Urea-formaldehyde resins disadvantages

The main outlet for urea formaldehyde resins is in adhesives for plywood and chipboard. The ratio of urea to formaldehyde used will influence the properties of the adhesive. For example, a resin with a high formaldehyde to urea ratio will give an adhesive having the best clarity, water resistance and mechanical properties. The main disadvantage of this type of adhesive is its poor water resistance. Hence, it cannot be used for exterior applications where it is superseded by adhesives based on phenolic resins. 

The major disadvantage associated with urea-formaldehyde adhesives as compared with the other thermosetting wood adhesives, such as phenol-formaldehyde and polymeric diisocyanates, is their lack of resistance to moist conditions, especially in combination with heat. These conditions lead to a reversal of the bond-forming reactions and the release of formaldehyde, so these resins are usually used for the manufacture of products intended for interior use only. However, even when used for interior purposes, the slow release of formaldehyde (a suspected carcinogen) from products bonded with urea-formaldehyde adhesives is observed. 

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