WO2018205020A1 - Depolymerization of lignin for the production of bio-based polyols and phenols and lignin-based pf/pu/epoxy resins/foams - Google Patents

Abstract

The present relates to a process for the depolymerization of a feedstock comprising lignin producing depolymerized lignins comprising the loading of the feedstock, a catalyst, a polyalcohol, and water into a reactor; heating the reactor to about 150-300°C to depolymerize the lignin producing a depolymerized lignin mixture; stopping the depolymerization reaction by quenching with cold water; acidifying/neutralizing the depolymerized lignin mixture derived products; precipitating depolymerized lignin and solid residues from the depolymerized lignin; dissolving the precipitated depolymerized lignin and solid residues in acetone; and separating the depolymerized lignin from the solid residues by filtration producing a solid depolymerized lignin. The produced solid depolymerized lignin can be used in the production of lignin-based rigid polyurethane foam, a phenol formaldehyde resole and a lignin-based epoxy resin with a high percentage of bio-content (≥ 50 wt. %).

Description

DEPOLYMERIZATION OF LIGNIN FOR THE PRODUCTION OF BIO-BASED POLYOLS AND PHENOLS AND LIGNIN-BASED PF/PU/EPOXY RESINS/FOAMS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims benefit of U.S. Provisional Application No. 62/503,375 filed May 9, 2017, the content of which is hereby incorporated by reference in their entirety.

TECHNICAL FIELD

[0002] The present relates to a low-pressure and low-temperature process of depolymerization of lignin to obtain low molecular weight depolymerized lignin and lignin-based phenol formaldehyde (PF), polyurethane (PU) and epoxy resins/foams.

BACKGROUND ART

[0003] The production of bio-based chemicals/fuels/materials from renewable resources is a major component of the international renewable resource technology efforts. To date, most research efforts have focused on the utilization of cellulose/hemicellulose components of biomass. However, lignin constitutes approximately 30-35wt% of the dry weight of softwoods, about 20-25wt% of hardwoods and 15-20wt% of non-woods. Lignin represents a rich source of organic macromolecules that can serve as precursor for aromatics and their derivatives but lignin is an underutilized valuable resource in current biomass conversion technologies due to a lack of economic and technical feasibility routes for lignin utilization.

[0004] Lignin is generated industrially in large quantities especially from kraft pulping processes in the form of "black liquor". Black liquor is the major byproduct/residual stream from the kraft pulping process, containing 30-40 wt.% lignin. According to the International Lignin Institute, about 40-50 million tonnes of kraft lignin (KL) are generated worldwide each year in the form of "black liquor". While combustion of black liquor to regenerate pulping chemicals and to produce steam and power is an integral part of the kraft process, a small portion of the lignin can be removed without compromising mill material and energy balances. 60-70% of North American kraft mills experience production bottlenecks due to the thermal capacity of their recovery boilers. A moderate-capital solution to this problem is to precipitate some portion of kraft lignin from the black liquor, thereby allowing for incremental pulp production and an additional revenue stream from the sale of isolated kraft lignin. While currently worldwide 1 -1.5 million tonnes/year of lignin is utilized for a wide range of applications, almost all of this is lignosulfonates from sulfite pulping. Lignosulfonates are water-soluble, and highly sulfonated substances, quite different from kraft lignin. Until recently, the only commercial source of kraft lignin has been from Mead-Westvaco, which produces approximately 20,000 metric tons/year of kraft lignin under the trade name Indulin from a plant in South Carolina.

[0005] Hydrolyzed/Hydrolysis lignin (HL) is a byproduct from pretreatment processes in cellulosic ethanol and other byproduct plants. HL could be, for example, the solid residue (WO 201 1/057413) from the enzymatic hydrolysis of woody biomass and is mainly composed of lignin (56-57 wt.%), unreacted cellulose and mono and oligosaccharides. Compared with sulfur-containing kraft lignin (KL), HL is a sulfur-free lignin with a chemical structure close to native lignin. Extensive research has been undertaken in the former Soviet Union to find uses for this material as they had several hydrolysis plants. Several chemical modifications of HL were carried out to make effective uses of this abundantly available phenolic-rich polymer, however, the majority of the HL was disposed of because the required modifications were either too expensive or the material did not function well enough in application. The same problems are faced by researchers today in developing effective uses for HL.

[0006] There are many challenges in utilizing lignin for chemicals or materials, mainly due to its poor reactivity and compatibility with other materials which are both related to its large molecular weight. Thus, enormous research efforts have been made in developing technologies for depolymerization of lignin and utilization of the depolymerized products with lower molecular weight and, hence, improved reactivity for the production of valuable biomaterials such as bio-based polyurethane (PU) foams, phenolic resins/foams and epoxy resins.

[0007] Lignin is a branched phenolic natural biopolymer primarily composed of three phenylpropanoid building units: p-hydroxyphenylpropane, guaiacylpropane, and syringylpropane interconnected by etheric and carbon-to-carbon linkages. Generally, in an unprocessed native lignin, two thirds or more of these linkages are ether bonds, while the remaining linkages are carbon-carbon bonds. Different types of lignin vary significantly in the ratio between these monomers. Various lignin depolymerization processes (via hydrolytic, reductive or oxidative routes) were reported in the literature. Nguyen et al. (2014, Journal of Supercritical Fluids, 86: 67-75) reported a high- pressure pilot process for the hydrolytic conversion of KL into bio-oil and chemicals in near critical water (350 °C, 25 MPa), employing a fixed-bed catalytic reactor filled with Zr0₂ pellets, while the lignin was dispersed in an aqueous solution containing K₂C0₃ (catalyst) and phenol (co-solvent). However, the system was complex and operated at high pressure which is usually not preferred for industrial applications. Mahmood et al. , (2013, Bioresource Technology, 139: 13-20) achieved the depolymerization of KL via hydrolysis, using water alone as the solvent, under alkaline conditions using NaOH as a catalyst. The process itself was very effective for achieving good quality depolymerized kraft lignin (DKL). However, the M_w of the DKL was >5000 g/mole from the operations at 250 °C for 45 min at 20 wt.% KL concentration. The M_w of the DKL could be reduced to -1500 g/mole by operating at 350 °C or at 250°C for 2h at a 10 wt.% KL concentration. However, the reactor pressure increased from 5 MPa to 16 MPa with the increase in temperature from 250 °C to 350 °C. Therefore, the operating pressure of the process was very high. In other work, Yuan et al. (2010, Bioresource Technology, 101 : 9308-9313) also achieved a successful depolymerization of KL into oligomers in hot-compressed water-ethanol medium with NaOH as the catalyst and phenol as a capping agent. Similarly, the lignin depolymerization process was complex and the pressure of the reactor system was very high.

[0008] Typically, kraft lignin (KL) is de-polymerized into oligomers and monomers via hydrolytic depolymerization (using water) or reductive depolymerization (using hydrogen) in various solvents and catalysts. The most commonly used solvents include water, water-ethanol , water-ethanol-formic acid, methanol, acetone, etc. Also a range of various homogeneous, heterogonous, metallic, commercial and industrial catalysts have been tested for the depolymerization of lignin. However, all the depolymerization processes known operate under conditions of high temperature and pressure (as high as 8-12 MPa). The high temperature-pressure processes are associated with high capital/operating costs and impose more challenges in large-scale industrial applications/operations.

[0009] Polyols having multiple hydroxyl groups (-OH) in their structures are one of the essential constituents of polyurethanes (PUs). A wide range of polyols are available as feedstock in polyurethane production. Polyols can be aromatic or aliphatic. The most commonly used polyols are polyethers, polyesters and acrylic polyols. The critical factors for polyols regarding the performance of the final product are molecular weight, structure and functionality/hydroxyl number. Polyethers and polyesters are two major kinds of polyols consumed in the global polyol market. In 1994, nearly 90% of 1.8 million metric tons of polyurethanes consumed in the United States were based on polyethers, 9% on polyesters and 1 % on other specialty polyols. Currently, both the polyisocyanates and polyols are mostly derived from petroleum resources. PUs have rapidly grown to be one of the most widely used synthetic polymers in the global polymer markets with varied applications in different areas, including: liquid coatings and paints, adhesives, tough elastomers, rigid foams, flexible foams, and fibers. Rigid PU foam is a highly cross linked polymer with a closed cell structure. These materials offer low density, low thermal conductivity, low moisture permeability, high dimensional stability and strength leading to a wide range of applications in construction, refrigeration appliances, and technical insulations. Polyols are mostly derived from petroleum resources.

[0010] Resole Phenol formaldehyde (PF) resins are the most commonly used resins in engineered wood product applications as adhesives following urea formaldehyde (UF) resins. They are employed, for example in the manufacture of softwood plywood and oriented strandboard (OSB) for exterior building and construction purposes. Resoles are preferred for wood adhesives because of their ability to form three dimensional networks that lead to favorably high tensile strength, high modulus, dimensional stability, and resistance to moisture. Around 95% of the phenol used in the production of PF resins is derived from petroleum products.

[0011] The properties of phenolic resins can be tailored to foamable phenolic resins/resoles for their further utilization in the preparation of phenolic foams. Phenolic foams can be made from mixtures of foamable phenolic resin, a blowing agent, a surfactant, and optional additives. Rigid closed cell phenolic foam shows low thermal conductivity and exceptional flame-retardant properties, including low flammability with no dripping during combustion, low smoke and toxicity. PF foams can be utilized as fire-resistant, thermal insulation materials in applications such as civil construction, military aircraft and marine vessels. Moreover, the inherent chemical-resistance property of phenolic foam makes it outstanding in fields where chemical resistance is critical. [0012] Epoxy resins, also known as polyepoxides are a class of reactive prepolymer and polymers which contain epoxide groups. Epoxy resins are one of the most versatile materials due to their unique properties such as good chemical resistance, excellent moisture and solvent resistance, good thermal and dimensional stability, high adhesion strength and superior electrical properties. These properties provide diverse applications for epoxy resins, in such fields as high performance composites, industrial coatings, adhesives, electrical-electronic laminates, flooring and paving applications, etc. Epoxy resins are currently produced mainly from the petroleum-based chemicals bisphenol-A (BPA) and epichlorohydrin.

[0013] However, due to dwindling natural resources, associated environmental concerns and, the toxicity of the products derived from petroleum resources, there is growing interest in exploring and utilizing the abundant renewable resources as alternative feedstocks for the production of bio-based chemicals and materials such as Bio-based Polyurethane (BPU) foams, Biobased Phenol Formaldehyde (BPF) foams/resins and, bioepoxy resins etc. Lignin can be a suitable precursor for the production of phenolic/epoxy resins because of its phenolic structure. Lignin is expected to replace petroleum-derived polymers/chemicals either partially or completely with/without modification and to have a positive impact on the characteristics of the resulting products. Although with much lower reactivity, even crude lignin can be directly incorporated into PU products, however, more than 30 wt.% incorporation was found to deteriorate the properties of rigid PU foams. Direct utilization of lignin as a green substitute for polyols or phenol/bis-phenol A (BPA) is challenging due to the large molecular weight of lignin, lower functionality/hydroxyl number, poor solubility in many solvents and the lower reactivity towards isocyanate/formaldehyde/epichlorohydrin in the synthesis process. Depolymerization of lignin is a viable route for the preparation of low molecular weight products i.e. , depolymerized lignin, with higher functionality/hydroxyl number and better reactivity, making it a promising feedstock for the preparation of BPU, BPF and bioepoxy resin (or foam) materials.

[0014] Therefore, it would be highly beneficial to develop novel lignin depolymerization processes that operate under low-pressure and low-temperature conditions. SUM MARY

[0015] In accordance with the present disclosure there is now provided a process for depolymerization of a feedstock comprising lignin producing depolymerized lignin, the process comprising the steps of loading the feedstock, a catalyst, a polyalcohol, and water into a reactor; heating the reactor to about 150-300 °C to depolymerize the lignin producing depolymerized lignin mixture; stopping the depolymerization reaction by quenching with cold water; acidifying/neutralizing the depolymerized lignin mixture; precipitating depolymerized lignin and solid residues from the depolymerized lignin mixture; dissolving/dispersing the precipitated depolymerized lignin and solid residues in acetone; and separating the depolymerized lignin from the solid residues by filtration producing a solid depolymerized lignin.

[0016] In an embodiment, the reactor is heated to about 250 °C.

[0017] In another embodiment, the reactor as a pressure at most of 150 psig.

[0018] In a further embodiment, the feedstock comprises kraft lignin, hydrolysis lignin, or a combination thereof.

[0019] In another embodiment, the feedstock comprises kraft lignin at a large molecular weight of at least 10,000 g/mole.

[0020] In an additional embodiment, the feedstock comprises hydrolysis lignin at a very large molecular weight of at least 20,000 g/mole.

[0021] In another embodiment, the solid depolymerized lignin is at least one of depolymerized kraft lignin, depolymerized hydrolysis lignin or a combination thereof.

[0022] In a supplemental embodiment, the solid depolymerized lignin has a molecular weight of about 1000-2000 g/mol.

[0023] In another embodiment, the polyalcohol is at least one of ethylene glycol, propylene glycol or glycerol.

[0024] In a further embodiment, the catalyst is at least one of NaOH, KOH, NaOH/KOH mixture or H₂S0₄. [0025] In an additional embodiment, the feedstock comprises kraft lignin and the catalyst used is NaOH, KOH or NaOH/KOH mixture.

[0026] In another embodiment, the feedstock comprises hydrolysis lignin and the catalyst used is H₂S0₄.

[0027] In an additional embodiment, the concentration of the feedstock loaded into the reactor is of 5-30 wt. %.

[0028] In a further embodiment, the ratio of polyalcohol/lignin feedstock is of 2.0 to 10.0 w/w.

[0029] In an additional embodiment, the yield of recovery of depolymerized kraft lignin is of about 90 wt.% with a recovery yield of solid residues of about 0.3 wt.%.

[0030] In another embodiment, the yield of recovery of depolymerized hydrolysis lignin is of about 70 wt.% with a recovery yield of solid residues of about 10 wt.%.

[0031] In another embodiment, the hydroxyl number of the recovered depolymerized kraft lignin is about 670.1 mg KOH/g.

[0032] In a further embodiment, the hydroxyl number of the recovered depolymerized hydrolysis lignin is about 247.1 mg KOH/g.

[0033] In an further embodiment, the process described herein further comprises the step of adding a stoichiometric amount of NaOH prior to separating the depolymerized lignin from the solid residues by filtration.

[0034] In an further embodiment, the process described herein further comprises the step of removing the acetone and polyalcohol from the dissolved depolymerized lignin by evaporation.

[0035] In another embodiment, the polyalcohol is recovered.

[0036] In an additional embodiment, 90-96 wt% of the polyalcohol is recovered.

[0037] In an further embodiment, the process described herein further comprises the step of loading the solid depolymerized lignin, propylene oxide, glycerol and KOH (or NaOH) into a reactor at atmospheric pressure and heating the reactor to about 120- 190 °C producing an oxypropylated sample.

[0038] In an embodiment, the process described herein further comprises the step of washing the oxypropylated sample with acetone, neutralizing with H₂S0₄ and evaporation to produce a purified oxypropylated sample.

[0039] It is also provided herein a lignin-based rigid polyurethane foam comprising the oxypropylated sample produced by the process encompassed herein.

[0040] In an embodiment, the foam comprises up to 50 wt.% of lignin.

[0041] In another embodiment, the foam has a thermal conductivity of about 0.030- 0.036 W/mK.

[0042] It is further provided a phenol formaldehyde resole comprising the depolymerized lignin produced by the process described herein, the depolymerized lignin mixed with phenol, NaOH, ethanol and water at 60-90 °C followed by addition of formalin and reaction with formaldehyde to form the phenol formaldehyde resole.

[0043] In accordance with another embodiment, it is provided an engineered wood product such as plywood or oriented strandboard (OSB) comprising the phenol formaldehyde resole of as encompassed herein as an adhesive.

[0044] In accordance with an additional embodiment, it is provided a lignin based epoxy resin comprising the depolymerized lignin produced by the process described hrein, the depolymerized lignin reacted with epichlorhydrin, tetrabutylammonium bromide, NaOH and water in a reactor at 55-80 °C.

[0045] In a further embodiment, it is provided a fiber-reinforced plastic comprising the lignin-based epoxy resin of as described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Reference will now be made to the accompanying drawings.

[0047] Fig. 1 illustrates a schematic representation of the depolymerization scheme for kraft lignin/hydrolysis lignin (or lignin in general) according to one embodiment described herein. [0048] Fig. 2 illustrates a lignin-based rigid polyurethane (BRPU) foams from DKL50PO50 and its SEM image (average cell size -422.1 Mm and 572.9 Mm).

[0049] Fig. 3 illustrates the rate of weight loss with increasing temperature of DKL- based BRPU foam in (B) as compared to a reference foam in (A) under a nitrogen atmosphere using thermogravimetric analysis (TGA).

[0050] Fig. 4 illustrates a SEM image of BRPU foam prepared with DHL50PO50 (average cell size -162.3 Mm and -272.1 Mm).

[0051] Fig. 5 illustrates the rate of weight loss of DKL-based BRPU foams (DHL50PO50 (B) and DHL60PO40 (C)) as compared to a reference foam (A) under a nitrogen atmosphere using thermogravimetric analysis TGA.

[0052] Fig. 6 illustrates the form and dimensions of a test specimen of a bio-based phenol-formaldehyde veneer.

[0053] Fig. 7 illustrates the dry shear stress of 2-ply plywood samples bonded with various BPF resoles compared with such samples bonded with pure PF resole.

[0054] Fig. 8 illustrates the rate of weight loss with increasing temperature of DHL- Epoxy-DDM and DGEBA-DDM using thermogravimetric analysis (TGA).

[0055] Fig. 9 illustrates the mechanical properties (flexural properties (A) and strength properties (B)) of FRPs with DGEBA resin blended with various levels of DKL- based epoxy resin (0-100 wt%).

[0056] Fig. 10 illustrates the image and morphology for 30wt% DHL-PF foam (a) and 50wt% DHL-PF foam (b).

[0057] Fig. 1 1 illustrates the rate of weight loss with increasing temperature of phenol-formaldehyde (PF) and depolymerized hydrolysis (DHL) lignin-based PF foams using thermogravimetric analysis (TGA). It will be noted that throughout the appended drawings, like features are identified by like reference numerals.

DETAILED DESCRIPTION

[0058] It is provided a process for the low-pressure and low-temperature (low- P/low-T) depolymerization of kraft/hydrolysis lignin or other types of lignin to obtain low molecular weight depolymerized lignins (DLs) for the production of bio-based polyols and phenols, and their applications in, for example, polyurethane foams/resins/adhesives/coatings, epoxy resins and phenolic resins/adhesives/foams.

[0059] As depicted in Fig. 1 , it is provided a process for the depolymerization of lignin producing depolymerized lignin comprising loading of the lignin, a catalyst, a high-boiling-point polyalcohol, and water into a reactor and heating the reactor to about 150-300 °C to depolymerize the lignin producing a depolymerized lignin 10. The depolymerization reaction is stopped by quenching the reactor through cooling coils with cold water/acetone in the reactor 12. The depolymerized lignin (DKL or DHL or DL in general) is neutralized/acidified and recovered by precipitation (for DKL) or organic solvent washing (for DHL) or other methods depending on the types of lignin 14. The solid product is dissolved in acetone and separated by filtration 16 producing a solid depolymerized lignin. The produced solid depolymerized lignin can be used in the production of lignin-based rigid polyurethane foams after an oxypropylation step, or can be further used to produce a phenol formaldehyde resole or a lignin based epoxy resin.

[0060] It is thus provided a moderately cost-effective and efficient low- pressure/low-temperature process (low-P/low-T) (<150 psig and <300°C) for the depolymerization of high molecular weight kraft lignin (e.g. , KL of Mw -10,000 g/mole was used in the examples) and complex hydrolysis or hydrolyzed lignin (e.g. HL of an Mw that is not measureable, Mw >20,000 g/mole for the HL sample used in the examples) or other types of lignin into depolymerized KL (DKL), depolymerized hydrolysis lignin (DHL), or de-polymerized lignin (DL) in general, with a much lower molecular weight (varying ranges can be achieved depending on target applications, e.g. , 1000-2000 g/mol in the applications demonstrated in the examples). This novel low-P/low-T process developed for lignin depolymerization operates in a water- polyalcohol co-solvent system (containing 2-10 wt.% water) using NaOH/KOH (for KL) or H₂S0₄ (for HL) as a catalyst. The polyalcohol can be any high boiling point polyalcohol including: ethylene glycol (EG), propylene glycol (PG), glycerol, etc. Typical operating conditions are: reaction temperature of 150-300°C; reaction time: 30-120 min; substrate concentration: 5-30 wt.%; polyalcohol to KL or HL ratio: 2.0 to 10.0 (w/w), etc. The process resulted in a high yield of DKL (up to 90 wt.%) and a very low yield (-0.3 wt.%) of solid residues (SR), while producing a moderately high yield of DHL (-70 wt.%) with an SR of -10 wt.%. The obtained DKL had a total hydroxyl number of -670.1 mg KOH/g, and the produced DHL has a total hydroxyl number of -247.1 mg KOH/g, which makes them both a suitable feedstock as bio-based polyols and/or phenolic bio-oils for the synthesis of polyurethane foams/resins, epoxy resins and phenolic resins/adhesives/foams, etc. In this process, the solvent used, EG, PG or glycerol, was recoverable at a recovery rate of -95-96 wt.%, which is very important in relation to the economic viability of this process. The obtained DKL and DHL, although in solid form, has a suitable hydroxyl number, and can be further transformed into liquid polyols via oxypropylation using propylene oxide in a unique medium that is a mixture of glycerol, acetone and KOH at 120 to 190 °C. The obtained oxypropylated DKL/DHL with a high bio-content (>50 wt.%) can be used directly for the production of bio-based polyurethane (BPU) foams. Similarly, the obtained DKL/DHL can replace phenol or bisphenol A at a high substitution ratio (>50 wt.%) for the preparation of bio-based phenol-formaldehyde (BPF) resole resins/adhesives and lignin-based epoxy resins, respectively. BPF resoles/adhesives were prepared using an F/P ratio of 0.8-3.0 by reacting DKL/DHL and phenol with formalin (37 wt.% formaldehyde), in the presence of NaOH in an ethanol-water solution at 60-90 °C. Similarly, foamable BPF resole resins were prepared using DKL/DHL and formaldehyde at an F/P ratio of 1.3. The foamable BPF resoles were used for the preparation of phenolic foams with up to 50 wt.% bio- content. Lignin-based epoxy resins were produced successfully by reacting DKL/DHL with epichlorohydrin (ECH) (molar ratio of ECH to DHL or DKL was as low as 6) at 55- 80 °C in the presence of tetrabutylammonium bromide (0.2 wt.%) and NaOH in water solution. Overall the low-P/low-T lignin depolymerization process offers a product which is suitable for multiple bio-based polymers/materials.

[0061] Accordingly, the process described herein comprises: (a) efficient depolymerization of KL/HL under low-pressure and low-temperature conditions employing a polyalcohol (EG/PG/Glycerol) as the reaction medium; (b) separation of solvent and low molecular weight products (DKL/DHL); (c) recovery of solvent (EG/PG/Glycerol) at a high recovery rate; and (d) effective utilization of produced DKL/DHL in the preparation BPU foams/resins, BPF resoles/adhesives/foams, epoxy resins, etc.

[0062] Lignin as encompassed herein refers to kraft lignin and/or hydrolyzed lignin for example, and not limited to. [0063] It is disclosed that KL depolymerization (catalyzed by NaOH) or HL (catalyzed by H₂S0₄) employing water-EG or PG or glycerol co-solvent produced DKL or DHL product of a better quality when compared to other available processes. It was discovered that employing water-EG or PG or glycerol co-solvent has many advantages over other conventional methods. Lower operating temperatures (<250°C) and pressures (<150 psi) are needed in the described process and DKL or DHL products with a low M_w and other acceptable characteristics are produced. Furthermore, a very high solvent (EG/PG/Glycerol) recovery rate (>90%) was observed and high yields of the desired product (DKL up to 90% or DHL up to 70%) is noted.

[0064] An efficient oxypropylation of solid/powdered DKL/DHL at 110-160 °C using propylene oxide in a medium that consists of a mixture of glycerol, acetone and KOH to produce liquid polyols for the synthesis of BRPU foams with bio-contents of >50 wt.% is disclosed. Preparation of BPF resoles/adhesives by reacting DKL/DHL or bio-oils plus phenol with formaldehyde at F/P ratio of 0.8-3.0 in the presence of NaOH, ethanol and water at 60-80°C is described. Preparation of BPF foamable phenolic resoles using DKL/DHL at F/P ratio 1.0-2.0 in NaOH water solution at 84 °C and preparation of phenolic foams from foamable phenolic resins/resoles at 30 wt.% and 50 wt.% replacement ratios is also described herein. Preparation of lignin-based epoxy resins using DKL/DHL at 55-80 °C in a mixture consisting of epichlorohydrin (molar ratio of DHL or DKL to ECH was 6) water, tetrabutylammonium bromide (0.2 wt.%) and NaOH is further disclosed.

[0065] Accordingly, a novel low-P/low-T highly efficient process was developed for the depolymerization of a high molecular weight kraft lignin (KL of varying Mw, e.g. , Mw -10,000 g/mole for the KL sample used in the examples) and complex hydrolysis or hydrolyzed lignin (HL, Mw not measureable, e.g. , we assumed Mw >20,000 g/mole for the HL sample used in the examples) or other types of lignin into depolymerized KL (DKL)/ depolymerized hydrolysis lignin (DHL) or de-polymerized lignin (DL) with a much lower molecular weight (1000-2000 g/mol). This process operates in water-polyalcohol (EG, PG or glycerol) co-solvent media containing 2-10 wt.% water using NaOH (for KL) or H₂S0₄ (for HL) as a catalyst. The process resulted in a high yield of DKL (up to 90 wt.%) and a very low yield (-0.3 wt.%) of solid residues (SR), while the process produced a moderately high yield of DHL (70 wt.%) with an SR of -10 wt.%. The obtained DKL had a total hydroxyl number of -670.1 mg KOH/g, and the produced DHL has a total hydroxyl number of - 247.1 mg KOH/g, which make them both suitable feedstock for the synthesis of polyurethane resins/foams, phenolic resin/foam, epoxy resins etc. In this process, the solvent used, EG or PG or glycerol, was recoverable at a recovery rate of -94-96 wt.%, which makes this process economically viable. The obtained solvent-free DKL/DHL products are solid powders, but can be further transformed into liquid polyols via oxypropylation using propylene oxide in a unique medium that consists of a mixture of glycerol, acetone and NaOH/KOH. The obtained oxypropylated polyols can be used as polyols for commercial production of bio-based rigid polyurethane foams. Also, the obtained DKL/DHL can be used for the preparation of epoxy resins via grafting epichlorohydrin onto DKL/DHL in the presence of water, NaOH solution and tetrabutylammonium bromide. The obtained epoxy resin can be used for the preparation of fiber-reinforced plastics at a high replacement ratio (>50- 75%). Finally, the reaction of DKL/DHL plus phenol with formaldehyde in the presence of water, ethanol and NaOH leads to the preparation of bio- based PF resin which can be used as plywood adhesive at a very high phenol replacement level (up to 75 %) and as foamable resin for the production of BPF foam at a high phenol substitution ratio (>50 %).

[0066] Previously, lignin-based PU resins/foams were produced using crude lignin, however the substitution ratio of lignin in the polyols was generally low (<20-30 wt.%) due to the poor solubility of lignin in polyols and its low reactivity in the PU synthesis. Similarly, lignin-based phenolic foams/resins (resoles) or epoxy resins were produced at low substitution ratios due to the inherent high molecular weight of crude lignin. Lignin depolymerization can reduce the molecular weight and polydispersity (PDI) of lignin. The de-polymerized lignin described herein has an improved solubility and reactivity, so when replacing commercial polyols or resins with the de-polymerized lignin for the synthesis of bio-based PU resins/foams, PF resoles/adhesives/foams/, and epoxy resins, etc. a higher substitution ratio >50 wt.% can be achieved.

[0067] All the existing methods for lignin depolymerization employ a combination of high temperature and pressure to achieve lower M_w products. The solvents used in these processes are usually non-recoverable. The present disclosure will be more readily understood by referring to the following examples. EXAMPLE I

Depolymerization of KL/HL

[0068] Both KL and HL lignin used in the process herein were obtained from FPInnovations from its lignin demonstration plant (capacity of 100 kg/day) in Thunder Bay, ON and from its patented TMP-BIO process. The properties of KL and HL are provided in Table 1 and Table 2.

Table 1

Proximate & ultimate analysis of original KL

Proximate analysis, wt% (d.b)^a Ultimate analysis, wt% (d.a.f.

VM^b FC^C As ? TS/MC^e C hi N S O

56.3 43.1 0.57 98.5/1.5 63.8 5.4 0.02 5.2 25.6 ^a On dry basis; ^D VM: volatile matter; ^c FC: Fixed carbon (VM and FC was determined by thermogravimetric analysis (TGA) in at 10 °C/min to 900 °C); ^d Ash content determined gravimetrically in a muffle furnace at 700 °C for 4 hours; ^e TS/MC: Total solids /moisture contents in the sample was determined by placing 1- 2 g of sample in an oven at 105 °C for 24 hours; ^f On dry and ash free basis; ⁹ By difference.

Table 2

Chemical (d. b. )^a and elemental composition (d.a.f. )^b of hydrolysis lignin (HL)

Lignin Carbohydrates Ash Others, Carbon, Hydrogen, Nitrogen, Others,

% % % % % % % %

56.7 29.8 1.2 12.3 62.8 6.1 4.0 28.3 a _Λ b . .

a On dry basis. ^D On dry and ash free basis

[0069] In a typical run, 12 g KL with 3.4 g NaOH [NaOH/KL ratio = 0.28 (w/w)] (or 12 g HL with 0.22 g H₂S0₄), 0.0-2.5 g water and 42-48 g EG (or PG or glycerol) were loaded into an autoclave reactor (100 mL stirred batch reactor). The reactor was tested for leakages using compressed nitrogen and was heated up to the desired temperature (150-300 °C) under stirring (290 rpm). After the desired temperature was reached, the reaction time was recorded. Once the desired reaction time elapsed, the reaction was stopped by quenching with cold water. The reaction products were washed from the reactor using distilled water followed by acidification to pH~2-3 in the case of KL in order to facilitate the precipitation of the depolymerized lignin products. The precipitated depolymerized KL (DKL) together with the solid residues (SRs) were separated from the solution by filtration. The obtained solid cake was dissolved in acetone followed by filtration to separate SRs from acetone-soluble DKL products. Finally, the DKL was obtained by evaporation of the acetone-soluble phase and the product yields were determined. The aqueous phase was evaporated to recover EG (or PG or glycerol). In the case of depolymerized HL (DHL), after reaction, the reaction products were collected by acetone washing followed by addition of a stoichiometric amount of NaOH to neutralize the added H₂S0₄. The solid residues (SRs) were separated by filtration. DHL was isolated via evaporation first to remove acetone, then EG (or PG or glycerol) under vacuum. In this process, the recovery rate of the solvent used, i.e. , EG or PG was at -90-96 wt.%. The SRs were dried at 105 °C for 24 hr to determine their yield. The M_w of DKL or DHL was analyzed by GPC-UV.

[0070] The following Table 3 shows the results achieved from the depolymerization of KL employing various water-polyalcohol co-solvent media.

Table 3

Yields and M_w of DKL with various solvent systems

Solvent DKL yield (wt.% ) SR's yield (wt.%) M_w (g/mol)

EG 90.1 0.27 1050

PG 79.1 0.36 1330

Glycerol 85.1 0.30 1490

Table 4

Yield and M_w of DHL with polyalcohol solvent

Solvent DKL yield (wt.%) SR's yield (wt.%) M_w (g/mol)

EG 70.0 10.0 1420

[0071] The process resulted in a high yield of DKL (up to 90 wt.%) accompanied by a very low yield (-0.3 wt.%) of solid residues (SR), while the process produced DHL at a moderately high yield (-70 wt.%) and an SR yield of -10 wt.%. The obtained DHL had a M_w of 1500-2000 g/mol. The obtained DKL had a total hydroxyl number of -670.1 mg KOH/g, and the produced DHL had a total hydroxyl number of -247.1 mg KOH/g. FTIR, NMR spectra and GC-MS analyses demonstrated that the DKL/DHL are aromatic and phenolic in nature. Thus, these products can be a suitable feedstock for the synthesis of polyurethane foams/resins, phenolic resins/resoles, epoxy resins, phenolic foams etc.

[0072] The elemental composition (the CHNS contents) of the KL and DKL samples were analyzed to provide information on the fate of elements such as S that are associated with environmental concerns in certain specific industrial applications of lignin.

Table 5

Elemental composition of the original KL and typical DKL products obtained from KL depolymerization at different temperatures

Reaction condition Elements (%, d.a.f)³

T (°C) N C H S O^b

Original KL 0.02 63.8 5.4 5.2 25.6

180 0.10 63.3 5.4 0.8 30.4

200 0.10 64.1 5.4 0.4 30.0

250 0.04 68.8 5.6 0.5 25.1

260 0.05 69.7 5.6 0.6 24.1 ^a Dry and ash free basis. ^D Determined by difference

EXAMPLE II

Oxypropylation of DKL/DHL to produce liquid polyols for the preparation of bio- based rigid polyurethane (BRPU) foams

[0073] The obtained DKL or DHL products obtained after depolymerization in a water-EG/PG/Glycerol co-solvent medium were in solid/powder form before oxypropylation. The oxypropylation of DKL/DHL was carried out in a 100-mL Parr reactor at three different bio content loadings i.e. , 50 wt.%, 60 wt.% and 70 wt.%. In a typical run at a bio-polyols content of 50 wt.% the following chemicals were added to the reactor: 18.9 g of DKL or DHL, 21.21 g propylene oxide (PO), anhydrous mixture of 2.31 g glycerol and KOH (%KOH in mixture varied from 2-20 wt.%) and 16.8 g of acetone. After all the ingredients were added in the reactor, the reactor was heated, and the reaction was allowed to take place at 150 °C for 2 h. Initially, the reactor pressure increased while heating, however, after a while the pressure returned to approximately the initial pressure, implying complete utilization of PO or completion of the reaction. After the reactor was cooled, the oxypropylated sample was washed from the reactor using acetone followed by neutralization with H₂S0₄, filtration and evaporation under reduced pressure to remove acetone and the unused PO (if any). The final weight of the sample was equal to the total amount of the DHL/DKL, PO and glycerol added; showing the yield for the oxypropylated sample was close to -100%.

Table 6

Characteristics of DKL, DHL and oxypropylated DKLs and DHLs

Total Hydroxyl number (mg Viscosity at 80 °C

Sample ID MvP (g/mole) State

KOH/g) (Pa.s)

DKL 1050 670.5 - Solid powder

DKL50PO50 1550 331.0 0.812

DKL60PO40 1440 340.4 1.101 Viscous Liquid

DKL70PO30 1420 347.5 1.232

DHL 1420 247.1 - Solid powder

DHL50PO50 3160 118.2 0.78

DHL60PO40 3130 138.0 0.89 Viscous Liquid

DHL70PO30 2530 153.0 1.431

[0074] Lignin-based rigid polyurethane (RPU) foams were prepared using oxypropylated samples of DKL/DHL and tested for their properties. All the foam samples were prepared using the one-pot method. Typically, the rigid PU foam formulation in this study included a polyol combined with 0-20% (w/w) glycerol (a co- crosslinking agent). For comparison, reference foam was prepared using sucrose polyols at 0% DKL or DHL. Additionally, the formulation included a physical blowing agent (acetone at 5-30% (w/w)), a catalyst combination (mixture with equal amounts of stannous octoate and Diaza or TEDA at 2% (w/w)), surfactant at 2% (w/w) and water at 2% (w/w). The amounts of the blowing agent, catalyst, surfactant and water to be used were determined on the basis of the total weight of polyol used. PMDI was added at an NCO/OH ratio of 1.1. The foam preparation procedure used was comprised of the following steps: (1 ) the desired amounts of polyols, catalysts and blowing agents were all weighed in a cup and the premixing of the mixture was carried out at 550 rpm for 5- 20s to obtain a homogeneous mixture and (2) the pre-calculated amount of PMDI was then transferred into the cup and the mixture was stirred vigorously for another 5-20s. The mixture was then placed on a leveled surface in a fume hood and the foam was allowed to rise at the ambient temperature (23±2 °C). All the foam samples were left in the fume hood for 24-48 h for post-curing before the sample was further analyzed. The sample shrinkage, structural uniformity, stability and cell appearance could be observed at this point. However, prior to characterization, the foam samples were further conditioned for a minimum of 24 h to a maximum of one week, depending on the requirements. In the synthesis of bio-based RPU (BRPU) foams at different bio- replacement ratios, sucrose polyol was not used and glycerol was kept at 10 wt.% based on the total weight of polyols used.

[0075] The apparent densities of foam samples were measured according to ASTM D1622-03. The mechanical properties of PUF samples were measured at ambient conditions on an ADMET Universal Testing Machine ( Model SM-1000-38). Modulus of elasticity (Young's modulus or compressive modulus) was determined from the initial linear slope of the stress-strain curve and compressive strength at 10% deformation, was determined by performing the stress-strain tests according to ASTM D 1621 -00. The thermal conductivities of the foam samples were measured using a KD2 PRO thermal properties analyzer with SH-1 dual needle sensor ( 1.3 mm diameter x 3 cm long, 6 mm spacing) capable of measuring thermal conductivity in the range of 0.02 to 2.00 VV/mK. The specimen size used for thermal conductivity analysis was -50 mm x 50 mm x 30 mm. As listed in Tables 7 and 8, the thermal conductivity of all BRPU foams was in the range of 0.030-0.036 VV/mK, comparable to the reference foam (0.033 VV/mK). However, all BRPU foams had better compressive strength than the reference foam. The morphology of the foams was observed using a Hitachi S-4500 field emission cross beam scanning electron microscope (SEM). After examination by SEM, selected locations on the foam surface were subjected to a cross-sectional cut and the sample was coated with osmium, and imaged using a focused ion beam LEO (Zeiss, Thornwood, NY, USA) 1540XB SEM (Figs. 2, and 4). The morphology of foam samples was observed using a Motic stereo microscope. The SEM imaging proved that the foams had a closed-cell structure. The thermal stability of the foams was measured by a Pyris 1 TGA Diamond, Perkin-Elmer Thermogravimetric analyzer (TGA), in a N₂ flow of 20 mL/min, heated from 30 °C to 800 °C at 10 °C/min, as illustrated in Figs. 3, and 5. The foams made were stable up to 250°C as compared to the reference foams which were stable up to about 350°C. Table 7

Density, mechanical strength and thermal conductivity of reference and DKL-derived

BRPU foams

Compression strength Thermal

Density Compressive

Sample ID at 10% deformation conductivity

(kg/m³) modulus (kPa)

(kPa) (W/mK)

Sucrose Ref. Foam 42.5±0.5 2695.0±100.0 182.0±45.0 0.033±0.0010

At varying percentage of physical blowing agent

DKL50PO50 46.0±1.0 6936.0±55.0 356.0±41.0 0.033±0.0010

DKL60PO40 40.0±0.5 5273.0±70.0 348.1±21.0 0.031 ±0.0010

DKL70PO30 38.0±1.0 4743.0±120.0 315.0±85.0 0.032±0.0010

At fixed percentage of physical blowing agent

DKL50PO50 46.0±1.0 6936.0±55.0 356.0±41.0 0.033±0.0010

DKL60PO40 61.8±0.2 8902.0±35.0 381.0±11.0 0.034±0.0010

DKL70PO30 82.7±2.0 22436.0±22.0 566.0±10.0 0.036±0.0010

Table 8

Density, mechanical strength and thermal conductivity of reference and DHL-derived

BRPU foams

Density Compressive Compression strength at Thermal conductivity

Foam ID

(kg/m³) modulus (kPa) 10% deformation (kPa) (W/mK)

At fixed percentage of physical blowing agent

Sucrose

42.5±0.5 2695.0±100.0 182.0±45.0 0.033±0.0010

Ref. Foam

DHL50PO50 45.0±2.0 5381.0±100.0 235.0±75.0 0.030±0.0010

DHL60PO40 62.1±2.0 12360.0±55.0 513.0±45.0 0.032±0.0010

DHL70PO30 Due to high viscosity of DHL70PO30 foam did not form

At varying percentage of physical blowing agent

DHL50PO50 45.0±2.0 5381.0±100.0 235.0±75.0 0.030±0.0010

DHL60PO40 39.0±2.0 2825.0±80.0 193.0±42.0 0.031±0.0010

DHL70PO30 Due to high viscosity of DHL70PO30 foam did not form

EXAMPLE III

Preparation of BPF resoles for adhesive or foamable resins

[0076] Various PF resoles were synthesized with DKL/DHL obtained after depolymerization of KL/HL. The resinification was carried out in a 250-mL three-neck flask equipped with a thermometer, a pressure-equalizing addition funnel, and a condenser and then placed over a water-bath on top of a hot plate. The mixture of phenol, DKL/DHL, sodium hydroxide, ethanol and water were added at pre-determined amounts into the three-neck flask. The required amounts of phenol and lignin were calculated based on the phenol percent substitution ratio. NaOH solution and water were added at concentrations of 10 wt.% and 40 wt.%, respectively, based on the amount of phenolic compounds. . Ethanol was added to improve the solubility of DKL/DHL at a charge equal to that all of phenolic compounds including pure phenol and DKL, to avoid the formation of coagulated products during the reaction especially at high percentage level of phenol substitution with depolymerized lignin. The NaOH solution was mixed with phenol and added dropwise. The mixture was allowed to mix for a period of two hours under magnetic stirring at 60 °C to ensure a homogenous lignin-phenol solution. The reaction temperature was then increased to 80 °C and formalin (37% formaldehyde by weight) was added dropwise into the three-neck flask using an addition funnel given that the reaction was exothermic. The amount of formaldehyde added was determined by the required F/P molar ratio of the experimental run, where P denotes the moles of all phenolic compounds including phenol and DKL/DHL (assuming M_w of lignin unit to be 180 g/mol to calculate F/P ratios). The reaction was held at 80°C for two hours, and then stopped by cooling to room temperature. The resultant BPF resin was then recovered into labeled 250-mL plastic bottles and stored in the freezer at -2°C for further characterization purposes. Plywood samples were prepared using depolymerized-lignin based BPF resoles as adhesives and then tested .

Table 9

Properties of prepared lignin-based resoles (LPF) at 50 wt.% lignin-content at F/P ratio of 1.2

Non-volatile content Curing temperature (°C)

Viscosity @ 25 °C (cP)

(NVC) (wt.%)

Onset Peak Endset

229±8.5 44.0 187.8 219.5 293.0

[0077] For testing of the BPF resoles as adhesives for plywood, adhesive application on the pre-conditioned veneers was 250 g/m². The veneers were pressed at a temperature of 180°C and a press-pressure of 1.4 MPa or around 203 psi for 6 minutes in accordance to the two-ply requirement of ASTM D2339. The pressed veneers were then cut into test specimen sizes with a slight modification of ASTM D2339 - the sizes of the test specimens were reduced in half to accommodate the constraints of the UTM used for mechanical testing (see Fig. 6). The changes in size of the test specimens were taken into consideration when conducting mechanical testing of the specimens. The test specimens were re-conditioned in environmental chambers at 23 °C and 50% relative humidity for a period of seven days prior to mechanical testing. A total of 10 specimens per resin sample were tested to obtain an average maximum shear stress at failure point using the INSTRON UTM. The specimens were placed and gripped tightly in the jaws of the grips in the testing machine and load was applied at a crosshead speed of 1 mm/min, thereby subjecting the specimens to increasing shear strain until failure. This was repeated for 15 lignin-based phenol formaldehyde resins and one pure lab synthesized phenol formaldehyde resin. Due to time constraints, only the dry tensile strength of the specimens was tested. Results of typical dry shear strength of the 2-ply plywood samples are shown in Fig. 7. The adhesives prepared using BPF resoles at 75 wt.% phenol substitution with DKL (high or low M_w, i.e. , 1700 g/mol and 800 g/mol) at F/P ratio of 2.1 , showed maximum shear stress of ~9 MPa, comparable to the pure PF resole (Fig. 7).

[0078] For the synthesis of foamable lignin-derived resoles at 30 wt.% and 50 wt.% phenol substitution, the F/P ratio was kept at 1.3. For the synthesis of resole with 30 wt.% phenol substitution, 60 g of DHL, 140 g of phenol, 50 g of water and 18 g of a 50 wt. % sodium hydroxide solution were charged into a flask and then heated to 84 °C for half an hour under continuous stirring. Subsequently , 226 g of formaldehyde (ca 37%) was added dropwise to the flask. After further reaction for 2 h, the obtained resole was cooled down in a water bath until it reached 60 °C. The pH of resoles was then adjusted to 5.0-6.5 by adding acetic acid. Finally, the resoles were concentrated by a vacuum rotary evaporator until the solids content of the resins reached about 70-85%. For the preparation of foamable resole with DHL, approximately 100 g of DHL, 100 g of phenol, 50 g of water, 18 g of a 50 wt. % sodium hydroxide solution, and 172 g of formaldehyde (ca 37%) were used while keeping the remaining procedure the same as that for foamable FPF resole at 30 wt.% phenol substitution .

Table 10

Properties of foamable bio-based PF resoles

Resole pH value Viscosity (P, at 60°C) Solids content (%)

PF resole 5.69(±0.02) 1.36(±0.05) 78.33(±0.71)

30% BPF 5.71 (±0.01) 1.77(±0.08) 76.59(±0.95)

50% BPF 5.68(±0.03) 1.98(±0.12) 74.44(±1 .03)

EXAMPLE IV

Preparation of DKL/DHL based epoxy

[0079] 4 g DHL/DKL was dissolved in 12 g epichlorohydrin (the molar ratio of DHL/DKL to ECH was 6) and added to a three-neck round-bottom flask, followed by 12 mL of distilled water and 0.2 wt.% tetrabutylammonium bromide (TBAB) as a phase transfer catalyst. The reactor (equipped with a reflux condenser and a magnetic stirrer) was heated to 80 °C and maintained at this temperature for 1 h under stirring. Then, the system was cooled to 55 °C and sodium hydroxide solution (NaOH/lignin molar ratio was 6.3) was added dropwise into flask in 15 min and kept at this temperature for 8h. By cooling the system to room temperature, the organic phase was separated and any excess of epichlorohydrin was evaporated using a rotary evaporator at 100 °C under reduced pressure. The obtained epoxy resin product was dissolved in acetone and the by-products were filtered out using a a glass fiber filter paper. The filtrate containing lignin-based epoxy resin was concentrated using a rotary evaporator. The yields of epoxidation for DKL and DHL were 97% and 95%, respectively. The characteristics of depolymerized lignin-derived epoxy resins are shown in Table 1 1 , and the stability of the DHL-Epoxy-DDM (DHL-based epoxy resin cured with 4,4'- diaminodiphenyl methane (DDM) as the curing agent), and DGEBA-DDM (conventional bis-Phenol A type epoxy cured with DDM) is illustrated in Fig. 8. As seen herein, the decomposition peak temperature of the lignin-based epoxy resin was about 350 °C which is about 50°C lower than that of the conventional bis-phenol A type of epoxy resin. The epoxy resins were utilized as a polymer matrix in the manufacture of Fiber- reinforced plastics (FRPs), and the mechanical properties of FRPs with DGEBA resin blended with various wt% DKL-based epoxy resin (0-100 wt%) are presented in Fig. 8.

Table 1 1

Characteristics of depolymerized lignin-derived epoxy

Sample Mw PDI Epoxy content¹

DKL-Epoxy 790 2800 3.5 5.6

DHL-Epoxy 1 183 5530 4.6 5.13

Epoxy content is defined as weight percent epoxide in the epoxy resins. The epoxy content of the synthesized lignin-based epoxy resins was determined with a potentiometric titrator (Titroline 7000 Titrator) according to ASTM D1652-11 standard. Briefly, 0.3-0.6 g of sample was placed in a 100 mL beaker and dissolved in 30 ml of methylene chloride and 15 ml of tetraethylammonium bromide solution in glacial acetic acid. The resulted solution was titrated with perchloric acid (0.1 N in glacial acetic acid). The normality of perchloric acid was determined before each measurement by 0.25 g of potassium acid phthalate.

EXAMPLE V

Preparation of BPF foams

[0080] For the preparation of 30% DHL-PF foam, 6.2 g of p-toluenesulfonic acid and 2 g glycerol were fully dissolved in 2.4 g distilled water in a beaker ( Mixture-1 ). Then, 1.2 g of polyetherpolysiloxane-copolymer and 4 g of hexanes were added into 40 g of foamable 30% DHL-PF resole in a paper cup, followed by mixing with a mechanical stirrer until the mixture became homogeneous (Mixture-2). Subsequently, Mixture-1 was added into Mixture-2 with vigorous agitation for -30-40 seconds at room temperature. The mixture was then moved to a preheated oven at 70 °C for 30 min. The 50% DHL-PF foam was prepared using 50% DHL-PF resole using the same recipe except that the amount of p-toluenesulfonic acid added was increased to 6.6 g. Fig. 10 illustrates images and morphologies for (a) 30% DHL-PF foam and (b) 50% DHL-PF foam. The density, compressive strength and thermal conductivity of BPF foams are compared with those of pure PF foam in Table 12. 30% DHL-PF foam is very close to the pure PF foam with respect to density, strength and thermal conductivity, while the 50% DHL-PF foam has higher density, better strength and comparable thermal conductivity compared with the PF foam. For DHL-PF foams, their thermal stability decreases with increasing phenol substitution ratio, as shown in Fig. 1 1.

Table 12

Density, compressive strength and thermal conductivity of phenolic foams

Foam sample Density (kg/m^J) Compressive strength at Thermal

10% strain (MPa) conductivity (W/m/k)

PF 43.2 (±1.5) 0.19 (±0.01) 0.034 (±0.011)

30% DHL-PF 39.9 (±1.3) 0.17 (±0.03) 0.033 (±0.013)

50% DHL-PF 98.5 (±3.1) 0.42 (±0.06) 0.040 (±0.012)

[0081] While the present disclosure has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modifications and this application is intended to cover any variations, uses, or adaptations of the invention, including such departures from the present disclosure as come within known or customary practice within the art and as may be applied to the essential features hereinbefore set forth, and as follows in the scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A process for depolymerization of a feedstock comprising lignin producing depolymerized lignin, the process comprising the steps of: a) loading the feedstock, a catalyst, a polyalcohol, and water into a reactor; b) heating the reactor to about 150-300 °C to depolymerize the lignin producing depolymerized lignin mixture; c) stopping the depolymerization reaction by quenching with cold water; d) acidifying/neutralizing the depolymerized lignin mixture; e) precipitating depolymerized lignin and solid residues from the depolymerized lignin mixture; f) dissolving/dispersing the precipitated depolymerized lignin and solid residues in acetone; and g) separating the depolymerized lignin from the solid residues by filtration producing a solid depolymerized lignin.

2. The process of claim 1 , wherein the reactor is heated to about 250 °C.

3. The process of claim 1 or 2, wherein the reactor as a pressure at most of 150 psig.

4. The process of any one of claims 1 -3, wherein the feedstock comprises kraft lignin, hydrolysis lignin, or a combination thereof.

5. The process of claim 4, wherein the feedstock comprises kraft lignin at a large molecular weight of at least 10,000 g/mole.

6. The process of claim 4, wherein the feedstock comprises hydrolysis lignin at a very large molecular weight of at least 20,000 g/mole.

7. The process of any one of claims 1 -6, wherein the solid depolymerized lignin is at least one of depolymerized kraft lignin, depolymerized hydrolysis lignin or a combination thereof.

8. The process of any one of claims 1 -7, wherein the solid depolymerized lignin has a molecular weight of about 1000-2000 g/mol.

9. The process of any one of claims 1 -8, wherein the polyalcohol is at least one of ethylene glycol, propylene glycol or glycerol.

10. The process of any one of claims 1 -9, wherein the catalyst is at least one of NaOH, KOH, NaOH/KOH mixture or H₂S0₄.

1 1. The process of claim 1 , wherein the feedstock comprises kraft lignin and the catalyst used is NaOH, KOH or NaOH/KOH mixture.

12. The process of claim 1 , wherein the feedstock comprises hydrolysis lignin and the catalyst used is H₂S0₄.

13. The process of any one of claims 1 -12, wherein the concentration of the feedstock loaded into the reactor is of 5-30 wt.%.

14. The process of any one of claims 1-13, wherein the ratio of polyalcohol/lignin feedstock is of 2.0 to 10.0 w/w.

15. The process of claim 7, wherein the yield of recovery of depolymerized kraft lignin is of about 90 wt.% with a recovery yield of solid residues of about 0.3 wt.%.

16. The process of claim 7, wherein the yield of recovery of depolymerized hydrolysis lignin is of about 70 wt.% with a recovery yield of solid residues of about 10 wt.%.

17. The process of claim 7 or 15, wherein the hydroxyl number of the recovered depolymerized kraft lignin is about 670.1 mg KOH/g.

18. The process of claim 7 or 17, wherein the hydroxyl number of the recovered depolymerized hydrolysis lignin is about 247.1 mg KOH/g.

19. The process of any one of claims 1 -18, further comprising the step of adding a stoichiometric amount of NaOH prior to separating the depolymerized lignin from the solid residues by filtration.

20. The process of any one of claims 1 -19, further comprising the step of removing the acetone and polyalcohol from the dissolved depolymerized lignin by evaporation.

21. The process of claim 20, wherein the polyalcohol is recovered.

22. The process of claim 21 , wherein 90-96 wt% of the polyalcohol is recovered.

23. The process of any one of claims 1 -22, further comprising the step of loading the solid depolymerized lignin, propylene oxide, glycerol and KOH (or NaOH) into a reactor at atmospheric pressure and heating the reactor to about 120-190 °C producing an oxypropylated sample.

24. The process of claim 23, further comprising the step of washing the oxypropylated sample with acetone, neutralizing with H₂S0₄ and evaporation to produce a purified oxypropylated sample.

25. A lignin-based rigid polyurethane foam comprising the oxypropylated sample produced in claim 24.

26. The foam of claim 25, comprising up to 50 wt.% of lignin.

27. The foam of claim 25 or 26, said foam having a thermal conductivity of about 0.030- 0.036 W/mK.

28. A phenol formaldehyde resole comprising the depolymerized lignin produced by the process of any one of claims 1 -22, said depolymerized lignin mixed with phenol, NaOH, ethanol and water at 60-90 °C followed by addition of formalin and reaction with formaldehyde to form said phenol formaldehyde resole.

29. An engineered wood product such as plywood or oriented strandboard (OSB) comprising the phenol formaldehyde resole of claim 28 as an adhesive.

30. A lignin based epoxy resin comprising the depolymerized lignin produced by the process of any one of claims 1 -22, said depolymerized lignin reacted with epichlorhydrin, tetrabutylammonium bromide, NaOH and water in a reactor at 55-80 °C.

31. A fiber-reinforced plastic comprising the lignin-based epoxy resin of claim 30.