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US-12624171-B2 - Lignin-based phenolic adhesives, related compositions, and related methods

US12624171B2US 12624171 B2US12624171 B2US 12624171B2US-12624171-B2

Abstract

The disclosure relates to adhesive compositions, including non-crosslinked resins and crosslinked/cured adhesives joining substrates, as well as related methods for making the compositions and articles. Compared to a conventional phenol (P) and formaldehyde (F) resin, the disclosed methods and compositions use lignin (L) and higher aldehydes (A) as corresponding replacements to provide an analog to a conventional PF resin with biobased reactants. Due to the differing reactivity of the LA components compared to the PF components, the initial condensation reaction between ortho-reactive sites in the lignin and the aldehyde is controlled to prevent gelation of the aqueous reaction mixture while reacting substantially all of the LA reactants to provide a non-crosslinked resin reaction product. The resin reaction product can then be cured at high temperature/high pressure conditions to provide a crosslinked adhesive, for example joining two substrates.

Inventors

  • Mojgan Nejad
  • Sasha Bell
  • Mohsen Siahkamari

Assignees

  • BOARD OF TRUSTEES OF MICHIGAN STATE UNIVERSITY

Dates

Publication Date
20260512
Application Date
20210122

Claims (20)

  1. 1 . A method for forming an adhesive composition, the method comprising: providing an aqueous reaction mixture comprising water, a lignin comprising aromatic hydroxyl groups and ortho-reactive carbon atoms relative to the hydroxyl groups, a base catalyst to solubilize the lignin in the aqueous reaction mixture, and an aldehyde having at least 2 carbon atoms and having at least 2 aldehyde functional groups (—CHO), wherein: (i) the aldehyde is added to the aqueous reaction mixture in a controlled manner and in the presence of the base catalyst solubilizing the lignin, thereby beginning a condensation reaction between the lignin and the aldehyde, (ii) adding the aldehyde in the controlled manner to comprises adding the aldehyde batchwise in 2 or more batch additions or continuously over time, while maintaining the aldehyde concentration in the aqueous reaction mixture below a level that would induce gelation, and (iii) a molar ratio of lignin aromatic hydroxyl groups to aldehyde functional groups in the aqueous reaction mixture is in a range of 1:1.1 to 1:4; adding further base catalyst in a controlled manner to the aqueous reaction mixture, thereby catalyzing the condensation reaction between the lignin and the aldehyde while maintaining a viscosity of the aqueous reaction mixture below a gelation point of the aqueous reaction mixture, wherein: (i) a molar ratio of total aromatic hydroxyl groups originally present in the lignin to total aldehyde functional groups added to the aqueous reaction mixture is less than 1 during the condensation reaction, and (ii) adding the further base catalyst in the controlled manner to the aqueous reaction mixture comprises adding the further base catalyst batchwise in 2 or more batch additions or continuously over time to the reaction mixture, while maintaining the base catalyst concentration in the reaction mixture below a level that would induce gelation; continuing the condensation reaction between the lignin and the aldehyde to form a resin reaction product while maintaining the viscosity of aqueous reaction mixture below the gelation point of the aqueous reaction mixture until a completion point is reached, wherein, at the completion point, at least some unreacted ortho-reactive carbon atoms remain, at least some substituted methylol functional groups have been formed by the condensation reaction, and the resin reaction product is not crosslinked and has a gelation time measured at 25° C. in a range of 2 minutes to 6 minutes.
  2. 2 . The method of claim 1 , comprising forming the resin reaction product at a reaction temperature in a range from 40° C. to 95° C. while avoiding gelation and crosslinking.
  3. 3 . The method of claim 1 , wherein the lignin is derived from a biomass selected from the group consisting of hardwoods, softwoods, grasses, and combinations thereof.
  4. 4 . The method of claim 1 , wherein the lignin is isolated from an extraction process selected from the group consisting of Kraft extraction, soda extraction, organosolv extraction, enzymatic hydrolysis extraction, ionic liquid, extraction, sulfite extraction, and combinations thereof.
  5. 5 . The method of claim 1 , wherein the lignin has at least one of the following properties: a weight-average molecular weight of 2000 or less; a polydispersity of 2.0 or less; and at least 60% of the aromatic hydroxy groups have at least 1 ortho-reactive carbon relative to the hydroxy group.
  6. 6 . The method of claim 1 , wherein at least 60% of the aromatic hydroxy groups in the lignin have at least 1 ortho-reactive carbon relative to the hydroxy group.
  7. 7 . The method of claim 1 , wherein the aldehyde has 2 to 50 carbon atoms and has 2 to 4 aldehyde functional groups.
  8. 8 . The method of claim 1 , wherein the aldehyde comprises glyoxal.
  9. 9 . The method of claim 1 , wherein the aqueous reaction mixture is free from phenol and formaldehyde.
  10. 10 . The method of claim 1 , wherein the aqueous reaction mixture comprises formaldehyde.
  11. 11 . The method of claim 10 , wherein: 5% to 50% of the aldehyde functional groups in the aqueous reaction mixture are from the formaldehyde; and 50% to 95% of the aldehyde functional groups in the aqueous reaction mixture are from the aldehyde having at least 2 carbon atoms and having at least 2 aldehyde functional groups.
  12. 12 . The method of claim 11 , wherein the resin reaction product has an alkalinity value in a range of 2% to 3%.
  13. 13 . The method of claim 11 , wherein the resin reaction product has a gelation time measured at 25° C. in a range of 4 minutes to 6 minutes.
  14. 14 . The method of claim 10 , wherein: 20% to 60% of the aldehyde functional groups in the aqueous reaction mixture are from the formaldehyde; and 40% to 80% of the aldehyde functional groups in the aqueous reaction mixture are from the aldehyde having at least 2 carbon atoms and having at least 2 aldehyde functional groups.
  15. 15 . The method of claim 10 , 20% to 40% of the aldehyde functional groups in the aqueous reaction mixture are from the formaldehyde; and 60% to 80% of the aldehyde functional groups in the aqueous reaction mixture are from the aldehyde having at least 2 carbon atoms and having at least 2 aldehyde functional groups.
  16. 16 . The method of claim 15 , wherein the resin reaction product has a pH value in a range of 10 to 11.
  17. 17 . The method of claim 1 , further comprising: adding one or more adhesive components to the aqueous reaction mixture at or after the completion point, the adhesive components being selected from the group consisting of fillers, further catalyst, and further water; and continuing the condensation reaction between remaining unreacted ortho-reactive carbon atoms and the substituted methylol groups in the resin reaction product, thereby forming a crosslinked adhesive composition.
  18. 18 . The method of claim 17 , comprising continuing the condensation reaction at a reaction temperature in a range from 100° C. to 200° C. while crosslinking.
  19. 19 . The method of claim 17 , comprising continuing the condensation reaction when the aqueous reaction mixture is in contact with one or more substrates.
  20. 20 . The method of claim 1 , wherein a molar ratio of lignin aromatic hydroxyl groups to aldehyde functional groups in the aqueous reaction mixture is in a range of 1:1.5 to 1:3.

Description

CROSS REFERENCE TO RELATED APPLICATION This application is a U.S. National Stage of PCT/US21/14568, filed Jan. 22, 2021, which claims priority to U.S. Provisional Application No. 62/964,897 (filed Jan. 23, 2020), both of which are incorporated herein by reference in their entireties. STATEMENT OF GOVERNMENT INTEREST This invention was made with government support under 2018-67009-27900 awarded by the U.S. Department of Agriculture. The government has certain rights in the invention. BACKGROUND OF THE DISCLOSURE Field of the Disclosure The disclosure relates to adhesive compositions and related methods for making the compositions and articles. The disclosed methods and compositions use lignin (L) and higher aldehydes (A) to provide an analog to a conventional phenol-formaldehyde (PF) resin with biobased reactants. The condensation reaction between ortho-reactive sites in the lignin and the aldehyde is controlled to prevent gelation of the aqueous reaction mixture while reacting substantially all of the LA reactants to provide a non-crosslinked resin reaction product. The resin reaction product can then be cured to provide a crosslinked adhesive. Brief Description of Related Technology Phenol formaldehyde (PF) is the most commonly used adhesive in the production of construction wood products like plywood, oriented strand board (OSB), laminated veneer lumber (LVL) and other engineered wood products. Accounting for more than 54% of worldwide consumption, North America is the largest market for PF resin in wood adhesive applications. Phenol formaldehyde resin is currently produced through condensation polymerization of fossil-derived compounds, specifically formaldehyde (made from methanol) and phenol (produced from benzene using the cumene process). Depending on the ratio of formaldehyde to phenol in the mixture and the type of catalyst used (basic or acidic), the final resin is either Resol or Novolac. Resol is the most commonly used phenolic resin in wood products today, and is produced from formaldehyde to phenol ratio of approximately 1.5:1.0 (or about 2.0-1.1 (formaldehyde):1.0 (phenol)) in the presence of an alkaline catalyst (NaOH or a caustic/ammonia combination). The corresponding thermosetting resin (Resol) forms a 3D network in a one step process and, when cured at about 120° C. to 175° C. for 3 to 5 minutes, depending on the type of adhesive and thickness of the resin wood layers (e.g., 3-, 5-, or 7-ply plywood), provides excellent water and chemical resistance to wood products, as well as high mechanical performance. Different lignin types have been evaluated as phenol substitutes in the production of phenolic resin to be used in engineered wood products. Exterior grade plywood, oriented strand board (OSB), and laminated veneer lumber (LVL) are typically made using phenolic resin which is competitively priced and imparts excellent moisture as well as chemical resistance. Lignin is a naturally occurring polyphenolic compound that has the potential to be used as a phenol replacement in the production of phenolic resin. New extraction processes and the availability of lignin in large quantities from different resources including wood and annual crops provide a variety of different lignin types, particularly from agricultural sources. Kalami et al. J. Appl. Polymer Sci., vol. 134, pp. 45124-45132 (2017) (Kalami 2017), and Kalami et al. Ind. Crops & Products., vol. 125, pp. 520-528 (2018) (Kalami 2018) are directed to adhesive compositions formed from lignin (L) and formaldehyde (F). Lignins from different sources (softwood, hardwood, or annual crop) and different isolation methods (kraft, organosolv, sulfite, soda, or enzymatic hydrolysis) were used as a phenol replacement in phenolic adhesive formulations. Despite the high performance of formaldehyde-based resins, there are major concerns regarding exposure to phenol and formaldehyde during the manufacturing process and free formaldehyde from corresponding wood to a lesser extent. Although the cured phenolic resin does not emit formaldehyde like urea-formaldehyde resins do, chronic exposure to formaldehyde during the manufacturing process of the resin is a health concern. According to a formaldehyde risk assessment study by the EPA (1991), this is generally due to potential reactions of formaldehyde with proteins, which can cause skin irritation, and inflammation of eye membranes, nose and throat. SUMMARY In one aspect, the disclosure relates to a method for forming an adhesive composition, the method comprising: providing an aqueous reaction mixture comprising water, a lignin comprising aromatic hydroxyl groups and ortho-reactive carbon atoms relative to the hydroxyl groups, and an aldehyde having at least 2 carbon atoms and having at least 1 aldehyde functional group (—CHO); adding a base catalyst in a controlled manner to the aqueous reaction mixture, thereby catalyzing a condensation reaction between the lignin and the aldehyde while maintaining a