Properties of cellulose nanofibers and their sheets prepared from recycled pulp fiber

概要

（別紙様式 14）
2020年

8月 21日

論文の内容の要約
氏

名

Aminah Balfas

学位の種類

博士（農学）

学府又は研究科・専攻

連合農学研究科 環境資源共生科学専攻

指導を受けた大学

東京農工大学

学位論文名

Properties of Cellulose Nanofibers and their Sheets Prepared
from Recycled Pulp Fiber

【論文の内容の要約】
In this thesis, I have stated my overall opinion about the properties of cellulose
nanofibers and their sheets prepared from recycled pulp fiber, supported by
experimental results from investigation of the morphology, crystal and molecular
structures of cellulose nanofibers (CNFs), and mechanical properties and wettability of
their sheets.
In Chapter 1, I review the biorefining and cascading concepts in the materials
field, aimed at achieving an environmentally conscious society. Furthermore, the
applications and resources of CNF have been described. This study was targeted at the
production of CNF from recycled pulp fiber, investigation of its properties, and
comparison of its sheets with sheets from CNF from virgin pulp fiber, using the aqueous
counter collision (ACC) method.
In Chapter 2, I describe the treatment of virgin pulp fiber and recycled pulp
fiber by the ACC method to produce CNFs. The morphology of these CNFs was observed
by optical and transmission electron microscopy. The width of the CNFs produced from
the recycled pulp fiber, treated by repeated wetting and drying, was less than 100 nm.
The widths of CNFs prepared from the recycled pulp fiber at 30 and 60 passes
(processing cycles) were 14 ± 4 nm and 9.6 ± 3 nm, respectively. Fourier transform
infrared spectroscopic spectra of freeze-dried samples prepared from the virgin and
recycled pulp fibers were measured. The spectra of both samples after ACC treatment
under the same number of collisions had almost identical shapes. This result indicates
that the molecular structure of CNF from the recycled pulp fiber is almost identical to
that derived from the virgin pulp fiber. The X-ray diffraction (XRD) profile was
measured to characterize the crystal structure of the cellulosic material and compare
the structural changes between the CNFs prepared from the recycled and virgin pulp

fibers. The XRD patterns of both CNF samples showed peaks around 2θ = 16° and 23°,
indicating typical cellulose I crystals. This is the same crystal structure as that of the
initial pulp fibers. In other words, ACC treatment did not result in transformation to
other types of crystalline cellulose allomorphs. The crystallinity was found to be 82%
and 80% for CNFs from virgin pulp fiber and recycled pulp fiber, respectively. These
results indicated that the crystal structure of CNF prepared from the recycled pulp fiber
was not different from that of CNF from the virgin pulp fiber. These results indicate
that recycled pulp fiber can be used as a raw material for CNFs. Furthermore, these
results suggest that the structure of CNFs inside the pulp fiber is not broken even after
changes in the structure of the pulp fiber from the wetting and drying processes during
recycling.
In Chapter 3, I describe the measurement of drainage of the CNF suspension
and mechanical properties of the CNF sheet. The drainage could be estimated by the
filtration time of the CNF suspension. The filtration time for the CNF suspension from
the recycled pulp fiber was lower than that for the CNF suspension from the virgin pulp
fiber prepared under the same number of passes in the ACC method. The CNF sheet
was prepared with 60 g/m2 basis weight using filter paper. After obtaining a wet sheet
from filter paper, we used a press machine according to ISO 5269-1, in which the first
press was at a pressure of 0.3 MPa for 5 min and the second press was at a pressure of
0.3 MPa for 2 min. Finally, the sheet was dried using a hot press at a temperature of
105 °C for 10 min under a pointer pressure of 10 MPa. The mechanical properties were
measured based on ISO 1924-2, with specimens having a width and length of 1 cm and 5
cm, respectively. Then, the tensile strength, elongation at break, and elastic modulus of
the CNF sheets were measured based on ISO 1924-2. The examinations were carried
out using more than 15 specimens. After 30 passes, the CNF sheet from the recycled
pulp fiber showed not only a higher tensile index than the sheet from the recycled pulp
fiber without drying, which was used as a reference, but also the same tensile index as
the sheet from virgin pulp fiber at 30 passes despite its low density. Therefore, the CNF
from recycled pulp fiber used as a component of a sheet was useful from the viewpoint of
the cascading process in biorefineries.
In Chapter 4, I describe the estimation of the wettability of the CNF sheets.
Wettability is a property related to the spread of liquids on the substrate surface and
penetration into a substrate. The most common method of assessing wettability is
measuring the contact angle between the liquid and the substrate surface. A 1 L drop
of deionized water was placed on the CNF sheet and images were obtained every 1 s in a
10 second time frame using the DMs-401 (Kyowa Interface Science, Inc., Japan) at a

temperature of 23 °C and relative humidity of 50% to estimate the water contact angle.
To determine the surface free energy of the CNF sheet, water and methylene iodide
were used. The water and methylene iodide contact angles of the CNF sheets from the
recycled pulp fiber were almost the same as those of the CNF sheets from the virgin
pulp fiber. These liquids could not penetrate the CNF sheets from the recycled and
virgin pulp fibers. Then, the polar components of the solid surface free energy (γSp) and
the dispersion component of the solid surface free energy (γSd) were calculated. These
surface free energies were the same between the CNF sheets from the recycled pulp
fiber and the virgin pulp fiber. Therefore, the CNF sheet wettability from the recycled
pulp fiber corresponded to that of the CNF from the virgin pulp fiber.
In Chapter 5, I summarize the possibility of producing CNFs from recycled
pulp fiber by the ACC method. Some properties of the CNFs and their sheets are
identical to or better than those of the virgin pulp fiber. Finally, it is expected that the
use of recycled pulp fiber as a raw material for CNFs will be promising for applications
in biorefineries.