Nanomaterials 2023 , 13 , 2536
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The aspect ratio decreased (Figure 7) while the consistency of the gel increased (Figure 6). This is due to the presence of non-settled particles during the sedimentation experiments. To better measure the aspect ratio, different, very diluted suspensions were prepared and the peak of sediment was measured after a long time (at the end of sedimentation process). In the case of TEMPO_15 CNF, there were some very stable nanoparticles in the suspension that did not settle even after several weeks, and the final aspect ratio was not real since it corresponded to the settleable material. The increase in HPH intensity increased the degree of nanofibrillation and CD values, which implies that a higher anionic charge is available to generate repulsive forces among particles, which can interact more strongly with water, forming a stable gel.
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Figure 7. Nanofibrillation yield ( a ), transmittance ( b ) cationic demand ( c ) and aspect ratio ( d ) of the different CNF suspensions. 4. Conclusions By carefully selecting an appropriate pretreatment and level of severity, as well as an optimal HPH intensity, different CNF qualities can be produced from recovered paperboard. Based on the pretreatment and HPH intensity, the results can be used to predict the expected quality of CNFs. Recycled paperboard pulp allows one to obtain cost-effective colored and turbid hydrogels with a notable nanofibrillation yield (63%) and transmittance (60%), which can be used as reinforcing aids in board-recycling mills. The hornification of the fibers and the presence of ashes and lignin affects the efficiency of enzymatic hydrolysis, with a dose of 80 mg/g of pulp being enough to obtain the maximal performance of the produced CNF. The characteristics of the produced CNFs and the impact of HPH on nanofibrillation are both significantly influenced by the pulp pretreatment. This enables one to choose the best
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