polymers
Article
Preparation, Structure, and Properties of Silk Fabric
Grafted with 2-Hydroxypropyl Methacrylate Using
the HRP Biocatalyzed ATRP Method
Jinqiu Yang, Shenzhou Lu
ID
, Tieling Xing *
ID
and Guoqiang Chen
National Engineering Laboratory for Modern Silk, Soochow University, Suzhou 215123, China;
yjq8440@163.com (J.Y.); lushenzhou@suda.edu.cn (S.L.); chenguojiang@suda.edu.cn (G.C.)
* Correspondence: xingtieling@suda.edu.cn; Tel.: +86-512-6706-1175
Received: 13 April 2018; Accepted: 19 May 2018; Published: 21 May 2018
Abstract: Atom transfer radical polymerization (ATRP) is a “living”/controlled radical polymerization,
which is also used for surface grafting of various materials including textiles. However, the commonly
used metal complex catalyst, CuBr, is mildly toxic and results in unwanted color for textiles. In order to
replace the transition metal catalyst of surface-initiated ATRP, the possibility of HRP biocatalyst was
investigated in this work. 2-hydroxypropyl methacrylate (HPMA) was grafted onto the surface of silk
fabric using the horseradish peroxidase (HRP) biocatalyzed ATRP method, which is used to improve the
crease resistance of silk fabric. The structure of grafted silk fabric was characterized by Fourier transform
infrared spectrum, X-ray photoelectron spectroscopy, thermogravimetic analysis, and scanning electron
microscopy. The results showed that HPMA was successfully grafted onto silk fabric. Compared with
the control silk sample, the wrinkle recovery property of grafted silk fabric was greatly improved,
especially the wet crease recovery property. However, the whiteness, breaking strength, and moisture
regain of grafted silk fabric decreased somewhat. The present work provides a novel, biocatalyzed,
environmentally friendly ATRP method to obtain functional silk fabric, which is favorable for clothing
application and has potential for medical materials.
Keywords: horseradish peroxidase; atom transfer radical polymerization; bio-catalysis; silk
1. Introduction
Silk is a natural protein fiber. It is widely used in the textile field because of its outstanding mechanical
strength, wear comfortability, and elegant luster, which has been praised as the queen of fibers [1–3].
However, silk has some shortcomings, such as bad crease recovery property and photo-yellowing
stability [4–6]. Silk is very easy to wrinkle during wearing, especially after sweating or washing.
This shortage seriously affects the utilization of silk and limits its application scope. In recently years,
high-quality and functional silk has be prepared to improve the performance of the end products and
satisfy the specific requirements with vinyl monomers using the grafting technique [7,8]. Silk fabric
can be grafted with vinyl monomer by conventional radical polymerization through various chemical
initiators or by irradiation, and the controlled/living radical polymerization process (CRP). Atom transfer
free radical polymerization (ATRP) is the most widely used CRP method [9].The ATRP method is
used in mild reaction conditions, which provide well-defined polymers and show high tolerance for
monomer structures with a variety of functional groups [10–13]. Surface-initiated ATRP has been
applied in materials to provide their wettability, wrinkle resistance, anti-bacterial property, and flame
retardancy, etc. Teramoto [14] prepared cellulose diacetate-graft-poly(lactic acid)s (CDA-g-PLAs) through
ATRP, and the thermal characteristics of cellulose diacetatewaereimproved. Kang [15] synthesized ethyl
cellulose-graft-poly(2-hydroxyethyl methacrylate) (EC-graft-PHEMA) copolymers using the ATRP in
Polymers 2018, 10, 557; doi:10.3390/polym10050557
www.mdpi.com/journal/polymers
Polymers 2018, 10, x FOR PEER REVIEW
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Polymers 2018, 10, 557of
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characteristics
cellulose diacetatewaereimproved. Kang [15] synthesized ethyl
cellulose-graft-poly(2-hydroxyethyl methacrylate) (EC-graft-PHEMA) copolymers using the ATRP
in methanol to improve the hydrophilic property of ethyl cellulose. Xing [16] prepared
methanol to improve the hydrophilic property of ethyl cellulose. Xing [16] prepared multi-functional silk
multi-functional silk with flame retardancy and antibacterial properties using flame retardant
with flame retardancy and antibacterial properties using flame retardant dimethyl methacryloyloxyethyl
dimethyl methacryloyloxyethyl phosphate (DMMEP) as the first monomer and dimethylaminoethyl
phosphate (DMMEP) as the first monomer and dimethylaminoethyl methacrylate (DMAEMA) as the
methacrylate (DMAEMA) as the second monomer using the ATRP method.
second monomer using the ATRP method.
However, a major disadvantage of the ATRP method is the usage of the transition metal
However, a major disadvantage of the ATRP method is the usage of the transition metal complex
complex catalyst, which is usually used inrelatively large amounts. The commonly used metal
catalyst, which is usually used inrelatively large amounts. The commonly used metal catalyst, CuBr,
catalyst, CuBr, is mildly toxic and renders ATRP environmentally unfavorable. The copper ion
is mildly toxic and renders ATRP environmentally unfavorable. The copper ion residuals are difficult to
residuals are difficult to remove from the polymer materials and hinder the application of the
remove from the polymer materials and hinder the application of the resulting polymers in biomedical
resulting polymers in biomedical and food fields [17,18]. Meanwhile, the colored catalyst is easy to
and food fields [17,18]. Meanwhile, the colored catalyst is easy to stain the grafted materials and
stain the grafted materials and results in the unwanted color for textiles.
results in the unwanted color for textiles.
Enzymes can be an alternative to the transition metal catalyst because of their non-toxicity and
Enzymes can be an alternative to the transition metal catalyst because of their non-toxicity
eco-friendly nature [8,19]. A lot of enzymes have catalytic active sites comprising metal ions like
and eco-friendly nature [8,19]. A lot of enzymes have catalytic active sites comprising metal ions
peroxidase. Horseradish peroxidase (HRP; EC1.11.1.7) is a kind of heme protein, containing active
like peroxidase. Horseradish peroxidase (HRP; EC1.11.1.7) is a kind of heme protein, containing
sites on the ferric protoporphyrin ring. Recently, HRP-catalyzed ATRP has been used for the
active sites on the ferric protoporphyrin ring. Recently, HRP-catalyzed ATRP has been used for the
synthesis of polymers. Sigget al. [20] catalyzed N-isopropyl-acrylamide using activators generated
synthesis of polymers. Sigget al. [20] catalyzed N-isopropyl-acrylamide using activators generated
by electron transfer for the ATRP (ARGET ATRP) method using HRP. This method allows an ATRP
by electron transfer for the ATRP (ARGET ATRP) method using HRP. This method allows an ATRP
process to be conducted with a tiny amount of transition metal catalyst in thepresence of excess
process to be conducted with a tiny amount of transition metal catalyst in thepresence of excess
reducing agent such as ascorbic acid, which could effectively scavenge and remove dissolved
reducing agent such as ascorbic acid, which could effectively scavenge and remove dissolved oxygen
oxygen from the polymerization system. Renggli [21] obtained a protein cage nano reactor using
from the polymerization system. Renggli [21] obtained a protein cage nano reactor using HRP as
HRP as biocatalyst, which was further polymerized with an acrylate. These works provided the
biocatalyst, which was further polymerized with an acrylate. These works provided the foundation
foundation for HRPcatalyzed grafting using the surface-initiated ATRP method.
for HRPcatalyzed grafting using the surface-initiated ATRP method.
The active group of HRP contains a ferric protoporphyrin structure to catalyze ATRP, which is
The active group of HRP contains a ferric protoporphyrin structure to catalyze ATRP, which is
equivalent to the CuBr/ligand metal complex catalyst. The schematic of silk fabric grafted with
equivalent to the CuBr/ligand metal complex catalyst. The schematic of silk fabric grafted with
monomers using the HRP-catalyzed ATRP method is shown in Figure 1.
monomers using the HRP-catalyzed ATRP method is shown in Figure 1.
Figure 1. Schematic
grafted
with
monomers
usingusing
HRP HRP
biocatalytic
ATRP (M
= vinyl
Figure
Schematicofofsilk
silk
grafted
with
monomers
biocatalytic
ATRP
(M monomer,
= vinyl
Mn = polymer
repeat units,
NaAsc
sodiumunits
ascorbate,
DHA== dehydroascorbic
acid).
monomer,
Mwith
n = npolymer
with
n =repeat
, NaAsc
sodium ascorbate,
DHA =
dehydroascorbic acid).
In this work, HRP was used as biocatalyst for the ATRP grafting of 2-hydroxypropyl methacrylate
In
work,
HRPtowas
used the
as wrinkle
biocatalyst
for the
ATRP
grafting
of 2-hydroxypropyl
(HPMA)this
on silk
surface
improve
resistance
of silk
fabric.
Sodiumascorbate
(NaAsc)
methacrylate
(HPMA)
on
silk
surface
to
improve
the
wrinkle
resistance
silk fabric.
with higher water solubility than ascorbic acid was used as the reducing agent inofARGET
ATRP.
Sodiumascorbate
with
higher
water
solubility
thaninvestigated.
ascorbic acid was used as the reducing
The structure and(NaAsc)
properties
of the
grafted
silk
fabric were
agent in ARGET ATRP. The structure and properties of the grafted silk fabric were investigated.
2. Materials and Methods
2. Materials and Methods
2.1. Materials and Reagents
2.1. Materials
and Reagents
Degummed
silk fabric, with a 36 g/m2 density, was purchased from Suzhou Huajia Silk Group.
2-Hydroxypropyl
methacrylate
purchased
from Macklin.
Triethylamine
(TEA)
and
Degummed silk
fabric, with (HPMA)
a 36 g/m2was
density,
was purchased
from Suzhou
Huajia Silk
Group.
tetrahydrofuran (THF)
were distilled
under
pressure
use.Triethylamine
Horseradish (TEA)
peroxidase
2-Hydroxypropyl
methacrylate
(HPMA)
wasreduced
purchased
from before
Macklin.
and
tetrahydrofuran (THF) were distilled under reduced pressure before use. Horseradish peroxidase
Polymers 2018, 10, 557
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(HRP; EC1.11.1.7) was supplied by Aladdin Reagent and stored at −20 ◦ C. All other reagents in this
study were used without further purification.
2.2. Preparation of the Silk Macroinitiator
The silk fabric (1 g) reacted with 2-bromoisobutyryl bromide (BriB-Br) (2.22 mL) in the presence
ofTEA (1.23 mL) and 4-(dimethylamino) pyridine (DMAP, 0.5 g). The mixture was stirred at 10 ◦ C for
1 h, then warmed up to 50 ◦ C for 24 h. The silk sample was thoroughly washed with water and finally
dried at 60 ◦ C in vacuum oven [10,15]. Thus, the silk-Br macroinitiator was prepared.
2.3. Surface-Initiated ATRP
2.3.1. HRP-Mediated Grafting of HPMA on Silk Fabric’s Surfaces
The silk-Br macroinitiator (1 g) was incubated with 50 mL of phosphate buffer (1/15 M, pH 8.0),
containing a certain volume of monomer (HPMA), L-sodiumascorbate (NaAsc), and HRP in a 100 mL
round-bottom flask ([HPMA] = 0.16 mol/L, [HRP] = 0.027 mmol/L, n(HRP):n(NaAsc) = 1:150).
Then, the flask was evacuated and filled with nitrogen for three times. The mixture was vibrated in the
water bath at 60 ◦ C for certain time (Sample b: 8 h, Sample c: 16 h, Sample d: 24 h). Then, HRP catalyzed
silk-grafted-poly(HPMA) (HC-silk-g-PHPMA) sample was obtained and washed with methyl alcohol
and water, and finally dried at room temperature under vacuum to a constant weight.
2.3.2. CuBr-Mediated Grafting of HPMA on Silk Fabric’s Surfaces
The silk-Br macroinitiator (1 g) was immersed into a reaction mixture containing certain HPMA,
CuBr/PMDETA(N,N,N0 ,N00 ,N00 -pentamethyldiethylenetriamine), and 50 mL of deionized water in a 100 mL
round-bottom flask ([HPMA] = 0.24 mol/L, [CuBr] = 0.16 mmol/L, n(PMDETA):n(CuBr) = 2:1). After sealing
it with a polytetrafluoroethylene three-way stopcock, the flask was evacuated and flushed with nitrogen,
which was repeated three times. The mixture was placed in water bath and polymerized under oscillation
at 80 ◦ C for 6 h. The sample was rinsed with dilutedhydrochloric acid to remove the blue color caused
by CuBr, and then washed with acetylacetone/ethanol (volume ration: 1/5) and water, and dried under
a vacuum oven. Thus, CuBr/PMDETA catalyzed silk-grafted-poly(HPMA) (CC-silk-g-PHPMA) sample
was obtained.
2.3.3. Grafting Yield Calculation
Grafting yield was calculated as follows:
Grafting yield (%) =
w2 − w1
× 100
w1
(1)
in which w1 and w2 denote the weight of the control silk and the PHPMA grafted silk fabric, respectively.
2.4. Characterization and Measurements
2.4.1. Fourier Transform Infrared (FT-IR) Analysis
The FTIR spectra were recorded using a Nicolet5700 FTIR (Nicolet Co., Madison, WI, USA).
The scan range was from 4000 to 400 cm−1 .
2.4.2. X-ray Diffraction (XRD) Analysis
XRD patterns were obtained at a scanning rate of 1◦ /min using an X’Pert PRO MPD diffractometer
(Holland Panalytical, Almelo, Holland). The voltage and current of the X-ray source were 40 kV and
30 mA, respectively.
Polymers 2018, 10, 557
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2.4.3. X-ray Photoelectron Spectroscopy (XPS) Analysis
X-ray photoelectron spectroscopy (XPS) was carried out on a Thermo ESCALAB 250 X-ray
photoelectron spectroscopy(Thermo Fisher Scientific, Waltham, MA, USA) using Al Ka (1486.6 eV)
excitatior with pass energy of 20 eV at a reduced power of 150 W. The samples were attached to the
spectrometer probe with double-sided adhesive tape, and the X-ray beam was 500 µm.
2.4.4. Thermal Properties
Thermogravimetic analysis (TGA) measurements were performed on a Diamond 5700 thermal
analyzer at a heating rate of 10 ◦ C/min with a temperature range from 40 to 600 ◦ C. The open
aluminum cell was swept with N2 during the analysis.
2.4.5. Scanning Electron Microscopy (SEM) Analysis
Morphology of the silk samples was observed at 3.00 k magnification by a Hitachi TM3030
Desktop SEM (Hitachi TM3030, Hitachi Ltd., Tokyo, Japan) at an acceleration voltage of 3 kV under
vacuum condition. The samples were mounted on a conductive adhesive tape and coated with gold
before testing.
2.4.6. Crease-Resistant Recovery and Physical Properties Measurement
The wrinkle recovery angle of the fabric was measured according to AATCC66-2003 (Wrinkle
Recovery of Woven Fabric: Recovery Angle). Each result was the average of six measurements.
The tensile strength of the fabric was tested by an Instron 3365 Universal Testing Machine (IllinoisTool
Works Inc., High Wycombe, Buckinghamshire, UK) according to ISO 13934-1-2013. The sample was
cut into the size of 30 cm × 5 cm and the average value was obtained after 5 times tests. The whiteness
of silk fabric was measured by WSD III whiteness instrument (Wenzhou Darong Textile Instrument
Co., Ltd., Wenzhou, China), and the result was the average of eight measurements. Moisture regain
(MR) was evaluated in the standard conditions at 20 ◦ C and 65% relative humidity (RH) (ISO 2060:
Determination of moisture content and moisture regain of textile-oven-drying method, 1994).MR was
calculated according to the following equation:
MR (%) =
m1 − m0
× 100
m0
(2)
in which m0 is weight of dried fabric, and m1 is weight of moist fabric.
3. Results and Discussion
3.1. Fourier Transform Infrared (FTIR)Spectra and X-ray Diffraction (XRD) Curves
Figure 2 shows the FTIR spectra and XRD curves of the silk samples before and after grafting.
The FTIR spectra (Figure 2A) of the silk all show the characteristic absorption peaks of silk fibroin
including amide IυC=O 1726 cm−1 , amide IIδN-H 1623 cm−1 , and amide IIIυC-N 1260 cm−1 . Compared
with the control silk fabric, additional peak appeared at 1726 cm−1 for HC-silk-g-PHPMA, which is
characteristic absorption peak of carbonyl stretching vibration of ester, indicating that the HPMA
monomers were successfully grafted onto silk fabric.XRD patterns are analyzed as shown in Figure 2B.
It could be seen that control silk fabric and the grafted silk fabric all exhibited a major X-ray diffraction
peak at 20.5◦ , which is characteristic peak of silk with highly ordered β-structure [4]. The position and
intensity of the major X-ray diffraction peak did not change regardless of the grafting. That is to say,
the grafting has no effect on the crystalline region of silk fibers, and it is also reasonable to assume that
the grafting is not harsh and causes no damage to the crystalline region of silk fibers.
Polymers 2018, 10, 557
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esterνc=o amideⅡδN-H
20.5°
Polymers1726
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FOR PEER REVIEW
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d
20.5°
dc
Intensity Intensity
Transmittance
Transmittance
esterνc=o amideⅡδN-H
1520
1726
cb
ba
a
1260
amide ⅢνC-N
1623
amideⅠνc=o
1800
1600
1623
amideⅠνc=o
1800
d
c
d
b
ca
b
1400
1200
1000
-1
Wavenumbers
/cm
1260
a
800
10
20
amide(A)
ⅢνC-N
1600
2θ/°
30
40
(B)
1400
1200
1000
800
10
20
30
40
-1
Figure 2.FTIR Wavenumbers
spectra (A) /cm
and
XRD curves (B) of (a) the control silk
fabric, (b) 15.62% of
2θ/°
Figure 2. FTIR spectra (A) and XRD curves (B) of (a) the control silk fabric, (b) 15.62% of
HC-silk-g-PHPMA, (c)
(A)29.01% of HC-silk-g-PHPMA, and (d) 38.87% of HC-silk-g-PHPMA.
(B)
HC-silk-g-PHPMA, (c) 29.01% of HC-silk-g-PHPMA, and (d) 38.87% of HC-silk-g-PHPMA.
Figure 2.FTIR spectra (A) and XRD curves (B) of (a) the control silk fabric, (b) 15.62% of
HC-silk-g-PHPMA, (c) 29.01% of HC-silk-g-PHPMA, and (d) 38.87% of HC-silk-g-PHPMA.
3.2. X-ray Photoelectron Spectroscopy (XPS)
3.2. X-ray Photoelectron Spectroscopy (XPS)
The XPS C1s spectra of silk fabric are shown in Figure 3. The C1s spectrum of the control silk
3.2.
X-ray
Photoelectron
Spectroscopy
(XPS)
fabric
contains
three distinct
at are
284.5
(C–C),in286.0
(C–OH/C–N),
and
288.1 eV of
(N–C=O)
[22], silk
The
XPS
C1s spectra
of silkpeaks
fabric
shown
Figure
3. The C1s
spectrum
the control
while
the
C1s
spectrum
of
HC-silk-g-PHPMA
contains
three
distinct
peaks
at
284.5
(C–C),
286.3
fabric contains
three
peaks
at 284.5
(C–C), in
286.0
(C–OH/C–N),
and 288.1
eVcontrol
(N–C=O)
The XPS
C1s distinct
spectra of
silk fabric
are shown
Figure
3. The C1s spectrum
of the
silk [22],
(C–OH),
and
288.6 eV
(O–C=O).
The C–OH contains
(286.3 eV)three
and O–C=O
(288.6
eV)
mainly
originated
from
whilefabric
the C1s
spectrum
of
HC-silk-g-PHPMA
distinct
peaks
at
284.5
(C–C),
286.3
(C–OH),
contains three distinct peaks at 284.5 (C–C), 286.0 (C–OH/C–N), and 288.1 eV (N–C=O) [22],
the hydroxyl and ether of HPMA. Table 1 liststhe carbon-to-nitrogen (C/N) ratio of silk fabric, which
while the
spectrum
of HC-silk-g-PHPMA
three distinct
at 284.5 originated
(C–C), 286.3 from
and 288.6
eV C1s
(O–C=O).
The
C–OH (286.3 eV)contains
and O–C=O
(288.6 peaks
eV) mainly
increased after grafting with HPMA. Less N element content was detected for the grafted silk
(C–OH), and
288.6
eV (O–C=O).
TheTable
C–OH1(286.3
eV) carbon-to-nitrogen
and O–C=O (288.6 eV)(C/N)
mainly originated
from
the hydroxyl
and
ether
of HPMA.
liststhe
ratio of silk
fabric,
sample compared with the control silk fabric. The reason was that the surface of the grafted silk
theincreased
hydroxyl and
ether
of HPMA.
Table
1 liststhe
carbon-to-nitrogen
(C/N)
ratio
of silk fabric,
which
which
after
grafting
with
HPMA.
Less
N
element
content
was
detected
for
the
grafted
fabric was covered by PHPMA polymer, which mainly contains C, O, and H elements. N element
increased
after grafting
with
HPMA. Less
N element
content
was
detected
for the
silk silk
silk sample
compared
the control
fabric.
Themonomers
reason
was
that
the surface
ofgrafted
theonto
grafted
was weakened
afterwith
grafting,
further silk
indicating
that
were
successfully
grafted
the
sample compared with the control silk fabric. The reason was that the surface of the grafted silk
fabricsilk
was
covered
PHPMA
polymer,
which mainly contains C, O, and H elements. N element
fabric
using by
HRP
biocatalytic
ATRP method.
fabric was covered by PHPMA polymer, which mainly contains C, O, and H elements. N element
was weakened after grafting, further indicating that monomers were successfully grafted onto the silk
was weakened
after grafting, further indicating that monomers
were successfully grafted onto the
8000
8000
b
a
fabricsilk
using
HRP
biocatalytic
ATRP
method.
BE/eV FWHM/eV
%
BE/
eV FWHM/eV
%
fabric
using
HRP
biocatalytic
ATRP
method.
C-C
4000
6000
1.21
1.20
1.17
69.3
20.0
10.7
BE/ eV FWHM/eV %
C-C
284.5 1.21
69.3
C-OH/C-N 286.0 1.20
20.0
N-C=O
288.1 1.17
10.7
a
C-C
C-OH
N-C=O
2000
4000
C-OH
20000
N-C=O
290
6000
8000
Counts / sCounts / s
Counts / s Counts / s
6000
8000
C-C
284.5
C-OH/C-N 286.0
N-C=O
288.1
288
286
284
Binding energy / eV
282
4000
6000
C-C
284.5
C-OH 286.3
O-C=O 288.6
1.21
1.28
1.02
BE/eV FWHM/eV
C-C
284.5
1.21
C-OH 286.3
1.28
O-C=O 288.6
1.02
71.2
23.5
5.3
C-C
%
71.2
23.5
5.3
C-C
b
C-OH
2000
4000
O-C=O
C-OH
20000
290
O-C=O
288
286
284
282
Binding energy / eV
0
0
Figure
3.The curve
fitting
analysis
of C1s
spectra of (a)
the
control
silk fabric
and284
(b) 38.87%
290
288
286
282
290
288
286
284
282
Binding energy / eV
Binding energy / eV
ofHC-silk-g-PHPMA.
Figure 3.The curve fitting analysis of C1s spectra of (a) the control silk fabric and (b) 38.87%
Table
1. curve
The element
weight of
percent
of (a) ofthe
control
silk silk
fabric
and
Figure
3. The
fitting analysis
C1s spectra
(a) the
control
fabric
and(b)(b)38.87%
38.87% of
ofHC-silk-g-PHPMA.
ofHC-silk-g-PHPMA.
HC-silk-g-PHPMA.
Table 1. The element weight percent Element
of (a) content/%
the control silk fabric and (b) 38.87%
sample
C/N
TableofHC-silk-g-PHPMA.
1. The element Silk
weight
percent of (a)Cthe controlOsilk fabric and
N (b) 38.87% ofHC-silk-g-PHPMA.
Control
silk-g-PHPMA
Silk sample
Silk Sample
Control
silk-g-PHPMA
Control
silk-g-PHPMA
69.98
24.08
5.94
Element content/%
71.20Element
26.31
Content/%2.49
C
O
N
C69.98
O
24.08
5.94 N
71.20
26.31
2.49 5.94
69.98
24.08
71.20
26.31
2.49
11.78
28.59
C/N
C/N
11.78
28.59 11.78
28.59
Polymers 2018, 10, 557
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3.3. Thermal
Properties
Polymers
2018, 10, x FOR PEER REVIEW
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Figure
4 shows
the TG (A) and DTG (B) curves of the silk fabric. It can be seen from Figure 4A that
3.3. Thermal
Properties
Polymers 2018,
x FOR
PEER REVIEW
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the evaporation
of10,
the
absorbed
moisture caused slight weight loss of silk fabric when temperature
was
Figure
4 shows the TG (A) and DTG (B) curves of the silk fabric. It can be seen from Figure 4A
◦
less than
200
The
weight loss ratio of the control silk fabric was 32.5% when the weight loss rate
that
theC.evaporation
3.3.
Thermal
Properties of the absorbed moisture caused slight weight loss of silk fabric when
◦ C, which could be attributed to the decomposition of silk fabric into
reachedtemperature
its highestwas
point
320200
lessatthan
°C. The weight loss ratio of the control silk fabric was 32.5% when the
Figure 4 shows the TG (A) and DTG (B) curves of the silk fabric. It can be seen from Figure 4A
weight loss
rate reached
highest
point
320 °C, which could
be attributed
to the decomposition
small molecules
including
COits
and
H2 O.
Theatdecomposition
process
of the grafted
silk fabric contained
that the evaporation of 2the absorbed
moisture caused slight weight loss of silk◦ fabric when
of
silk
fabric
into
small
molecules
including
CO
2
and
H
2
O.
The
decomposition
process
of and
the grafted
two stages,
and thewas
weight
loss200
rate
its highest
the first
stagewas
33132.5%
C
second
temperature
less than
°C.reached
The weight
loss ratiopoint
of the at
control
silk fabric
when
the stage
silk fabric contained two stages, and the weight loss rate reached
its highest point at the first stage
◦
◦
410 C weight
(for 29.01%
of
HC-silk-g-PHPMA),
and
335
and
416
C
(for
38.87%
of
HC-silk-g-PHPMA),
loss rate reached its highest point at 320 °C, which could be attributed to the decomposition
331 °C and second stage 410 °C (for 29.01% of HC-silk-g-PHPMA),◦ and 335 and 416 °C(for 38.87% of
of silk From
fabric into
small
molecules
including
H2O.
The335
decomposition
process
of the grafted
respectively.
Figure
4B,
the peaks
at 331CO
(b,2 and
DTG)
and
C (c, DTG)
of HC-silk-g-PHPMA
in
HC-silk-g-PHPMA), respectively. From Figure 4B, the peaks at 331 (b, DTG) and 335 °C (c, DTG) of
silk
fabric
contained
two
stages,
and
the
weight
loss
rate
reached
its
highest
point
at
the
first
stage
the firstHC-silk-g-PHPMA
stage were caused
of silk
fibroin,
which corresponded
the peak at
in by
the the
firstdecomposition
stage were caused
by the
decomposition
of silk fibroin,towhich
331 °C and second stage 410 °C (for 29.01% of HC-silk-g-PHPMA), and 335 and 416 °C(for 38.87% of
320 ◦ C (a,
DTG) of control
silk at
fabric.
second
stage,
the
grafted
silk
fabricstage,
had the
additional
corresponded
to the peak
320 °CAt(a,the
DTG)
of control
silk
fabric.
At the
second
grafted peaks
HC-silk-g-PHPMA),
respectively. From Figure 4B, the peaks at 331 (b, DTG) and 335 °C (c, DTG) of
◦ C,
silk 416
fabric
had
additional
peaks
at 410 and
°C,decomposition
which can be explained
by the decomposition
of heated
at 410 and
which
can be
explained
by416
the
of poly(HPMA)
[23]. When
HC-silk-g-PHPMA in the first stage were caused by the decomposition of silk fibroin, which
◦
poly(HPMA)
[23].
When
heated
up
to
600
°C,
the
final
residual
of
the
control
silk
fabric
(28.5%)
was
up to 600
C, the final
residual
the°Ccontrol
silk
was
than stage,
that of
grafted silk
corresponded
to the
peak atof320
(a, DTG)
of fabric
control(28.5%)
silk fabric.
At more
the second
thethe
grafted
more than that of the grafted silk fabric (15.4%), which may be due to the decomposition of the
fabric (15.4%),
which
may
be
due
to
the
decomposition
of
the
poly-(HPMA)
into
small
molecules
such
silk fabric had additional peaks at 410 and 416 °C, which can be explained by the decomposition of
poly-(HPMA) into small molecules such as CO2 and H2O. This phenomenon further indicated the
poly(HPMA)
[23].
When
heated
up
to
600
°C,
the
final
residual
of
the
control
silk
fabric
(28.5%)
was
as CO2 and
H2 O.were
Thissuccessfully
phenomenon
further indicated the monomers were successfully grafted onto
monomers
grafted onto the silk fabric using HRP-catalyzed atom transfer radical
than
thatHRP-catalyzed
of the grafted silk
fabric
(15.4%),radical
which polymerization
may be due to themethod.
decomposition of the
the silk more
fabric
using
atom
transfer
polymerization method.
poly-(HPMA) into small molecules such as CO2 and H2O. This phenomenon further indicated the
monomers were successfully grafted onto the silk fabric using HRP-catalyzed atom transfer radical
100
polymerization method.
90
a
20
a
b
c
100
200
10
300
400
Temperature / ℃
500
200
Figure 4. TG
300
400
curves
(A) and
Temperature
/℃
ab
320
410
c
b
335
320
c
a
600
500
600
416
410
331
100
200
100
200
b
c
(A)
100
dW/ dt
dW/ dt
weight retention
weight/ %
retention / %
80
100
70
90
60
80
50
70
40
60
30
50
20
40
10
30
300335
400
416
Temperature /℃
500
600
500
600
331
(B)
300
400
DTG curves (B) of (a) the control Temperature
silk fabric,
/℃ (b) 29.01% of
Figure 4.
TG curves (A) and
DTG curves (B) of (a) the control silk fabric, (b) 29.01% of HC-silk-g-PHPMA,
HC-silk-g-PHPMA,
and
(A)(c) 38.87% of HC-silk-g-PHPMA.
(B)
and (c) 38.87% of HC-silk-g-PHPMA.
Figure 4.Electron
TG curves
(A) and
DTG curves (B) of (a) the control silk fabric, (b) 29.01% of
3.4. Scanning
Microscopy
(SEM)
HC-silk-g-PHPMA, and (c) 38.87% of HC-silk-g-PHPMA.
3.4. ScanningFigure
Electron
Microscopy
(SEM) of silk fabrics. The control silk fabric had a smooth and uniform
5 shows
the morphology
appearance
portraitMicroscopy
orientation.
The surfaces of the grafted silk fabric were covered with PHPMA
3.4.
ScanninginElectron
(SEM)
Figure 5 shows the morphology of silk fabrics. The control silk fabric had a smooth and uniform
and became tough. Moreover, the surfaces of the silk fabric were rougher as the grafting yield of the
Figure
5 shows the morphology
silk fabrics.
Thegrafted
control silk
hadwere
a smooth
and uniform
appearance
in portrait
The of
surfaces
of the
silkfabric
fabric
covered
with PHPMA
silk fabric
becameorientation.
higher.
appearance
in
portrait
orientation.
The
surfaces
of
the
grafted
silk
fabric
were
covered
with
PHPMA
and became tough. Moreover, the surfaces of the silk fabric were rougher as the grafting
yield of the
and became tough. Moreover, the surfaces of the silk fabric were rougher as the grafting yield of the
silk fabric became higher.
silk fabric became higher.
Figure 5. Cont.
Polymers 2018, 10, 557
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Polymers 2018, 10, x FOR PEER REVIEW
7 of 9
Figure 5.SEM images of (a) the control silk fabric, (b) 29.01% the HC-silk-g-PHPMA, and (c) 38.87% the
Figure
5. SEM images of (a) the control silk fabric, (b) 29.01% the HC-silk-g-PHPMA, and (c) 38.87%
HC-silk-g-PHPMA.
the HC-silk-g-PHPMA.
3.5. Crease-Resistant Recovery
3.5. Crease-Resistant
ComparedRecovery
with the control silk fabric, the crease-resistant recovery properties of the silk fabric
grafted with HPMA using HRP biocatalys is and metal complex catalysis method were both
Compared with the control silk fabric, the crease-resistant recovery properties of the silk fabric
improved (Table 2). With the increase of grafting yield, the dry crease recovery angle (DCRA) and
grafted wet
with crease
HPMArecovery
using HRP
biocatalys
andHC-silk-g-PHPMA
metal complex catalysis
bothand
improved
angle
(WCRA)is of
increasedmethod
up towere
18.41%
(Table 2).
With the increase ofcan
grafting
yield, to
thetwo
dryreasons:
crease(1)
recovery
angle (DCRA)
and wet
51.56%,respectively.This
be attributed
The copolymerization
reaction
of crease
and silkof
fabric
occurred in amorphous
areaup
of to
silk
fiber, and
which
weakenrespectively.
the hydrogenThis can
recoverymonomer
angle (WCRA)
HC-silk-g-PHPMA
increased
18.41%
51.56%,
bonding
in amorphous
areaThe
andcopolymerization
decreased the creep
deformation
and permanent
be attributed
to two
reasons: (1)
reaction
of monomer
and silkdeformation
fabric occurred in
caused by breaking up of hydrogen bonding; (2) The grafting copolymerization in amorphous area
amorphous area of silk fiber, which weaken the hydrogen bonding in amorphous area and decreased
limited relative slippage of silk macromolecules. Additionally, the WCRA of grafted silk fabric
the creep
deformation and permanent deformation caused by breaking up of hydrogen bonding;
increased higher than that of the DRCA, which is favorable for silk fabric easy to wrinkle at wet
(2) The grafting
in amorphous
area limited
relative
silkDCRA
macromolecules.
state. Thiscopolymerization
result can be attributed
to the occurrence
of grafting
underslippage
wet state.ofThe
and
Additionally,
theCC-silk-g-PHPMA
WCRA of grafted
silk the
fabric
higher
than that of the DRCA, which is
WCRA of
also have
sameincreased
increase trend
with HC-silk-g-PHPMA.
favorable for silk fabric easy to wrinkle at wet state. This result can be attributed to the occurrence of
Table 2.The CRA of silk fabric with different grafting yield under dry and wet conditions.
grafting under wet state. The DCRA and WCRA of CC-silk-g-PHPMA also have the same increase
Grafting samples
Grafting yield/%
DCRA/°
WCRA/°
trend with HC-silk-g-PHPMA.
0
201
128
15.62
220
168
Table 2. The CRA of silk fabric with different grafting yield under dry and wet conditions.
HC-silk-g-PHPMA
29.01
233
180
38.87
238
194
◦
Grafting Samples
Grafting
Yield/%
DCRA/
WCRA/◦ 195
CC-silk-g-PHPMA
37.82
229
3.6.Physical Properties
0
201
128
15.62
220
168
Compared
with control silk fabric, HC-silk-g-PHPMA
and233
CC-silk-g-PHPMA
HC-silk-g-PHPMA
29.01
180were somewhat
damaged in the whiteness index and breaking
strength
(Table
3).
For
HC-silk-g-PHPMA,
the
38.87
238
194
inactive enzymes adhered to the surface of silk fabrics reduced the whiteness of silk fabrics. For
CC-silk-g-PHPMA
37.82
229
195
CC-silk-g-PHPMA, the colored CuBr stained the silk fabric and also caused the decrease of
whiteness. The mechanical properties of fibers partly depend on the orientation of macromolecule.
After Properties
grafting with HPMA, the orientation of macromolecule of silk fiber was changed, and the
3.6. Physical
breaking strength decreased. The balance moisture regain of grafted silk fabrics reduced because the
Compared
with
control
fabric,
HC-silk-g-PHPMA
CC-silk-g-PHPMA
were somewhat
hydrophilic
groups
of silksilk
fabric
surface
were covered by the and
polymers.
The physical properties
of
damaged
in the whitenessand
index
and breaking strength
(Table 3).
HC-silk-g-PHPMA,
HC-silk-g-PHPMA
CC-silk-g-PHPMA
were basically
the For
same,
but the advantagetheofinactive
is the usage
of fabrics
HRP biocatalyst.
enzymesHC-silk-g-PHPMA
adhered to the surface
of silk
reduced the whiteness of silk fabrics. For CC-silk-g-PHPMA,
the colored CuBr stained the silk fabric and also caused the decrease of whiteness. The mechanical properties
of fibers partly depend on the orientation of macromolecule. After grafting with HPMA, the orientation of
macromolecule of silk fiber was changed, and the breaking strength decreased. The balance moisture regain
of grafted silk fabrics reduced because the hydrophilic groups of silk fabric surface were covered by the
polymers. The physical properties of HC-silk-g-PHPMA and CC-silk-g-PHPMA were basically the same,
but the advantage of HC-silk-g-PHPMA is the usage of HRP biocatalyst.
Polymers 2018, 10, 557
8 of 9
Table 3. Whiteness, breaking strength, and moisture regain of silk fabrics.
Grafting Samples
Grafting Yield/%
Whiteness/%
Breaking Strength/N
Moisture Regain/%
0
79.02
479.74
8.45
HC-silk-g-PHPMA
15.62
29.01
38.87
75.68
74.26
70.39
428.25
415.36
391.59
8.03
7.96
7.78
CC-silk-g-PHPMA
37.82
70.23
396.86
7.98
4. Conclusions
In conclusion, silk fabric was successfully grafted with 2-hydroxypropyl methacrylate (HPMA) using
the HRP-mediated ATRP method. The structure of control silk and grafted silk fabric was characterized
by Fourier transform infrared, XRD, XPS, TG, and SEM. The results indicated HPMA was grafted
onto the surface of silk fabric, and the copolymerization occurred in the amorphous region of silk fabric.
Compared with the control sample, the grafted silk fabric showed greatimprovement in the crease-resistant
recovery property, especially in the wet crease recovery angle. However, the whiteness, breaking
strength, and moisture regain of grafted silk fabric decreased.In comparison with HC-silk-g-PHPMA
and CC-silk-g-PHPMA, its properties were nearly the same, and the biocatalyst HRP was applied in the
preparation of HC-silk-g-PHPMA. Consequently, this work provides a biocatalyzed ATRP method with
which to obtain functionalsilk fabric, which might realize the potential application of the ATRP grafting
method in textile and medical materialsmodification.
Author Contributions: Tieling Xing and Guoqiang Chen conceived and designed the experiments; Jinqiu Yang
and Shenzhou Lu performed the experiments and analyzed the data; Jinqiu Yang and Tieling Xing wrote the
paper. All authors discussed the results and improved the final text of the paper.
Acknowledgments: The work is supported by NaturalScience Foundation of Jiangsu Province (BK20151242,
BK20171239), National Nature Science Foundationof China (51741301), the Six Talent Peaks Project of Jiangsu Province
(JNHB-066), and Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD).
Conflicts of Interest: The authors declare no conflict of interest.
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