Kinetic study and real-time monitoring strategy for tempo-mediated oxidation of bleached eucalyptus fibers

Fig. 1 Evolution of the CC with NaOH consumption at different temperatures (A), TEMPO dosages (B), NaBr dosages (C) and 
cationic demand (D)

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Cellulose 
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32 mg/g are reported, indicating the achievement of 
lower CC for a certain amount of NaOH.
TEMPO has been reported to prevent polysac-
charide depolymerization. Indeed, Spier et al. (
2017
) 
demonstrated that TEMPO acts as a “sacrificial mol-
ecule” in polysaccharide TEMPO-mediated oxida-
tion, reporting that TEMPO protects the polysaccha-
rides during oxidation from depolymerization and 
non-selective oxidations. This is of particular interest 
for the present study, as the oxidation, expressed in 
terms of CC, decreased with the amount of TEMPO. 
The oxidant was consumed during the process, as the 
reaction was stopped once no changes were observed 
on the pH. However, the obtained results indicate that 
a higher amount of the spent oxidant (i.e. NaClO) was 
consumed by non-selective oxidations, also described 
in the literature as side-reactions, and for fiber degra-
dation. In this sense, the concentration of TEMPO not 
only affects the kinetics of the main reaction, but also 
the selectivity and, thus, the resulting fiber properties 
and characteristics.
TEMPO-mediated oxidation kinetics: effect of 
processing conditions
While the correlation between CC and NaOH 
consumption remained constant for all process 
conditions, except for the case of modifying TEMPO 
dosages, the evolution of the CC with time, this 
is the reaction rate, was significantly influenced 
by temperature, TEMPO and NaBr dosages, and 
the CD of the suspension, this is the surface area 
(Serra-Parareda et al. 
2021b
). Figure 
2
provides the 
evolution of CC as function of time for the tested 
temperatures (A), TEMPO and NaBr dosages (B and 
C, respectively) and the CD (D).
Figure 
2
A clearly indicates an effect of temperature 
over the kinetic constant of the reactions, particularly 
in k
1
, which was taken as rate-determinant. The 
differences on the slope correspond to the increasing 
temperatures. In addition, those reactions carried out 
between 5 and 20 °C exhibited a slight temporal shift 
compared to those occurring at higher temperatures,