Urea-formaldehyde

Urea-formaldehyde, also known as urea-methanal, so named for its common synthesis pathway and overall structure, is a non-transparent thermosetting resin or plastic. It is produced from urea and formaldehyde. These resins are used in adhesives, finishes, particle board, MDF, and molded objects. UF and related amino resins are a class of thermosetting resins of which urea-formaldehyde resins make up 80% produced globally. Examples of amino resins use include in automobile tires to improve the bonding of rubber to tire cord, in paper for improving tear strength, in molding electrical devices, jar caps, etc.

Urea-formaldehyde resin's attributes include high tensile strength, flexural modulus, and a high heat distortion temperature, low water absorption, mould shrinkage, high surface hardness, elongation at break, and volume resistance. Index of Refraction = 1.55

The chemical structure of UF polymer consists of [(O)CNCH₂]_n repeat units. In contrast melanine-formaldehyde resins feature NCH₂OCH₂N repeat units. Depending on the polymerization conditions, some branching can occur. Early stages in the reaction of formaldehyde and urea produce bis(hydroxymethyl)urea.

Approximately 1 million metric tons of urea-formaldehyde are produced annually. Over 70% of this production is then put into use by the forest products industry for bonding particleboard (61%), medium density fiberboard (27%), hardwood plywood (5%), and laminating adhesive (7%).

Urea-formaldehyde is pervasive. Examples include decorative laminates, textiles, paper, foundry sand molds, wrinkle resistant fabrics, cotton blends, rayon, corduroy, etc. It is also used to glue wood together. Urea formaldehyde was commonly used when producing electrical appliances casing (e.g. desk lamps).

Urea formaldehyde is also used in agriculture as a controlled release source of nitrogen fertilizer. Urea formaldehyde’s rate of decomposition into CO₂ and NH
3 is determined by the action of microbes found naturally in most soils. The activity of these microbes, and, therefore, the rate of nitrogen release, is temperature dependent. The optimum temperature for microbe activity is approximately 70-90 °F (approx 20-30 °C).

...
Wikipedia