Nanomaterials 2023 , 13 , 2536
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followed by mechanical defibrillation using HPH. Different pretreatments were explored, and five levels of HPH energy were applied during the process.
Table1. Chemical composition of recycled paperboard pulp.
Compound
Percentage (wt%)
Cellulose
56.8 ± 0.4 14.0 ± 0.2 4.6 ± 0.2 11.6 ± 0.2 1.7 ± 0.1 11.3 ± 0.4
Hemicelluloses Soluble lignin Klason lignin
Extractives
Ashes
2.2.1. Pretreatments The five different pretreatments considered in the study are summarized in Table 2.
Table2. Pretreatments studied to produce CNFs from recycled paperboard.
Pretreatment Identification
Description
Intensity
Conditions
Refining at PFI refiner ISO standard 5264-2 (2011)
PC=10% 25 ◦ C
Mec
20,000 revolutions
Dose of enzyme: 80mg/kg
Enz_80
PC=5% pH=7 Time=4h T=50 ◦ C
Enzymatic hydrolysis Denaturalization
(80 ◦ C, 15min) Pulp washing
Enz_240
240mg/kg
TEMPO-mediated oxidation Pulp washing with water and filtration up topH=7
TEMPO_5
5 mol NaClO/kg
PC=1% pH=10 T=25 ◦ C
TEMPO_15
15 mol NaClO/kg
All the doses are expressed as dry agent per kg of dry pulp. PC: Pulp consistency.
The mechanical pretreatment was conducted in accordance with the ISO standard 5264-2 (2011) [30]; the enzymatic hydrolysis procedure followed the methodology outlined inTarr é s et al. (2016) [31] and TEMPO-mediated oxidation was performed following the method described by Saito et al. (2007) [32]. 2.2.2. High-Pressure Homogenization In this research, a total of 25 different types of CNFs were produced. The nanofibrilla- tion of the samples was carried out by passing the pretreated pulp suspensions at 1 % of consistency through a PANDA Plus 2000 laboratory homogenizer (Gea Niro Soavi, Italy) using different pressure sequences as detailed in Table 3. All CNFs produced were named using the following nomenclature: Pretreatment_dose- CNF-HPH sequence number. As an example of this, CNFs produced through enzymatic hydrolysis pretreatment using an enzyme dosage of 80 mg/kg, followed by a HPH se- quence of three passes at 300 bar, three passes at 600 bar, and three passes at 900 bar, are designated Enz_80-CNF-5. The energy consumption of the HPH process was continuously monitored using a Circutor CVM-C10 measuring device (Barcelona, Spain), providing real-time readings of
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