Prevention of photoyellowing of high-yield pulps using ternary mixtures containing a UV screen, a polyethylene oxide dithiol and sucrose

Trials were carried out on printing papers containing different high-yield pulps (SGW) poplar CTMP softwood PGW) to protect them against photoyellowing using mixtures containing the commercial UV absorber Tinuvin 1130 (T1130), a polyethylene oxide dithiol (PEG) and sucrose. Emulsions were prepared with these chemicals and oleic acid by dynamic stirring. Size-press technology was used to deposit each protecting emulsion on the surface of papers. Colour reversion was efficiently reduced by the three-component mixture; nevertheless to limit significantly the brightness reversion the sucrose charge must be sufficiently high. Trials with an experimental paper machine equipped with a size press confirmed the laboratory results and showed that the protecting emulsion does not perturb the paper sheet formation.