Next-generation urea resins: formaldehyde-free coating materials based on higher aldehydes and amides

Urea-formaldehyde resins, which are often used indoors as coatings or adhesives due to their limited resistance to moisture, are becoming less and less important, particularly due to the increasingly strict limit values for formaldehyde.¹ The release of toxicologically harmful formaldehyde is possible even after curing, so that these resins, which have been favored in terms of price, are increasingly being substituted.² This work focused on the synthesis of formaldehyde-free coating materials based on higher aldehydes, which can be cured with urea or urea derivatives. The substitution of formaldehyde, which is becoming more and more restricted, also makes it easier to produce and handle these resins on an industrial scale. Especially higher aldehydes of the benzaldehyde type were investigated, as these do not mechanistically release formaldehyde during the curing reaction with urea and are also unable to form colored enamides.³ Both aspects were confirmed in this work. The crosslinking mechanism was investigated using spectroscopic methods such as IR or Raman, and the mechanical properties of the resulting coatings were examined using DMA and rheometer-DMTA. Furthermore, application tests in accordance with DIN were carried out. Especially adducts from renewable 5-hydroxymetylfurfural turned out to form high performance coatings when crosslinked with urea.