Preparation and characterization of high-yield cellulose nanocrystals (CNCs) from softwood kraft pulp

B3 Non-refereed conference proceedings


Internal Authors/Editors


Publication Details

List of Authors: Anna Sundberg, Anders Strand, Weihua Zhang, Tiffany Abitbol
Place: Tokyo
Publication year: 2019
Book title: The 20th ISWFPC


Abstract


The
preparation of CNCs in yield higher than 50% from wood pulp is challenging and
requires fine tuning of the reaction conditions in order to avoid degradation
of cellulose but to remove hemicelluloses and traces of extractives found in
the original pulp.



The pulp
used was ECF-bleached softwood kraft pulp than contained about 26 wt-% easily
hydrolysable carbohydrates. The dry pulp was ground and freeze-dried to remove
all moisture. Batches of 10, 25, 35 and 40 g of freeze-dried pulp were weighed
into glass bottles, and 250 mL of cold 60 wt-% H2SO4 was
added to each bottle. The pulp suspension was shaken manually for 10 min at
room temperature in order to homogenize the mixture. The temperature of the
suspension did not increase, since the pulp was completely dry when the acid
was added. The glass bottle was sealed and placed in a 45°C water bath for 120
min under agitation. The hydrolysis was stopped after 120 min by diluting the
suspension ten-fold with distilled water. The following day, the cellulose
fractions were washed by centrifugation, and dialyzed against distilled water
for 4-5 days or until the pH of the dialysis water remained unchanged over the
course of a day. The CNCs were then disintegrated mechanically using a kitchen
blender and with a homogenizer. The disintegrated suspension was next filtered
through a 280 mesh polyamide fabric in order to remove any large fibre
fragments that may have remained intact.



The
yield of the 25 g batch was 61.4% and for the 35 g batch 65.3%, i.e. very close
to the theoretical maximum value of 74%, since the easily hydrolysable
carbohydrates should be removed during the hydrolyses. About 1% of xylose and
1% of mannose were detected in the resulting CNCs, and only traces of other
sugar units.



Dynamic
light scattering gave a z-average size of approximately 100 nm. The content of
sulfur was lower for the 10 g batch, about 0.35 %S, than for the 35 and 40 g
batch, about 0.7 %S. The zeta-potential was about -30 mV and the
electrophoretic mobility was approximately -2 µmcm/Vs. CP/MAS 13C-NMR
analysis gave a crystallinity of 53% compared to 55% for a commercial CNC
sample. The properties of the prepared CNC from softwood kraft pulp in high-yield
were similar to other CNCs.



It was also shown with flow
cytometry that CNCs prepared from softwood kraft pulp contained less
hydrophobic material than CNCs from hardwood kraft pulps.


Keywords

biomass yield, CNC, Flow cytometry, Nanocellulose


Documents


Last updated on 2020-01-04 at 09:15