Production of nanocellulose from renewable resources and conductivity measurements of polypyrrole hybrid nanocomposites.
Loading...
Date
2018
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
The extraction of nanocellulose (NC) from i) bacterial cellulose (grown using "Symbiotic
'Colony' of Bacteria and Yeast" or SCOBY), ii) Whatman filter paper, and iii) hardwood
pulp was successfully investigated in this study. Acid hydrolysis was applied to these
three materials and nano-fibrous whiskers were formed. When the nano-fibres were
subjected to dialysis, the nano-fibres exhibited a crystalline structure known as
nanocrystalline cellulose (NCC). Harmless disposal of the residual hydrolysis acid byproduct
is still an obstacle that hinders large-scale production of NCC and NCC-based
nanocomposites. In this work, the hydrolysis products of NC without further separation
was studied to produce nanofibrous cellulose (NFC). The NFC structural integrity was
compared to conventional NCC. The structural composition was verified using Fourier -
transform infrared spectroscopy (FT-IR) and Raman spectroscopy. The nanofibers were
examined with Scanning Electron Microscopy coupled with Energy Dispersive X-ray
spectroscopy (SEM-EDS) and Transmission Electron Microscopy (TEM).
The dimensions of the nanocellulose were within the nanometre range that has acceptable
aspect ratios for ideal stress transfer of the fibre-matrix interaction. For the various
nanocellulose samples, i.e. from Bacterial cellulose, Whatman Filter paper and hardwood
pulp, it was found that the concentration of the dialysis-free nano-fibrous cellulose has a
higher concentration and longer dimensions than that of dialysed nanocrystalline cellulose.
The nanocellulose was then utilized as a stabilizer for the synthesis of polypyrrole using a
pyrrole monomer and ferric chloride hexahydrate initiator that produced a well dispersed
network of polypyrrole@nanocellulose (PPy@NC) hybrid nanocomposite. Various
concentrations were produced to find the optimum ratio of polypyrrole to nanocellulose to
give excellent stability and dispersity. The ratio of 1:1 polypyrrole to nanocellulose
exhibited good suspension of the nanohybrid, forming a well dispersed network. The
nanohybrid formation was confirmed using TEM, SEM, FT-IR, Raman spectroscopy and
Ultraviolet-visible spectroscopy (UV-Vis). Interestingly, the PPy@NC nanohybrid could
be easily isolated from the polymerization products due to the decreased surface charge.
The PPy@NC nanohybrid was subsequently suspended in polyvinyl alcohol (PVA), which
facilitated the construction of a continuous PPy@NC conductive network in the polymermatrix for both NCC and NFC. The development of a novel resistivity apparatus and tests
were conducted for the first time on all samples using an expedient method and the results
were similar with that of the commonly used but restrictive four-point probe method. The
PPy@NFC/PVA nanocomposite showed significant improvement in electrical
conductivity and mechanical properties when compared with neat PPy/PVA composites
and exhibited slightly improved performance when compared to the dialysed
nanocellulose composite, PPy@NCC/PVA, at the same ratio. This was due to the dialysisfree
synthesis process allowing the residual hydrolysis acid to act as a doping agent for
the synthesized PPy, endowing PPy@NFC nanohybrid with improved electrical
conductivity. Dialysis is a time-consuming step during acid hydrolysis, and this study
investigated the both the effect of products formed and their electrical properties with and
without the dialysis step. It was found that the nanohybrid synthesized from bacterial
nanocellulose in a dialysis-free step, showed a resistivity of 2.341 Ω/m that has an
improved resistivity result compared to the nanohybrid prepared from bacterial cellulose
that was dialysed which was 2.928 Ω/m; a lower resistance value allows for greater
conductance. The nanohybrid made from nanocellulose sourced from Whatman filter
paper, that was not subjected to dialysis gave a better resistivity of 2.287 Ω/m as compared
to the nanohybrid from the nanocellulose subjected to dialysis, which was 4.954 Ω/m. The
dialysis-free hardwood pulp nanohybrid produced a nanohybrid with a resistance of 6.515
Ω/m and the dialysed gave a resistance of 8.402 Ω/m which had the greatest opposition of
the flow of current through the material. When the samples were viewed under a
microscope before and after being subjected to an applied voltage, the samples retained
their integrity and could be re-used several times. This work conclusively demonstrated
that by capitalizing on the physiognomies of nanocellulose not subjected to dialysis, its
unique traits can be further exploited for useful applications. By avoiding the costly and
laborious dialysis step, one could easily utilize the residual acid as a doping agent that
contributed to the desired conductance required. The straightforward and sustainability of
this dialysis-free and in-situ doping synthesis of the PPy@NFC nanohybrid should
facilitate in a significant way the scalable fabrication and application of nanocellulose
based conductive nanocomposites with high performance.
Description
Master’s degree. University of KwaZulu-Natal, Durban.