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In this study, we used a self-neutralizing system to counteract too acidic a pH, unsuitable for wood adhesives, and tested it on MUF resins augmented by the addition of citric acid or other organic acids, based on the addition of small percentages of hexamine or another suitable organic base to form an acid-base buffer. In this manner, the pH of the adhesive was maintained above the minimum allowed value of 4, and the strength results of wood particleboard and plywood bonded with this adhesive system increased due to the additional cross-linking imparted by the citric acid. Thus, the wood constituents at the wood/adhesive interface were not damaged/degraded by too low a pH, thus avoiding longer-term service failure of the bonded joints. The addition of the buffering system increased the strength of the bondline in both the plywood and particleboard, both when dry and after hot water and boiling water tests. The IB strength of the particleboard was then increased by 15-17% when dry but by 82% after boiling. For the plywood, the shear strengths when dry and after 3 h in hot water at 63 °C were, respectively, 37% and 90% higher than for the control. The improvement in the bonded panel strength is ascribed to multiple reasons: (i) the slower, more regular cross-linking rate due to the action of the buffer; (ii) the shift in the polycondensation-degradation equilibrium to the left induced by the higher pH and the long-term stability of the organic buffer; (iii) the additional cross-linking by citric acid of some of the MUF resin amine groups; (iv) the already known direct linking of citric acid with the carbohydrates and lignin constituents at the interface of the wood substrate; and (v) the likely covalent linking to the interfacial wood constituents of the prelinked MUF-citric acid resin by some of the unreacted citric acid carboxyl groups.
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Non-isocyanate polyurethane (NIPU) as a new type of polyurethane material has become a hot research topic in the polyurethane industry due to its no utilization of toxic isocyanates during the synthesis process. And the developing on recyclable biomass materials has also much attention in the industrial sector, hence the preparation and application of bio-based NIPU has also become a very meaningful study work. So, in this paper, tannin as a biomass material was used to synthesize tannin based non-isocyanate polyurethanes (TNIPU) resin, and then successfully prepared a self-blowing TNIPU foam at room temperature by using formic acid as initiator and glutaraldehyde as cross-linking agent. The compressive strength of this foam as high as 0.8 MPa, which is an excellent compressive performance. Meanwhile it will return to the state before compression when removing the pressure. This indicating that the foam has good toughness. In addition, formic acid can react with the amino groups in TNIPU to form amide substances, and generated enough heat to initiate the foaming process. Glutaraldehyde, as a crosslinking agent, reacts with the amino group in TNIPU to form a network structure system. By scanning electron microscope (SEM) observation of the cell shapes, it can be seen that the foam cells were uniform in size and shape, and the cell pores showed open and closed cells. The limiting oxygen index (LOI) tested value of this TNIPU foam is 24.45 % without any flame retardant added, but compared to the LOI value of polyurethane foam (17 %-19 %), TNIPU foam reveal a better fire resistance. It has a wider application prospect.
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Formiatos , Isocianatos , Poliuretanos , Taninos , GlutaralRESUMO
Wood-based panels find widespread application in the furniture and construction industries. However, over 90â¯% of adhesives used are synthesized with formaldehyde, leading to formaldehyde emission and associated health risks. In this study, an entirely bio-based adhesive (OSL) was innovatively proposed through the condensation of multi-aldehyde derived from the oxidization of sucrose (OS) with sodium lignosulfonate (L). This approach positioned oxidized sucrose (OS) as a viable substitute for formaldehyde, ensuring safety, simplicity, and enhance water resistance upon reaction with L. The optimization of the OSL adhesive preparation process involved determining the oxidant level for high sucrose conversion to aldehyde (13â¯% based on sucrose), the mass ratio of OS to L (0.8), and hot-pressing temperature (200⯰C). Notably, the shear strength of 3-plywood bonded with the developed adhesive (1.04â¯MPa) increased to 1.42â¯MPa after being immersed in hot water at 63⯱â¯3⯰C for 3â¯h. Additionally, the plywood specimens exhibited excellent performance after soaking in boiling water for 3â¯h, resulting in a shear strength of 1.03â¯MPa. Chemical analysis using Fourier-transform infrared spectroscopy (FTIR), 1H nuclear magnetic resonance (NMR), and X-ray photoelectron spectroscopy (XPS) confirmed an addition reaction between L and OS, forming a dense network structure, effectively enhanceing the water resistance of OSL adhesives. Furthermore, compared with lignin-formaldehyde resin adhesive (LF), the OSL adhesive exhibited superior wet shear strength. This study offered an innovative approach for developing lignin-based adhesives utilizing a biomass aldehyde (OS), as a promising substitute for formaldehyde in the wood industry. The findings indicated that this approach may advance lignin-based adhesives, ensuring resistance to strength deterioration under highly humid environmental conditions.
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Lignina , Água , Lignina/química , Aldeídos , Adesivos/química , Formaldeído/química , SacaroseRESUMO
Starch adhesive is a commonly used bonding glue that is sustainable, formaldehyde-free and biodegradable. However, there are obviously some problems related to its high viscosity, poor water and mildew resistance. Hence, exploring a starch-based adhesive with good properties that satisfies the requirements of wood processing presents the context of the current research. Thus, corn starch was used as raw material to form oxidized starch (OCS) via oxidation using sodium periodate, it was reacted with a synthesis polyurea compound that prepared from hexanediamine-urea (HU) obtained by deamination to yield a oxidized starch-hexanediamine-urea adhesive (denoted hereafter as OCSHU). The oxidation process was optimized in terms of oxidant concentration, reaction time and temperature. Furthermore, the impact of HU addition on the mechanical properties of the adhesive was explored. Results indicate adhesive exhibited outstanding shear strength, when 13 % of NaIO4 was used as an oxidant to treat starch at 55 °C for 24 h, and involved in a subsequent reaction with 40 % of HU. The dry shear strength, 24 h cold water strength, 3 h hot water strength and 3 h boiling water strength are 1.84, 1.50, 1.32, and 1.31 MPa. Meantime, OCSHU adhesive solution revealed good storage stability whereas cured resin exhibited mildew resistance. The developed adhesive is a simple and green biomass wood adhesive.
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Adesivos , Amido , Água , Zea mays , Amido/química , Água/química , Adesivos/química , Zea mays/química , Oxirredução , Temperatura , Resistência ao Cisalhamento , Ureia/químicaRESUMO
Three plasmids from Lactobacillus plantarum G63, pG6301, pG6302 and pG6303, were sequenced and have molecular sizes of 3516-bp, 9112-bp and 10047-bp, respectively. We determined the replicons of these plasmids. The pG6301 plasmid carried a replication gene that functioned by the rolling-circle replication mechanism. The Rep protein of pG6302 shared extremely low similarity with a reported plasmid, pLME300, which replicated by a bi-directional mechanism. Both the Rep protein and OriV analyses indicated a similar replication mechanism in pG6302. Conversely, we found neither the Rep protein nor OriV when we analyzed the whole sequence of pG6303. This finding may illustrate a novel replication mechanism. Additionally, the transposon, a mobilization element, was analyzed and compared to a similar insertion sequence (IS) element. A predicted lysozyme gene, pG6303 guhA, was heterologously expressed, but no activity was detected. The pG6302 and pG6303 plasmids contain new replicons and may be useful vector candidates for future molecular manipulation of L. plantarum.
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Proteínas de Bactérias/genética , DNA Bacteriano/genética , Regulação Bacteriana da Expressão Gênica , Lactobacillus plantarum/genética , Muramidase/genética , Plasmídeos , Sequência de Aminoácidos , Sequência de Bases , Replicação do DNA , Elementos de DNA Transponíveis , Fermentação , Lactobacillus plantarum/isolamento & purificação , Dados de Sequência Molecular , Origem de Replicação , Análise de Sequência de DNA , Homologia de Sequência de Aminoácidos , Verduras/microbiologiaRESUMO
A novel Gram-negative, non-spore-forming, rod-shaped strain, H1(T), was isolated from activated sludge by micromanipulation. No close relatives among cultured bacterial isolates were found; phylogenetic analysis based on 16S rRNA gene sequences revealed that strain H1(T) forms a deep single branch in the family Rhodospirillaceae. Cells of strain H1(T) were slightly curved to straight rods (1.2-1.4 × 1.5-1.7 µm) and motile by a single polar flagellum. Strain H1(T) was able to grow in the presence of 0-4 % NaCl and grew optimally at 37 °C and pH 6.0-7.0. Chemotaxonomic analysis revealed that strain H1(T) possessed Q-10 as the predominant ubiquinone and C18 : 1ω7c, C16 : 0 and C19 : 0 cyclo ω8c as the major fatty acids. The DNA G+C content of strain H1(T) was 65.1 mol%. Comparative analysis of 16S rRNA gene sequences, and phenotypic and chemotaxonomic data, indicate that strain H1(T) should represent a novel genus and species of the family Rhodospirillaceae. The name Taonella mepensis gen. nov., sp. nov. is proposed. The type strain of Taonella mepensis is H1(T) ( = CICC 10529(T) = CCTCC AB 2012861(T) = KACC 16940(T)).
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Filogenia , Rhodospirillaceae/classificação , Esgotos/microbiologia , Técnicas de Tipagem Bacteriana , Composição de Bases , China , DNA Bacteriano/genética , Ácidos Graxos/análise , Dados de Sequência Molecular , RNA Ribossômico 16S/genética , Rhodospirillaceae/genética , Rhodospirillaceae/isolamento & purificação , Análise de Sequência de DNA , Ubiquinona/análogos & derivados , Ubiquinona/análiseRESUMO
Despite the widespread application prospect of soybean meal flour (SF) as a non-toxic and renewable wood adhesive, the practical application is limited by its poor mechanical properties and water resistance. In this work, a novel SF-based wood adhesive (CSP) was developed using citric acid (CA) as a modifier, which was further designated to produce plywood on a laboratory scale. Moreover, the effects of the mass ratio of CA/SF, hot-pressing temperature, and hot-pressing time on the bonding properties and water resistance of the resulting plywood were investigated in detail. As a result, under the optimal hot-pressing conditions (180 °C, 5 min), high-performance plywood bonded by CSP (CA/SF = 15/100) adhesive was fabricated, whose dry shear strength, cold-water wet shear strength (20 °C for 24 h), and hot-water wet shear strength (63 °C for 3 h) reached 1.65 MPa, 1.99 MPa, and 1.58 MPa, respectively. Due to the easy preparation process, sustainability, and favorable properties, the proposed fully bio-based CSP wood adhesive has great potential for the large-scale fabrication of eco-friendly wood panels in industry.
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Proteínas de Soja , Madeira , Glycine max , Farinha , Ácido Cítrico , ÁguaRESUMO
As a biomass material, tannins are used in the preparation of wood adhesives, but their poor strength and water resistance has greatly limited their application. Therefore, it is necessary to prepare tannin-based wood adhesives with good water resistance. In the present study, tannin and hexanediamine were simply mixed at room temperature to prepare tannin-hexanediamine (TH) adhesive and then used to prepare plywood. Effects of mass ratio of hexanediamine to tannin and pH value of TH adhesive are studied. The results indicating the effects of mass ratio and pH value are apparent on shear strength. When the mass ratio is above 25 % and the pH value is above 9, the plywood shows good water resistance. Fourier transform-infrared (FTIR), X-ray photoelectron spectroscopy (XPS), liquid chromatography-mass spectrometry (LCMS) and X-ray diffraction (XRD) are used to determine the structures of TH adhesive, confirmed the reaction between tannin and hexanediamine to form macromolecules. Simultaneous thermal analyzer (TG-DSC) and Dynamic mechanical analysis (DMA) are used to analyze the thermal properties, indicate TH resin contains a good storage module and heat resistance. Therefore, with its good shear strength and water resistance, this newly developed tannin-based adhesive has the potential to application in wood-based panel industry, as an alternative of formaldehyde-based adhesive.
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Adesivos , Taninos , Taninos/química , Adesivos/química , Madeira/química , Difração de Raios X , Resistência ao CisalhamentoRESUMO
Starch is one of the important raw materials for the preparation of biomass adhesives for its good viscosity and low-cost properties. However, the drawbacks of poor water resistance and bonding performance seriously restrict its application in the wood industry. To resolve those problems, an environment-friendly renewable, and high water resistance starch-based adhesive (OSTH) was prepared with oxidized starch and hexanediamine by Schiff base reaction. In order to optimize the adhesive preparation process, the effect of different oxidation times and oxidant addition on the mechanical performance of plywood were investigated. In addition, the curing behavior characteristics, thermomechanical properties, and thermal stability of the OSTH adhesives were analyzed by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and thermogravimetric analysis (TG). Fourier-transform infrared (FTIR) spectrometry and Liquid Chromatography-Mass Spectrometry (LC-MS) were used to explain the reaction mechanisms involved. The results show this adhesive has an excellent bonding performance at the oxidation time of 12 h with 11 % (w/w, dry starch basis) NaIO4 as an oxidant. The dry shear strength, 24-hour cold water, and 3-hour hot water (63 °C) soaking shear strength of the plywood bonded with this resin were respectively 1.87 MPa, 0.96 MPa, and 0.91 MPa, which satisfied the standard requirement of GB/T 9846-2015 (≥0.7 MPa). Thus, this study provided a potential strategy to prepare starch-based wood adhesives with good bonding performance and water resistance.
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Starch adhesive, as a sustainable biomass-based adhesive, could be used to solve environmental problems from petroleum-derived adhesive. But its application is hindered by poor water resistance, mildew resistance, and storage stability. Here, a fully bio-based citric acid-starch adhesive (CASt) with high properties was successfully introduced by a simple method. Liquid chromatography/mass spectrometry (LC-MS), and Fourier Transform Infrared spectroscopy (FT-IR) determined that esterification of citric acid (CA) and starch (St) occurred to form a stable three-dimensional crosslinking structure, which strengthened water resistance and bonding strength of the starch adhesive. Compared with native starch (100 %), the soluble content of cured CASt was 1-16 %. CASt adhesive has well storage stability and high mildew resistance. Even after being stored for 5 months, the CASt-1 adhesive (mass ratio of CA/St = 1:1, and reaction time = 1 h) still have good liquidity. And its hot water strength (1.05 ± 0.22 MPa) also satisfied the standard requirements (≥0.7 MPa). The exhibited CASt adhesive is eco-friendly with components from plant resources, which performed as a bright alternative that can substitute petroleum-based adhesives in the artificial board industry.
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Adesivos , Amido , Amido/química , Adesivos/química , Água/química , Espectroscopia de Infravermelho com Transformada de Fourier , Ácido CítricoRESUMO
Condensed tannin copolymerized with hyperbranched tris(2-aminoethyl)amine-urea formed by amine-amido deamination yields a particleboard thermosetting adhesive without any aldehydes satisfying the requirements of relevant standards for the particleboard internal bond strength. The tannin-triamine-urea cures well at 180 °C, a relatively low temperature for today's particleboard hot pressing. As aldehydes were not used, the formaldehyde emission was found to be zero, not even in traces due to the heating of wood. The effect is ascribed to the presence of many reactive sites, such as amide, amino, and phenolic groups belonging to the three reagents used. The tannin appears to function as an additional cross-linking agent, almost a nucleating agent, for the triamine-urea hyperbranched oligomers. Chemical analysis by MALDI ToF and 13C NMR has shown that the predominant cross-linking reaction is that of the substitution of the tannin phenolic hydroxyls by the amino groups of the triamine. The reaction of tannin with the still-free amide groups of urea is rather rare, but it may occur with the rarer tannin flavonoid units in which the heterocyclic ring is opened. Due to the temperature gradient between the surfaces and the board core in the particleboard during hot pressing, the type and the relative balance of covalent and ionic bonds in the resin structure may differ in the surfaces and the board core.
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Biomass-based adhesives have attracted much attention due to their eco-friendly, sustainable characteristics compared to formaldehyde-based adhesives; however, their low bonding strength and water resistance restrict their application. Thus, developing a high-performance biomass-based adhesive with excellent bonding strength and water resistance is necessary. In this work, a fully biomass-based citric acid-glucose (CAG) adhesive was produced by the esterification reaction of glucose and citric acid, which was validated by Fourier transform infrared (FT-IR), 13C nuclear magnetic resonance (13C NMR), and liquid chromatography-mass spectrometry (LC-MS). Furthermore, the properties of the CAG adhesive were tuned considering the effects of reaction time and molar ratio of citric acid/glucose (CA/G). It was revealed that increasing the molar ratio of CA/G is more advantageous to improve the shear strength and water resistance of plywood than the reaction time. The dry and wet strengths of plywood bonded by the CAG adhesive can reach the standard requirement (≥0.7 MPa) when the molar ratios of CA/G were more than 0.6 and the reaction time was 1 h. These results were better than those bonded by the urea-formaldehyde (UF) resin. Therefore, this green adhesive shows great potential to replace the existing industrial UF resin adhesives.
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Glyoxal is considered to be the most likely substitute for formaldehyde to synthesize resin adhesives for wood bonding due to its reactivity, structural characteristics, being non-toxic, low volatility, and acceptable cost. Regrettably, the performance of the resin synthesized using glyoxal to directly replace all formaldehyde is not totally satisfactory, especially as it has almost no water resistance. This makes such a simple alternative fail to be suitable for industrial production. To prepare an environment-friendly glyoxal-based adhesive with good bonding performance, the work presented here relies first on reacting citric acid and hexamethylene diamine, producing a polyamide, with glyoxal, and then crosslinking it, thus synthesizing a thermosetting resin (namely CHG) adhesive and applying it for plywood bonding. The plywood prepared exhibits excellent dry and wet shear strength, which are better than GB/T9846-2015 standard requirements (≥0.7 MPa), and even after being soaked in hot water at 63 °C for 3 h, its strength is still as high as 1.35 MPa. The CHG resin is then potentially an adhesive for industrial application for replacing UF (urea-formaldehyde) and MUF (melamine-urea-formaldehyde) adhesives for wood composites.
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Synthetic foams have become an essential industrial product for a great variety of applications. Furfuryl alcohol, as a biomass chemical, was reacted with glyoxal at room temperature to prepare furanic-glyoxal rigid foams, and p-toluenesulfonic acid was used as a catalyst to initiate the reaction. Foams with different molar ratios (furfuryl alcohol/glyoxal) were prepared in this work, and uniform cells foams have been obtained. Their compression resistance, 24-h water absorption, density, and other basic properties were tested. Scanning electron microscopy (SEM) was used to observe the cellular morphology of the foams prepared, thermogravimetric analysis (TGA) helped to understand their thermal and combustion properties, and FTIR and Matrix Assisted Laser Desorption Ionisation Time of Flight (MALDI ToF) mass spectroscopy to explain the structure of the resulting foams to clarify the reactions occurring during foaming. The results show that the compression resistance of furanic-glyoxal foams declined as the furfuryl alcohol/glyoxal ratio decreases also. SEM observations revealed that foams with open-cell were obtained when furfuryl alcohol was added in greater amounts, and more closed cell structures were formed as the proportion of glyoxal increased. TGA results showed that the initial ignition temperature of furanic-glyoxal foams is ~200 °C higher than that of wood, and the smaller comprehensive combustion index S (about 0.15 × 10-7 (%2 K-3 min-2)) indicates that the foam burns slowly and has poor flammability, that is, it is not easy to burn.
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Ambient temperature self-blowing mimosa tannin-based non-isocyanate polyurethane (NIPU) rigid foam was produced, based on a formulation of tannin-based non-isocyanate polyurethane (NIPU) resin. A citric acid and glutaraldehyde mixture served as a blowing agent used to provide foaming energy and cross-link the tannin-derived products to synthesize the NIPU foams. Series of tannin-based NIPU foams containing a different amount of citric acid and glutaraldehyde were prepared. The reaction mechanism of tannin-based NIPU foams were investigated by Fourier Trasform InfraRed (FT-IR), Matrix Assisted Laser Desorption Ionization (MALDI-TOF) mass spectrometry, and 13C Nuclear Magnetic Resonance (13C NMR). The results indicated that urethane linkages were formed. The Tannin-based NIPU foams morphology including physical and mechanical properties were characterized by mechanical compression, by scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). All the foams prepared showed a similar open-cell morphology. Nevertheless, the number of cell-wall pores decreased with increasing additions of glutaraldehyde, while bigger foam cells were obtained with increasing additions of citric acid. The compressive mechanical properties improved with the higher level of crosslinking at the higher amount of glutaraldehyde. Moreover, the TGA results showed that the tannin-based NIPU foams prepared had similar thermal stability, although one of them (T-Fs-7) presented the highest char production and residual matter, approaching 18.7% at 790 °C.
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Soy protein isolate (SPI) and insoluble soy flour polymeric carbohydrates have been reacted with sodium periodate for the specific oxidation of vicinal -OH groups to investigate the reactions involved in this approach to soy flour adhesives. The reactions have been shown to generate carbohydrate oligomer fractions presenting one, two or multiple aldehyde groups. With the exception of the small molecular weight heptanedial, the smaller molecular weight aldehydes generated from mono- and disaccharides by the same reaction do not appear to form from the insoluble soy flour carbohydrates, or have already reacted. The reaction of periodate with soy protein isolate has been shown to generate some aldehydes too. When the mix of SPI and soy insoluble carbohydrates is treated with periodate, the majority of the observed aldehyde carrying species appear to be higher molecular weight carbohydrate oligomer fractions.
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A partially biobased self-blowing and self-hardening polyurethane foam from glucose-based non-isocyanate polyurethanes (g-NIPU) was prepared by reaction of glucose with dimethyl carbonate and hexamethylene diamine. However, these foam types generally require a high foaming temperature. In this paper, a self-blowing foam based on g-NIPU was prepared at room temperature by using maleic acid as an initiator and glutaraldehyde as a crosslinker. Water absorption, compression resistance, and fire resistance were tested. Scanning electron microscopy (SEM) was used to observe the foam cells structure. Middle infrared (ATR FT-MIR) and Matrix Assisted Laser Desorption Ionization Time-of-Flight (MALDI-TOF) mass spectrometry were used to help to analyze the reactions during the foaming process. The results obtained showed that self- blowing rigid foams have good compression, this being directly proportional to the foam density. Increasing the amount of glutaraldehyde or reducing maleic acid thickens the cell walls and increases the density of the foams. MALDI-TOF analysis showed that g-NIPU reacts with both maleic acid and glutaraldehyde. The foams presented poor fire resistance indicating that, as for isocyanate based polyurethane foams, addition of a fire retardant would be necessary.
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To find the effects of cross-linker phenol-formaldehyde (PF) resin on the performance of soy-based adhesives, the reaction between model compounds hydroxymethyl phenol (HPF) and glutamic acid were studied in this paper. HPF prepared in laboratory conditions showed higher content of hydroxymethyl groups than normal PF resin, which was proved by the results of Electrospray Ionization Mass Spectrometry (ESI-MS) and 13C Nuclear Magnetic Resonance (13C-NMR). The results of ESI-MS, Fourier transform infrared spectroscopy (FT-IR), and 13C-NMR based on resultant products obtained from model compounds showed better water resistance of the soy protein-based adhesive modified by PF-based resin, which indicated the reaction between PF resin and soy protein. However, it seemed that the soy-based adhesive cross-linked by HPF with the maximum content of hydroxymethyl groups did not show the best water resistance.
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Tannin and lignin were blended with polypropylene (PP) through dynamic vulcanization technique. Their influence of mechanical property, crystallinity, thermal stability, as well as ultraviolet (UV) protection property on the PP matrix was investigated and compared with native tannin and lignin. According to our experimental results, tannin and lignin undergo dynamic vulcanization and were more compatible with the PP matrix. Besides, tannin and vulcanized tannin can perform as nucleating agents of PP because of their relatively small particle size. Moreover, vulcanized tannin/lignin have a better performance on the thermal stability of PP compared with native tannin/lignin, especially PP/vulcanized lignin blend. Furthermore, vulcanized tannin/lignin present better UV protective performance, concluded from fewer changes on surface morphology, carbonyl index, crystallinity, viscosity, and tensile property.
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Two novel depsipeptides xenematides F and G (1, 2), were isolated from entomopathogenic Xenorhabdus budapestensis SN84 along with a known compound xenematide B. The structures of the two new molecules were elucidated using NMR, MS and Marfey's method. The xenematide G (2) contains α-aminoheptanoic acid, a non-protein amino acid that is rarely found in secondary metabolites from entomopathogenic bacteria. Xenematides F and G were tested for antibacterial activity. Xenematide G (2) exhibited moderate antibacterial activity.