Discoloration of celluloses treated with amino compounds

Degradation and discoloration of celluloses treated with different amino compounds, including primary amines and hexamethylenetetramine (HMTA), were studied using spectroscopic techniques. The colour generation was measured using standard colorimetry and the degradation and discoloration were characterized using diffuse reflectance FTIR spectroscopy and diffuse reflectance UV-visible spectroscopy. The colour of all the treated celluloses was due to the same chromophores, thus revealing that the discoloration mechanism was essentially the same. The most important reaction was the condensation between carbonyl and amino groups to form coloured imines, and secondary processes were detected at high temperatures and long heating times. The discoloration of celluloses modified with primary amines followed first-order kinetics. However, the discoloration of HMTA-treated cellulose showed an induction period which was related to the thermal decomposition of HMTA.