The influence of pulping and washing conditions on the properties of Eucalyptus grandis unbleached kraft pulps treated with chelants

The influence of different addition points of a chelating agent and a counter-ion exchange on the properties of Eucalyptus grandis unbleached kraft pulps is studied. Seven pulps were considered: two laboratory kraft pulps with or without the inclusion of the chelant DTPMPA (diethylene triamine penta (methylene phosphonic acid)), a mill kraft pulp and four mill pulps after Ca+2 or Na+ counter-ion exchange followed, or not, by washing with DTPMPA addition. The laboratory pulps required lower beating energy than the industrial pulps for achieving 30°SR, and the corresponding handsheets also showed better strength and optical properties, as well as a more homogeneous and smooth surface. The counter-ion exchange decreases the mechanical resistances and increases brightness. However, the effects of Ca+2 are deeper than those of Na+. DTPMPA added to pulping causes a decrease in calcium content whereas as a washing additive does not have a relevant impact on the mechanical and optical properties.