- Email: [email protected]
polycaprolactone fiber films for antibacterial food packaging
Journal Pre-proof Size effect-inspired fabrication of konjac glucomannan/ polycaprolactone fiber films for antibacterial food packaging
Wanmei Lin, Yongsheng Ni, Jie Pang PII:
S0141-8130(19)37125-9
DOI:
https://doi.org/10.1016/j.ijbiomac.2020.01.242
Reference:
BIOMAC 14546
To appear in:
International Journal of Biological Macromolecules
Received date:
3 September 2019
Revised date:
6 January 2020
Accepted date:
23 January 2020
Please cite this article as: W. Lin, Y. Ni and J. Pang, Size effect-inspired fabrication of konjac glucomannan/polycaprolactone fiber films for antibacterial food packaging, International Journal of Biological Macromolecules(2018), https://doi.org/10.1016/ j.ijbiomac.2020.01.242
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2018 Published by Elsevier.
Journal Pre-proof Size effect-inspired fabrication of konjac glucomannan/polycaprolactone fiber films for antibacterial food packaging
Wanmei Lin1, Yongsheng Ni1, Jie Pang* College of Food Science, Fujian Agriculture and Forestry University, Fuzhou 350002, China *Corresponding author: Jie Pang
These authors contributed equally to this work.
ro
1
of
E-mail: [email protected]; Tel/Fax: 86-591-83756316
-p
Abstract
re
The exploration of new methods to produce food packaging with excellent
lP
physicochemical and antibacterial properties is of great scientific and technological interest.
na
Here, we successfully prepare the food packaging films that are composed of konjac glucomannan (KGM), poly(-caprolactone) (PCL) and silver nanoparticles (AgNPs) via
Jo ur
microfluidic spinning technology (MST). The obtained fiber films (average fiber diameter: 7.8 ± 0.2 m) exhibit excellent antibacterial activities against S. aureus (34 ± 0.71 mm) and E. coli (39 ± 5.66 mm), which is ascribed to the good swelling of KGM in KGM/PCL/AgNPs fiber films (SD: 37.86 ± 6.87%). Fourier transform infrared (FT-IR) spectroscopy and X-ray diffraction
(XRD)
are
employed
to
study
the
interactions
between
polymers.
Thermogravimetric analysis (TGA), derivative thermogravimetry (DTG), water vapor permeability (WVP), and mechanical property measurements are conducted to evaluate the thermal properties, hydrophilicity and mechanical performances of the films. The results show that the films are thermal stable and relatively hydrophobic (WVP: 5.8 10-6 ± 1.44 1
Journal Pre-proof
g/(mhkPa), WCA: 101.0) as well as have terrific elongation at break (EB: 223.59 ± 98.14%), which is beneficial for food packaging. This strategy provides a facile and green pathway for the construction of promising antibacterial food packaging. Keywords:
Size
effect;
Microfluidic
spinning technology;
Konjac
glucomannan;
Polycaprolactone; Silver nanoparticles; Antimicrobial food packaging
of
1. Introduction
ro
Food packaging films are significant for food processing, transport, storage and marketing. Nowadays, most food packaging materials mainly consist of petrochemical-based
-p
polymers because they are convenient, low-cost and have excellent barrier performances [1].
re
However, it is commonly accepted that those nonbiodegradable materials will cause
lP
irreversible environmental contaminations both in the long and short terms and are harmful to public health [2]. Thus, it is urgent and promising to explore food packaging films that are
na
composed of biodegradable materials. Except for the raw materials used in fabricating the food packaging films, the preparation process is also significant and valuable to be
Jo ur
investigated. Conventional approaches in preparing films such as electrospinning and casting have some inevitable disadvantages. For example, the preparation process of electrospinning nanocomposite reported by Schmatz, Costa and Morais needs high electric potential of more than 25 kV [3], which may affect the activities of the incorporated functional substances thus weaken their efficacy. Moreover, the arrangement of the fibers in the obtained nanocomposite is disordered. As for the casting method, for instance, the casting chitosan antioxidant films incorporated with the mango leaf extract lack large specific areas, which may have negative influence on the antioxidant activities [4]. Therefore, microfluidic spinning technology (MST) was employed to prepare the active food packaging films in our present study. MST has drawn considerable attention owing to its safe, simple, controllable, high-efficient, non-toxic and green attributes [5-7]. More importantly, the activities of the incorporated functional 2
Journal Pre-proof compounds in the as-prepared films could be maintained due to the mild fabrication process and be maximized on account of the large specific surface area owned by the neatly arranged fibers. Konjac glucomannan (KGM), a kind of natural heteropolysaccharide, consist of β-1,4-linked D-glucose and D-mannose with a reported ratio of 1:1.6 [8, 9]. The acetyl groups randomly existed at C-6 position per every 19 sugar unites in the polymer chains [10, 11]. Numerous KGM-based food packaging films has been reported such as KGM/pectin films
of
[12], KGM/carrageenan/nano-silica films and KGM/zein blend films [7, 13] because of its biodegradability, biocompatibility and non-toxicity [12]. More importantly, KGM may
ro
contribute to relatively even dispersion of active substance in the microchannel during
-p
microfluidic spinning owing to its stabilizing ability in solutions [14]. Also, the good swelling
re
property of KGM may play a significant role in the release of functional compounds loaded in the films [15]. According to our previous works, the pure KGM is difficult to be spinned by
lP
MST due to its poor mechanical forces [16-18]. Thus, blended spinning by incorporating
na
polymers is necessary in present study. Actually, we have successfully fabricated the hybrid ordered KGM/PVP/EGCG films via MST and investigated its potential applications in wound
Jo ur
dressings, which laid the foundation for our present research [17]. Poly(-caprolactone) (PCL) was chosen as a potential polymer for hybrid spinning. It is a kind of aliphatic polyesters and has been intensively investigated in the field of pharmacy, tissue engineering, wound healing etc. owing to its excellent biocompatibility, biodegradability and moldability [19-23]. It also has been extensively used in food packaging because of its good mechanical properties [24-26]. Besides, the barrier properties of chitosan/polycaprolactone based active bilayer films
were
enhanced
resulted
from
the
addition
of
PCL
[27].
And
polyethylene/polycaprolactone (PE/PCL) bilayer films are more thermal stable than neat PE films due to the existence of PCL [28]. And to the best of our knowledge, there is no research reporting the application of PCL in microfluidic spinning field for preparing food packaging films. Therefore, in this study, PCL was employed to enhance thermal stabilities, water vapor barrier properties and mechanical properties of fiber films. 3
Journal Pre-proof Active food packaging films have attracted ever increasing attentions in recent years especially for those ones with antibacterial or antioxidant properties such as the essential oil incorporated chitosan nanofibers and protein-based films incorporated with mango kernel extract [29, 30]. Several attempts have been made to incorporate nanoparticles (NPs) to the packaging materials because nanocomposites so formed presented not only outstanding barrier and mechanical properties but also terrific antibacterial activities on account of size effect of NPs [31]. Silver nanoparticles (AgNPs) could confer potent antibacterial abilities on
of
the fiber films [32, 33]. Thus, we employed AgNPs to prepare the KGM-based food packaging films via MST in our present research.
ro
Previous published articles primarily focused on the fabrication of microfiber films with
-p
enhanced antibacterial properties for food packaging materials inspired by the
re
hydrophilic/hydrophobic theory [5, 34]. Natural compounds such as chlorogenic acid and trans-cinnamic acid had been loaded into the fiber films for investigations. It is worth
lP
mentioning that the try of antibacterial food packaging films inspired by the
na
hydrophilic/hydrophobic theory had signified that KGM has potential applications in enhancing antibacterial activities, which laid the foundation for its further exploration in
Jo ur
strengthening antibacterial properties of food packaging materials. Despite the fact that KGM films based on hydrophilic/hydrophobic theory had been developed, it is still challenging to meet the needs of practical application. Besides, most antibacterial materials loaded with AgNPs emerged in recent years were formed in situ by reduction of silver nitrate. Regretfully, these approaches have the following potential demerits: 1) The AgNPs was on the surface of the substrate, which is difficult to achieve sustained release; 2) Chemical reaction will occur during in situ synthesis of AgNPs, which may threaten the surrounding environment, especially in the context of high usage of food packaging materials nowadays. In this paper, we provide another new strategy inspired by the size effect of NPs for the preparation of food packaging films with reinforced antibacterial performances. Artful loading of AgNPs into the fiber films and directional arrangement of fibers to form the films can be achieved by MST. Physicochemical and antibacterial properties of the prepared fiber 4
Journal Pre-proof films were evaluated. The four main innovations are as follows: 1) Nano-sized functional particles were loaded into micron-sized fibers, which could increase the antibacterial efficiency of the fiber films; 2) The aggregation of AgNPs could be effectively prevented and the even dispersion of AgNPs in fibers could be realized because of KGM's good stabilizing ability; 3) AgNPs was allowed to be loaded inside the fibers through microchannel during microfluidic spinning process, achieving slow migration from inside to outside; 4) A new method of constructing polysaccharide micro-nano antibacterial materials with controllable,
ro
of
non-toxic and green attributes was provided.
2. Materials and methods
-p
2.1. Materials
re
Konjac glucomannan (KGM, Mw = 1.0 × 106 Da, viscosity: 1% solution, ≥35, 000 MPas at 30 C, purity ≥90%) was supported by San Ai Konjac Food Co. Ltd. (Shaotong,
lP
Yunnan, China). Poly(-caprolactone) (PCL, Mn = 8.0 × 104 Da) was supplied by
na
Sigma-Aldrich Co. Ltd. (Shanghai, China). Silver nanoparticles (AgNPs) was bought from Aladdin Chemical Reagent Co. Ltd. (Shanghai, China). Other reagents and chemicals were
Jo ur
coming from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Bacterial strains including the Gram-negative bacteria Escherichia coli (ATCC25922) and the Gram-positive bacteria Staphylococcus aureus (ATCC25923) were supplied by TransGen Biotech (China).
2.2. Fabrication of KGM/PCL/AgNPs fiber films Firstly, a 25wt% PCL solution was prepared: 25g PCL was put into a beaker, adding 100 mL of CH2Cl2/CH₃CH₂OH (2:1, V/V), soaking for 24 h under a closed environment. And the solution was then stirred at the stirring rate of 600 rad/min for 12 h. Then, mixing KGM and 25wt% PCL at the stirring rate of 600 rad/min for 2 h at a weight ratio of 1:10 to form KGM/PCL solution. Finally, AgNPs (WPCL:WAgNPs = 30:1) was loaded into KGM/PCL solution at the stirring rate of 600 rad/min for 2 h to form KGM/PCL/AgNPs spinning 5
Journal Pre-proof foundation liquid. And the air bubbles in the solution were removed by ultrasonic treatment. The spinning foundation liquid of KGM/PCL and PCL/AgNPs were also obtained subsequently. KGM/PCL/AgNPs fiber films were prepared according to the previously described microfluidic spinning method with some modifications [34]. In brief, the solution was loaded into a syringe (20 mL) with 16 G stainless steel needles and then were ejected by a syringe pump. The frame receiver was employed to receive the fibers, and fiber films were formed by
of
directionally weaving with the help of horizontal step process. Schematic diagram of the microfluidic spinning process is shown in Fig. 1a and the operating parameters are as follows:
ro
speed of the syringe pump = 0.5 mL/h, speed of the frame receiver = 400 rad/min, frequency
re
prepared under the same operation condition.
-p
of the horizontal step process = 25 Hz. KGM/PCL and PCL/AgNPs fiber films were also
lP
2.3. Morphologies of KGM/PCL/AgNPs fiber films
na
Scanning electron microscopy (SEM, Hitachi S-4800, Japan) analysis was undertaken to study the morphologies of fiber films. The sputtered time was about 60 s and the accelerating
Jo ur
voltage was 5 kV.
2.4. Fourier-transform infrared (FT-IR) spectra Samples were qualitatively analyzed by using the Nicolet 6700 FT-IR spectrometer (Thermo Fisher Scientific, MA, USA) at ambient temperature in a wavenumber range of 4000 - 400 cm-1.
2.5. X-ray diffraction (XRD) The crystal structures were characterized by using an X-ray diffractometer (D8 Advance, Bruker Inc., Germany) equipped with Ni-filtered Cu Kα radiation source (λ = 0.1542 nm). The XRD curves were recorded at a scanning speed of 5/min with the 6
Journal Pre-proof diffraction angle 2θ between 5° and 80°.
2.6. Thermal properties Thermogravimetric analysis (TGA) was performed by using a synchronous thermal analyzer (STA409-PC, Netzsch, Germany) in the Nitrogen atmosphere. All
of
tested samples were heated from 25 °C to 600 °C at a heating rate of 15 °C/min.
2.7. Water vapor permeability (WVP) and water contact angle (WCA)
ro
The WVP test of fiber films was carried out according to the Chinese National Standard
-p
GB/T 1037-70 with some modifications [35]. Firstly, the fiber films were sealed over a
re
weighing bottle (25 mm × 40 mm) containing 3.0 ± 0.1 g anhydrous CaCl2. Then, the
lP
saturated NaCl solution was prepared to obtain relative humidity of 75 ± 5% in the
na
desiccators. The weighing bottles were placed in a desiccator (temperature maintained at 25 ± 5 °C) and weighted every 8 h for two consecutive days until the weight change was stable.
Jo ur
The following equation was used to calculate the WVP (g/(m2·h·kPa)): WVP =
∆𝑚 × 𝑑 S × ∆𝑡 × ∆p
where ∆𝑚 (g) represents the weight difference between initial and final, 𝑑 (mm) represents the average thickness of fiber films, S (m2) represents the permeation area of fiber films, ∆𝑡 (h) represents the permeation time, ∆p (kPa) represents the pressure difference on both sides of the fiber films. The hydrophilicity of the fiber films was also characterized by the WCA measurements. The test was conducted by using an Optical Contact Angle Meter (OCA 20, Germany) at ambient temperature. The selected water droplet volume was 4 L. At last, three angles were 7
Journal Pre-proof
measured for each sample at different regions. Photos were obtained at least 30 s after the water was placed on film surface to make sure the droplet has sufficient time to spread and realize a stable contact angle. The final reported WCA was calculated according to the averaged value.
of
2.8. Swelling degree (SD)
ro
Predefined approach was adopted to determine the SD of the fiber films. The samples (dimension of 2 cm × 2 cm) were cut from the fiber films, then were placed in a beaker
-p
containing 50 mL of distilled water. The fiber films were swelled at ambient temperature for a
re
period of time. The moisture content of the films was measured at specific time interval. The
lP
SD was calculated by the following formula:
𝑊 − W0 × 100 W0
na
SD(%) =
Jo ur
Where 𝑊 and W0 are the weights of swelled and initial dried specimens.
2.9. Antibacterial activity test
The antibacterial activity test of fiber films was conducted by using the disc diffusion method reported by Lee et al. [36], with slight modifications. Staphylococcus aureus and Escherichia coli were chosen as the representative Gram-positive and Gram-negative bacteria, respectively. All tested fiber films were sterilized before the tests by UV for 20 min. In brief, the nutrient broth (3 g beef extract, 10 g peptone and 5 g sodium chloride per 1000 mL water) was used to grow the S. aureus and E. coli. Then, 0.9% of sterile saline was used to dilute the bacterial suspension to obtained an inoculum of approximately 106 - 108 CFU/mL. 150 L of 8
Journal Pre-proof
this bacterial suspension was spread evenly over Luria-Bertani (LB) agar plates, then the center of the plates was covered with a circular sample (10 mm in diameter). After that, all LB plates were incubated at 37 °C for 24 h. The inhibition zones were measured in mm by using a Vernier caliper.
of
2.10. Mechanical properties
ro
The mechanical properties of the fiber films were evaluated by using a texture analyzer
-p
(EZ-SX, Shimadzu, Japan) with a load cell of 500 N. The tested samples were tailored into 10
re
mm × 40 mm rectangles for test. The initial clamping length was 20 mm and crosshead speed
lP
were set at 10 mm/min. The TS and EB were calculated by the following equations: TS =
𝐹 S
na
where TS (Pa) is the tensile strength, 𝐹 (N) is the maximum stress of stretching, S (m2) is
Jo ur
the initial sectional area of sample.
EB (%) =
(𝐿𝑚𝑎𝑥 − L0 ) × 100% L0
where EB is the elongation at break, L0 (mm) is the initial length of sample, 𝐿𝑚𝑎𝑥 (mm) is the length of the sample at the time of break.
2.11. Statistical analysis Experimental data were presented as the mean ± standard deviation for triplications. Date analysis and calculations were performed by using the SPSS software (SPSS 20.0 for windows, SPSS Inc., Chicago, IL). 9
Journal Pre-proof
3. Results and discussion 3.1. SEM analysis Fig. 1b exhibits the surface morphologies of KGM/PCL/AgNPs fiber films. As shown in Fig. 1b, the fiber films fabricated by MST are composed of orderly arranged fibers with relatively uniform diameters in the overall morphologies. The orderly arrangement of fibers would facilitate the uniform distribution of loaded nanoparticles in the fiber films. The mean
of
diameter of a single fiber in KGM/PCL/AgNPs fiber films is 7.8 ± 0.2 m. The main
ro
difference between the fiber films and the one that prepared through conventional casting method is the specific areas. The large specific surface areas of fiber films are beneficial for
-p
increasing the contact surface of fibers and surrounding environment, which may be
re
conducive to improve the antibacterial activities of KGM/PCL/AgNPs fiber films. Besides,
lP
the size effect of AgNPs could be enhanced through this special micromorphology viz., neatly
performances.
Jo ur
3.2. FT-IR analysis
na
arranged fibers with relatively even diameters, thereby contribute to efficient antibacterial
FT-IR spectroscopy was performed to identify the functional groups and the structural changes within the fiber film matrix. The FT-IR spectra of KGM, PCL, KGM/PCL and KGM/PCL/AgNPs are shown in Fig. 2. FT-IR spectrum of neat KGM at around 3432 cm-1, 2923 cm-1, 1726 cm-1, 1099 cm-1 were related to the vibration of O-H, C-H, C=O, C-O-C, respectively [37]. For neat PCL, the absorption peak at 3428 cm-1 was due to the stretching vibration of O-H [38]; the peaks observed at 2921 cm-1 and 2854 cm-1 were ascribed to asymmetric and symmetric modes of CH2 [39]; the peak appeared at 1797 cm-1 was attributed to the stretching vibration of C=O in the ester carbonyl group [40]; the peak at 1284 cm-1 represented the asymmetric stretching of C-O-C, which revealed the presence of -caprolactone [41]. In comparison with the FT-IR spectra of neat KGM and neat PCL, no 10
Journal Pre-proof new peaks are observed in the spectrum of KGM/PCL or KGM/PCL/AgNPs, which signified no chemical reactions occur during microfluidic spinning. But the absorption peak of O-H became narrow in the spectra of KGM/PCL and KGM/PCL/AgNPs, which probably associated with the formation of intermolecular hydrogen bonds between KGM and PCL [42]. The peak at 1726 cm-1 shifted to higher wavenumbers with increased intensity in the spectra of KGM/PCL and KGM/PCL/AgNPs, which could be assigned to the formation of hydrogen bonds between KGM and PCL. Besides, the intensity of some peaks increased in the
of
spectrum of KGM/PCL/AgNPs, which may result from van der Waals interactions between
ro
KGM and AgNPs or between PCL and AgNPs [43].
-p
3.3. XRD analysis
re
XRD analysis was performed to investigate the crystal structure changes in the fiber films [44]. The XRD patterns of KGM, PCL, KGM/PCL and KGM/PCL/AgNPs are
lP
presented in Fig. 3. For the neat PCL, two strong peaks are observed at 2 = 21.9 and 24.3,
na
which was ascribe to the Bragg angles and the diffraction of the lattice plane and the lattice plane of semi-crystalline [45]. It is noticeable that, compared with PCL, the intensity of peak
Jo ur
at 2 = 21.9 slightly decreased in the XRD pattern of KGM/PCL, which signified that the KGM may influence the crystallization of PCL. Compared with KGM/PCL, the peak at 2 = 21.9 was replaced by a gentler peak located at 2 = 21.5 in the pattern of KGM/PCL/AgNPs, and the peak at 2 = 24.3 shifted to higher diffraction angle (2 = 24.5), which could be attributed to the incorporation of silver nanoparticles. In addition, compared with KGM/PCL, no obvious increase in peak intense was observed at 2 = 21.5 and 2 = 24.5 in the XRD patterns of KGM/PCL/AgNPs, which indicated that the addition of KGM could prevent the aggregation of AgNPs. The uniform distribution of AgNPs in the KGM/PCL/AgNPs is beneficial for enhancing antibacterial effects of the fiber films.
3.4. TGA analysis 11
Journal Pre-proof Thermal analysis was conducted through TGA and DTG. The TGA and DTG curves of KGM, PCL, KGM/PCL and KGM/PCL/AgNPs are shown in Fig. 4. Detailed thermal data is provided in Table 1. KGM has two mass loss stages. The first stage of mass loss occurred at around 56.6 C, which was the consequence of water evaporation. The second stage began at around 279.2 C, which was attributed to structural damages of molecular chains and thermal decomposition [42]. While the rest of three samples only have one degradation temperature compared with KGM, which may due to incorporation of hydrophobic PCL [46]. The delayed
of
degradation temperature of KGM/PCL demonstrated that PCL could greatly improve the
ro
thermal stabilities of the fiber films [28]. Besides, the KGM/PCL/AgNPs fiber film also exhibited good thermal properties, which could be the consequence of AgNPs incorporation.
-p
This is similar to previous research that reported the addition of AgNPs could significantly
re
improve the thermal stabilities of the PLA/nano-TiO2/nano-Ag blends films [47]. Overall, the
na
potentials in food packaging.
lP
resultant KGM/PCL/AgNPs fiber film has excellent thermal stabilities, which indicated its
3.5. WVP and WCA measurements
Jo ur
Sorption and diffusion of water vapor are key factors in food packaging and storage [48]. Therefore, WVP measurements were conducted to evaluate the hydrophilicity of the obtained fiber films. WVP is the quality of water vapor permeating a unit area of film per unit time [49]. Lower WVP value of the films means higher ability of resisting water permeation. As shown in Fig. 5a, the WVP value of KGM/PCL/AgNPs is 5.8 10-6 ± 1.44 g/(mhkPa), which is lower than that of recently reported KGM-based or PCL-based films [49-51]. This may primarily due to the formation of hydrogen bonds between KGM and PCL, confirmed by the FT-IR analysis, which could decrease the number of polar groups, hence decrease the WVP value [52]. Moreover, the addition of AgNPs could increase the density of the KGM/PCL/AgNPs fiber films therefore lead to the lower WVP value. Similar results can be found in previous researches [53]. Besides, WCA measurements were also conducted to 12
Journal Pre-proof evaluate the hydrophobicity of the films, which could provide the information of the wettability of the film surface. Higher WCA value of the tested films means less water can pass through the films, which is desirable for food packaging materials. As the droplet photos shown in Fig. 5a, the KGM/PCL/AgNPs has a larger contact angle with 101.0 compared to KGM/PCL (88.4). The improved hydrophobicity can be explained by the addition of AgNPs, which is corresponding to the WVP results. Overall, the KGM/PCL/AgNPs fiber films were
of
promising for food packaging owing to its good water barrier properties.
ro
3.6. Swelling degree (SD) measurement
The SD of KGM/PCL, KGM/PCL/AgNPs and PCL/AgNPs fiber films were investigated.
-p
As shown in Fig. 5b, compared with the SD (8.10 ± 2.02%) of PCL/AgNPs fiber films, the
re
KGM/PCL (SD: 46.71 ± 5.30%) and KGM/PCL/AgNPs (SD: 37.86 ± 6.87%) fiber films present better water uptake capability. This was due to the good swelling properties of KGM
lP
[54]. It is worth mentioning that the good SD of KGM/PCL/AgNPs may promote the release
na
of AgNPs, which is similar to previous reports that mentioned the swelling properties could
Jo ur
significantly influence the drug release behavior [15].
3.7. Antibacterial analysis
Antibacterial experiments were conducted to evaluate the antibacterial properties of fiber films. As showed in Fig. 6a, there is no inhibition zones observed in the KGM/PCL group, which indicated that both KGM and PCL had no antibacterial activities. This is consistent with the previous researches [17, 55]. KGM/PCL/AgNPs displayed significant antibacterial performances against S. aureus and E. coli with inhibition diameters of 34 ± 0.71 mm and 39 ± 5.66 mm, respectively. This demonstrated that the AgNPs is successfully released from the KGM/PCL/AgNPs fiber films, which may be ascribed from the good swelling of KGM [15]. AgNPs is efficient in inhibiting the growth of bacteria because it can penetrate the bacterial and kill them by attaching to the cell membranes [47]. By contrast, nearly no inhibition zone 13
Journal Pre-proof was observed in PCL/AgNPs fiber films though loaded with AgNPs, which signified the key role of KGM in contributing to promote antibacterial efficiency. It is worth mentioning that the inhibition zones of KGM/PCL/AgNPs fiber films are larger than recent reported antibacterial KGM composite films such as the konjac glucomannan-montmorillonite nacre-like composite films (20 ~ 23 mm) and the pectin-konjac glucomannan composite edible films (13 ~ 20 mm) [56]. The antibacterial effects were greatly enhanced due to the size effect of NPs [57]. According to the abovementioned characterization analysis, we may
of
conclude that the size effect could be enhanced by three factors viz., the fibers with special micro-morphologies (neatly arranged fibers with relatively even diameters obtained via MST),
ro
good swelling and anti-aggregation properties of KGM. In addition, the inhibition area of the
-p
films against E. coli is slightly larger than that of S. aureus, which is in the line with previous
re
results [58]. This could be ascribed from the different antibacterial effects of AgNPs on
lP
different bacterium strains.
na
3.8. Mechanical analysis
Good mechanical properties of food packaging materials play an important role in
Jo ur
storage, transport and marketing. It may further influence the quality of food products. As shown in Table 2, though KGM/PCL/AgNPs was found to have relatively low tensile strength (TS), the elongation at break (EB) of KGM/PCL/AgNPs is significantly higher than that of KGM/PCL, which may primarily result from the addition of silver nanoparticles. The EB is related to the surface defects such as pits, holes, impurities, etc. Those defects tend to cause stress concentration of the films and then prematurely break from the defect. The loading of AgNPs may decrease the surface defect by increasing the dense of the fiber films. Also, the SEM images of the fibers showed that the surface was relatively smooth and free of cracks, which indicated the integrity of the KGM/PCL/AgNPs fiber films. Moreover, the EB of KGM/PCL/AgNPs is superior to the recent reported food packaging films [4, 30], which indicated its good flexibility. The results of the increased EB after the addition of AgNPs is similar to previous researches. 14
Journal Pre-proof
4
Conclusion In summary, a novel green KGM/PCL/AgNPs food packaging films was prepared via
MST which has safe, simple, controllable, high-efficient, non-toxic and green attributes. This fiber films are hydrophobic and have good thermal stabilities and mechanical properties, which indicated their promising applications in food packaging. Moreover, the films have large specific surface area and consist of neatly arranged fibers, which was beneficial for
of
enhancing the size effect of AgNPs thereby improve the antibacterial activities. More
ro
importantly, the good swelling of KGM could significantly promote the release of AgNPs thus improve the antibacterial efficiency. Meanwhile, the addition of KGM could prevent the
-p
aggregation of AgNPs, which is beneficial for AgNPs to better exert antibacterial efficacy.
lP
properties inspired by size effect of NPs.
re
Overall, our study presented a novel green packaging films with excellent antibacterial
na
Acknowledgements
The authors are grateful to the National Natural Science Foundation of China (grant
References
Jo ur
number: 31772045, 31471704).
[1] R. Accorsi, A. Cascini, S. Cholette, R. Manzini, C. Mora, Economic and environmental assessment of reusable plastic containers: A food catering supply chain case study, Int. J. Prod. Econ. 152 (2014) 88-101. [2] D. Plackett, Biodegradable polymer composites from natural fibres, Biodegradable Polym. Ind. Appl. (2005) 189-218. [3] D.A. Schmatz, J.A.V. Costa, M.G.d. Morais, A novel nanocomposite for food packaging developed by electrospinning and electrospraying, Food Packaging Shelf 20 (2019) 100314-100314. [4] K. Rambabu, G. Bharath, F. Banat, P.L. Show, H.H. Cocoletzi, Mango leaf extract incorporated chitosan antioxidant film for active food packaging, Int. J. Biol. Macromol. 126 (2019) 1234-1243. [5] W. Lin, Y. Ni, D. liu, Y. Yao, J. Pang, Robust microfluidic construction of konjac glucomannan-based micro-films for active food packaging, Int. J. Biol. Macromol. 137 (2019) 982-991. [6] W. Liu, Y. Zhang, C.F. Wang, S. Chen, Fabrication of highly fluorescent CdSe quantum dots via 15
Journal Pre-proof solvent-free microfluidic spinning microreactors, RSC Adv. 5 (2015) 107804-107810. [7] Z. Yu, C.F. Wang, L. Ling, L. Chen, S. Chen, Triphase microfluidic-directed self-assembly: anisotropic colloidal photonic crystal supraparticles and multicolor patterns made easy, Angew. Chem. Int. Edi. 51 (2012) 2375-2378. [8] K. Kato, K. Matsuda, Studies on the chemical structure of konjac mannan, Agr. Biol. Chem. 33 (1969) 1446-1453. [9] W. Lin, Y. Ni, L. Wang, D. Liu, C. Wu, J. Pang, Physicochemical properties of degraded konjac glucomannan prepared by laser assisted with hydrogen peroxide, Int. J. Biol. Macromol. 129 (2019) 78-83. [10] M. Maeda, H. Shimahara, N. Sugiyama, Detailed examination of the branched structure of konjac glucomannan, Agr. Biol. Chem. 44 (1980) 245-252. [11] K. Maekaji, Determination of acidic component of konjac mannan, Agr. Biol. Chem. 42 (1978)
of
177-178.
[12] Y. Lei, H. Wu, C. Jiao, Y. Jiang, R. Liu, D. Xiao, J. Lu, Z. Zhang, G. Shen, S. Li, Investigation of
ro
the structural and physical properties, antioxidant and antimicrobial activity of pectin-konjac glucomannan composite edible films incorporated with tea polyphenol, Food Hydrocoll. 94 (2019)
-p
128-135.
[13] R. Zhang, X. Wang, J. Wang, M. Cheng, Synthesis and characterization of konjac
re
glucomannan/carrageenan/nano-silica films for the preservation of postharvest white mushrooms, Polymers 11 (2018) 6-6.
[14] K. An, H. Kang, D. Tian, Stabilization of soy milk using konjac glucomannan, Emir. J. Food Agr.
lP
31 (2019) 526-534.
[15] Y. Yuan, X. Xu, J. Gong, R. Mu, Y. Li, C. Wu, J. Pang, Fabrication of chitosan-coated konjac glucomannan/sodium alginate/graphene oxide microspheres with enhanced colon-targeted delivery, Int.
na
J. Biol. Macromol. 131 (2019) 209-217.
[16] Y. Ni, W. Lin, R.J. Mu, L. Wang, X. Zhang, C. Wu, J. Pang, Microfluidic fabrication of robust
Jo ur
konjac glucomannan-based microfiber scaffolds with high antioxidant performance, J. Sol-Gel Sci. Techn. 90 (2019) 214-220.
[17] Y. Ni, W. Lin, R. Mu, C. Wu, Z. Lin, S. Chen, J. Pang, Facile fabrication of novel konjac glucomannan films with antibacterial properties via microfluidic spinning strategy, Carbohydr. Polym. 208 (2019) 469-476.
[18] Y. Ni, W. Lin, R.J. Mu, C. Wu, L. Wang, D. Wu, S. Chen, J. Pang, Robust microfluidic construction of hybrid microfibers based on konjac glucomannan and their drug release performance, RSC Adv. 8 (2018) 26432-26439. [19] Y. Ren, L. Wang, X. Cui, L. Han, Q. Zhou, X. Song, Synthesis and characterization of lactose grafted polycaprolactone-polysiloxane-polycaprolactone copolymers, Polym. Int. 68 (2019) 83-87. [20] P. Douglas, M. Kuhs, M. Sajjia, M. Khraisheh, G. Walker, M.N. Collins, A.B. Albadarin, Bioactive PCL matrices with a range of structural & rheological properties, React. Funct. Polym. 101 (2016) 54-62. [21] P. Douglas, A.B. Albadarin, M. Sajjia, C. Mangwandi, M. Kuhs, M.N. Collins, G.M. Walker, Effect of poly ethylene glycol on the mechanical and thermal properties of bioactive poly(epsilon-caprolactone) melt extrudates for pharmaceutical applications, Int. J. Pharm. 500 (2016) 179-186. [22] N. Gomez-Cerezo, L. Casarrubios, M. Saiz-Pardo, L. Ortega, D. de Pablo, I. Diaz-Guemes, B. 16
Journal Pre-proof Fernandez-Tome, S. Enciso, F.M. Sanchez-Margallo, M.T. Portoles, D. Arcos, M. Vallet-Regi, Mesoporous bioactive glass/varepsilon-polycaprolactone scaffolds promote bone regeneration in osteoporotic sheep, Acta Biomater. 90 (2019) 393-402. [23] B. Joseph, R. Augustine, N. Kalarikkal, S. Thomas, B. Seantier, Y. Grohens, Recent advances in electrospun polycaprolactone based scaffolds for wound healing and skin bioengineering applications, Mater. Today Commun. 19 (2019) 319-335. [24] S. Alix, A. Mahieu, C. Terrie, J. Soulestin, E. Gerault, M.G.J. Feuilloley, R. Gattin, V. Edon, T. Ait-Younes, N. Leblanc, Active pseudo-multilayered films from polycaprolactone and starch based matrix for food-packaging applications, Eur. Polym. J. 49 (2013) 1234-1242. [25] S. Cesur, C. Köroğlu, H.T. Yalçın, Antimicrobial and biodegradable food packaging applications of polycaprolactone/organo nanoclay/chitosan polymeric composite films, J. Vinyl Additive Technol. 24 (2018) 376-3877.
of
[26] J.M. Ferri, O. Fenollar, A. Jorda-Vilaplana, D. García-Sanoguera, R. Balart, Effect of miscibility on mechanical and thermal properties of poly(lactic acid)/polycaprolactone blends, Polym. Int. 65
ro
(2016) 453-463.
[27] E. Sogut, A.C. Seydim, Development of chitosan and polycaprolactone based active bilayer films
-p
enhanced with nanocellulose and grape seed extract, Carbohydr. Polym. 195 (2018) 180-188. [28] A. Rešček, M. Ščetar, Z. Hrnjak-Murgić, N. Dimitrov, K. Galić, Polyethylene/polycaprolactone
re
nanocomposite films for food packaging modified with magnetite and casein: Oxygen barrier, mechanical, and thermal properties, Polym-Plast. Technol. 55 (2016) 1450-1459. [29] L. Lin, X. Mao, Y. Sun, G. Rajivgandhi, H. Cui, Antibacterial properties of nanofibers containing 21-30.
lP
chrysanthemum essential oil and their application as beef packaging, Int. J. Food Microbiol. 292 (2019) [30] Z.A. Maryam Adilah, B. Jamilah, Z.A. Nur Hanani, Functional and antioxidant properties of (2018) 207-218.
na
protein-based films incorporated with mango kernel extract for active packaging, Food Hydrocoll. 74
Jo ur
[31] R. Priyadarshi, Y.S. Negi, Effect of varying filler concentration on zinc oxide nanoparticle embedded chitosan films as potential food packaging material, J. Polym. Environ. 25 (2016) 1087-1098.
[32] M. Carbone, D.T. Donia, G. Sabbatella, R. Antiochia, Silver nanoparticles in polymeric matrices for fresh food packaging, Journal of King Saud University - Science 28 (2016) 273-279. [33] G. Franci, A. Falanga, S. Galdiero, L. Palomba, M. Rai, G. Morelli, M. Galdiero, Silver nanoparticles as potential antibacterial agents, Molecules 20 (2015) 8856-8874. [34] W. Lin, Y. Ni, J. Pang, Microfluidic spinning of poly (methyl methacrylate)/konjac glucomannan active food packaging films based on hydrophilic/hydrophobic strategy, Carbohydr. Polym. 222 (2019) 114986-114986. [35] L. Lin, L. Xue, S. Duraiarasan, C. Haiying, Preparation of ε-polylysine/chitosan nanofibers for food packaging against Salmonella on chicken, Food Packaging Shelf 17 (2018) 134-141. [36] J.Y. Lee, C.V. Garcia, G.H. Shin, J.T. Kim, Antibacterial and antioxidant properties of hydroxypropyl methylcellulose-based active composite films incorporating oregano essential oil nanoemulsions, LWT - Food Sci. Technol. 106 (2019) 164-171. [37] K. Wang, S. Gao, C. Shen, J. Liu, S. Li, J. Chen, X. Ren, Y. Yuan, Preparation of cationic konjac glucomannan in NaOH/urea aqueous solution, Carbohydr. Polym. 181 (2018) 736-743. [38] Y. Yao, H. Wei, J. Wang, H. Lu, J. Leng, D. Hui, Fabrication of hybrid membrane of electrospun 17
Journal Pre-proof polycaprolactone and polyethylene oxide with shape memory property, Compos. Part B 83 (2015) 264-269. [39] Y.S. Joo, J.R. Cha, M.S. Gong, Biodegradable shape-memory polymers using polycaprolactone and isosorbide based polyurethane blends, Mat. Sci. Eng. C 91 (2018) 426-435. [40] J. Kim, H.M. Mousa, C.H. Park, C.S. Kim, Enhanced corrosion resistance and biocompatibility of AZ31 Mg alloy using PCL/ZnO NPs via electrospinning, Appl. Surf. Sci. 396 (2017) 249-258. [41] J. Amirian, S.Y. Lee, B.T. Lee, Designing of combined nano and microfiber network by immobilization of oxidized cellulose nanofiber on polycaprolactone fibrous scaffold, J. Biomed. Nanotechnol. 12 (2016) 1864-1875. [42] T. Chen, P. Shi, J. Zhang, Y. Li, T. Duan, L. Dai, L. Wang, X. Yu, W. Zhu, Natural polymer konjac glucomannan mediated assembly of graphene oxide as versatile sponges for water pollution control, Carbohydr. Polym. 202 (2018) 425-433.
of
[43] S. Roy, S. Shankar, J.W. Rhim, Melanin-mediated synthesis of silver nanoparticle and its use for the preparation of carrageenan-based antibacterial films, Food Hydrocoll. 88 (2019) 237-246.
ro
[44] L. Wang, Y. Du, Y. Yuan, R.J. Mu, J. Gong, Y. Ni, J. Pang, C. Wu, Mussel-inspired fabrication of konjac glucomannan/microcrystalline cellulose intelligent hydrogel with pH-responsive sustained
-p
release behavior, Int. J. Biol. Macromol. 113 (2018) 285-293.
[45] D. Ponnamma, K.K. Sadasivuni, M. Strankowski, P. Kasak, I. Krupa, M.A.-A. AlMaadeed,
re
Eco-friendly electromagnetic interference shielding materials from flexible reduced graphene oxide filled polycaprolactone/polyaniline nanocomposites, Polym-Plast. Technol. Eng. 55 (2016) 920-928. [46] A. Bhaskaran, T. Prasad, T.V. Kumary, P.R. Anil Kumar, Simple and efficient approach for
lP
improved cytocompatibility and faster degradation of electrospun polycaprolactone fibers, Polym. Bull. 76 (2018) 1333-1347.
[47] W. Li, C. Zhang, H. Chi, L. Li, T. Lan, P. Han, H. Chen, Y. Qin, Development of antimicrobial
na
packaging film made from poly(lactic acid) incorporating titanium dioxide and silver nanoparticles, Molecules 22 (2017) 1170-1170.
Jo ur
[48] Z.J. Zhang, N. Li, H.Z. Li, X.J. Li, J.M. Cao, G.P. Zhang, D.L. He, Preparation and characterization of biocomposite chitosan film containing Perilla frutescens (L.) Britt. essential oil, Ind. Crop. Prod. 112 (2018) 660-667.
[49] J.P. Correa, V. Molina, M. Sanchez, C. Kainz, P. Eisenberg, M.B. Massani, Improving ham shelf life with a polyhydroxybutyrate/polycaprolactone biodegradable film activated with nisin, Food Packaging Shelf 11 (2017) 31-39.
[50] T. Janjarasskul, K. Tananuwong, M. Leuangsukrerk, T. Phupoksakul, C. Borompichaichartkul, Effects of hasten drying and storage conditions on properties and microstructure of konjac glucomannan-whey protein isolate blend films, Food Biophys. 13 (2017) 49-59. [51] X. Wei, J. Pang, C. Zhang, C. Yu, H. Chen, B. Xie, Structure and properties of moisture-resistant konjac glucomannan films coated with shellac/stearic acid coating, Carbohydr. Polym. 118 (2015) 119-125. [52] L. Ren, X. Yan, J. Zhou, J. Tong, X. Su, Influence of chitosan concentration on mechanical and barrier properties of corn starch/chitosan films, Int. J. Biol. Macromol. 105 (2017) 1636-1643. [53] H. Jafari, M. Pirouzifard, M.A. Khaledabad, H. Almasi, Effect of chitin nanofiber on the morphological and physical properties of chitosan/silver nanoparticle bionanocomposite films, Int. J. Biol. Macromol. 92 (2016) 461-466. [54] Y. Yuan, L. Wang, R.J. Mu, J. Gong, Y. Wang, Y. Li, J. Ma, J. Pang, C. Wu, Effects of konjac 18
Journal Pre-proof glucomannan on the structure, properties, and drug release characteristics of agarose hydrogels, Carbohydr. Polym. 190 (2018) 196-203. [55] Y. Huang, N. Dan, W. Dan, W. Zhao, Z. Bai, Y. Chen, C. Yang, Facile fabrication of gelatin and polycaprolactone based bilayered membranes via spin coating method with antibacterial and cyto-compatible properties, Int. J. Biol. Macromol. 124 (2019) 699-707. [56] W. Zhu, J. Li, J. Lei, Y. Li, T. Chen, T. Duan, W. Yao, J. Zhou, Y. Yu, Y. Liu, Silver nanoparticles incorporated konjac glucomannan-montmorillonite nacre-like composite films for antibacterial applications, Carbohydr. Polym. 197 (2018) 253-259. [57] H. Ji, J. Zhou, M. Liang, H. Lu, M. Li, Ultra-low temperature sintering of Cu@Ag core-shell nanoparticle
paste
by
ultrasonic
in
air
for
high-temperature
power
device
packaging,
Ultrasonics-Sonochem. 41 (2018) 375-381. [58] U.K. Fatema, M.M. Rahman, M.R. Islam, M.Y.A. Mollah, M. Susan, Silver/poly(vinyl alcohol)
of
nanocomposite film prepared using water in oil microemulsion for antibacterial applications, J. Colloid
Jo ur
na
lP
re
-p
ro
Interf. Sci. 514 (2018) 648-655.
19
Journal Pre-proof Figure captions Fig. 1. (a) Schematic diagram of microfluidic spinning process, (b) Morphologies of the KGM/PCL/AgNPs fiber films. Fig. 2. FT-IR spectra of KGM, PCL, KGM/PCL and KGM/PCL/AgNPs. Fig. 3. XRD patterns of KGM, PCL, KGM/PCL and KGM/PCL/AgNPs. Fig. 4. TGA and DTG curves of a) KGM; b) PCL; c) KGM/PCL and d) KGM/PCL/AgNPs. Fig. 5. (a) Hydrophilicity evaluations and (b) swelling degree of KGM/PCL,
of
KGM/PCL/AgNPs and PCL/AgNPs fiber films.
Jo ur
na
lP
re
-p
ro
Fig. 6. (a) Antibacterial activities against S. aureus and E. coli (the red and black arrows represent the diameter of inhibition zones and samples respectively) and (b) Inhibition zones of KGM/PCL, KGM/PCL/AgNPs and PCL/AgNPs fiber films.
20
Journal Pre-proof Tables Table 1 Thermal data details of different samples. Onset degradation temperature (C)
Residual mass (%)
KGM
279.2
26.91
PCL
409.2
2.54
KGM/PCL
415.6
3.16
KGM/PCL/AgNPs
415.4
4.44
of
Sample code
ro
Table 2 Mechanical properties of KGM/PCL and KGM/PCL/AgNPs. Tensile strength (MPa)
Elongation at break (%)
KGM/PCL
5.91 ± 0.05a
66.95 ± 34.47a
KGM/PCL/AgNPs
3.33 ± 0.03a
223.59 ± 98.14b
PCL/AgNPs
4.52 ± 0.83a
134.06 ± 81.22b
re
-p
Film Type
lP
Date are expressed in the form of mean ± SD (n = 3). Column with different superscript letters means that values are significantly different according to Duncan’s Multiple Range
Jo ur
na
Test (p < 0.05).
21
Journal Pre-proof Author statement
I have made substantial contributions to the conception of the work. And I have revised it critically for important intellectual content. I have approved the final version to be published. I agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All persons who have made substantial contributions to the work reported in the
Jo ur
na
lP
re
-p
ro
of
manuscript, are named in the manuscript.
22
Journal Pre-proof
Jo ur
na
lP
re
-p
ro
of
Graphical abstract
23
Journal Pre-proof Highlights: 1. Enhancement of antibacterial activity of fiber films was inspired by size effect (Nano-sized functional particles were loaded into micron-sized fibers via MST). 2. Even dispersion of AgNPs in fibers was achieved due to stabilizing ability of KGM. 3. Good
SD
of
KGM
contributed
to
promote
the
antibacterial
activities
of
KGM/PCL/AgNPs fiber films. 4. A new method of constructing polysaccharide micro-nano antibacterial materials was
Jo ur
na
lP
re
-p
ro
of
provided.
24
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Wanmei Lin, Yongsheng Ni, Jie Pang PII:
S0141-8130(19)37125-9
DOI:
https://doi.org/10.1016/j.ijbiomac.2020.01.242
Reference:
BIOMAC 14546
To appear in:
International Journal of Biological Macromolecules
Received date:
3 September 2019
Revised date:
6 January 2020
Accepted date:
23 January 2020
Please cite this article as: W. Lin, Y. Ni and J. Pang, Size effect-inspired fabrication of konjac glucomannan/polycaprolactone fiber films for antibacterial food packaging, International Journal of Biological Macromolecules(2018), https://doi.org/10.1016/ j.ijbiomac.2020.01.242
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2018 Published by Elsevier.
Journal Pre-proof Size effect-inspired fabrication of konjac glucomannan/polycaprolactone fiber films for antibacterial food packaging
Wanmei Lin1, Yongsheng Ni1, Jie Pang* College of Food Science, Fujian Agriculture and Forestry University, Fuzhou 350002, China *Corresponding author: Jie Pang
These authors contributed equally to this work.
ro
1
of
E-mail: [email protected]; Tel/Fax: 86-591-83756316
-p
Abstract
re
The exploration of new methods to produce food packaging with excellent
lP
physicochemical and antibacterial properties is of great scientific and technological interest.
na
Here, we successfully prepare the food packaging films that are composed of konjac glucomannan (KGM), poly(-caprolactone) (PCL) and silver nanoparticles (AgNPs) via
Jo ur
microfluidic spinning technology (MST). The obtained fiber films (average fiber diameter: 7.8 ± 0.2 m) exhibit excellent antibacterial activities against S. aureus (34 ± 0.71 mm) and E. coli (39 ± 5.66 mm), which is ascribed to the good swelling of KGM in KGM/PCL/AgNPs fiber films (SD: 37.86 ± 6.87%). Fourier transform infrared (FT-IR) spectroscopy and X-ray diffraction
(XRD)
are
employed
to
study
the
interactions
between
polymers.
Thermogravimetric analysis (TGA), derivative thermogravimetry (DTG), water vapor permeability (WVP), and mechanical property measurements are conducted to evaluate the thermal properties, hydrophilicity and mechanical performances of the films. The results show that the films are thermal stable and relatively hydrophobic (WVP: 5.8 10-6 ± 1.44 1
Journal Pre-proof
g/(mhkPa), WCA: 101.0) as well as have terrific elongation at break (EB: 223.59 ± 98.14%), which is beneficial for food packaging. This strategy provides a facile and green pathway for the construction of promising antibacterial food packaging. Keywords:
Size
effect;
Microfluidic
spinning technology;
Konjac
glucomannan;
Polycaprolactone; Silver nanoparticles; Antimicrobial food packaging
of
1. Introduction
ro
Food packaging films are significant for food processing, transport, storage and marketing. Nowadays, most food packaging materials mainly consist of petrochemical-based
-p
polymers because they are convenient, low-cost and have excellent barrier performances [1].
re
However, it is commonly accepted that those nonbiodegradable materials will cause
lP
irreversible environmental contaminations both in the long and short terms and are harmful to public health [2]. Thus, it is urgent and promising to explore food packaging films that are
na
composed of biodegradable materials. Except for the raw materials used in fabricating the food packaging films, the preparation process is also significant and valuable to be
Jo ur
investigated. Conventional approaches in preparing films such as electrospinning and casting have some inevitable disadvantages. For example, the preparation process of electrospinning nanocomposite reported by Schmatz, Costa and Morais needs high electric potential of more than 25 kV [3], which may affect the activities of the incorporated functional substances thus weaken their efficacy. Moreover, the arrangement of the fibers in the obtained nanocomposite is disordered. As for the casting method, for instance, the casting chitosan antioxidant films incorporated with the mango leaf extract lack large specific areas, which may have negative influence on the antioxidant activities [4]. Therefore, microfluidic spinning technology (MST) was employed to prepare the active food packaging films in our present study. MST has drawn considerable attention owing to its safe, simple, controllable, high-efficient, non-toxic and green attributes [5-7]. More importantly, the activities of the incorporated functional 2
Journal Pre-proof compounds in the as-prepared films could be maintained due to the mild fabrication process and be maximized on account of the large specific surface area owned by the neatly arranged fibers. Konjac glucomannan (KGM), a kind of natural heteropolysaccharide, consist of β-1,4-linked D-glucose and D-mannose with a reported ratio of 1:1.6 [8, 9]. The acetyl groups randomly existed at C-6 position per every 19 sugar unites in the polymer chains [10, 11]. Numerous KGM-based food packaging films has been reported such as KGM/pectin films
of
[12], KGM/carrageenan/nano-silica films and KGM/zein blend films [7, 13] because of its biodegradability, biocompatibility and non-toxicity [12]. More importantly, KGM may
ro
contribute to relatively even dispersion of active substance in the microchannel during
-p
microfluidic spinning owing to its stabilizing ability in solutions [14]. Also, the good swelling
re
property of KGM may play a significant role in the release of functional compounds loaded in the films [15]. According to our previous works, the pure KGM is difficult to be spinned by
lP
MST due to its poor mechanical forces [16-18]. Thus, blended spinning by incorporating
na
polymers is necessary in present study. Actually, we have successfully fabricated the hybrid ordered KGM/PVP/EGCG films via MST and investigated its potential applications in wound
Jo ur
dressings, which laid the foundation for our present research [17]. Poly(-caprolactone) (PCL) was chosen as a potential polymer for hybrid spinning. It is a kind of aliphatic polyesters and has been intensively investigated in the field of pharmacy, tissue engineering, wound healing etc. owing to its excellent biocompatibility, biodegradability and moldability [19-23]. It also has been extensively used in food packaging because of its good mechanical properties [24-26]. Besides, the barrier properties of chitosan/polycaprolactone based active bilayer films
were
enhanced
resulted
from
the
addition
of
PCL
[27].
And
polyethylene/polycaprolactone (PE/PCL) bilayer films are more thermal stable than neat PE films due to the existence of PCL [28]. And to the best of our knowledge, there is no research reporting the application of PCL in microfluidic spinning field for preparing food packaging films. Therefore, in this study, PCL was employed to enhance thermal stabilities, water vapor barrier properties and mechanical properties of fiber films. 3
Journal Pre-proof Active food packaging films have attracted ever increasing attentions in recent years especially for those ones with antibacterial or antioxidant properties such as the essential oil incorporated chitosan nanofibers and protein-based films incorporated with mango kernel extract [29, 30]. Several attempts have been made to incorporate nanoparticles (NPs) to the packaging materials because nanocomposites so formed presented not only outstanding barrier and mechanical properties but also terrific antibacterial activities on account of size effect of NPs [31]. Silver nanoparticles (AgNPs) could confer potent antibacterial abilities on
of
the fiber films [32, 33]. Thus, we employed AgNPs to prepare the KGM-based food packaging films via MST in our present research.
ro
Previous published articles primarily focused on the fabrication of microfiber films with
-p
enhanced antibacterial properties for food packaging materials inspired by the
re
hydrophilic/hydrophobic theory [5, 34]. Natural compounds such as chlorogenic acid and trans-cinnamic acid had been loaded into the fiber films for investigations. It is worth
lP
mentioning that the try of antibacterial food packaging films inspired by the
na
hydrophilic/hydrophobic theory had signified that KGM has potential applications in enhancing antibacterial activities, which laid the foundation for its further exploration in
Jo ur
strengthening antibacterial properties of food packaging materials. Despite the fact that KGM films based on hydrophilic/hydrophobic theory had been developed, it is still challenging to meet the needs of practical application. Besides, most antibacterial materials loaded with AgNPs emerged in recent years were formed in situ by reduction of silver nitrate. Regretfully, these approaches have the following potential demerits: 1) The AgNPs was on the surface of the substrate, which is difficult to achieve sustained release; 2) Chemical reaction will occur during in situ synthesis of AgNPs, which may threaten the surrounding environment, especially in the context of high usage of food packaging materials nowadays. In this paper, we provide another new strategy inspired by the size effect of NPs for the preparation of food packaging films with reinforced antibacterial performances. Artful loading of AgNPs into the fiber films and directional arrangement of fibers to form the films can be achieved by MST. Physicochemical and antibacterial properties of the prepared fiber 4
Journal Pre-proof films were evaluated. The four main innovations are as follows: 1) Nano-sized functional particles were loaded into micron-sized fibers, which could increase the antibacterial efficiency of the fiber films; 2) The aggregation of AgNPs could be effectively prevented and the even dispersion of AgNPs in fibers could be realized because of KGM's good stabilizing ability; 3) AgNPs was allowed to be loaded inside the fibers through microchannel during microfluidic spinning process, achieving slow migration from inside to outside; 4) A new method of constructing polysaccharide micro-nano antibacterial materials with controllable,
ro
of
non-toxic and green attributes was provided.
2. Materials and methods
-p
2.1. Materials
re
Konjac glucomannan (KGM, Mw = 1.0 × 106 Da, viscosity: 1% solution, ≥35, 000 MPas at 30 C, purity ≥90%) was supported by San Ai Konjac Food Co. Ltd. (Shaotong,
lP
Yunnan, China). Poly(-caprolactone) (PCL, Mn = 8.0 × 104 Da) was supplied by
na
Sigma-Aldrich Co. Ltd. (Shanghai, China). Silver nanoparticles (AgNPs) was bought from Aladdin Chemical Reagent Co. Ltd. (Shanghai, China). Other reagents and chemicals were
Jo ur
coming from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Bacterial strains including the Gram-negative bacteria Escherichia coli (ATCC25922) and the Gram-positive bacteria Staphylococcus aureus (ATCC25923) were supplied by TransGen Biotech (China).
2.2. Fabrication of KGM/PCL/AgNPs fiber films Firstly, a 25wt% PCL solution was prepared: 25g PCL was put into a beaker, adding 100 mL of CH2Cl2/CH₃CH₂OH (2:1, V/V), soaking for 24 h under a closed environment. And the solution was then stirred at the stirring rate of 600 rad/min for 12 h. Then, mixing KGM and 25wt% PCL at the stirring rate of 600 rad/min for 2 h at a weight ratio of 1:10 to form KGM/PCL solution. Finally, AgNPs (WPCL:WAgNPs = 30:1) was loaded into KGM/PCL solution at the stirring rate of 600 rad/min for 2 h to form KGM/PCL/AgNPs spinning 5
Journal Pre-proof foundation liquid. And the air bubbles in the solution were removed by ultrasonic treatment. The spinning foundation liquid of KGM/PCL and PCL/AgNPs were also obtained subsequently. KGM/PCL/AgNPs fiber films were prepared according to the previously described microfluidic spinning method with some modifications [34]. In brief, the solution was loaded into a syringe (20 mL) with 16 G stainless steel needles and then were ejected by a syringe pump. The frame receiver was employed to receive the fibers, and fiber films were formed by
of
directionally weaving with the help of horizontal step process. Schematic diagram of the microfluidic spinning process is shown in Fig. 1a and the operating parameters are as follows:
ro
speed of the syringe pump = 0.5 mL/h, speed of the frame receiver = 400 rad/min, frequency
re
prepared under the same operation condition.
-p
of the horizontal step process = 25 Hz. KGM/PCL and PCL/AgNPs fiber films were also
lP
2.3. Morphologies of KGM/PCL/AgNPs fiber films
na
Scanning electron microscopy (SEM, Hitachi S-4800, Japan) analysis was undertaken to study the morphologies of fiber films. The sputtered time was about 60 s and the accelerating
Jo ur
voltage was 5 kV.
2.4. Fourier-transform infrared (FT-IR) spectra Samples were qualitatively analyzed by using the Nicolet 6700 FT-IR spectrometer (Thermo Fisher Scientific, MA, USA) at ambient temperature in a wavenumber range of 4000 - 400 cm-1.
2.5. X-ray diffraction (XRD) The crystal structures were characterized by using an X-ray diffractometer (D8 Advance, Bruker Inc., Germany) equipped with Ni-filtered Cu Kα radiation source (λ = 0.1542 nm). The XRD curves were recorded at a scanning speed of 5/min with the 6
Journal Pre-proof diffraction angle 2θ between 5° and 80°.
2.6. Thermal properties Thermogravimetric analysis (TGA) was performed by using a synchronous thermal analyzer (STA409-PC, Netzsch, Germany) in the Nitrogen atmosphere. All
of
tested samples were heated from 25 °C to 600 °C at a heating rate of 15 °C/min.
2.7. Water vapor permeability (WVP) and water contact angle (WCA)
ro
The WVP test of fiber films was carried out according to the Chinese National Standard
-p
GB/T 1037-70 with some modifications [35]. Firstly, the fiber films were sealed over a
re
weighing bottle (25 mm × 40 mm) containing 3.0 ± 0.1 g anhydrous CaCl2. Then, the
lP
saturated NaCl solution was prepared to obtain relative humidity of 75 ± 5% in the
na
desiccators. The weighing bottles were placed in a desiccator (temperature maintained at 25 ± 5 °C) and weighted every 8 h for two consecutive days until the weight change was stable.
Jo ur
The following equation was used to calculate the WVP (g/(m2·h·kPa)): WVP =
∆𝑚 × 𝑑 S × ∆𝑡 × ∆p
where ∆𝑚 (g) represents the weight difference between initial and final, 𝑑 (mm) represents the average thickness of fiber films, S (m2) represents the permeation area of fiber films, ∆𝑡 (h) represents the permeation time, ∆p (kPa) represents the pressure difference on both sides of the fiber films. The hydrophilicity of the fiber films was also characterized by the WCA measurements. The test was conducted by using an Optical Contact Angle Meter (OCA 20, Germany) at ambient temperature. The selected water droplet volume was 4 L. At last, three angles were 7
Journal Pre-proof
measured for each sample at different regions. Photos were obtained at least 30 s after the water was placed on film surface to make sure the droplet has sufficient time to spread and realize a stable contact angle. The final reported WCA was calculated according to the averaged value.
of
2.8. Swelling degree (SD)
ro
Predefined approach was adopted to determine the SD of the fiber films. The samples (dimension of 2 cm × 2 cm) were cut from the fiber films, then were placed in a beaker
-p
containing 50 mL of distilled water. The fiber films were swelled at ambient temperature for a
re
period of time. The moisture content of the films was measured at specific time interval. The
lP
SD was calculated by the following formula:
𝑊 − W0 × 100 W0
na
SD(%) =
Jo ur
Where 𝑊 and W0 are the weights of swelled and initial dried specimens.
2.9. Antibacterial activity test
The antibacterial activity test of fiber films was conducted by using the disc diffusion method reported by Lee et al. [36], with slight modifications. Staphylococcus aureus and Escherichia coli were chosen as the representative Gram-positive and Gram-negative bacteria, respectively. All tested fiber films were sterilized before the tests by UV for 20 min. In brief, the nutrient broth (3 g beef extract, 10 g peptone and 5 g sodium chloride per 1000 mL water) was used to grow the S. aureus and E. coli. Then, 0.9% of sterile saline was used to dilute the bacterial suspension to obtained an inoculum of approximately 106 - 108 CFU/mL. 150 L of 8
Journal Pre-proof
this bacterial suspension was spread evenly over Luria-Bertani (LB) agar plates, then the center of the plates was covered with a circular sample (10 mm in diameter). After that, all LB plates were incubated at 37 °C for 24 h. The inhibition zones were measured in mm by using a Vernier caliper.
of
2.10. Mechanical properties
ro
The mechanical properties of the fiber films were evaluated by using a texture analyzer
-p
(EZ-SX, Shimadzu, Japan) with a load cell of 500 N. The tested samples were tailored into 10
re
mm × 40 mm rectangles for test. The initial clamping length was 20 mm and crosshead speed
lP
were set at 10 mm/min. The TS and EB were calculated by the following equations: TS =
𝐹 S
na
where TS (Pa) is the tensile strength, 𝐹 (N) is the maximum stress of stretching, S (m2) is
Jo ur
the initial sectional area of sample.
EB (%) =
(𝐿𝑚𝑎𝑥 − L0 ) × 100% L0
where EB is the elongation at break, L0 (mm) is the initial length of sample, 𝐿𝑚𝑎𝑥 (mm) is the length of the sample at the time of break.
2.11. Statistical analysis Experimental data were presented as the mean ± standard deviation for triplications. Date analysis and calculations were performed by using the SPSS software (SPSS 20.0 for windows, SPSS Inc., Chicago, IL). 9
Journal Pre-proof
3. Results and discussion 3.1. SEM analysis Fig. 1b exhibits the surface morphologies of KGM/PCL/AgNPs fiber films. As shown in Fig. 1b, the fiber films fabricated by MST are composed of orderly arranged fibers with relatively uniform diameters in the overall morphologies. The orderly arrangement of fibers would facilitate the uniform distribution of loaded nanoparticles in the fiber films. The mean
of
diameter of a single fiber in KGM/PCL/AgNPs fiber films is 7.8 ± 0.2 m. The main
ro
difference between the fiber films and the one that prepared through conventional casting method is the specific areas. The large specific surface areas of fiber films are beneficial for
-p
increasing the contact surface of fibers and surrounding environment, which may be
re
conducive to improve the antibacterial activities of KGM/PCL/AgNPs fiber films. Besides,
lP
the size effect of AgNPs could be enhanced through this special micromorphology viz., neatly
performances.
Jo ur
3.2. FT-IR analysis
na
arranged fibers with relatively even diameters, thereby contribute to efficient antibacterial
FT-IR spectroscopy was performed to identify the functional groups and the structural changes within the fiber film matrix. The FT-IR spectra of KGM, PCL, KGM/PCL and KGM/PCL/AgNPs are shown in Fig. 2. FT-IR spectrum of neat KGM at around 3432 cm-1, 2923 cm-1, 1726 cm-1, 1099 cm-1 were related to the vibration of O-H, C-H, C=O, C-O-C, respectively [37]. For neat PCL, the absorption peak at 3428 cm-1 was due to the stretching vibration of O-H [38]; the peaks observed at 2921 cm-1 and 2854 cm-1 were ascribed to asymmetric and symmetric modes of CH2 [39]; the peak appeared at 1797 cm-1 was attributed to the stretching vibration of C=O in the ester carbonyl group [40]; the peak at 1284 cm-1 represented the asymmetric stretching of C-O-C, which revealed the presence of -caprolactone [41]. In comparison with the FT-IR spectra of neat KGM and neat PCL, no 10
Journal Pre-proof new peaks are observed in the spectrum of KGM/PCL or KGM/PCL/AgNPs, which signified no chemical reactions occur during microfluidic spinning. But the absorption peak of O-H became narrow in the spectra of KGM/PCL and KGM/PCL/AgNPs, which probably associated with the formation of intermolecular hydrogen bonds between KGM and PCL [42]. The peak at 1726 cm-1 shifted to higher wavenumbers with increased intensity in the spectra of KGM/PCL and KGM/PCL/AgNPs, which could be assigned to the formation of hydrogen bonds between KGM and PCL. Besides, the intensity of some peaks increased in the
of
spectrum of KGM/PCL/AgNPs, which may result from van der Waals interactions between
ro
KGM and AgNPs or between PCL and AgNPs [43].
-p
3.3. XRD analysis
re
XRD analysis was performed to investigate the crystal structure changes in the fiber films [44]. The XRD patterns of KGM, PCL, KGM/PCL and KGM/PCL/AgNPs are
lP
presented in Fig. 3. For the neat PCL, two strong peaks are observed at 2 = 21.9 and 24.3,
na
which was ascribe to the Bragg angles and the diffraction of the lattice plane and the lattice plane of semi-crystalline [45]. It is noticeable that, compared with PCL, the intensity of peak
Jo ur
at 2 = 21.9 slightly decreased in the XRD pattern of KGM/PCL, which signified that the KGM may influence the crystallization of PCL. Compared with KGM/PCL, the peak at 2 = 21.9 was replaced by a gentler peak located at 2 = 21.5 in the pattern of KGM/PCL/AgNPs, and the peak at 2 = 24.3 shifted to higher diffraction angle (2 = 24.5), which could be attributed to the incorporation of silver nanoparticles. In addition, compared with KGM/PCL, no obvious increase in peak intense was observed at 2 = 21.5 and 2 = 24.5 in the XRD patterns of KGM/PCL/AgNPs, which indicated that the addition of KGM could prevent the aggregation of AgNPs. The uniform distribution of AgNPs in the KGM/PCL/AgNPs is beneficial for enhancing antibacterial effects of the fiber films.
3.4. TGA analysis 11
Journal Pre-proof Thermal analysis was conducted through TGA and DTG. The TGA and DTG curves of KGM, PCL, KGM/PCL and KGM/PCL/AgNPs are shown in Fig. 4. Detailed thermal data is provided in Table 1. KGM has two mass loss stages. The first stage of mass loss occurred at around 56.6 C, which was the consequence of water evaporation. The second stage began at around 279.2 C, which was attributed to structural damages of molecular chains and thermal decomposition [42]. While the rest of three samples only have one degradation temperature compared with KGM, which may due to incorporation of hydrophobic PCL [46]. The delayed
of
degradation temperature of KGM/PCL demonstrated that PCL could greatly improve the
ro
thermal stabilities of the fiber films [28]. Besides, the KGM/PCL/AgNPs fiber film also exhibited good thermal properties, which could be the consequence of AgNPs incorporation.
-p
This is similar to previous research that reported the addition of AgNPs could significantly
re
improve the thermal stabilities of the PLA/nano-TiO2/nano-Ag blends films [47]. Overall, the
na
potentials in food packaging.
lP
resultant KGM/PCL/AgNPs fiber film has excellent thermal stabilities, which indicated its
3.5. WVP and WCA measurements
Jo ur
Sorption and diffusion of water vapor are key factors in food packaging and storage [48]. Therefore, WVP measurements were conducted to evaluate the hydrophilicity of the obtained fiber films. WVP is the quality of water vapor permeating a unit area of film per unit time [49]. Lower WVP value of the films means higher ability of resisting water permeation. As shown in Fig. 5a, the WVP value of KGM/PCL/AgNPs is 5.8 10-6 ± 1.44 g/(mhkPa), which is lower than that of recently reported KGM-based or PCL-based films [49-51]. This may primarily due to the formation of hydrogen bonds between KGM and PCL, confirmed by the FT-IR analysis, which could decrease the number of polar groups, hence decrease the WVP value [52]. Moreover, the addition of AgNPs could increase the density of the KGM/PCL/AgNPs fiber films therefore lead to the lower WVP value. Similar results can be found in previous researches [53]. Besides, WCA measurements were also conducted to 12
Journal Pre-proof evaluate the hydrophobicity of the films, which could provide the information of the wettability of the film surface. Higher WCA value of the tested films means less water can pass through the films, which is desirable for food packaging materials. As the droplet photos shown in Fig. 5a, the KGM/PCL/AgNPs has a larger contact angle with 101.0 compared to KGM/PCL (88.4). The improved hydrophobicity can be explained by the addition of AgNPs, which is corresponding to the WVP results. Overall, the KGM/PCL/AgNPs fiber films were
of
promising for food packaging owing to its good water barrier properties.
ro
3.6. Swelling degree (SD) measurement
The SD of KGM/PCL, KGM/PCL/AgNPs and PCL/AgNPs fiber films were investigated.
-p
As shown in Fig. 5b, compared with the SD (8.10 ± 2.02%) of PCL/AgNPs fiber films, the
re
KGM/PCL (SD: 46.71 ± 5.30%) and KGM/PCL/AgNPs (SD: 37.86 ± 6.87%) fiber films present better water uptake capability. This was due to the good swelling properties of KGM
lP
[54]. It is worth mentioning that the good SD of KGM/PCL/AgNPs may promote the release
na
of AgNPs, which is similar to previous reports that mentioned the swelling properties could
Jo ur
significantly influence the drug release behavior [15].
3.7. Antibacterial analysis
Antibacterial experiments were conducted to evaluate the antibacterial properties of fiber films. As showed in Fig. 6a, there is no inhibition zones observed in the KGM/PCL group, which indicated that both KGM and PCL had no antibacterial activities. This is consistent with the previous researches [17, 55]. KGM/PCL/AgNPs displayed significant antibacterial performances against S. aureus and E. coli with inhibition diameters of 34 ± 0.71 mm and 39 ± 5.66 mm, respectively. This demonstrated that the AgNPs is successfully released from the KGM/PCL/AgNPs fiber films, which may be ascribed from the good swelling of KGM [15]. AgNPs is efficient in inhibiting the growth of bacteria because it can penetrate the bacterial and kill them by attaching to the cell membranes [47]. By contrast, nearly no inhibition zone 13
Journal Pre-proof was observed in PCL/AgNPs fiber films though loaded with AgNPs, which signified the key role of KGM in contributing to promote antibacterial efficiency. It is worth mentioning that the inhibition zones of KGM/PCL/AgNPs fiber films are larger than recent reported antibacterial KGM composite films such as the konjac glucomannan-montmorillonite nacre-like composite films (20 ~ 23 mm) and the pectin-konjac glucomannan composite edible films (13 ~ 20 mm) [56]. The antibacterial effects were greatly enhanced due to the size effect of NPs [57]. According to the abovementioned characterization analysis, we may
of
conclude that the size effect could be enhanced by three factors viz., the fibers with special micro-morphologies (neatly arranged fibers with relatively even diameters obtained via MST),
ro
good swelling and anti-aggregation properties of KGM. In addition, the inhibition area of the
-p
films against E. coli is slightly larger than that of S. aureus, which is in the line with previous
re
results [58]. This could be ascribed from the different antibacterial effects of AgNPs on
lP
different bacterium strains.
na
3.8. Mechanical analysis
Good mechanical properties of food packaging materials play an important role in
Jo ur
storage, transport and marketing. It may further influence the quality of food products. As shown in Table 2, though KGM/PCL/AgNPs was found to have relatively low tensile strength (TS), the elongation at break (EB) of KGM/PCL/AgNPs is significantly higher than that of KGM/PCL, which may primarily result from the addition of silver nanoparticles. The EB is related to the surface defects such as pits, holes, impurities, etc. Those defects tend to cause stress concentration of the films and then prematurely break from the defect. The loading of AgNPs may decrease the surface defect by increasing the dense of the fiber films. Also, the SEM images of the fibers showed that the surface was relatively smooth and free of cracks, which indicated the integrity of the KGM/PCL/AgNPs fiber films. Moreover, the EB of KGM/PCL/AgNPs is superior to the recent reported food packaging films [4, 30], which indicated its good flexibility. The results of the increased EB after the addition of AgNPs is similar to previous researches. 14
Journal Pre-proof
4
Conclusion In summary, a novel green KGM/PCL/AgNPs food packaging films was prepared via
MST which has safe, simple, controllable, high-efficient, non-toxic and green attributes. This fiber films are hydrophobic and have good thermal stabilities and mechanical properties, which indicated their promising applications in food packaging. Moreover, the films have large specific surface area and consist of neatly arranged fibers, which was beneficial for
of
enhancing the size effect of AgNPs thereby improve the antibacterial activities. More
ro
importantly, the good swelling of KGM could significantly promote the release of AgNPs thus improve the antibacterial efficiency. Meanwhile, the addition of KGM could prevent the
-p
aggregation of AgNPs, which is beneficial for AgNPs to better exert antibacterial efficacy.
lP
properties inspired by size effect of NPs.
re
Overall, our study presented a novel green packaging films with excellent antibacterial
na
Acknowledgements
The authors are grateful to the National Natural Science Foundation of China (grant
References
Jo ur
number: 31772045, 31471704).
[1] R. Accorsi, A. Cascini, S. Cholette, R. Manzini, C. Mora, Economic and environmental assessment of reusable plastic containers: A food catering supply chain case study, Int. J. Prod. Econ. 152 (2014) 88-101. [2] D. Plackett, Biodegradable polymer composites from natural fibres, Biodegradable Polym. Ind. Appl. (2005) 189-218. [3] D.A. Schmatz, J.A.V. Costa, M.G.d. Morais, A novel nanocomposite for food packaging developed by electrospinning and electrospraying, Food Packaging Shelf 20 (2019) 100314-100314. [4] K. Rambabu, G. Bharath, F. Banat, P.L. Show, H.H. Cocoletzi, Mango leaf extract incorporated chitosan antioxidant film for active food packaging, Int. J. Biol. Macromol. 126 (2019) 1234-1243. [5] W. Lin, Y. Ni, D. liu, Y. Yao, J. Pang, Robust microfluidic construction of konjac glucomannan-based micro-films for active food packaging, Int. J. Biol. Macromol. 137 (2019) 982-991. [6] W. Liu, Y. Zhang, C.F. Wang, S. Chen, Fabrication of highly fluorescent CdSe quantum dots via 15
Journal Pre-proof solvent-free microfluidic spinning microreactors, RSC Adv. 5 (2015) 107804-107810. [7] Z. Yu, C.F. Wang, L. Ling, L. Chen, S. Chen, Triphase microfluidic-directed self-assembly: anisotropic colloidal photonic crystal supraparticles and multicolor patterns made easy, Angew. Chem. Int. Edi. 51 (2012) 2375-2378. [8] K. Kato, K. Matsuda, Studies on the chemical structure of konjac mannan, Agr. Biol. Chem. 33 (1969) 1446-1453. [9] W. Lin, Y. Ni, L. Wang, D. Liu, C. Wu, J. Pang, Physicochemical properties of degraded konjac glucomannan prepared by laser assisted with hydrogen peroxide, Int. J. Biol. Macromol. 129 (2019) 78-83. [10] M. Maeda, H. Shimahara, N. Sugiyama, Detailed examination of the branched structure of konjac glucomannan, Agr. Biol. Chem. 44 (1980) 245-252. [11] K. Maekaji, Determination of acidic component of konjac mannan, Agr. Biol. Chem. 42 (1978)
of
177-178.
[12] Y. Lei, H. Wu, C. Jiao, Y. Jiang, R. Liu, D. Xiao, J. Lu, Z. Zhang, G. Shen, S. Li, Investigation of
ro
the structural and physical properties, antioxidant and antimicrobial activity of pectin-konjac glucomannan composite edible films incorporated with tea polyphenol, Food Hydrocoll. 94 (2019)
-p
128-135.
[13] R. Zhang, X. Wang, J. Wang, M. Cheng, Synthesis and characterization of konjac
re
glucomannan/carrageenan/nano-silica films for the preservation of postharvest white mushrooms, Polymers 11 (2018) 6-6.
[14] K. An, H. Kang, D. Tian, Stabilization of soy milk using konjac glucomannan, Emir. J. Food Agr.
lP
31 (2019) 526-534.
[15] Y. Yuan, X. Xu, J. Gong, R. Mu, Y. Li, C. Wu, J. Pang, Fabrication of chitosan-coated konjac glucomannan/sodium alginate/graphene oxide microspheres with enhanced colon-targeted delivery, Int.
na
J. Biol. Macromol. 131 (2019) 209-217.
[16] Y. Ni, W. Lin, R.J. Mu, L. Wang, X. Zhang, C. Wu, J. Pang, Microfluidic fabrication of robust
Jo ur
konjac glucomannan-based microfiber scaffolds with high antioxidant performance, J. Sol-Gel Sci. Techn. 90 (2019) 214-220.
[17] Y. Ni, W. Lin, R. Mu, C. Wu, Z. Lin, S. Chen, J. Pang, Facile fabrication of novel konjac glucomannan films with antibacterial properties via microfluidic spinning strategy, Carbohydr. Polym. 208 (2019) 469-476.
[18] Y. Ni, W. Lin, R.J. Mu, C. Wu, L. Wang, D. Wu, S. Chen, J. Pang, Robust microfluidic construction of hybrid microfibers based on konjac glucomannan and their drug release performance, RSC Adv. 8 (2018) 26432-26439. [19] Y. Ren, L. Wang, X. Cui, L. Han, Q. Zhou, X. Song, Synthesis and characterization of lactose grafted polycaprolactone-polysiloxane-polycaprolactone copolymers, Polym. Int. 68 (2019) 83-87. [20] P. Douglas, M. Kuhs, M. Sajjia, M. Khraisheh, G. Walker, M.N. Collins, A.B. Albadarin, Bioactive PCL matrices with a range of structural & rheological properties, React. Funct. Polym. 101 (2016) 54-62. [21] P. Douglas, A.B. Albadarin, M. Sajjia, C. Mangwandi, M. Kuhs, M.N. Collins, G.M. Walker, Effect of poly ethylene glycol on the mechanical and thermal properties of bioactive poly(epsilon-caprolactone) melt extrudates for pharmaceutical applications, Int. J. Pharm. 500 (2016) 179-186. [22] N. Gomez-Cerezo, L. Casarrubios, M. Saiz-Pardo, L. Ortega, D. de Pablo, I. Diaz-Guemes, B. 16
Journal Pre-proof Fernandez-Tome, S. Enciso, F.M. Sanchez-Margallo, M.T. Portoles, D. Arcos, M. Vallet-Regi, Mesoporous bioactive glass/varepsilon-polycaprolactone scaffolds promote bone regeneration in osteoporotic sheep, Acta Biomater. 90 (2019) 393-402. [23] B. Joseph, R. Augustine, N. Kalarikkal, S. Thomas, B. Seantier, Y. Grohens, Recent advances in electrospun polycaprolactone based scaffolds for wound healing and skin bioengineering applications, Mater. Today Commun. 19 (2019) 319-335. [24] S. Alix, A. Mahieu, C. Terrie, J. Soulestin, E. Gerault, M.G.J. Feuilloley, R. Gattin, V. Edon, T. Ait-Younes, N. Leblanc, Active pseudo-multilayered films from polycaprolactone and starch based matrix for food-packaging applications, Eur. Polym. J. 49 (2013) 1234-1242. [25] S. Cesur, C. Köroğlu, H.T. Yalçın, Antimicrobial and biodegradable food packaging applications of polycaprolactone/organo nanoclay/chitosan polymeric composite films, J. Vinyl Additive Technol. 24 (2018) 376-3877.
of
[26] J.M. Ferri, O. Fenollar, A. Jorda-Vilaplana, D. García-Sanoguera, R. Balart, Effect of miscibility on mechanical and thermal properties of poly(lactic acid)/polycaprolactone blends, Polym. Int. 65
ro
(2016) 453-463.
[27] E. Sogut, A.C. Seydim, Development of chitosan and polycaprolactone based active bilayer films
-p
enhanced with nanocellulose and grape seed extract, Carbohydr. Polym. 195 (2018) 180-188. [28] A. Rešček, M. Ščetar, Z. Hrnjak-Murgić, N. Dimitrov, K. Galić, Polyethylene/polycaprolactone
re
nanocomposite films for food packaging modified with magnetite and casein: Oxygen barrier, mechanical, and thermal properties, Polym-Plast. Technol. 55 (2016) 1450-1459. [29] L. Lin, X. Mao, Y. Sun, G. Rajivgandhi, H. Cui, Antibacterial properties of nanofibers containing 21-30.
lP
chrysanthemum essential oil and their application as beef packaging, Int. J. Food Microbiol. 292 (2019) [30] Z.A. Maryam Adilah, B. Jamilah, Z.A. Nur Hanani, Functional and antioxidant properties of (2018) 207-218.
na
protein-based films incorporated with mango kernel extract for active packaging, Food Hydrocoll. 74
Jo ur
[31] R. Priyadarshi, Y.S. Negi, Effect of varying filler concentration on zinc oxide nanoparticle embedded chitosan films as potential food packaging material, J. Polym. Environ. 25 (2016) 1087-1098.
[32] M. Carbone, D.T. Donia, G. Sabbatella, R. Antiochia, Silver nanoparticles in polymeric matrices for fresh food packaging, Journal of King Saud University - Science 28 (2016) 273-279. [33] G. Franci, A. Falanga, S. Galdiero, L. Palomba, M. Rai, G. Morelli, M. Galdiero, Silver nanoparticles as potential antibacterial agents, Molecules 20 (2015) 8856-8874. [34] W. Lin, Y. Ni, J. Pang, Microfluidic spinning of poly (methyl methacrylate)/konjac glucomannan active food packaging films based on hydrophilic/hydrophobic strategy, Carbohydr. Polym. 222 (2019) 114986-114986. [35] L. Lin, L. Xue, S. Duraiarasan, C. Haiying, Preparation of ε-polylysine/chitosan nanofibers for food packaging against Salmonella on chicken, Food Packaging Shelf 17 (2018) 134-141. [36] J.Y. Lee, C.V. Garcia, G.H. Shin, J.T. Kim, Antibacterial and antioxidant properties of hydroxypropyl methylcellulose-based active composite films incorporating oregano essential oil nanoemulsions, LWT - Food Sci. Technol. 106 (2019) 164-171. [37] K. Wang, S. Gao, C. Shen, J. Liu, S. Li, J. Chen, X. Ren, Y. Yuan, Preparation of cationic konjac glucomannan in NaOH/urea aqueous solution, Carbohydr. Polym. 181 (2018) 736-743. [38] Y. Yao, H. Wei, J. Wang, H. Lu, J. Leng, D. Hui, Fabrication of hybrid membrane of electrospun 17
Journal Pre-proof polycaprolactone and polyethylene oxide with shape memory property, Compos. Part B 83 (2015) 264-269. [39] Y.S. Joo, J.R. Cha, M.S. Gong, Biodegradable shape-memory polymers using polycaprolactone and isosorbide based polyurethane blends, Mat. Sci. Eng. C 91 (2018) 426-435. [40] J. Kim, H.M. Mousa, C.H. Park, C.S. Kim, Enhanced corrosion resistance and biocompatibility of AZ31 Mg alloy using PCL/ZnO NPs via electrospinning, Appl. Surf. Sci. 396 (2017) 249-258. [41] J. Amirian, S.Y. Lee, B.T. Lee, Designing of combined nano and microfiber network by immobilization of oxidized cellulose nanofiber on polycaprolactone fibrous scaffold, J. Biomed. Nanotechnol. 12 (2016) 1864-1875. [42] T. Chen, P. Shi, J. Zhang, Y. Li, T. Duan, L. Dai, L. Wang, X. Yu, W. Zhu, Natural polymer konjac glucomannan mediated assembly of graphene oxide as versatile sponges for water pollution control, Carbohydr. Polym. 202 (2018) 425-433.
of
[43] S. Roy, S. Shankar, J.W. Rhim, Melanin-mediated synthesis of silver nanoparticle and its use for the preparation of carrageenan-based antibacterial films, Food Hydrocoll. 88 (2019) 237-246.
ro
[44] L. Wang, Y. Du, Y. Yuan, R.J. Mu, J. Gong, Y. Ni, J. Pang, C. Wu, Mussel-inspired fabrication of konjac glucomannan/microcrystalline cellulose intelligent hydrogel with pH-responsive sustained
-p
release behavior, Int. J. Biol. Macromol. 113 (2018) 285-293.
[45] D. Ponnamma, K.K. Sadasivuni, M. Strankowski, P. Kasak, I. Krupa, M.A.-A. AlMaadeed,
re
Eco-friendly electromagnetic interference shielding materials from flexible reduced graphene oxide filled polycaprolactone/polyaniline nanocomposites, Polym-Plast. Technol. Eng. 55 (2016) 920-928. [46] A. Bhaskaran, T. Prasad, T.V. Kumary, P.R. Anil Kumar, Simple and efficient approach for
lP
improved cytocompatibility and faster degradation of electrospun polycaprolactone fibers, Polym. Bull. 76 (2018) 1333-1347.
[47] W. Li, C. Zhang, H. Chi, L. Li, T. Lan, P. Han, H. Chen, Y. Qin, Development of antimicrobial
na
packaging film made from poly(lactic acid) incorporating titanium dioxide and silver nanoparticles, Molecules 22 (2017) 1170-1170.
Jo ur
[48] Z.J. Zhang, N. Li, H.Z. Li, X.J. Li, J.M. Cao, G.P. Zhang, D.L. He, Preparation and characterization of biocomposite chitosan film containing Perilla frutescens (L.) Britt. essential oil, Ind. Crop. Prod. 112 (2018) 660-667.
[49] J.P. Correa, V. Molina, M. Sanchez, C. Kainz, P. Eisenberg, M.B. Massani, Improving ham shelf life with a polyhydroxybutyrate/polycaprolactone biodegradable film activated with nisin, Food Packaging Shelf 11 (2017) 31-39.
[50] T. Janjarasskul, K. Tananuwong, M. Leuangsukrerk, T. Phupoksakul, C. Borompichaichartkul, Effects of hasten drying and storage conditions on properties and microstructure of konjac glucomannan-whey protein isolate blend films, Food Biophys. 13 (2017) 49-59. [51] X. Wei, J. Pang, C. Zhang, C. Yu, H. Chen, B. Xie, Structure and properties of moisture-resistant konjac glucomannan films coated with shellac/stearic acid coating, Carbohydr. Polym. 118 (2015) 119-125. [52] L. Ren, X. Yan, J. Zhou, J. Tong, X. Su, Influence of chitosan concentration on mechanical and barrier properties of corn starch/chitosan films, Int. J. Biol. Macromol. 105 (2017) 1636-1643. [53] H. Jafari, M. Pirouzifard, M.A. Khaledabad, H. Almasi, Effect of chitin nanofiber on the morphological and physical properties of chitosan/silver nanoparticle bionanocomposite films, Int. J. Biol. Macromol. 92 (2016) 461-466. [54] Y. Yuan, L. Wang, R.J. Mu, J. Gong, Y. Wang, Y. Li, J. Ma, J. Pang, C. Wu, Effects of konjac 18
Journal Pre-proof glucomannan on the structure, properties, and drug release characteristics of agarose hydrogels, Carbohydr. Polym. 190 (2018) 196-203. [55] Y. Huang, N. Dan, W. Dan, W. Zhao, Z. Bai, Y. Chen, C. Yang, Facile fabrication of gelatin and polycaprolactone based bilayered membranes via spin coating method with antibacterial and cyto-compatible properties, Int. J. Biol. Macromol. 124 (2019) 699-707. [56] W. Zhu, J. Li, J. Lei, Y. Li, T. Chen, T. Duan, W. Yao, J. Zhou, Y. Yu, Y. Liu, Silver nanoparticles incorporated konjac glucomannan-montmorillonite nacre-like composite films for antibacterial applications, Carbohydr. Polym. 197 (2018) 253-259. [57] H. Ji, J. Zhou, M. Liang, H. Lu, M. Li, Ultra-low temperature sintering of Cu@Ag core-shell nanoparticle
paste
by
ultrasonic
in
air
for
high-temperature
power
device
packaging,
Ultrasonics-Sonochem. 41 (2018) 375-381. [58] U.K. Fatema, M.M. Rahman, M.R. Islam, M.Y.A. Mollah, M. Susan, Silver/poly(vinyl alcohol)
of
nanocomposite film prepared using water in oil microemulsion for antibacterial applications, J. Colloid
Jo ur
na
lP
re
-p
ro
Interf. Sci. 514 (2018) 648-655.
19
Journal Pre-proof Figure captions Fig. 1. (a) Schematic diagram of microfluidic spinning process, (b) Morphologies of the KGM/PCL/AgNPs fiber films. Fig. 2. FT-IR spectra of KGM, PCL, KGM/PCL and KGM/PCL/AgNPs. Fig. 3. XRD patterns of KGM, PCL, KGM/PCL and KGM/PCL/AgNPs. Fig. 4. TGA and DTG curves of a) KGM; b) PCL; c) KGM/PCL and d) KGM/PCL/AgNPs. Fig. 5. (a) Hydrophilicity evaluations and (b) swelling degree of KGM/PCL,
of
KGM/PCL/AgNPs and PCL/AgNPs fiber films.
Jo ur
na
lP
re
-p
ro
Fig. 6. (a) Antibacterial activities against S. aureus and E. coli (the red and black arrows represent the diameter of inhibition zones and samples respectively) and (b) Inhibition zones of KGM/PCL, KGM/PCL/AgNPs and PCL/AgNPs fiber films.
20
Journal Pre-proof Tables Table 1 Thermal data details of different samples. Onset degradation temperature (C)
Residual mass (%)
KGM
279.2
26.91
PCL
409.2
2.54
KGM/PCL
415.6
3.16
KGM/PCL/AgNPs
415.4
4.44
of
Sample code
ro
Table 2 Mechanical properties of KGM/PCL and KGM/PCL/AgNPs. Tensile strength (MPa)
Elongation at break (%)
KGM/PCL
5.91 ± 0.05a
66.95 ± 34.47a
KGM/PCL/AgNPs
3.33 ± 0.03a
223.59 ± 98.14b
PCL/AgNPs
4.52 ± 0.83a
134.06 ± 81.22b
re
-p
Film Type
lP
Date are expressed in the form of mean ± SD (n = 3). Column with different superscript letters means that values are significantly different according to Duncan’s Multiple Range
Jo ur
na
Test (p < 0.05).
21
Journal Pre-proof Author statement
I have made substantial contributions to the conception of the work. And I have revised it critically for important intellectual content. I have approved the final version to be published. I agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All persons who have made substantial contributions to the work reported in the
Jo ur
na
lP
re
-p
ro
of
manuscript, are named in the manuscript.
22
Journal Pre-proof
Jo ur
na
lP
re
-p
ro
of
Graphical abstract
23
Journal Pre-proof Highlights: 1. Enhancement of antibacterial activity of fiber films was inspired by size effect (Nano-sized functional particles were loaded into micron-sized fibers via MST). 2. Even dispersion of AgNPs in fibers was achieved due to stabilizing ability of KGM. 3. Good
SD
of
KGM
contributed
to
promote
the
antibacterial
activities
of
KGM/PCL/AgNPs fiber films. 4. A new method of constructing polysaccharide micro-nano antibacterial materials was
Jo ur
na
lP
re
-p
ro
of
provided.
24
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6