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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. 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 1⁄2 in (13 mm) plunger 4 mm (0.16 in) into a 12.5% protein solution of the glue at 10 °C (50 °F). Glue is manufactured in standard grades from 32–512 grams (1.1–18.1 oz). 192-gram (6.8 oz) strength is the most commonly used for woodworking; 251-gram (8.9 oz) is the highest normally used for instrument building; 135-gram (4.8 oz) is the lowest used for general woodwork. Glue above 250-gram (8.8 oz) 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.
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). 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, unused powder has a shelf life of up to a year. The adhesive has the ability to fill gaps between ill-fitting components. It has been produced since the 1930s as Aerolite to bond plywood for use in aircraft construction.
The greenhouse gas emissions are 2.04 kg CO2 equivalent/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, and has a dark purple cured color, which may not be acceptable in some uses. For many years, the Federal Aviation Administration (FAA) has stated that "Resorcinol is the only known adhesive recommended and approved for use in wooden aircraft structure and fully meets necessary strength and durability requirements" for certificated aircraft. 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. Most newer adhesives are much more tolerant to typical construction mistakes (such as small gaps or misalignments between parts) than resorcinol, which offers virtually no tolerance for such everyday construction situations. This can pose major difficulties, especially in complex assemblies. Resorcinol is, however, still used by some builders/restorers, and is commonly seen in vintage aircraft.
Phenol formaldehyde resin is commonly used for making waterproof plywood. It is cured at elevated temperature and pressure and also available as a dry film to be sandwiched in between layers of veneer (Tego film). The greenhouse gas emissions are 2.88 kg CO2 equivalent/kg of PF adhesive.
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.
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. 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.
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. 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 1⁄2 in (13 mm) plunger 4 mm (0.16 in) into a 12.5% protein solution of the glue at 10 °C (50 °F). Glue is manufactured in standard grades from 32–512 grams (1.1–18.1 oz). 192-gram (6.8 oz) strength is the most commonly used for woodworking; 251-gram (8.9 oz) is the highest normally used for instrument building; 135-gram (4.8 oz) is the lowest used for general woodwork. Glue above 250-gram (8.8 oz) 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.
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). 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, unused powder has a shelf life of up to a year. The adhesive has the ability to fill gaps between ill-fitting components. It has been produced since the 1930s as Aerolite to bond plywood for use in aircraft construction.
The greenhouse gas emissions are 2.04 kg CO2 equivalent/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, and has a dark purple cured color, which may not be acceptable in some uses. For many years, the Federal Aviation Administration (FAA) has stated that "Resorcinol is the only known adhesive recommended and approved for use in wooden aircraft structure and fully meets necessary strength and durability requirements" for certificated aircraft. 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. Most newer adhesives are much more tolerant to typical construction mistakes (such as small gaps or misalignments between parts) than resorcinol, which offers virtually no tolerance for such everyday construction situations. This can pose major difficulties, especially in complex assemblies. Resorcinol is, however, still used by some builders/restorers, and is commonly seen in vintage aircraft.
Phenol formaldehyde resin is commonly used for making waterproof plywood. It is cured at elevated temperature and pressure and also available as a dry film to be sandwiched in between layers of veneer (Tego film). The greenhouse gas emissions are 2.88 kg CO2 equivalent/kg of PF adhesive.
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.
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. 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.