Preparation and characterization of antibacterial films based on polyvinyl alcohol/quaternized cellulose

Article abstract of DOI:10.1016/j.reactfunctpolym.2016.02.012

Quaternized cellulose (YM) was homogeneously synthesized by grafting 3-chloro-2-hydroxypropyldodecyldimethylammonium groups onto cellulose molecules in a NaOH/urea aqueous solution. YM was blended with a poly(vinyl alcohol) (PVA) matrix to prepare composite films via co-regeneration from the alkaline solution. The PVA film and the blend films were characterized by Fourier transform infrared spectroscopy, X-ray diffraction measurements, thermogravimetric analysis, and scanning electron microscopy. Mechanical properties, water vapor barrier properties, light transmission, and antibacterial activity against Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria were also evaluated. The results reveal that PVA and YM in the composite films interacted by hydrogen bonding. Compared with pure PVA film, the PVA/YM blend films had higher tensile strength, higher thermostability, lower water permeability, and especially, higher antibacterial activity. The blend films exhibited good UV-shielding performance. Our study demonstrates a simple and efficient method for preparing a functional, environment-friendly composite film.

Full text of DOI:10.1016/j.reactfunctpolym.2016.02.012

Reactive and Functional Polymers 101 (2016) 90–98
Contents lists available at ScienceDirect
Reactive and Functional Polymers
journal homepage: www.elsevier.com/locate/react
Preparation and characterization of antibacterial films based on polyvinyl
alcohol/quaternized cellulose
Dongying Hu, Lijuan Wang ⁎
Key Laboratory of Bio-based Material Science and Technology of Ministry of Education, Northeast Forestry University, 26 Hexing Road, Harbin 150040, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 18 June 2015
Received in revised form 11 February 2016
Accepted 28 February 2016
Available online 2 March 2016
Quaternized cellulose (YM) was homogeneously synthesized by grafting 3-chloro-2-hydroxy-
propyldodecyldimethylammonium groups onto cellulose molecules in a NaOH/urea aqueous solution. YM was
blended with a poly(vinyl alcohol) (PVA) matrix to prepare composite films via co-regeneration from the alka-
line solution. The PVA film and the blend films were characterized by Fourier transform infrared spectroscopy,
X-ray diffraction measurements, thermogravimetric analysis, and scanning electron microscopy. Mechanical
properties, water vapor barrier properties, light transmission, and antibacterial activity against Gram-positive
Keywords:
(
Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria were also evaluated. The results reveal
Poly(vinyl alcohol)
Quaternized cellulose
Regenerated composite film
Antibacterial activity
Physical property
that PVA and YM in the composite films interacted by hydrogen bonding. Compared with pure PVA film, the
PVA/YM blend films had higher tensile strength, higher thermostability, lower water permeability, and especial-
ly, higher antibacterial activity. The blend films exhibited good UV-shielding performance. Our study demon-
strates a simple and efficient method for preparing a functional, environment-friendly composite film.
©
2016 Published by Elsevier B.V.
1
. Introduction
limited application in functional packaging because of their lack of anti-
bacterial activity. Thus, improving the antimicrobial activity of PVA-
based composite films is of importance.
The massive use of non-degradable plastic materials has caused seri-
ous “white pollution”. Many efforts have been made to develop
environment-friendly biomaterials to solve environmental problems
while reducing the dependence on petroleum-based fuel and products.
Cellulose, a natural polymer, has become an attractive solution to the in-
creasing demand for environment-friendly and biocompatible materials
The use of natural and synthetic antibacterial agents is considered as
a promising approach to control the growth of microorganisms [13]. An-
tibacterial agents include nanometal or metal oxides [14,15], antibiotics,
halogens [16], and essential oils from herbs and spices [17]. However,
there are several disadvantages associated with the use of these antibac-
terial agents. Use of nanometal or metal oxides, antibiotics, and halo-
gens can readily lead to secondary pollution. The antibacterial activity
of essential oils is transient because of their volatility. On the other
hand, quaternary ammonium compounds are widely used because of
their antibacterial properties, low toxicity, low cost, and environmental
compatibility [18]. They have recently been used to modify cellulose de-
rivatives used as bioadsorbents, flocculants, and gene carriers [19,20].
However, there are no reports on the incorporation of quaternized cel-
lulose (YM) in the preparation of antibacterial films with PVA as matrix.
In the present study, 3-chloro-2-hydroxypropyldodecyldimethylam-
monium chloride (YB) was synthesized through a reaction between
N,N-dimethyl-1-dodecylamine and epichlorohydrin (EH) in alkali/urea
aqueous solution. The obtained YB was used to modify cellulose for syn-
thesis of the quaternized cellulose (YM). The PVA/YM composite films
were regenerated from the alkali/urea aqueous solution. YM, PVA film,
and YM/PVA films were characterized by Fourier transfer infrared
[1,2]. Many works have intensively investigated materials from regener-
ated cellulose films because of their high mechanical strength, thermal
stability, biocompatibility, and nontoxicity [3–6]. However, pure regener-
ated cellulose films are highly hydrophilic, have poor barrier properties,
and lack antimicrobial activity. These characteristics have limited their
potential applications [7–9]. Chemical modification or combination with
other polymers effectively overcomes these problems.
Poly(vinyl alcohol) (PVA) is a highly biocompatible, nontoxic syn-
thetic polymer with high water solubility. It can be blended with other
natural polymers to produce biodegradable composites. It has promis-
ing industrial applications in many fields because of its film-forming,
emulsifying, and adhesive properties [10–12]. PVA films have remark-
able barrier properties due to their small, dense, and closely packed
monoclinic crystal structure. Cellulose is often used as reinforcement
filler for PVA. However, cellulose-reinforced PVA-based films have
(FTIR) spectroscopy, X-ray diffraction (XRD) measurements, thermogra-
vimetric analysis (TGA), scanning electron microscopy, tensile tests, oxy-
gen permeability (OP) measurements, water vapor permeability (WVP)
tests, and light-transmission measurements. Their activity against
⁎
Corresponding author.
E-mail address: donglinwlj@163.com (L. Wang).
http://dx.doi.org/10.1016/j.reactfunctpolym.2016.02.012
381-5148/© 2016 Published by Elsevier B.V.
1

D. Hu, L. Wang / Reactive and Functional Polymers 101 (2016) 90–98
91
solution of N,N-dimethyl-1-dodecylamine [21]. The mixture was stirred
at 60 °C for 2 h to obtain a highly viscous solution, and the residual EH
was removed by a procedure using vacuum–rotary evaporation. After
the product was cooled to room temperature, it was dissolved in ace-
tone (500 mL). Crystals began to separate in a few minutes. After the
mixture was stored for 8 h at 25 °C, it was filtered. The crystal-like prod-
ucts were washed with diethyl ether and then dried at 60 °C under vac-
uum for 24 h. The product obtained was labeled as YB. The yield was
7
6% which approximated to the yield of 77% in the reference [21]. The
reaction involved in this process is shown in Fig. 1. Results of its analysis
are given below:
Elemental analysis (YB, C17
2
H37Cl NO). Measured (%): N 4.14%, C
5
3
9.73%, H 10.86%; calculated (%): N 4.09%, C 59.65%, H 10.82%.
YB: H nuclear magnetic resonance spectrometer ( H NMR) (D
00 MHz): δ 0.75 (t, 3H, J = 3.75), 1.16 (q, 18H, J = 8.2), 1.57 (q, 2H,
Fig. 1. Synthetic reaction for the YB.
1
1
2
O,
Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia
coli) bacteria were also investigated.
J = 7.8), 3.20 (s, 6H), 3.45 (t, 2H, J = 4.8), 4.15 (d, 2H, J = 2.4), 6.18
(d, 2H, J = 8.4), 6.29 (q, 1H, J = 2.8).
2
. Materials and methods
2.2.2. Preparation of YM
A cellulose solution was prepared according to a previously reported
method [22]. Predetermined amounts of NaOH, urea, and distilled water
2
.1. Materials
(
7:12:81 by weight) were combined in a 100 mL beaker to obtain a so-
Microcrystalline cellulose (MCC, Comprecel M101; degree of poly-
merization (DP) = 200), was purchased from Shanghai Shenmei Phar-
maceutical Technology Co., Ltd. (Shanghai, China). PVA (average
lution. MCC (2 g) was dispersed in the NaOH/urea solution, which was
then cooled to −12.5 °C. The frozen mixture was then thawed and vig-
orously stirred for 5 min at ambient temperature to obtain a transparent
solution of 2 wt.% cellulose. A specified amount of YB was added to the
cellulose solution, and the mixture was stirred at 25 °C for 24 h. The
mole ratio of YB to anhydroglucose units in the cellulose molecules
was 6:1. The resulting solution of quaternized MCC derivative was sep-
arated into two parts. One was used to obtain the purified quaternized
MCC derivative (YM) [23] for further analysis. The other was stored at
0 °C for direct use in the preparation of YM/PVA blend films. The possi-
ble synthesis scheme of YM is shown in Fig. 2.
molecular weight M
hydrolysis = 88%) was purchased from Sinopec Shanghai Petrochemical
Co., Ltd. (Shanghai, China). N,N-Dimethyl-1-dodecylamine (C14 31N; 98%
pure; M = 213.4) was obtained from Heowns Chemical Reagent Co.
W
= 84,000–89,000; DP = 1700–1800; degree of
H
W
Ltd. (Tianjin, China). All other reagents and solvents were of analytical
grade and were used as received. The microorganisms used in this
study were obtained from Qingdao Hope Bio-Technology Co., Ltd.
(
Qingdao, China) and were stored at 4 °C before use. Biochemical re-
agents for the nutrient agar were purchased from AoBoXing Bio-tech
Co., Ltd. (Beijing, China).
2.2.3. Preparation of YM/PVA blend films
PVA was stirred into distilled water at 80 °C for 2 h to achieve a clear
PVA solution (8.80%). Specified amounts of PVA and YM solution were
mixed, and the resulting solution was stirred vigorously for 30 min.
After the solution was degassed in a vacuum oven, it was spread onto
a glass sheet to form a gel with a thickness of ~0.2 mm. The sheet was
2
2
.2. Preparation of blend films
.2.1. Preparation of YB
YB was synthesized from N,N-dimethyl-1-dodecylamine and EH. EH
solution (219 mL, 2.79 mol) was added dropwise to a 300 mL (1.11 mol)
immersed in a coagulation bath containing of 5 wt.% CaCl
2
and 3 wt.%
Fig. 2. Synthetic reactions for the YM.

92
D. Hu, L. Wang / Reactive and Functional Polymers 101 (2016) 90–98
Fig. 3. Process of preparation of the PVA/YM composite films.
HCl at 25 °C for 10 min to obtain regenerated YM/PVA blend films with
uniform thickness. The films were washed with running water and then
with deionized water. The wet films were then fixed onto a polyvinyl
chloride (PVC) sheet to prevent shrinkage and finally air-dried at
addition of YM solution. The preparation procedure for the blend films
is shown in Fig. 3.
2.3. Characterization
2
2
5 °C. The blend films, denoted as YMP-5, YMP-10, YMP-15, and YMP-
0, contained 5, 10, 15, and 20 wt.% YM, respectively. The control
FTIR spectra of the films were obtained on a Nicolet 6700 spectrome-
ter (Thermo Fisher Scientific Co., Ltd., MA, USA). Measurements were
(
PVA film) was obtained through the above process but without
Fig. 4. FTIR spectra of (a) YM, (b) PVA, (c) YMP-5, (d) YMP-10, (e) YMP-15, and (f) YMP-20. (b) N1s XPS spectra of YMP films.

D. Hu, L. Wang / Reactive and Functional Polymers 101 (2016) 90–98
93
Fig. 5. X-ray diffraction patterns of (a) MCC, quaternized MCC (YM), and (b) PVA, YM-5, YMP-10, YMP-15, and YM-20 films.
−
1
done in attenuated total reflection mode at a resolution of 4 cm in a
auto tensile tester (XLW-PC, Param, Jinan, China) equipped with a
500 N load cell. The film specimens had width and length of 10
and 150 mm, respectively. Light transmission through the blend
films (4 cm × 3 cm) was measured on an ultraviolet–visible (UV–vis)
spectrophotometer (UV-2600, Shimadzu, Kyoto, Japan) in the range of
800–200 nm.
−
1
range of wavenumber from 4000 to 700 cm . These films were dried
at 40 °C for 24 h and cut into 1 cm × 1 cm before the measurement. H
NMR spectrum was recorded on a spectrometer (AVANCE DRX-500,
Bruker, Germany), operating at 300 MHz. XRD patterns of the films
1
were obtained by using a D/max-2200 diffractometer (Cu-K
α
target,
40 kV, 30 mA) operated at 1200 W (Rigaku, Japan) with a scanning rate
of 5°/min and the scanning scope of 2θ (5–40°) at ambient temperature.
2.4. Antibacterial activity
The nitrogen content (N%) was measured on an element analyzer (EA
3
000, Arvator, Italy), and the valence state of nitrogen in the composite
Antimicrobial activities of the films were assessed by measuring the
inhibition zone around each disc of film. Bacteria were grown in nutri-
ent broth (NB) liquid medium at 37 °C for 12 h and further diluted to ob-
films was determined by using a K-Alpha X-ray photoelectron spectros-
copy (XPS) analyzer (Thermo Fisher Scientific Company, USA). The mor-
phology of the films was examined under a Quanta 200 scanning electron
microscope (Philips-FEI Co., AMS, The Netherlands) with an accelerating
voltage of 5 kV. Prior to the observation, the films were frozen in liquid
nitrogen and snapped immediately to prepare the sample of upper sur-
face and cross-sections, then, the samples were coated with a thin gold
layer. TGA of the films was carried out on a TA Instruments TGA Q500
8
tain a concentration of ~10 CFU/mL. Dilute suspensions (0.1 mL) of
E. coli and S. aureus were separately combined with nutrient agar (NA)
agar medium. Control films (PVA) and YMP films were used. The films
were cut into circular discs 8 mm in diameter, and were centrally placed
on the solid agar plates inoculated with the test bacteria. Each agar plate
was incubated at 37 °C for 24 h before examination for clear zones
around test materials. Clear zones are sites where bacterial growth
was inhibited. Three replicate tests were carried out under the same
conditions for each sample.
(TA Instruments, USA) with a heating rate of 10 °C/min in the tempera-
ture range from 30 °C to 600 °C and the nitrogen flow of 20 mL/min.
Brunauer–Emmett–Teller (BET) surface areas of samples were measured
by using a JW-BK132F instrument (JWGB Sci. & Tech. Co., Ltd., Beijing,
China). Films thicknesses were measured with an ID-C112XBS microme-
ter (Mitutoyo Corp., Tokyo, Japan) and reported as the average from ten
points. The OP and WVP of the films were determined at 30 °C by using
a Perme OX2/230 (Lab-think, Jinan, China) according to ASTM D3985-
2.5. Statistical analysis
Multiple samples were tested, and all data were reported are aver-
age values ± standard deviation. The statistical analysis was done by
one way analysis of variance (ANOVA) using SPSS software, and differ-
ences among mean values were processed by Duncan's multiple-range
tests. Significance was determined at p values of b0.05.
05 (2002), and a Mocon Permatran-W 3/61 (MOCON, MN, USA) accord-
ing to GB/T 26253 (GB/T, 2010), respectively. Tensile tests were per-
formed on the films at a strain rate of 300 mm/min at 25 °C by using an
Fig. 6. Thermograms of (a) MCC, PVA, YM, and the blend films (b) YMP-5, YMP-10, YMP-15, and YMP-20.

94
D. Hu, L. Wang / Reactive and Functional Polymers 101 (2016) 90–98
Fig. 7. SEM micrographs of the surfaces (a–e) and cross sections (f–j) of the films.

D. Hu, L. Wang / Reactive and Functional Polymers 101 (2016) 90–98
95
3
. Results and discussion
or of YM. These results further suggest the strong interaction between
YM and PVA, which enhanced the thermostability of the blend films
[29]. However, the onset decomposition temperature and the major de-
composition temperature of the PVA/YM composite films markedly
shifted to lower temperature as the YM content increased from 5 to
20 wt.%. The decrease in thermal stability of PVA with increasing
amount of incorporated YM may be explained by the decrease in com-
patibility between YM and PVA matrixes and by the decrease in crystal-
linity of the composite film. These conclusions are strongly supported
by the XRD results.
3
.1. FTIR spectroscopy
FTIR spectroscopy, a common method for studying the structural
and chemical properties of materials, was performed (results are
shown in Fig. 4(a)). Bands for YM appeared at 3339 cm
stretching), at 2921 and 2854 cm (υas (CH ), υ (CH
2 s 2
−
1
(O–H
)), as well as at
(glucopyranose ring). The band at
−
1
−
1
1
1
310, 1102, 1024, and 895 cm
−
1
+
456 cm
is due to the introduction of C–N –C in the structure,
which indicates the formation of YM [24]. The degree of substitution
of YM from element analysis is 0.48, which further supports the above
results. Characteristic peaks of PVA film could be observed at
3
.4. Morphology of PVA and YMP films
−
1
−1
−1
3
283 cm (O–H stretching), 2913 cm (C–H bending), 1732 cm
SEM images of the upper surfaces and cross sections of the films are
−
1
(
CO stretching), and 1086 cm (C–O stretching) [25]. Characteristic
shown in Fig. 7. The surface of the PVA film was homogeneous, but its
cross section is heterogeneous because of the coexistence of crystalline
and amorphous regions [30]. The YMP films had a microstructure that
was rougher than of the PVA films; phase separation occurred when
the YM content increased from 5% to 20%. These observations suggest
that PVA and YM became more incompatible with the increase in YM
content. Therefore, YM was miscible with PVA, and both formed a uni-
form film at low YM concentrations.
bands of PVA in the YMP films are apparent; however, characteristic
bands of YM almost overlap. As shown in Fig. 4(b), the peak at
~
402.23 eV in the XPS spectra is consistent with nitrogen in quaternary
ammonium groups [26], which further confirms the introduction of YM
into the blend films. Furthermore, the O–H stretching vibration bands of
−
1
the YMP blend films at 3260–3240 cm
broadened and shifted to
lower wavenumber, indicating the strong intermolecular hydrogen
bonding between YM and PVA in the blend films [27]. The interaction
between PVA and YM thus increased the tensile strength of the blend
films.
3
.5. Mechanical properties
The mechanical properties of samples are presented in Table 1
p b 0.05). The tensile strength and elongation at break of the PVA film
3
.2. XRD analysis
(
are 28.83 ± 1.04 MPa and 331.48% ± 2.57%, respectively. The tensile
strengths of YMP-5, YMP-10, YMP-15, and YMP-20 were higher than
that of the PVA film but had relatively short elongation at break. This re-
sult implies that addition of YM to the films could improve their me-
chanical properties by causing the formation of strong hydrogen
bonds between PVA and YM. The tensile strength of YMP-5 was higher
than those of cellulose/PVA film (29 MPa) [31], 5 wt.% NFC/PVA film
XRD measurement is commonly used to investigate the crystalline
nature of materials. As shown in Fig. 5, characteristic peaks of MCC are
located at 2θ values of 14.9°, 16.4°, 22.6°, and 34.6°, which correspond
to the typical structure of cellulose І. However, weaker peaks of YM at
2
θ values of 12.3°, 20.1°, and 22.0° represent the structure of cellulose
ІІ. These changes indicate that cellulose molecules rearranged and that
the cellulose І structure transformed to cellulose ІІ structure during
quaternization and subsequent regeneration from the NaOH/urea solu-
tion. Peaks of pure PVA film at 2θ values of 19.2° and 22.1° are character-
istic of the structure of crystalline PVA. Furthermore, peaks of the YMP
films at 2θ values of 19.5° and 22.4° are close to those of the PVA film.
The intensities of the peaks of YMP films are greater than those of
pure PVA film. These results indicate that hydrogen bonds between
PVA and YM in the blend films were strong. However, the intensity of
the peak at 2θ value of 19.5° markedly decreased upon addition of YM.
During regeneration, greater amounts of urea, which came from the
NaOH/urea aqueous solution used during film preparation, remained
(
44.25 MPa) [32], 7 wt.% CN/starch/PVA film (19.5 MPa) [33], 32 wt.%
of α-CNFs/PVA (39 MPa) [34], and 50 wt.% cellulose/PVA film
20 MPa) [35]. The tensile strength decreased and the elongation at
(
break increased with increasing YM content because of the decreased
YM dispersion. It may also be due to the residual urea from regeneration
of the YMP films, which reduced the degree of crystallinity. These obser-
vations also reveal that addition of YM decreased the elasticity of PVA
film.
3.6. Barrier properties
in the blend film as the YM content increased. –OH, CO and –NH
2
groups
in urea could form hydrogen bonds with hydroxyl groups of YM or PVA
molecules, which hindered the primary interactions between hydroxyl
groups in YM or PVA molecules. Meanwhile, the decreased dispersion
of YM with the increase in YM content of the blend films could also
lead to lower crystallinity.
The gas permeability of packaging materials is of great importance to
their use in preservation. A packaging system's barrier to oxygen can ex-
tend product shelf life and thus improve product quality [36]. All of our
films had low OP, implying that they had high imperviousness toward
oxygen. Moreover, the OP values of YMP films obtained in this work
were lower than those of some polymer films, such as methyl cellulose
[37], native and denatured whey protein isolate [38], calcium-
crosslinked peach puree [39], high or low density polyethylene [40],
3
.3. TGA
Fig. 6 shows thermograms of MCC, YM, neat PVA film, and PVA/YM
composite films. As shown in Fig. 6(a), the major degradation tempera-
ture of MCC was 331.11 °C, which is higher than that of YM (283.74 °C).
This difference indicates that the thermal stability of MCC decreased
after the modification. The weight loss of PVA observed at 83 °C is attrib-
uted to moisture removal, and the two subsequent major weight losses
within 220–500 °C could be attributed to structural decomposition and
to the release of acetyl groups from PVA [28]. Thermograms of the YMP
films (YMP-5, YMP-10, YMP-15, and YMP-20) are shown in Fig. 6(b).
The initial weight loss observed at ~90 °C is due to water evaporation.
Subsequent major degradation occurred at temperatures of 368.40,
Table 1
Mechanical properties of the films.
Sample
σ
b
(MPa)
b
ε (%)
PVA
28.83 ± 1.04e
82.97 ± 0.70a
72.82 ± 1.15b
45.35 ± 0.71c
37.87 ± 0.85d
331.48 ± 2.57a
52.08 ± 0.64e
58.04 ± 1.31d
62.52 ± 1.28c
65.32 ± 1.62b
YMP-5
YMP-10
YMP-15
YMP-20
Values are expressed as mean ± standard deviation. Different letters in the same column
3
54.38, 348.74 and 342.59 °C, which are all higher than those of PVA
indicate significant differences (p b 0.05).

96
D. Hu, L. Wang / Reactive and Functional Polymers 101 (2016) 90–98
Table 2
et al. [45], urea/PVA/xylan and glycerol/PVA/xylan composite films re-
ported by Wang et al. [46]. At YM content higher than 5 wt%, the WVP
values increased with increasing of YM content. This trend may also be
attributed to the hydrophilic nature of YM and the lower crystallinity of
the blend film.
BET surface areas and barrier properties of PVA and YMP films.
OP × 10−
6
WVP × 10−8
Sample
S
BET
m2 g−1
(cm3 mm m−2 atm−1 day−1
(g cm−1 s−1 Pa−1
)
(
)
)
PVA
1.94 ± 0.32d
2.92 ± 0.59c
3.38 ± 0.26c
4.37 ± 0.23b
7.22 ± 0.42a
2.48 ± 0.29e
4.50 ± 0.54d
6.81 ± 0.50c
8.60 ± 0.48b
12.67 ± 1.45a
25.82 ± 1.84d
9.73 ± 0.80d
11.7 ± 1.74d
16.03 ± 1.50c
21.77 ± 1.53b
YMP-5
YMP-10
YMP-15
YMP-20
3.7. UV transmittance of the composite films
Photographs of the films and UV–vis spectra of PVA and YMP films
Data are derived from the results of three independent experiments and are expressed as
mean ± standard deviation. Different letters in the same column indicate significant dif-
ferences (p b 0.05).
with 68 ± 4 μm thicknesses are presented in Fig. 8 (p b 0.05). The PVA
film was relatively transparent; its transmittance reached 77.43 ±
0.74% at 280 nm. In contrast, the transparency of YMP-5 film was
3.65 ± 0.60%; an object on the other side of the film appeared hazy. In-
4
creasing the YM content from 5 to 10 wt.% drastically decreased the light
transmittance. The transmittance at 280 nm was only 0.03 ± 0.01% at
YM content of 20 wt.%. The blend film became completely opaque at
YM concentrations of 10, 15, and 20 wt.%. The film gradually became
whiter, completely obscuring the object underneath it. The decreased
transmittance is related to the decreased dispersion and to the increased
incompatibility between YM and PVA at higher YM content. These in
turn increase the number of interfaces in the blend films, leading to op-
tical scattering and refraction. The above results indicate that YM plays
an important role in blocking UV light through the films. Therefore, com-
posite films have potential application in UV-screening materials.
and chitosan [41]. The BET surface area and OP of the YMP films in-
creased with the increase in YM content. A larger BET surface area cor-
responds to a structure with more pores, which increases the oxygen
gas permeance. Moreover, the hydrogen bonds between the PVA and
YM molecular chains become stronger as the crystallinity of the film in-
creases. This further hinders passage of O through the film [42].
2
In general, water vapor transmission through a hydrophilic film de-
pends on the diffusivity and solubility of water molecules in the film
[43]. Water vapor barrier properties of the films as determined by the
WVP are shown in Table 2 (p b 0.05). Films with greater hydrophilicity
have greater WVP (i.e., they have a lower barrier against water vapor).
−
8
−1 −1
−1
The WVP of PVA film is 25.82 ± 1.84 × 10 g cm
s
Pa . Thus, ad-
3.8. Antibacterial properties
dition of YM to PVA film had a marked effect on the water vapor barrier
properties of the films compared with those of PVA film. The WVP values
The antibacterial activity of the composite films was determined by
disc diffusion method. Fig. 9 shows the effects of the films against Gram-
positive (S. aureus) and Gram-negative (E. coli) bacteria (p b 0.05). The
control films (PVA) did not have a surrounding inhibition zone, suggest-
ing that PVA film had no antibacterial activity. In contrast, the YMP film
disc had a clear inhibition zone around it, indicating an antibacterial ef-
fect. The antibacterial component in the blend films diffused to the sur-
rounding area of the film, suppressing the growth of E. coli and S. aureus
and thus forming an inhibition zone around the film. Quaternary
−
8
−1 −1
−1
of YMP films reached a minimum of 9.73 ± 0.80 × 10 g cm
s
Pa
when the YM content was 5 wt.%. This minimum indicates that a strong
interaction existed between YM and PVA molecules and that the water
vapor barrier properties of the PVA matrix improved upon the addition
of YM. The WVP values of YMP films obtained in this work were higher
than those of hydrophobic polymeric films such as PVA, LDPE, and
HDPE [44]. However, the WVP value of YMP-5 was lower than those of
chitosan and chitosan-cinnamon leaf oil films reported by Perdones
Fig. 8. Photographs and visible-light transmittance curves of the films.

D. Hu, L. Wang / Reactive and Functional Polymers 101 (2016) 90–98
97
Fig. 9. Activities of the composite films against E. coli and S. aureus, as determined by the disc diffusion method. Different letters indicate significant differences among films as determined
by Duncan's multiple-range tests (p b 0.05).
[
[
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