A detailed investigation of the effect of calcium crosslinking and glycerol plasticizing on the physical properties of alginate films

Journal Pre-proof A detailed investigation of the effect of calcium crosslinking and glycerol plasticizing on the physical properties of alginate films

Ayse Su Giz, Melisa Berberoglu, Semira Bener, Sena AydelikAyazoglu, Halil Bayraktar, B. Erdem Alaca, Huceste Catalgil-Giz PII:

S0141-8130(19)37887-0

DOI:

https://doi.org/10.1016/j.ijbiomac.2020.01.103

Reference:

BIOMAC 14407

To appear in:

International Journal of Biological Macromolecules

Received date:

29 September 2019

Revised date:

4 January 2020

Accepted date:

9 January 2020

Please cite this article as: A.S. Giz, M. Berberoglu, S. Bener, et al., A detailed investigation of the effect of calcium crosslinking and glycerol plasticizing on the physical properties of alginate films, International Journal of Biological Macromolecules(2020), https://doi.org/ 10.1016/j.ijbiomac.2020.01.103

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© 2020 Published by Elsevier.

Journal Pre-proof

A detailed investigation of the effect of calcium crosslinking and glycerol plasticizing on the physical properties of alginate films Ayse Su Giz1a, Melisa Berberoglu2, Semira Bener2, Sena Aydelik-Ayazoglu2, Halil Bayraktar3, B. Erdem Alaca1,4, Huceste Catalgil-Giz2* 1

Dep. of Mech. Engineering, Koc University, Rumelifeneri Yolu, Sariyer 34450 Istanbul, Turkey Dept. of Chemistry, Faculty of Sciences, ITU, Maslak 34467 Istanbul, Turkey

3

Dept. of Molecular Biology and Genetics, ITU, Maslak 34467 Istanbul, Turkey

4

Surface Sci.&Techn. Center, KUYTAM, Koc University, Sariyer 34450 Istanbul,Turkey

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Present address: ITU, Faculty of Mechanical Engineering, 34437 Beyoglu, Istanbul, Turkey

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Abstract

Alginates attract growing interest due to their biocompatible and biodegradable nature. Here, a wide

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spectrum of glycerol added alginate films (from 0 to 30% w/w, glycerol/alginate) were prepared and

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crosslinked by four different concentrations of calcium chloride solutions (0.5, 1, 1.5, 2%, w/w). This

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is the first investigation involving variation of both the plasticizer and cross linker concentrations in twenty different compositions. It is shown that glycerol and calcium have a synergic effect on the mechanical properties and the behavior of crosslinked and plasticized alginate films cannot be predicted by studies, which vary only one of these, keeping the other constant. Without glycerol, crosslinking had a negligible effect on tensile behavior, but with glycerol addition, the effect of crosslinking became evident in mechanical properties. Calcium and glycerol concentrations exhibited a combined effect, displaying optimum combinations with good strength and fracture strain properties. Crosslinking increased the thermal resistance of all films. Low crosslinked high swelling films and highly crosslinked low swelling films were prepared. Water vapor permeability of films

Journal Pre-proof decreased regularly with increasing calcium concentration. The films exhibited high transmittance in the visible region. The results showed that alginate films have an appreciable potential in wound dressing and food packaging applications. Key words: Alginate films; crosslinking; wound dressing; food packaging. 1.

Introduction

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The severe environmental problems created by packaging wastes necessitate the use of biodegradable

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and edible packaging materials [1]. Polysaccharides with biodegradable and biocompatible nature have drawn great interest in this area [2]. Alginic acid is a linear polysaccharide, obtained from brown

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algae which consists of mannuronic acid and guluronic acid monomers. Sodium alginate (alginate) is

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its sodium salt and it is a naturally occurring anionic polymer that has found many applications from

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wound dressings [3–6] to food packaging [7–9]. Pure alginate films are not suitable for these applications since they are water soluble and brittle with poor tensile properties but these properties

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can be improved through application of different plasticizers and crosslinking agents. Plasticizing

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with glycerol and externally crosslinking with calcium chloride is a very popular way to improve

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physical properties of alginate films [10–14]. Reports in the literature are either based on a specific set of fixed concentrations or are on the effects of the variation of either the glycerol (Gly) or the calcium crosslinking on the physical properties of alginate films while the other concentration is kept fixed. Properties of 28% Gly added alginate based films reinforced with cellulose fibers and cellulose nanowhiskers were examined [10]. Silicon dioxide containing nanocomposite sodium alginate films were prepared with 25% Gly and 5% Ca crosslinking and physical properties were investigated [11]. The effect of gluronate / mannuronate ratio on the alginate film quality was investigated in 28 % glycerol added and dipped into 10 % Ca solution for 1, 3, 5, 10 and 20 1 to 20 minutes [12]. Physical parameters of 50% Gly plasticized and 1,

Journal Pre-proof 2, 3, 5% Ca crosslinked alginate films were measured [13]. Alginate films prepared with 23% Gly and crosslinked with different concentrations of Mn, Zn, Ca salts were prepared and physical properties of films were investigated [14]. Recently calcium alginate containing hydrogels have found applications in adsorption, filitration, nano-filitration and photo catalytic degradation fields [15-19] The thicknesses of above films also varied. The differences in film thicknesses, alginate percentage and experimental conditions all affect the outcomes. All above work covered some specific points in

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the externally Ca crosslinked alginate films subject.

Up to the authors knowledge none of them had a parametric study varying both glycerol and calcium

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chloride concentrations. In this work, glycerol amounts in the films were varied from 0 to 30% (w/w,

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glycerol/alginate) and calcium chloride amounts in the crosslinking solutions were varied from 0 to

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2% (w/w). Mechanical and thermal properties, transmittance, thicknesses, water vapor permeability and swelling properties of the films were investigated as functions of calcium and glycerol

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concentrations. From these results one can decide on a suitable set of parameters for a desired

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2. Experimental

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application such as a wound dressing or food packaging.

2.1. Materials and film preparation Alginate (Aldrich, medium viscosity, composed of approximately 61% of mannuronic and 39% of guluronic acid units and M/G ratio of 1.56. (R&A - WE - Tech Support, Aldrich)), glycerol (Gly, Merck, anhydrous, purity ≥ 99.5 %, boiling point 290oC) and calcium chloride (Ca, Aldrich) were used as received. Distilled water was used in the film preparations. 1 % (w/w, by weight) alginate solution was prepared by mixing alginate in water vigorously for 2 hours and a homogenous solution was obtained. 0, 10, 20, 30% Gly (w/w with respect to alginate mass) was added to the alginate

Journal Pre-proof solution. 30g of the alginate-Gly solution was poured in an 8.5 cm diameter polystyrene petri dish and dried at 60oC overnight. Smooth films were obtained by externally crosslinking dry films by dipping into three calcium chloride solutions in 100 % ethanol, 50 % ethanol – 50 % water (by weight) mixture and 100% water consecutively. Films were dipped into 50 ml of fresh calcium chloride solution in a 10 cm diameter beaker, for 15 minutes for each side (30 minutes total), for each concentration. Schematic preparation of the films are shown in Fig.1. Wet films were whipped off

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with a paper towel and left to dry at 24oC and 38±1% relative humidity until constant weight. The

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films were labelled according to their Gly and calcium chloride concentrations in the crosslinking

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solutions as given in Fig. 2. Digital photos of the films were placed over the corresponding labels.

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Fig. 1. Schematic preparation of calcium chloride crosslinked alginate films 2.2. Spectrometric analysis and film thickness Fourier transform infrared (FTIR) analyses were performed using a Perkin Elmer FT-IR 100 Spectrometer in the range of 600-4000 cm-1. A Shimadzu double beam spectrophotometer UV-150-02 was used for UV measurements. Film samples (1.5 cm x 4 cm) were placed in the cells and measured against air. Transmittance was calculated according to the formula [20].

Journal Pre-proof Transmittance=10-Abs

(1)

Here Abs is the normalized absorbance of the film for the mean film thickness. According to above equation, low Abs values indicate high degree of transmittance and low opacity. The thickness of each film was determined using a digital micrometer (0 - 25 mm, 1 µm sensitivity) at four randomly selected points of the film. The mean value of these four measurements was used.

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Fig.2. The labels of the alginate films according to their glycerol content and calcium chloride

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the films were placed over the corresponding labels.

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content of the cross-linking solution. To show the transparency of the alginate films digital photos of

2.2.Mechanical properties

Stress-strain measurements were performed with a custom-built tensile stretcher composed of a load cell and a stepper motor, details of which were described elsewhere [21, 22]. The alginate films were cut into dogbone shapes according to the ASTM D638-01 43 standard scaled by a factor of 0.2 with spots drilled on both ends for attachment to grips [23]. Four to six samples were tested for each composition to obtain a set of statistically significant results. The ratio of the force to the initial cross-sectional area of the sample gage section was designated as stress. Stress and

Journal Pre-proof strain measurements at the fracture point provided the tensile strength (TS) and the fracture strain (%E) values through following formulas [13, 14]. Maximum force at break (N)

TS = Initial cross sectional area of film (mm2 ) E=

Elongation at break (Δl mm) Initial length (mm)

(2)

× 100

(3)

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Experiments were performed at 24 oC and relative humidity (RH) level of 38 ± 1%. Temperature and

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RH levels were monitored by taking measurements every 15 minutes throughout each experiment with an accuracy of 0.1°C and 0.1% RH, respectively (Termolog® Standart / Wifi temperature and

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RH sensor).

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2.4. Thermal properties

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Thermogravimetric analysis (TGA) of the samples were carried out using a SEIKO EXTAR 6200

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TG/DTA instrument under nitrogen flow of 150 mL/min. 5 mg samples were heated from 30°C to

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900 °C at a heating rate of 10 °C/min.

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2.5. Swelling and water vapor permeability Swelling measurements were performed in three solutions, water, 1M acetic acid and 1M citric acid which are among the most frequently used solutions in food industry. Alginate film samples of 7 cm2 area were placed in petri dishes containing 25 ml of the soaking solution. The samples were periodically drained and dried with a dry paper towel and weighed until 100th minute. Mean value of three measurements are quoted. Swelling ratio was calculated by the following equation [4, 5, 6, 9, 13]. Swelling ratio (%) =

Wt −W0 W0

× 100.

(4)

Journal Pre-proof Here W0 and Wt are the weights of the films at the beginning and at time t. The water vapor permeability (WVP) values of the films were measured gravimetrically according to the ASTM, E96-05 standard [10, 13, 14, 24]. 100 ml beakers (with 5.57cm diameter) containing 50 ml water were covered with alginate films and tightly sealed. Water inside the beaker was 40 mm below the film surface and was magnetically stirred. Air was continuously blown by fan over the beaker to prevent formation of a stagnant humid air layer above the film which can affect water vapor

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transport [25]. Experiments were performed at 24±1oC and relative humidity of 38±1%. The beakers

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were weighed every hour for 8 hours, then at the 24th hour. Water vapor transmission rate (WVTR)

𝑑𝑚⁄𝑑𝑡

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𝑊𝑉𝑇𝑅 = −

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was calculated by dividing the mass loss rate (− 𝑑𝑚⁄𝑑𝑡 ) to the film area (A).

𝐴

(5)

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The WVP of the films in (g.mm) / (kPa.h.m2) were calculated from Eq.6. Here L is the thickness of

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2.6. Statistical analysis

(6)

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𝑊𝑉𝑃 = 𝑊𝑉𝑇𝑅 × L / ΔP

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the film and ΔP is the difference of the water vapor pressures inside and outside of the cup.

Statistical analysis was accomplished by Matlab software and Student t test was applied to the results and differences were accepted as significant when p-values were less than 0.05. 3. Results 3.1. Spectrometric analysis and film thickness For the IR analysis of the films, three representative spectra are shown in Fig. 3 (with maximum glycerol (30Gly-0Ca, at the top); pure alginate (0Gly-0Ca, in the middle) and with maximum calcium (0Gly-2Ca, at the bottom). Varying Gly concentrations did not make any difference in the IR bands. The O-H and C-H bonds at 3255 cm-1 and 2931cm-1 can be seen in all three spectra in the figure. The

Journal Pre-proof peaks at 1595 cm-1 and 1406 cm-1 belong to the -COO- group. Peaks at 1081cm-1 and 1024 cm-1 represent stretching vibrations of C-O-C bonds. The peak near 1027 cm-1 originates from the coupling of the C-O, C-C and C-O-H vibrations in the carbohydrate region (1200-870 cm-1). The peaks at 819, 886 and 935 cm-1 are characteristic for polysaccharide structures. The strong absorption band at 30003500 cm-1 is due to OH groups. Due to Ca crosslinking, the O-H absorbance of the 2Ca crosslinked film has shifted from 3254 (0Gly-0Ca) to 3231 cm-1 (0Gly-2Ca) as compared to the 0Ca pure alginate

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film. Similarly, the C-O-O band has shifted from 1591 to 1583 cm-1 and the –COO band has shifted

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Fig. 3. IR spectra of three films, 30Gly-0Ca (top trace), 0Gly-0Ca (middle trace), 0Gly-2Ca (bottom trace)

Fig. 4. Transmittance of all 10Gly films

from 1406 to 1413 cm-1. Polysaccharide structure and effect of Ca crosslinking are evident in representing films [26-28]. Transmittance of all films had similar character and as a representative 10Gly films are shown in Fig. 4. Films had low transmittance (40-50%) before 400 nm (UV band), and high transmittance (>75%) in the visible region which is important in food packaging and wound dressing applications. At all regions transmittance decreased as the crosslinking was increased. UV degradation is important in the ripening process of fruits and vegetables and low transmittance of films in UV region will decrease

Journal Pre-proof the UV degradation rate of fruits or vegetables in the package. High transmittance in the visible region is a must because see trough packaging material is demanded in the market. Low transmittance in the UV region, is also important in wound dressing and high transmittance in the visible region is required to monitor the healing process. Thickness

WVPx10-10

WVTR

label

mm

g/(m s Pa)

g/ (m2 day)

0Gly-1Ca

0.0413±0.0011

5.45 ± 0.5

1294±12

0Gly-2Ca

0.0320±0.0012

3.72 ± 0.9

1080±26

10Gly-1Ca

0.0385±0.0009

5.79 ± 0.6

1577±16

10Gly-2Ca

0.0382±0.0011

4.55 ± 0.4

20Gly-1Ca

0.0384±0.0011

5.18 ± 0.9

1433±25

20Gly-2Ca

0.0297±0.0012

3.17 ± 0.4

1042±13

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Film

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1188±10

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Table 1. Thicknesses and water vapor permeability and water vapor transfer values of OGly, 10Gly,

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20Gly and 1Ca and 2Ca films

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O, 10, 20Gly and 1% and 2% Ca film thicknesses are given in Table 1 as a representative of all films.

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For wound dressing, a thickness lower than that of human skin is desirable [29]. The dermis thickness depends on age, gender, and place in the body and varies from 0.5mm to 2.0 mm [29, 30]. For food packaging, films in the market are usually in 0.080-0.300 mm range [8]. All film thicknesses were less than 0.5 mm and were appropriate for wound dressing applications. For food packaging applications, appropriate film thickness can be obtained with higher alginate concentrations. Transmittance of films were both appropriate for wound dressing and food packaging applications. 3. 2. Mechanical properties

Journal Pre-proof The effect of Ca crosslinking and the effect of Gly concentration on the stress-strain behavior of all

c

d

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films are shown in Fig. 5 a-d, where the results are plotted up to a strain of 3% for clarity. Young’s

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Fig. 5. Stress strain behavior of all alginate films up to 3% strain.

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Table 2. Young’s Moduli of all films tested

Young’s Moduli, MPa

Ca

0Gly

10Gly

20Gly

30Gly

0

2034 ± 548

1028±278

1132±334

632 ± 316

0.5

2136± 597

1815±159

1844±534

2111 ± 612

1.0 2093 ± 491

3387 ± 381

2156 ± 494

2530 ± 736

1.5 1936 ± 276

2894 ± 577

2232 ± 773

2015 ± 297

2.0 1976 ± 521

3161 ± 646

2847 ± 328

2019 ± 365

Journal Pre-proof

moduli of all films are given in Table 2. The elastic behavior of 0Gly films were almost independent of Ca concentrations in Fig. 5a. The Young’s moduli of these 0Gly films were similar at around 2GPa. An addition of 10% Gly lead to a spread out of stress-strain curves as seen in Fig. 5b and similarly affected the Young’s modulus. Young’s modulus of 2Ca film increased up to 3 GPa, while Young’s modulus of 0 Ca film decreased to 1.3 GPa. Further addition of glycerol decreased the

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Young’s moduli once again (Fig. 5c and 5d) indicating the impressively high performance at

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10%Gly. At 30%Gly the distinction between the films stiffness once again decreased, this time

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because all films became softer with considerable increase of Gly content.

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The nonlinear effect of glycerol and calcium crosslinking is more clearly visible in 3-dimensional

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(3D) plots. In Fig. 6a, the effects of Gly and Ca on the fracture strain are shown, and in Fig. 6b the effects of Gly and Ca on the tensile strength are shown in 3D plots. In Fig. 6a, the fracture strain

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values of the films show that Gly addition provided more mobility by replacing hydrogen bonds and

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increased the fracture strain in all samples. The effects of Ca addition were more complex, displaying

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optimum balance points for each Gly level. For 0Gly films, fracture strain first decreased from 5.22 % at 0Ca, to 3.19 % at 2Ca, but displayed a minor peak at 4.59 at 1.5Ca. 10Gly and 20Gly films had similar fracture strain values for all Ca concentrations except for 20Gly-1.5Ca, where the fracture strain was about 6.6%, the highest fracture strain for films with Ca crosslinking. The overall highest fracture strain value was observed for 30Gly-0Ca films at 8.6 %. For 30Gly films the strain decreased to 3.49 % as the Ca crosslinking was increased up to 2Ca. In Fig. 6b, for 0Gly and 30 Gly, increasing the crosslinking from 0Ca to 0.5Ca increased the tensile strength from 71.1 to 134.8 Mpa, and 60.6 to 146.5 MPa respectively. This low Ca cross linking had a great effect, increasing stiffness and strength of the film by ionically bonding alginate chains.

Journal Pre-proof However further increase of Ca caused brittleness, lowering the film strength to 85MPa for 0Gly-2Ca and 90.5Mpa for 30Gly-2Ca. In the cases of 10Gly, and 20Gly films, strength increased with increasing Ca concentration, from 68.8 and 69 MPa at 0Ca to up to 186.5MPa at 10Gly-2Ca and 189.8MPa at 20Gly-1.5Ca, displaying the highest tensile strength among all concentrations. As can be seen from Fig. 6b, the increasing Gly content reduced brittleness and increased the tensile strength for crosslinked samples. However, increasing Gly beyond a certain limit lowered the film

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strength. A clear peak was formed at these concentrations, indicating a balance point between the

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strength increase from Ca and ductility improvement from Gly. As Gly and Ca are the plasticizing

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and crosslinking agents, respectively, this behavior is expected. 10Gly films showed the best

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mechanical properties.

b)

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Fig. 6. The effect of Ca and Gly on (a) fracture strain, and (b) on tensile strength. In the case of food packaging applications, biopolymers of tensile strength of 4-150 MPa and elongation at break of 4-103% have found applications [8] with the films in this study exhibiting similar values. For wound-dressing applications, films must present similar physical properties to human skin. In the literature, for human skin, a tensile strength of 5-30MPa and fracture strains on the

Journal Pre-proof order of 35–115% were cited [31]. Although our films have higher tensile strength and lower elongation values, there is room for optimization, especially with higher Gly concentrations. Student’s t test comparison of all films with different Gly concentrations showed that 10Gly and 20Gly films were statistically distinguishable from 0Gly and 30Gly films (with p < 0.05). Brittle films with 0Gly and 0Ca form one end of the spectrum and are clearly distinguishable from all others. Similarly soft 30Gly- 0Ca formed the other end, and were statistically distinguishable from most

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combinations.

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3.3. Thermal properties

Thermo-gravimetric analysis was used to investigate the thermal stability of films [1, 6, 7]. Glycerol

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concentration did not have any effect on the thermo-gravimetric profiles. To demonstrate the effect of

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Gly and Ca crosslinking on alginate films only the results of 10Gly films are shown in Fig. 7. In Fig.

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7a, derivative thermo-gravimetric (DTG), and in Fig. 7b, thermo-gravimetric (TG) results in air atmosphere are shown. To improve the clarity DTG curves of 10Gly-0Ca and 0Gly-2Ca curves were

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shifted vertically. The first peaks in the DTG curves, below 200oC, correspond to moisture loss.

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Polysaccharides have a strong affinity for water, and alginate contains two hydroxyl segments and one carboxylate segment, the water molecules can be bound to alginate by the hydrophilic -COONa and –OH groups. Because -COONa groups of alginate are bound by Ca++ ions, crosslinked films adsorb less moisture than uncrosslinked films, and for that reason, the crosslinked films in Fig.7a lost less weight than the 10Gly-0Ca film. Alginate degradation occurs around 200-230oC. 10Gly-0Ca film gave a sharp peak at 202.6oC due to degradation of alginate. In the case of 10Gly-2Ca and 0Gly2Ca crosslinked films, degradation peak is broader and a shoulder appears indicating that the crosslink structure is shifting the alginate degradation to relatively higher temperatures. The effect of Ca crosslinking can be seen more clearly on the TG plot in Fig.7b. Before 200oC 20% moisture loss

Journal Pre-proof is evident in all films. After 200oC, 10Gly-0Ca film degraded rapidly up to 70% until 500oC, however, crosslinked films degraded slowly and still 20% material is left even after 800oC.10Gly-0Ca film is totally disintegrated before 900oC.

b)

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Fig. 7. (a) Derivative termo-gravimetric (DTG) results of 10Gly-2Ca, 0Gly-2Ca and 10Gly-

3.4.

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0Ca (b) Termo-gravimetric (TG) results of pure and crosslinked all 10Gly films,

Water vapor permeability

WVPs of the 0, 10, 20Gly films cross linked 1Ca and 2Ca were chosen to represent the film character. In Table 1, the third column is WVP, the forth column is WVTR. At the third column the WVP of 0Gly-1Ca was 5.45, and for 0Gly-2Ca it decreased to 3.72. For 10Gly samples, the WVP of 10Gly-1Ca was 5.79 and decreased to 4.55 in 10Gly-2Ca. For 20Gly samples, WVP decreased from 5.18 for 20Gly-1Ca to 3.17 in 20Gly-2Ca. It is seen that, as crosslinking is increased, the chain

Journal Pre-proof entanglements increase, and therefore the water diffusion through the films becomes difficult and WVP decreased as Ca crosslinking was increased. Water vapor permeability is an important parameter in wound healing films. If the WVP is too high any moisture on the skin will be rapidly dissipated which leads to skin dehydration. On the other hand, if it is too low, the film will block fluid output and cause a buildup of exudative fluid on the skin. Recommended value for wound dressing applications is 300-3000 g/(m2day) [29]. Considering

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this value the films prepared in this work are appropriate range for wound dressing applications as

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can be seen from the column four. For food packaging applications, depending on the film material

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within this range as seen in Table 2 column three.

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for alginate based films WVP values are 0.4 10-10- 1.410-9g/s.m.Pa range [10-14] and our films were

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A comparison of samples with 1Ca and 2Ca and equal amounts of glycerol showed that the samples

probability 0.036. Swelling

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3.5.

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with 1Ca have greater WVP and the difference was statistically significant by Student’s t test with

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Pure alginate films quickly dissolved in water, while crosslinked alginate films swelled but did not dissolve. 10Gly and 20Gly films with 0.5Ca and 2Ca were chosen as representative in swelling experiments shown as the least and the most crosslinked films in Fig.8. Swelling profiles of films in water, in acetic acid and in citric acid were monitored. All films rapidly swelled in 5 minutes after insertion into the solution. Limit swellings in water and acetic acid were between 50%-70% and in citric acid between 120%-150% and reached in 50-60 mins. Films were observed for several weeks and were stable for the whole period. Limit swelling decreased with increasing Ca in all three solvents, and increased with increasing Gly concentrations in water and citric acid. For example,

Journal Pre-proof swelling in water decreased from 66 % for (10Gly-0.5Ca) to 51 % for (10Gly-2 Ca) as Ca increased and it increased from 66% at 10Gly to 68% as Gly content was increased to 20%. In the case of acetic acid, Gly did not show

b)

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Fig. 8. % Swelling values of alginate films with 0.5 Ca and 2 Ca in water, in acetic acid and

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in citric acid. a) 10Gly, b) 20Gly

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any effect. The films swelled the most in citric acid.

10Gly-0.5Ca and 20Gly-0.5Ca films were indistinguishable from each other with 93% probability. All other combinations were clearly distinguishable with Student’s t test values 10-4 or less. Limit swelling value of each film in citric acid was different from all other’s. Student’s t test giving probabilities of 10-3 or less. 4. Conclusion The properties of alginate films can easily be modified by Ca cross linking and Gly addition. Films

Journal Pre-proof with desirable water vapor permeability, swelling, and mechanical properties can therefore be obtained by tuning their Gly and Ca contents for applications ranging from wound dressing to food packaging High UV absorbance of the harmful UV radiation is a valuable property both for wound dressing and food packaging applications. WVP values of the prepared films were in appropriate range for wound dressing applications but high for food packaging applications. When the swelling results are

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considered, rapid swelling in 5 minutes in water is also useful for rapid removal of extrudes from

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injured skin.

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An increase in tensile strength and a decrease in fracture strain with Ca crosslinking was observed.

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Gly increased the fracture strain in all cases. In terms of tensile strength, when Ca concentration was

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equal to or greater than 1%, small amounts of Gly increased tensile strength but larger amounts of Gly decreased it. Increasing either Gly or Ca beyond certain limits resulted in weaker films. It became

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possible to observe this complex behavior by investigating the effects of a wide range of both Ca and

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Gly concentrations. It is clear that the effects of Gly plasticizing and Ca crosslinking are nonlinear

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and synergic. For this reason, single parameter studies varying one of these concentrations and keeping the other constant are inadequate for predicting the behavior of both Gly and Ca added alginate films.

Because of the nonlinearity and synergy in the effects of plasticizer and cross linker concentrations the behavior, especially the mechanical behavior of plasticized and cross linked alginate films can not be predicted by studies which keep one these concentrations constant. Wide parametric studies varying both concentrations are needed for accurate predictions.

Journal Pre-proof Acknowledgement: Research Fund of the Istanbul Technical University supported this work. Project Number: 40821. References [1] Z. Kalaycıoğlu, E. Torlak, G. Akın-Evingür, İ. Özen, F.B. Erim, Antimicrobial and physical properties of chitosan films incorporated with turmeric extract, Int. J. Biol. Macromol. 101 (2017)

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882–888. doi:10.1016/j.ijbiomac.2017.03.174.

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[2] C.H. Unlu, E. Gunister, O. Atici, Synthesis and characterization of NaMt biocomposites with

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corncob xylan in aqueous media, Carbohydr. Polym. 76 (2009) 585–592. doi:https ://doi.org/ 10.1016

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/ j.carbpol. 2008.11.029.

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[3] A. Shahzad, A. Khan, Z. Afzal, M.F. Umer, J. Khan, G.M. Khan, Formulation development and characterization of cefazolin nanoparticles-loaded cross-linked films of sodium alginate and pectin as

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wound dressings, Int. J. Biol. Macromol. 124 (2019) 255–269. doi:10.1016/j.ijbiomac.2018.11.090.

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[4] H. Kaygusuz, E. Torlak, G. Akın-Evingür, İ. Özen, R. von Klitzing, F.B. Erim, Antimicrobial cerium ion-chitosan crosslinked alginate biopolymer films: A novel and potential wound dressing,

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Journal Pre-proof Author Statment Conceptualization Ideas; Huceste Catalgil-Giz Methodology Development, design of methodology; Huceste Catalgil-Giz, Ayse Su Giz, Halil Bayraktar, Erdem Alaca Software Programming; Ayse Su Giz, Halil Bayraktar, Erdem Alaca Validation; Huceste Catalgil-Giz Formal analysis; Huceste Catalgil-Giz, Ayse Su Giz, Halil Bayraktar, Erdem Alaca Investigation Performing the experiments; Ayse Su Giz, Melisa Berberoglu, Semira Bener, Sena

Resources; Huceste Catalgil-Giz, Halil Bayraktar, Erdem Alaca

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Data Curation Management; Ayse Su Giz, Huceste Catalgil-Giz

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Aydelik-Ayazoglu, Halil Bayraktar, Erdem Alaca.

Writing - Original Draft Preparation; Huceste Catalgil-Giz , Ayse Su Giz, Melisa Bereroglu, Semira

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Bener, Sena Aydelik-Ayazoglu.

Visualization, Ayse Su Giz

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Project administration; Huceste Catalgil-Giz

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Writing - Review & Editing; H.Catalgil-Giz, Halil Bayraktar, Erdem Alaca.

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Funding acquisition; Huceste Catalgil-Giz, Halil Bayraktar, Erdem Alaca

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Graphical abstract

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