Endoglucanase treatments for improving pulp reactivity in biobleached and commercial dissolving pulps

In this study, a bleached commercial dissolving pulp and a TCF sulphite pulp, bleached at the laboratory scale with a laccase–violuric acid system and complemented with a pressurized hydrogen peroxide stage (LVAPO), were treated with two endoglucanases, one obtained from Paenibacillus barcinonensis (B) and the other one produced from Cerrena unicolor (F), with the intention to improve cellulose reactivity. The B enzyme was used at 120 U/g oven dried pulp (odp) and the F enzyme at 12 and 60 U/g odp. In addition, a purification treatment, i.e. a cold caustic extraction (CCE) at 9% w/v NaOH, was applied before or after the respective hydrolytic treatments in order to reduce the global amount of hemicelluloses. Testing commercial dissolving pulp let to observe that both cellulases increased Fock solubility, although in a different way. Thus, B caused no scissions in the cellulose chain and no significant reduction in fibre length, whereas F strongly decreased viscosity and shortened fibre length, leading to lower reactivity. However, the most salient contribution was the combination of a biobleaching sequence involving a laccase-mediator system (LMS) which provided an environmentally friendly process without detracting the final characteristics of a dissolving pulp, and the subsequent endoglucanase treatment (L_B120) which reached a 91% of Fock solubilit