Lignin Phenol Formaldehyde Resin Research Articles

Effect of demethylation of acetone-soluble softwood kraft lignin on adhesion of lignin–phenol–formaldehyde resins

Owing to the increasing interest in sustainability and bio-based materials, softwood kraft lignin (SKL) was acetone-fractionated to reduce its heterogeneity and then demethylated to substitute phenol in lignin–phenol–formaldehyde (LPF) resins to be used as bio-based wood adhesives. This study investigated the effect of the demethylation of acetone-soluble SKL (AS-SKL) on the adhesion of LPF resins, where phenol was partially replaced with acetone-soluble demethylated kraft lignin (AS-DKL). Characterization of SKL, AS-KL, and AS-DKL using gel permeation chromatography (GPC), FTIR, and 31P NMR spectroscopy showed that the demethylation was successfully performed; the molecular weight (MW) and the number of methoxy groups decreased, and the number of –OH groups increased. The MW, chemical reactions, and curing behavior of LPF resins synthesized with different AS-DKL levels (10, 20, 30, and 50 wt%) were also characterized. With the increase in AS-DKL content, the viscosity and MW of the resin increased, whereas the gelation time decreased. LPF resins with 10% AS-DKL showed the highest tensile shear strength and lowest peak curing temperature. These results suggest that 10% is an optimal AS-DKL level in LPF resins for plywood bonding and that demethylation is an effective way of utilizing SKL.

Bonding wood with uncondensed lignins as adhesives

Plywood is widely used in construction, such as for flooring and interior walls, as well as in the manufacture of household items such as furniture and cabinets. Such items are made of wood veneers that are bonded together with adhesives such as urea–formaldehyde and phenol–formaldehyde resins1,2. Researchers in academia and industry have long aimed to synthesize lignin–phenol–formaldehyde resin adhesives using biomass-derived lignin, a phenolic polymer that can be used to substitute the petroleum-derived phenol3–6. However, lignin–phenol–formaldehyde resin adhesives are less attractive to plywood manufacturers than urea–formaldehyde and phenol–formaldehyde resins owing to their appearance and cost. Here we report a simple and practical strategy for preparing lignin-based wood adhesives from lignocellulosic biomass. Our strategy involves separation of uncondensed or slightly condensed lignins from biomass followed by direct application of a suspension of the lignin and water as an adhesive on wood veneers. Plywood products with superior performances could be prepared with such lignin adhesives at a wide range of hot-pressing temperatures, enabling the use of these adhesives as promising alternatives to traditional wood adhesives in different market segments. Mechanistic studies indicate that the adhesion mechanism of such lignin adhesives may involve softening of lignin by water, filling of vessels with softened lignin and crosslinking of lignins in adhesives with those in the cell wall.

Selected Kraft lignin fractions as precursor for carbon foam: Structure-performance correlation and electrochemical applications

The rapid exhaustion of fossil fuels brings to the fore the need to search for energy efficient strategies. The conversion of lignin into advanced functional carbon-based materials is considered one of the most promising solutions for environmental protection and the use of renewable resources. This study analyzed the structure-performance correlation of carbon foams (CF) when lignin-phenol-formaldehyde (LPF) resins produced with different fractions of kraft lignin (KL) were employed as carbon source, and polyurethane foam (PU) as sacrificial mold. The lignin fractions employed were KL, fraction of KL insoluble in ethyl acetate (LFIns) and fraction of KL soluble in ethyl acetate (LFSol). The produced CFs were characterized by thermogravimetric analysis (TGA), X-ray diffractometry (XRD), Raman spectroscopy, 2D HSQC Nuclear magnetic resonance (NMR) analysis, scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), and electrochemical measurements. The results showed that when LFSol was employed as a partial substitute for phenol in LPF resin synthesis, the final performance of the produced CF was infinitely higher. The improved solubility parameters of LFSol along with the higher S/G ratio and β-O-4/α-OH content after fractionation were the key to produce CF with better carbon yields (54 %). The electrochemical measurements showed that LFSol presented the highest current density (2.11 × 10−4 mA.cm−2) and the lowest value of resistance to charge transfer (0.26 KΩ) in relation to the other samples, indicating that the process of electron transfer was faster in the sensor produced with LFSol. LFSol's potential for application as an electrochemical sensor was tested as a proof of concept and demonstrated excellent selectivity for the detection of hydroquinone in water.

Effects of Precipitation pH of Black Liquor on Characteristics of Precipitated and Acetone-Fractionated Kraft Lignin

Two important steps in utilizing technical kraft lignin (KL) from black liquor to synthesize lignin-phenol-formaldehyde (LPF) resin are its extraction via precipitation and fractionation. However, the effects of precipitation pH and acetone fractionation on the characteristics of hardwood KL have not been studied for LPF resins. Therefore, this paper reports the effects of the precipitation pH of black liquor and acetone fractionation on the characteristics of KL from mixed hardwood species for LPF resins. The precipitation was conducted at various pH levels from 3 to 9 of black liquor to obtain crude KL (C-KL), which was used in acetone fractionation to produce acetone-soluble KL (AS-KL) and acetone-insoluble KL (AI-KL). Precipitation at pH 3 and 9 produced the highest and lowest yields of C-KL, respectively. As expected, the C-KL infrared spectra were similar regardless of the precipitation pH levels. As the pH increased, the molecular weight of C-KL increased. However, the molecular weight of AS-KL and AI-KL after acetone fractionation increased to a maximum of 4,170 and 47,190 g/mol at pH 7, then decreased to 3,210 and 19,970 g/mol at pH 9, respectively. The smallest molecular weights of AS-KL and AI-KL were 3,210 and 15,480 g/mol and were found at pH 9 and 3, respectively. These results suggest that both AS-KL at pH 9 and AI-KL at pH 3 have good potential as starting lignins for synthesizing LPF resins that require cross-linking for polymerization.

Selection of kraft lignin fractions as a partial substitute for phenol in synthesis of phenolic resins: Structure-property correlation

In this work, a strategy was proposed aiming to describe an efficient kraft lignin (KL) fractionation method to extract large amounts of low molar mass lignin to partially replace non-renewable phenol with the KL fractions in the synthesis of phenolic resins. KL from Eucalyptus urograndis wood was refined by a fractionation process in ethyl acetate (EtAc). The lignin-phenol-formaldehyde (LPF) resins were formulated by replacing 25% and 50% of phenol with the fractionated lignin. The lignin employed were KL, fraction of KL insoluble in EtAc (LFIns) and fraction of KL soluble in EtAc (LFSol). The LFSol and LFIns fractions were analyzed for composition, functional group content, and thermal properties. Gel Permeation Chromatography (GPC) results indicated that the lower molar mass lignin fractions (LFSol) showed higher solubility in EtAc. The total hydroxyl groups content (by 31 P NMR) of the soluble EtAc fraction increased to 4.73 mmol.g −1 after fractionation. The phenolic resin based on monomers derived from LFSol showed adhesion strength, glass transition temperature and thermal stability with values close to commercial phenolic resins. The better homogeneity of the LPF resin produced from LFSol at 25% phenol substitution resulted in adhesion properties similar to the control resin. On the other hand, LFSol could successfully directly replace 15% of the commercial PF resin (corresponding to > 30% phenol replacement) showing the performance similar to the commercial PF control and significantly higher than the LFIns and non-fractionated KL. • Extraction method of low molar mass kraft lignin. • Structure-performance correlation of selection of kraft lignin fractions. • Partial replacement of non-renewable phenol by lignin fractions. • Improved performance of the soluble lignin fraction as an adhesive.

Lignin-based wood adhesives: A comparison between the influence of soda and Kraft lignin

Due to the various chemical properties of lignins, one has different effects on the resins prepared with them. The aim of this research was to compare the influence of Soda and Kraft lignins on the physical and mechanical properties of the particleboards bonded with lignin-urea-formaldehyde (LUF) and lignin-phenol-formaldehyde (LPF) resins. According to the FTIR spectra and DSC analysis of lignin, Soda lignin exhibited higher phenolic hydroxyl groups and lower glass transition temperature (Tg) value compared to Kraft lignin. Also DSC analysis results indicated that the resins based on Soda lignin need a lower temperature for curing than those based on Kraft lignin. Based on physicochemical test results, the resins containing Soda lignin exhibit a faster gel time and higher viscosity compared to those prepared with Kraft lignin in the both types of resins. Generally physical and mechanical properties results indicated that the panels made from LPF resin have higher mechanical strength and dimensional stability compared to those made from LUF resins at constant level of lignin. The particleboards bonded with Soda-based resin yielded lower water absorption and formaldehyde emission as well as higher flexural strength and internal bonding strength when compared to those bonded with the Kraft-based resin. The mechanical properties of the particleboards bonded with LPG resins could be significantly improved by increasing percentages of lignin while it was decreased for LUF resin.

Preparation of Lignosulfonate‐Based Phenol Formaldehyde Foam with Excellent Thermal Performance

AbstractAn efficient route for the synthesis of lignin phenol formaldehyde (LPF) foams through the foaming process of LPF resin is described. The one‐pot method is used to prepare the resin. To obtain the resin, lignosulfonate is phenolic modified under alkaline conditions. The resin is obtained by incorporating the modified lignosulfonate with phenol via phenol‐formaldehyde condensation. Subsequently, the LPF resin is subjected to a foaming process that yields LPF foam, and the thermal properties of the foam are investigated. The results of 1H nuclear magnetic resonance (1H‐NMR), Fourier transform infrared (FT‐IR) spectroscopy, and gel permeation chromatography (GPC) analyses indicate that compared with lignosulfonate, the molecular weight of phenolated lignin decreases significantly, and the content of phenolic and aliphatic hydroxyl groups increases. Thermogravimetric, thermal conductivity, and limiting oxygen index analyses are also conducted. The results reveal that the maximum carbon residue rate (43.76% at 800 °C), maximum thermal conductivity (0.0344 W m−1 K−1), and maximum oxygen index (39.1%) occur for the LPF foam with 20 wt% lignin. These results demonstrate that lignosulfonate is a promising candidate for the use of phenol modification in preparing LPF foam. Furthermore, this study provides a new direction for the modification and application of lignin.

Lignin Phenol Formaldehyde Resins Synthesised Using South African Spent Pulping Liquor

The current study investigated to which extent phenol could be replaced by lignins to produce lignin phenol formaldehyde (LPF) resins, utilising soda lignin and sodium lignosulphonate as by-products from the South African pulping industry. The lignins were characterised and soda lignin indicated the highest reactivity. It was therefore utilised to produce LPF resins at 60%, 80%, and 100% phenol substitution, using central composite designs to maximise the adhesive strength. A one-pot method allowing direct transition from phenolation to resin synthesis was used for the first time with a pulping lignin at 60% and 80% substitution. Plywood made with LPF60, LPF80, and LPF100 resins attained their highest shear strengths of 0.786, 1.09, and 0.987 MPa, respectively, which adhered to the GB/T 14,732–2013 standard (≥ 0.7 MPa). A substitution level of 68% produced the highest shear strength of 1.11 MPa. High-density particleboard made with this LPF68 resin gave a MOR and MOE of 40 and 3209 MPa, respectively, adhering to the ANSI A208.1 requirements. Thickness swelling and water absorption was 13.5% and 37.2%, respectively. The soda-lignin isolated by precipitation from sugarcane bagasse pulping liquor is the first industrial lignin shown to produce LPF100 resins adhering to standard requirements, without modification or additives.

Maleated lignin coreaction with phenol-formaldehyde resins for improved wood adhesives performance

This research work investigated the physical and mechanical properties of particleboard panels bonded with maleated-lignin-phenol-formaldehyde (mLPF) resin. For this purpose, lignin was modified by maleic anhydride and then various contents of unmodified/modified lignin (30, 40 and 50 wt%) were added as a substitute for phenol in the phenol-formaldehyde (PF) resin synthesis. The properties of the synthesized resins were compared with those of an unmodified LPF and a control PF resin. The structure of the modified lignin was studied by FTIR, and the changes in curing behavior of the resins prepared were analyzed by DSC. The physicochemical properties of the synthesized resins (such as gel time, viscosity, solid content and density) and physical (water absorption) and mechanical properties (flexural properties, internal bond strength) of the prepared particleboard panels bonded with LPF resins were measured. The FTIR analysis indicated that, by treatment of lignin, the COOH, C–O and CC bonds increase while the content of O–H bond markedly decreases. The DSC analysis showed that curing of the mLPF resin occurred at a lower temperature than for the control PF resin and the unmodified lignin-phenol-formaldehyde (LPF) resins. The viscosity increased and the gel time was shortened by adding maleated lignin to the PF resin. The panels bonded with the modified lignin resins presented a lower formaldehyde emission, and a higher dimensional stability and mechanical strength than those bonded with the control PF resin and the unmodified lignin adhesive. Moreover, the mechanical strength and dimensional stability of the particleboard panels were significantly improved by increasing the resin content of maleated lignin from 0 to 50 wt%.

A Comparison among Lignin Modification Methods on the Properties of Lignin-Phenol-Formaldehyde Resin as Wood Adhesive.

The research aim of this work is to determine the influence of lignin modification methods on lignin–phenol–formaldehyde (LPF) adhesive properties. Thus, glyoxal (G), phenol (P), ionic liquid (IL), and maleic anhydride (MA) were used to modify lignin. The modified lignins were used for phenol substitution (50 wt%) in phenol–formaldehyde adhesives. The prepared resins were then used for the preparation of wood particleboard. These LPF resins were characterized physicochemically, namely by using standard methods to determine gel time, solids content, density, and viscosity, thus the physicochemical properties of the LPF resins synthesized. The panels dimensional stability, formaldehyde emission, bending modulus, bending strength, and internal bond (IB) strength were also measured. MA-modified lignin showed by differential scanning calorimetry (DSC) the lowest temperature of curing than the resins with non-modified lignin and modified with IL, phenolared lignin, and glyoxal. LPF resins with lignin treated with maleic anhydride presented a shorter gel time, higher viscosity, and solids content than the resins with other lignin modifications. Equally, the particleboard panels prepared with LPF resins with maleic anhydride or with ionic liquid had the lowest formaldehyde emission and the highest mechanical strength among all the synthesized resins. The dimensional stability of all panels bonded with modified lignin LPF resins presented no difference of any significance.

Pretreatment of kraft lignin by deep eutectic solvent and its utilization in preparation of lignin-based phenolic formaldehyde adhesive

To improve the reactive sites of kraft technical lignin, a deep eutectic solvent (DES) composed of ZnCl2 / lactic acid was used to pretreat kraft lignin from coniferous wood. The modified and unmodified lignin were used to replace different proportions of phenol (50%, 60%, and 70%) to prepare the lignin-phenol-formaldehyde (LPF) adhesive. The phenolic hydroxyl content of DES-treated lignin increased from 3.12 wt% to 3.93 wt% and methoxy content decreased from 11.83 wt% to 6.64 wt% under optimized experimental conditions. The bond strength of LPF adhesive prepared by DES reagent activated lignin was higher than that of the control sample. When the substitution degree of modified lignin for phenol reached 70%, the bond strength of the plywood prepared by the DES-pretreated lignin was 0.79 MPa and the free formaldehyde content was 0.28%, which met the requirements of the Chinese national standard GB/T 9846 (2015). However, the viscosity was higher than the control sample, and results indicate that DES reagent modification cannot improve the viscosity of LPF resin.

The Use of South African Spent Pulping Liquor to Synthesize Lignin Phenol-Formaldehyde Resins

Abstract This study aims to investigate the potential of using lignin sourced from South African black liquor as a total phenol substitute in phenol-formaldehyde resins (PFRs), with a particular focus on bonding strength and curing properties. Four South African pulping-based lignins were used to synthesize these lignin-phenol formaldehyde resins (LPF100 resins), namely Eucalyptus Kraft lignin, Pine Kraft lignin, Bagasse Soda lignin, and Bagasse Steam Exploded lignin. Fourier-transform infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry were used to determine structural and curing properties. These resins were then used directly (unmodified) as adhesives to test shear bonding strength (R0 LPF100 adhesives). To improve the bonding properties of the unmodified LPF100 adhesives, the LPF100 resins were modified via the addition of a crosslinker (hexamine) as well as a hardener (either glyoxal, R1, or epichlorohydrin, R2). All R0 LPF100 adhesives fell below the GB/T 17657-2013 plywood standard of ≥0.7 MPa, with the Bagasse Soda LPF100 adhesive recording the highest bonding performance of 0.5 MPa, and the lowest curing temperature of 68°C. From the modified adhesives, the best performing were the Pine Kraft (R1) and the Eucalyptus Kraft (R2) LPF100 adhesives, recording 1.4 and 1.3 MPa, respectively. The curing temperatures of both these resins were 71°C and 80°C, respectively. Ultimately, the results of this study indicated that favorable adhesive properties may be obtained with the use of South African pulping-based lignins as a 100 percent phenol substitute in PFRs.

Thermoplastic and moisture‐dependent behavior of lignin phenol formaldehyde resins

ABSTRACTBonding kinetics of thermosetting adhesives is influenced by a variety of factors such as temperature, humidity, and resin properties. A comparison of lignin‐based phenol formaldehyde (LPF) and phenol formaldehyde (PF) adhesive in terms of reactivity and mechanical properties referring to testing conditions (temperature, moisture of specimen) were investigated. For this purpose, two resins were manufactured aiming for similar technological resin properties. The reactivity was evaluated by B‐time measurements at different temperatures and the development of bonding strength at three different conditions, testing immediately after hot pressing, after applying a cooling phase after hot pressing, or sample conditioning at standard climate. In addition, the moisture stability of the two fully cured resins was examined. The calculated reactivity index demonstrated that LPF requires more energy for curing than PF. Further results indicate that lignin as substituent for phenol in PF resin has a negative impact on its moisture resistance. Additionally, the known thermoplastic behavior of lignin could also be detected in the behavior of the cured resin. This behavior is relevant for the adhesive in use and necessitates a cooling phase before testing the bonding strength development of lignin‐based adhesive systems. © 2019 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48011.

Modification of beech veneers with lignin phenol formaldehyde resins in the production of laminated veneer lumber (LVL)

Rotary cut beech (Fagus sylvatica L.) veneers were treated with four different lignin phenol formaldehyde (LPF) solutions using dimethyl sulfoxide (DMSO) as a solvent. Four of these veneers were bonded with PF adhesive to produce four-layer laminated veneer lumber (LVL). To synthesize the LPF solutions, a commercial phenol formaldehyde resin (PF resin) was individually mixed with three different technical lignins (Indulin AT, BioChoice lignin, organosolv lignin) and lignin cleavage products (LCP) at a ratio of 3:2 (60%:40%). Differential scanning calorimetry showed an increased curing temperature for the LPF resins in comparison to the PF resin. The mechanical and water-related properties of the LPF-modified LVL were shown to be similar or slightly improved compared to PF-modified LVL. Fungal degradation experiments with white-rot fungus (Trametes versicolor) and brown-rot fungus (Coniophora puteana) exhibited no significant differences in the mass loss of the LPF-modified and PF-modified samples except in one case: LVL made from veneers treated with Indulin AT exposed to the white-rot fungus. The resistance to weathering of LVL samples made from veneers treated with technical lignins was low; however, specimens treated with LCP and the reference PF resin displayed a higher resistance to weathering. It is concluded that technical lignins or LCP can, to a certain extent, be used as a substitute for crude-oil based PF resin.

Carbon foams produced from lignin-phenol-formaldehyde resin for oil/water separation

Carbon foams for oil/water separation were synthesized using lignin-phenol-formaldehyde (LPF) resin as the carbon source and polyurethane (PU) foam as the template. Lignin was extracted from sedge grass and was used to replace 25 wt% of the phenol to prepare a LPF resin in an alkaline medium. The carbon foams exhibit unique properties such as open macropores, low bulk density, good water repellency and efficient oil absorption. The absorption capacities of the carbon foams are 12 to 41 times their own weight for a wide range of oils and organic solvents. The foams can be recycled by directly burning the oil within their pores and absorption capacity remains above 83% after 10 absorption test cycles, indicating that the carbon foams are promising oil sorbents with a good recyclability.

Properties of plywood panels bonded with ionic liquid-modified lignin–phenol–formaldehyde resin

ABSTRACTThe aim of this research was to investigate the physical and mechanical properties of plywood panels bonded with ionic liquid-modified lignin–phenol–formaldehyde (LPF) resin. For this purpose, soda bagasse lignin was modified by 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) ionic liquid, and then, various contents of modified lignins (10, 15, and 20 wt%) were added as a substitute of phenol in phenol–formaldehyde (PF) resin synthesis. The properties of the synthesized resin were compared with those of a control PF resin. The changes in curing behavior of the resins prepared were analyzed by differential scanning calorimetry (DSC). The physical properties of the resins prepared, as well as the water absorption, thickness swelling, shear strength, and formaldehyde emission of the plywood panels bonded with these adhesives, were measured according to standard methods. DSC analysis indicated that in comparison with PF resins, curing of the LPF resin occurred at lower temperatures. The physical properties of the synthesized resins indicated that viscosity and solid content increased, while gel time and density decreased by addition of treated lignin to the PF resin. Although the panels containing resins with modified lignin yielded low formaldehyde emission, their dimensional stability was worse than those bonded with a commercial PF adhesive. The plywood prepared using IL-treated lignin PF resins has shear strength, which satisfy the requirements of the relevant standards specifications and significantly better than that of panels prepared with the control PF resin. The mechanical properties of the panels could be significantly enhanced with increased percentage of treated lignin content from 0 to 20 wt%.

Valorization of lignin and cellulose in acid-steam-exploded corn stover by a moderate alkaline ethanol post-treatment based on an integrated biorefinery concept.

BackgroundDue to the unsustainable consumption of fossil resources, great efforts have been made to convert lignocellulose into bioethanol and commodity organic compounds through biological methods. The conversion of cellulose is impeded by the compactness of plant cell wall matrix and crystalline structure of the native cellulose. Therefore, appropriate pretreatment and even post-treatment are indispensable to overcome this problem. Additionally, an adequate utilization of coproduct lignin will be important for improving the economic viability of modern biorefinery industries.ResultsThe effectiveness of moderate alkaline ethanol post-treatment on the bioconversion efficiency of cellulose in the acid-steam-exploded corn stover was investigated in this study. Results showed that an increase of the alcoholic sodium hydroxide (NaOH) concentration from 0.05 to 4% led to a decrease in the lignin content in the post-treated samples from 32.8 to 10.7%, while the cellulose digestibility consequently increased. The cellulose conversion of the 4% alcoholic NaOH integrally treated corn stover reached up to 99.3% after 72 h, which was significantly higher than that of the acid steam exploded corn stover without post-treatment (57.3%). In addition to the decrease in lignin content, an expansion of cellulose I lattice induced by the 4% alcoholic NaOH post-treatment played a significant role in promoting the enzymatic hydrolysis of corn stover. More importantly, the lignin fraction (AL) released during the 4% alcoholic NaOH post-treatment and the lignin-rich residue (EHR) remained after the enzymatic hydrolysis of the 4% alcoholic NaOH post-treated acid-steam-exploded corn stover were employed to synthesize lignin-phenol-formaldehyde (LPF) resins. The plywoods prepared with the resins exhibit satisfactory performances.ConclusionsAn alkaline ethanol system with an appropriate NaOH concentration could improve the removal of lignin and modification of the crystalline structure of cellulose in acid-steam-exploded corn stover, and consequently significantly improve the conversion of cellulose through enzymatic hydrolysis for biofuel production. The lignin fractions obtained as byproducts could be applied in high performance LPF resin preparation. The proposed model for the integral valorization of corn stover in this study is worth of popularization.

Preparation and Characterization of a Phenol-formaldehyde Resin Adhesive Obtained from Bio-ethanol Production Residue

Enzymatic hydrolysis (EH) lignin was utilized to replace phenol partially for preparing phenol-formaldehyde (PF) resin adhesives. The influence of the degree of lignin substitution on the properties of the lignin phenol-formaldehyde (LPF) resin adhesive was investigated. The results demonstrated that up to 50% of phenol in the resin could be replaced by EH lignin without damaging the bonding strength of the adhesive, and a lower free phenol content was observed in LPF resin adhesives. Fourier transform infrared spectroscopy spectra of the resins revealed that the introduction of lignin did not appreciably change the final chemical structure of the adhesive, but did negatively impact the resin's thermal ultimate stability. Furthermore, compared to bio-ethanol production residue-modified phenol-formaldehyde (ERPF) resin, the LPF resin exhibited higher bonding strength at the same level of the phenol substitution. This result of the comparison indicated that the raw biomass extraction process improved the performance of the bio-based PF resin.

Lignin–phenol–formaldehyde resin adhesives prepared with biorefinery technical lignins

ABSTRACTIn this study, four biorefinery technical lignins were used to synthesize lignin–phenol–formaldehyde (LPF) resin adhesives with a proposed formulation that was designed based on accurate analysis of the active sites in lignin with 31P nuclear magnetic resonance (NMR). The properties of the LPF resin adhesives and the plywoods prepared with them were tested. The structural features and curing behavior of the LPF resin adhesives were thoroughly investigated by solution‐ and solid‐state 13C NMR. Results indicated that the proposed formulation exhibited favorable adaptability for all four of these technical lignins for synthesis of LPF resin adhesives. High‐performance plywood with low emissions of formaldehyde could be successfully prepared with the synthesized LPF resin adhesives. All the LPF resin adhesives exhibited similar structure and curing behavior with the commercial phenol–formaldehyde (CPF) resin adhesive. However, the LPF resin adhesives showed relatively higher curing temperatures as compared with the CPF resin adhesive. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42493.

Fungus-Modified Lignin and Its Use in Wood Adhesive for Manufacturing Wood Composites*

Abstract Organosolv lignins were modified with different fungal species. The modified lignins were used as raw materials for preparing lignin-phenol-formaldehyde (LPF) resins. Oriented strandboard (OSB) panels were produced with these laboratory-synthesized LPF resins for evaluating the bond performance of the LPF resins in the manufacturing of wood composites. Ultraviolet spectroscopy results show that the phenolic hydroxyl contents in the lignins were changed after the lignins were treated with fungi. The lignin modified with the brown-rot fungi extended the gel time of the LPF resin compared with the corresponding unmodified lignin, while the lignin modified with the white-rot fungi shortened the gel time. The OSB test results show that the internal bond strength and the bending properties of the panels bonded with the LPF resins containing the modified lignin were comparable to or better than those of the panels bonded with the commercial phenolic resin or the LPF resin containing the unmodified lignin. It is worth noting that the fungi-modified lignin reduced the thickness swell and water absorption of the OSB panels, implying the water resistance of the LPF resins was improved with the fungi-modified lignin. It is also suggested that up to 50 percent of phenol can be potentially replaced with fungi-modified lignin in phenolic resins used as wood adhesives.