In this study, a poplar high-yield pulp [preconditioning refiner alkaline peroxide mechanical pulp (P-RC APMP)] was used to produce lignin-containing cellulose nanofibril (LCCNF) dispersions through a sequential process of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation followed by high pressure homogenization. To produce LCCNF with different lignin contents, sodium hypochlorite loadings of 4−12 mmol/g fiber during TEMPO-mediated oxidation step were explored. The effect of lignin content on morphology, thermal stability, crystallinity, and rheological properties of the produced LCCNFs was investigated. The results showed that the TEMPO-mediated oxidation of cellulose was largely limited to the fiber surface. The residual lignin on the surface of LCCNF was presented as small particles. The increase of lignin content increased the thermal stability and decreased the viscosity of the LCCNF. Moreover, at higher lignin content, greater flocculation and aggregation of fibrils took place, which resulted in lower gel-like characteristics of the resultant LCCNF. The results of water contact angle determination also demonstrated that the increase of lignin content significantly increased the hydrophobicity of the LCCNF.
The
oxidation of cellulose to modify the fiber surface is widely
recognized as a promising strategy to improve the production of cellulose
nanofibrils (CNFs) from pulp fibers. In this study, an eco-friendly
advanced oxidation process combining ozone gas, ultraviolet (UV) light,
and hydrogen peroxide (H2O2) was proposed and
investigated to oxidize cellulose for the production of CNFs from
Northern bleached softwood kraft (NBSK) pulp fibers. The results demonstrated
that oxidation with the ternary combination of ozone gas, UV radiation,
and H2O2 could significantly reduce the degree
of polymerization (DP) of cellulose from ∼1036 to ∼330
(reduced by about 68%) and increase the content of carboxyl groups
from 0.04 to 0.32 mmol/g fibers. Moreover, the oxidation also considerably
disrupted the fiber surface. Following high-pressure homogenization,
the ζ potential value of the CNFs produced from the oxidized
pulps was also much higher (∼32 mV) than that of the control
(∼9 mV). Moreover, the energy consumption during nanofibrillation
of the oxidized NBSK pulp fibers (1.52 kW·h/kg CNFs) was also
significantly reduced by approximately 80% compared to that of the
control (6.6 kW·h/kg CNFs).
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