Fate of Lipophilic Wood Extractives in Oxygen-Based Cellulose Bleaching
2021
Orozco, Sebastian España | Bischof, Robert H. | Barbini, Stefano | Sriranganadane, Dev | Fackler, Karin | Potthast, Antje
The impact of totally chlorine-free (TCF) bleaching chemicals on the composition and behavior of detrimental lipophilic wood extractives in a mixed hardwood sulfite pulp was studied to determine their potential for pitch control without the need for additional reagents. Toward this end, the acetone extracts of pulp were analyzed with commonly used gas chromatography (GC) and more sophisticated ultraperformance convergence chromatography (UPC²). During EO(P)–Z–P bleaching, the highest decrease in the lipophilic extractive content was achieved after ozone bleaching (Z), with a 38% reduction of GC-FID/MS-detectable resins. Oxygen-reinforced alkaline extraction EO(P) and peroxide bleaching (P) were less effective in terms of resin quality and quantity (−30 and −27%, respectively). Analyzing the acetone extracts after alkaline hydrolysis revealed a different pattern: EO(P) with −44%, P with −20%, and Z with only −8% less lipophilic extractives. A series of oxidized compounds, such as acyl chain-oxidized sterol esters and acylglycerols, and acidic secosterol analogues, were detected for the first time with UPC²-ESI-QToF-MS after ozone bleaching. These compounds lead to an underestimation of the GC-detectable resin content and may be involved in the formation of deposits during lignocellulosic processing. Reaction pathways for lipophilic extractives during ozone bleaching were established.
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