Nanomaterials 2023 , 13 , 1931
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Figure3. Planar hot-pressing unit with temperature and load controlled pressing plates built into an MTS equipment (developed) at Mid Sweden University. 3. Results and Discussion 3.1. Characterization of the Cellulosic Raw Material and the CMNF Suspensions Chemical characterization of the spruce CTMP used as the HYP and the broke liner used to produce the CMNFs is shown in Table 1, together with the composition of the oxidized pulp after 5T-Oxidation. Pulp after refining was not characterized due to the pretreatment only being mechanical. The raw materials (spruce and liner) were dried to obtain a total solid content amounting to 96.6 ± 0.2% and 96.8 ± 0.2% for liner and spruce, respectively. The ash content due to the presence of fillers in the recycled paper was elevated with an average value of 14.2%, whereas in the spruce this value was under 1% [87]. On the other hand, the content of total lignin in both raw materials was also elevated with an average value of 17.2% and 29.9%, indicating that only part of the initial lignin was removed to facilitate the separation of the virgin fibers, as usually performed in packaging paper. The cellulose content was similar in both cases with a 55.2 ± 0.9%in the liner and 48.8 ± 1.2% for the spruce CTMP. The hemicellulose content, formed in the chemical composition by arabinose and the overlapping of xylose, mannose, and galactose, was 10.6% in liner while the spruce almost doubled this value with 18.5%. Finally, the extractive content was under 2% for the liner and around 0.5% for the spruce whereas the pectin content was also low, around 1.5% in both cases. This last parameter was calculated as the galacturonic acid content in the hydrolyzed sample, but also the rhamnose, which majoritively proceeds from pectin, although to a lesser extent from hemicellulose. However, the content of rhamnose is insignificant in the sample under 0.4%, assuming all rhamnose came from the pectin [88].
Table 1. Chemical composition of spruce CTMP as HYP and recycled liner for CMNF production before and after 5T-oxidation.
Chemical Composition (Dry Basis)
Liner after 5T-Oxidation
Spruce CTMP
Liner
Ash (%)
0.7 ± 0.2 48.8 ± 1.2 18.5 ± 0.9 25.6 ± 0.4 4.3 ± 0.1 1.6 ± 0.3 0.5 ± 0.1
14.2 ± 0.1 55.2 ± 0.9 10.6 ± 0.6 11.7 ± 0.4 5.5 ± 0.1 1.2 ± 0.3 1.7 ± 0.3
16.0 ± 0.5 52.7 ± 1.5 13.1 ± 0.4 7.1 ± 0.5 9.0 ± 1.5 <0.5 1.9 ± 0.2
Cellulose (%)
Hemicellulose (%)
Acid insoluble lignin (%) Acid soluble lignin (%)
Pectin (%)
Extractives (%)
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