Клеи для дерева: состав, виды и применение.

Adhesive made of natural or synthetic raw materials for bonding wood and wood based materials
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. 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. 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”.

Animal glue, especially hoof glue and hide glue, was the primary adhesive of choice for many types of woodworking, including furniture and lutherie, for many centuries. It is manufactured from rendered collagen from the skins (hides) or hooves of animals. It is chemically similar to edible gelatin and is non toxic if ingested. Hide glue is still used today in specialized applications: musical instruments (lutherie), for replica furniture, and for conservation grade repairs to antique woodwork. Hide glue is measured on the basis of its gel strength, a measure of how many grams of force it requires to depress a plunger into a 12.5% protein solution of the glue at Glue is manufactured in standard grades from strength is the most commonly used for woodworking; is the highest normally used for instrument building; is the lowest used for general woodwork. Glue above strength requires excessive dilution and so leaves too little glue in joints for effective adhesion, so it is not commonly used. Liquid versions of hide glue are now available; typically they have urea added to keep the glue liquid at room temperature and to extend drying time. Examples of liquid hide glue are Old Brown Glue or Titebond Liquid Hide. Hide glue does not creep. Hide glue joints are easy to repair, by just heating and adding more hide glue. The greenhouse gas emissions is 2.04 kg CO2 eq./kg of Urea formaldehyde adhesive.

Resorcinol formaldehyde resin glue is very strong and durable (resisting immersion in boiling water, mild acids, salt water, solvents, mold, fungus, ultraviolet, etc.). Historically, it was the dominant glue in exterior grade plywood manufacture and the production of wooden aircraft. It must be mixed before use (liquid resin and powdered catalyst), is toxic, 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. In lignocellulosic biomass, lignin acts as a glue that provides strength to cell walls by effectively binding cellulose and hemicelluloses together. 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. 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. Lignin adhesives prepared from lignins protected with other aldehydes (for example, acetaldehyde, propionaldehyde, and furfural showed qualified adhesion performances >0.7 MPa. 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 glue (trade names include Gorilla Glue and Excel) is becoming increasingly popular in the USA after being used for years in other countries. It bonds to textile fibers, metals, plastics, glass, sand, ceramics and rubber, in addition to wood. Polyurethane wood adhesives are normally prepolymers terminated with isocyanate groups. When exposed to moisture, isocyanates react with water and thus cure the adhesives. Therefore, one component polyurethane adhesives are also named as moisture cure polyurethanes. In addition, interactions between polyurethanes and wood polymers can significantly influence bond performance. It has less tendency to "creep" (slide during clamping) than white glue. Aliphatic resin has a similar use profile and relative ultimate strength as PVA. The two glues differ in grip characteristics before initial set, with PVAs exhibiting more slip during assembly and yellow glue having more initial grip. Brands include Titebond and Lepage.

Contact cement for wood veneers.

Hot glue for temporary uses.

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, woodworkers commonly use tight fitting joints that need surprisingly little glue to hold large pieces of wood. Most wood glues need to be clamped while the glue sets.