Wood glue
Wood glue is an adhesive used to tightly bond pieces of wood together. Many substances have been used as glues. Traditionally animal proteins like casein from milk or collagen from animal hides and bones were boiled down to make early glues. They worked by solidifying as they dried. Later, glues were made from plant starches like flour or potato starch. When combined with water and heated, the starch gelatinizes and forms a sticky paste as it dries. Plant-based glues were common for books and paper products, though they can break down more easily over time compared to animal-based glues.[1][2][3] Examples of modern wood glues include polyvinyl acetate (PVA) and epoxy resins. Some resins (i.e., glues) used in producing composite wood products may contain formaldehyde.[4] As of 2021, “the wood panel industry uses almost 95% of synthetic petroleum-derived thermosetting adhesives, mainly based on urea, phenol, and melamine, among others”.[5]
Types
Animal glue
Urea-formaldehyde
Urea-formaldehyde resin adhesives feature a low effective cost, low cure temperatures, resistance to microorganisms and abrasion, and light color. It does not creep, and can be repaired with epoxy. It can rapidly deteriorate in hot, moist environments, releasing formaldehyde (a carcinogen).[9][10][11] Supplied as a fine white powder which is mixed with half its weight of cold water for use. Mixed adhesive remains usable for around three hours depending on temperature. Providing it is kept dry, un-used powder has a shelf-life of up to a year. The adhesive has the ability to fill gaps between ill-fitting components. A popular brand is Cascamite.[12]
The greenhouse gas emissions is 2.04 kg CO2-eq./kg of Urea-formaldehyde adhesive.[13]
Resorcinol-formaldehyde
Phenol formaldehyde
Phenol formaldehyde resin is commonly used for making plywood. It is cured at elevated temperature and pressure.[9] The greenhouse gas emissions is 2.88 kg CO2-eq./kg of PF adhesive.[13]
In terms of the overall environmental impacts, it was found that Urea-formaldehyde adhesive had a nearly 50% higher life cycle impact than Phenol formaldehyde adhesive. Comparing the energy consumption used in Urea-formaldehyde and Phenol formaldehyde adhesives, Urea-formaldehyde adhesive was much lower than Phenol formaldehyde adhesive.[15][13]
Lignin–phenol–formaldehyde
Lignin–phenol–formaldehyde resin adhesives are generally synthesized by reacting a mixture of isolated lignin (for example, kraft, soda or biorefinery lignin) and phenol with formaldehyde under alkaline conditions.[16] Lignin–phenol–formaldehyde resin adhesives have higher viscosity, are more deeply coloured and require more severe curing conditions than urea–formaldehyde and phenol–formaldehyde resin adhesives.[17]
In lignocellulosic biomass, lignin acts as a glue that provides strength to cell walls by effectively binding cellulose and hemicelluloses together.[18] Milled wood lignin(MWL), formaldehyde-protected lignin (FPL) and acetone-protected lignin adhesives that were prepared with lignins separated under either mild conditions or protection by aldehyde or ketone demonstrated reasonable bonding strengths after hot pressing at 190 °C and 1.5 MPa for 8 min; both the dry and wet adhesion strengths met the minimum requirement of 0.7 MPa. From the results, the slightly condensed or protected lignins from different sources could be directly used as wood adhesives without additional physical or chemical treatments.[19] Adhesion performance of these adhesives improved with reduced condensation degrees and increased with higher hot-pressing temperatures. Multilayer plywood products using lignin adhesives met the mechanical requirements for applications in various fields.[19][20]
Lignin adhesives prepared from lignins protected with other aldehydes (for example, acetaldehyde, propionaldehyde, and furfural showed qualified adhesion performances >0.7 MPa.[21][22]
Preparing lignin-based wood adhesives from lignocellulosic biomass promotes the use of green adhesives and contributes to the development of profitable biorefining schemes. It is a significant advancement in the field of sustainable adhesive technology and has the potential to impact the plywood manufacturing industry positively.
Polyurethane
Epoxy
Cyanoacrylate
Casein
Polyvinyl acetate (PVA)
Polyvinyl acetate (PVA), also known as "white glue", "hobby and craft" or “school glue” is non toxic, PH neutral, inexpensive, and easy to use, and is therefore the most commonly used type of wood glue. Joints should be tight fitting and clamped during curing for maximum strength. PVAs remain flexible after they have cured, however, and will creep under constant load. Joints that were previously glued with PVA may be hard to repair since most glues (including PVA itself) do not adhere well to cured PVA glue. PVA glues are not waterproof, however type 2 PVAs are water resistant.
Aliphatic resin
Aliphatic resin, also known as "carpenter's glue" and "yellow glue," is a
Contact cement
Hot glue
Usage
Several wood glues have poor "gap-filling" ability, meaning they either soak into the wood and leave the gap empty, or remain to fill the gap but have little structural integrity. Therefore,
Mechanical resistance
Fine Woodworking magazine ran a number of tests to evaluate the mechanical resistance of wood joints with different glues:[29]
Glue | Joint strength as a percentage of Type I PVA glue |
---|---|
Type I PVA glue | 100% |
Slow-set epoxy | 99% |
PVA glue | 95% |
Liquid hide glue | 79% |
Hot hide glue | 76% |
Polyurethane | 58% |
The type I PVA glue was Titebond III, a waterproof glue. The epoxy was from System Three. The PVA glue was Elmer's Carpenter's glue. The liquid hide glue was from Old Brown Glue. The hot hide glue was J.E. Moser's. The polyurethane was Gorilla brand.
See also
- Air pollution
- Bioadhesive
- Carpenter
- Plant glue
- Pollutant
- Postage stamp gum (a starch-based adhesive)
- Sawdust (wood dust)
- Solvent
- TVOC
- Wood preservative
References
- ^ "A low-cost, formaldehyde-free, and high-performance starch-based wood adhesive :: BioResources". BioResources (in Kinyarwanda). 30 Apr 2018. Retrieved 12 Sep 2023.
- PMID 25439864.
- ISSN 1999-4907.
- ^ "Frequent Questions for Consumers about the Formaldehyde Standards for Composite Wood Products Act". US EPA. 26 Jul 2016. Retrieved 13 Sep 2023.
- PMID 34946693.
- ISBN 978-0-8069-6274-0. Archivedfrom the original on 2023-07-19. Retrieved 2016-11-04.
- ^ ISBN 978-1-60239-057-7. Archived from the original(PDF) on 2022-06-07. Retrieved 2009-11-01.
- ^ "Wood Glue FAQ on ChemicalWiki". ChemicalWiki.com. 30 September 2019. Archived from the original on 18 September 2020. Retrieved 9 September 2020.
- ^ a b c "AC 43.13-1B CHG 1 [Large AC. This includes Change 1.] Acceptable Methods, Techniques, and Practices - Aircraft Inspection and Repair". faa.gov. Archived from the original on 2009-10-09. Retrieved 2009-11-01.
- ISBN 978-0-8493-2470-3. Archived from the original(PDF) on 2022-03-05. Retrieved 2009-11-01.
- ^ Marks, David J. (September–October 2007). "Working with Urea Formaldehyde Glues". Woodworker West. Archived from the original on 2011-07-10.
- ^ "Polyvine - CASCAMITE". Archived from the original on 2022-05-26. Retrieved 2022-04-07.
- ^ S2CID 218082255.
- ^ DAP® Weldwood Waterproof Resorcinol Glue Archived 2018-02-18 at the Wayback Machine (Technical Bulletin), retrieved 2017-11-17
- ISSN 0026-0576.
- S2CID 251148187.
- S2CID 216764947.
- S2CID 210890119.
- ^ PMID 37553075.
- ISSN 0926-6690.
- PMID 29210487.
- PMID 32017337.
- ISSN 0143-7496.
- ^ Vick, C. B.; Okkonen, E. A (Nov–Dec 1998). "Strength and durability of one-part polyurethane adhesive bonds to wood". Forest Products Journal. 48 (11/12): 71–76. Archived from the original on 2008-05-19. Retrieved 2009-11-01.
- ^ "Bonding with Epoxy in Wood Construction", Gurit, retrieved 2009-11-03[permanent dead link] Archived copy Archived 2017-11-12 at the Wayback Machine at WebCite (January 26, 2006).
- ^ "Superior Adhesives for the Millennium". CP Adhesives, Inc. Archived from the original on 2011-07-04. Retrieved 2009-11-08.
- ISBN 978-0-8069-0858-8.
- ISBN 978-0-8069-7238-1.
- ^ "Reference Fine Woodworking, August 2007, N° 192" (PDF). oldbrownglue.com. Archived (PDF) from the original on 2014-08-19. Retrieved 2014-08-17.
Further reading
- "Forests | Special Issue : Advanced Eco-Friendly Wood-Based Composites II".
- Gonçalves, Diogo; Bordado, João Moura; Marques, Ana C.; Galhano dos Santos, Rui (24 Nov 2021). "Non-Formaldehyde, Bio-Based Adhesives for Use in Wood-Based Panel Manufacturing Industry—A Review". Polymers. 13 (23). MDPI AG: 4086. PMID 34883590.