Search Results (20)

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

Tannin-furanic foams with excellent properties have attracted increasing interest due to their advantages such as easy preparation, light weight, and thermal insulation. However, unsatisfactory mechanical strength has limited the expansion of their applications. Herein, three different metal ions (Cu²⁺, Fe³⁺, and Zn²⁺) were chosen to enhance the properties of tannin-furanic foam prepared by mechanical stirring provoked a foaming approach. The positive effects originating from the complexation are attributed to the associated connection between tannin molecules and metal ions. The results indicated that the apparent performance was improved, resulting in even foam cell structures. The apparent densities for the tannin-furanic foam modified with metal ions were located in the range of 36.57–47.84 kg/m³, showing the feature of lightweight material. The enhanced mechanical strength was verified by the compression strength (0.097–0.163 MPa) and pulverization ratio (7.57–11.01%) of the modified foams, which increased by 56–163% and decreased by 61–73%, respectively, in comparison with tannin-furanic foam without the metal ions. Additionally, the thermal conductivity of the modified tannin-furanic foams was in the range of 0.0443 to 0.0552 W/m·K. This indicates that they inherited the excellent thermal insulation typically associated with tannin-based foams. Interestingly, higher mechanical performance was obtained by comparison with other bio-sourced foams even with similar densities. In summary, by introducing only a small amount of metal ions, the foam performance was greatly improved, with a moderate cost increase, which reflects a good development prospect. Full article

Worldwide, populations face issues related to water and energy consumption. Water scarcity has intensified globally, particularly in arid and semiarid regions. Projections indicate that by 2030, global water demand will rise by 50%, leading to critical shortages, further intensified by the impacts of climate change. Moreover, wastewater treatment needs further development, given the presence of persistent organic pollutants, such as dyes and pharmaceuticals. In addition, the continuous increase in energy demand and rising prices directly impact households and businesses, highlighting the importance of energy savings through effective building insulation. In this regard, tannin-furanic foams are recognized as promising sustainable foams due to their fire resistance, low thermal conductivity, and high water and chemical stability. In this study, tannin and lignin rigid foams were explored not only for their traditional applications but also as versatile materials suitable for wastewater treatment. Furthermore, a systematic approach demonstrates the complete replacement of the tannin-furan foam phenol source with two lignins that mainly differ in molecular weight and pH, as well as how these parameters affect the rigid foam structure and methylene blue (MB) removal capacity. Alkali-lignin-based foams exhibited notable MB adsorption capacity (220 mg g⁻¹), with kinetic and equilibrium data analysis suggesting a multilayer adsorption process. The prepared foams demonstrated the ability to be recycled for at least five adsorption-desorption cycles and exhibited effective flame retardant properties. When exposed to a butane flame for 5 min, the foams did not release smoke or ignite, nor did they contribute to flame propagation, with the red glow dissipating only 20 s after flame exposure. Full article

Four types of classical tannin-based foam samples were prepared via different methods in the current study with an attempt to find out the impact of each one on the physico-mechanical properties. The results of performed tests showed similarity to the general trend of related research, with typical negative relation between the foam density and mechanical strength. A critical point was found for each type of foam samples, for example, for tannin-formaldehyde foams (TFF), they were in the range of 85–95 kg/m³, while for tannin-glutaraldehyde foams (TGF), mechanically-generated tannin foams (MTF) and steam-driven tannin furanic foams (STDF), they were about 52–62 kg/m³, 53–63 kg/m³, and 73–83 kg/m³, respectively. This implies a significant change for density and mechanical strength, has been dig out by intensive experimental results and analysis. In addition, a non-liner relationship between density and pulverization ratio was obtained by fitting the curves obtained by the experiment results. Finally, visualization using scanning electron microscopy (SEM) together with evaluation of the compression strength presented a deeper insight to illustrate the different factors affecting foam density and pulverization ratio. Full article

The exploitation of bio-based foams implies an increase in the use of renewable biological resources to reduce the rapid consumption of petroleum-derived resources. Both tannins and furfuryl alcohol are derived from forestry resources and are, therefore, considered attractive precursors for the preparation of tannin–furanic foams. In addition, toughening modification of tannin–furanic foams using polyvinyl alcohol (PVOH) results in a more flexible network-like structure, which imparts excellent flexibility to the foams, whose relative properties are even close to those of polyurethane foams, which are the most used for fabrication of insoles for athletes. In addition, the addition of PVOH does not affect the thermal insulation properties of the foams by testing the thermal conductivity, resilience, and elongation at break, while reducing the brittleness of the samples and improving the mechanical properties. Also, the observation of the morphology of the foam shows that the compatibility between PVOH and tannin–furanic resin is good, and the cured foam does not show fragmentation and collapse, while the bubble pore structure is uniform. The developed flexible foam derived from biomass resources endows the foam with good thermal insulation properties and high mechanical properties, and the samples exhibit suitable physical parameters to be used as flexible insoles for athletes. Full article

In this paper we produced a bio-based polyether-polyurethane foam PU1 through the prepolymer method. The prepolymer was obtained by the reaction of PEG 400 with _L-Lysine ethyl ester diisocyanate (L-LDI). The freshly prepared prepolymer was extended with 2,5-bis(hydroxymethyl)furan (BHMF) to produce the final polyurethane. The renewable chemical BHMF was produced through the chemical reduction of HMF by sodium borohydride. HMF was produced by a previously reported procedure from fructose using choline chloride and ytterbium triflate. To evaluate the degradation rate of the foam PU1, we tested the chemical stability by soaking it in a 10% sodium hydroxide solution. The weight loss was only 12% after 30 days. After that, we proved that enzymatic hydrolysis after 30 days using cholesterol esterase was more favoured than hydrolysis with NaOH, with a weight loss of 24%, probably due to the hydrophobic character of the PU1 and a better adhesion of the enzyme on the surface with respect to water. BHMF was proved to be of crucial importance for the enzymatic degradation assay at 37 °C in phosphate buffer solution, because it represents the breaking point inside the polyurethane chain. Soil burial degradation test was monitored for three months to evaluate whether the joint activity of sunlight, climate changes and microorganisms, including bacteria and fungi, could further increase the biodegradation. The unexpected weight loss after soil burial degradation test was 45% after three months. This paper highlights the potential of using sustainable resources to produce new biodegradable materials. Full article

This study examined the potential of hydrolysable tannin in comparison to condensed tannins for the production of furanic foams. The results indicate that chestnut tannin presents lower reactivity and requires a stronger acid for the polymerization. Additionally, foamability and density were found to be dependent on both surfactant concentration and tannin type, allowing lower densities for mimosa tannin and lower thermal conductivities for chestnut-based foams. Mimosa tannin was found to have the highest compression strength, followed by quebracho and chestnut, promising thermal conductivity of around 50 mW/m·K for 300 kg/m³ foams, which suggests that chestnut foams have the potential to performing highly when the density is reduced. Chemical analysis revealed that the methylene moieties of the furanics are non-specific and produces new covalent bonds with nucleophilic substrates: -OH groups and free-positions in the flavonoids. Overall, this study opens new perspectives for the application of hydrolysable tannins in polymer and material science. Full article

Bio-based biodegradable foams were formulated from a crosslinkable network structure combining starch, furfuryl alcohol, glyoxal, and condensed tannin in the presence of p-toluenesulfonic acid (pTSA) and azodicarbonamide (AC) as a foaming agent. More importantly, the reinforcement of gelatinized starch–furanic foam using tannin, originating from forestry, resulted in an excellent compressive strength and lower pulverization ratio. Moreover, the addition of tannin guaranteed a low thermal conductivity and moderate flame retardancy. Fourier transform infrared (FTIR) spectroscopy approved the successful polycondensation of these condensing agents under the employed acidic conditions. Moreover, the catalytic effect of pTSA on the foaming agent induced liberation of gases, which are necessary for foam formation during crosslinking. Scanning electron microscopy (SEM) showed foam formation comprising closed cells with uniform cell distribution and appropriate apparent density. Meanwhile, the novel foam exhibited biodegradation under the action of Penicillium sp., as identified by the damage of cell walls of this foam over a period of 30 days. Full article

Tannin-furanic foams were prepared with a good yield using the addition of relatively small proportions of a polyflavonoid tannin extract esterified with either palmitic acid, oleic acid, or lauric acid by its reaction with palmitoyl chloride, oleyl chloride, or lauryl chloride. FTIR analysis allowed us to ascertain the esterification of the tannin, and MALDI-TOF analysis allowed us to identify a number of multi-esterified flavonoid oligomers as well as some linked to residual carbohydrates related to the equally esterified tannin. These foams presented a markedly decreased surface friability or no friability at all, and at densities lower than the standard foam they were compared to. Equally, these experimental foams presented a much-improved water repellence, as indicated by their initial wetting angle, its small variation over time, and its stabilization at a high wetting angle value, while the wetting angle of the standard foam control went to zero very rapidly. This conclusion was supported by the calculation of the total surface energy of their surfaces as well as of their dispersive and polar components. Full article

This paper aims to present the possibility of producing cast porous metals (or metallic foams) in a low-tech way by the use of conventional foundry technologies, i.e., the common procedures and materials. Due to the technological and economic complexity of the production processes of cast metallic foams, research into this material currently focuses on the development of less demanding technologies. The introduction of such production processes may help to exploit the full application potential of metallic foams. Within the framework of our proposed procedure, molding and core mixtures are used for the production of molds and filler material (space holder), also called precursors. It is the shape, size, and relative position of the individual precursors that determines the shape of the internal structure of the resulting metallic foam. The core mixture for the production of precursors is evaluated in terms of changes in properties with respect to storage time. Attention is focused on one of the most common bonding systems, furan no-bake. Casting tests are carried out for the possibility of making cast porous metals from aluminum alloy with different shapes of internal cavities depending on the different shapes of the filler material. The collapsibility of the cores after casting is evaluated for the test castings. The results show that even using commonly available materials and processes, cast metallic foams with complex internal structures can be produced. Full article

Tannin-furanic rigid foams are bio-based copolymers of tannin plant extract and furfuryl alcohol, promising candidates to replace synthetic insulation foams, as for example polyurethanes and phenolics, in eco-sustainable buildings thanks to their functional properties, such as lightness of the material and fire resistance. Despite their relevance as environmental-friendly alternatives to petroleum derivatives, many aspects of the polymerization chemistry still remain unclear. One of the open issues is on the spatial heterogeneity of the foam, i.e., whether the foam constituents prevalently polymerize in spatially segregated blocks or distribute almost homogenously in the foam volume. To address this matter, here we propose a multiscale FTIR study encompassing 1D FTIR spectroscopy, 2D FTIR imaging and 3D FTIR micro-tomography (FTIR-μCT) on tannin-furanic rigid foams obtained by varying the synthesis parameters in a controlled way. Thanks to the implementation of the acquisition and processing pipeline of FTIR-μCT, we were able for the first time to demonstrate that the polymer formulations influence the spatial organization of the foam at the microscale and, at the same time, prove the reliability of FTIR-μCT data by comparing 2D FTIR images and the projection of the 3D chemical images on the same plane. Full article

The electrochemical production of 2,5-furandicarboxylic acid (FDCA) from 5-(hydroxymethyl)furfural (HMF) is receiving growing attention. The FDCA-based polyethylene 2,5-furan dicarboxylate (PEF) polymer is a green candidate for substituting polyethylene terephthalate. This work demonstrated a highly efficient CoB/g-C₃N₄ nanosheet on the surface of the nickel foam as an electrode for the HMF electrooxidation reaction. Electrolysis at a constant potential combined with liquid chromatography showed the formation of FDCA with a yield of 97% with an excellent faradaic efficiency of near 95%. CoB/g-C₃N₄ achieved a current density of 20 mA cm⁻² for HMF oxidation in 1.0 M KOH with 10 mM HMF at 1.37 V vs. RHE before the competing oxygen evolution reaction. The electrocatalyst was effectively reused up to three times without compromising efficiency. This work demonstrates a cheap and active electrocatalyst material for the electrochemical formation of FDCA from HMF and gives perception into the reaction mechanism. Full article

With increasing demand of alternatives to oil-based lightweight materials, the development of tannin-based foams is getting more and more attention. In this paper, an alternative to traditionally used solvent-evaporation in the production of tannin-foams is presented. Mixing the tannin-furanic resin with different amounts of ionic and non-ionic surfactants at high agitational speed allows for the formation of highly porous, mechanically stable tannin-foams. Investigations on the influence of surfactant type and ingredient ratios on the foaming behavior and properties of the final foams were conducted. Materials obtained via this route do present extraordinary compression resistance (about 0.8 MPa), good thermal insulation (40 mW/m·K) and are suitable as a wastewater treatment agent at the end-of-life. It was shown that during mechanical blowing, homogeneous cross-sections and almost perfectly round pores form, leading to the high compression resistance. Investigations by means of Fourier transform infrared and ¹³C nuclear magnetic resonance spectroscopy show that the milder reaction environment leads to more linear poly(furfuryl alcohol)-tannin chains. This new type of tannin foam allows for use in various different fields of application ranging from durable building insulation to wastewater treatment. Full article

Ambient temperature self-blowing tannin–furanic foams have been prepared by substituting a great part—even a majority—of furfuryl alcohol with humins, a polyfuranic material derived from the acid treatment at high temperature of fructose. Closed-cell foams were prepared at room temperature and curing, while interconnected-cell foams were prepared at 80 °C and curing, this being due to the more vigorous evaporation of the solvent. These foams appear to present similar characteristics as other tannin–furanic foams based only on furfuryl alcohol. A series of tannin–humins–furfuryl alcohol oligomer structures have been defined indicating that all three reagents co-react. Humins appeared to react well with condensed tannins, even higher molecular weight humins species, and even at ambient temperature, but they react slower than furfuryl alcohol. This is due to their high average molecular weight and high viscosity, causing their reaction with other species to be diffusion controlled. Thus, small increases in solvent led to foams with less cracks and open structures. It showed that furfuryl alcohol appears to also have a role as a humins solvent, and not just as a co-reagent and self-polymerization heat generator for foam expansion and hardening. Stress-strain for the different foams showed a higher compressive strength for both the foam with the lowest and the highest proportion of humins, thus in the dominant proportions of either furfuryl alcohol or the humins. Thus, due to their slower reactivity as their proportion increases to a certain critical level, more of them do proportionally participate within the expansion/curing time of the foam to the reaction. Full article

With the extensive use of nitrogen-based fertilizer in agriculture, ammonia emissions, especially from cattle manure, are a serious environmental threat for soil and air. The European community committed to reduce the ammonia emissions by 30% by the year 2030 compared to 2005. After a moderate initial reduction, the last report showed no further improvements in the last four years, keeping the 30% reduction a very challenging target for the next decade. In this study, the mitigation effect of different types of tannin and tannin-based adsorbent on the ammonia emission from manure was investigated. Firstly, we conducted a template study monitoring the ammonia emissions registered by addition of the tannin-based powders to a 0.1% ammonia solution and then we repeated the experiments with ready-to-spread farm-made manure slurry. The results showed that all tannin-based powders induced sensible reduction of pH and ammonia emitted. Reductions higher than 75% and 95% were registered for ammonia solution and cattle slurry, respectively, when using flavonoid-based powders. These findings are very promising considering that tannins and their derivatives will be extensively available due to the increasing interest on their exploitation for the synthesis of new-generation “green” materials. Full article