(261k) Micro/Nano Lignocellulosic Fibrils (MNLCF) Aerogels from Coconut and Oil Palm Tree Residuals and Application for Environmental Remediation

The extensive utilization of oil palm
and coir plantations worldwide has led to a substantial generation of residual
biomass¹. Therefore, an integrated
utilization of related biomass streams is a necessity that, in fact, can become
a source of valuable natural fibers. In addition, replanting operations and
environmental issues can be avoided this way. The lignocellulose sources used in
this study, include coir fibers and oil palm empty fruit bunches (EFB), both of
which have high microfibril angle (~45⁰) that imparts high breaking
strain and low elastic modulus, making them useful for producing ropes, mats
and fishing nets^2,3. Coir and EFB fibers are cheap and
a renewable resource but a vast supply is wasted due to a lack of better
utilization. These fibers have high lignin content, approximately 43% and 36%
dry weight in coir and EFB, respectively. Lignin is an undesirable component in
paper manufacturing as it causes yellowing of the paper and hence, coir and EFB
fibers do not find their use in high-volume papermaking. In fact, the current
research on nanocellulose also focuses on producing lignin-free cellulose
nanofibers which leaves a high carbon footprint on the environment^4,5. Currently, lignin is utilized for
their high calorific value which is a result of a cross-linked phenolic
structure⁶. Recently, lignin has been shown
to act as cementing material between cellulose nanofibers⁷. In addition, it has also been
demonstrated that the porosity, hydrophilicity and the barrier properties of
nanopapers or films of nanocellulose can be tuned via lignin content.

A high microfibril
angle and a high lignin content, limits the applications of coir and EFB fibers.
In the present study, we approach this problem by isolating micro/nano fibrils
from the source fiber, thus foregoing effects related to the microfibril angle.
We also target retaining the native lignin of coir and EFB by subjecting them to
mild pulping conditions via hydrothermal treatment (see Table 1). A recently
reported micro-emulsion method is used to facilitate defibrillation of the
fibers⁸. The micro-emulsions swell and
delaminate different structures of the fibers by disrupting intra-molecular
hydrogen bonding. The micro/nano lignocellulosic fibrils (MNLCF) are obtained
through microfluidization. A detailed characterization of the fiber
defibrillation process is carried out via composition analysis, scanning
electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction
(XRD). The migration of lignin from cell wall to the defibrillated fibers is
studied via confocal microscopy. The thermal properties of MNLCF is studied via
thermogravimetric analyses (TGA) and differential scanning calorimetry (DSC).
Our detailed analyses provide useful information to identify potential
applications for the produced MNLCF. As a proof of concept, water-resistant and
durable aerogels are synthesized from MNLCF via freeze drying (see Figure 1) and
tested for adsorption of Zn(II), Pb(II) and Cd(II) salts.

Table 1: Chemical composition of fiber precursor before and
after the treatment. All values are in %

Figure
1: As-prepared
aerogels from EFB (left) and coir (right) micro/nano lignocellulosic fibrils
(MNLCF) along with their SEM images. The scale bar corresponds to 50µm

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