Wood Lignin Research Articles

Measurements and applications of δ2H values of wood lignin methoxy groups for paleoclimatic studies

Stable hydrogen isotope values of wood lignin methoxy groups (δ2HLM) are increasingly applied to reconstruct the stable hydrogen isotope composition of precipitation (δ2Hprecip) and mean annual temperatures (MAT) of mid latitudes regions. Recently, the analytical procedure for measuring δ2HLM values was considerably improved by the availability of new reference materials that are in full accordance with the requirements of normalising stable isotope measurements. Using this improved procedure we determined the δ2HLM values of tree rings from 40 geographical locations. Using these values, we present a revised relationship between δ2HLM and δ2Hprecip which is: δ2Hprecip [mUr] = (δ2HLM [mUr] + 206 mUr)/0.67. In addition, a new equation for reconstructions of MAT is: MAT [°C] = (δ2HLM [mUr] + 272 mUr)/3.04 [mUr/°C]. We provide a simple numerical model that explains the observed biosynthetic isotope fraction pattern between δ2HLM and δ2Hprecip. Finally, we applied the new equations to a previous data set for wood samples collected close to the Hohenpeißenberg Meteorological Observatory in Germany. The data set included a 100-year-chronology (1916–2015) from nine tree ring cores removed from four beech trees. The MAT from δ2HLM values reconstructed for this geographical location was 7.96 ± 2.17 °C and in very good agreement with the observed mean MAT of 7.82 ± 0.75 °C during this time period. Therefore, we conclude that the revised relationships between δ2HLM, δ2Hprecip and MAT provide the basis for reliable application for paleoclimate reconstructions.

Densification of wood – Chemical and structural changes due to ultrasonic and mechanical treatment

This paper presents the state of the art of wood surface densification method by pressing with ultrasound. The properties of ultrasound and its effects on the structure and properties of wood, as well as ultrasound-induced chemical changes in wood material, are described. The following research results were analyzed: the effects of acoustic cavitation in wood material, plasticization of wood lignin by processing with ultrasound, the influence of ultrasound on the wood anatomical structure, the combined effect of ultrasound and wood pressing, and the sterilization of wood using ultrasonic action. Ultrasound causes conversion of lignin from glassy into a quasi-rubbery state, which facilitates compaction of the workpiece surface. Additionally, under ultrasound, growth and collapse of gas bubbles (cavitation phenomena) occur within a liquid medium of wooden substance accompanied by high local temperatures and production of chemically active radicals. This contributes to the destruction of the former and the formation of new bonds in the wood substance, which is important for increasing the stability of the workpiece size after densification. The conclusions made about the ultrasound can be effectively used for the wood plasticization and about prospects of joint use of wood pressing and ultrasound for wood surface densification.

Densification of wood – Chemical and structural changes due to ultrasonic and mechanical treatment

This paper presents the state of the art of wood surface densification method by pressing with ultrasound. The properties of ultrasound and its effects on the structure and properties of wood, as well as ultrasound-induced chemical changes in wood material, are described. The following research results were analyzed: the effects of acoustic cavitation in wood material, plasticization of wood lignin by processing with ultrasound, the influence of ultrasound on the wood anatomical structure, the combined effect of ultrasound and wood pressing, and the sterilization of wood using ultrasonic action. Ultrasound causes conversion of lignin from glassy into a quasi-rubbery state, which facilitates compaction of the workpiece surface. Additionally, under ultrasound, growth and collapse of gas bubbles (cavitation phenomena) occur within a liquid medium of wooden substance accompanied by high local temperatures and production of chemically active radicals. This contributes to the destruction of the former and the formation of new bonds in the wood substance, which is important for increasing the stability of the workpiece size after densification. The conclusions made about the ultrasound can be effectively used for the wood plasticization and about prospects of joint use of wood pressing and ultrasound for wood surface densification.

Chemical Characterization of Kraft Lignin Prepared from Mixed Hardwoods.

Chemical characterization of kraft lignin (KL) from mixed hardwoods (Acacia spp. from Vietnam and mixed hardwoods (mainly Quercus spp.) from Korea) was conducted for its future applications. To compare the structural changes that occurred in KL, two milled wood lignins (MWLs) were prepared from the same hardwood samples used in the production of KL. Elemental analysis showed that the MWL from acacia (MWL-aca) and mixed hardwood (MWL-mhw) had almost similar carbon content, methoxyl content, and C9 formula. KL had high carbon content but low oxygen and methoxyl contents compared to MWLs. The C9 formula of KL was determined to be C9H7.29O2.26N0.07S0.12(OCH3)1.24. The Mw of KL and MWLs was about 3000 Da and 12,000–13,000 Da, respectively. The structural features of KL and MWLs were investigated by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance spectrometry (1H, 13C NMR). The analyses indicated that KL underwent severe structural modifications, such as γ-carbon cleavage, demethylation, and polycondensation reactions during kraft pulping, which resulted in increased aromatic content and decreased aliphatic content. The main linkages in lignin, β-O-4 moieties, were hardly detected in the analysis as these linkages were extensively cleaved by nucleophilic attack of SH- and OH- during pulping.

Thermal properties of biomass‐based form‐stable phase change material for latent heat thermal energy storage

Considering platane wood as a kind of natural biomass building material, it features a structure with abundant pores and lightweight, which can be used as a supporting material to prevent the liquid leakage of phase change materials (PCMs). In this work, the lignin of the platane wood is removed, and then, a series of the form-stable PCMs (FSPCMs) are prepared by the vacuum impregnation method, for which implemented the delignified wood (DW) as a supporting material and four kinds of fatty acid (FA) as PCMs. The microstructure and thermophysical characteristics of the FSPCMs are investigated. Furthermore, the results show that DW preserves the inherent porous structure of the platane wood, and the specific surface area and total pore volume of DW are greater than those of the platane wood. Thus, the DW adsorbs more PCMs than platane wood by the physical connection. The maximum impregnation rate of FA in the DW is as high as 76 wt%. There is a little variation in the phase change temperature of DW/FA FSPCMs compared with that of the FA, while the latent heat of DW/FA FSPCMs is almost consistent with the content of FA in the composite. Thermogravimetric analysis results show that DW/FA FSPCMs present good thermal stability. Moreover, DW/FA FSPCMs have good thermal reliability after 500 thermal cycles. Therefore, the prepared DW/FA FSPCMs show a potential application prospect in the thermal energy storage system.

P-Coumaroylation of poplar lignins impacts lignin structure and improves wood saccharification.

The enzymatic hydrolysis of cellulose into glucose, referred to as saccharification, is severely hampered by lignins. Here, we analyzed transgenic poplars (Populus tremula × Populus alba) expressing the Brachypodium (Brachypodium distachyon) p-coumaroyl-Coenzyme A monolignol transferase 1 (BdPMT1) gene driven by the Arabidopsis (Arabidopsis thaliana) Cinnamate 4-Hydroxylase (AtC4H) promoter in the wild-type (WT) line and in a line overexpressing the Arabidopsis Ferulate 5-Hydroxylase (AtF5H). BdPMT1 encodes a transferase which catalyzes the acylation of monolignols by p-coumaric acid (pCA). Several BdPMT1-OE/WT and BdPMT1-OE/AtF5H-OE lines were grown in the greenhouse, and BdPMT1 expression in xylem was confirmed by RT-PCR. Analyses of poplar stem cell walls (CWs) and of the corresponding purified dioxan lignins (DLs) revealed that BdPMT1-OE lignins were as p-coumaroylated as lignins from C3 grass straws. For some transformants, pCA levels reached 11 mg·g−1 CW and 66 mg·g−1 DL, exceeding levels in Brachypodium or wheat (Triticum aestivum) samples. This unprecedentedly high lignin p-coumaroylation affected neither poplar growth nor stem lignin content. Interestingly, p-coumaroylation of poplar lignins was not favored in BdPMT1-OE/AtF5H-OE transgenic lines despite their high frequency of syringyl units. However, lignins of all BdPMT1-OE lines were structurally modified, with an increase of terminal unit with free phenolic groups. Relative to controls, this increase argues for a reduced polymerization degree of BdPMT1-OE lignins and makes them more soluble in cold NaOH solution. The p-coumaroylation of poplar samples improved the saccharification yield of alkali-pretreated CW, demonstrating that the genetically driven p-coumaroylation of lignins is a promising strategy to make wood lignins more susceptible to alkaline treatments used during the industrial processing of lignocellulosics.

Catalytic fast pyrolysis of beech wood lignin isolated by different biomass (pre)treatment processes: Organosolv, hydrothermal and enzymatic hydrolysis

Lignin is one of the three main structural components of lignocellulosic biomass and is considered as the most abundant source of aromatic and phenolic compounds. Lignin is produced as side-stream in the pulp/paper industry or as residue in the production of second-generation bioethanol. More recently, novel biomass fractionation processes in biorefineries have been developed aiming at the production of high quality/purity lignin towards its more efficient down-stream catalytic conversion to chemicals, monomers, and fuels. Within this context, in this work, we studied the thermal (non-catalytic) and catalytic fast pyrolysis on a Py/GC–MS system and a fixed-bed reactor unit of three types of lignin, all originating from the same biomass (beech wood sawdust) but with different isolation processes: organosolv lignin derived by the organosolv pretreatment/fractionation of biomass, surface extracted lignin derived by the mild Soxhlet extraction (with ethanol or acetone) from the hydrothermally (HT) in pure water pretreated biomass, and the enzymatic hydrolysis lignin derived as a lignin-rich solid residue from the enzymatic hydrolysis of the HT pretreated biomass. Conventional microporous ZSM-5 and mesoporous ZSM-5 zeolites (with intracrystal mesopores, ˜ 9 nm) were used as catalysts in the pyrolysis experiments. Both zeolites were very active in converting the initially produced via thermal pyrolysis methoxy-substituted phenols, benzenes and benzaldehydes mainly towards BTX mono-aromatics, such as 1,3-dimethylbenzene/p- and o-xylenes, toluene and trimethylbenzenes, as well as polycyclic aromatic hydrocarbons (PAHs, mainly naphthalenes). The mesoporous ZSM-5 induced higher dealkoxylation reactivity compared to the microporous ZSM-5 leading to higher concentration of BTX aromatics without a consequent increase of PAHs. The pronounced dealkoxylation/aromatization reactivity of both ZSM-5 zeolites resulted to lower yields (but highly aromatic) organic bio-oils (e.g. from 32−35 wt.% to 15−22 wt.%) compared to thermal pyrolysis, increased non-condensable gases (mainly CO, CO2, methane, ethylene and propylene) and formation of relatively low amounts of coke on catalysts (e.g. 3−5 wt.% on lignin) in addition to thermal pyrolysis char. The observed moderate variations in the characteristics of the three types of beech wood lignin, i.e. molecular weight (GPC), S/G ratio, inter-unit linkages (2D HSQC NMR) and elemental composition, did not induce a systematic/substantial differentiation in the thermal and catalytic fast pyrolysis product yields and composition.

Changes in the Physical and Chemical Properties of Alder Wood in the Process of Thermal Treatment with Saturated Water Steam

The paper presents changes in color and selected physico-chemical properties of alder (Alnus glutinosa) wood during the process of thermal treatment of the wood with a saturated steam-air mixture or saturated water steam in the temperature range t = 95–125 °C for τ = 3 to 12 h. During the process of thermal treatment of alder wood, the original light white-gray color changes depending on the temperature and time of modification to soft reddish-brown to dark brown color shades. Color changes of alder wood expressed in the form of the total color difference are in the range of values ∆E* = 2.7–31.7. Measurements of the density of thermally treated alder wood in the dry state indicate that due to the thermal treatment of alder wood, the density decreases by ρ ≤ 4.6% compared to the average density of native alder wood. Due to the hydrolysis of hemicelluloses, in the process of thermal treatment of wet alder wood, its acidity changes in the range of values: pH = 4.9 to 3.1. Analyzes of ATR-FTIR spectroscopy indicate changes in alder wood extractants and hemicellulose degradation. A decrease in unconjugated and an increase in conjugated carbonyls was observed at all temperatures of thermal modification of alder wood. Measurements indicate changes in the lignin of alder wood and the fact that as the temperature increases, the formation of new carbonyls increases, which is reflected in the change of the chromophoric system.

A Novel Polyaniline Nanofiber Combined with Toluidine Blue as a Sensitive Detection Platform for Lignin by Raman Spectroscopy

Raman spectroscopy is widely applied in wood science because of its features of being nondestructive, rapidity, and high resolution. However, Raman scattering is weak, and the Raman signal is easily disturbed by autofluorescence arising from endogenous fluorescent molecules in biological tissue. In this work, a sensitive lignin detection platform was fabricated by a composite with a polyaniline (PANI) nanofiber and toluidine blue (TB) under the excitation of visible light. In this platform, TB acts as a specific marker for lignin, and a PANI nanofiber was used as a reinforcing reagent to improve the Raman intensity of TB. When wood slice is impregnated with TB/PANI, the lignin in wood can be precisely labeled with the TB, and the Raman intensity of TB had a threefold increase at 532 nm excitation. This TB/PANI detection platform is expected to make a significant contribution in qualitative and quantitative analysis of lignin to avoid autofluorescence in various lignin-based biosciences.

Estimation of Plant Biomass Lignin Content using Thioglycolic Acid (TGA).

Lignin is a natural polymer that is the second most abundant polymer on Earth after cellulose. Lignin is mainly deposited in plant secondary cell walls and is an aromatic heteropolymer primarily composed of three monolignols with significant industrial importance. Lignin plays an important role in plant growth and development, protectsfrom biotic and abiotic stresses, and in the quality of animal fodder, the wood, and industrial lignin products. Accurate estimation of lignin content is essential for both fundamental understanding of the lignin biosynthesis and industrial applications of biomass. The thioglycolic acid (TGA) method is a highly reliable method of estimating the total lignin content in the plant biomass. This method estimates the lignin content by forming thioethers with the benzyl alcohol groups of lignin, which are soluble in alkaline conditions and insoluble in acidic conditions. The total lignin content is estimated using a standard curve generated from commercial bamboo lignin.

Molecular self-organization of wood lignin-carbohydrate matrix.

The analysis of the state of research on the chemical composition, functional nature and structure of the main components of the lignin-carbohydrate matrix allows considering the wood substance as a thermodynamically self-organizing nanobiocomposite system. Features of biosynthesis of the wood matrix main biopolymers, the formation of their functional nature and structure determine the complex hierarchical organization of cell walls. The supramolecular level of biosynthesis considers the interaction of cell wall components. On the one hand, these are questions of dynamics of cell walls synthesis and processes of self-organization that control the formation of chaotic objects of biological origin; on the other hand, it is the question of thermodynamic compatibility of plant tissue components. Various models of structural organization are currently being considered, focusing on various features (biological, chemical, structural) of wood substance. At the same time, the lignin-carbohydrate matrix is a three-component system of natural polymers: lignin-hemicelluloses-cellulose, the state of which is described by specific values of thermodynamic parameters that characterize the degree of its stability. The new approach proposed in this paper allows considering the plant lignin-carbohydrate matrix from the standpoint of physical chemistry of polymer as quasi-equilibrium, thermodynamically limited ordered system of biopolymers. Thus, the biochemical processes of synthesis and self-organization lead to the formation of a complex multicomponent system of wood substance, considered as a nanobiocomposite. This determines the need to study the applicability of the fundamental cycle "structure-functional nature-properties" from the standpoint of physical chemistry of biopolymers both for the investigation of plant objects and for the development of modern technologies for complex processing based on the principles of "green chemistry".

Dopant-assisted atmospheric pressure photoionization Orbitrap mass spectrometry – An approach to molecular characterization of lignin oligomers

Lignin is the second most abundant biopolymer in nature and is considered an important renewable source of aromatic compounds. One of the most promising analytical methods for molecular characterization of lignin is Orbitrap high-resolution mass spectrometry with atmospheric pressure photoionization (APPI), proved itself in the study of lignins of various origins and their depolymerization products. In this work, the photoionization of lignin using acetone, 1,4-dioxane, and THF as solvents for the biopolymer and APPI dopants providing the generation of protonated and deprotonated molecules of lignin oligomers has been studied. The ionization conditions were optimized on the basis of the dependences of the total ion current on temperature and the flow rate of the solution into the ion source. Lignin degradation processes under APPI conditions occur mainly with the cleavage of ether β-O-4 bonds between phenylpropane structural units, demethylation (negative ion mode), as well as the loss of water and formaldehyde (positive ion mode). Negative ion mode APPI provides a higher ionization efficiency in the region of high molecular weights, however, it is characterized by an increased fragmentation of β-O-4 ether bonds compared to APPI(+) leading to a partial depolymerization of lignin in the ion source. The combination of APPI with Orbitrap high-resolution mass spectrometry allows obtaining mass spectra of coniferous and deciduous wood lignins with resolved fine structure and containing signals of up to 3000 oligomers in the mass range of 300–1800 Da. This can be used for comprehensive characterization of lignins at molecular level and tracking changes in biopolymer chemical composition in various processes.

Residual-lignin-endowed molded pulp lunchbox with a sustained wet support strength

A significant challenge in the design of pulp lunchboxes (PLBs) is the structural collapse driven by moisture. Inspired by the lignin in wood bonding activation, a simple and novel strategy is proposed in this study to sustain the wet support strength of PLB. Pulp with residual lignin (RL) is prepared from bamboo by bath treatment with HNO3 and H2O2, and the resulting PLB (RL-PLB) is obtained from the pulp by a mature molding process. Residual lignin with thermoplastic properties acts as a filler, binder, and hydrophobic agent, endowing the RL-PLB with wet-stability adhesion. Consequently, the RL-PLB exhibits a high mechanical strength of 44 MPa, stiffness of 12.9 mN m sustained wet support strength for over 30 d, and excellent wet stability. The RL-pulp used for manufacturing RL-PLB exhibits a high biomass-utilization efficiency with a yield of 75 %. RL-PLB is a biodegradable and eco-friendly substitute for non-biodegradable plastics.

Bacterial Community Coexisting with White-Rot Fungi in Decayed Wood in Nature.

Lignin-decomposing ability of several bacteria and the degradation mechanism have been revealed in vitro. However, the abundance of such bacteria in decayed wood in nature remains unknown at genus and species levels. This study was aimed at identifying bacterial communities in the decayed wood coexisting with white-rot fungi, which play a potential role in lignin degradation, and predicting the functional profile of bacterial lignin degradation in wood via bacterial community analyses. The bacterial flora of forest soil and four decayed wood samples showed marked differences; particularly, in addition to Methylobacterium and Acidibrevibacterium, sphingomonads, which degrade the major skeleton of lignin in vitro, were more abundant in the decayed wood than in forest soil, suggesting that multiple bacteria were involved in lignin degradation. The bacterial community in the decayed wood was more influenced by wood type and lignin structure than the fungal species observed in the decayed wood.

Understanding the effects of different residual lignin fractions in acid-pretreated bamboo residues on its enzymatic digestibility

BackgroundDuring the dilute acid pretreatment process, the resulting pseudo-lignin and lignin droplets deposited on the surface of lignocellulose and inhibit the enzymatic digestibility of cellulose in lignocellulose. However, how these lignins interact with cellulase enzymes and then affect enzymatic hydrolysis is still unknown. In this work, different fractions of surface lignin (SL) obtained from dilute acid-pretreated bamboo residues (DAP-BR) were extracted by various organic reagents and the residual lignin in extracted DAP-BR was obtained by the milled wood lignin (MWL) method. All of the lignin fractions obtained from DAP-BR were used to investigate the mechanism for interaction between lignin and cellulase using surface plasmon resonance (SPR) technology to understand how they affect enzymatic hydrolysisResultsThe results showed that removing surface lignin significantly decreased the yield for enzymatic hydrolysis DAP-BR from 36.5% to 18.6%. The addition of MWL samples to Avicel inhibited its enzymatic hydrolysis, while different SL samples showed slight increases in enzymatic digestibility. Due to the higher molecular weight and hydrophobicity of MWL samples versus SL samples, a stronger affinity for MWL (KD = 6.8–24.7 nM) was found versus that of SL (KD = 39.4–52.6 nM) by SPR analysis. The affinity constants of all tested lignins exhibited good correlations (r > 0.6) with the effects on enzymatic digestibility of extracted DAP-BR and Avicel.ConclusionsThis work revealed that the surface lignin on DAP-BR is necessary for maintaining enzyme digestibility levels, and its removal has a negative impact on substrate digestibility.

Autothermal fast pyrolysis of waste biomass for wood adhesives

Biomass fast pyrolysis was performed in a bubbling fluidized bed reactor that incorporated two crucial innovations. A fractional condensation train provided dry bio-oils with only 1% of moisture and much reduced acidity. Autothermal pyrolysis with partial oxidation enhanced dry bio-oil quality while reducing the capital and operating costs by eliminating the need for external heating. Both endothermic pyrolysis with pure N2 and autothermal pyrolysis with oxidant fluidization gases were carried out at 500 °C. Dry bio-oils of birch wood, birch bark or hydrolysis lignin, from both endothermic and autothermal pyrolysis, could substitute up to 65 % of phenol in reacting with formaldehyde to produce wood adhesives that met the international standard specifications on mechanical strength and formaldehyde emissions. Therefore, autothermal pyrolysis did not harm the bio-oil quality for phenol substitution. Dry bio-oil from autothermal pyrolysis of kraft lignin was able to replace 80 % of the phenol.

Time-dependent desorption of anilines, phenols, and nitrobenzenes from biochar produced at 700 °C: Insight into desorption hysteresis

Biochar, once amended or released into the soil environment, may alter the transport, fate, and bioavailability of organic contaminants in the environment by adsorption and desorption. In this study, adsorption–desorption of aniline, 4-nitroaniline, phenol, 4-nitrophenol, nitrobenzene, and trinitrobenzene on biochars produced at 700 °C from 5 biomass including wood chips, chitin, cellulose, lignin, and rice straw (i.e., W700, Ch700, Ce700, Li700, and S700, respectively) was investigated to examine the underlying mechanisms for desorption hysteresis of organic contaminants. The desorption hysteresis was dependent on the adsorption–desorption time and should be attributed to the nonequilibrium adsorption–desorption, i.e., it was apparent and an artifact. Moreover, within 2-day equilibration, the desorption hysteresis was observed for trinitrobenzene (with the maximum cross-sectional area of 0.890 nm2) but not for the other organic contaminants with smaller sizes (the maximum cross-sectional area ≤ 0.611 nm2). Similarly, trinitrobenzene had a shorter equilibrium time on Ch700 (15 days) than on Ce700, Li700, and S700 (>30 days) because of the larger pores of Ch700. Diffusion rates (kip2) of trinitrobenzene on biochars were positively correlated with the Raman spectra ID/IG values of biochars (R2 = 0.928) because higher ID/IG values are possibly associated with the looser structure of biochars which having faster diffusion of molecules in pores. The time-dependent desorption hysteresis suggests that the adsorbed organic contaminants by biochars can be re-released into the soil environment for a long period. Thus, the long-term releasing of adsorbed organic contaminants on biochars should be investigated more for assessing the environmental risks of organic contaminants.

The effects of mild Lewis acids-catalyzed ethanol pretreatment on the structural variations of lignin and cellulose conversion in balsa wood

Ethanol organosolv pretreatment is a green and effective deconstruction process for main components in lignocellulose biomass. Herein, balsa wood was firstly subjected to a modified ethanol/water solution (EWS) pretreatment with different Lewis acids catalysts (AlCl3, CuCl2, FeCl3) at 140–180 °C. The delignification ratios and structural characteristics of the dissociated lignin, enzymatic hydrolysis of cellulose in the pretreated substrates as well as the degradation products from hemicellulose during the pretreatment process were comprehensively investigated. Results showed that dissociation and depolymerization of lignin fragments was robust in AlCl3-catalyzed pretreatment than those by CuCl2 and FeCl3-catalyzed pretreatment. In detail, the results showed that the optimal delignification ratio and removal of the hemicelluloses occurred in AlCl3-catalyzed pretreatment. Moreover, the structural characterizations of lignin fractions by 2D-HSQC, 31P NMR and GPC also revealed that the obtained lignin has the advantages of small and homogeneous molecules as well as abundant functional groups. As a result of adequate removal of hemicellulose and lignin, the enzymatic digestibility of cellulose in the pretreated residue was significantly elevated. In short, the above findings are also in line with the concept of maximizing the utilization of bioresources, which will be beneficial for value-added applications of balsa wood in the biorefinery.

Colloidal lignin nanoparticles from acid hydrotropic fractionation for producing tough, biodegradable, and UV blocking PVA nanocomposite

Colloidal lignin nanoparticles (LNPs) from low temperature acid hydrotropic fractionation (AHF) of poplar wood and commercial alkali lignin using p-Toluenesulfonic acid (p-TsOH) were directly mixed with PVA to make PVA/AHF-LNP nanocomposite films. p-TsOH itself acted as a plasticizer for PVA; however the application of p-TsOH alone reduced PVA film tensile strength and therefore toughness. At proper loadings of LNPs and p-TsOH, both the failure strain and tensile strength of PVA/AHF-LNP composites were improved. The formation of hydrogen bonding between the p-TsOH/AHF-LNP aggregates with hydroxyl groups on PVA molecular chains, and the breakage and reforming of p-TsOH/AHF-LNP aggregates, along with the nanophase crazing due to the presence of p-TsOH/AHF-LNP aggregates were identified as the main mechanisms for improving the toughness of PVA/AHF-LNP nanocomposite. The composite also had improved UV shielding performance and biodegradability due to the presence of p-TsOH and LNPs compared with neat PVA. This nanocomposite film could be used as biodegradable anti-ultraviolet packing film.

Effect of metal triflates on the microwave-assisted catalytic hydrogenolysis of birch wood lignin to monophenolic compounds

The lignin-first biorefinery strategy could produce bio-based phenols from the extraction and depolymerization of native lignin in lignocellulosic biomass. Herein, we report an effective Lewis acid-promoted delignification and production of monophenolic compounds in birch sawdust assisted by microwave heating without external hydrogen for the first time. The screening of different metal triflates revealed that Fe(OTf)3 was best for the delignification and depolymerization of birch sawdust. Without the addition of a Lewis acid, the yield of monophenolic compounds was 10.5 wt% (based on the lignin content in birch sawdust), while it increased significantly to 32.9 wt% with the addition of Fe(OTf)3 (0.0276 g) under the identical conditions (190 °C, 1 h), which demonstrated the catalytic COC bond scission promoted by Fe(OTf)3. Simultaneously, the delignification degree also rose sharply from 32.6 wt% to 47.5 wt%. This work demonstrated the efficient Fe(OTf)3-induced delignification and depolymerization of lignin in birch sawdust to obtain a high yield of monophenolic compounds without external hydrogen assisted by microwave heating, representing a novel advance in the “lignin-first” biorefinery field.