inorganic ions, hardly targets carbohydrates but can react with aromatics, nucleic acids, lipids, or proteins (Liu et al., 2021). Hence, results indicate that the best effect is achieved by removing, by extraction, as many non-carbohydrate compounds as possible. When H 2 O 2 concentration was 3% (w/w), the presence of HCl removed more extracts and, thus, less yield, since both alkali and acid solutions help extracting proteins, and some oxidizing power should be expected from the small amounts of chlorine that are generated. This chlorine was rapidly reduced to chloride by H 2 O 2 under more severe conditions (6%), in which HCl was actually a deactivator. As for sodium perborate, it has been demonstrated to be a more powerful bleaching agent than peroxide as long as high temperatures (70-80ºC) are used (Pesman et al., 2014). However, possibly due to its low concentration, additions of SPB did not give out a consistent increase of brightness. In addition, Table 3 shows that samples obtained after extracting with soda or sodium hypochlorite treatments results in paper sheets with higher quality than those obtained with hydrogen peroxide (alone or combined). In all cases, the relative standard deviation lied below 5%. As the best results were obtained at the highest concentrations of reagent, experiments with 9 and 12% of soda or sodium hypochlorite where carried out and presented in Figures 2 and 3, in order to compare both process with paper sheets formed with the greater proportion of algae (75%).
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