Softwood Kraft Lignin Research Articles

On the Feasibility of a pMDI-Reduced Production of Wood Fiber Insulation Boards by Means of Kraft Lignin and Ligneous Canola Hulls.

The thermal insulation of buildings using wood fiber insulation boards (WFIBs) constitutes a positive contribution towards climate change. Thereby, the bonding of wood fibers using mainly petrochemical-based resins such as polymeric diphenylmethane diisocyanate (pMDI) is an important measure to meet required board properties. Still there is a need to reduce or partial substitute the amount of these kinds of resins in favor of a greener product. This study therefore focusses on the feasibility of reducing the amount of pMDI by 50% through the addition of 1% BioPiva 395 or Indulin as two types of softwood Kraft-Lignin and lignin rich canola hulls together with propylene carbonate as a diluent. A panel density of 160 kg/m3 and a thickness of 40 mm was aimed. The curing of these modified pMDI was investigated by using two types of techniques: hot-steam (HS) and innovative hot-air/hot-steam-process (HA/HS). The WFIBs were then tested on their physical-mechanical properties. The equilibrium moisture content (EMC) was determined at two different climates. An exemplary investigation of thermal conductivity was conducted as well. The WFIBs did undergo a further chemically based analysis towards extractives content and elemental (C, N) composition. The results show that it is feasible to produce WFIBs with lower quantities of pMDI resin and added lignin with enhanced physical-mechanical board properties, which were lacking no disadvantages towards thermal conductivity or behavior towards moisture, especially when cured via HA/HS-process.

Solvent-Resistant Lignin-Epoxy Hybrid Nanoparticles for Covalent Surface Modification and High-Strength Particulate Adhesives.

Fabrication of spherical lignin nanoparticles (LNPs) is opening more application opportunities for lignin. However, dissolution of LNPs at a strongly alkaline pH or in common organic solvent systems has prevented their surface functionalization in a dispersion state as well as processing and applications that require maintaining the particle morphology under harsh conditions. Here, we report a simple method to stabilize LNPs through intraparticle cross-linking. Bisphenol A diglycidyl ether (BADGE), a cross-linker that, like lignin, contains substituted benzene rings, is coprecipitated with softwood Kraft lignin to form hybrid LNPs (hy-LNPs). The hy-LNPs with a BADGE content ≤20 wt % could be intraparticle cross-linked in the dispersion state without altering their colloidal stability. Atomic force microscopy and quartz crystal microbalance with dissipation monitoring were used to show that the internally cross-linked particles were resistant to dissolution under strongly alkaline conditions and in acetone-water binary solvent that dissolved unmodified LNPs entirely. We further demonstrated covalent surface functionalization of the internally cross-linked particles at pH 12 through an epoxy ring-opening reaction to obtain particles with pH-switchable surface charge. Moreover, the hy-LNPs with BADGE content ≥30% allowed both inter- and intraparticle cross-linking at >150 °C, which enabled their application as waterborne wood adhesives with competitive dry/wet adhesive strength (5.4/3.5 MPa).

Hydroxymethylation of softwood kraft lignin and phenol with paraformaldehyde

Phenol-formaldehyde (PF) resins are the most commonly used adhesives in particleboard and plywood production. Lignin, the second most abundant biopolymer, has the potential to be a valuable resource for phenolic compounds; therefore, lignin could serve as an inexpensive and nontoxic candidate to partly replace phenol in resin preparation. The use of lignin saves fossil resources, but the difficulty in lignin utilization is the low reactivity compared to that of phenol. Furthermore, the complicated structure of lignin can cause problems, for example, in the condensation of methylol groups. In this study, the progress of hydroxymethylation of mixtures of softwood kraft lignin and phenol at molar ratios of 1:1 and 3:1 was studied in the temperature range of 80–120 °C. The formaldehyde source used was paraformaldehyde due to its simple methylene glycol composition and absence of methanol. The reaction products were analyzed by using the lignin-specific 31P and 1H–13C HSQC methods together with the quantitative 13C NMR method. The NMR results indicated that methylolation and condensation of methylols to methylene bridges occurred as a function of the increasing reaction temperature. The reaction at 120 °C using the L:P molar ratio of 1:1 showed hydroxymethylation of both phenol and lignin. However, the same reaction at the 3:1 L:P molar ratio gave fewer methylol and methylene bridge products due to the lower reactivity of lignin. The 13C and 1H–13C HSQC NMR results indicated that the methylene linkages are formed mainly between the methylolated phenols through condensation in the temperature range studied.

Refining the Properties of Softwood Kraft Lignin with Acetone: Effect of Solvent Fractionation on the Thermomechanical Behavior of Electrospun Fibers

The complexity and polydispersity of lignin, the most abundant aromatic polymer in nature, create great challenges for its valorization for value-added materials and products. Reducing the heterogeneity of industrial lignin and identifying the structure–property relationships are a necessity to achieve predictable and high performance materials for polymeric applications. In this study, a simple one-step solvent extraction method using an industrial solvent, acetone, was presented as a tool to improve the homogeneity of softwood kraft lignin (SKL). The effect of acetone fractionation on the molecular weight (GPC), chemical structure (13C and HSQC NMR), and thermal (DSC and TGA) and dynamical mechanical properties (compressive-torsion DMA) of soluble (ASKL) and insoluble (AISKL) lignin fractions was evaluated. Results showed that two fractions had significant differences in Mw, chemical structure, and functional groups, showing distinct thermal flow and viscoelastic behaviors along with large shifts in the glass-to-rubbery transition temperatures of nearly 80 °C. Electrospun submicron fibers composed of 99 wt % lignin were produced from ASKL and AISKL fractions, which had improved spinnability characteristics compared to their parent SKL lignin. Thermomechanical properties of fiber mats were studied by a tensile dynamical mechanical analyzer, and the heat-induced change in the morphology of fibers was evaluated by SEM. Fiber mats produced from ASKL fractions showed increased water resistance and hydrophobicity as revealed by water contact angle measurements.

Effect of plasticizers and polymer blends for processing softwood kraft lignin as carbon fiber precursors

Plasticizers depress the glass transition temperature (Tg) of polymers and produce a flowable material at lower temperatures. The use of plasticizers to depress Tg of lignin is important, since at high processing temperatures lignin crosslinks, making it intractable. The goal of this study was to assess plasticizers and polymer blends for the ability to retard a commercial softwood kraft lignin from crosslinking and also serve as thermal and rheological property modifiers during thermal processing in the attempt to produced moldable and spinnable lignin for lignin and carbon fiber products. The Tg of the lignin and the lignin mixed with various amounts of plasticizers and with different thermo-mechanical mixing were determined using differential scanning calorimetry. The Tg and the change in heat capacity at the glass transition (ΔCp) decreased and increased, respectively, about linearly within this plasticizers range with increased plasticizer weight percentage. Gel permeation chromatography results for extruded lignin as well as extruded lignin-plasticizer blends with glycerol, N-allyurea, citric acid with and without sodium hypophosphite, and oleic acid indicate that the presence of these materials reduced the rate of molecular weight increase at temperatures between 100 and 200 °C. Continuous, homogenous films and fibers could be produced by thermal processing with plasticized lignin samples and plasticized lignin-polymer blends, but not with lignin alone. These fibers could be carbonized, yielding up to about 50% of carbon. The present findings have shown the advantages of plasticizers in thermally processing a commercial softwood kraft lignin.

Case Study in Kraft Lignin Fractionation: “Structurally Purified” Lignin Fractions—The Role of Solvent H-Bonding Affinity

Softwood kraft lignin SKL was fractionated using aprotic acetone and protic methanol to yield both previously reported “traditional” fractions and novel refined fractions thereof. Based on differences in mutual H-bonding affinities exerted by the solvents on one side and the OH group characteristics of the lignin oligo- and polymers on the other side, the 85% acetone-insoluble kraft lignin fraction AIKL, for example, could be further fractionated in 16% methanol-soluble and 67% methanol-insoluble parts. Sequential use of the two solvents practically resembled a refinement protocol that shed light on eventual “structural impurities” contained in the traditional fractions, which is not delineable easily in front of the background of a dominating spectroscopic image. Exploiting H-bonding characteristics offers a valid option for the facile generation of truly “structurally purified” lignin fractions. Acetone-insoluble, methanol-soluble MSAIKL, for example, exhibits 25% less aliphatic interunit bonding while being enriched in phenolic groups up to 25%, thus representing condensed, lower-molecular-weight structures with overall H-bond accepting character that was still contained in the overall larger-molecular-weight acetone-insoluble AIKL. More “polyphenylpropanoidic” parts practically free of condensed units, determining the overall structural picture of the unrefined lignins due to their overall abundance, are represented by the globally insoluble fractions like acetone-insoluble, methanol-insoluble MIAIKL. The original fractions and refined fractions generated based on targeting specific H-bonding affinities give a more homogeneous picture with respect to trends in glass transition temperatures, clearly indicating that Tg is dominated by actually both MW and nature of OH groups.

Preparation of an amphoteric lignin copolymer and its value in the papermaking industry

Lignin biomass is an important renewable woody material that can be converted into high value-added products through physical and chemical reactions, such as paper strength additives. In this study, a cationic methacryloyloxyethyl trimethylammonium chloride monomer (DMC) and anionic acrylic monomer (AA) were grafted onto softwood kraft lignin through free radical polymerization to prepare an amphoteric lignin copolymer. Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance spectroscopy (1H NMR), elemental analysis, and charge density analysis methods confirmed that the anionic and cationic monomers were successfully grafted onto the lignin. The grafting ratios of AA and DMC monomer in the lignin-DMC-AA copolymer were 62.4% and 51.3%, respectively. The application of lignin-DMC-AA copolymer as a paper additive for enhancing the physical properties of paper sheets was studied in the papermaking industry. The results indicated that the copolymer had a maximum increase in physical strength at around 2 wt% lignin-DMC-AA. The amount absorbed on the fibers was 18.5 mg/g, and the retention of the lignin-DMC-AA copolymer was over 90%.

Lignin-Based Polyethylene Films with Enhanced Thermal, Opacity and Biodegradability Properties for Agricultural Mulch Applications

Lignins are promising alternative raw materials for biocomposites due to their renewability, low cost and abundance. In this work, the use of (softwood and hardwood) Kraft lignins in the development of LLDPE/lignin films for agricultural mulch applications is studied. Processable blends were obtained from unmodified softwood lignin (SW) and from hardwood lignin modified by esterification (HWE). LLDPE was pelletized with (2.5%, 5% and 10%) lignin with particle size between 38 and 75 μm and flexible films were blown extruded. Processable extrusion blends showed temperature differences lower than 20 °C between the Tg of lignin and the melting temperature of LLPDE. Films from neat LLPDE and with 2.5% of HWE and up to 5% SW exhibited statistically comparable (≅ 349%) values of ductility. Ester groups present in lignin improve weight loss of lignin-based blends after soil buried test.

Insights into the Potential of Hardwood Kraft Lignin to Be a Green Platform Material for Emergence of the Biorefinery.

Lignin is an abundant, renewable, and relatively cheap biobased feedstock that has potential in energy, chemicals, and materials. Kraft lignin, more specifically, has been used for more than 100 years as a self-sustaining energy feedstock for industry after which it has finally reached more widespread commercial appeal. Unfortunately, hardwood kraft lignin (HWKL) has been neglected over these years when compared to softwood kraft lignin (SWKL). Therefore, the present work summarizes and critically reviews the research and development (R&D) dealing specifically with HWKL. It will also cover methods for HWKL extraction from black liquor, as well as its structure, properties, fractionation, and modification. Finally, it will reveal several interesting opportunities for HWKL that include dispersants, adsorbents, antioxidants, aromatic compounds (chemicals), and additives in briquettes, pellets, hydrogels, carbon fibers and polymer blends and composites. HWKL shows great potential for all these applications, however more R&D is needed to make its utilization economically feasible and reach the levels in the commercial lignin market commensurate with SWKL. The motivation for this critical review is to galvanize further studies, especially increased understandings in the field of HWKL, and hence amplify much greater utilization.

Sustainable Strategies in the Synthesis of Lignin Nanoparticles for the Release of Active Compounds: A Comparison.

The preparation of nanoparticles represents a powerful tool for lignin valorization, as it combines easy methodologies with high application potential. Different synthetic strategies and various lignin sources have been employed in the process. However, the great variability in the lignin structure prevents a direct comparison of the so far reported lignin nanoparticles (LNPs), especially as regards their physicochemical and functional properties. To this purpose, two green protocols, that is, solvent-antisolvent and hydrotropic, were optimized and used to generate LNPs from the same softwood kraft lignin. The nanomaterials were fully characterized to extrapolate structure/property relationships and reveal any differences in the mechanism of self-assembly. Furthermore, tests on methylene blue entrapment capacity and release behavior at two different pH values (2.0 and 7.4) evidenced a clear dependence on the LNPs characteristics and thus on the strategy adopted for their production.

Development of a Novel Curing Accelerator-Blowing Agent for Formulating Epoxy Rigid Foam Containing Aminated-Lignin

Rapid curing of epoxy foams at room temperature is critical to reducing energy consumption and processing time at the manufacturing sites. In this work, a novel ultra-accelerator was developed by mixing calcium carbonate with nitric acid, which acted as a blowing agent and remarkably stimulated foam hardening. Softwood kraft lignin was aminated via Mannich reaction and utilized as a cohardener to cure commercial diglycidyl ether of bisphenol A (DGEBA) to formulate a series of epoxy foams. The foams prepared with this novel accelerator-blowing agent were cured in 1 min at room temperature, which is significantly lower than the time (usually several hours at low temperatures) that takes for an epoxy foam to cure using currently available hardeners in the market, that is, primary amine (m-phenylenediamine) or anhydride (methyltetrahydrophthalic anhydride). Also, use of this novel blowing agent provided opportunities to prepare an epoxy foam at room temperature without the need to postcure. On the other hand, epoxy foams cured by aminated-lignin (EFAL) displayed comparable thermal stability to epoxy foams cured with a pure petroleum-based hardener [isophorone diamine (IPDA)]. Benefiting from the rigidity of the aromatic skeleton of lignin, the epoxy foam EFAL-15, which was prepared by using 15 wt % (based on the epoxy resin) of aminated-lignin as a cohardener, showed much higher compressive strength (6466 kPa) than the foam cured using commercial hardener IPDA (3437 kPa).

High performance electrospun carbon nanofiber mats derived from flax lignin

Flax (Linum usitatissimum) is an abundant source of natural fiber that is industrially cultivated globally for the production of linen as well as for linseed oil. Flax shives isolated from these operations represent a significant source of underutilized biomass. This study reports a novel method to delignify flax shives, describes the characteristics of the isolated flax lignin, and the properties of carbonized fiber derived from the lignin. Knife-milled flax straw was pretreated using a glycerol thermal process that permitted the fractionation of lignin via solvent extraction. The resulting lignin was characterized for its thermal properties, chemical structure, and molecular weight using differential scanning calorimetry, 31P nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and gel permeation chromatography. Additionally, the isolated lignin was transformed into continuous nanofiber mats by electrospinning, using blends of lignin and differing concentrations of polyethylene oxide (PEO). The addition of PEO as a co-processing polymer facilitated the production of uniform nanofibers without defects, such as beading. As-spun nanofiber mats were thermally stabilized in an oxygen environment and subsequently carbonized at 1000 °C. The ensuing nanofiber mats had similar mechanical properties to carbon nanofiber mats spun from softwood kraft lignin, and outperformed those derived from organosolv processed hardwoods.

Effect of Kraft lignins on the stability and thermal decomposition kinetics of nitrocellulose

In this work, the stabilizing effect of softwood and hardwood Kraft lignins on nitrocellulose (NC) was assessed. Four samples containing 3% of stabilizer were prepared. DSC and FTIR analyses have been used to check the compatibility of the different systems. The effect of these organic compounds on the stability of NC has been investigated using the conventional stability tests (Vacuum Stability Test (VST) and Bergmann-Jung (BJ)) and the kinetic modeling. The obtained results via VST and BJ suggested that the prepared mixtures are stable. Furthermore, Kinetic modeling, performed by isoconversional methods based on DSC data, revealed that the new stabilizers displayed excellent thermal stability. The reactivity between different Kraft lignins and NOx has been well highlighted by means of FTIR and TGA techniques as well, confirming the potential of these environmentally friendly substances as promising stabilizers for NC-based propellants.

Fractionating and Purifying Softwood Kraft Lignin with Aqueous Renewable Solvents: Liquid-Liquid Equilibrium for the Lignin-Ethanol-Water System.

Hot ethanol-water solutions can be used to simultaneously fractionate and purify softwood Kraft lignin through the Aqueous Lignin Purification with Hot Agents (ALPHA) process, using the regions of liquid-liquid equilibrium (LLE) that form at selected temperatures and solvent-to-lignin feed (S/F) ratios. Lignin, ethanol, and water compositions are measured for the solvent-rich (SR) and lignin-rich (LR) liquid phases in mutual equilibrium, as well as the lignin and metals mass distributions between the two phases. As depicted in quasi-ternary diagrams for clarity, both temperature and S/F ratio can be used to grow, merge, and even split the regions of LLE, giving significant control over both molecular weight (MW) and lignin purity. For example, a solvent comprising 45:55 EtOH/H2 O at 75 °C and an S/F ratio of 6:1 enables recovery of an ultrapure (95 % of Na removed), higher MW (Mn =8400 Da) lignin fraction in the LR phase. On the other hand, 95:5 EtOH/H2 O at 45 °C and S/F=3:1 enables recovery of an ultrapure, low MW (1500 Da) lignin in the SR phase.

Base-catalyzed oxidative depolymerization of softwood kraft lignin

Lignin is an important aromatic biopolymer with the structure based on phenolic units. Depolymerized lignin materials can be useful substitutes for phenol in phenol-formaldehyde resins. Our aim was to examine the potential of the base-catalyzed oxidation method to provide reactive oligomeric lignin fragments from softwood kraft lignin through the cleavage of the ether bonds. Three different bases, namely, NaOH, KOH, and NH4OH, were used as the catalyst in an aerobic oxidation, in which the influence of the reaction time was examined for 2 h and 6 h. Oxidized lignin materials were characterized with high-resolution Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry and nuclear magnetic resonance spectroscopy (13C, 1H-13C HSQC, and 31P NMR). The presence of methanol in the oxidation gas phase and formation of carboxylic acids indicate that some of the lignin structures were degraded in the oxidation. Guaiacyl units, the major phenolic structure of softwood kraft lignin, survived the oxidation. The oxidatively depolymerized lignin materials showed a reactivity close to that of pristine lignin in a reaction with formaldehyde, as determined by differential scanning calorimetry (DSC). Overall, the FT-ICR MS, NMR, and DSC results proved that the oxidized lignin materials maintained their oligomeric nature and possess the reactivity with formaldehyde.

Sustainable Process for the Depolymerization/Oxidation of Softwood and Hardwood Kraft Lignins Using Hydrogen Peroxide under Ambient Conditions.

The present study demonstrated a sustainable and cost-effective approach to depolymerize/oxidize softwood (SW) and hardwood (HW) kraft lignins using concentrated hydrogen peroxide at temperatures ranging from 25 to 35 °C, in the absence of catalysts or organic solvents. The degree of lignin depolymerization could be simply controlled by reaction time, and no further separation process was needed at the completion of the treatment. The obtained depolymerized lignin products were comprehensively characterized by GPC–UV, FTIR, 31P-NMR, TGA, Py-GC/MS and elemental analysis. The weight-average molecular weights (Mw) of the depolymerized lignins obtained from SW or HW lignin at a lignin/H2O2 mass ratio of 1:1 after treatment for 120 h at room temperature (≈25 °C) were approximately 1420 Da. The contents of carboxylic acid groups in the obtained depolymerized lignins were found to significantly increase compared with those of the untreated raw lignins. Moreover, the depolymerized lignin products had lower thermal decomposition temperatures than those of the raw lignins, as expected, owing to the greatly reduced Mw. These findings represent a novel solution to lignin depolymerization for the production of chemicals that can be utilized as a bio-substitute for petroleum-based polyols in polyurethane production.

A branched structure provides kraft lignins a denser morphology and a high molar mass for a given hydrodynamic radius

AbstractSize exclusion chromatography with multi-angle laser light-scattering detectors was applied for acetylated softwood and hardwood kraft lignins (Ac-SKL and Ac-HKL) and 8-O-4′ type of linear polymeric lignin model (Ac-M-8O4′) to compare their swelling behaviors. The plot of molar mass (MM) vs. retention time for Ac-M-8O4′ was similar to that of polystyrene, which revealed that Ac-M-8O4′ exhibited swelling behavior that was similar to that of polystyrene. However, the MM values of both Ac-KLs were larger than those of polystyrene standards at any retention time. This difference indicated that both Ac-KLs had a more compact structure than those of polystyrene and Ac-M-8O4′. One hypothesis is that the larger MM of both Ac-KLs stems from their branched structures. To verify this hypothesis, the frequency of 5-5′ interunit linkage in lignin samples was determined by1H NMR after nitrobenzene oxidation. A linear relationship between MM and 5-5′ abundance was observed in the high MM region.

Lignin-fatty acid hybrid nanocapsules for scalable thermal energy storage in phase-change materials

Abstract Development of affordable thermal energy storage (TES) has been hampered by the lack of environmentally benign and scalable phase-change materials (PCM). Here we show size-controlled colloidal synthesis of fatty acid-lignin hybrid nanocapsules and demonstrate their applicability as PCM in dry and wet states. The one-pot fabrication allowed for facile preparation of hybrid capsules with a predictable concentration of tall oil fatty acid, oleic acid, or lauric acid in core-shell particles stabilized by softwood kraft lignin. Phase-change peaks of capsules containing 40 wt% of lauric acid were observed in aqueous dispersion, indicating a possibility to develop colloidal TES systems. In dry form, the hybrid capsules prevented fragmentation of the phase-change peaks during 290 heating-cooling cycles, while in wet state the capsules appeared stable for 25 cycles. The nanoscaled morphology of the capsules was characterized using thermoporometry-differential scanning calorimetry (tp-DSC), transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic light scattering (DLS), and small angle X-ray scattering (SAXS). Extraction of lauric acid from the capsules allowed for investigation of the intraparticle space previously occupied by the fatty acid. The fatty acid-deficient nanocapsules were found to contain an internal volume that was 19 times as high as that of lignin nanoparticles. Approximately 20 nm thick lignin shells of the capsules were found to be readily accessible to water, permitting heat transfer across the capsules. The possibility to tailor the hybrid capsules by altering the chain length and saturation degree of the fatty acids opens applications that extend beyond the TES systems.

Agglomeration of Viruses by Cationic Lignin Particles for Facilitated Water Purification.

Virus contamination of water is a threat to human health in many countries. Current solutions for inactivation of viruses mainly rely on environmentally burdensome chemical oxidation or energy-intensive ultraviolet irradiation, which may create toxic secondary products. Here, we show that renewable plant biomass-sourced colloidal lignin particles (CLPs) can be used as agglomeration agents to facilitate removal of viruses from water. We used dynamic light scattering (DLS), electrophoretic mobility shift assay (EMSA), atomic force microscopy and transmission electron microscopy (AFM, TEM), and UV spectrophotometry to quantify and visualize adherence of cowpea chlorotic mottle viruses (CCMVs) on CLPs. Our results show that CCMVs form agglomerated complexes with CLPs that, unlike pristine virus particles, can be easily removed from water either by filtration or centrifugation. Additionally, cationic particles formed by adsorption of quaternary amine-modified softwood kraft lignin on the CLPs were also evaluated to improve the binding interactions with these anionic viruses. We foresee that due to their moderate production cost, and high availability of lignin as a side-stream from biorefineries, CLPs could be an alternative water pretreatment material in a large variety of systems such as filters, packed columns, or flocculants.

Effect of highly selective oxypropylation of phenolic hydroxyl groups on subsequent lignin pyrolysis: Toward the lignin valorization

For the valorization of lignin, it is important and a great challenge to prevent the negative impact of phenolic hydroxyl (Ph-OH) on lignin pyrolysis by blocking the Ph-OH. Herein, lignin samples with different oxypropylation degree are prepared to investigate the effect of masking of Ph-OH on subsequent pyrolysis of softwood kraft lignin (SKL). It is found that the propylene oxide shows high selectivity (~94%) towards the oxypropylation of Ph-OH, which enhances the hydrogen to carbon effective ratio (H/Ceff) of SKL. In addition, the acquired oxypropylated lignins (OPLs) display a slight change in the structure compared to the original lignin except for their Ph-OH content. Moreover, the maximum degradation rate of lignin during heating significantly increases with the increase of oxypropylation degree. Noticeably, the relative content of low-oxygen aromatic compounds derived from lignin pyrolysis shows a positive correlation with the oxypropylation degree. More importantly, the oxypropylation of Ph-OH has a great contribution to improving the bio-oil yield from lignin pyrolysis. The reveal of the relationship between specific OPLs and pyrolysis behavior is of great significance for the highly selective conversion of lignin into high value-added specific compounds.