Biomedical Engineering Reference
In-Depth Information
Mo et al. [
38
] obtained a strain of white-rot fungi that produced Lac in the
laboratory; they studied the fruiting body and basidiospore morphology as well as
the molecular characteristics, and they analyzed the amplified 18srDNA sequence.
They found that the strain belongs to
Panus rudis
. In the solid fermentation of
straw through white-rot fungi, the producing Lac peak appeared in 21 days; the
activity was 3,895 IU
L
1
. The Lac collaborating with ABTS were used to treat
sulfate bamboo pulp, then used hydrogen peroxide to bleach. The results showed
that the pulp brightness through the Laccase biobleaching, chelating treatment
and peroxide bleaching (LQP) and aerobic delignification, Laccase biobleaching,
chelating treatment and peroxide bleaching (OLQP) bleaching was higher than that
through chelating treatment and peroxide bleaching (QP) or aerobic delignification,
chelating treatment and peroxide bleaching (OQP) bleaching without enzyme
treatment (by 4-7 %), with the Kappa value decreasing, and a high viscosity was
maintained.
Wang et al. [
39
] applied Lac to treat the lignin of needlebush KP in the mediators
of 1-hydroxyphenyl benzotriazole (HBT), N-hydroxy-acetyl-aniline (NHA), and
violuric acid (VA). The degradation ability in the VA mediator was superior to the
other two. Residual lignin was analyzed by nuclear magnetic resonance (NMR)
before and after the biobleaching; the results showed that lignin was greatly
oxidized, and its structure was mostly changed in the Lac-VA system after the
biological bleaching treatment. In the three LMSs, the carboxyl group content was
increased, and the methoxy group was correspondingly reduced. The condensed C
5
phenolic lignin was directly acted on by the biological bleaching.
Liu et al. [
40
] used two Lacs or an Lac/mediator system to treat kraft bamboo
pulp, then carried out the TCF bleaching. The results showed that kraft bamboo
pulp took the OLQP bleaching by LMS to obtain the bleached pulp; the bleached
pulp had a similar brightness compared with traditional CEH bleaching including
chlorination, alkali treatment and hypochlorite bleaching, and was maintained at
good pulp strength. The KP was treated by Lac under the existence of hydroxyben-
zene and HBT. After OLQP bleaching, the pulp brightness was 80.7 % ISO, and
the viscosity was more than 800 mL
g
1
. In the case of no additional mediator,
the Lac-treated pulp remained with a better delignification effect after OL
0
QP
(bleaching steps with aerobic delignification, then Laccase biobleaching without
adding external mediator, then chelating treatment and peroxide bleaching; L
0
means Laccase biobleaching without adding external mediator) bleaching. The pulp
brightness was up to 76.7 % ISO and increased by 23.2 % compared with OQP
bleaching.
At present, the enzyme of the lignin pulp biobleaching needs to be further
researched, and the regulation mechanism remains unclear. Once the research
progress of ligninase biobleaching has a breakthrough, it will become possible to put
the industrialization of biobleaching into practice, achieving the goal of biological
pollution-free bleaching.
