Low viscosity BIO-based wood adhesive for engineered wood

Abstract

A bio-based wood adhesive composition has 40-70% protein, 20-40% carbohydrates, and a viscosity of 10-100 PaS (at 10 / S shear rate) at 20-60% solid level. The composition comprises (i) a carbohydrate rich dry strength component (60-90% dry basis); (ii) a protein rich wet strength component (10-40% dry basis); (iii) optional additives, e.g., crosslinking agents, pH modifiers, rheology modifiers, antimicrobial agents, and fillers (1-30% dry basis); and (iv) water (40-80% wet basis). Synergistic adhesive compositions of the present invention comprise dry-strength and wet-strength components to achieve good water resistance, reduce the level of crosslinking agent, high bio-based content, high solid content, homogeneity and spreadability. The components in the adhesive form a strong network after application on a wood surface, followed by compression and heating. The adhesive can be used in a number of engineered wood panels such as plywood, particle board, MDF, HDF, OSB, etc.

Description

[0001] LOW VISCOSITY BIO-BASED WOOD ADHESIVE FOR ENGINEERED WOOD FIELD OF THE INVENTION This invention relates to a bio-based wood adhesive. BACKGROUND OF THE INVENTION Wood adhesives are used in engineered wood products (EWP) such as plywood, particle board (PB), medium density fiberboard (MDF), oriented strand board (OSB), etc. EWP are more prevalent than solid wood due to several advantages, including processibility, mechanical and thermal performance, sustainability, and lower cost. Adhesives bind wood fibers, veneers, strands, etc. to form engineered wood products. See e.g., An overview of bio- adhesives for engineered wood products, C. Kumar et al., International Journal of Adhesion and Adhesives, 118 (2022), 103187. Synthetic thermosetting adhesives are widely used in EWP. Such synthetic thermosetting adhesives include urea-formaldehyde (UF), phenol-formaldehyde (PF), polymeric diphenylmethane diisocyanate (pMDI) adhesives. UF, PF, and pMDI are petroleum-derived and can release toxic vapor into the air during and after production. Regulatory organizations such as the U.S. Environmental Protection Agency (EPA) and European Chemicals Agency (ECHA) have set strict formaldehyde emission limits on EWP. Bio-based wood adhesives, such as soy protein based products, are safer and more sustainable for consumers and the environment. Conventional bio-based wood adhesives have undesirable characteristics such as high viscosity, low solid content, high level of crosslinking agent, and / or poor water resistance. Conventional bio-based wood adhesives are also more costly than typical synthetic adhesive compositions, such as urea-formaldehyde based adhesive resin systems. There is a need for high performance bio-based adhesives with good adhesive strength, lower level of crosslinking agent, good water resistance, and good processibility. It would be beneficial to have bio-based products and processes that do not have the disadvantages of conventional products and processes. BRIEF SUMMARY OF THE INVENTION The present disclosure provides advantages over conventional products and methods. In an aspect, a bio-based blend adhesive composition comprises 40-70% protein (dry basis), 20-40% carbohydrates (dry basis), and a viscosity of 10-100 PaS (at 10 / S shear rate) at 25- 60% solid level or loading. In an aspect, the bio-based adhesive composition comprises a mixture of a carbohydrate-rich dry-strength component (60-90% inclusion level on dry basis), a protein-rich wet-strength component (10-40% inclusion level on dry basis). In an aspect, the bio-based adhesive composition may further comprise optional additives (0-30% dry basis) and water. Dry basis % is defined herein as the mass percentage of each component, excluding water in the calculation. In an aspect, water may be mixed with other components to form an adhesive composition with 25-60% total solids. In an aspect, the composition has 25-50% total solids. In an aspect, the composition has 28-40% total solids. In an aspect, the carbohydrate-rich dry-strength component has 30-50% carbohydrate and 30-60% protein. In an aspect, the protein-rich wet-strength component has 60-98% protein and <30% carbohydrates. In an aspect, optional additives are selected from the group consisting of a crosslinking agent, a surfactant, an emulsifier, a defoamer, a plasticizer, a rheology modifier, an antimicrobial agent, a colorant, a pH adjustment agent, an adhesion promoter, a film former, a filler, etc., and combinations thereof. In an aspect, the components of the bio-based adhesive composition form a strong network after application on a wood surface, followed by compression and heating. In an aspect, the bio-based adhesive composition can be used for engineered wood products, such as plywood, particle board, medium density fiberboard (MDF), high density fiberboard (HDF), oriented strand board (OSB), etc. In an aspect, the bio-based adhesive compositions disclosed herein are predominately bio-based (bio-based components are greater than 60% dry basis, e.g., greater than 75% dry basis), low in formaldehyde emission, easy to process, low in viscosity with relatively high solid (greater than 20%, e.g., greater than or equal to 25%) and high protein (50-70% dry basis) content, with good cohesive and adhesive strength in dry and wet conditions. In an aspect, the bio-based adhesive composition has good water resistance. In another aspect, the bio-based adhesive composition comprises lower levels of crosslinking agent as compared to other bio-based adhesives. In an aspect, the protein-rich component of bio-based adhesive composition may comprise a non-food grade protein, and thus not impact food supply. In a further aspect, a bio-based adhesive blend composition comprises a first protein and a second protein, wherein the bio-based adhesive blend composition comprises 40-70% protein (dry basis), 20-40% carbohydrates (dry basis), and a viscosity of 10-100 PaS (at 10 / S shear rate) at 25-60% solid level. The first protein may be selected from the group consisting of defatted soy flour, toasted soy flour, ground soy flake, soybean meal, soy flour co- products, and mixtures thereof, and the second protein may be selected from the group consisting of soy protein isolate, soy protein concentrate, soy protein flush coproducts, wheat gluten, pea protein, zein, albumin, and combinations thereof. In a further aspect, a bio-based adhesive formulation in the form of a slurry, comprises a protein component and 0-15% of a cross-linking agent. The bio-based adhesive formulation has a wet strength of at least 3 MPa as determined by ASTM-D7998-19, comprises 40-70% protein (dry basis), a solids level of 25-40%, and a viscosity of 50-120 PaS. In a further aspect, the protein component comprises soy flour and a soy protein concentrate, soy protein isolate, or a combination thereof. The cross-linking agent comprises PAE. These and other aspects, embodiments, and associated advantages will become apparent from the following Detailed Description. BRIEF DESCRIPTION OF THE DRAWINGS FIG.1 is a chart showing the components and their functions in a bio-based wood adhesive formulation in accordance with aspects of the disclosure. FIG.2 depicts a three-layer embodiment in accordance with aspects of the disclosure. FIG.3 is a graph of viscosity versus solid % dispersion of seven (7) representative samples in accordance with aspects of the disclosure. FIG.4 is a graph of FTIR absorbance units and wave number of soy protein materials with different amounts of crosslinker in accordance with aspects of the disclosure. FIG.5 is a graph showing crosslinking reaction with soy protein materials in accordance with aspects of the disclosure. FIG.6 is a graph of ABES wet strength of six (6) samples with 0% and 5% PAE as a crosslinking agent. FIG.7 is a graph of ABES wet strength of seven (7) examples with 10% PAE as a crosslinking agent. FIG.8 is a graph of ABES wet strength of three (3) examples with 5%, 10%, and 20% PAE as a crosslinking agent. FIG.9 is a graph of ABES wet strength of three (3) examples with 5%, 10%, and 20% PAE as a crosslinking agent, as compared with soy flour (Example 1) with 10% PAE as a crosslinking agent. FIG.10 is a graph of plywood (D906) wet strength (closed) of five (5) examples with 10% PAE as a crosslinking agent. FIG.11 is a graph of plywood (D906) wet strength (closed) of three (3) examples with 5%, 10%, and 15% PAE as a crosslinking agent. FIG.12 is a graph showing maximum total solid fraction (solid line) and water resistance (dashed line) of blends of varying amount of a wet-strength component in accordance with aspects of the disclosure. DETAILED DESCRIPTION In an aspect, an adhesive composition comprises soy co-products, which are not food grade, and thus, do not impact food supply. The high solid and protein content in the adhesive formula minimizes the negative impact of carbohydrate components. A bio-based wood adhesive composition has 40-70% protein and a viscosity of 10-100 PaS (at 10 / S shear rate or less than 100 PaS, with Brookfield spindle -7 at 20 revolutions per minute (rpm)) at 25-60% solid level. In an embodiment, the solid level is about 25-50% solid level. In an embodiment, the solid level is 28-40% solid level. In an aspect, the composition comprises (i) a carbohydrate rich dry strength component (60-90% dry basis); (ii) a protein rich wet strength component (10-40% dry basis); (iii) optional additives, e.g., crosslinking agents, pH modifiers, rheology modifiers, antimicrobial agents, film formers, and fillers (0-30% dry basis); and (iv) water (40-75% inclusion level on wet basis). The dry-strength and wet- strength components are blended to achieve synergistic performance of water resistance, high solid content, homogeneity, lower level of crosslinking agent, and spreadability. The components in the adhesive composition form a strong network after application on a wood surface, followed by compression and heating. The adhesive composition can be used in a number of engineered wood panels such as plywood, particle board, MDF, HDF, OSB, etc. The adhesive is predominantly (>75% dry basis) bio-based, comprising low levels of crosslinking agent, low in formaldehyde emission, easy to process, low in viscosity with relatively high solid and high protein content, with good cohesive and adhesive strength. The adhesive has good moisture resistance, with or without a crosslinking agent. Materials: wood adhesive composition The following is a general description of compositions and processes in accordance with aspects of the disclosure. Compositions in accordance with the disclosure comprise wood adhesive / binder formulations as disclosed in Table 1. The compositions may comprise two main components (a carbohydrate-rich dry-strength component and a protein-rich wet- strength component) and optional components. The carbohydrate-rich dry-strength component may comprise defatted soy flour, toasted soy flour, ground soy flake, soybean meal, soy hulls, soy flour co-products, ingredients from soy processing side streams, pea flour, cottonseed flour, corn germ meal, non-food grade proteinaceous materials, and mixtures thereof etc., which have 30-50% carbohydrates and 30-60% protein. The protein- rich wet-strength component may comprise soy protein isolate, soy protein concentrate, soy protein coproducts, etc., which have 60-98% protein and <30% carbohydrates. The protein in the wet-strength component can be un-hydrolyzed soy proteins to impart water resistance. The optional components may comprise a crosslinker, surfactant, emulsifier, defoamer, plasticizer, rheology modifier, antimicrobial agents, colorant, pH adjustment agents, adhesion promoter, film former, filler, etc. Table 1. Components, functions, and mass fractions of wood adhesive formulations. Components % (dry and function Composition basis in Examples adhesive)*- n, s, n; c e, s, s, e m s, n , , e Components % (dry and function Composition basis in Examples adhesive)*s, ;* All solids are dissolved or dispersed in water to form a homogeneous and spreadable formulation, with 25-60% solids. FIG.1 is a graph showing the components and their functions in a bio-based wood adhesive formulation in accordance with aspects of the disclosure. In FIG.1, bio-based wood adhesive formulation 10 comprises dry ingredients 12 and water 14. Dry ingredients 12 are 25-60% wet basis in bio-based wood adhesive formulation 10, and water 14 is 40-75% wet basis in bio-based wood adhesive formulation 10. In FIG.1, dry ingredients 12 comprises dry-strength component 16 and wet-strength component 18. Dry-strength component 16 is 60-90% dry basis and wet-strength component 18 is 10-40% dry basis. As shown in FIG.1, dry ingredients 12 may also comprise optional crosslinker component 20, optional functional additive component 22, and / or optional filler / film former component 24. Optional components 20, 22, and 24 may be collectively present in dry ingredients 12 in an amount of 0-30% dry basis. Process: Preparation procedure of wood adhesives, 3-layer plywood samples, and compressed wood samples. Adhesive formulations in accordance with aspects of the disclosure can be prepared by the following steps. (i) Weigh solid ingredients, and premix uniformly. (ii) Dissolve liquid ingredients in water to form an aqueous mixture. (iii) Blend solid premix with the aqueous mixture uniformly by a mixing device such as a paddle mixer, a slurry mixer, a high shear homogenizer, etc. (iv) Optionally, add a curing / crosslinking package in the formulation to improve water resistance of the engineered wood panel. (v) Optionally, grind the solids to reduce the particle size and improve uniformity. (vi) Optionally, heat the formulation to reduce viscosity and promote crosslinking reaction. (vii) Optionally, the mixture is processed with a high speed homogenizer to form a uniform paste. (viii) Optionally, the wet formulation is freeze dried followed by grinding to form a solid adhesive powder material, which is a one-part homogeneous product with extended shelf life. (ix) Optionally, the wet formulation is spray dried followed by grinding to form a solid adhesive powder material, which is a one-part homogeneous product with extended shelf life. For adhesive formulations including a PAE crosslinker, the percentage of total solids is determined by the PAE / soy ratio and spreadability of the adhesive formulation. The PAE / soy ratio (typically 0-20%) is defined as parts of PAE per 100 parts of soy material on a solids basis. If the viscosity is too low, the adhesive formulation may runoff or there may be bond starvation of the adhesive formulation. If the viscosity is too high, the adhesive formulation may restrict the transfer, application, and / or wetting of the adhesive formulation on the wood surface. A target viscosity range of 50-120 PaS with a Brookfield spindle 7 at 20 rpm is desired for the adhesive formulation. The percentage of total solids in the soy based adhesive formulation for 2-layer ABES wet strength (determined by ASTM D7998-19 method) and 3-layer plywood wet strength (determined by ASTM D906 method) tests are 25- 40%. The adhesive performance is not sensitive to the solid percentage if the formulation’s viscosity is in the appropriate range. The polyamidoamine-epichlorohydrin (PAE) crosslinker has 20% solids according to CA1920 by Solenis, LLC. The adhesive formulations also include 0.5 part (per 100 parts of soy) of a rheology modifier (such as sodium metabisulfide, available from INEOS) and 0.3 part (per 100 parts of soy) of a defoamer (such as Advantage 1529 available from Solenis, LLC), and 0-0.5 part of sodium hydroxide to adjust the pH of the adhesive composition to about 6.5. Engineered wood samples in accordance with the disclosure may be prepared by the following steps. Plywood product: (i) Condition wood veneers for at least 24 hours at prescribed condition (e.g., 20-30 ^C and 40-60% relative humidity). (ii) Coat veneers with prescribed amount of wood adhesive (10-100 g / m2solid basis of each interface) between layers; the adhesive should have an apparent viscosity of 10-100 PaS (at 10 / s shear rate) when being coated onto the plywood. (iii) Stack odd number (3, 5, 7, etc.) of veneers with the wood grains perpendicular to the adjacent layers. The wood grains of the two outmost layers are parallel to the long axis. Each interface is coated with prescribed amount of adhesive before stacking. (iv) Cold press the plywood layers at prescribed pressure (50-300 psi) and duration (1-20 minutes) at ambient temperature. (v) Hot press the plywood layers at prescribed pressure (50-300 psi), temperature (110 -180 ^C), and duration (1-20 minutes). (vi) Cool off the product. (vii) Trim the edges of the product. (viii) Store the product in temperature and humidity controlled environment. Compressed wood product: (i) Mix wood particles uniformly with the adhesive / binder at prescribed ratio (adhesive / binder is 1-25% on dry basis, preferably 5-25% on dry basis). The adhesive / binder may be heated to enhance flowability and mixing with wood particles. (ii) Form a thick mat of fiber + adhesive blend. (iii) Press the mat for prescribed pressure, temperature, and duration. (iv) Cool off, sand, and cut the mat to desirable sizes. (v) Store the product in temperature and humidity-controlled environment. Plywood product tests can be done as follows. Plywood samples (3 ply) were prepared for selected formulations in order to test the shear strength via the ASTM D906 method and for water resistance via the 3 cycle soak test, HPVA HP-1, with a customized 10 point grading system. The panels were made using 1 / 7 inch poplar veneers, 12 inch by 12 inch, and standardized with respect to grain direction and lathe check orientation. The upper veneer in each panel were placed with grain vertical and lathe checks down. The middle veneer were placed with vertical grain matching the upper veneer and lathe checks up to the lower bond line. Methods of testing wood adhesive formulations and ingredients: Moisture (Loss on drying): heat sample to 120 ^C and record weight loss%. Bio-based adhesive / binder has moisture content of 40-75%. Solid content is 25-60%. Protein: Kjeldahl method (digestion by acid, distillation, and titration). (Reference: Kjeldahl, J. (1883) "Neue Methode zur Bestimmung des Stickstoffs in organischen Körpern" (New method for the determination of nitrogen in organic substances), Zeitschrift für analytische Chemie, 22 (1) : 366-383.) Viscosity and thixotropic index: Viscosity profile is measured by an AR2000 rheometer (TA instruments) with a concentric cylinder geometry. A shear rate sweep is performed from 0.05 to 500 S. All measurements are made in duplicate. Thixotropic index is defined by the ratio of viscosities at 1 / S and 10 / S shear rates. Brookfield viscosity: for adhesive formulations with PAE crosslinker, viscosity was measured with a Brookfield DV-E model rheometer using spindle 7 at 20 revolutions per minute (rpm)) with practical (25-60%) solid loading level. The wet formula is rapidly hand mixed for 30 seconds at room temperature, pause for 5 seconds, then measured with spindle 7 at 20 rpm. Particle size distribution analysis (for dry powders, freeze dried powders or aqueous dispersions): The dry powder or slurry may be analyzed by a Malvern 3000 instrument for particle size distribution using laser diffraction technique. Particle size can be reduced if the material is milled or processed with a Fitzmill, hammer mill, high pressure homogenizer, etc. Water resistance evaluation of dried adhesive: The adhesive formulation is uniformly applied onto a smooth metal surface by a bar shaped film applicator of 25-150 micron gap. The wet film, 5 cm x 5 cm in size, is air dried or oven dried at prescribed temperatures (50 - 150 ^C) and duration (1 – 24 hrs). About 0.1g of dried film is placed in 50g of deionized water, with constant stirring at 300 rpm. The disintegration of the film and turbidity of the solution is observed and recorded for 24 hours. Water resistant films remain intact, and solutions remain transparent over time. If the film disintegrates within one hour of stirring, the adhesive’s water resistance is rated “poor”; if the film is intact and solution remains transparent after 4 hours of stirring, the adhesive’s water resistance is rated “strong”. The drying temperature (50 to 150 ^C) and duration (1 – 24 hrs) can be selected to differentiate the water resistance of dried films. This test method was used to qualitatively evaluate water resistance of examples without PAE crosslinker. Overall water holding capacity (WHC), insoluble %, and water holding capacity (WHC) of insolubles: 1 g of solid may be dispersed in 19 g of deionized water in a 50 ml centrifuge tube. Shake the dispersion for 3 hours, followed by centrifugation for 20 minutes at 5000 rpm. Excess water was removed. The remaining wet insoluble portion was weighed, followed by 24 hour drying at 100 ^C. The final weight of the dried powder is defined as the insoluble portion. WHC is defined as the difference between the wet insoluble portion and the dried portion. Overall WHC is the ratio of held water (g) to initial solid mass (g); WHC of Insoluble is the ratio of held water (g) to the insoluble solid mass (g). ATR-FTIR analysis (for crosslinked samples): To illustrate the crosslinking reaction of soy protein-based formulations, PAE (polyamidoamine epichlorohydrin) resin (10-40% solid) was mixed with soy ingredients and water to form a homogeneous slurry. The slurry is transferred into an aluminum pan, and cured at 150 ^C for 1 hour to form a film of 0.1-0.5mm thickness. The film was analyzed by ATR-FTIR (BRUKER® Tensor model) instrument, with an attenuated total reflectance (ATR) accessory (a single reflection diamond crystal from 400 to 4000 cm-1 with 4 resolution over 32 scans. Methods of preparing and testing engineered wood panel FIG.2 depicts a side view of a three-layer wood embodiment in accordance with aspects of the disclosure. As shown in FIG.2, three-layer wood panel 200, comprises middle wood layer 202, first exterior wood layer 204, and second exterior wood layer 206. Middle wood layer 202 comprises front side 208 and rear side 210. A first film of an adhesive composition in accordance with aspects of the disclosure is located at interface 212 between front side 208 of middle wood layer 202 and first exterior wood layer 204. A second film of adhesive composition in accordance with aspects of the disclosure is also located at interface 214 between rear side 210 of middle wood layer 202 and second exterior wood layer 206. First film and second film have the same adhesive composition. Plywood shear strength: The method is similar to the procedure described by ASTM D906-20 “Standard Test Method for Strength Properties of Adhesives in Plywood Type Construction in Shear by Tension Loading”, with minor modifications as following. Plywood sample preparation: Three-layer plywood samples may be prepared by applying adhesives onto a wood surface area of 25.4 mm (width) x 76.2 mm (length) x 1.6mm (thickness) with a brush or spatula. The wood veneer was purchased from The Wood & Shop Inc. Alternatively, tongue depressors of 6 inch in length (Puritan Medical Products, Maine, USA) were cut in half to form 18 mm (width) x 75 mm (length) x 1.6 mm (thickness) pieces. The pieces with the grains parallel to the long axis were used as the outer layers; pieces with grains perpendicular to the long axis were used as the middle layer. Application of adhesives. About 20g of wet adhesive formulation (about 20-40% total solids) were applied to the lower bond line with a roller for full coverage. The middle and lower veneers were stacked aside with no pressure applied. About 20g of adhesive formulation is applied to the upper veneer with a roller for full coverage. The upper veneer is added to the panel stack without pressure. After a five minute stand time without pressure, the panels were cold pressed at 0.69 MPa for 5 minutes, follow by hot pressing (0.83 MPa and 120°C) for five minutes to ensure 120 second above 100°C is achieved. Panels were cooled and conditioned at 21°C and 50% relative humidity for a minimum of two days. The surface area of the plywood was 929 square centimeters. About 22 mg of wet adhesive is applied onto 1 square centimeter of wood surface. Plywood shear strength. The produced plywood specimens were tested by the procedure described by ASTM D906-20 “Standard Test Method for Strength Properties of Adhesives in Plywood Type Construction in Shear by Tension Loading.” For the wet strength test, 18 plywood specimens were immersed in a 20°C water bath for 24 hours, followed by drying for 48 hours at room temperature. The lathe checks of 9 plywood specimens were pulled closed and the other 9 plywood specimens were pulled open. The average peak force values in Newton of “lathe check closed” specimens were reported as the wet strength of the adhesive. The area of the bond surface was 2.54 cm x 2.54 cm. The middle wood layer may also be coated on both sides before bonding with the two exterior wood layers without coating. The two exterior layers have the wood grain parallel to the long axis, which is the pull direction of subsequent shear test. For soy based adhesive samples, the coating dosage is approximately 6 mg / cm2regardless of the solid content. The three-layer samples are pressed at room temperature for 5 minutes at 100-200 psi, by a hydraulic press (Model C, Carver Inc, USA), followed by 10 minutes at 120 ^C and 100-200 psi (Model 3851, Carver Inc, USA). If the interface has excess coating, the first pressing step typically squeezes out the excess adhesive. After hot-pressed samples are cooled to room temperature, samples are conditioned for at least 48 hours at 23 ^C and 50% relative humidity. As shown in FIG.2, notches 216, 218 may be cut, e.g., through one exterior layer and the middle wood layer, and not extend into the other exterior wood layer, to perform a shear test, e.g., according to ASTM D906-20. Shear test: An adhesion shear test may be conducted with a TA-XT-Plus analyzer with a modified T-96A grip. The setup is similar to an Instron® tester. Sample is pulled apart at 0.1 mm / S. The maximum strength at break is recorded. Shear strength is calculated as the maximum force divided by adhesive area. At least 3 replicate samples are tested and averaged for each adhesive formula. Plywood moisture resistance: Moisture resistance may be evaluated by soaking the plywood samples in room temperature or boiling water for various duration, such as room temperature tap water for 1-24 hours or boiling water for 1-4 hours. Shear strength test is performed on wet samples or fume-hood 24-hour-dired samples, using ASTM D906-20 or similar test methods. ABES cohesive strength: ASTM D7998-19 “Standard Test Method for Measuring the Effect of Temperature on the Cohesive Strength Development of Adhesives using Lap Shear Bonds under Tensile Loading”. The instrument is named Automated Bond Evaluation System (ABES) manufactured by Adhesive Evaluation Systems, Inc. The bond surface area was 1square centimeter (0.5 cm x 2 cm). About 5 mg of adhesive is applied to the bond surface, followed by a 2 minute pressing at 0.92 MPa and 120°C. Wet shear strength values in Newton were based on a 10 sample average after 4 hours soaking and at 22°C, and pulling the samples until failure. Results: examples and performance data. Soy flour, toasted soy flour, soy protein concentrate, soy protein isolate ingredients and coproducts are commercially available materials. PAE (polyamidoamine epichlorohydrin) resin is a commercial product with 12.5% - 40% solids. Protein containing soy based ingredients can be dispersed in water to form a slurry. The solid content of these ingredients should be sufficient to form a viscous dispersion. These viscous dispersions are typically shear thinning. Lower viscosity at high shear rate is beneficial for spreading adhesive onto wood surface. High solid level is preferred to minimize amount of water in the formula. To determine the optimal solids level of soy ingredients, slurries of at least 10% solids were prepared. The solid level is increased gradually until the formula is too dry to mix uniformly. For each formula with uniform texture, viscosity values at 10 / s shear rate are measured by AR2000 rheometer (by TA Instrument) using concentric cylinder setup. FIG.3 is a graph of viscosity (PaS) at 10 / second shear rate for seven representative ingredients at varying solid % in aqueous slurry. The seven representative ingredients shown in FIG.3 are: (i) Example 11, 300; (ii) Example 6, 302; (iii) inventive blend Example 29, 304, (iv) inventive blend Example 24, 306, (v) Example 1, 308; (vi) Example 2, 310; and (vii) Example 9, 312. In an embodiment, <100 PaS viscosity at 10 / S shear rate is recommended for adhesive performance evaluation in plywood samples. Example 11, 300, has the highest viscosity at 10 / second shear rate, followed by Example 6, 302, inventive Example 29, 304, inventive Example 25, 306, Example 1, 308, inventive Example 2, 310, and Example 9, 312. The 30 PaS dashed line intersects with each curve, indicating the solid% of each dispersion are approximately 17%, 18%, 27%, 28%, 29%, 32%, 39% at this viscosity. The inventive blends have the benefits of high solid % and strong water resistance. For solid %, the two inventive blends (27% and 28%) are similar to soy flour (29%); for water resistance, the two inventive blends are similar to soy protein isolate unhydrolyzed 1 and soy protein concentrate, which are superior to soy flour. Soy protein coproducts have similar rheological property to the soy protein isolates or concentrates during the manufacturing process. Soy flour coproducts have similar rheological properties to the soy flour during the manufacturing process. Those skilled in the art having the benefit of the present disclosure will recognize that the rheological properties of soy protein coproducts can be designed to match viscosity profiles of soy protein isolates or concentrates, or viscosity profiles anywhere in between. The ingredients, solid %, protein %, viscosity (PaS) at 10 / S, and thixotropic index, and water resistance of Examples 1-17 are listed in Table 2. The solid% is chosen at the highest level that the dispersion is still uniform and spreadable. Table 2. Ingredients, % solids, % protein, and viscosities at 10 / S, thixotropic index, and water resistance of Examples 1-17. % Ingredient Protein % Total Viscosity Thi r Carbo xotropic Water (d hydrate Solids (PaS) Index resistance Function h nt h nt h nt h nt h nt h nt h nt h nt h nt h nt h nt h nt h nt Soy Protein Example Isolate, Wet 14 unhydrolyzed 90-95 <5 20 30 5.2 strong Strength C m nent h nt h nt h nt p , g The ingredients, solid %, protein %, and viscosity (PaS) at 1 / S and 10 / S and thixotropic index, and water resistance of Examples 18-22 are listed in Table 3. Examples 18-22 are blends of dry-strength and wet-strength components that resulted in poor water resistance. The wet-strength component in Examples 18-20 is a hydrolyzed soy protein isolate coproduct. The dried films of these three examples all have poor water resistance despite high level of protein%. The dry strength component in Examples 21 and 22 are hydrolyzed soy protein isolate, which itself has poor water resistance even after crosslinking. Despite the strong water resistance of the wet strength component (SPI unhydrolyzed 1) in Examples 21 and 22, the blend has poor water resistance after drying. Hydrolyzed protein should not be used as a dry-strength or wet-strength component despite its low viscosity at relatively high solid loading.

[0002] Table 3. Ingredients, % solids, % protein, and viscosities at 1 / S and 10 / S, thixotropic index, and water resistance of Examples 18-22. % % Total Dry W t St th P t i C b h d Solids Viscosit Thi t i W t e *Wet basis includes all components, including water The fractions of dry-strength to wet-strength components should be balanced for high solid % and low viscosity. The dry strength component should be the majority portion of the total solid due to its lower viscosity than the wet strength component. The wet strength component should be no less than 10% of total solid to impart significant water resistance. Appropriate dry-strength components may comprise soy flour, defatted soy flour, toasted soy flour, soy flour coproducts, etc. which have 30-50% carbohydrate and 30-60% protein. Wet-strength components should have >60% unhydrolyzed protein and <30% carbohydrates and be at greater than 10% dry basis. Wet-strength components may comprise soy protein isolate and / or soy protein concentrate. Examples 23-35 listed in Table 4 all have strong water resistance. Table 4 is a list of high performance blends of dry-strength and wet-strength components: % protein (dry basis), % carbohydrate (dry basis), total solid (wet basis) in the formulation, viscosities at 10 / S shear rate, thixotropic index, and water resistance of dry films. In an aspect, the adhesive composition has a water holding capacity (WHC) of 150-400%, preferably 200-400%, and more preferably 200-300%, with an insoluble portion of 35-60%, preferably 40- 50%, at neutral pH of 6.5-7.5. Table 4. Ingredients, % solids, % protein, and viscosities at 10 / S, thixotropic index, and water resistance of Examples 23-35. % Protein Total es Dry Strength Wet Streng % Viscosity Exampl th Solids% Thixotropic Water Component Component (Dry Carbohydrate (Wet (PaS) Index Resistance Figure 6 depicts the cohesive strength of 6 examples with 0% and 5% PAE crosslinker, using ABES (Automated Bonding Evaluation System) instrument with ASTM D 7998-19 (Cohesive Strength Development of Wood Adhesives) method. It is a useful tool to evaluate the adhesive’s cohesive performance of a two layer sample. The wet strength values are in line with the qualitative water resistance results (of film examples without PAE crosslinking agent) in Tables 2 and 3. The first 3 examples are soy flour, toasted soy flour, and soy flour coproduct (non-food grade). The 4th example (Example 9) is hydrolyzed soy protein isolate and has minimal wet strength even with 5% PAE crosslinker. For the last two examples, the 80% hydrolyzed protein (dry basis) should not contribute to wet strength – the 20% soy coproduct (Example 20) contributed to 115N wet strength, and 20% soy protein isolate unhydrolyzed 1 contributed to 197N wet strength (Example 21). 20% inclusion of protein-rich ingredient resulted in similar wet strength to soy flour based adhesive formulation. Hydrolyzed soy protein imparts poor wet strength without or with PAE crosslinker (Reference: C. Frihart et al., Proceedings of the 59th International Convention of Society of Wood Science and Technology, 2016) . A high performance adhesive composition should have high level of unhydrolyzed protein to act as a wet-strength component, especially in the presence of crosslinker. The effective range of inclusion level is illustrated and optimized as described herein to result in a good balance of these characteristics: good wet strength, high protein, high solid, high water resistance, high wet strength, with potentially less PAE. Figure 7 depicts the ABES wet strength performance of soy flour (Example 1) and 6 inventive examples with wet strength component between 10% and 40%. All of these examples have 10% PAE crosslinking agent. Example 1 is a standard soy flour with 10% PAE crosslinking agent. The dry strength component of the 6 inventive examples is a standard soy flour (Example 1) of 70 PDI (protein dispersibility index), which is currently used as a main ingredient in plywood adhesive. All of the examples have 10% PAE crosslinker. In Examples 23, 24, and 25, soy flour was replaced partially by unhydrolyzed soy protein isolate 1. Much higher ABES wet strength values were achieved. The unhydrolyzed soy protein isolate is an effective wet strength component at 10-40% inclusion ratio. Similarly, Examples 28, 29, 30 have varying levels of soy protein concentrate 1 as the wet strength component, and achieved higher ABES wet strength than soy flour. The effective inclusion ratio is 10-40%. The total solid % of the 6 inventive examples are 30- 32%, with viscosities less than 100 PaS at 10 / S shear rate. Figure 8 depicts the ABES wet strength of 3 inventive formulas with 5, 10, and 20% PAE crosslinker. Examples 28 and 29 have soy protein concentrate 1 as the wet strength component. Example 35 is a representative tertiary mixture which has both soy protein isolate 1 and soy concentrate 1 as the wet-strength component. All 3 inventive blend examples achieved higher wet strength at all PAE dosages as compared to soy flour. Figure 9 depicts 3 inventive examples (Examples 28, 29, 35) achieving higher ABES wet strength as compared to Example 1 (soy flour), the soy flour based adhesive. The examples all have approximately 32% total solid. Partial replacement of soy flour with high wet strength ingredient significantly improves the wet strength performance as shown in ABES test. In addition to ABES test of bi-layer wood veneers, 3-layer plywood samples were also made with soy flour and inventive formulas with PAE crosslinker. They were tested by ASTM D906 method. Figure 10 shows that plywood samples with inventive examples (23, 25, 28, 29) outperforms soy flour at 10% PAE crosslinker. To meet the viscosity target of <100PaS and accommodate the inclusion of PAE crosslinker, the total solid content of Examples 1, 23.25. 28.29 are in the range of 30-37%. Figure 11 shows the two inventive formulas (Examples 25 and 29) outperforming soy flour (Example 1) at 5% and 10% PAE in plywood (ASTM-D906) wet strength (closed). This agrees with wet strength results of ABES (ASTM-D7998-19) test at 10% PAE shown in FIG.7. These adhesive formulas were further tested by 3-cycle soak test. Table 5 shows that 3-cycle-soak test performance of Examples 25 and 29 are better than Example 1, especially at 5% and 10% PAE levels. Lower PAE crosslinking agent can be used in the inventive formulas (Examples 25 and 29) to pass 3-cycle-soak test. Table 5: 3-Cycle-soak test results of Examples 1, 25, 29 with 5%, 10%, and 15% PAE crosslinker. PAE level Total 3-Cycle Soak Examples (%) Solid% Test Procedures for preparing Examples Example 1 To a beaker with 67.5 grams of deionized water, 32.5 grams of soy flour powder was added and dispersed thoroughly with a Silverson L5M-A Laboratory Mixer. The soy flour (ADM Bakers Soy Flour, available from Archer-Daniels-Midland Company, Decatur, IL) powder has 70 PDI (PDI = Protein Dispersibility Index represents the solubility of soybean protein in water). About 35 grams of the dispersion was transferred to a concentric cylinder of an AR2000 rheometer (TA Instruments). A shear rate sweep is performed from 0.05 to 500 / s to obtain a viscosity profile. All measurements are made in duplicate. Viscosities at 1 / s and 10 / s were 221 and 47 PaS, with a thixotropic index of 4.7. Using a bar shaped film applicator, the 32.5% solid dispersion is coated onto a metal surface, and dried for 2 hours at 150 ˚C. The dried film is evaluated for water resistance. Examples 2-17 Examples 2-17 were prepared in a similar process by mixing the solids with water at prescribed solid% listed in table 2. The viscosities at 10 / S shear rates and thixotropic indexes were recorded. Water resistance of dried films were evaluated. The results of Examples 1-17 are listed in Table 2. Example 18 To a beaker with 60 grams of deionized water, 40 grams, on a dry basis, of the compositions described in Example 18 were added and dispersed thoroughly with a Silverson L5M-A Laboratory Mixer for 30 minutes. The resultant dispersion has 40% total solids, and 75% protein and 15% carbohydrate on a dry basis. About 35 grams of the dispersion was transferred to a concentric cylinder of an AR2000 rheometer (TA Instruments). A shear rate sweep is performed from 0.05 to 500 / S to obtain a viscosity profile. All measurements are made in duplicate. Viscosity at 10 / S was 54 PaS, with a thixotropic index of 9.4. Using a bar shaped film applicator, the 40% solid dispersion is coated onto a metal surface, and dried for 2 hours at 150 ˚C. The dried film is evaluated for water resistance. Example 19-22 Examples 19-22 were prepared in a similar process by mixing the solids with water to reach target solid %, protein%, and carbohydrate% listed in table 3. The viscosities at 10 / S shear rates and thixotropic indexes were recorded. Water resistance of dried films were evaluated. The results of Examples 18-22 are listed in Table 3. Example 23 To a beaker with 73 grams of deionized water, 27 grams (on a dry basis) of the compositions described in Example 23 were added and dispersed thoroughly with a Silverson L5M-A Laboratory Mixer for 30 minutes. The resultant dispersion had 27% total solids, and 75% protein and 15% carbohydrate on a dry basis. About 35 grams of the dispersion was transferred to a concentric cylinder of an AR2000 rheometer (TA Instruments). A shear rate sweep is performed from 0.05 to 500 / S to obtain a viscosity profile. All measurements are made in duplicate. Viscosity at 10 / S was 23 PaS, with a thixotropic index of 5.5. Using a bar shaped film applicator, the 27% solid dispersion is coated onto a metal surface, and dried for 2 hours at 150 ˚C. The dried film is evaluated for water resistance. Examples 24-35 Examples 24-35 were prepared in a similar process as Example 23 by mixing the solids with water to reach the target solid%, protein%, and carbohydrate% listed in table 4. The viscosities at 10 / S and thixotropic indexes were recorded. Water resistance of dried films were evaluated. The dry-strength and wet-strength components, protein %, carbohydrate%, total solid%, and film’s water resistance are listed in Table 4. ATR-FTIR analysis results (for crosslinked samples): Crosslinking reaction of soy protein (Example 3 – Soy Flour Coproduct and Example 9 – Soy Protein Isolate (SPI), Hydrolyzed 1) with PAE (polyamidoamine epichlorohydrin) is analyzed by ATR-FTIR technique. The soy protein is cured with 0.1 (at 1 hour at 150 degrees C, and at 2 hours at 150 degrees C), 0.2, 0.4, and 0.75 parts of PAE crosslinker on a dry solid basis. FIG.4 shows the 1730 cm-1peak intensity increases with the amount of PAE crosslinker. The following blends are shown FIG.4: (i) blend 400 is 1 part of Example 9 + 0.1 part of PAE crosslinker cured at 1 hour at 150 degrees C; (ii) blend 402 is 1 part of Example 9 + 0.1 part of PAE crosslinker cured at 2 hours at 150 degrees C); (iii) blend 404 is 1 part of Example 9 + 0.2 part of PAE crosslinker; (iv) blend 406 is 1 part of Example 9 + 0.4 part of PAE crosslinker; (v) blend 408 is 1 part of Example 9 + 0.75 part of PAE crosslinker; and (vi) blend 410 is 1 part of Example 3 + 0.75 of PAE crosslinker. All samples with soy protein exhibit 1730 cm-1absorption if sufficient PAE and crosslinking condition are present. FIG.5 shows the crosslinking reaction of the following materials cured with 0.75 parts PAE crosslinker on a dry solid basis for 1 hour at 150 degrees C, for both top and bottom surfaces of the cured films: material 502 (top surface), 504 (bottom surface), i.e., Soy Protein Isolate Coproduct 1 (Example 4, 35% protein coproduct); material 506 (top surface), 508 (bottom surface), i.e., Soy Protein Isolate Coproduct 2 (Example 5, 90% protein coproduct); and material 510 (top surface), 512 (bottom surface), i.e., Soy Protein Isolate, Unhydrolyzed 1 (Example 11, 90% protein isolate). Those skilled in the art having the benefit of the present disclosure will recognize that a combination of multiple components can be varied for one of more characteristics. For example, a combination of components can be made in accordance with the present disclosure to provide for a characteristic selected from the group consisting of a particular rheology (such as a particular rheology for more efficient processing, adhesion (such as cohesive and adhesive strength), optimal protein content for crosslinking and water resistance, water absorption, high solid, low viscosity, low level of carbohydrates, and combinations thereof. Those skilled in the art having the benefit of the present disclosure will recognize that a particular blend of protein and carbohydrates for interlocking microstructure for water resistance and mechanical strength can be prepared at desired pH conditions. For example, a carbohydrate-rich dry-strength ingredient (defatted soy flour or toasted soy flour), when blended with a protein-rich wet-strength ingredient (hydrothermally processed and unhydrolyzed protein) at appropriate ratios, resulted in a high solid % dispersion with excellent water resistance. The ingredients absorb water, control the wicking by wood surfaces, and minimize moisture penetration into the interface. Those skilled in the art having the benefit of the present disclosure will recognize that a protein rich wet-strength ingredient when included in the formula at 10-40% on dry basis, such as a unhydrolyzed soy protein isolate, provides a high performance and low cost adhesive component that reduces protein isolate requirement in a blend of protein and carbohydrate, and that after crosslinking, moisture resistance is improved. When adding a wet-strength component (such as soy protein isolate unhydrolyzed 1, with maximum solid loading of 15-17.5% by itself, with strong water resistance) to a dry- strength component (such as defatted soy flour, with maximum solid loading of 30-40% by itself, with poor water resistance) at various ratios, the water resistance improves, whereas the maximum solid loading decreases (35% ~15% in this case), as the fraction of wet-strength component increases. It was discovered that 10~40% of wet-strength component in the blends have satisfactory performance: >10% wet-strength component contributes to strong water resistance; <40% wet-strength component keeps the maximum solid% sufficiently high, which is beneficial for manufacturing of engineered wood panels. FIG.12 is a graph showing maximum total solid fraction (solid line) and water resistance (dashed line) of blends of varying amount of a wet-strength component in accordance with aspects of the disclosure. As shown in FIG.12, a small fraction of wet-strength component, as small as 10%, can significantly improve wet-strength of the blend without substantial decrease in maximum solid %. The high limit of wet-strength component is determined by the maximum solid% of the blend. The practical inclusion ratio may be determined by the physical properties (water holding capacity, dispersibility, particle size distribution, protein and carbohydrate levels, hydrophobicity, etc.) of the components, process conditions, and cost of the components. The present disclosure provides a commercially feasible solution to significantly improve wet strength with minimal decrease of solid %, using a small fraction of wet-strength component in the adhesive formulation, with lower levels of PAE crosslinker. Those skilled in the art having the benefit of the present disclosure will recognize that a blend of dry-strength and wet-strength components as disclosed herein provides advantages over conventional formulations, including but not limited to, lower cost versus synthetic and conventional bio-based adhesives, lower outgassing and lower delamination due to higher solid content and less water in adhesives, and / or potential reduction of crosslinking agents, which are more costly than other ingredients found in synthetic and conventional bio-based adhesives. Those skilled in the art having the benefit of the present disclosure will recognize that blends of plant-based ingredients, such as plant-based protein (e.g., from zein, wheat gluten, cottonseed flour, soy protein, pea protein, rice protein, and combinations thereof), plant-based carbohydrate(s) (e.g., insoluble and soluble carbohydrates, gums, and combinations thereof) that provide one or more characteristics including dry strength and wet strength functions, and one or more additives selected from the group consisting of crosslinkers, surfactant, emulsifier, defoamer, plasticizer, rheology modifier, antimicrobial agents, colorant, pH adjustment agents, adhesion promoter, film former, filler, etc., and combinations thereof, provide adhesive compositions having benefits over conventional formulations. In accordance with aspects of the disclosure, adhesive compositions comprise specific range of soy protein % and carbohydrate %, which are the result of mixing ratio of a carbohydrate-rich component(s) such as soy flour (with insoluble and soluble carbohydrates) and a protein-rich component (60-98% protein). The adhesive compositions disclosed here provide synergistic performance in that they provide compositions with high solid % (greater than 25%), high protein (greater than 40%), low viscosity (less than 100 PaS), strong adhesion and cohesion, and excellent water resistance. Benefits of the adhesive compositions disclosed herein include superior water resistance (demonstrated by soaking and delamination observation, high wet shear strength, high solid % (greater than 25%) – thereby minimizing outgassing, delamination, and press time in manufacture of engineered wood products (EWP); appropriate processing viscosity range for a consistent and spreadable paste. The adhesive compositions disclosed herein may comprise a blend of two ingredients, with the first ingredient 60-90% on dry basis and the second ingredient 10-40% on dry basis. The first ingredient is a dry-strength carbohydrate-rich component (such as soy flour) having 30-60% protein and 30-50% carbohydrates. The second ingredient is a wet-strength protein- rich component (such as soy protein isolate (SPI) or soy protein coproduct (SPC)) having 60- 98% in protein and less than 20% carbohydrates. In an aspect, the first and second ingredients are mixed at 1.5:1 to 9:1 ratios (i.e., 10% - 40% inclusion rate of the second ingredient) for a good balance of high protein functionality and spreadable viscosity. Those skilled in the art having the benefit of the present disclosure will recognize that one or more components such as rheology modifier(s), coloring agent(s), and / or antimicrobial agent(s), and combinations thereof, may be included in the adhesives disclosed herein. Although the foregoing description has presented a number of embodiments of the invention, those of ordinary skill in the relevant art will appreciate that various changes in the components, details, materials, and process parameters of the examples that have been herein described and illustrated in order to explain the nature of the invention may be made by those skilled in the art, and all such modifications will remain within the principle and scope of the invention as expressed herein in the appended claims. It will also be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications that are within the principle and scope of the invention, as defined by the claims.

Claims

WHAT IS CLAIMED IS:

1. A bio-based adhesive blend composition comprising: (i) 40-70% protein (dry basis), 20-40% carbohydrates (dry basis), and a viscosity of 10-100 PaS (at 10 / S shear rate) at 25-60% solid level.

2. A bio-based adhesive composition of claim 1, comprising: (i) a carbohydrate-rich dry-strength component (60-90% inclusion level on dry basis), and (ii) a protein-rich wet-strength component (10-40% inclusion level on dry basis).

3. A bio-based adhesive composition of claim 2, wherein the carbohydrate-rich dry- strength component has 30-50% carbohydrates and 30-60% protein on dry basis.

4. A bio-based adhesive composition of claim 2, whereas dry-strength component is dispersed in water to form a homogenous slurry of more than 30% solids.

5. A bio-based adhesive composition of claim 2, wherein the protein-rich wet-strength component has 60-98% protein and <30% carbohydrates on dry basis.

6. The bio-based adhesive composition of claim 2, further comprising water (40-75% inclusion level on wet basis).

7. A bio-based adhesive composition of claim 2, whereas the dry-strength and wet- strength components have 35-65% insolubles and overall water holding capacity of 150-400%.

8. A bio-based adhesive composition of claim 2, wherein the protein-rich wet-strength component is dispersed in water to form a homogenous slurry of more than 10% solids.

9. The bio-based adhesive composition of claim 2, wherein the carbohydrate-rich dry-strength component is selected from the group consisting of defatted soy flour, toasted soy flour, ground soy flake, soybean meal, soy hulls, soy flour co-products, ingredients from soyprocessing side streams, pea flour, cottonseed flour, corn germ meal, non-food grade proteinaceous materials, and mixtures thereof.

10. The bio-based adhesive composition of claim 2, wherein the protein-rich wet-strength component is selected from the group consisting of soy protein isolate, soy protein concentrate, soy protein flush coproducts, wheat gluten, pea protein, zein, albumin, and combinations thereof.

11. The bio-based adhesive composition of claim 2, wherein the wet-strength and dry-strength components are pre-mixed by a process selected from the group consisting of dry blending, spray-drying, and freeze-drying processes, and combinations thereof.

12. The bio-based adhesive composition of claim 8, wherein the carbohydrate-rich dry strength component is a defatted soy flour or toasted soy flour with particle size of US 100 mesh or smaller.

13. The bio-based adhesive composition of claim 9, wherein the protein-rich wet-strength component is a soy protein isolate or soy protein concentrate that went through hydrothermal process.

14. The bio-based adhesive composition of claim 9, wherein the protein-rich wet-strength component is a soy protein isolate or soy protein concentrate that are not hydrolyzed.

15. The bio-based adhesive composition of claim 9, wherein the protein-rich wet-strength component is a soy protein isolate or soy protein concentrate that have particle size that are smaller than US 100 mesh.

16. A bio-based adhesive composition of claim 10, whereas the mixture of dry-strength and wet-strength components have 30-60% insolubles and overall water holding capacity of 200-500%.

17. The bio-based adhesive composition of claim 2, further comprising a cross-linking agent (0-30% dry basis) selected from the group consisting of Ethylene diamine, carbodiimides, polyamidoamine epichlorohydrin, epoxides, glutaraldehyde, polyfunctional isocyanates, tannic acid, genipin, citric acid, phosphoric acid, transglutaminase, urea, sodium dodecyl sulfate, magnesium oxide, zinc oxide, alkali, etc., and combinations thereof.

18. The bio-based adhesive composition of claim 2, further comprising functional additives (0- 30% dry basis) selected from the group consisting of a surfactant, emulsifier, defoamer, plasticizer, rheology modifier, antimicrobial agents, colorant, pH adjustment agents, adhesion promoter, and combinations thereof.

19. The bio-based adhesive composition of claim 2, further comprising a film former and / or a filler (0-30% dry basis).

20. The bio-based adhesive composition of claim 18, wherein the functional additives are selected from the group consisting of polyethylene glycol, sorbitan esters, ethoxylated sorbitan esters, alky sulfates, alkyl ether sulfates, ethoxylated fatty alcohols, alkylphenol ethoxylates, silicone surfactants, quaternary ammonium compounds, amine oxides, dioctyl phthalate, diisononyl phthalate, dioctyl adipate, trioctyl trimellitate, epoxidized soybean oil, clay minerals, polyurethanes, polyethylene glycols, sodium metabisulfate, essential oils, plant extracts, isothiazolinones, organosulfur compounds, titanium dioxide, iron oxides, carbon black, citric acid, sulfuric acid, sodium hydroxide, ammonium hydroxide, phosphate salts, isocyanates, silane coupling agents, epoxies, maleic anhydride, polyamines, and combinations thereof.

21. The bio-based adhesive composition of claim 19, wherein the film former and filler are selected from the group consisting of acrylics, vinyl acrylics, vinyl acetate / ethylene, alkyds, polyurethanes, polyesters, melamine resins, epoxies, silanes, siloxanes, waxes, silica, clay, cellulosic materials, ground soy hull, pea fiber, dried distillers grains, cottonseed flour, and combinations thereof.

22. The bio-based adhesive composition of claim 2, wherein all solids are dissolved or dispersed in water to form a spreadable formulation with 25-60% solids.

23. An engineered wood panel comprising the bio-based adhesive of claim 2, a plywood layer, and a wood veneer layer, wherein the bio-based adhesive is between the plywood layer and the wood veneer layer.

24. A compressed wood product comprising the bio-based adhesive of claim 2 and wood particles.

25. An engineered wood panel comprising the bio-based adhesive of claim 2, where the bio- based adhesive is thermally treated and compressed to form a cured formulation.

26. A bio-based adhesive blend composition comprising: a first protein; and a second protein; wherein the bio-based adhesive blend composition comprises 40-70% protein (dry basis), 20-40% carbohydrates (dry basis), and a viscosity of 10-100 PaS (at 10 / S shear rate) at 25-60% solid level.

27. The bio-based adhesive blend composition of claim 26, wherein the first protein is selected from the group consisting of defatted soy flour, toasted soy flour, ground soy flake, soybean meal, soy flake co-products, and mixtures thereof.

28. The bio-based adhesive blend composition of claim 26 or claim 27, wherein the second protein is selected from the group consisting of soy protein isolate, soy protein concentrate, soy protein flush coproducts, protein processing side stream products, non-food grade protein ingredients, wheat gluten, pea protein, zein, albumin, and combinations thereof.

29. A bio-based adhesive formulation in the form of a slurry, comprising:a protein component; and 0-15% of a cross-linking agent; wherein the bio-based adhesive formulation has a wet strength of at least 3 MPa as determined by ASTM-D7998-19;. wherein the bio-based adhesive formulation comprises 40-70% protein (dry basis), a solids level of 25-40%, and a viscosity of 50-120 PaS.

30. The bio-based adhesive formulation of claim 29, wherein: the protein component comprises: soy flour; and a soy protein concentrate, soy protein isolate, or a combination thereof; and the cross-linking agent comprises PAE.

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