Carbohydrate Polymers 273 (2021) 118593
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Carbohydrate Polymers
journal homepage: www.elsevier.com/locate/carbpol
Green electrospinning of chitin propionate to manufacture nanofiber mats
Tuhua Zhong a, b, 1, Wangcheng Liu b, 1, Hang Liu b, c, *
a
Institute of New Bamboo and Rattan Based Biomaterials, International Center for Bamboo and Rattan, Beijing 100102, China
Composite Materials and Engineering Center, Washington State University, Pullman, WA 99164, USA
c
Apparel, Merchandising, Design and Textiles, Washington State University, Pullman, WA 99164, USA
b
A R T I C L E I N F O
A B S T R A C T
Keywords:
Chitin propionate
Ethanol/water
Electrospinning
Nanofiber
Filtration
Chitin is the second most abundant biopolymer after cellulose in nature, and it is currently under-utilized
partially because of its insolubility in common solvents. Herein, chitin was propionylated to improve its disso­
lution in green solvents, i.e., ethanol and water, and manufactured nanofibers and nonwoven mats via elec­
trospinning with poly(ethylene oxide) (PEO) as a co-spinning aid. Polymer solution viscosity, electrospun CP/
PEO fiber morphology, mechanical, thermal, dynamic thermal, and surface contact angle of nanofiber mats were
evaluated. Results showed that fibers with CP content up to 97% could be produced. The electrospun CP/PEO
nanofiber mats exhibited good mechanical strength, thermal stability, and hydrophobicity with water contact
angles up to 133◦ . Filtration test of separating carbon nanofibers and carbon nanotubes from water demonstrated
the potential use of the CP/PEO nanofiber mats in fluid filtration of fibrous pollutants.
1. Introduction
Land and ocean pollution resulting from non-biodegradable petro­
leum-based products has become increasingly severe. Therefore, natu­
rally produced biopolymers for sustainable products have drawn
considerable attention. Among biopolymers, cellulose and chitin are the
two most abundant polymers. Chitin can be extracted from food wastes,
such as the shells of shrimp, crab, and lobster. Compared to cellulose,
chitin is under-researched and under-utilized. Part of the reason is that
its insolvability in commonly used organic solvents poses challenges in
processing. Existing research has been focusing on extracting nanofibers
from chitin via either mechanical or chemical techniques. Chitin nano­
fibers can disperse in water and have a length from several nanometers
to several microns, depending on the manufacturing methods. They
have remarkable features, such as high specific surface area, high
strength and modulus, low density, low coefficient of thermal expan­
sion, biodegradability, biocompatibility, and low immunogenicity (Ding
et al., 2014). They can be used as reinforcement or functional fillers in
composites, coatings, and cosmetics, or can be applied as drug delivery
systems, tissue engineering scaffolds, etc. (Ding et al., 2014; Fan et al.,
2008; Ifuku, 2014; Ifuku & Saimoto, 2012; Zhong et al., 2019).
Although very limited, there are a few reports on processing chitin
into manufactured continuous fibers (Barber, Griggs, Bonner, & Rogers,
2013; Barber, Griggs, Gurau, et al., 2013; Min et al., 2004; Zhang &
Rolandi, 2017). These fibers have a considerably larger length to width
ratio than chitin fibers directly extracted from shells and are suitable to
be further processed into nonwoven mats, fabrics, and 3D objects for a
broader range of applications (Azimi et al., 2020; Ponnamma et al.,
2019; Xue et al., 2019). Chemicals, including 1,1,1,3,3,3-hexafluoro-2propanol (HFIP) and 1-ethyl-3-methylimidazolium acetate, have been
applied to dissolve chitin for fiber spinning in these studies. These sol­
vents are either toxic or expensive, limiting the applications of the
manufactured fibers or hindering industry adoption. Xin et al. (2021)
produced a water-soluble chitin derivative by carboxymethylation and
then manufactured composite nanofibrous mats with polyvinyl alcohol
as an electrospinning aid and organic rectorite as the functional filler.
The product demonstrated good cell compatibility. However, little has
been reported when chitin or chitin derivatives dissolving in less-toxic
common organic solvents (i.e., ethanol) for electrospinning.
Previous research on using propionic anhydride to treat chitin to
obtain chitin propionate (CP) found that CP is soluble in a mixture of
ethanol and water (Zhong et al., 2020). These two solvents are inex­
pensive, non-toxic, and easy to recycle. This finding has opened doors
for processing chitin in a green fashion for a variety of products,
including sustainable package film and coating applications. In this
study, we processed chitin propionate into nanofiber mats via
* Corresponding author at: Apparel, Merchandising, Design and Textiles, Washington State University, Pullman, WA 99164, USA.
E-mail address: hangliu@wsu.edu (H. Liu).
1
Tuhua Zhong and Wangcheng Liu contributed equally to this work.
https://doi.org/10.1016/j.carbpol.2021.118593
Received 16 June 2021; Received in revised form 4 August 2021; Accepted 18 August 2021
Available online 21 August 2021
0144-8617/© 2021 Elsevier Ltd. All rights reserved.
T. Zhong et al.
Carbohydrate Polymers 273 (2021) 118593
electrospinning using ethanol/water as the solvents, which has not been
reported previously. Electrospinning is one of the most commonly used
methods to produce continuous nanofibers and has been extensively
exploited due to its versatility and easy spinning parameter adjustment
(Ago et al., 2012; Baji et al., 2010; Dobosz et al., 2017). High specific
surface area, excellent mechanical strength, great potential for func­
tionalization, and high porosity are advantages of nanofiber mats, which
may have great potential in filtration applications (Deitzel et al., 2001;
Lu et al., 2006; Matthews et al., 2002; Veleirinho & Lopes-da-Silva,
2009).
CP has a rigid pyranose ring structure, and its ethanol/water solution
has low viscosity; therefore, it is not spinnable by itself (Saquing et al.,
2013). In this study, PEO was used as a processing aid to blend with CP
for fiber spinning. The hypothesis is that CP can be successfully spun into
nanofibers using ethanol/water as the solvent and a small amount of
PEO as the spinning aid. To test the hypothesis, various CP and PEO
ratios were experimented to investigate the influence of the two com­
ponents on fiber properties and the maximum amount of CP that could
be obtained in a fiber. Fiber diameter, morphology, and the mechanical,
thermal, thermomechanical, and surface wettability of the nanofiber
mats were evaluated. Given the biodegradability, biocompatibility, nontoxic solvents used, and the advantages of nanofibers, the obtained CP/
PEO nanofiber mats should have great potential for biomaterial appli­
cations and as sustainable alternatives to non-biodegradable petroleumbased products in filtration. A simple filtration test was carried out to
demonstrate a potential application of the nanofiber mats.
and 0.75%), and flow rates (0.3, 0.6, and 0.9 mL/h), were experimented
to study their influences on fiber properties. Samples were labeled as
CPa/PEOb/FRc, with a, b, and c representing the levels. Pure 0.85% PEO
solution was used for electrospinning to produce nonwoven mats as a
control, labeled as Pure PEO. All fiber samples were conditioned in a
well-vented chamber at room temperature overnight and stored in a
desiccator before characterization.
2.4. Formulation viscosity measurement
Viscosities of the spinning formulations were determined using a
universal viscometer (DV-E viscometer, AMETEK Brookfield) at 25 ◦ C.
The shearing rate was 0.5 RPM, and the spindle model was S18. The
measurements were performed in triplicate.
2.5. Scanning electron microscopy (SEM) characterization
Morphology of the electrospun CP/PEO fibers and fiber nonwoven
mats before and after filtration for CNF suspension and CNT suspension
was observed with a Quanta 200F scanning electron microscope (SEM,
FEI, USA) at 20 kV. Before SEM observation, all samples were coated
with platinum. Fiber average diameter and standard deviation were
obtained by measuring the diameters of sixty fibers using ImageJ.
2.6. Water contact angle measurement
2. Materials and methods
The nonwoven mats' water contact angles were measured with a VCA
Optima Video Contact Angle System (AST Products Co., USA). The water
contact angles were recorded at the fourth second after the water droplet
contacted the sample surface. The measurements were performed in
triplicate.
2.1. Materials
Chitin from shrimp shell (powder, practical grade), propionic an­
hydride (97%), perchloric acid (ACS reagent, 70%), PEO (MW:
5,000,000 g/mol), carbon nanofibers (CNF, diameter: 100nm, length:
20–200 μm) and carbon nanotubes (CNT, outer diameter: 10 ± 1 nm,
inner diameter: 4.5 ± 0.5 nm, and length: 3–6 μm) were purchased from
Sigma-Aldrich. Glacial acetic acid (ACS reagent) was purchased from
EMD Millipore Corporation. Ethanol (200 proof, anhydrous) was pur­
chased from Decon Labs, Inc. Surfactant Tween 80 (polyethylene sor­
bitol ester) was from Acros Organics.
2.7. Tensile test
Tensile strength, elongation, and modulus of fiber mats were eval­
uated on a universal testing machine (Instron 5565, USA) equipped with
a 100 N load cell. Samples were 40 mm in length and 10 mm in width.
The grip distance was 1.5 cm, and the crosshead speed was 1.5 cm/min
(100% extension per minute). Six replications for each sample were
measured. The testing was performed under 21 ◦ C. The fiber mat crosssection area was determined using Eq. (1)
2.2. Chitin propionate (CP) preparation
Chitin propionate was prepared following the method described in
previous work (Zhong et al., 2020). Briefly, chitin powder was treated
by propionic anhydride as an acylation agent in the presence of catalyst
perchloric acid. The reaction took place at 0 ◦ C for 0.5 h and then at
room temperature for 2.5 h. After that, the reaction was quenched by
adding diluted acetic acid followed by water to precipitate insoluble
chitin propionate. Chitin propionate was washed with water and then
dried at 70 ◦ C overnight.
A=
m
L×p
(1)
where A is the cross-section area (mm2), m is the specimen mass (mg), p
is the theoretical density of the mat based on the composition (mg/
mm3), and L is the specimen length (mm).
2.8. Thermogravimetric analysis (TGA)
2.3. Fabrication of electrospun CP/PEO fibers mats and sample labeling
Thermal stability of nanofiber mats was performed using TGA
(Mettler Toledo TGA/DSC 1, Switzerland) in a nitrogen atmosphere
from room temperature to 600 ◦ C with a heating rate of 10 ◦ C/min. All
specimens were stored in a desiccator for 12 h prior to testing.
PEO was dissolved in a mixture of ethanol and water (90/10%w/w)
at 50 ◦ C overnight to ensure complete dissolution. Subsequently, chitin
propionate was added to the PEO solution and stirred until no undis­
solved chitin propionate was observed. To maintain the stability of the
chitin propionate/PEO solution, 2% acetic acid was added.
Electrospinning was carried out with a system consisting of a high
voltage supplier (Gamma high voltage), a syringe pump (Fusion 100T),
and a grounded aluminum foil fiber collector. The polymer solution was
transferred into a 6-mL syringe equipped with a 22-gauge needle. The
voltage used for spinning was 12 kV, and the distance from the fiber
collector to the nozzle tip was 10 cm. The combinations of different CP
concentration (5%, 7%, and 9%), PEO concentration (0%, 0.25%, 0.5%,
2.9. Dynamic mechanical analysis (DMA)
Thermomechanical analysis of nanofiber mats was performed using a
DMA machine (TA Q800, USA) with tension testing mode from 30to
200◦ C at a ramp rate of 3 ◦ C/min. The strain was set at 0.05%, and the
dynamic frequency was 1.0 Hz. The size of the nanofiber mats was 24
mm in length and 8 mm in width. Solvent-cast CP/PEO films were
prepared for comparison to the nanofiber mats.
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Carbohydrate Polymers 273 (2021) 118593
2.10. Filtration property evaluation
spinning. Chain entanglements have been acknowledged to play a sig­
nificant role in fiber formation during polymer electrospinning. The
extent of chain entanglements is governed by polymer molecular
weight, polymer solution concentration, and polymer structure (Gupta
& Wilkes, 2003; Kenawy et al., 2003; Nie et al., 2009; Saquing et al.,
2013; Shenoy et al., 2005). In our previous work, the intrinsic viscosity
of CP was measured and estimated as 15-fold lower than that of chitin
(chitin molecular weight of around 310 KDa), indicating the molecular
weight was significantly decreased after propionylation (Zhong et al.,
2020). The flexible PEO molecular chains plus the high molecular
weight of PEO (5,000,000 g/mol) played a significant role in improving
the spinnability of CP. Twelve solutions with CP concentrations of 5, 7,
and 9% and PEO concentrations of 0, 0.25, 0.5, and 0.75% were pre­
pared, and their viscosity is shown in Table 1. Pure CP solutions had
viscosities from 67 mPa⋅s to 1291 mPa⋅s. With PEO, the CP/PEO solution
viscosities ranged from 204 mPa⋅s to 5012 mPa⋅s. Fibers produced from
some of these solutions are shown in Fig. 2b–f. The spinning process for
most of the CP/PEO solutions was smooth, yielding uniform fibers.
When PEO concentration increased to 0.75%, ribbon-like fibers were
frequently seen in the mats as the solution became too viscous.
Fig. 3 displays nanofiber diameters spun from various formulations
at different solution flow rates during spinning (i.e., 0.3, 0.6, and 0.9
mL/h). The fiber diameters were from 0.6 μm to 1.2 μm. Increased PEO
content generally resulted in larger fiber diameters, so did the increased
flow rate. Electrospinning with the lowest PEO concentration (0.25%) at
0.3 mL/h flow rate generated fibers with the smallest diameter of
approximately 0.6 μm regardless of the CP concentrations. In the
following study, the flow rate of 0.3 mL/h was chosen to produce
nanofiber mats for characterizing mechanical and thermal properties,
surface wettability, and filtration efficiency.
The filtration efficiency of the nanofiber mats separating CNF and
CNT from water was evaluated using a Buchner funnel connected with a
filter flask. Nanofiber mats were cut and placed onto a Buchner funnel,
then the CNF or CNT suspensions were forced to pass through the mat
under reduced pressure by a vacuum pump. Before filtration, 0.01 wt%
of CNF and CNT were well dispersed in water with surfactant poly­
ethylene sorbitol ester under sonication for 1 h.
3. Results and discussion
3.1. Dissolution of chitin propionate in ethanol and water mixture
CP could not be dissolved in 100% ethanol or pure water, but its
dissolution in ethanol was considerably enhanced by adding 10–30wt%
water. As shown in Fig. 1, a clear solution was obtained when CP was
dissolved in ethanol/water (90/10%w/w). Similar dissolution behavior
of polymers bearing ester groups in a mixture of ethanol and water has
also been reported by Hoogenboom et al. (2009) and Zhang and Hoo­
genboom (2015). One possible explanation for this phenomenon is that
water molecules and the carbonyls of ester groups form hydration shells,
which then interact with ethanol molecules. This leads to the solubility
maxima in the mixture of ethanol and water, as schematically depicted
in Fig. 1. There is no doubt that ethanol and water would be ideal sol­
vents for solution electrospinning of chitin derivatives because ethanol
is cheaper and less toxic than other organic solvents that are commonly
used to dissolve natural polymers and their derivatives, such as DMF,
DMAc, DMC, and chloroform (Jayakumar et al., 2010; Lee et al., 2009).
3.2. Formulation viscosity, fiber diameter, and morphology
3.3. Mechanical properties
The addition of PEO largely improved the spinnability of CP. The CP
molecular chains do not create sufficient entanglement in the solution
for fiber processing due to their low molecular weight and molecular
chain rigidity. Pure CP did not form a continuous polymer jet for fibers
during spinning but particles (Fig. 2a). Even in a small amount (e.g.,
0.25%), the addition of PEO could increase the molecular chain in­
teractions between PEO-PEO and PEO-CP to the extent of successful
Table 2 summarizes the tensile modulus, strength, and elongation at
break of several nanofiber mats, and Fig. 4 exhibits the typical stressstrain curves of these mats. The electrospun nanofiber mats from pure
PEO exhibited a ductile behavior. Comparatively, the CP/PEO nanofiber
mats were much more rigid with significantly enhanced modulus and
reduced elongation due to the rigid nature of CP. The CP/PEO mats
Fig. 1. Scheme of potential interactions of chitin propionate with ethanol/water (inset: 5% chitin propionate in ethanol/water (9/1%w/w) mixture).
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Carbohydrate Polymers 273 (2021) 118593
Fig. 2. SEM images of the morphology of electrospun CP/PEO fibers.
Table 1
The viscosity of various electrospinning formulations.
Table 2
Tensile properties of electrospun CP/PEO mats.
Sample code
PEO (w%)
CP (w%)
CP:PEO ratio
Viscosity (mPa⋅s)
CP9/PEO0
CP7/PEO0
CP5/PEO0
CP9/PEO0.25
CP7/PEO0.25
CP5/PEO0.25
CP9/PEO0.5
CP7/PEO0.5
CP5/PEO0.5
CP9/PEO0.75
CP7/PEO0.75
CP5/PEO0.75
0
9
7
5
9
7
5
9
7
5
9
7
5
100:0
1291 ± 32
201 ± 10
66.5 ± 6.6
1902 ± 71
502 ± 40
204 ± 8.8
2803 ± 193
918 ± 27
410 ± 45
5012 ± 206
2012 ± 96
916 ± 54
0.25
0.5
0.75
36:1
28:1
20:1
18:1
14:1
10:1
12:1
9.3:1
6.7:1
Sample
Modulus
(MPa)
Maximum strength
(MPa)
Elongation at break
(%)
Pure PEO
CP5/
PEO0.75
CP5/
PEO0.25
CP7/
PEO0.25
CP9/
PEO0.25
55.2 ± 11.8
124.8 ± 21.7
10.0 ± 1.1
12.2 ± 1.9
73.4 ± 4.2
11.1 ± 2.0
138.7 ± 19.7
12.1 ± 0.6
10.5 ± 0.8
147.7 ± 15.5
11.7 ± 1.1
11.4 ± 0.8
121.7 ± 11.3
7.2 ± 1.0
8.9 ± 1.0
Fig. 4. Typical stress-strain curves of nanofiber mats.
Fig. 3. Diameters of electrospun CP/PEO fibers.
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Carbohydrate Polymers 273 (2021) 118593
showed an amorphous structure because the crystalline structure of
chitin was destroyed after propionylation (Fig. S1). The elongation of
the nanofiber mats containing CP was between approximately 9% and
11%, while pure PEO was 73%. The moduli of mats with CP increased
from 55MPa for pure PEO to 122 MPa or higher. With 5% and 7% of CP
added to 0.25 and 0.75% PEO (resulting in fibers with CP/PEO ratio
between 6.7 and 28), the average maximum strength of the mats
improved to approximately 12 MPa from 10 MPa. When the CP amount
was further increased to 9% in 0.25% PEO (CP/PEO = 36), the mat
displayed reduced modulus, maximum strength, and elongation. The
flexible and long chains of PEO in the CP/PEO functioned as the “car­
rier” to facilitate the entanglement of CP chains. Such enhancing effect
in chain entanglement decreased when the CP to PEO ratio reached such
a high level. In this study, the electrospun CP/PEO fibrous mats
exhibited comparable strength and modulus compared with synthetic or
natural polymer nanofiber mats reported in the literature. For instance,
the electrospun chitin fiber mat had a tensile strength of about 14 MPa as
reported by Jung et al. (2018), similar to our CP5/PEO0.75and CP5/
PEO0.25; that for rubber/polycaprolactone was 9.2 MPa (Maccaferri
et al., 2020).
spun from β-chitin without propionylation modification (8◦ ) and
β-chitin/PEO nanofiber mat (41◦ ) (Jung et al., 2018). The propionyl
modification of chitin increased its surface hydrophobicity in this study,
and this will broaden its applications to where a hydrophobic surface is
required.
3.5. Thermal and dynamic mechanical properties
Thermal properties of two nanofiber mats containing the lowest CP:
PEO ratio (6.7:1) and the highest CP:PEO ratio (36:1), i.e., CP5/PEO0.75
and CP9/PEO0.25, were investigated. The starting materials PEO and CP
were characterized as controls. The thermogravimetric (TG) and deriv­
ative thermogravimetric (DTG) curves are displayed in Fig. 6. CP5/
PEO0.75 sample exhibited three distinct stages of mass loss. The first
stage at around 190 ◦ C–200 ◦ C was due to the degradation of the pro­
pionyl side groups on CP molecules, the second stage was between
200 ◦ C and 350 ◦ C for CP backbone degradation, and the third stage at
around 350 ◦ C–450 ◦ C was attributed to the PEO degradation. For the
CP9/PEO0.25 sample with the highest CP content in this study, the first
two degradation stages were the same as those of the CP5/PEO0.75
samples, but the third stage was not evident. This was attributed to a low
PEO content in this fiber mat and the homogenous blending of PEO in
the CP matrix. The FTIR analysis showed the spectra of the CP/PEO
nanofiber mats were similar to that of the pure CP (Fig. S2). No char­
acteristic bands assigned to PEO were reflected on these spectra. This
might be because the low content of PEO in the composite mats could
not be detected by FTIR with low sensitivity. There was no weight loss
below 150 ◦ C observed in the nanofiber mats, which indicated no sol­
vent (i.e., ethanol, water, and acetic acid) was left in the samples. The
high ethanol fraction in the solvent mixture (90%) used in this study is
highly desirable for electrospinning because ethanol has a low boiling
point (78 ◦ C) that promotes fast evaporation under ambient conditions.
The thermal results also indicated that the electrospun CP/PEO nano­
fiber mat did not start to decompose until around 180 ◦ C, and the
temperature is adequate for most applications in biomaterials and
filtration. The char residue yielded at 550 ◦ C for nanofiber mats was
consistent with their CP and PEO composition in the fibers. Pure PEO
showed a very low char residue of 2.7 wt%, much lower than neat CP
(23.8 wt%). CP9/PEO0.25 fiber mats containing a small amount of PEO
had very similar high char residue of 22.8 wt% to that of neat CP, but the
CP5/PEO0.75 fiber mats had less char residue of 18.0 wt%.
Dynamic mechanical properties of the CP9/PEO0.25 and CP5/
PEO0.75 samples were also assessed to evaluate their viscoelastic
behavior as a function of temperature. The storage modulus (E′ ) and loss
tangent (tanδ) curves between 30 ◦ C to 200 ◦ C are displayed in Fig. 6c.
The dynamic mechanical properties of a solvent-cast CP5/PEO0.75 solid
film are shown in Fig. S3. It is interesting to note the general slightly
upward storage modulus with increased temperature for the nanofiber
mats, which was distinct from the general downward trend of solid
polymer films. The storage modulus slightly decreased as the tempera­
ture rose to 65 ◦ C and then increased for the CP5/PEO0.75 sample. The
decrease in modulus at around 65 ◦ C was mainly ascribed to the melting
of crystalline PEO. Above 65 ◦ C, an increased modulus was observed.
This may be likely due to the molten PEO-induced physical cross-linking
of fibers and fiber mat densification (Cho et al., 2018; Sughanthy et al.,
2020). The CP9/PEO0.25 sample did not show a decrease in storage
modulus at 65 ◦ C because of the low PEO content.
It is important to point out that the storage modulus of the CP9/
PEO0.25 nanofiber mat did not dramatically alter until about 170 ◦ C.
The tanδ is often used to determine the occurrence of molecular mobility
transition and the glass transition temperature (Tg) of a material (Gru­
nert & Winter, 2002). However, as observed from Fig. 6c, the integral
tanδ peak was not obtained, indicating that CP/PEO0.25 nanofiber mat
started to decompose at around 180 ◦ C before reaching the Tg point. In
the previous TGA testing, we also observed an early decomposition
behavior of CP starting at about 180 ◦ C. As for the CP5/PEO0.75 sample,
3.4. Surface wettability
Fig. 5 compares the water contact angles of different nanofiber mats
and the corresponding water droplet photographs at the fourth second
following the waterdrop's initial contact with the mat. Hydrophobicity
or water-resistance is of great importance for some potential end uses,
including biomaterials, membranes for liquid filtration, and layered
composites (Arrieta et al., 2016; Cui et al., 2008). The results showed
that the CP/PEO nanofiber mats were hydrophobic with water contact
angles between 95◦ to 133◦ , much higher than pure PEO mats (39◦ ). The
higher the CP-to-PEO ratios, the larger the angles. PEO is highly hy­
drophilic, and the physical structure of PEO mats is less stable and may
be damaged when in contact with water (Greiner & Wendorff, 2007;
Korehei & Kadla, 2014). However, due to the hydrophobic nature of CP
and its relatively large content in the fibers, the addition of PEO did not
affect the mat's water repellency. The lotus effect resulting from the
porous structure of the nanofiber mats further contributed to the high
contact angle, as evidenced by the higher water contact angle of CP/PEO
mats than pure CP film (75◦ ) (Mikaeili & Gouma, 2018). Compared to
those in the literature, the contact angle of CP9/PEO0.25 nanofiber mat
(133◦ ) was close to that of poly (D,L-lactide) (PDLLA) nanofiber mat
(132◦ ) and substantially higher than superhydrophilic nanofiber mats
Fig. 5. Water contact angles and photographs of the water drop on the
mat surface.
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Carbohydrate Polymers 273 (2021) 118593
Fig. 6. TGA (a) and DTG (b) curves of PEO, CP, electrospun CP5/PEO0.75 and CP9/PEO0.25 nanofiber mats; (c) storage modulus and tanδ of CP5/PEO0.75 and
CP9/PEO0.25 nanofiber mats.
the dramatic decrease in modulus occurred at a lower temperature due
to the high content of PEO. As discussed previously, PEO melted at
around 65 ◦ C, facilitating the CP chain movement or thermal
decomposition. Overall, the DMA results demonstrated that the CP/PEO
nanofiber mats were capable of maintaining a decent mechanical elas­
ticity against heat distortion at a temperature of 150 ◦ C or lower. This
Fig. 7. (a) Filtration process for separating CNF from water, (b) the photographs of the obtained filtrates after filtration.
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Carbohydrate Polymers 273 (2021) 118593
robust and stable thermomechanical performance makes the mats suit­
able for applications such as filters involving hot liquid. Therefore, the
CP/PEO nanofiber mats displayed an advantage over some synthetic
hydrophobic biopolymers, such as polycaprolactone and poly(lactic)
acid, both of which exhibited a dramatic decline of elasticity at
55 ◦ C–75 ◦ C due to melting or state transition from glass state to a
rubbery state (Cacciotti et al., 2014; Ji et al., 2014).
efficiency will be evaluated. The integrity of the nanofiber structure was
well maintained (Fig. 8c and e–f) after the fluid filtration under applied
pressure, indicating the good mechanical robustness of the CP/PEO
nanofiber mat for water filtration and separation applications.
4. Conclusions
Chitin propionate was successfully electrospun into nanofibers with
the aid of PEO in small amounts using ethanol/water as the solvent. The
hypothesis was validated. The fiber morphology and fiber diameter
could be controlled by varying the spinning parameters, including
polymer solution concentration, polymer mixing ratio, and spinning
flow rates. The resulting electrospun nanofiber mats showed good me­
chanical and thermal properties and improved water hydrophobicity
and water stability. The nanofiber mat exhibited effective filtration and
separation of CNF from water but relatively less efficient blocking CNT.
The result demonstrated the applicability of the electrospun CP/PEO
nanofiber mat in fluid filtration and separation of certain nanomaterials.
This study provided a promising electrospinning approach using bio­
based component chitin propionate and non-toxic solvents ethanol and
water to produce electrospun nanofiber mats, which will have broad
potential applications as biomaterial and filters.
3.6. Filtration property evaluation
Two distinct carbon nanomaterials, CNF and CNT, were used as
model pollutants to evaluate the filtration efficiency of the CP5/
PEO0.25 nanofiber mats used as filters. Fig. 7a shows the filtration
process. As shown in Fig. 7b, a clear filtrate was collected after passing
the CNF suspension through the nanofiber mat once, indicating high
filtration efficiency and effective separation of the suspended CNF from
water. The filtration mechanism behind the electrospun nanofiber mat is
often attributed mainly to physical sieving effects because of the com­
plex arrangement of nanofibers in the mat (Lv et al., 2018; Veleirinho &
Lopes-da-Silva, 2009). As shown in Fig. 8a, randomly oriented nano­
fibers in the mat interlaid, forming a network structure. After the
filtration of CNF suspension through the CP/PEO nanofiber mat, most
CNFs were deposited on the top surface of the mat or entrapped inside
the complex network as the bottom of the mat was clean (Fig. 8b–c). The
larger diameter and high aspect ratio of CNF also increased the filtration
efficiency compared to CNT, as evidenced by the visual photograph of
CNT filtrate in Fig. 7b and the SEM images in Fig. 8e–f. Some CNT
escaped with water, so the filtrate was not as clear as that of CNF. The
bottom of the mat was attached with some CNT. The discrepancy in char
residues was observed when comparing the TGA curves of the mats after
CNF and CNT filtration (Fig. S4). The char residue for the mats used for
CNF filtration (approximately 50%) was much higher than that after
CNT filtration (about 20%), indicating much more CNF was intercepted
by the mats compared to CNT. The char residue for the mats before and
after CNT filtration was almost the same (Figs. 6a and S4), suggesting
that the mats were much less effective in blocking CNT. In future work,
the structure of mats still needs to be further improved to make it more
suited to small-sized pollutant blocking and more quantitative filtration
Funding
This research did not receive any specific grant from funding
agencies in the public, commercial, or not-for-profit sectors.
CRediT authorship contribution statement
Tuhua Zhong: Conceptualization, Methodology, Validation, Formal
analysis, Writing – original draft, Writing – review & editing, Visuali­
zation. Wangcheng Liu: Conceptualization, Methodology, Validation,
Formal analysis, Writing – original draft, Visualization. Hang Liu:
Conceptualization, Methodology, Writing – review & editing, Supervi­
sion, Project administration, Funding acquisition.
Fig. 8. SEM images of (a) the CP5/PEO0.25 nanofiber mat surface before filtration, (b) the top-side mat surface, (c) the bottom-side mat surface after the CNF
filtration, (d) the top-side mat surface, and (e–f) the bottom-side mat surface after CNT filtration.
7
T. Zhong et al.
Carbohydrate Polymers 273 (2021) 118593
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Appendix A. Supplementary data
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org/10.1016/j.carbpol.2021.118593.
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