Overview / Technology routes / Tannins
Polyphenolic extractives
Tannins
Condensed tannins from bark and wood, the longest-running industrial bio-phenolic wood adhesive.
Overview
Condensed (flavonoid) tannins are extracted from mimosa (wattle) and pine bark, quebracho wood and similar sources. They have been used industrially for wood adhesives in several countries since the 1970s.
Classic systems harden tannin with formaldehyde or paraformaldehyde. Lower-emission variants use hexamine, glyoxal or furfuryl alcohol, or rely on autocondensation catalysed by silica or alkali.
Chemistry and bonding mechanism
The A-ring of the flavan-3-ol unit (resorcinol or phloroglucinol type) is strongly nucleophilic and reacts with aldehydes faster than phenol does. The B-ring (catechol or pyrogallol type) mainly contributes metal chelation and oxidation reactions.
Tannin extracts are viscous because they contain gums (carbohydrates). The reactive A-ring sites sit close together, so a crosslinked network can stall before it is complete; this is one reason tannin bonds are brittle.
Representative structures
Monomers and model units, drawn from SMILES with RDKit. Polymers are shown by a representative unit, not a full structure.
(+)-Catechin (flavan-3-ol unit)
Representative monomer unit of condensed tannins; the A-ring is the nucleophilic site toward aldehydes.
O[C@H]1Cc2c(O)cc(O)cc2O[C@@H]1c1ccc(O)c(O)c1Formaldehyde
Incumbent crosslinker in UF, MUF and PF resins; the substance the new rules limit.
C=OHexamine (hexamethylenetetramine)
Hardener for tannin and lignin resins; it is itself a formaldehyde-releasing compound.
C1N2CN3CN1CN(C2)C3Furfuryl alcohol
Furanic co-reactant in tannin-furanic systems; self-condenses under acid.
OCc1ccco1Position and maturity
- Typical products
- particleboard, plywood, exterior and marine grade panels, finger joints
- Incumbent to beat
- PF and MUF for exterior and moisture-resistant panels.
- Maturity
- Industrial in niche markets; formaldehyde-free tannin systems are mostly laboratory to pilot scale.
Strengths
- High reactivity and good moisture resistance once crosslinked.
- Established extraction industry in some regions.
What to watch
- Bark-extraction capacity at sawmills; tannin-furanic and tannin-NIPU systems with panel results.
Technical challenges
- Limited, regional supply, and price tied to the leather-tanning market.
- Hexamine hardeners release formaldehyde during cure, so they need emission testing rather than a "formaldehyde-free" label.
- Viscosity, short pot life, and variation in extract quality.
Cross-cutting: Press time, temperature and line throughput · Viscosity, solids content and pot life · Formaldehyde and VOC emissions · Feedstock variability and supply · Cost per qualified bond · Comparable life-cycle evidence
Quarterly track
2026-Q4 · Sept 2026 – Nov 2026
Machine-triaged leads (1)
Development of a semi-closed foaming system for tannin-formaldehyde-based foamable adhesives to produce lightweight particleboard
A semi-closed foaming system was developed for tannin-formaldehyde-based foamable adhesives used to produce lightweight particleboard.
2026-Q3 · Jun 2026 – Aug 2026
Machine-triaged leads (4)
Development of a high-performance glyoxal–tannin–epoxy wood adhesive modified with triethylenetetramine
The study develops a glyoxal–tannin–epoxy wood adhesive modified with triethylenetetramine.
“glyoxal–tannin–epoxy wood adhesive modified with triethylenetetramine”
Proučevanje utrjevanja lepil na osnovi tanina in lignina s sistemom za avtomatizirano vrednotenje zlepljenosti
The study evaluated lignin- and tannin-based adhesive mixtures crosslinked with HMTA and HMDA, measuring curing and shear strength by ABES and standard methods.
“lepilne mešanice na osnovi lignina in tanina, zamrežene s heksametilentetraminom (HMTA) in heksametilendiaminom (HMDA).”
Covalent Grafting of the Phosphorus Element Endows the Tannin–Gelatin-Based Adhesive with Intrinsic Flame Retardancy and Water Resistance
Maleated tannic acid was reacted with gelatin and phosphorus-functionalized to give a formaldehyde-free adhesive for plywood, with reported hot-water and boiling-water shear strengths.
“tannic acid was maleated to form maleated tannic acid (MA@TA)”
Effect of Glycerin Addition as an Extender on the Properties of Mahogany Tannin-Based Adhesive and Particleboard Performance
Mahogany bark tannin-based resorcinol formaldehyde adhesive with glycerin extender was evaluated for adhesive and particleboard properties.
“the use of tannin extracted from mahogany (Acacia sp.) bark as the basis for a Tannin Resorcinol Formaldehyde (TRF) adhesive”
2026-Q2 · Mar 2026 – May 2026
Machine-triaged leads (5)
The Effect of Hardeners on the Dry and Wet Bondline Strength of Quebracho Tannin Resin in Three-Layer Plywood
Quebracho tannin adhesives with hexamine, paraformaldehyde or MDI hardeners were tested for dry and wet bondline strength in three-layer maple plywood.
“paraformaldehyde-modified tannin adhesives achieved the highest dry strength, 3.5 MPa”
Performance of Agro-Forestry Biomass Particleboards Bonded with Tannin-Based Bio-Adhesives
Agro-forestry biomass particleboards were bonded with mimosa tannin adhesive and compared with urea-formaldehyde, assessing mechanical and water durability.
“These are bonded using an ecological mimosa tannin adhesive in comparison to a conventional urea–formaldehyde-based adhesive.”
Tannic Acid‐Ethanolamine Modified LDPE Films for the Fabrication of Interfacially Reinforced Thermoplastic Resin‐Bonded Plywood
Tannic acid and ethanolamine self-polymerize on LDPE film surfaces to form an adhesive layer used to prepare formaldehyde-free thermoplastic resin-bonded plywood.
“the interfacial bonding between LDPE film and wood is effectively improved”
Moisture durability of welded-joints reinforced with a novel Eucalyptus globulus tannin-based adhesive: experimental investigation and coupled thermal-mechanical modeling using RSM and FEM
Moisture durability of welded joints reinforced with a Eucalyptus globulus tannin-based adhesive was investigated experimentally and modelled with RSM and FEM.
“Moisture durability of welded-joints reinforced with a novel Eucalyptus globulus tannin-based adhesive”
Optimization of condensed tannin extraction from Pinus taeda bark for sustainable wood adhesives
The study optimizes condensed tannin extraction from Pinus taeda bark for sustainable wood adhesives.
2026-Q1 · Dec 2025 – Feb 2026
Machine-triaged leads (9)
One-pot, synthesis-free tannin-furfuryl alcohol-phytic acid adhesive: A scalable bio-based alternative to formaldehyde resins with ultra-high flame retardancy, exceptional water resistance and life-cycle benefits
A one-pot, synthesis-free tannin-furfuryl alcohol-phytic acid adhesive is reported as a scalable bio-based alternative to formaldehyde resins.
“One-pot, synthesis-free tannin-furfuryl alcohol-phytic acid adhesive: A scalable bio-based alternative to formaldehyde resins”
Preparation and performance evaluation of valonia tannin-sucrose wood adhesive based on sucrose proportion regulation
Valonia tannin with sucrose as crosslinking agent was evaluated as a wood adhesive; higher sucrose proportions increased dry and warm-water bond strength, meeting GB/T Class II plywood requirements.
“the dry strength increased from 1.04 to 1.43 MPa, and the warm-water strength increased from 0.46 to 0.84 MPa”
Recent Developments in Super-Hydrophobicity and Fire-Resistance of Tannin-Based Non-Isocyanate Polyurethane Resins for Wood-Based Composites
Reviews recent developments in super-hydrophobicity and fire resistance of tannin-based non-isocyanate polyurethane resins for wood-based composites.
Potential of Quebracho Tannin to Substitute Urea-Formaldehyde Adhesive in Plywood: Comparative Technical and Environmental Performance
Quebracho tannin is evaluated as a substitute for urea-formaldehyde adhesive in plywood, comparing technical and environmental performance.
Adhesive Characterization of Acacia mangium Bark Extract and Its Effects on Properties and Formaldehyde Emissions of Rubberwood Particleboard
The study characterizes Acacia mangium bark extract as an adhesive and its effects on properties and formaldehyde emissions of rubberwood particleboard.
Adhesives from Anadenanthera peregrina tannin for plywood production: effect of sodium bisulfite concentration on gluing quality
Tannin adhesives from Anadenanthera peregrina bark extracted with 0, 3 and 5% sodium bisulfite were tested on plywood, with 3% giving better mechanical properties and higher water absorption.
“The objective of this study was to develop natural polyphenol adhesives extracted with different concentrations of sodium bisulfite (NaHSO 3 ) for the production of plywood panels.”
The efficacy of formaldehyde-free tannin resin in comparison with melamine-formaldehyde resin for enhancing the biological durability of ancient wooden copings
Formaldehyde-free tannin resin was compared with melamine-formaldehyde resin for enhancing biological durability of ancient wooden copings.
“formaldehyde-free tannin resin in comparison with melamine-formaldehyde resin”
Biobenzoxazines Generated in Hardened Tannin-Hexamine Wood Adhesives
The study examines biobenzoxazines formed in hardened tannin-hexamine wood adhesives.
Preparation and performance optimization of tannin-modified cold-setting MUF resin and glued wood
Bayberry tannin was added to melamine-urea-formaldehyde resin at different stages; first-stage 6% addition gave the best balance of properties.
“First-stage addition of bayberry tannin yielded optimal results, with 6% identified as the critical optimal dosage.”
Key literature
- Pizzi A. (2019). Tannins: prospectives and actual industrial applications. Biomolecules. doi:10.3390/biom9080344 review
- Oktay S., Pizzi A., Köken N., Bengü B. (2024). Tannin-based wood panel adhesives. International Journal of Adhesion and Adhesives. doi:10.1016/j.ijadhadh.2024.103621 review
- Abdullah U.H.B., Pizzi A. (2012). Tannin-furfuryl alcohol wood panel adhesives without formaldehyde. European Journal of Wood and Wood Products. doi:10.1007/s00107-012-0629-4 research
- Mansouri H.R., Navarrete P., Pizzi A., Tapin-Lingua S., Benjelloun-Mlayah B., et al. (2010). Synthetic-resin-free wood panel adhesives from mixed low molecular mass lignin and tannin. European Journal of Wood and Wood Products. doi:10.1007/s00107-010-0423-0 research
- Pizzi A. (2006). Recent developments in eco-efficient bio-based adhesives for wood bonding: opportunities and issues. Journal of Adhesion Science and Technology. doi:10.1163/156856106777638635 review