Participation of carbohydrate-derived chromophores in the yellowing of high-yield and TCF pulps

Pulp carbohydrates are modified under conditions such as extreme pH values, in the presence of bleaching chemicals and thermally. The colour-forming ability of 5-hydroxymethyl-2-furaldehyde (HMF), which is readily formed from carbohydrates, hexuronic acids and other sugar fragments, was studied in relation to bleached and unbleached pulps using UV-VIS reflectance and fluorescence spectroscopy. Doped pulps as well as cellulose were subjected to heat and light. Addition of HMF reinforced colour formation in the pulp at exactly the same wavelengths as observed for yellowing without additives. The sensitivity of the individual pulps treated with HMF was assessed by means of kinetic and spectroscopic studies.