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Chemical characteristics and stability of eucalyptus kraft pulps bleached with tertiary amine catalyzed hypochlorous acid

Afsahi, Ghazaleh, Rojalin, Tatu, Vuorinen, Tapani
Cellulose 2019 v.26 no.3 pp. 2047-2054
Eucalyptus, cellulose, chlorine, discoloration, hardwood, hydrogen peroxide, kraft pulp, moieties, ozone, physicochemical properties, polymerization
We recently found that subsequent treatments of hardwood kraft pulps with a tertiary amine (DABCO; 1,4-diazabicyclo[2.2.2]octane) catalyzed hypochlorous acid (Hcₐₜ), ozone (Z) and hydrogen peroxide (P) may provide full brightness with low chemical dosages in a short overall reaction time. Here we report chemical characteristics and stability of Hcₐₜ–Z–P bleached eucalyptus kraft pulps. In comparison with a normal ECF (elementary chlorine free) bleached pulp the Hcₐₜ–Z–P bleached pulps had low carbonyl group content while the degree of polymerization of cellulose remained at high level. However, the brightness of the Hcₐₜ–Z–P bleached pulps was reversed more easily under humid ageing conditions in comparison with the ECF bleached pulp. The discoloration was accompanied by an increase in Raman emission at 1560 cm⁻¹ which is indicative of formation of highly conjugated chromophores. The brightness reversion did not correlate with the carbonyl content that is often considered to be the main origin of the brightness loss under humid conditions. In contrast, the brightness instability of the catalytically bleached pulps possibly resulted from the relatively high organochlorine content.