promise of diethanolamine-modified rigid polyurethane (PU) foams for protective applications. Full article

Rigid polyurethane foam was evaluated as a filler material for a tubular railway vehicle energy absorber. Cubic samples cut from a cylindrical PU foam sample with a density of 175 kg/m³ were tested under quasi-static uniaxial compression to determine the material’s compressive response and provide input data for finite element modelling. The experimental results showed a non-linear stress–strain response typical of cellular foams, while samples from the central region of the cylinder exhibited a lower stress response than those from the outer region. An Ogden foam material model was calibrated in Ansys using compression data obtained by experimental tests and then applied to numerical models of three absorber configurations: an empty steel tube, a fully foam-filled steel tube, and a foam-filled tube with an additional concentric steel core. The simulations compared the force–stroke response and absorbed energy of each configuration under quasi-static axial loading through a conical bushing. Over a 60 mm stroke, compared to the empty tube, the fully foam-filled tube absorbed an additional 16% energy and the concentric-core configuration absorbed an additional 9.5%. These results indicate that rigid PU foam filling can improve the quasi-static energy absorption capacity of tubular railway collision absorbers. Full article

The construction sector’s substantial contribution to global energy consumption and CO₂ emissions motivates the development of bio-based alternatives to fossil-derived rigid polyurethane (PUR) foam cores in structural sandwich panels. This study presents a comprehensive comparison of plywood sandwich panels manufactured with a rigid PUR foam containing a fast pyrolysis bio-oil (FPBO)-derived sugar polyol diluted with triethyl phosphate and panels of identical topology produced with a commercial reference PUR foam. In the bio-based formulation, a fraction of the sorbitol-based polyether polyol was replaced with the FPBO-derived sugar polyol. Both systems were characterized at the foam and panel levels for cellular microstructure, skeletal and envelope density, thermogravimetric stability, flammability, color, thermal conductivity and heat capacity, internal bond strength, compressive properties, and normal-incidence sound absorption and transmission loss. The newly developed foam exhibited similar skeletal density and porosity to the reference, comparable thermogravimetric stability with a slightly higher char residue, and lower thermal conductivity across the tested temperature range. Mechanical properties, including compressive strength, compressive modulus, and internal bond strength, showed minor reduction but remained within a comparable range. A distinct color change was observed, attributable to the presence of chromophoric constituents of the FPBO fraction. Overall, the results indicate that partial substitution of the fossil polyol with an FPBO-derived sugar polyol is technically feasible, yielding materials with comparable thermal, mechanical, or acoustic performance. No consistent performance advantage of either system was observed across the evaluated properties. The results support the potential of pyrolysis-derived bio-polyols for use in sustainable structural insulation products. Full article

The study presents the results of research on the preparation of biopolyols based on organosolv lignin and their application in the synthesis of rigid polyurethane foams. The research was conducted in order to develop a sustainable alternative to the previously used ethylene carbonate in lignin oxyalkylation processes. The main objective was to replace the previously used ethylene carbonate with propylene carbonate in a stoichiometrically equivalent molar amount in order to reduce polyol viscosity and improve the performance properties of the resulting foams. The syntheses were carried out without the need for isolation and purification of intermediate products. Polyols analogous to those described previously were obtained and subsequently used for the preparation of rigid polyurethane foams employing polymeric diphenylmethane diisocyanate. The properties of the obtained foams were investigated and compared with those of foams prepared from ethylene carbonate-based polyols. The results demonstrated that the use of propylene carbonate leads to the formation of lower-viscosity polyols, facilitating homogenization of the reaction systems and enabling the production of foams with advantageous performance characteristics, generally superior to those of foams based on ethylene carbonate. The obtained materials constitute a promising alternative to conventional polyurethane foams derived from petrochemical raw materials. Full article

Various forms of Bacopa monnieri (BM), including original powder (Mp), tea form (Mo), and post-extraction residues (Mf), were used as natural bio-based additives in rigid polyurethane–polyisocyanurate (RPU/PIR) foams. The study investigated the influence of BM form and content on the physical, mechanical, thermal, and flammability properties of the foams. The results demonstrated that both the type and concentration of BM significantly affected foam performance. Foams containing Mf exhibited the lowest apparent density and reduced brittleness, whereas foams modified with Mp showed the highest compressive strength. The incorporation of BM also contributed to reduced flammability and enhanced thermal resistance of the foams. Thermal analysis indicated that BM additives modified the degradation behavior of RPU/PIR foams by promoting char formation and improving thermal stability at elevated temperatures. In particular, samples containing tea and post-extraction residues showed increased stability of the carbonized residue during the final degradation stage. The most favorable overall properties were obtained for BM contents between 3 and 7 wt%, while higher filler concentrations negatively affected the structural integrity of the foam matrix. The results confirm that the performance of RPU/PIR foams strongly depends on the balance between matrix continuity and biofiller functionality. The obtained materials show potential for application in floristry products and lightweight insulating systems where low density, dimensional stability, and enhanced thermal resistance are required. Full article

This study investigates the sampling sufficiency required for accurately characterizing the morphological properties of rigid polyurethane foams across three distinct regions: core, crown, and lateral edge. A total of 200 individual cells were analyzed from 30 SEM micrographs, enabling the quantification of cell length, cell width, anisotropy index, linear cell density, and shape index. Average cell length ranged from 715 to 763 μm, while cell width varied between 386 and 531 μm depending on the region. The anisotropy index increased from 0.186 in the core to 0.289 in the lateral edge, indicating progressively more elongated cells. Linear cell density showed a marked decrease from 0.062 in the core to 0.001 in the crown, reflecting differences in cellular packing. Shape index values remained relatively stable, confirming its lower sensitivity to structural variations. Monte Carlo simulations were employed to evaluate sampling sufficiency for sample sizes ranging from 2 to 30. Results demonstrated that optimal sample sizes varied with foam region and parameter: 16 cells were sufficient for core and lateral regions, whereas up to 22 cells were required for the crown to capture higher structural heterogeneity. For anisotropy and shape indices, sufficient sampling ranged between 13 and 20 cells depending on the region. The results confirm that the core exhibits lower variability (CoV for cell length: 29.1%) compared to the crown (36.4%) and lateral edge (34.9%), supporting its more homogeneous structure. However, exclusive sampling from the core may lead to biased characterization, as crown and lateral regions display significantly higher variability in both geometry and orientation. These findings establish quantitative guidelines for sampling strategies in polyurethane foam morphology, contributing to improved reproducibility and reliability in structure–property investigations of cellular materials. Full article

Suberinic acids (SA) derived from birch outer bark are renewable feedstocks for bio-based polyols suitable for rigid polyurethane (PU) foams. Three SA fractions were prepared under different depolymerization conditions: acidification at pH 1 (SA1), pH 5 (SA2), and FeCl₃-assisted treatment (SA3), and their chemical composition was analysed by GC–MS, Py–GC/MS, and GPC–RID. Polyols derived from tall oil fatty acids (TOFA) or epoxidized TOFA with trimethylolpropane were used as the sole polyol components in foam formulations. The SA fractions differed in molecular weight distribution, affecting polyol processability. All foams exhibited similar limiting oxygen index (19–20) and cone calorimetry results, showing no statistically significant differences in flammability. This indicates that variations in depolymerization conditions, including polyphenolic content and removal of higher-molecular-weight fractions during FeCl₃ treatment, do not dominate fire performance under the studied conditions. SA3-based polyols showed the lowest viscosity and produced foams with optimal mechanical and thermal properties, while SA1 offered higher yield with comparable performance. These results demonstrate the feasibility of converting SA fractions into functional polyols for rigid PU foams and highlight the FeCl₃-treated SA3 fraction and SA1 as the most promising candidates for further development. Full article

This study evaluates the performance of foamed geopolymer concrete (FGC) incorporating rigid polyurethane (PU) waste as a partial sand replacement and aluminum powder (AP, 1%) as a foaming agent. The mixtures were based on metakaolin, fly ash, and silica fume. Fresh and hardened properties were assessed, including workability, setting time, density, compressive strength, flexural strength, splitting tensile strength, elastic modulus, water absorption, porosity, gas permeability, and chloride ion penetration. Microstructural characteristics were examined using scanning electron microscopy (SEM). The results show that moderate PU incorporation significantly enhances mechanical performance. The optimal mixture (PU30) achieved a compressive strength of 47.25 MPa at 180 days, representing a 15.6% increase compared to the control. Flexural and splitting tensile strengths improved by 19.9% and 16.7%, respectively, while the elastic modulus increased by 33.8% to 0.95 GPa. These improvements are attributed to enhanced particle packing and more efficient stress transfer within the matrix. In contrast, higher PU contents (>30%) reduced mechanical performance due to increased total porosity and weakened interfacial bonding. Durability-related properties indicated that mixtures PU20–PU30 exhibited reduced permeability and optimized pore structure, characterized by lower pore connectivity. SEM observations confirmed a denser matrix with uniformly distributed pores at optimal PU levels. Additionally, the integration of Random Forest regression with GLCM-based texture analysis demonstrated strong capability in predicting mechanical properties from SEM images. Overall, the combined use of PU waste and AP enables the production of lightweight, structurally efficient, and sustainable FGC with improved mechanical and durability performance. Full article

Articular fractures require precise anatomical reduction and rigid fixation to heal appropriately. In veterinary cases that involve fracturing of the lateral humeral condyle, cortical bone screws inserted in lag fashion with Kirschner wire are the preferred method for surgical fixation. However, relatively high complication rates associated with cortical lag screws (CLSs) highlights the need to investigate alternate screw designs. Variable-pitch headless compression screws (VPHCSs) are unique as they advance beneath the cortical surface. Although the use of VPHCSs are widely utilised in human orthopaedics, the current use in veterinary orthopaedics is limited. This study aimed to evaluate the peak interfragmentary force (PIF) and area of compression (AOC) generated by a 3.5 mm self-tapping cortical screw placed in lag fashion and a 3.5 mm VPHCS inserted to four depths. PIF and AOC were measured using a pressure-sensitive film placed between two blocks of polyurethane foam (0.24 g/cm³), simulating a transverse fracture. CLSs were inserted by hand into predrilled 2.5 mm pilot holes. PIF and AOC were measured at full insertion. VPHCSs were placed into predrilled 2.5 mm pilot holes, followed by a 3.5 mm tapered countersink. The screw was inserted until the head was level with the surface. PIF and AOC were measured between the two blocks. The screw was continued until the head was at a depth of 2, 5, and 9 mm below the surface, and the PIF and AOC were measured again at each stage. There was no detectable difference in PIF and AOC between CLSs and VPHCSs countersunk to −2 mm (PIF–CLS: Mean = 12.886, SD = 2.370; 2 mm: Mean = 17.301, SD = 8.858, p = 0.319; AOC–CLS: Mean = 0.936, SD = 0.291; 2 mm: Mean = 0.925, SD = 0.447, p = 0.872). VPHCSs countersunk to −5 mm and −9 mm produced significantly greater PIF compared to CLSs (5 mm: Mean = 16.086, SD = 6.799, p = 0.002; 9 mm: Mean = 34.987, SD = 4.015, p < 0.001). VPHCSs countersunk to −5 and −9 mm produced significantly greater PIF and AOC compared to CLSs in this model. Further investigation is required to produce recommendations for clinical use. Full article

The need to reduce polyurethane (PU) foam waste has encouraged the development of sustainable foam formulations based on recycled raw materials and environmentally friendly additives, addressing both waste management and comparable foam properties to those based on fossil resources. In the present investigation, more sustainable water-blown rigid PU foams were investigated using recycled polyol and halogen-free flame retardants (FRs) for fire-resistant insulation applications. Two series of foam formulations were prepared: a first series with virgin polyol and the inclusion of a halogen-free FR additive (6 wt%) and a second series with recycled polyol (10% added respect to the total polyol) and halogen-free FR additives (6 wt%). Two types of FR were used: FR900, specifically identified as 3,9-Dimethyl-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane-3,9-dioxide, in powder form with 24% phosphorus content and reactive polyol based FR140, an oligomeric ethyl ethylene phosphate, in liquid form with 19% phosphorus content. The density, cellular structure, aged thermal conductivity, dimensional and hydrolytic stability, fire properties, and mechanical properties were characterized for novel foamed systems. Rigid foamed materials with very low densities around 50 kg/m³ were obtained. On the one hand, the inclusion of FR900 into the PU formulation containing virgin polyol generated foam with the lowest thermal conductivity (36.10 mW/mK) due to the smaller open cell content (11.7%) and cell size reduction (433 microns). On the other hand, the inclusion of recycled polyol reduced the foam density by 6 kg/m³ (44.1 kg/m³), increased the cell size average (848 microns) and open cell content (15.1%), maintained thermal conductivity (38.73 mW/mK), slightly improved the fire properties, and worsened the mechanical properties in comparison with the PU reference containing only virgin polyol. The results obtained by the foam containing recycled polyol and 6% FR900 are remarkable, presenting an increase in density (50.3 kg/m³) and in open cell content (73%), but a very high reduction in cell size (465 microns) and thus a low value of thermal conductivity of 37.04 mW/mK with respect to the reference material containing recycled polyol. Moreover, this PU foam containing recycled polyol and FR900 offered improved fire resistance (148.2 kW/m² of Maximum Average Rate of Heat Emission (MARHE), 179.1 kW/m² of Maximum Heat Release Rate (HRRmax), and 24.6 MJ/m² of Total Heat Release (THR)) and mechanical properties (6.97 MPa of Young’s modulus and 0.24 MPa of collapsed stress) for the construction sector. The inclusion of FR140 does not improve the properties of the foam system containing recycled polyol, mainly due to the deterioration of the cellular structure (in the open cell content and cell size). Full article

Rigid polyurethane foams are often manufactured in sealed molds, so knowledge of the density distribution in the molded blocks is essential. A study was conducted with the aim to estimate density distribution within a rigid polyurethane foam block (average core density of ≈96 kg/m³) manufactured in a rectangular sealed mold. The density of 150 rectangular samples was determined experimentally. Characteristic locations of the foams’ columns in the block were outlined, having similar foaming conditions. Averaged density in the characteristic columns was calculated for each characteristic location. A mathematical model was developed based on density data of characteristic columns, approximated with second- and third-degree polynomials. Density distribution was calculated, and corresponding color charts with density zones and equidensity lines were constructed for six horizontal and two vertical sections of the block. It was found that the common center of the elliptical equidensity lines is located asymmetrically, ≈17 mm above the geometric center of the untrimmed block. Density gradients were calculated in directions parallel and perpendicular to the foams’ rise direction. The developed mathematical model allowed us to estimate density distribution within the rigid polyurethane foam block manufactured in a rectangular sealed mold. Full article

Polymer-based insulation materials are widely used to enhance the energy efficiency of buildings; however, their growing application raises concerns related to resource use and end-of-life management. Rigid polyurethane (PUR) foams are key core materials in structural insulated panels due to their favorable thermal and mechanical performance, yet their life cycle environmental impacts—particularly at end-of-life—remain insufficiently quantified. In this study, a cradle-to-grave life cycle assessment (LCA) of PUR-based insulation used in structural insulated panel systems is conducted in accordance with ISO 14040/44 and EN 15804 standards. The assessment is performed using Sphera LCA software (version: GaBi 10.5) and the CML 2016 impact assessment method. Formulation-level variations in rigid PUR foams, including changes in methylene diphenyl diisocyanate content and pentane blowing agent ratio, are explicitly incorporated to evaluate their influence on key environmental impact categories. The results indicate that increasing pentane content leads to higher global warming potential, while this effect may be mitigated or intensified by concurrent changes in diisocyanate content and foam density in fully formulated systems. Three end-of-life scenarios—landfilling, incineration with energy recovery, and mechanical recycling—are analyzed. The findings provide material-level, decision-relevant insights that support environmentally informed formulation strategies and contribute to the development of more circular polymer-based insulation solutions for the built environment. Full article