Aiming to sustainable manufacturing options, materials that are discarded from the industry and to which a second life may be given are highly desirable. Condensed tannins constitute the starting point to create tannin-furanic foams, a rigid biobased material that could be a sustainable alternative to those derived from fossil fuel-based chemicals. With the objective of developing novel foam production strategies, three different tannin-furanic foams, namely mechanical, sulfuric and nitric, were thoroughly chemically characterized, and their morphological and macroscopic properties were compared with those of commercial plastic foams made of polystyrene and of polyethylene terephthalate. Understanding the influence of the foaming method on the foam properties is of utmost importance when aiming to substitute existing, well-established products. The chemical characterization was performed by using NMR, FTIR and UV Raman, assisted by DFT quantum mechanics simulations. The morphological characterization was done by Scanning Electron Microscopy and X-ray micro-Tomography. Macroscopic characterization was done by strain–stress, thermal conductivity, and thermal gravimetric analysis. Our studies demonstrated nitric tannin-furanic foams as the closest to an insulating material, while mechanical tannin-furanic foam is more appropriate as a tough material. Overall, they prove that bio-based tannin-furanic foams appear to be a feasible green alternative to conventional plastic foams.

Tannins, which can be extracted from certain tree barks, are polyphenolic compounds, that gain a lot of interest in industry, as they can be utilized to replace petroleum-based chemicals. Currently, they are used in the leather industry, as flocculants or as adhesives. To further increase their potential, an increase in purity is necessary. To do so, various methods are available, in this study we present a 2-step approach consisting of (i) depolymerization and cleavage of glycosidic bonds and (ii) separation of phenolic-rich and phenolic-poor fractions. Commercially available mimosa tannin is treated with various concentrations of hydrochloric and sulfuric acid (0.4 M and 0.8 M) and separated with chromatographic resin. Resulting fractions are characterized by UV/Vis spectroscopy for phenolic content and antioxidant activity, infrared spectroscopy, NMR, HPLC-DAD and GPC to determine their composition and molecular size as well as their reactivity towards formaldehyde. It was observed that mild acidic cleavage with 0.4 M HCl results in more phenol-rich material (TPC 1124 µgGAE mg−1) while 0.8 M sulfuric acid leads to tannin fractions with higher antioxidative properties. Amberlite resin yields fractions with higher reactivity towards formaldehyde (gel time below 60 seconds compared to over 90 originally) while the Sephadex fractions present the highest values for total phenolic content.

Tannin-furanic foams are biogenic, lightweight material comprising of up 95% renewable resources. Replacing 5 to 30% of the tannin powder in the formulation for new foam with finely grinded, recycled tannin-furanic polymer powder was investigated. While 5% and 10% of recycled material did not have a significant influ-ence on the mechanical properties (bending strength, modulus of elasticity, tensile strength and compression resistance) a slight decrease is observed for 15 to 25% replacement, but within these groups, results are not significantly different. An overall decrease of 30% for mechanical properties was observed for foams made with 15% to 25% recycled material. The addition of 30% recycling material in the production of tannin foams is not feasible, as the foaming process is disturbed.

Tannin-furanic foams are a promising and biogenic alternative to oil-based porous materials. Their hydrophilic character, typically indicated by a contact angle to water of 70 & DEG;, limits some potential applications (for instance outdoor thermal insulation). To overcome this, a post-synthetic surface modification step with different fluorine-free organosilanes at 323 K was investigated with a focus on the final, hydrophobic performance. On the one side, methyltrimethoxysilane, and 3-(chloropropyl)trimethoxysi lane, which undergo self-condensation as well as bonding to the hydroxy groups of the tannin polymer, were applied. A modified surface structure and a 25 to 50 % weight increase, depending on the molecular weight of the silylation agent, were observed. Contrary, a mono-functional silane, precicely trimethylchlorosilane, shows only a slight increase in weight, yet also condenses onto the polymer surface without forming a protective surface coating layer. Contact angle measurements using water show an increase from 70 & DEG; (unmodified) up to 145 & DEG; for a silane-modified foam. Nuclear magnetic resonance and infrared spectroscopy show the formation of covalent bonds between the silane and the biogenic polymer matrix. The obtained material is less prone to absorb water from a humid atmosphere (reduction of 75 %) and is highly efficient for the removal of non-polar contaminants from water, featuring new pos-sible applications in humid surrounds.

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.

The addition of tree bark extracts, commercial tannin powder and a tannin-based polymer to cattle manure was investigated for its influence on the gaseous emission and nitrogen conservation potential for 28 days. In lab trials with ammonia solution as reference, the retention of ammonia was 13%, 40% and up to 65% for untreated solution, spruce bark extract and chestnut tannin respectively. The gaseous emission from manure was reduced by 40%, 58% and 66% for chestnut tannin and spruce bark extract, larch bark extract and the tannin polymer, and oak tannin, respectively. For long-term nitrogen loss mitigation, 20% more nitrogen was preserved when spruce or larch bark extract or oak tannin was added to the manure compared to the reference measurements. A combination of the pH lowering effect of tannins and covalently bonding ammonia to flavonoid hydroxy groups provides a viable method for reduction of nitrogen loss in cattle manure.

Tannin-silica hybrid materials are expected to feature excellent mechanic-chemical stability, large surface areas, high porosity and possess, after carbothermal reduction, high thermal stability as well as high thermal conductivity. Typically, a commercially available tetraethoxysilane is used, but in this study, a more sustainable route was developed by using a glycol-based silica precursor, tetrakis(2-hydroxyethyl)orthosilicate (EGMS), which is highly water-soluble. In order to produce highly porous, homogeneous hybrid tannin-silica aerogels in a one-pot approach, a suitable crosslinker has to be used. It was found that an aldehyde-functionalized silane (triethoxysilylbutyraldehyde) enables the covalent bonding of tannin and silica. Solely by altering the processing parameters, distinctly different tannin-silica hybrid material properties could be achieved. In particular, the amount of crosslinker is a significant factor with respect to altering the materials’ properties, e.g., the specific surface area. Notably, 5 wt% of crosslinker presents an optimal percentage to obtain a sustainable tannin-silica hybrid system with high specific surface areas of roughly 800–900 m2 g−1 as well as a high mesopore volume. The synthesized tannin-silica hybrid aerogels permit the usage as green precursor for silicon carbide materials.

With the increasing demand for food worldwide, the use of fertilizers in the agricultural industry has grown. Natural fertilizers derived from the use of animal manure slurry, especially cattle and cow, are responsible for 40% of the agricultural ammonia emission. The EU defined the goal to reduce NH3 emission drastically until 2030, yet until today an overall increase has been observed, making it more difficult to reach the target. In this study, we used two by-products from the dairy industry, namely flushing milk and acidic whey, to lower the pH of cattle manure slurry and therefore mitigate the loss of nitrogen in the form of ammonia into the atmosphere, making it available in the soil. Measurements of pH, ammonium nitrogen, total Kjeldahl nitrogen, and lactic acid bacteria colonies were conducted in a lab-scale experiment to test the hypothesis. Afterwards, pH measurements were conducted on bigger samples. We found that whey effectively reduced the pH of manure below 5, therefore moving the ammonia/ammonium equilibrium strongly towards ammonium. Flushing milk on the other hand lowered the pH to a smaller extent, yet allowed for faster hydrolysis of urea into ammonium. The findings in this study present a suitable and environmentally friendly approach to help reach the climate goals set by the EU by using by-products from the same industry branch, therefore being a suitable example of circular economy.

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.

Simple substrates for surface enhanced Raman spectroscopy (SERS), producible in a cost-efficient way, are of growing interest both for scientific and for environmental applications. In this study, we demonstrate the use of three types of bio-based tannin-furanic rigid foams as precursor materials for SERS substrates. Coated with a silver layer, these substrates allowed the detection of several well-known analytes in the mM regime by Raman spectroscopy. Specific optimization of the standard tannin-furanic foam morphology by tuning the chemical synthesis led to a smaller and more homogeneously distributed pore structure, supplying more active hot spot areas. Thus, we obtained a significant increase and a lower relative standard deviation (RSD) of the SERS signal recorded over the mapped SERS substrate area, for several analytes, in particular for Malachite Green dye. This work represents a feasibility study opening several potential applications of this biopolymers in fields such as the detection of water pollutants, virtually combining filtration and SERS capabilities driven by a controlled porosity.

The actual chemical structure of polyfurfuryl alcohol (PFA) is still uncertain in spite of several studies on the topic, variations during the polymerization processes being one reason that must be addressed. The use of a limited set of analytical techniques is often insufficient to provide an exhaustive chemical characterization. Moreover, it is still not possible to exactly determine presence and amount of each specific functional group in the polymeric structure. We employed both Fourier Transform Infrared Spectroscopy (FTIR) and Resonant Raman spectroscopy (RR), corroborated by quantum mechanically aided analysis of the experimental spectra, to infer about the chemical structure of two samples of PFAs, synthetized in different ways and appearing macroscopically different, the first one being a liquid and viscous commercial sample, the second one being a self-prepared solid and rigid sample produced following a thermosetting procedure. The vibrational spectroscopic analysis confirms the presence of differences in their chemical structures. The viscous form of PFA is mainly composed by short polymeric chains, and is characterized by the presence of isolated furfuryl alcohol and furfural residues similar to 5-hydroxymethylfurfural; the thermosetted PFA is formed by more cross-linked structures, characterized by several ketones and alkene double bonds, as well as a significant presence of Diels-Alder structures. In summary, the present study evidences how the use of both FTIR and RR spectroscopy, the latter carried out at several laser excitation wavelengths, indicates an accurate way to spectroscopically investigate complex polymers enabling to satisfactorily infer about their peculiar chemical structure.

As lignin is becoming more and more attractive to industry and the circular economy continues to grow, the utilization of a byproduct that, to date, has been underrated by the wood industry is investigated as an abundantly available source of lignin. Bark from spruce, larch and beech tress is extracted using the organosolv process with and without prior hot water extraction. The influence of the treatment on chemical properties of the lignin was determined by spectrophotometric, chromatographic, and vibrational spectroscopy. It was found that hot water extraction prior to organosolv extraction influences the chemical composition, antioxidative properties and molecular weight distribution of the obtained extracts. While hot water extracts are rich in flavonoids, organosolv fractions can contain high amounts of organic acids depending on whether they are from a hardwood or softwood source. This investigation lays the foundation for further research into the utilization of byproducts to generate high-value resources.

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.

Tannin foams are green lightweight materials that have attracted industrial interest for the manufacturing of sandwich panels for insulation purposes. However, the dimensions of the cells and the presence of sulfur in the formulation developed until now have discouraged their upscaling. In this work, we present the synthesis and the characterization of the more promising small cell and sulfur-free materials. It was observed that, with respect to standard ones, foams catalyzed with nitric acid present similar physical properties and more phenolic character, which favors the absorption of ionic pollutants. Conversely, the foams blown with aliphatic solvents and surfactants present smaller pores, and higher mechanical and insulating properties, without affecting the chemical properties or the heating value. The combined foam produced with nitric acid as a catalyst and petroleum ether as a blowing agent result in sulfur-free and small cell material with overall improved features. These foams have been produced at 30 × 30 × 3 cm3, with high homogeneity and, to date, they represent the most suitable formulation for industrial upscaling.

New functions of wood may lead to innovative products and the usability of bio-based materials. This study deals with the analysis of magnetic functionalization of beech and poplar wood. Samples of size 20 x 5 x 10 mm were impregnated with Fe3O4 nanoparticles synthesized with either an oleic acid coating or uncoated. The oleic acid coated particles were suspended in linseed oil as impregnation medium. The uncoated particles were dissolved in a tannin-hexamine solution for infiltration and fixation. Different impregnation parameters (e.g. alternation of vacuum or vacuum-pressure cycles and number of cycles) were investigated. To evaluate efficacy of the procedure the wood samples were placed onto a magnet after curing and assessments on e.g. maximum tilt of the magnet at which the sample was still hold in place were made. Other investigations dealt with the penetration depth of the magnetite and the carrier solution as well as the distribution within. Results show that a magnetite NP content of 5wt% in linseed oil results in pleasing magnetic properties while not altering the optical appearance of the impregnated beechwood specimen in a negative way. The so obtained product could be used for different applications (e.g. bio-based giveaways and office products).

Walnut and hazelnut shells are agricultural by-products, available in high quantities during the harvest season. The potential of using these two agricultural residues as raw materials in particleboard production has been evaluated in this study. Different panels with either walnut or hazelnut shells in combination with melamine-urea formaldehyde or polyurethane at the same level of 1000 kg/m3 density were produced in a laboratory hot press and mechanical properties (modulus of elasticity, bending strength, and Brinell hardness) and physical properties (thickness swelling and water absorption) were determined, together with formaldehyde content. Although Brinell hardness was 35% to 65% higher for the nutshell-based panels, bending strength and modulus of elasticity were 40% to 50% lower for the melamine-urea formaldehyde bonded nutshells compared to spruce particleboards, but was 65% higher in the case of using polyurethane. Water absorption and thickness swelling could be reduced significantly for the nutshell-based boards compared to the spruce boards (the values recorded ranged between 58% to 87% lower as for the particleboards). Using polyurethane as an adhesive has benefits for water uptake and thickness swelling and also for bending strength and modulus of elasticity. The free formaldehyde content of the lignocellulosic-based panels was included in the E0 category (≤2.5 mg/100 g) for both walnut and hazelnut shell raw materials and the use of polyurethane improved these values to super E0 category (≤1.5 mg/100 g).

Polyfurfuryl alcohol (PFA) is one of the most intriguing polymers because, despite its easy polymerization in acid environment, its molecular structure is definitely not obvious. Many studies have been performed in recent decades, and every time, surprising aspects came out. With the present study, we aim to take advantage of all of the findings of previous investigations and exploit them for the interpretation of the completely cured PFA spectra registered with three of the most powerful techniques for the characterization of solid, insoluble polymers: Solid-State 13C-NMR, Attenuated Total Reflectance (ATR), Fourier Transform Infrared (FTIR) spectroscopy, and UV-resonant Raman spectroscopy at different excitation wavelengths, using both an UV laser source and UV synchrotron radiation. In addition, the foreseen structures were modeled and the corresponding 13C-NMR and FTIR spectra were simulated with first-principles and semi-empiric methods to evaluate their matching with experimental ones. Thanks to this multi-technique approach, based on complementary analytical tools and computational support, it was possible to conclude that, in addition to the major linear unconjugated polymerization, the PFA structure consists of Diels-Alder rearrangements occurring after the opening of some furanic units, while the terminal moieties of the chain involves γ-lactone arrangements. The occurrence of head-head methylene ether bridges and free hydroxyl groups (from unreacted furfuryl alcohol, FA, or terminal chains) could be excluded, while the conjugated systems could be considered rather limited.

Tannin- and lignin-furanic foams are natural porous materials that have attracted high interest in the scientific and industrial communities for their high thermal and fire-resistant properties. However, no interesting solutions have been proposed for the management of their end-life as yet. In this study, the phenolic-furanic powders derived from the foams were analyzed for their capacity to remove different pollutants like neutral, cationic, and anionic organic molecules from wastewater. It was observed that the macromolecules produced from initially bigger fractions were more suitable to remove methylene blue and sodium dodecyl sulfate (SDS) while contained absorptions were observed for riboflavin. Acidified tannin powders were also prepared to understand the role of the flavonoid in the absorption mechanism. The latter showed outstanding absorption capacity against all of the tested pollutants, highlighting the key-role of the flavonoid fraction and suggesting the limited contribution of the furanic part. All adsorbents were investigated through FT-IR and solid state 13C-NMR. Finally, the powders were successfully regenerated by simple ethanol washing, showing almost complete absorption recovery.

Furfuryl alcohol (FA) and lactic acid (LA) are two of the most interesting biomolecules, easily obtainable from sugars and hence extremely attractive for green chemistry solutions. These substances undergo homopolymerization and they have been rarely considered for copolymerization. Typically, FA homopolymerizes exothermically in an acid environment producing inhomogeneous porous materials, but recent studies have shown that this reaction can be controlled and therefore we have implemented this process to trigger the copolymerization with LA. The mechanical tests have shown that the blend containing small amount of FA were rigid and the fracture showed patterns more similar to the one of neat polyfurfuryl alcohol (PFA). This LA-rich blend exhibited higher chloroform and water resistances, while thermal analyses (TG and DSC) also indicated a higher furanic character than expected. These observations suggested an intimate interconnection between precursors which was highlighted by the presence of a small band in the ester region of the solid state 13C–NMR, even if the FT-IR did not evidence any new signal. These studies show that these bioplastics are basically constituted of PLA and PFA homopolymers with some small portion of covalent bonds between the two moieties.