Nanomaterials 2023 , 13 , 2536
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the consumed energy. The energy consumption was recorded after every HPH cycle and was then normalized to the processed dry mass.
Table3. HPH conditions to produce CNFs.
Number of Cycles
HPH Sequence Number
300bar
600bar
900bar
1 2 3 4 5
3 3 3 3 3
0 1 3 3 3
0 0 0 1 3
2.3. Characterization of the Pulps 2.3.1. Chemical Composition
The composition analysis of both unpretreated and pretreated pulps (Table 4) was conducted according to TAPPI T204 for extractive determination, TAPPI T211 for ash deter- mination, and NREL/TP-510-42618 for additional laboratory analytical procedures [33–35]. Briefly, the extractives were determined using the Soxhlet extraction method with acetone as solvent. The ash content was determined through calcination at 525 ◦ C. For lignin analysis, the following steps were followed: (i) acid hydrolysis of 0.3 g of dry pulp using 3mLof 72%H 2 SO 4 for 1 h at 30 ◦ C, (ii) dilution with 84 g of distilled water to prevent phase separation between high and low concentration acid layers, and (iii) autoclaving at 121 ◦ C for 1 h, followed by filtration to determine Klason lignin by drying and weighing the filtration cake. The percentage of soluble lignin, cellulose, and hemicellulose were deter- mined by analyzing the filtrate; soluble lignin was obtained by measuring the absorbance of the filtrate at 240 nm using a UV–vis spectrophotometer. Cellulose and hemicellulose were analyzed using high-performance liquid chromatography (HPLC) of the filtrate after neutralization with CaCO 3 and microfiltration through a 0.2 μ mfilter.
Table4. Composition of pretreated pulps.
Extractives
Ashes
Soluble Lignin Klason Lignin
Cellulose 56.4 ± 0.4 60.6 ± 0.4 54.8 ± 0.4 55.1 ± 1.6 45.5 ± 1.1
Hemi-Cellulose
Mec
1.8 ± 0.1 1.1 ± 0.1 1.0 ± 0.1 2.0 ± 0.2 1.9 ± 0.2
12.6 ± 0.3 7.4 ± 0.2 8.1 ± 0.2 12.2 ± 0.2
4.3 ± 0.2 4.5 ± 0.2 4.9 ± 0.2 9.5 ± 1.6 10.5 ± 1.4
12.5 ± 0.2 12.5 ± 0.2 15.6 ± 0.2 7.5 ± 0.5 3.2 ± 0.2
12.5 ± 0.2 13.8 ± 0.2 15.3 ± 0.2 13.7 ± 0.4
Enz_80
Enz_240
TEMPO_5 TEMPO_15
16.2 ± 0.3 22.7 ± 0.5 The behavior of pretreated pulps is influenced by the functional groups present on the surface of cellulose. Therefore, conductimetric titration was used to determine the content of carboxyl groups per gram of the pretreated pulps, by following the method described in previous studies. In this method, a dried sample weighing between 0.05 and 0.1 g was suspended in 15 mL of 0.01 N HCl solution and stirred for 10 min and then taken to a conductivity sensor. The titration was performed by consecutively adding 0.1 mL of 0.05 N NaOH solution to the suspension until a noticeable increase in conductivity was observed. As the alkali neutralizes the chlorohydric acid, the conductivity initially decreases. Once the acid groups are neutralized, the conductivity remains constant. Finally, the excess of NaOH leads to an increase in conductivity. The number of carboxyl groups was calculated from the titration curve, which relates conductivity vs. amount (meq) of NaOH added, following the methodology described by Habibi et al. (2006) [36].
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