Search Results (216)

To investigate the impermeability of foam concrete in various challenging environments, this study evaluates its water resistance by measuring the water contact angle and water absorption. Polyurethane (PU) was used to fabricate polyurethane foam concrete (PFC), enabling a monolithic hydrophobic modification to improve the permeation performance of foam concrete. The study also examines the effects of carbonation and freeze–thaw environments on the permeation resistance of PFC. Graphene oxide (GO), KH-550, and a composite hydrophobic coating (G/S) consisting of GO and KH-550 were employed to enhance the permeation resistance of PFC through surface hydrophobic modification. The functionality of the G/S composite hydrophobic coating was confirmed using energy dispersive X-ray spectrometry (EDS) and Fourier transform infrared spectroscopy (FTIR). The results showed the following: (1) The water contact angle of PFC increased by 20.2° compared to that of ordinary foam concrete, indicating that PU-based hydrophobic modification can significantly improve its impermeability. (2) After carbonation, a micro–nano composite structure resembling the surface of a lotus leaf developed on the surface of PFC, further enhancing its impermeability. However, freeze–thaw cycles led to the formation and widening of microcracks in the PFC, which compromised its hydrophobic properties. (3) Surface hydrophobic modifications using GO, KH-550, and the G/S composite coating improved the anti-permeability properties of PFC, with the G/S composite showing the most significant enhancement. (4) GO filled the tiny voids and pores on the surface of the PFC, thereby improving its anti-permeability properties. KH-550 replaced water on the surface of PFC and encapsulated surface particles, orienting its R-groups outward to enhance hydrophobicity. The G/S composite emulsion coating formed a hydrophobic silane layer inside the concrete, which enhanced water resistance by blocking water penetration, reducing microscopic pores in the hydrophobic layer, and improving impermeability characteristics. Full article

In this study, we tested a flexible polyurethane (PU) foam, synthesized from bio-based components, for the removal of petroleum-derived fuels from water samples. The PU was synthesized via the prepolymer method through the reaction of PEG 400 with L-lysine ethyl ester diisocyanate (L-LDI), followed by chain extension with 2,5-bis(hydroxymethyl)furan (BHMF), a renewable platform molecule derived from carbohydrates. Freshwater and seawater samples were artificially contaminated with commercial diesel, gasoline, and kerosene. Batch adsorption experiments revealed that the total sorption capacity (S, g/g) of the PU was slightly higher for diesel in both water types, with values of 67 g/g in freshwater and 70 g/g in seawater. Sorption kinetic analysis indicated that the process follows a pseudo-second-order kinetic model, suggesting strong chemical interactions. Equilibrium data were fitted using Langmuir and Freundlich isotherm models, with the best fit achieved by the Langmuir model, supporting a monolayer adsorption mechanism on homogeneous surfaces. The PU foam can be regenerated up to 50 times by centrifugation, maintaining excellent performance. This study demonstrates a promising application of this sustainable and bio-based polyurethane foam for environmental remediation. Full article

Polyurethane (PU) foam, renowned for its structural versatility, elasticity, compressibility, and adaptability, has garnered significant attention for its use in flexible strain sensors due to its capability to detect mechanical deformation. This review presents a comprehensive analysis of both the studies and recent advancements in PU foam-based strain sensors, particularly those incorporating conductive materials. The review begins by examining the chemical composition and structural characteristics of PU foam, followed by a discussion of various fabrication methods and their effects on sensor performance. It also explores the sensing mechanisms, including piezoresistive, piezoelectric, and capacitive effects. Moreover, key applications in motion detection, health monitoring, and environmental and industrial sensing are examined. Finally, the review addresses technological advancements, current challenges, and prospects. Full article

Marine oil spills have caused significant environmental problems. Among the array of clean-up methods, the utilization of sorbents emerges as promising for removing and recovering oil from spills. Developing cost-effective, reliable, and eco-friendly material that efficiently and sustainably removes oil from water is increasingly seen as crucial and pressing. In the present study, we report the development of coco-polyurethane (PU) foam (CCF) through the conventional foaming process using varying amounts of coconut-oil-derived polyol (CODP) in a PU matrix. Characterization of the foams showed an increased ester band with the incorporation of COPD into the polyurethane networks and no direct influence of the cell size distribution on the surface morphology. Furthermore, this study highlighted the increasing CODP in every CCF formulation, showing high oil sorption and low water uptake due to its porous structure. The experimental results revealed that CCF is a potential candidate sorbent for the recovery of spilled oil. This signifies a significant leap towards reducing the dependency on petroleum in developing sorbent materials and advancing sustainable responses to oil spills in marine environments. Full article

Polyurethanes (PUs) are extremely versatile materials used across different industries. Traditionally, they are synthesized by reacting polyols and isocyanates, both of which are petroleum-derived reagents. In response to the demand for more eco-friendly materials, research has increasingly focused on developing new routes for PU synthesis using renewable feedstocks. While substituting isocyanates remains a greater challenge, replacing fossil-based polyols with bio-based alternatives is now a promising strategy. This review explores the main natural sources and their transformations into bio-polyols, the incorporation of bio-fillers into PU formulations, and the production of non-isocyanate polyurethanes (NIPUs). Additionally, the study summarizes the growing body of research that has reported successful outcomes using bio-polyols in PU foams for distinct applications. Full article

The accelerated weathering of polyurethanes (PUs) is a process induced by exposure to ultraviolet (UV) radiation, resulting in the breakdown of chemical bonds and consequent changes in the material’s properties. The reason for this phenomenon is the oxidation, by free radicals, of the polymeric structure, caused by the absorption of energy by the chromophores present in it. This paper studies the accelerated weathering of PU foams synthesized by linseed and passion fruit oil (OL and PFO, respectively), prepared with 0.8 and 1.2 [NCO]/[OH] ratios. After weathering, the samples were analyzed by Fourier transform infrared spectroscopy (FTIR), stereomicroscopy, thermogravimetry (TG), and derivative thermogravimetry (DTG). After the accelerated weathering process, changes were observed in the FTIR spectra of the PU samples compared to the spectra of the original PUs, indicating that the process occurred, even if partially. TG/DTG analysis of the photoaged PUs showed that the degradation process had started, as these materials presented lower thermal stability than the original PUs. Full article

The growing production of polyurethane foam (PUF) and increasing global PUF waste generation urges the development of a circular economy strategy to promote the recovery of its raw materials, namely polyether polyols, in a sustainable and economically feasible way. This work assesses the promising microwave-assisted PUF aminolysis technology from three different perspectives: (a) evaluating the experimental feasibility and characteristics of the recycled products; (b) modeling an industrially relevant holistic process based on experimental findings to assess energy requirements and c) comparing the environmental impacts ascribed to the production of virgin vs. recycled polyols. The most relevant findings are as follows: (1) the recycled polyols out of MW-aminolysis are indistinguishable from virgin polyols; (2) the potential energy consumption of the overall process (including post-processing steps) for a continuous PUF depolymerization process with a 14.8 kg/h RP production capacity is as low as 1.9 kWh/kg RP and (3) recycled polyols have a substantially lower environmental footprint than virgin polyols in all selected impact categories, ranging from a reduction in CO₂ emissions (38% decrease) to water consumption (74% decrease). These results and analyses pave the way for enhancing material circularity in the PU sector. Full article

Open-cell PU foams have a wide range of industrial applications due to their excellent cushioning, impact protection, packaging, thermal insulation, and sound reduction benefits. The foams absorb impact energy while deforming under compressing and are ideal for applications with severe and repeated loading conditions. Enhancing and improving their compressive durability is a vital area of ongoing research. We investigated the effect of incorporating shear-stiffening polymers (SSPs) and shear-thickening fluids (STFs) on the compression properties of open-cell foams. Rheological properties of STFs and SSPs prepared for incorporation into the foams confirmed the shear-thickening and shear-stiffening characteristics. Quasi-static compression tests performed at different speeds (6, 60, 120, 180, and 240 mm/s), as well as load-unload compression tests (6 and 24 mm/s), showed that the SSP-filled foam exhibited the most pronounced improvement in the elastic, plateau, and densification regions compared to the neat foam. While the STF-filled foam also improved performance over the neat foam, its advantages over the SSP-filled foam were less pronounced. The performance of the SSP-filled foam improved with increasing compression speeds, while the performance of the STF-filled foam remained relatively stable between 60 and 240 mm/s of load-unload tests. Post-test compression evaluations showed that neat and STF-filled foams quickly regained their original shape, while SSP-filled foams required more time before recovery. This research shows that combining SSP and STF smart materials with open-cell foams substantially improves their compressive performance, especially at high compression rates and load-unloading scenarios, increasing their functional life. Full article

Discharging oil-contaminated wastewater into the environment without adequate treatment can have a negative impact on water resources, public water and wastewater treatment systems, and even human health. In this sense, it is essential to develop compact, easily automated, low-cost, and highly efficient unitary treatment processes in order to comply with legal requirements regarding effluent emission standards for water bodies. Therefore, the present study consisted of the development of two treatment processes aimed at the separation of oil emulsions stabilised by anionic surfactants: a sorption column using polyurethane/graphene foam composites as sorbent material and a continuous flow AC electroflotation reactor. Initially, composites with 0.5% and 1% w/w graphene (based on polyol mass) were developed using a dispersing agent (1-methyl-2-pyrrolidone). The foams were characterised in terms of morphology and mechanical and sorption properties. In the fixed bed column, the foams retained up to 77.15% of the emulsified oil and 52.36% of the anionic surfactants. In the continuous flow electroflotation reactor, emulsified oil removal efficiencies above 90% were achieved at all electrical currents tested, and up to 88.6% of anionic surfactants were removed at an electrical current of 150 A. Given the advantages and disadvantages of the two oily effluent treatment processes, their combined use in the same system proved promising. Full article

The interaction of microplastics (MPs) with organic micropollutants, such as antibiotics, facilitates their transport in aquatic environments, increasing mobility and toxicological risk. The diverse polymer types, sizes, and shapes in wastewater present a challenge in understanding the fate of persistent organic micropollutants. This study examines ceftazidime adsorption on five polymer types—polyethylene terephthalate (PET), polyethylene (PE), hard and soft polystyrene (PS), hard and soft polyurethane (PU), and tyre wear particles (TWPs, including three passenger tyres and one truck tyre) in various forms (fibres, beads, foam, and fragments) and sizes (10–1000 µm). MPs underwent weathering (alkaline hydrolysis, UVC-activated H₂O₂, and Xenon lamp irradiation) to simulate environmental conditions. Their physical and chemical changes were analysed through mass loss, carbonyl index, scanning electron microscopy, and atomic force microscopy. The adsorption values (mg g⁻¹) for pristine and weathered MPs, respectively, were as follows: PET (0.664 and 1.432), PE (0.210 and 0.234), hard PS (0.17 and 0.24), soft PS (0.53 and 0.48), hard PU (0.19), soft PU (0.17), and passenger TWPs—Bridgestone (0.212), Michelin (0.273), Goodyear (0.288), and Kumho truck TWPs (0.495). The highest and lowest adsorption were observed in weathered PET (1.432 mg g⁻¹) and pristine hard PS/soft PU (0.17 mg g⁻¹), respectively. Sorption kinetics and isothermal models showed that aged MPs exhibited higher sorption due to surface cracks, fragmentation, and increased adsorption sites. These findings enhance scientific knowledge of MP–antibiotic interactions in wastewater and can underpin studies to mitigate MP pollution and their adverse effects on the environment and humans. Full article

As an environmentally friendly and clean energy technology, solar-driven interfacial evaporation technology has attracted wide attention. However, organic pollutants can easily pollute distilled water during the evaporation of wastewater. In this work, we report a strategy of N-TiO₂/C solar absorption with a low bandgap (2.33 eV), excellent light absorption ability, and high photothermal conversion efficiency (48.2%). Black N-TiO₂/C was prepared by the sol-gel method in the presence of hexamethylenetetramine as a source of nitrogen and carbon. The simultaneous N doping and C with superior photothermal effect rapidly increased the surface temperature of the material, reduced the recombination rate of electrons and holes, and improved the photocatalytic activity, showing great potential for solar thermal energy conversion. The prepared solar absorbent and polyurethane (PU) were mixed evenly to form a porous N-TiO₂/C/PU (NTCP) foam for purifying water. The evaporator produced clean water at a rate of 1.73 kg m⁻² h⁻¹ under the simulated sunlight of 1 sun irradiation. Meanwhile, the evaporator simultaneously photodegraded methylene blue (MB) and rhodamine B (RhB) underwater at a removal rate > 90%. The bifunctional solar water evaporation device combining photocatalytic and photothermal effects holds great potential for water purification. Full article

With the increasing demand for environmental protection, flattened bamboo is gradually attracting attention as a sustainable material. The purpose of this study was to compare and analyze the surface properties of flattened bamboo and PU self-foaming plastic by subjective and objective evaluation methods, and to explore the substitutability of flattened bamboo and PU self-foaming plastic in furniture design. Objective test methods such as surface hardness testing, gloss measurement, and friction coefficient determination were used in the experiments, and the subjective evaluation of visual and tactile perception of the materials were combined with the semantic differential method. It was found that the flattened bamboo was generally superior to the PU self-foaming plastics in terms of color, gloss, roughness, and wettability, giving a more delicate, warm and comfortable feeling, while the PU self-foaming plastics stood out in terms of personalized style. Further correlation analysis showed that surface gloss and color saturation had a significant effect on the users’ psychological feelings. This study provides a scientific basis for replacing PU self-foaming plastic with bamboo in furniture design and also provides a valuable reference for “bamboo instead of plastic” product design. Full article

Tissue-engineered biocompatible scaffolds could mimic the extracellular matrix structure for cell adhesion and proliferation; however, patients suffer from large volume implantation. In this study, a thermal sensitive shape memory polyurethane porous 3D scaffold based on poly(ε-caprolactone) and poly(ethylene glycol adipate) was developed, utilizing the water-splitting property of aliphatic hexamethylene diisocyanate (HDI) to crosslink rigid segments during the polymerization process. The chemical structure, microstructure, and morphology, as well as mechanical strength, of the scaffolds were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), a scanning electron microscope (SEM), and tensile tests. The results show that gas foaming action caused by the release of CO₂ occurred simultaneously in the reactive process, resulting in the interconnective porous structure of the PU scaffolds with a porosity of over 70% and pore sizes from 100 μm to 800 μm. Additionally, after programming to a temporary shape, the scaffolds could recover to their initial shapes and could be programmed into various shapes according to different defects. These smart shape-changeable scaffolds with high porosity and good physio-chemical properties are a promising material for minimally invasive tissue engineering. Full article

In this article, an attempt was made to model the body of a person moving in a passive manner (movement forced by another person) in a wheelchair. For this purpose, the Wan–Schimmels model was modified by 4 DOF, supplementing it with the weight of the wheelchair and a polyurethane cushion. The study was designed to test the effectiveness of utilizing a polyurethane cushion to reduce the whole-body vibration acting on a person while moving in a wheelchair. The study used a rheological model of polyurethane (PU) foam with concentrated parameters. Harmonic and random vibration analysis was carried out for this model. At the same time, the model with 5 DOF seems to be sufficient to describe vibrations transmitted to wheelchair users. The model presented in this paper can become a tool for future analysis of vibrations of people of different weights, moving passively on various types of wheelchairs on surfaces whose irregularities can be given by an appropriate form of kinematic excitation. The approach used in this study is likely to be useful in selecting a wheelchair and seat cushion so as to counteract and minimize vibrations perceived by humans. Full article

This study investigates the effects of microencapsulated phase-change materials (PCMs) on the density and thermal conductivity of rigid polyurethane (PU) foams, alongside their mechanical properties. Introducing PCMs into the foam composition results in increased viscosity, complicating the mixing of polyol and isocyanate components. This viscosity increase can slow the foaming rate and subsequently raise the foam density, as observed in both poured and sprayed rigid PU foams containing 5% and 10% PCM, leading to density increases of up to 9%. Despite these slight density changes, the thermal conductivity remained relatively stable due to the preservation of the foam’s closed-cell structure. The mechanical evaluation revealed a decrease in compressive and tensile strength with a higher PCM content attributed to defects arising in the foam’s cellular architecture. However, adhesive strength to aluminum substrates improved, particularly with 5% PCM, possibly due to a more consistent foam structure during the slower foaming process. Differential scanning calorimetry and a dynamic mechanical analysis indicated that the incorporation of PCM increased the glass transition temperature and affected the foam’s mechanical properties. This research underscores the potential of microencapsulated PCMs to enhance the functionality of rigid PU foams while needing careful consideration of their concentration to avoid compromising the structural integrity. Full article