Hydroxypropyl methylcellulose-TiO2 and gelatin-TiO2 nanocomposite films: Physicochemical and structural properties

BIOMAC-13863; No of Pages 13 International Journal of Biological Macromolecules xxx (xxxx) xxx

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Hydroxypropyl methylcellulose-TiO2 and gelatin-TiO2 nanocomposite films: Physicochemical and structural properties Jéssica de Matos Fonseca a,⁎, Germán Ayala Valencia a, Lenilton Santos Soares a, Marta Elisa Rosso Dotto b, Carlos Eduardo Maduro Campos c, Regina de Fátima Peralta Muniz Moreira d, Alcilene Rodrigues Monteiro Fritz a,⁎ a

Laboratory of Physical Properties of Foods, Chemical and Food Engineering Department, Federal University of Santa Catarina, UFSC, Brazil Laboratory of Organic Optoelectronics and Anisotropic Systems, Physical Department, Federal University of Santa Catarina, UFSC, Brazil c Laboratory of X-ray Diffraction, Physical Department, Federal University of Santa Catarina, UFSC, Brazil d Laboratory of Energy and Environment, Chemical and Food Engineering Department, Federal University of Santa Catarina, UFSC, Brazil b

a r t i c l e

i n f o

Article history: Received 29 July 2019 Received in revised form 28 October 2019 Accepted 8 November 2019 Available online xxxx Keywords: Titanium dioxide Biopolymer matrices Dispersion

a b s t r a c t Photocatalytic properties of titanium dioxide (TiO2) have been widely studied. However, its tendency to aggregation in biopolymer-based nanocomposites limits its application for food packaging and has been few studied. The aim of this work was to study the dispersion of TiO2 (0–2 wt%) incorporated in the hydroxypropyl methylcellulose (HPMC-TiO2) and gelatin (gelatin-TiO2) film forming solutions. Particle size and zeta potential of TiO2 nanoparticles were investigated. Nanocomposite films were characterized as to the thickness, moisture content, solubility, color, absorption to the light, relative opacity, morphology, chemical composition, crystallinity, thermal and mechanical properties and water vapor permeability (WVP). TiO2 nanoparticles showed better dispersion in acid medium than water. Moisture content, water solubility and WVP of the gelatin-TiO2 films were influenced by the incorporation of TiO2, while HPMC-TiO2 films were not. The increase of relative opacity of the films as TiO2 was more attenuated for the gelatin-TiO2 films due to lower TiO2 aggregation in gelatin. Morphology, chemical composition, crystallinity and thermal properties of the films evidenced that TiO2 was better dispersed in both matrices at 1 wt%. It was also concluded that TiO2 aggregation generated more biphasic regions in HPMC than generated in gelatin, which caused a microstructural reorganization in the matrices. © 2019 Elsevier B.V. All rights reserved.

1. Introduction Titanium dioxide (TiO2) is an amphoteric oxide, a photocatalyst semiconductor, non-toxic, eco-friendly, inexpensive, abundant, biologically and chemically inert. It has a high redox potential and a good thermal/chemical stability when compared with other photocatalysts [1,2]. TiO2 has three polymorphs: anatase (tetragonal), rutile (tetragonal) and brookite (orthorhombic), whose anatase is the most photoactive structure [1]. The oxidant property of the TiO2 is already well-known. When exposed to the ultraviolet (UV) light, TiO2 particles generate strong reactive oxygen species, e.g. hydroxyl (HO•), hydroperoxyl (HO2•) and superoxide (O2•−) radicals able to degrade gas and liquid compounds [1,3–6]. TiO2 has been used to degrade several types of pollutants as organic dyes [2,7,8], improve the protection of sunscreens against solar radiation [9], increase the paper whiteness [10], provide self-cleaning and ⁎ Corresponding authors. E-mail addresses: [email protected] (J.M. Fonseca), [email protected] (A.R.M. Fritz).

anti-fogging properties to other materials [8], disinfect water [11], inactive microorganisms [12–14] and degrade ethylene produced by fruits and vegetables [15–18]. Especially for application in climacteric fruits, TiO2 has been immobilized in biopolymer matrices as chitosan [18,19] and starch [20] in order to produce photoactive packages able to scavenge ethylene and extend their shelf-life of these fruits [21,22]. However, this innovative postharvest technology has shown a limited efficiency to degrade ethylene probably due to the TiO2 agglomeration on the polymeric matrix [18–20]. Other limitation of the TiO2 is associated with its wide band gap (3.2 eV, e.g. anatase) that absorbs b5% of solar energy, restricting its excitation ability to the UV light wavelengths below 387.5 nm [23,24]. This photocatalyst have also been incorporated in biopolymer matrices as chitosan [13,18,19], starch [20,25,26], whey protein [27,28], soybean protein [29], polylactide acid (PLA) [30], gelatin [31] and cellulose acetate [30] in order to obtain active surfaces with antimicrobial properties or reinforced materials. Besides biopolymers, synthetic polymers as polyethylene [24], polypropylene [32], polycaprolactam (PCL) [30] and polyvinylpyrrolidone (PVP) [24], polymer blends as PCL/starch [33], polyvinyl alcohol/xylan [34] collagen/chitosan [35] and κ-

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carrageenan/xanthan/gellan [36] and inorganic supports as borosilicate and quartz [15,37] have also been used to immobilize TiO2. Nevertheless, the concern with the environment associated with the use of biodegradable food-grade materials has been one of the focus of our research team. Thus, two biomaterials with different hydrophilicities were used in this work to immobilize TiO2 nanoparticles and study their dispersion degree: a hydrophilic, non-ionic saccharide derived from cellulose (hydroxypropyl methylcellulose, HPMC) [38,39] and a bovine protein (gelatin) composed of hydrophilic and hydrophobic amino acids chains [39–41]. Both materials have good film-forming properties [42,43] and have been widely studied for food packaging applications, especially for fruits and vegetables, due to their non-toxicity, biodegradability and good barrier properties [44]. Therefore, the aim of this work was to study the effect of TiO2 dispersion on the physicochemical and structural properties of HPMC and gelatin-based films. 2. Materials and methods 2.1. Materials Commercial HPMC (Methocel E19®, Dow Chemical Company, USA) and bovine gelatin type B, bloom 250 (Gelnex®, Brazil) were used as biopolymer matrices. Glycerol (99%, Neon, Brazil) was used as plasticizer. Commercial titanium dioxide (TiO2, anatase, Hombikat UV 100®) nanopowder with a particle size b 10 nm was used as photocatalyst (oxidant agent). Distilled water and acetic acid (99%, Navelab, Brazil) were used as solvents. 2.2. HPMC-TiO2 and gelatin-TiO2 nanocomposite film preparation HPMC-TiO2 and gelatin-TiO2 nanocomposite films were prepared by casting method adapting from Oleyaei et al. [25] and Valencia et al. [45], respectively. Briefly, HPMC (4 g) was dissolved in acid acetic solution (70 g, 0.087 M) under magnetic stirring (1000 rpm) for 30 min. Separately, TiO2 nanopowder (0, 0.5, 1 and 2 wt%, related to HPMC) was suspended in acid acetic solution (30 g, 0.087 M), homogenized in ultrasonic bath (Ultrasonic Maxi Clean 1400 A Unique®, 40 kHz) for 15 min and stirred (1500 rpm) for 20 min. The HPMC solution (pH 3.2) was heated at 70 °C and glycerol was added (25 wt%, related to HPMC) as plasticizer. The polymer solution was gradually heated at 85 °C and cooled to 50 °C. TiO2 suspensions (pH 3.2) were dripped (1.5 mL·min−1) into HPMC solutions (HPMC-0%TiO2, HPMC-0.5%TiO2, HPMC-1%TiO2 and HPMC-2%TiO2, respectively). After, HPMC-TiO2 film forming solutions were homogenized in an Ultraturrax T25®, IKA (16,000 rpm, 10 min) and degassed in ultrasonic bath. Film forming solutions (10 g) were casted on acrylic petri-dishes (9 cm, internal diameter). For the preparation of gelatin-TiO2 nanocomposite films, 4 g of gelatin was dissolved in acid acetic solution (60 g, 0.087 M) under magnetic stirring (1000 rpm) for 20 min until addition of glycerol (25 wt%, related to gelatin) and acid acetic solution (10 g, 1 M). After 10 min, gelatin solution (pH 3.2) was heated at 85 °C under moderate stirring and water bath. The polymer solution was held at this temperature for 10 min and cooled to 50 °C. 30 g of TiO2 suspensions was added (Gel-0%, Gel-0.5%; Gel-1.0% and Gel-2.0%) at the same concentrations used to prepare HPMC-TiO2 nanocomposites. Gelatin-TiO2 film forming solutions were homogenized (16,000 rpm, 3 min, Ultraturrax), degassed and casted on petri-dishes. Acid acetic solution was used in order to enhance the dispersion of TiO2 nanopowder by the stabilization of their positive charges [46]. HPMC-TiO2 film forming solutions were dried at 25 °C for 48 h in a BOD refrigerated incubator, while gelatin-TiO2 film forming solutions were firstly stored at 15 °C for 15 min in order to avoid TiO2 nanoparticle aggregation and dried at 25 °C for 48 h. All films were stored in a chamber (25 °C, 58% relative humidity, RH) for at least 48 h before characterizations. Except for the scanning electronic atomic and force

microscopies, Fourier transform infrared and Raman spectroscopies, X-ray diffraction and solubility characterizations, the film samples were stored in desiccators over silica gel (0% RH) at 25 °C for at least 7 days. All experiments and characterizations related to the preparation of the film form solutions and nanocomposite films were carried out at least in triplicate. 2.3. HPMC-TiO2 and gelatin-TiO2 film forming solution characterizations 2.3.1. Particle size and zeta potential Particle size of TiO2 suspended into water, acetic solution and dispersed in HPMC and gelatin film forming solutions was characterized by the dynamic light scattering (DLS) (Zetasizer Nano ZS, Malvern Instruments, UK). Three measurements were taken for each sample after diluting a drop of the original solution in 4 mL of acetic solution (0.087 M) or water. Water, acetic solution and film forming solutions without TiO2 were used as blanks. The zeta potential of TiO2 was evaluated by electrophoretic mobility measurements and under the same equipment and conditions used to the DLS analysis. 2.4. HPMC-TiO2 and gelatin-TiO2 nanocomposite film characterizations 2.4.1. Thickness Average thickness was determined using a digital micrometer (0.001 mm, Mitutoyo®). It was calculated the average of twelve different points measured in each HPMC-TiO2 and gelatin-TiO2 nanocomposite film [45]. 2.4.2. Moisture content and water solubility The moisture content of the HPMC-TiO2 and gelatin-TiO2 nanocomposite films was determined according to Jiang et al. [47]. One piece of each film with an average weight near to 0.54 g was dried at 105 °C oven for 24 h and cooled in a desiccator over silica gel and immediately weighted. The moisture content values of the samples were expressed in percentage (Eq. (1)): Moisture content ð % Þ ¼ W i −W f W i  100%

ð1Þ

where wi and wf are the weights of the samples before and after they are stored in an oven (105 °C/24 h), respectively. Water solubility of the films was obtained by the weight difference between film specimens (2 cm in diameter) after their storage in a desiccator over silica gel for 48 h and immersion into water (50 mL) under slight stirring for 24 h at 25 °C, followed by drying in an oven at 105 °C for 24 h [48]. The water solubility (%) of the nanocomposite films was determined by Eq. (2): Water solubility ð % Þ ¼ W i −W f W i  100%

ð2Þ

where wi and wf are the weights of the samples after they are stored in a desiccator over silica gel for 24 h and an oven (105 °C/24 h), respectively. 2.4.3. Color, light absorption and opacity The color of the HPMC-TiO2 and gelatin-TiO2 nanocomposite films was determined by a computational vision system composed of one high resolution camera (AF-S DX NIKKOR 18–55 mm f/3.5–5.6G VR, Nikon®) containing a fluorescent lamp connected to an illumination diffuser. The captured film images were evaluated in the Color Space Converter version 4.0-ImageJ® software. The parameters L⁎, a⁎ and b⁎ obtained by the software were used to calculate the total color difference (ΔE*, Eq. (3)) and whiteness (WI, Eq. (4)) and yellowness (YI, Eq. (5)) indexes [49]. The camera was configured in the manual mode, D65 illuminant, level of exposure 0.0, according to Arzate-Vázquez

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et al. [50]. Due to the color of the films tend to the white, the samples were positioned on a black standard plate. ΔE ¼

qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2 ðΔL Þ2 þ ðΔa Þ2 þ ðΔb Þ

rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2  2 WI ¼ 100− 100−Lsample þ a

sample

YI ¼

142:86 b L

ð3Þ 2

þ bsample

ð4Þ

ð5Þ

where ΔL⁎ = L⁎sample − L⁎standard, Δa⁎ = a⁎sample − a⁎standard and Δb⁎ = b⁎sample − b⁎standard. A spectrophotometer UV-VIS USB4000 Ocean Optics® equipped with a deuterium light source was used to evaluate the light absorbance properties of the HPMC-TiO2 and gelatin-TiO2 nanocomposite films. Rectangle pieces (1.5 cm × 2 cm) of the films were directly placed in a spectrophotometer test cell. Films without TiO2 were used as standard. UV–vis absorbance spectra of the samples were recorded at wavelength range from 200 to 650 nm. The film relative opacity was defined as the area under recorded curve at absorbance spectrum from 400 to 650 nm, which was calculated from the integration curve using the OriginPro software® version 2018 according to López [51] and Gontard [48]. The absorbance was expressed in absorbance units per wavelength in nanometers (AU·nm). 2.4.4. Scanning electronic microscopy The surface morphology of the HPMC-TiO2 and gelatin-TiO2 nanocomposite films (0.5 cm × 0.5 cm) was evaluated by scanning electronic microscopy (SEM) using a scanning electronic microscope model JSM 6390 LV-JEOL, Japan, with an accelerating voltage of 15 kV [13]. All samples were sputtered with a thin gold layer before microscopic observations. 2.4.5. Fourier transform infrared and Raman spectroscopies The chemical composition of the HPMC-TiO2 and gelatin-TiO2 nanocomposite films and possible interactions between biopolymer matrices and TiO2 were evaluated by Fourier transform infrared (FTIR) and Raman spectroscopies. The FTIR spectra of the TiO2 nanopowder and nanocomposite films were recorded at wavenumber range from 600 to 4000 cm−1, spectral resolution of 4.0 cm−1 and 32 scans using a FTIR spectrometer model Tensor 27 Bruker® equipped with Universal Attenuated Total Reflectance (ATR). Raman spectra of nanocomposite films were obtained at 23 °C ± 2 °C using a Raman spectrometer PeakSeeker PRO-785™, Agiltron/Raman Systems, equipped with a red solid-state laser as excitation source (λ = 785 nm) and L20× objective lens of a conventional optical microscope. The laser power was maintained at 100 mW for all measurements. 2.4.6. X-ray diffraction The crystallinity of the HPMC-TiO2 and gelatin-TiO2 nanocomposite films was evaluated by X-ray diffraction (XRD) using an X-ray diffraction X'PERT-PRO Multipurpose Powder diffractometer equipped with Position Sensitive Detector Xcelerator (CuKα radiation, λкα1 = 1.5406 Å and λкα2 = 1.5440 Å). The XRD patterns of the nanocomposite films were recorded at 25 °C between 2θ = 5° and 90° at 0.3°·s−1. The average diameter of TiO2 crystallites was calculated using the Scherrer equation (Eq. (6)) from X-ray pattern data [52]. d¼

0:89 λ β ð cos θÞ

ð6Þ

where d, λ, β and θ correspond to the average diameter of the TiO2 crystallites, wavelength of Cuκα radiation, peak width at half peak height (0.01499 rad) and the Bragg angle for the main anatase peak (25.3°), respectively.

3

2.4.7. Differential scanning calorimetry Glass temperature (Tg), melting temperature (Tm) and enthalpy melting (ΔH) of the HPMC-TiO2 and gelatin-TiO2 nanocomposite films were determined by differential scanning calorimetry (DSC) using a differential scanning calorimeter Perkin Elmer Jade®, USA equipped with a cryogenic quench cooling accessory and adapting the method used by Nascimento et al. [53]. Approximately 10.00 ± 0.01 mg of each film were hermetically sealed aluminum pan and scanned twice at scan rate of 10 °C·min−1. The HPMC-TiO2 and gelatin-TiO2 nanocomposite film samples were heated from −40 °C to 200 °C, and from −40 °C to 150 °C, respectively. Data were treated in the Pyris Data Analysis software®. 2.4.8. Mechanical properties Mechanical properties of the HPMC-TiO2 and gelatin-TiO2 nanocomposite films were evaluated by tensile tests (Young's modulus, YM, elongation at break, EB and tensile strength, TS) using a texture analyzer TA. HD.plus Stable Micro Systems® at 23 °C ± 2 °C and following the ASTM Standard Test Method D 882 [54]. The nanocomposite films were cut in strips (2.5 cm × 7.5 cm), fixed on the grip with separation of 50 mm and submitted to grip separation speed of 1 mm·s−1. Eight repetitions were performed for each nanocomposite film. TS, EB and YM (at elastic deformation) were calculated according to Siripatrawan and Kaewklin [19] and Valencia et al. [45]. 2.4.9. Water vapor permeability The water vapor permeability (WVP, g·mm·m−2·h−1·kPa−1) of nanocomposite films was gravimetrically determined according to the ASTM Standard Test Method E96 [54]. Film circular pieces were sealed in aluminum cells (internal diameter 6.3 cm) containing silica gel (0% RH) and placed in a sealed chamber with a container of distilled water (100% RH) at 25 °C. The cells were periodically weighted for at least 7 days in order to ensure the stead state permeation (±0.0001 g). WVP was calculated using Eq. (7):

WVP ¼

ΔW Δt



X A  ΔP

 ð7Þ

where Δw/Δt [g/h] is the mass transfer rate of water vapor through of a film area (A, 0.0031 m2), in other words, it is the weight (Δw) gained by the cells during a determined interval of time (Δt). The parameters x and ΔP are the film thickness [mm] and the partial water vapor pressure gradient (3.171 kPa at 25 °C) across the HPMC-TiO2 or gelatin-TiO2 nanocomposite film, respectively. 2.5. Statistical analysis Significant difference between experimental data were assessed by one-way analysis of variance (ANOVA) and Tukey test of multiple comparisons (p b 0.05) using Statistica® software (version 13.0). 3. Results 3.1. Particle size and zeta potential of film forming solutions TiO2 nanoparticles suspended in different media showed a significant difference (p b 0.05) in their colloidal stability (Table 1). It was observed that the particle size of TiO2 nanoparticles suspended in acetic solution was smaller than in water and their zeta potential value when suspended in acetic solution (27.8 ± 0.93 mV) was significantly higher than in water (10.17 ± 0.28 mV) (p b 0.05). The addition of HPMC in acetic solution gradually decreased the particle size of TiO2 as increase of its concentration (p b 0.05) stagnating at 1 wt% TiO2. Gelatin-TiO2 film forming solutions did not present significantly difference (p N 0.05) in particle size between them. Unlike

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Table 1 Particle size of TiO2 suspended in water, acetic solution and incorporated in biopolymer film forming solutions.

t1:4

Suspension/solution2

Particle size (nm)2

Dispersity2

t1:5 t1:6 t1:7 t1:8 t1:9 t1:10 t1:11 t1:12 t1:13 t1:14 t1:15 t1:16 t1:17

Group 1: Water-, acetic solution-, HPMC-TiO23 TiO2 + Water 859.53 ± 49.37a TiO2 + Ac. Sol1 537.27 ± 26.90b HPMC-0.5%TiO2 397.13 ± 27.40c HPMC-1%TiO2 293.57 ± 22.40d HPMC-2%TiO2 256.80 ± 31.16d

0.31 ± 0.03b 0.37 ± 0.03b 0.88 ± 0.12a 0.62 ± 0.09ab 0.33 ± 0.05b

Group 2: Water-, acetic solution-, gelatin-TiO23 TiO2 + Water 859.53 ± 49.37a TiO2 + Ac. Sol1 537.27 ± 26.90b Gel-0.5%TiO2 773.10 ± 10.40a Gel-1%TiO2 761.33 ± 54.59a Gel-2%TiO2 817.30 ± 11.85a

0.31 ± 0.03a 0.37 ± 0.03a 0.23 ± 0.05a 0.31 ± 0.03a 0.22 ± 0.04a

t1:18 t1:19 t1:20 t1:21 t1:22

1

Ac. Sol: acetic acid solution (0.087 M). All values were expressed as mean ± standard error (n = 3). Means within of the same column and for the same group having different superscripts are significantly different at level of 5% (p b 0.05). 3 HPMC: hydroxypropyl methylcellulose; Gel: gelatin; TiO2: titanium dioxide. 2

HPMC, gelatin caused an increase of the TiO2 nanoparticle size (p b 0.05) in comparison with TiO2 suspended in acetic solution. Concerning the colloidal dispersity, HPMC-0.5%TiO2 film forming solution showed higher value of dispersity (p b 0.5) than suspensions of TiO2 nanoparticles in water and acetic solution and other HPMC-TiO2 film forming solutions. The dispersity of the gelatin-TiO2 solutions was not significantly influenced (p N 0.05) by the increase of TiO2 content. According to the Derjaguin-Landau-Verwey-Overbeek (DLVO), surface steric force theory, a multi-phase system may be considered stable when its components have a zeta potential value near or higher than ± 30 mV [55]. TiO2 nanoparticles presented higher colloidal stability in acetic solution (near to ±30 mV, pH = 3.2) than in water probably due to the ionization of TiO2 nanoparticles (Ti4+) and repulsion between them. This improved their colloidal stability, hindered their agglomeration and formed smaller aggregates in acetic solution than in water [46]. Amir et al. [55] reported similar zeta potential value for TiO2 nanoparticles suspended in water (−12.3 ± 1.3 mV). The HPMC and gelatin played a role of stabilizers of TiO2 nanoparticles incorporated in film forming solution. The stabilizers provide a steric hindrance due to their migration to nanoparticle-solvent interface and absorption on the hydrophobic nanoparticle surface, which prevents the crystal growth [56]. TiO2 concentrations at 1 wt% and 2 wt% showed the best stability in HPMC-based film form solution than 0.5 wt% TiO2 probably due to the higher particle size and dispersity of TiO2 at 0.5 wt%. Apparently, gelatin increased the size of TiO2 agglomerates in comparison with TiO2 agglomerates suspended in acetic solution, probably due to the gelatin complex structure composed of triple helix. It was well documented that the disulfide linkages, intermolecular hydrogen bonds, Van der Waals attractive forces and electrostatic interactions cause the flocculation of protein, which increases its particle size [47]. Similar results were obtained by He et al. [31] and Li et al. [57] for the gelatin-TiO2 (pH 4.0) and whey protein-TiO2 film forming solutions, respectively. He et al. [31] supposed that interactions between gelatin (initial particle size of 648 nm) and TiO2 enhanced the particle size (622–785 nm) as increase of TiO2 content. Yadav et al. [58] reported HPMC and gelatin as efficient stabilizers to prevent curcumin nanocrystal growth in polymer solutions. 3.2. HPMC-TiO2 and gelatin-TiO2 nanocomposite films 3.2.1. Thickness, moisture content and water solubility The incorporation of the TiO2 in biopolymer matrices did not significantly change (p N 0.05) the thickness of the HPMC-TiO2 and gelatinTiO2 nanocomposite films, which remained around 0.077 ± 0.001 mm and 0.072 ± 0.003 mm, respectively. It suggests that the concentrations

of TiO2 tested did not altered the film density. Ding, Zhang and Li [57] and Valencia et al. [45] reported similar thickness values for HPMCbased films and gelatin-laponite nanocomposite films containing 1.5 wt% and 4 wt% of polymer related to solvent. Valencia et al. [45] still reported that the incorporation of the laponite in gelatin did not cause significant changes (p N 0.05) in the film thickness. The moisture of the HPMC-TiO2 nanocomposite films remained (p N 0.05) around 24.97 ± 0.39%, while gelatin-TiO2 nanocomposite films showed moisture contents significantly different (p b 0.05) (Table 2). Thus, the total void volume occupied by water molecules inside microstructure of the gelatin-TiO2 nanocomposite films decreased when TiO2 content increased from 0 wt% to 1 wt% [27]. For the Gel-2%TiO2 the moisture increased due to bigger TiO2 agglomerates, which suggest a large number of gelatin sites without TiO2 nanoparticles. It is expected that the water vapor permeability of the gelatin-TiO2 nanocomposite films are also affected by the incorporation of the photocatalyst. The water solubility of the gelatin-TiO2 nanocomposite films (Table 2) significantly decreased (p b 0.05) as increase of TiO2 content, while HPMC-TiO2 nanocomposite films solubilized in a few minutes completely (p N 0.05). This could indicate that TiO2 nanoparticles interacted with amino and hydroxyl groups of the gelatin at pH 3.2 by hydrogen bonds, decreasing interactions between polymer and water. In addition, TiO2 Hombikat UV 100® is hydrophobic when not exposed to the UV radiation [59]. Once photoinduced, the TiO2 is able to cause change in hydrophilicity of the surface containing it [60]. Similarly, the additions of the TiO2 nanoparticles (anatase, purity N 98,5%, Jiang Hu Industry, China) in whey protein [27] and TiO2 nanoparticles (80/20 of anatase/rutile, Evonik Degussa P25 GmbH, Germany) in potato starch [25] resulted in the decrease of the water solubility of the nanocomposites. Nevertheless, TiO2 was not sufficient to decrease the hydrophilicity of the HPMC matrix (p N 0.05). 3.2.2. Color, light absorption and opacity The TiO2 affected (p b 0.05) the color parameters of HPMC and gelatin-based films (Table 3). Color modifications in gelatin-TiO2 films were more evident by the addition of TiO2 than HPMC-TiO2 films. The lightness (L*) and color total difference (ΔE) of the gelatin-TiO2 films gradually enhanced (p b 0.05) as increase of TiO2 content, while the parameters a* and b* gradually decreased (p b 0.05). Although HPMC-TiO2 films have also exhibited a gradual increase (p b 0.05) of the ΔE, the parameters L* and a* did not presented significant differences (p N 0.05) between control film and nanocomposite films. Finally, the parameter b* was significantly different (p b 0.05) only at 2 wt% TiO2. The yellowness index (YI) significantly decreased (p b 0.05) for both biopolymer matrices containing TiO2 in comparison with their respective control film. However, there was no yellowness significant difference (p N 0.05) between films with different TiO2 contents. The opposite behavior was observed in the whiteness index (WI) as expected. The WI of the HPMC-TiO2 films increased (p b 0.05) as the incorporation of TiO2 content, but there were no significant differences (p N 0.05) between films containing TiO2, while for the gelatin-based films containing TiO2, the WI gradually increased. These results showed that inherent whiteness of TiO2 increased the whiteness of films [25]. However, gelatin-based films showed lower Table 2 Moisture content and water solubility of the gelatin-TiO2 nanocomposite films.

t2:1 t2:2

Film1,2

Moisture content (%)

Solubility (%)

t2:3

Gel-0%TiO2 Gel-0.5%TiO2 Gel-1%TiO2 Gel-2%TiO2

14.63 ± 0.07ab 13.87 ± 0.56ab 13.01 ± 0.28b 15.96 ± 0.88a

69.13 ± 4.75a 50.38 ± 3.07ab 45.83 ± 0.94b 48.43 ± 3.12b

t2:4 t2:5 t2:6 t2:7

1 All values were expressed as mean ± standard error (n = 3). Means within of the same column having different superscripts are significantly different at level of 5% (p b 0.05). 2 Gel: gelatin; TiO2: titanium dioxide.

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t2:8 t2:9 t2:10 t2:11

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Table 3 Colorimetric parameters, yellowness and whiteness indexes and opacity of the HPMC-TiO2 and gelatin-TiO2 nanocomposite films.

t3:3

Film1,2

L⁎3

a⁎3

b⁎3

ΔE⁎3

YI (%)3

WI (%)3

Relative opacity (AU·nm)3

t3:4 t3:5 t3:6 t3:7 t3:8 t3:9 t3:10 t3:11 t3:12 t3:13 t3:14

Group 1: HPMC-TiO2 HPMC-0%TiO2 HPMC-0.5%TiO2 HPMC-1%TiO2 HPMC-2%TiO2

42.47 ± 2.28b 64.65 ± 2.77a 68.14 ± 2.38a 70.89 ± 1.52a

0.84 ± 0.04a 0.78 ± 0.04a 0.75 ± 0.08a 0.33 ± 0.06b

−1.78 ± 0.15a −6.84 ± 0.40b −6.90 ± 0.49b −6.82 ± 0.08b

5.71 ± 0.92c 25.34 ± 4.10b 27.20 ± 2.51b 42.92 ± 0.50a

−6.02 ± 0.63a −15.11 ± 0.45b −14.46 ± 0.30b −13.75 ± 0.16b

42.44 ± 2.28a 63.96 ± 2.65b 67.37 ± 2.25b 70.10 ± 1.45b

0d 61.36 ± 1.34c 83.82 ± 1.86b 240.26 ± 2.06a

Group 2: gelatin-TiO2 Gel-0%TiO2 Gel-0.5%TiO2 Gel-1%TiO2 Gel-2%TiO2

50.26 ± 0.91c 62.99 ± 3.05b 66.89 ± 2.86ab 73.87 ± 0.48a

b10−3a 0.09 ± 0.04a −0.21 ± (0.01)b −0.52 ± 0.04c

−0.71 ± 0.02a −1.97 ± 0.02b −2.69 ± 2.35c −2.43 ± 0.23bc

9.06 ± 1.40c 12.23 ± 0.29c 27.95 ± 2.34b 38.86 ± 0.50a

−2.01 ± 0.03a −4.50 ± 0.20b −5.76 ± 0.43b −4.69 ± 0.40b

50.25 ± 0.91c 62.93 ± 3.05b 66.78 ± 2.85ab 73.75 ± 0.46a

0d 45.88 ± 2.23c 81.44 ± 1.43b 164.44 ± 2.82a

t3:15 t3:16 t3:17 t3:18 t3:19

1 All values were expressed as mean ± standard error (n = 3). Means within of the same column and for the same group having different superscripts are significantly different at level of 5% (p b 0.05). 2 HPMC: hydroxypropyl methylcellulose; Gel: gelatin; TiO2: titanium dioxide. 3 L*: luminosity (black-white; 0–100); a* (green/red; −a*/a*); b* (blue/yellow; −b*/b*); ΔE: total color difference; YI: yellowness index; WI: whiteness index; AU·nm: absorbance units per wavelength in nanometers.

color change than HPMC-based films. Similar nanocomposite film aspects were observed in whey protein-TiO2 [27] and starch-TiO2 [25] nanocomposites. Light absorption results (Fig. 1) showed that HPMC-TiO2 (Fig. 1a) and gelatin-TiO2 (Fig. 1b) nanocomposite films containing 2 wt% TiO2 absorbed more light (p b 0.05) at UV light wavelength range from 222 nm to 380 nm than other films. This wavelength range characterizes the UV-A (wavelength 315–400 nm), UV-B (wavelength 280–315 nm) and UV-C (wavelength 200–280 nm) radiation spectra [61]. These results are in agreement with the restricted UV region of the electromagnetic spectrum (λ ≤ 387.5 nm) used for TiO2 application [1]. Relative opacity of the nanocomposite films was calculated using the wavelength visible light range (λ = 600 nm). Regarding the opacity of the films used as standards (HPMC-0%TiO2 and Gel-0%TiO2) approximately zero, it was observed a sharp and progressive increase of their relative opacity as TiO2 content (p b 0.05). The TiO2 agglomeration causes a scattering of the UV-light on the film surface, which increases its reflectance, lightness (L*) and whiteness (WI) [20]. This indicates that nanocomposite films containing 0.5 wt% and 1 wt% TiO2 have photocatalyst nanoparticles more homogenously dispersed in biopolymer matrices than nanocomposite films containing 2 wt% TiO2. In

addition, the slighter increase of relative opacity for the gelatin-TiO2 films than HPMC-TiO2 films evidenced that TiO2 were more homogenously dispersed in gelatin than HPMC. Similar opacity result was obtained by Siripatrawan and Kaewklin [19] for chitosan-TiO2 nanocomposite films.

3.2.3. Scanning electronic microscopy TiO2 agglomerates were observed through SEM micrographs (Fig. 2) of the nanocomposite films. HPMC-2%TiO2 nanocomposite films displayed bigger and more agglomerates of TiO2 nanoparticles than films containing lower TiO2 content, while gelatin-TiO2 nanocomposite films did not exhibit TiO2 aggregation. It was also observed an apparent increase of the surface relief (protuberances) of the films containing TiO2 in comparison with the control films, especially for the HPMCbased films. This indicates that the incorporation of TiO2 nanoparticles in the biopolymer matrices enhanced their surface roughness. This result also confirms the hypothesis that the increase of the opacity, lightness and whiteness indexes were related to the increase of the TiO2 agglomeration and gelatin matrix was better to disperse TiO2 nanoparticles than HPMC.

Fig. 1. UV–vis spectra of the HPMC-TiO2 (a) and gelatin-TiO2 (b) nanocomposite films.

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Fig. 2. Cross-section (350× of magnification) and surface (30× of magnification) SEM micrographs of HPMC-TiO2 and gelatin-TiO2 nanocomposite films containing different concentrations of TiO2 (0, 0.5, 1 and 2% TiO2).

3.2.4. Fourier transform infrared and Raman spectroscopies Chemical composition and possible interactions between TiO2 and biopolymer matrices were evaluated by FTIR and Raman spectroscopies (Fig. 3). FTIR spectrum of the TiO2 nanoparticles exhibited a broad band centered at 3401 cm−1 associated with the stretching vibrational band of free O\\H axial stretching and hydrogen bonds on the TiO2 surface due to absorption of water molecules on it [25]. The absorption of these\\OH groups plays an important role in the photocatalysis, it stimulates photoreceptors, which trap charges to generate (OH•) reaction radical. These radicals trigger the photocatalysis and act as absorbents, which activate sites to degrade molecules or contaminants [62]. The band at 1634 cm−1 attributed to the water absorption, disappeared in the nanocomposite spectra. This suggests that the incorporation of the TiO2 in biopolymer matrices reduced its water absorption in conditions of non-exposure to the UV-light [62]. Finally, the broad band at 800–430 cm−1 was attributed to the Ti\\O\\Ti stretching band [63]. The HPMC-0%TiO2 spectrum also displayed a wide band centered at 3446 cm−1 attributed to the O\\H axial stretching of the HPMC and hydrogen bonds between polymer chains and water molecules [57]. There was an enlargement of this band and its center was displaced to 3419 cm−1 in the spectra of the HPMC-1%TiO2 and HPMC-2%TiO2 nanocomposite films. This indicates an increase of the hydrogen bond interactions between TiO2 and HPMC chains in the HPMC-1%TiO2 films due to better dispersion of 1 wt% TiO2 in the matrix [31] and increase of hydrogen bonds between HPMC and water molecules, which was induced by the TiO2 agglomeration and higher exposure of the matrix to the water. Thus, it is expected the decrease and increase of elongation of the HPMC-1%TiO2 and HPMC-2%TiO2 nanocomposite films, respectively. The bands at 2924 cm−1 and 2851 cm−1, which are also presented in the spectra of gelatin-TiO2 nanocomposite films, were

attributed to the C\\H stretching of \\CH3 and \\CH2 groups, respectively [64]. HPMC-TiO2 nanocomposite films also exhibited a band at 1465 cm−1 associated with C\\H in plane bending due to\\CH2 groups [65]. The bands from 1310 to 1027 cm−1, especially bands at 1111 cm−1 and 1065 cm−1, are associated with a combined band of ether C\\O stretching and secondary alcohol hydroxyl groups (O\\H) of the HPMC chains [66]. These bands could also have been superimposed by the C\\H in-planes and O\\H bending of glycerol molecules. Polymerglycerol interactions have also been observed at bands below 1000 cm−1 for both biopolymer matrices [67]. As well as HPMC-0%TiO2, the Gel-0%TiO2 spectrum was closed to the gelatin-based films spectra containing TiO2. However, it was observed a slight decrease of the band intensity and a displacement from (3396–2976 cm−1) to (3500–2976 cm−1) after incorporation of the TiO2 in the gelatin matrix. These bands are associated with the hydrogen bonds (O\\H) and N\\H vibrations of the gelatin amide-A groups. The decrease of intensity and displacement of the gelatin band (3396–2976 cm−1) could be attributed to the electrostatic repulsion be4+ tween protonated amino groups (\\NH+ ions at pH = 3.2. 3 ) and Ti Siripatrawan and Kaewklin [16] reported similar results and He et al. [31] obtained an increase of intensity for the band from 3600 to 3200 cm−1 as increase of the TiO2 content incorporated in gelatin matrix. The gelatin was dispersed in water and pH of the medium was adjusted to 4 using NaOH solution. The presence of counter ions (HO−) from the NaOH in film forming solution could have electrostatically shielded the Ti4+, decreasing the repulsion between TiO2 nanoparticles and gelatin chains [64]. Consequently, the number of hydrogen bonds between them was enhanced. In our tests, it was not used basic solution to adjust the pH of film forming solutions. So, the decrease of the intensity for the gelatin band (3396–2976 cm−1) could be justified.

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Fig. 3. FTIR (a), ATR-FTIR (a) and Raman (c) spectra of TiO2 nanopowder and HPMC-TiO2 nanocomposite films and FTIR (b), ATR-FTIR (b) and Raman (d) spectra of TiO2 nanopowder and gelatin-TiO2 nanocomposite films.

Vibrations of peculiar chemical groups of the gelatin, amide-I (C\\O), amide-II or triple helix (N\\H) and amide-III (C\\N), did not suffer alterations with incorporation of TiO2 and were observed at 1630, 1541 and 1238 cm−1, respectively [68]. The bands at 1401, 1111 and 1065 cm−1 were respectively attributed to the C\\H and C\\O vibrations of glycerol molecules [67]. It was not identified bands of chemical groups, which could also indicate that there was a polymer degradation. The anatase polymorphic phase of TiO2 has six typical active modes determined from group theory A1g + 2B1g + 3Eg [69], whose four modes, 393 cm−1 (B1g), 512 cm−1 (A1g), 519 cm−1 (B1g) and 634 cm−1 (Eg), could be identified in the Raman spectral window (Fig. 3) investigated for the single crystal TiO2. Ohsaka [70] identified the six typical modes of anatase TiO2 ionic crystals in a wider spectral window at 144 cm−1 (Eg), 197 cm−1 (Eg), 399 cm−1 (B1g), 513 cm−1 (A1g), 519 cm−1 (B1g) and 639 cm−1 (Eg).

In the Raman spectra of HPMC-TiO2 and gelatin-TiO2 nanocomposite films were identified typical vibrations of the HPMC and gelatin matrices (Table 4) without significant alterations, which also indicate that there was not any degradation of the biopolymers. Concerning TiO2 vibrations in the HPMC-TiO2 Raman spectra, it was observed an increase of their intensity in the spectra of nanocomposites containing TiO2 concentrations from 0% to 1 wt% TiO2, followed by a decrease of intensity for the concentration of 2 wt% TiO2. In addition, there was a slight enlargement of the TiO2 bands (512 and 634 cm−1) in the HPMC-0.5%TiO2 and HPMC-1%TiO2 Raman spectra and a displacement of their TiO2 bands in comparison with the HPMC-2%TiO2 and TiO2 nanopowder Raman spectra, respectively. This behavior could be attributed to the size effect of the TiO2 nanoparticle agglomerates on their Raman bands, which could be enlarged and shifted as decrease of TiO2 agglomerate size [71]. This result corroborates with the particle size results obtained by DLS for the HPMC-TiO2 film forming solutions. The supposed voids in the biopolymer matrix generated by the insufficient

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8 t4:1 t4:2

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Table 4 Typical Raman shifts for the hydroxypropyl methylcellulose (HPMC) and gelatin.

t4:3 t4:4

Raman shift (cm−1)1

t4:5 t4:6 t4:7 t4:8 t4:9 t4:10 t4:11 t4:12 t4:13 t4:14

HPMC 1459s 1372s 1096w 1011w N944m

t4:15 t4:16 t4:17 t4:18

1334m 1267s 1195w 1104w, 1091w 1054w 1041m 1004m N1000w

t4:19 t4:20 t4:21 t4:22 t4:23 t4:24

Gelatin 1661s 1451s

Assignment

Deformation of\ \CH2 and\ \CH3 groups \ \COH bending C\ \O stretching Out of plane bend of carboxyl OH Stretching C\ \C backbone stretch C_O (amide I) Deformation of\ \CH2 and\ \CH3 groups, in plane bend of carboxyl OH CH2 and\ \CH3 groups Proline and hydroxyproline residues (amide III) Tyrosine C\ \N stretching Out of plane bend of carboxyl OH Proline Phenylalanine Stretching C\ \C of the amino acid residues and polypeptide chains

1 w: weak; m: medium; s: strong. Based on Frushour & Koenig (1975) [65] and Remon, Vandenabeele, Moens, de Veij, & De Beer (2008) [66].

filling of the matrix in the HPMC-0.5%TiO2 and agglomeration of TiO2 in HPMC-2%TiO2 could have reduced the TiO2 band intensity in their Raman spectra, respectively. Below 1000 cm−1, TiO2 bands in the gelatin-TiO2 Raman spectra were overlapped by the typical bands of the gelatin structure. However, the slight displacement of the TiO2 bands (512 and 634 cm−1) in the Raman spectra of these nanocomposite films reinforces the hypothesis that the flocculation of the proteins masked the results of TiO2 particle size for the gelatin-TiO2 film forming solutions and TiO2 nanoparticles are more dispersed in gelatin matrix as showed by the SEM micrographs. Apparently, the difference of the intensity, displacement and broadening of the TiO2 bands between gelatin-TiO2 films containing different concentrations of TiO2 were less discrepant than HPMC-TiO2 films, which also suggests better dispersion of TiO2 nanoparticles in the gelatin than HPMC.

3.2.5. X-ray diffraction Typical peaks associated with the anatase TiO2 phase were observed in the TiO2 nanopowder X-ray pattern (Fig. 4) at 2θ = 25.2°, 37.8°, 47.9°, 54.7°, 62.5°, 69.2°, 75.4° and 82.7° and they are according to the ICSDcode: 9852 [72]. Peaks referring to the rutile phase were not observed (ICSD-code 9161) [73] and the average diameter of the TiO2 crystallites calculated (d = 9.38 ± 0.31 nm) is in accordance to the technical information provided by the supplier (d b 10 nm) [74]. Almost in all nanocomposite X-ray patterns, except for the Gel-0.5% TiO2, it was possible to observe a shoulder at 2θ = 25.2° referring to the presence of TiO2 in the biopolymer matrices. Similar results were observed in gelatin-TiO2, starch-TiO2 and chitosan-TiO2 by He et al. [31] Li et al. [27], Oleyaei et al. [25] and Siripatrawan and Kaewklin [19]. Two changes of intensity related to the incorporation of TiO2 were also noticed at 2θ = 47.9° in the HPMC-1%TiO2 and HPMC-2%TiO2 Xray patterns. Both biopolymer matrices exhibited a semi-crystalline structure, which was changed as addition of TiO2 (Fig. 4). HPMC showed a peak at 2θ = 7.6° associated with its crystalline fraction dominated by hydrogen bonds between polymer chains. A broader peak at 2θ = 20° is related to its amorphous phase, whose formation is caused by the side polar chemical groups that hindered the polymer chain packing [75]. It was observed an enlargement and gradual decrease of the intensity at 2θ = 7.6° for the HPMC-0.5%TiO2, HPMC-1%TiO2 and HPMC-2%TiO2 nanocomposite films, suggesting that the volume occupied by the TiO2 nanoparticles in biopolymer matrix weakened the hydrogen bonds between HPMC chains [64]. This allowed TiO2 nanoparticles were more uniformly dispersed in the matrix. On the other hand, the increase of the amorphous phase intensity at 2θ = 20° for the HPMC-0.5%TiO2 and HPMC-1%TiO2 nanocomposite films could be explained due to the superimposition to the characteristic peak of the anatase TiO2 at 2θ = 25.2° [31]. Furthermore, this increase of intensity could be associated with the increase of the nanocomposite stability as increase of the TiO2 content, which intensified the biopolymer-TiO2 interactions [31]. However, the intensity of the peak at 2θ = 20° for the HPMC-2%TiO2 decreased, suggesting that the TiO2 agglomerates interacted with HPMC matrix weakly. A similar behavior was noticed in all X-ray patterns of the gelatinTiO2 nanocomposite films containing TiO2. No one displacement in XRD pattern at 2θ = 7.6° indicated that the triple helix diameter of the gelatin protein chains was not altered. However, the decrease of

Fig. 4. X-ray patterns of TiO2 nanopowder, HPMC-TiO2 (a) and gelatin-TiO2 (b) nanocomposite films.

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the intensity at 2θ = 7.6° as incorporation of TiO2 indicated that the number of triple helices was reduced [76]. Regarding the supposed increase of the nanocomposite stability caused by the increase of the amorphous phase (2θ = 19.2°), which corresponds to the distance between amino acid residues along the helix [76], the Gel-1%TiO2 showed that could to be more stable than other gelatin-TiO2 nanocomposite films.

3.2.6. Differential scanning calorimetry Tg and Tm of the HPMC-TiO2 and gelatin-TiO2 nanocomposite films were investigated from DSC analyses. Thermograms referring to the first and second heat cycles for the TiO2 nanopowder and nanocomposite films are presented in the Fig. 5. In the first heat cycle, TiO2 nanopowder exhibited an endothermic peak at 87.3 °C attributed to the evaporation of water adsorbed on its surface [77]. All film samples exhibited a first-order endothermic transition related to the melting, Tm, of the biopolymer matrix. Wide melting peaks are characteristics of semi-crystalline polymers and they are associated with the disorganization of the biopolymer chains in the amorphous phase [78]. These peaks could also be superimposed by endothermic events related to

9

the water evaporation, melting and recrystallization of polymer crystallites [79]. HPMC-0%TiO2 showed a Tm = 83.6 °C and a melting enthalpy (ΔH) of 147.9 J/g. HPMC-0.5%TiO2, HPMC-1%TiO2 and HPMC-2%TiO2 showed similar Tm values of 88.9 °C, 86.9 °C and 86.2 °C and ΔH values of 118.3 J/g, 130.1 J/g and 125.8 J/g, respectively. The decrease of the ΔH values as incorporation of TiO2 into HPMC matrix could be associated with the decrease of hydrogen bonds between HPMC chains [79]. Gel-0%TiO2 and Gel-0.5%TiO2 showed close Tm values of 87.9 °C and 89.6 °C and melting enthalpy (ΔH) values of 175.2 J/g and 160.8 J/g, respectively, indicating that 0.5 wt% TiO2 caused slight changes in the thermal properties of the gelatin. These changes were even more pronounced for the Gel-1%TiO2, which showed lower Tm value (78.9 °C), but a ΔH = 220.57 J/g higher than other gelatin-TiO2 films. This characterizes an enlargement of the melting peak, suggesting that at 1 wt% TiO2 the number of hydrogen bonds between biopolymer chains decreased and the number of interactions between TiO2 nanoparticles and gelatin increased. Thus, the amorphous phase of nanocomposite is in accordance with XRD results. Finally, there was an increase in the Tm (95.1 °C) and a decrease in the ΔH (206.2 J/g) for the Gel-2%TiO2 followed by a sharpening of the melting peak. These results suggest

Fig. 5. DSC thermograms referring to the first (a, c) and second (b, d) heat cycles of the TiO2 nanopowder, HPMC-TiO2 and gelatin-TiO2 nanocomposite films, respectively.

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that TiO2 agglomerates at 2 wt% TiO2 more contributed to maintain the integrity of hydrogen bonds between biopolymer chains of Gel-2%TiO2 than other gelatin-TiO2 nanocomposite films. Tm values of the HPMC0%TiO2 and Gel-0%TiO2 nanocomposite films are in accordance with results reported by Sangappa et al. [80] and Rivero et al. [81], who studied structural and thermal properties of HPMC-based films modified by electron irradiation and gelatin-based films with different concentrations of plasticizer. Slight differences could be attributed to the different glycerol concentrations used to prepare the films [79]. During the second scan, HPMC-TiO2 films showed a typical thermal behavior of crystalline materials, being observed two slight exothermic transitions at 51.7 °C and 100 °C, which could be associated with the partial recrystallization of the HPMC chains [82]. For the gelatin-TiO2 nanocomposite films, the Tg decreased as TiO2 content from 1 wt% TiO2, probably due to the higher TiO2 dispersion degree in the matrices and plasticizing effect caused by water and glycerol molecules [83]. The lower Tg of the Gel-1%TiO2 (Tg = 6.4 °C) in comparison with Gel-2%TiO2 (Tg = 24.7 °C) also suggests better distribution of 1 wt% TiO2 in the gelatin and higher decrease of number of hydrogen bonds between polymer chains. In general, DSC results evidenced that when TiO2 was poorly dispersed in the HPMC and gelatin matrices, either by insufficient filling of the matrices (HPMC-0.5%TiO2, Gel-0.5%TiO2) or its excessive agglomeration (HPMC-1%TiO2, Gel-1%TiO2), did not caused significant changes in the thermal properties of the polymer matrices. The anatase TiO2, as well known, is a crystalline material with high Tm (1870 °C) [84] and indefinite Tg [85], which difficult its dispersion into supports and amorphization. Lastly, it was expected that the changes in the Tg of the HPMC-TiO2 nanocomposite films were barely perceptible because of insignificant difference (p N 0.05) of moisture content between them. On the other hand, the lower moisture content of the gelatin in comparison with HPMC matrix could have become possible to calculate the Tg for some gelatin-TiO2 samples. 3.2.7. Mechanical properties Mechanical properties of the HPMC-TiO2 were more affected by the increase of the TiO2 content than gelatin-TiO2 nanocomposite films. Elongation at break (EB) and tensile strength (TS) of the HPMC-TiO2 films (Fig. 6) significantly decreased (p b 0.05) from 0 to 1 wt% TiO2, and significantly increased (p b 0.05) for the films containing 2 wt% TiO2. The Young's modulus (YM) did not show significant difference (p N 0.05) and an average value of 0.34 ± 0.02 GPa was obtained for all samples. Gelatin-TiO2 nanocomposite films did not show significant

difference (p N 0.05) for any of the parameters evaluated, so the calculated average for each parameter was EB = 10.5 ± 1.3%, TS = 42.9 ± 2.4 MPa and YM = 1.01 ± 0.06 GPa. In general, YM results evidenced that the nanocomposite films are fragile and EB and TS results revealed that the gelatin-based films are more resistant to the structural changes caused by the incorporation of the TiO2 than HPMC-based films. This could be explained due to the complex macromolecular structure of the gelatin, which contains side chemical groups and ionic groups (NH+ 3 ) [86,87] that hinders the movement of the chains [25] and becomes the gelatin-based films more resistant to the mechanical stress and less flexible. This result is in agreement with the SEM micrographs of the gelatin-TiO2 films (Fig. 2) that showed a TiO2 agglomeration almost unnoticeable in all gelatin-TiO2 films and different levels of TiO2 agglomeration between the HPMC-TiO2 films. The continuous mechanical weakening of the HPMC-TiO2 nanocomposite films containing from 0 to 1 wt% TiO2 could be a consequence of the repulsion between Ti4+ ions, which simultaneously hindered the aggregation of TiO2 nanoparticles and decreased interactions between biopolymer chains leading the films to the failure quickly. HPMC-2%TiO2 showed an unexpected increase of EB and TS values when compared with the HPMC-0%TiO2 film. However, it was already expected the increase of EB and TS values for the HPMC-2%TiO2 when compared with the HPMC-1%TiO2 nanocomposite film, because of the conservation of fractions of the biopolymer matrix without TiO2. In comparison to EB, TS and YM values of the low density polyethylene (LDPE; EB = 100–650%; TS = 8.3–31.4 MPa; YM = 0.17–0.28 GPa) and high density polyethylene (HDPE; EB = 10−1200%; TS = 22.1–31.0 MPa; YM = 1.06–1.09 GPa) [78], both matrices exhibited typical EB, TS and YM values of polymers. HPMC-TiO2 nanocomposite films showed lower elasticity and resistance to the stress than LDPE and HDPE and stiffness slightly higher than LDPE. Gelatin-TiO2 nanocomposite films showed elasticity and stiffness close to the HDPE and resistance to the stress higher than LDPE and HDPE. Li et al. [27] classified the mechanical properties of whey proteinTiO2 nanocomposite films as catastrophic. The authors tested 0, 0.25, 0.5, 1 and 2 wt% TiO2 related to the whey protein weight and reported that there was no significant difference (p N 0.05) for the TS and EB parameters between 0 and 0.25 wt% TiO2. However, from 0.5 to 2 wt% TiO2, there was a high decrease (p b 0.05) of the 71.9% and 32.4% in the EB and TS values, respectively. They attributed this behavior to the discontinuity of the matrix caused by the TiO2 agglomerates, which damaged of the matrix network microstructure. 3.2.8. Water vapor permeability WVP is related to the facility or difficulty of water vapor molecules diffuse across the micro-pathways of the composite network microstructure [27]. This diffusion could be affected by the amount of \\OH groups, insoluble agglomerates and particles dispersed in the microstructure [25]. As expected, HPMC-TiO2 nanocomposite films did not showed significant difference (p N 0.05) of the barrier properties, so the calculated average for the WVP values was 0.60 ± 0.02 g·mm·m−2·h−1·kPa−1. The WVP of the gelatin-TiO2 nanocomposite films (Table 5) reduced as increase of the TiO2 content from 0 to 1 wt% TiO2 and increased for Table 5 Water vapor permeability of gelatin-TiO2 nanocomposite films.

Fig. 6. Elongation at break (EB) and tensile strength (TS) of the HPMC-TiO2 nanocomposite films. All values were expressed as mean ± standard error (n = 3). Means within the same parameter having different letters are significantly different at level of 5% (p b 0.05).

t5:1 t5:2

Film1,2

WVP (g·mm·m−2·h−1·kPa−1)

t5:3

Gel-0%TiO2 Gel-0.5%TiO2 Gel-1%TiO2 Gel-2%TiO2

0.45 ± (b10−2)a 0.40 ± (b10−2)ab 0.36 ± (b10−3)b 0.44 ± 0.02ab

t5:4 t5:5 t5:6 t5:7

1 All values were expressed as mean ± standard error (n = 3). Means within of the same column having different superscripts are significantly different at level of 5% (p b 0.05). 2 Gel: gelatin, TiO2: titanium dioxide.

t5:8 t5:9 t5:10 t5:11

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the 2 wt% TiO2 (p b 0.05). These results corroborate the moisture content and water solubility results, evidencing that even though TiO2 agglomerates have probably modified the micro-pathways of the HPMC matrix, the large number of \\OH groups that compose the HPMC chains provides strong interactions between water molecules and matrix. On the other hand, less affinity between gelatin matrix and water molecules and great dispersion of the TiO2 nanoparticles in gelatin justify the decrease of the WVP for the gelatin-TiO2 nanocomposite films. The TiO2 more homogenously dispersed in gelatin matrix increased the number of interactions between them, which modified the film structure micro-pathways. The hydrophobic characteristic of TiO2 when unexposed to the UV radiation decreased the number of interactions water-polymer reducing the WVP of the gelatin-TiO2 nanocomposite films. The increase of the WVP for the Gel-2%TiO2 film is associated with its biggest TiO2 agglomerates that cause the formation of sites in the gelatin matrix without TiO2, as already commented. Similar WVP values and behavior of gelatin-TiO2 nanocomposite films were reported by He et al. [31] and similar WVP values of HPMC-based films were obtained by Bilbao-Sainz et al. [88]. 3.2.9. Schematic representation of HPMC-TiO2 and gelatin-TiO2 nanocomposite film structures Based on all investigation carried out and results obtained in this work, structures able to schematically represent the generation of biphasic regions in the HPMC-TiO2 and gelatin-TiO2 nanocomposite films caused by the TiO2 aggregation (Fig. 7) were proposed. This separation of phases could be designed as micro-domain structures basically composed of sites containing polymer chains, glycerol and water molecules adsorbed, which could or not have TiO2 aggregates. It is observed in the Fig. 7 that the agglomeration of TiO2 nanoparticles is enhanced as

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increase of TiO2 content, especially for HPMC-TiO2 nanocomposite films. The large number of the micro-domains causes a microstructural reorganization of the system including changes in the number of interactions polymer-polymer, polymer-TiO2 nanoparticles, nanocompositeoutside molecules. Higher dispersion of TiO2 nanoparticles in gelatin than HPMC matrix does not mean that gelatin-TiO2 films will have the greatest photocatalytic activity, but this will be an indispensable characteristic to reach a high photocatalytic performance.

4. Conclusions In this work were studied and discussed how the variation of the concentration of TiO2 nanoparticles affects their dispersion in hydroxypropyl methylcellulose (HPMC) and gelatin matrices and how their dispersion degree directly affects the thermal, mechanical and barrier properties of the HPMC-TiO2 and gelatin-TiO2 nanocomposite films. Results showed that all changes of these properties are associated with the changes of physicochemical properties of the film forming solutions caused by the variation of TiO2 concentration. The hydrophilicity of the biopolymer matrices was a determinant characteristic in the dispersion degree of TiO2 nanoparticles in the nanocomposites. The natural hydrophobicity of TiO2, when unexposed to the UV light causes its better dispersion in the gelatin matrix, leading to its low discontinuity. Thus, the solubility, moisture content and water vapor permeability (WVP) of the gelatin-TiO2 films decreased as increase of TiO2 content, while for the HPMC-TiO2 films the TiO2 concentrations tested were not significantly enough to change these characteristics, as corroborated by the DSC results.

Fig. 7. Schematic representation of physical structure proposed for the HPMC-TiO2 and gelatin-TiO2 nanocomposite films containing different concentrations of TiO2.

Please cite this article as: J.M. Fonseca, G.A. Valencia, L.S. Soares, et al., Hydroxypropyl methylcellulose-TiO2 and gelatin-TiO2 nanocomposite films: Physicochemical and structu..., , https://doi.org/10.1016/j.ijbiomac.2019.11.082

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J.M. Fonseca et al. / International Journal of Biological Macromolecules xxx (xxxx) xxx

As well know, TiO2 requires the availability of water and oxygen molecules to generate radical species. Thus, HPMC could also be a good support to immobilize TiO2 nanoparticles in order to supply this requirement, while gelatin could be used to obtain the best dispersion of the photocatalyst. Finally, regarding the best concentration of TiO2, HPMC-1%TiO2 and gelatin-1%TiO2 nanocomposite films showed physicochemical and structural properties more appropriate to degrade ethylene or other substrates.

Declaration of competing interest None. Acknowledgements The authors are grateful to the CAPES-PRINT, whose project number is 88887.310727/2018-00, National Council for Scientific and Technological Development (CNPq) for the financial support-process 454841/ 2014-0, Coordination for the Improvement of Higher Education Personnel (Capes) by the scholarship support, Laboratories of Electronic Microscopy (LCME) and Synthesis and Characterization of nanoMaterials (LSCnM) of the UFSC by the analysis support. References [1] V. Etacheri, C. Di, J. Schneider, et al., Visible-light activation of TiO 2 photocatalysts: advances in theory and experiments, Journal of Photochemistry and Photobiology C: Photochemistry Reviews 25 (2015) 1–29, https://doi.org/10.1016/j.jphotochemrev. 2015.08.003. [2] M.A. Nawi, A.H. Jawad, S. Sabar, W.S.W. Ngah, Immobilized bilayer TiO2/chitosan system for the removal of phenol under irradiation by a 45 watt compact fluorescent lamp, DES 280 (2011) 288–296, https://doi.org/10.1016/j.desal.2011.07.013. [3] M.A. Fox, M.T. Dulay, Heterogeneous photocatalysis, Chem. Rev. 93 (1993) 341–357, https://doi.org/10.1021/cr00017a016. [4] S. Tunesi, M.A. Anderson, Photocatalysis of 3,4-DCB in TiO2 aqueous suspensions; effects of temperature and light intensity; CIR-FTIR interfacial analysis, Chemosphere 16 (1987) 1447–1456, https://doi.org/10.1016/0045-6535(87)90084-1. [5] A. Mills, S. Le Hunte, An overview of semiconductor photocatalysis, J. Photochem. Photobiol. A Chem. 108 (1997) 1–35, https://doi.org/10.1016/S1010-6030(97) 00118-4. [6] Dalrymple OK, Stefanakos E, Trotz M A., Goswami DY (2010) A review of the mechanisms and modeling of photocatalytic disinfection. Appl. Catal. B Environ. 98: 27–38. doi:https://doi.org/10.1016/j.apcatb.2010.05.001. [7] M.A. Ahmed, Synthesis of mesoporous TiO2–curcumin nanoparticles for photocatalytic degradation of methylene blue dye, Journal of Photochemistry & Photobiology, B: Biology 160 (2016) 134–141, https://doi.org/10.1016/j.jphotobiol.2016.03.054. [8] S. Berger, R. Singh, J.D. Sudha, et al., Microgel/clay nanohybrids as responsive scavenger systems, Polymer (Guildf) 51 (2010) 3829–3835, https://doi.org/10.1016/j. polymer.2010.06.039. [9] R.G. Van Der Molen, H.M.H. Hurks, C. Out-Luiting, et al., Efficacy of micronized titanium dioxide-containing compounds in protection against UVB-induced immunosuppression in humans in vivo, J. Photochem. Photobiol. B Biol. 44 (1998) 143–150, https://doi.org/10.1016/S1011-1344(98)00137-7. [10] B.M.K. Manda, K. Blok, M.K. Patel, Innovations in papermaking: an LCA of printing and writing paper from conventional and high yield pulp, Science of the Total Environment 439 (2012) 307–320. [11] M. Nan, B. Jin, C.W.K. Chow, C. Saint, Recent developments in photocatalytic water treatment technology: a review, Water Res. 44 (2010) 2997–3027, https://doi.org/ 10.1016/j.watres.2010.02.039. [12] S.H. Othman, N. Raudhah, A. Salam, et al., Antimicrobial Activity of TiO2 Nanoparticle-coated Film for Potential Food Packaging Applications, 2014, 2014. [13] X. Zhang, G. Xiao, Y. Wang, et al., Preparation of chitosan-TiO2 composite film with efficient antimicrobial activities under visible light for food packaging applications, Carbohydr. Polym. 169 (2017) 101–107, https://doi.org/10.1016/j.carbpol.2017.03. 073. [14] Z. Zhu, H. Cai, D. Sun, Titanium dioxide (TiO2) photocatalysis technology for nonthermal inactivation of microorganisms in foods, Trends Food Sci. Technol. 75 (2018) 23–35, https://doi.org/10.1016/j.tifs.2018.02.018. [15] Hussain M, Bensaid S, Geobaldo F, et al (2011) Photocatalytic degradation of ethylene emitted by fruits with TiO2 nanoparticles. 2536–2543. [16] P. Kaewklin, U. Siripatrawan, A. Suwanagul, Y.S. Lee, Active packaging from chitosan-titanium dioxide nanocomposite film for prolonging storage life of tomato fruit, Int. J. Biol. Macromol. 112 (2018) 523–529, https://doi.org/10.1016/j.ijbiomac. 2018.01.124. [17] R.E.R.S. Lourenço, A.A.N. Linhares, A.V. de Oliveira, et al., Photodegradation of ethylene by use of TiO2 sol-gel on polypropylene and on glass for application in the postharvest of papaya fruit, Environ. Sci. Pollut. Res. 24 (2017) 6047–6054, https://doi. org/10.1007/s11356-016-8197-5.

[18] X. Zhang, Y. Liu, H. Yong, et al., Development of multifunctional food packaging films based on chitosan, TiO2 nanoparticles and anthocyanin-rich black plum peel extract, Food Hydrocoll. 94 (2019) 80–92, https://doi.org/10.1016/j.foodhyd.2019.03.009. [19] U. Siripatrawan, P. Kaewklin, Fabrication and characterization of chitosan-titanium dioxide nanocomposite film as ethylene scavenging and antimicrobial active food packaging, Food Hydrocoll. 84 (2018) 125–134, https://doi.org/10.1016/j.foodhyd. 2018.04.049. [20] H. Wang, L. Wang, S. Ye, X. Song, Construction of Bi2WO6–TiO2/starch nanocomposite films for visible-light catalytic degradation of ethylene, Food Hydrocoll. 88 (2019) 92–100, https://doi.org/10.1016/j.foodhyd.2018.09.021. [21] X. Li, X. Zhu, J. Mao, et al., Isolation and characterization of ethylene response factor family genes during development, ethylene regulation and stress treatments in papaya fruit, Plant Physiol. Biochem. 70 (2013) 81–92, https://doi.org/10.1016/j. plaphy.2013.05.020. [22] S.B. Nogueira, C.A. Labate, F.C. Gozzo, et al., Proteomic analysis of papaya fruit ripening using 2DE-DIGE, J. Proteome 75 (2012) 1428–1439, https://doi.org/10.1016/J. JPROT.2011.11.015. [23] O.K. Dalrymple, E. Stefanakos, M.A. Trotz, D.Y. Goswami, A review of the mechanisms and modeling of photocatalytic disinfection, Applied Catal B, Environ 98 (2010) 27–38, https://doi.org/10.1016/j.apcatb.2010.05.001. [24] C. Maneerat, Y. Hayata, Gas-phase photocatalytic oxidation of ethylene with TiO2coated packaging film for horticultural products, Trans. ASABE 51 (2008) 163–168. [25] S.A. Oleyaei, Y. Zahedi, B. Ghanbarzadeh, A.A. Moayedi, Modification of physicochemical and thermal properties of starch films by incorporation of TiO2 nanoparticles, Int. J. Biol. Macromol. 89 (2016) 256–264, https://doi.org/10.1016/j. ijbiomac.2016.04.078. [26] C. Liu, H. Xiong, X. Chen, et al., Effects of nano-TiO2 on the performance of highamylose starch based antibacterial films, J. Appl. Polym. Sci. 132 (2015) 2–8, https://doi.org/10.1002/app.42339. [27] Y. Li, Y. Jiang, F. Liu, et al., Fabrication and characterization of TiO2/whey protein isolate nanocomposite film, Food Hydrocoll. 25 (2011) 1098–1104, https://doi.org/10. 1016/j.foodhyd.2010.10.006. [28] J.J. Zhou, S.Y. Wang, S. Gunasekaran, Preparation and characterization of whey protein film incorporated with TiO2 nanoparticles, J. Food Sci. 74 (2009) https://doi. org/10.1111/j.1750-3841.2009.01270.x. [29] S. Teymourpour, M.N. Abdorreza, F. Nahidi, Functional, thermal, and antimicrobial properties of soluble soybean polysaccharide biocomposites reinforced by nano TiO2, Carbohydr. Polym. 134 (2015) 726–731, https://doi.org/10.1016/j.carbpol. 2015.08.073. [30] J. Xie, Y.C. Hung, UV-A activated TiO2 embedded biodegradable polymer film for antimicrobial food packaging application, Lwt 96 (2018) 307–314, https://doi.org/10. 1016/j.lwt.2018.05.050. [31] Q. He, Y. Zhang, X. Cai, S. Wang, Fabrication of gelatin-TiO2nanocomposite film and its structural, antibacterial and physical properties, Int. J. Biol. Macromol. 84 (2016) 153–160, https://doi.org/10.1016/j.ijbiomac.2015.12.012. [32] D. Yanes, S. Guerrero, I. Lieberwirth, et al., Photocatalytic inhibition of bacteria by TiO 2 nanotubes-doped polyethylene composites, Applied Catalysis A: General 489 (2015) 255–261, https://doi.org/10.1016/j.apcata.2014.10.051. [33] P. Fei, Y. Shi, M. Zhou, et al., Effects of nano-TiO2 on the properties and structures of starch/poly(ε-caprolactone) composites, J. Appl. Polym. Sci. 130 (2013) 4129–4136, https://doi.org/10.1002/app.39695. [34] J. Ren, S. Wang, C. Gao, et al., TiO2-containing PVA/xylan composite films with enhanced mechanical properties, high hydrophobicity and UV shielding performance, Cellulose 22 (2015) 593–602, https://doi.org/10.1007/s10570-014-0482-1. [35] X. Fan, K. Chen, X. He, et al., Nano-TiO2/collagen-chitosan porous scaffold for wound repairing, Int. J. Biol. Macromol. 91 (2016) 15–22, https://doi.org/10.1016/j.ijbiomac. 2016.05.094. [36] R. Balasubramanian, S.S. Kim, J. Lee, J. Lee, Effect of TiO 2 on highly elastic, stretchable UV protective nanocomposite films formed by using a combination of kcarrageenan, xanthan gum and gellan gum, Int. J. Biol. Macromol. 123 (2019) 1020–1027, https://doi.org/10.1016/j.ijbiomac.2018.11.151. [37] A. Basso, R. de Fátima Peralta Muniz Moreira, H.J. José, Effect of operational conditions on photocatalytic ethylene degradation applied to control tomato ripening, J. Photochem. Photobiol. A Chem. 367 (2018) 294–301, https://doi.org/10.1016/j. jphotochem.2018.08.027. [38] Y. Sakata, S. Shiraishi, M. Otsuka, A novel white film for pharmaceutical coating formed by interaction of calcium lactate pentahydrate with hydroxypropyl methylcellulose, Int. J. Pharm. 317 (2006) 120–126, https://doi.org/10.1016/j.ijpharm. 2006.02.058. [39] Dow, METHOCEL Cellulose Ethers: Technical Handbook, Dow Chemical Company, USA, 2012. [40] A. Mihaly Cozmuta, A. Turila, R. Apjok, et al., Preparation and characterization of improved gelatin films incorporating hemp and sage oils, Food Hydrocoll. 49 (2015) 144–155, https://doi.org/10.1016/j.foodhyd.2015.03.022. [41] M.A.S.P. Nur Haziraha, M.I.N. Isab, N.M. Sarbona, Effect of xanthan gum on the physical and mechanical properties of gelatin-carboxymethyl cellulose film blends, Food Packag. Shelf Life 9 (2016) 55–63. [42] W. Weng, H. Zheng, Effect of transglutaminase on properties of tilapia scale gelatin films incorporated with soy protein isolate, Food Chem. 169 (2015) 255–260, https://doi.org/10.1016/j.foodchem.2014.08.012. [43] S.M. Noorbakhsh-Soltani, M.M. Zerafat, S. Sabbaghi, A comparative study of gelatin and starch-based nano-composite films modified by nano-cellulose and chitosan for food packaging applications, Carbohydr. Polym. 189 (2018) 48–55, https://doi. org/10.1016/j.carbpol.2018.02.012.

Please cite this article as: J.M. Fonseca, G.A. Valencia, L.S. Soares, et al., Hydroxypropyl methylcellulose-TiO2 and gelatin-TiO2 nanocomposite films: Physicochemical and structu..., , https://doi.org/10.1016/j.ijbiomac.2019.11.082

J.M. Fonseca et al. / International Journal of Biological Macromolecules xxx (xxxx) xxx [44] S. Dehghani, S.V. Hosseini, J.M. Regenstein, Edible films and coatings in seafood preservation: a review, Food Chem. 240 (2018) 505–513, https://doi.org/10.1016/j. foodchem.2017.07.034. [45] G.A. Valencia, R.V. Lourenço, A.M.Q.B. Bittante, P.J. do Amaral Sobral, Physical and morphological properties of nanocomposite films based on gelatin and laponite, Appl. Clay Sci. 124-125 (2016) 260–266, https://doi.org/10.1016/j.clay.2016.02.023. [46] M. Pacia, P. Warszyński, W. Macyk, UV and visible light active aqueous titanium dioxide colloids stabilized by surfactants, Dalt Trans 43 (2014) 12480–12485, https:// doi.org/10.1039/c4dt00285g. [47] Y. Jiang, Y. Li, Z. Chai, X. Leng, Study of the physical properties of whey protein isolate and gelatin composite films, J. Agric. Food Chem. 58 (2010) 5100–5108, https:// doi.org/10.1021/jf9040904. [48] N. Gontard, S. Guilbert, J. Cuq, Edible Wheat Gluten Films: Influence of the Main Process Variables on Film Properties Using Response Surface Methodology, 1992 57. [49] J. Caivano, M. del Pilar Buera, Color in Food: Technological and Psychophysical Aspects, 1st ed. CRC Press, Taylor & Francis Group, Boca Raton, 2012. [50] I. Arzate-Vázquez, J.J. Chanona-Pérez, M.J. de Perea-Flores, et al., Image processing applied to classification of avocado variety Hass (Persea americana Mill.) during the ripening process, Food Bioprocess Technol. 4 (2011) 1307–1313, https://doi. org/10.1007/s11947-011-0595-6. [51] López O V., García M A., Zaritzky NE (2008) Film forming capacity of chemically modified corn starches. Carbohydr. Polym. 73:573–581. doi:https://doi.org/10. 1016/j.carbpol.2007.12.023. [52] H.J. José, D.D.B. Luiz, S.L.F. Andersen, et al., Photocatalytic reduction of nitrate ions in water over metal-modified TiO2, J. Photochem. Photobiol. A Chem. 246 (2012) 36–44, https://doi.org/10.1016/j.jphotochem.2012.07.011. [53] M. Nascimento, Matos J. De, H. Kirchner, et al., Physical and morphological properties of hydroxypropyl methylcellulose fi lms with curcumin polymorphs, Food Hydrocoll. 97 (2019) 105217, https://doi.org/10.1016/j.foodhyd.2019.105217. [54] Annual Book of ASTM Standards. , ASTM, 2010 (Pensylvania, USA). [55] S. Amir, S. Mohammad, A. Razavi, K.S. Mikkonen, Physicochemical and rheomechanical properties of titanium dioxide reinforced sage seed gum nanohybrid hydrogel, Int. J. Biol. Macromol. 118 (2018) 661–670, https://doi.org/10.1016/j. ijbiomac.2018.06.049. [56] F. Sadeghi, M. Ashofteh, A. Homayouni, et al., Antisolvent precipitation technique: a very promising approach to crystallize curcumin in presence of polyvinyl pyrrolidon for solubility and dissolution enhancement, Colloids Surfaces B Biointerfaces 147 (2016) 258–264, https://doi.org/10.1016/j.colsurfb.2016.08.004. [57] C. Ding, M. Zhang, G. Li, Preparation and characterization of collagen/hydroxypropyl methylcellulose (HPMC) blend film, Carbohydr. Polym. 119 (2015) 194–201, https://doi.org/10.1016/j.carbpol.2014.11.057. [58] D. Yadav, N. Kumar, Nanonization of curcumin by antisolvent precipitation: process development, characterization, freeze drying and stability performance, Int. J. Pharm. 477 (2014) 564–577, https://doi.org/10.1016/J.IJPHARM.2014.10.070. [59] E.P. Reddy, L. Davydov, P. Smirniotis, TiO2-loaded zeolites and mesoporus materials in the sonophotocatalytic decomposition of acqueous organic pollutants: the role of the support, Appl. Catal. B Environ. 42 (2003) 1–11, https://doi.org/10.1016/S09263373(02)00192-3. [60] A. Manole, V. Dǎscǎleanu, M. Dobromir, D. Luca, Combining degradation and contact angle data in assessing the photocatalytic TiO2:N surface, Surf. Interface Anal. 42 (2010) 947–954, https://doi.org/10.1002/sia.3480. [61] I.G. Paulino-Lima, K. Fujishima, J.U. Navarrete, et al., Extremely high UV-C radiation resistant microorganisms from desert environments with different manganese concentrations, J. Photochem. Photobiol. B Biol. 163 (2016) 327–336, https://doi.org/10. 1016/j.jphotobiol.2016.08.017. [62] A. Haider, R. Al-Anbari, G. Kadhim, Z. Jameel, Synthesis and photocatalytic activity for TiO2 nanoparticles as air purification, MATEC Web Conf 162 (2018), 05006. https://doi.org/10.1051/matecconf/201816205006. [63] Y.H. Yun, J.W. Yun, Yoon S. Do, H.S. Byun, Physical properties and photocatalytic activity of chitosan-based nanocomposites added titanium oxide nanoparticles, Macromol. Res. 24 (2016) 51–59, https://doi.org/10.1007/s13233-016-4008-6. [64] J.D. Matos Fonseca, S.D. Fátima Medeiros, G.M. Alves, et al., Chitosan microparticles embedded with multi-responsive poly(N-vinylcaprolactam-co-itaconic acid-coethylene-glycol dimethacrylate)-based hydrogel nanoparticles as a new carrier for delivery of hydrophobic drugs, Colloids Surfaces B Biointerfaces 175 (2019) https://doi.org/10.1016/j.colsurfb.2018.11.042. [65] P.R.K. Mohan, G. Sreelakshmi, C.V. Muraleedharan, R. Joseph, Water soluble complexes of curcumin with cyclodextrins: characterization by FT-Raman spectroscopy, Vib. Spectrosc. 62 (2012) 77–84, https://doi.org/10.1016/j.vibspec.2012.05.002.

13

[66] M. Jacquot, M.J. Akhtar, M. Jamshidian, et al., Antioxidant capacity and light-aging study of HPMC films functionalized with natural plant extract, Carbohydr. Polym. 89 (2012) 1150–1158, https://doi.org/10.1016/j.carbpol.2012.03.088. [67] Hazimah a H, Ooi TL, Salmiah a (2003) Recovery of glycerol and diglycerol from glycerol pitch recovery of glycerol and diglycerol from glycerol pitch. J Oil Palm Res 15:1–5. [68] Y.A. Arfat, S. Benjakul, T. Prodpran, K. Osako, Development and characterisation of blend films based on fish protein isolate and fish skin gelatin, Food Hydrocoll. 39 (2014) 58–67, https://doi.org/10.1016/j.foodhyd.2013.12.028. [69] E. Dutu, I. Morjan, I. Mihailescu, et al., Principal component analysis of Raman spectra for TiO2 nanoparticle characterization, Appl. Surf. Sci. 417 (2017) 93–103, https://doi.org/10.1016/j.apsusc.2017.01.193. [70] T. Ohsaka, Ohsaka1980.Pdf, J. Phys. Soc. Jpn. 48 (1980) 1661–1668, https://doi.org/ 10.1143/JPSJ.48.1661. [71] H.C. Choi, Y.M. Jung, Kim S. Bin, Size effects in the Raman spectra of TiO2 nanoparticles, Vib. Spectrosc. 37 (2005) 33–38, https://doi.org/10.1016/j.vibspec.2004.05. 006. [72] ICSD code 9852 - inorganic crystal structure database TiO2 X-ray powder pattern, https://icsd-fiz-karlsruhe-de.proxy01.dotlib.com.br/display/list.xhtml (Accessed 4 Mar 2019). [73] ICSD code 9161 - inorganic crystal structure database rutile TiO2 powder X-ray pattern, https://icsd-fiz-karlsruhe-de.proxy01.dotlib.com.br/display/list.xhtml (Accessed 4 Mar 2019). [74] Sachtleben Chemie GmbH Technical Information Hombikat UV 100. 47184–47184. [75] J. Rotta, E. Minatti, P.L.M. Barreto, Determination of structural and mechanical properties, diffractometry, and thermal analysis of chitosan and hydroxypropylmethylcellulose (HPMC) films plasticized with sorbitol, Ciência e Tecnol Aliment 31 (2011) 450–455, https://doi.org/10.1590/S010120612011000200026. [76] F. Liu, J. Antoniou, Y. Li, et al., Effect of sodium acetate and drying temperature on physicochemical and thermomechanical properties of gelatin films, Food Hydrocoll. 45 (2015) 140–149, https://doi.org/10.1016/j.foodhyd.2014.10.009. [77] C. Marinescu, A. Sofronia, C. Rusti, et al., DSC investigation of nanocrystalline TiO2 powder, J. Therm. Anal. Calorim. 103 (2011) 49–57, https://doi.org/10.1007/ s10973-010-1072-6. [78] W.D.J. Callister, D.G. Rethwisch, Materials Science and Engineering an Introduction, 8th ed John Wiley & Sons, Inc, 2011. [79] M.F. Mullah, L. Joseph, Y.A. Arfat, J. Ahmed, Thermal properties of gelatin and chitosan, Glass Transition and Phase Transitions in Food and Biological Materials, John Wiley & Sons, Ltd, Chichester, UK 2017, pp. 281–304. [80] Sangappa, T. Demappa, Mahadevaiah, et al., Physical and thermal properties of 8 MeV electron beam irradiated HPMC polymer films, Nucl Instruments Methods Phys Res Sect B Beam Interact with Mater Atoms 266 (2008) 3975–3980, https:// doi.org/10.1016/j.nimb.2008.06.021. [81] S. Rivero, M.A. García, A. Pinotti, Correlations between structural, barrier, thermal and mechanical properties of plasticized gelatin films, Innov. Food Sci. Emerg. Technol. 11 (2010) 369–375, https://doi.org/10.1016/j.ifset.2009.07.005. [82] S.V. Canevarolo Junior, Técnicas de caracterização de polímeros, 2004 (Artliber, São Paulo, Brasil). [83] Y.A. Arfat, Plasticizers for biopolymer films, Glass Transition and Phase Transitions in Food and Biological Materials, John Wiley & Sons, Ltd, Chichester, UK 2017, pp. 159–182. [84] L. Miao, P. Jin, K. Kaneko, et al., Preparation and characterization of polycrystalline anatase and rutile TiO2 thin films by rf magnetron sputtering, Appl. Surf. Sci. 212213 (2003) 255–263, https://doi.org/10.1016/S0169-4332(03)00106-5. [85] Hoang V Van (2008) The glass transition and thermodynamics of liquid and amorphous TiO2 nanoparticles. Nanotechnology 19.: doi:https://doi.org/10.1088/09574484/19/10/105706. [86] M.C. Gomez-Guillen, B. Gimenez, M.E. Lopez-Caballero, M.P. Montero, Functional and bioactive properties of collagen and gelatin from alternative sources: a review, Food Hydrocoll. 25 (2011) 1813–1827, https://doi.org/10.1016/j.foodhyd.2011.02. 007. [87] J.M. Johlin, Isoelectric point of gelatin, J. Biol. Chem. 86 (1930) 231–234. [88] C. Bilbao-Sainz, J. Bras, T. Williams, et al., HPMC reinforced with different cellulose nano-particles, Carbohydr. Polym. 86 (2011) 1549–1557, https://doi.org/10.1016/j. carbpol.2011.06.060.

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