Wood glue
[1][2][3] Examples of modern wood glues include polyvinyl acetate (PVA) and epoxy resins.
[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”.
Hide glue is still used today in specialized applications: musical instruments (lutherie), for replica furniture, and for conservation-grade repairs to antique woodwork.
It must be mixed before use (liquid resin and powdered catalyst), is toxic,[14] and has a dark purple cured color, which may not be acceptable in some uses.
However, in fact the vast majority of wooden aircraft built in recent decades (mostly amateur-built aircraft) instead use other types of adhesives[citation needed] (primarily epoxy resin systems), which offer greater strength and, even more importantly, much less criticality in perfect application technique.
[13] The energy consumption and greenhouse gas emissions associated with the production of Urea-formaldehyde are lower than those of Phenol formaldehyde adhesives.
But Urea-formaldehyde adhesive is judged to have a nearly 50% higher life cycle impact than Phenol formaldehyde mainly because of acid based emissions during its production process.
[17] In lignocellulosic biomass, lignin acts as a glue that provides strength to cell walls by effectively binding cellulose and hemicelluloses together.
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.
Multilayer plywood products using lignin adhesives met the mechanical requirements for applications in various fields.
It is a significant advancement in the field of sustainable adhesive technology and has the potential to impact the plywood manufacturing industry positively.
It bonds to textile fibers, metals, plastics, glass, sand, ceramics and rubber, in addition to wood.
"[24] Epoxy resin, usually as a two-part mix system, cures under a wider range of temperatures and moisture content than other glues, does not require pressure while curing, and has good gap-filling properties: near-perfect joints with very small gaps actually produce weaker bonds.
Versions are available that are able to wick into tight joints but bond with reduced strength (because much drips out and much soaks into the wood leaving very little on the surface for the bond), or thicker formulations (gel) which can fill very small gaps, do not flow out of the joint, and do not soak so quickly into wood.
Thinner cyanoacrylate glue does not bond more quickly nor form shorter polymer chains than the gel version when used on wood.
Cyanoacrylate is stiff but has a low shear strength (brittle) thus normal wood bending can break the bond in some applications.
CA has quickly become the dominant adhesive used by builders of balsa wood models, where its strength far exceeds the base materials.
It was used to make strong and robust joints in early aviation, and was ubiquitous in the form of "white glue" such as Elmer's Glue-All, but fell out of favor due to its susceptibility to attack by bacteria.
Compared to other adhesives, it has low odor and flammability, good bonding strength, and moderate moisture resistance.
It is more heat- and water-resistant than polyvinyl acetate "white" glues, has a heavier consistency that results in fewer drips, and sets at temperatures above 50 °F (10 °C) and up to 110 °F (43 °C), though it is considered unsuitable for outdoor use.
Unlike white glue, its heat resistance and hardness when cured means it can be sanded, though it will not absorb wood stains applied on top of it.
Therefore, woodworkers commonly use tight-fitting joints that need surprisingly little glue to hold large pieces of wood.
