Brightness Improvement Of Douglas Fir Thermomechanical Pulp By Edta And Ascorbic Acid Treatments On Chips

Improving the photostability of whitened wool by applying an anti‐oxidant and metal chelator rinse

“…Another possible mechanism that may be involved is that the combined anti‐oxidant/metal chelator treatment may bleach (or photobleach) some of the yellow chromophores that would normally be formed when FWA‐treated wool is exposed to sunlight. It has previously been shown that a combination of AA and EDTA can be used to reduce the discoloration of Douglas fir wood pulps during bleaching, apparently by breaking down the flavenoids and polyphenolic compounds present and their highly coloured oxidation products [22]. Whilst the chromophores formed by exposure of natural wool to light certainly include oxidation products from aromatic amino acids, recent study [20] suggests that a major source of the yellow/brown photoproducts from FWA‐treated wool is from the photoreaction of the FWA itself with ROS.…”

Treatment of Douglas‐Fir Heartwood Thermomechanical Pulp with Laccases: Effect of Treatment Conditions on Peroxide Bleaching

“…As the polymerization of dihydroquercetin has been implicated in the formation of Douglas-fir brownstain, it is probable that DHQ is also a precursor to color formation in the Douglas-fir heartwood TMP. [2,29,30] …”

“…The color formation in Douglas-fir mechanical pulps has been shown to be a result of the abundance of polyphenolic extractives present in the heartwood portion of the tree. [1,2] The most significant polyphenolic extractive has been identified as the leucochromophore dihydroquercetin (DHQ). [2] During aging of the tree and the subsequent mechanical pulping of the wood, polyphenolic compounds such as DHQ undergo autooxidation, condensation, and metal chelation, resulting in the formation of colored complexes in the pulp that are detrimental to pulp brightness and bleaching response.…”

“…[1,2] The most significant polyphenolic extractive has been identified as the leucochromophore dihydroquercetin (DHQ). [2] During aging of the tree and the subsequent mechanical pulping of the wood, polyphenolic compounds such as DHQ undergo autooxidation, condensation, and metal chelation, resulting in the formation of colored complexes in the pulp that are detrimental to pulp brightness and bleaching response. [3 -5] Therefore, chemical or biological removal or alteration of the colored complexes and/or the extractives, would be an invaluable step toward production of a high brightness mechanical pulp from Douglas-fir.…”