20 августа, 2015 
Malyar Ecole Nationale Superieure des Technologies et Industries du Bois, Universite de Nancy I, Epinal, France
The urea-formaldehydes (UFs) are the most important and most used class of amino resin adhesives. Amino resins are polymeric condensation products of the reaction of aldehydes with compounds carrying aminic or amidic groups. Formaldehyde is by far the primary aldehyde used. The advantage of UF adhesives are their (1) initial water solubility (this renders them eminently suitable for bulk and relatively inexpensive production), (2) hardness, (3) nonflammability, (4) good thermal properties, (5) absence of color in cured polymers, and (6) easy adaptability to a variety of curing conditions [1,2].
Thermosetting amino resins produced from urea are built up by condensation polymerization. Urea is reacted with formaldehyde, which results in the formation of addition products such as methylol compounds. Further reaction and the concurrent elimination of water leads to the formation of low-molecular-weight condensates which are still soluble. Higher-molecular-weight products, which are insoluble and infusible, are obtained by further condensing the low-molecular-weight condensates. The greatest disadvantage of the amino resins is their bond deterioration caused by water and moisture. This is due to the hydrolysis of their aminomethylenic bond. Therefore, pure UF adhesives are used only for interior applications.
Опубликовано в рубрике 