Molecules 2019 , 24 , 1800
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the case of addition of CNF from recycled ONP. For CNF from recycled OCC, bursting strength index and short-span compressive strength (SCT) were also measured to evaluate the recycled cartonboard enhancement. Also, the e ff ect of both kinds of CNF on retention and drainage was studied, using di ff erent CNF doses and TRDS.
Figure1. In situ production of cellulose nanofibers (CNF) from recycled papermaking streams to be used as additive in the process. 2. Results and Discussion 2.1. Characterization of CNF from Recycled ONP and Recycled OCC Pulps The content of carboxylic groups of the recycled ONP was very low—below 0.2 mmol of COOH / g of dry pulp—compared to the content of carboxylic groups of recycled OCC (~0.85 mmol of COOH / g of dry pulp). In the case of recycled ONP, the COOH level increased linearly with increasing oxidation treatment up to a dose of 15 mmol of NaClO / g of dry pulp (Figure 2). In the case of recycled OCC, the first addition of NaClO decreased the content of carboxylic groups but higher additions produced an increase of the values, obtaining similar content of carboxylic groups to recycled ONP. This was probably due to the higher content of lignin and other impurities present in the recycled OCC (Table 1) that consume part of the NaClO [21].
Figure 2. Carboxylic groups in recycled old newsprint (ONP) and old corrugated container (OCC) pulps oxidized by NaClO in presence of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO).
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