Curing urea-formaldehyde adhesives with hydrolysates of chrome-tanned leather waste from leather production

Abstract

Non-isothermal thermogravimetry was applied to study the condensation kinetics of dimethylol-urea (DMU) as a model substance for methylol oligomers of urea in the presence, or absence, of an acid curing agent (phthalic acid), and of blends of DMU with urea and with the hydrolysate of chrome-tanned leather waste. Kinetics of the formation of oxymethylene and methylene bonds were evaluated, using the Arrhenius equation to obtain the parameters. Addition of a mass fraction of 0.05 H to DMU reduces the rate of formation of unstable oxymethylene cross-links in favour of more stable methylene bonds by 20-30%. Acid curing agents accelerate the rate of formation of both types of cross-links, but at the same time markedly affect transformation of oxymethylene cross-links to methylene cross-links. Reducing the content of oxymethylene cross-links in cured aminoplast adhesive films, to control their instability, may lower the levels of formaldehyde emissions by cured aminoplast-type films. (C) 2004 Elsevier Ltd. All rights reserved.