Tests were performed with cellulose acetate films (CA) incorporating 5, 10, 20, 30, and 50% (w/v) of glycerol with the purpose of evaluating the possible changes caused by the plasticizer on the functional properties of the packaging.
Carbohydrate Polymers 209 (2019) 190–197 Contents lists available at ScienceDirect Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol Structure and functional properties of cellulose acetate films incorporated with glycerol T ⁎ Sheyla Moreira Gonỗalvesa, , Daiane Cardial dos Santosb, Joyce Fagundes Gomes Mottac, Regiane Ribeiro dos Santosa, Davy William Hidalgo Cháveza, Nathália Ramos de Meloa,c a Departamento de Ciência e Tecnologia de Alimentos, Rodovia BR 465 - Km 7, UFRRJ, Seropédica, CEP:23891-360, RJ, Brazil Departamento de Engenharia Metalúrgica e Materiais, Av dos Trabalhadores 420 - Vila Sta Cecília, UFF, Volta Redonda, CEP: 27255-125, RJ, Brazil c Departamento de Engenharia de Agronegócios, Av dos Trabalhadores 420 - Vila Sta Cecília, UFF, Volta Redonda, CEP: 27255-125, RJ, Brazil b A R T I C LE I N FO A B S T R A C T Keywords: Food packaging Physicochemical properties Plasticizer Mechanical properties Tests were performed with cellulose acetate films (CA) incorporating 5, 10, 20, 30, and 50% (w/v) of glycerol with the purpose of evaluating the possible changes caused by the plasticizer on the functional properties of the packaging The glass transition temperature (Tg) and relative crystallinity (RC) were are obtained by DSC and XRD, respectively The results showed that, the presence of glycerol in the films caused increased thickness, water vapor transmission rate (WVTR), and optical properties for most treatments Moreover, morphological changes were evidenced in scanning electron microscopy (SEM) A reduction of tensile strength (TS) and Young's modulus (YM) was observed only in the concentration of 50% of glycerol Therefore, the results suggest that there was an interaction between glycerol and cellulose acetate, demonstrating that the film has potential for use as food packaging Introduction Consumer demand for quality, practical, and convenient food that is associated with growing global environmental awareness has been motivating the food industry to seek technologies for food production, storage, and conservation Thus, the natural polymers have gradually gained industrial importance (Canevaloro, 2006; Mano & Mendes, 2004) The environmental issue regarding the disposal of food packaging developed with non-biodegradable (petroleum-based) polymers can be solved by partially replacing these materials with biodegradable polymers from renewable sources In this context, industries have been looking for polymers such as cellulose acetate obtained by chemical modification of cellulose For this reason, cellulose derivatives have attracted the attention of researchers worldwide, due to their biodegradability, easy availability, respect for the environment, flexibility, ease of processing, and important physico-mechanical properties (Andrade-Molina, Shirai, Grossmann, & Yamashita, 2013; Thakur, Thakur, & Gupta, 2013; Thakur, Gupta, & Thakur, 2014) The increasing search for the development of food packaging with particular properties has motivated research to evaluate and demonstrate the possibility of plasticizer applications with the purpose of altering the polymeric characteristics that are desired, such as greater ⁎ malleability and improvement of the physical and mechanical properties Plasticizers are generally low volatility fluids used to increase flexibility and extensibility of films by reducing the intermolecular forces between polymer chains These tend to reduce the energy level required to give the chain mobility by reducing the glass transition temperature of the polymer Among the plasticizers, glycerol is one of the most used in biopolymers, since it behaves or has the qualities, such as hydrosoluble, polar, non-volatile, low molecular weight, and a hydroxyl group in each carbon (Moore, Martellia, Gandolfoa, Sobralb, & Laurindo, 2006; Azeredo, 2012) Extensive research has evaluated the possible changes caused by the addition of glycerol in films of different polymer bases and observed that among the alterations, reduction of tensile strength, increase in elongation at rupture, and thickness, are more evident (Liu, Adhikari, Guo, & Adhikari, 2013; Srinivasa, Ramesh, & Tharanathan, 2007) The use of polymer films commercially applicable as food packaging depends mainly on their functional properties as a barrier to water gases and vapors, mechanical and rheological properties, lipid and water solubility, and optical properties For this, both the chemical composition of the polymers and the interaction between the polymer matrix and the additive used must be considered Therefore, the characterization and collection of data on the main properties of the Corresponding author E-mail address: sheylapa1@hotmail.com (S.M Gonỗalves) https://doi.org/10.1016/j.carbpol.2019.01.031 Received May 2018; Received in revised form January 2019; Accepted 10 January 2019 Available online 11 January 2019 0144-8617/ © 2019 Elsevier Ltd All rights reserved Carbohydrate Polymers 209 (2019) 190197 S.M Gonỗalves et al 2.6 Water vapor transmission rate (WVTR) polymeric materials are of fundamental importance for the choice of the most appropriate polymer base for a given function and/or use The characterization predicts the polymer behavior in different conditions of use, as well as its useful life (Atarès, Jésus, Talens, & Chiralt, 2010; Gyawali & Ibrahim, 2014) This study therefore set out to assess the influence of the incorporation of different concentrations of glycerol in cellulose acetate films on visual, physical, thermal (DSC), and mechanical properties and evaluate the chemical interactions through the analysis of Fourier Transformation Infrared Spectroscopy (FTIR), X-ray diffractometer (XRD) and morphological changes by SEM WVTR was performed according to the gravimetric method (ASTM E96-95) with modifications according to the method described by Ghasemlou et al (Ghasemlou, Khodaiyan, Oromiehie, & Yarmand, 2011) Anhydrous calcium chloride (CaCl2) was used inside capsules, and they were packed in a desiccator containing saturated sodium chloride (NaCl) solution to promote controlled humidity (75% ± 2) and placed at room temperature (25 ± °C) The permeability of the films was determined by linear regression of the constant mass transfer region between the weight gain (g) and the time (t) that is correlated with the exposed area, allowing for determination of the WVTR (Eq (1)) Experimental WVTR = 2.1 Materials G t A (1) Where, WVTR: Water vapor transmission rate expressed in g m–2.day−1; G/t: Angular coefficient of the line expressed in g.day−1; A: Permeation area of the sample expressed in m2 The cellulose acetate (CA) resin was purchased from Sigma-Aldrich, Brazil, with a degree of substitution of 1.48°, Acetone PA was purchased from Cap-Lab, São Paulo, Brazil Glycerol 99.5% was purchased from Vetec, Rio de Janeiro, Brazil 2.2 Preparation of films 2.7 Mechanical properties The films were elaborated using the casting method, according to Melo (2003) with modifications The cellulose acetate was solubilized in acetone (1:10 w/v) and held for 12 h to form the gel Glycerol was added to the formed filmogenic solution in different concentrations (5, 10, 20, 30, and 50%) (w/v) The filmogenic solution prepared from each formulation was poured into glass plate and spread with the help of a glass rod having the predetermined height, using a calibrated spacer The solvent was evaporated under controlled temperature conditions (25 ± °C) for 10 Afterwards, the films were detached from the glass plates, packed in a vacuum, and stored for further analysis The control film was made with 0% glycerol The mechanical properties of tensile strength (TS), elongation at break (EB), and Young´s modulus (YM) of films were determined using the TA.XTplus Texturometer (Stable Micro Systems, Surrey, England), operating according to the standard ASTM D method 882-82 Samples with dimensions of 10 × 2.5 cm were fixed to the claws with initial separation of 25 mm in the texturometer operated with 30 kg cell, force of 0.049 N, and speed of mm/s The tensile strength was controlled by the program Exponent Texture TEE32 (Stable Micro Systems) through the relation of the maximum force (N) and the sample area (mm) The modulus of elasticity (Young´s modulus) was calculated from the linear region of the stress versus strain curve The elongation at break was given by the deformation at the moment the sample was ruptured by the initial length of the sample, according to Eq (2) 2.3 Thickness R= The films thickness (μm) was obtained with the aid of a digital micrometer (Datamed) Measurements were taken at ten points for each film L × 100 Ci (2) Where, R: elongation at rupture expressed in %; L: Distance at moment of rupture expressed in mm; Ci: Initial sample length in mm 2.4 Fourier transform infrared attenuated total reflection (FTIR-ATR) spectroscopy 2.8 Scanning electron microscopy (SEM) The structural chemical analysis of the films was performed using FTIR-ATR, (FT/IR-4700, Jasco Corporation) under attenuated total reflection (ATR) mode, according to Moura et al (Moura, Mattoso, & Zucolotto, 2012) and Ramos et al (2013) with modifications The spectra were obtained in the wavelength range of 500–4000 cm−1, cm−−1 resolution, and with 32 scans The surface analysis of the films were performed using the Scanning Electron Microscope (Carl Zeiss, model EVO MA 10) Samples of 1.5 × 0.7 cm were fixed on a specific support (stub) Being a material of low conductivity, samples were coated with gold (Au) (metallizer EMITEC K550X) with current of 25 mA/2 The SEM observation was performed in low vacuum with 3000 and 6000 Kv of acceleration voltage, 480 filament current, and scans with magnifications of 5000 and 500× The samples were evaluated on the surface and cross-sectional level (fracture region) 2.5 Visual aspect of the films The films were evaluated for color and transparency, and a sample (2 × cm) was placed on the inner side of a colorimeter/spectrophotometer cell (Minouta CM-5-ID) to obtain the luminosity degree L* and chromaticity a* and b* The opacity was determined according to ASTM D1746 (ASTM, 2003) at 560 nm wavelength, being evaluated according to the amount of light the films were able to absorb The greater the amount of light absorbed indicates greater opacity of the material (Fabra, Talens, & Chiralt, 2009) The color and opacity were determined by the average of three readings for each film 2.9 X-ray diffraction (XRD) The XRD standards were obtained in a Bruker D2 Phaser diffractometer (Bruker, Germany), operated at 30 kV and 10 mA The diffractograms were collected in the range of to 29° and ω-2θ The relative crystallinity (RC) was calculated according to Eq (3) (Candido, Godoy, & Gonỗalves, 2017): 191 Carbohydrate Polymers 209 (2019) 190197 S.M Gonỗalves et al RC = (TA-AA) × 100 TA structure containing CH and OH groups, so its incorporation into cellulose acetate may have caused an increase in the interactions between both compounds in the regions of the bands that represent these attributes Hydrogen bonds between OH groups of CA and glycerol may occur, since an OH group of the plasticizer is available for possible interactions However, glycerol has two more OH groups that will not be available for interactions Therefore, the OH prominent band may also be related to the higher amount of OH present in the film resulting from the addition of glycerol (3) Where, RC: Relative crystallinity in %; TA: Total area AA: Area of amorphous region 2.10 Differential scanning calorimetry (DSC) Samples of 3.5 mg of the preconditioned films at 75% relative humidity were analyzed in a Q200 DSC (TA Instruments, United States) The thermograms were recorded with heating of 20–250 °C at a heating rate of 10 °C/min, followed by cooling from 250-20 °C at a heating rate of 20 °C/min The glass transition temperatures (Tg) were determined from the second heating of 20–250 °C at a heating rate of 10 °C/min in order to discard the influence of thermal history 3.2 Visual aspect of the films The average values of color and transparency of the films are shown in Table 1, being the films with greater amount of light absorbed considered opaque (Fabra et al., 2009) The comparisons that evaluate the possible influence of the different concentrations of glycerol on the luminosity parameter (L*) of the cellulose acetate film show that there was a significant difference (p < 0.05) only for the concentration of 50% in relation to the control film For the opacity, the films with 30 and 50% of glycerol had the highest opacity Chia mucilage films containing a high concentration of glycerol (75% w/w) also showed highest opacity (Dick et al., 2015) Villalobos et al (Villalobos, Chanona, Hernández, Gutiérrez, & Chiralt, 2005) reported that the opacity of the polymer films is closely linked to the internal structure formed during drying, and this structure, in turn, is strongly influenced by the nature of the initial solution Therefore, higher opacity may be related to the presence of non-miscible dispersion, due to differences in refraction of the phases, as well as particle size and concentration However, in this work, glycerol and cellulose acetate, both of hydrophilic nature as demonstrated by the FTIR analysis (Fig 1), present a possible chemical interaction between their chains Thus, of miscible dispersion formed by CA and glycerol justify the maintenance of opacity by the films, even after incorporation of up to 20% glycerol Although, according to SEM images (Fig 2), the surfaces of the films with 30 and 50% glycerol were characterized by pore-like structures of different sizes, which may have influenced the opacity results Closer inspection of Table shows that the addition of glycerol to the cellulose acetate films caused an increase in the red coloration (a*), while only 20 and 30% of glycerol caused an increase in the yellow 2.11 Statistical analysis A one-way ANOVA and Tukey multi comparative test were performed to detect the differences between samples with a significant level of 5% Additionally, multivariate analyses were applied, such as Principal Component Analysis (PCA), for the study of correlations and similarities between variables and/or treatments All statistical analyses were carried out using software R version 3.2.4 (R Foundation for Statistical Computing, Viena, Áustria) and FactoMineR version 1.32 Results and discussion 3.1 Fourier transform infrared attenuated total reflection (FTIR-ATR) spectroscopy The spectra of the pure CA films and CA films incorporating 5, 10, 20, 30 and 50% glycerol analyzed by FTIR are show in Fig The CA is an ester, therefore, the presence of the bands at 1741 cm−1 (steric carbonyl elongation) and the band 3478 cm−1 (cellulosic OH elongation) characterize the film (Meireles, 2007) It was observed that the addition of glycerol caused an increase in the bands 2936 cm−1 (CH elongation), 3478 cm−1 (OH elongation), 1232 cm−1 and 1045 cm-1 (steric carbonyl elongation) Glycerol is an alcohol with a chemical Fig FTIR spectra of CA film (CA0%) and CA films incorporating with glycerol (CA5%, CA10%, CA20%, CA30% or CA50% w/v) 192 Carbohydrate Polymers 209 (2019) 190197 S.M Gonỗalves et al Table Average values of the visual appearance of the CA films (CA0%) and CA films incorporating with glycerol (CA5%, CA10%, CA20%, CA30%, or CA50% w/v), for the parameters the luminosity (L*), chromaticity (a* and b*), and opacity * Treatments L* CA0% Glycerol CA5% Glycerol CA10% Glycerol CA20% Glycerol CA30% Glycerol CA50% Glycerol 96.75 97.41 97.95 97.67 97.09 98.06 a* ± ± ± ± ± ± 1.46 0.41 0.68 0.47 1.14 0.45 b ab ab ab ab a 0.01 0.08 0.11 0.74 0.72 0.19 b* ± ± ± ± ± ± 0.01 0.09 0.09 0.09 0.16 0.09 c bc bc a a b 0.22 0.11 0.16 1.41 1.27 0.31 Opacity ± ± ± ± ± ± 0.12 b 0.08 b 0.16 b 0.3 a 0.36 a 0.41 b 92.85 93.48 94.81 94.13 92.69 95.07 ± ± ± ± ± ± 0.86 1.02 1.71 1.26 2.82 1.11 ab ab ab ab b a Average followed by the same letters not differ from each other (p > 0.05) by the Tukey test at the 5% level of significance the effect of glycerol and sorbitol on the barrier properties of starchbased films The researchers observed increased permeability to water vapor as the concentration of plasticizers increased from 15 to 45% (Sanyang, Sapuan, Jawaid, Ishak, & Sahari, 2015) However, incorporation of glycerol in chitosan-based films caused a 5.5% reduction in WVTR (Priyadarshi, Sauraj Kumar, & Negi, 2018) color (b*) Previous studies showed that an addition of 70% (v/v) glycerol to chia seed mucilage film caused an increase of the a* and b* parameters (Dick et al., 2015) However, in the present work, the films presented reduction of the red color for 50% addition of the plasticizer It is noteworthy that the film produced without the addition of glycerol already presented reddish and yellowish coloration, having the red coloration presenting a tendency to grayscale It must be remembered that, among the optical properties of importance for food packaging, color and opacity stand out According to consumer habits, packaging with a strong color, high brightness, or low opacity represent both a type of information and an emotional link between the consumer and the product, a tool widely explored by marketing (Yoshida & Antunes, 2009; Zanela et al., 2015) According to the values obtained in the present research, CA films are sufficiently bright and transparent, which makes them suitable for use as food packaging 3.5 Mechanical analysis All treatments with glycerol presented a difference (p < 0.05) in relation to the control film The incorporation of glycerol to the acetate film caused an increase in the tensile strength (46.56 N–51.28 N) up to the concentration of 30%, (Table 3), noting the highest average values were at the 10 and 20% of glycerol concentrations The literature reports that the presence of plasticizer leads to the disarrangement of the polymer network, giving greater flexibility to the material and consequent reduction of the tensile strength (Liu et al., 2013; Moore et al., 2006) However, when the final amount of plasticizer in the polymeric material is low or high, there may be few or excessive interactions, respectively, between the polymer network and the plasticizer modifying the flexibility of the films (Reis et al., 2015) It is noted that up to 30% glycerol concentration, the films were more resistant when compared to the control film However, it is worth noting that in comparison with the resistance values presented by the films with 10 and 20% of glycerol, the film with 30% already presented a reduction of the values for the parameter evaluated Nevertheless, with the concentration of 50% of glycerol, the films acquired high flexibility and presented less resistance to the traction This demonstrates that the concentrations of 5, 10, 20, and 30% of glycerol may not have been sufficient to plasticize the films, although morphologically the surfaces and fracture regions of 30 and 50% of glycerol films exhibit some similarity For the Young's modulus, the incorporation of glycerol to the cellulose acetate film provided increased stiffness for most films, and the highest values were observed for films with 10 and 20% glycerol For tensile strength, it is noted that at the concentration of 30% glycerol, there was a reduction of the stiffness of the material when compared to the film with 20% of the plasticizer Consequently, the film containing 50% of glycerol already presented a lower stiffness, presenting a difference (p < 0.05) from the control film, which confirms that plastification may have been achieved only in the presence of 50% glycerol The elongation at break (EB) reflects the degree of flexibility and extensibility of the films, i.e., it reflects how much the material will be able to stretch before rupture For this parameter, it was observed in Table that there was no difference (p > 0.05) caused by the incorporation of different concentrations of glycerol in the cellulose acetate film The mechanical behavior of polymeric packaging depends, especially, on its development, which depends among other factors, on polymer-additive interactions, as related by Laohakunjit et al (Laohakunjit & Noomhorm, 2004) The researchers showed that 20–30% glycerol increased EB in starch films, while 35% of plasticizer caused EB reduction 3.3 Thickness It was verified that the addition of glycerol contributed to increasing the thickness of the cellulose acetate films, presenting a difference (p < 0.05) for all plasticizer concentrations (Table 2) These results reflect those of Farias et al (Farias, Fakhouri, Carvalho, & Ascheri, 2012) and Shimazu et al (Shimazu, Mali, & Grossmann, 2007), who also verified the increase in the thickness of cassava starch films as a function of the incorporation of different glycerol concentrations In this way, the presence of the plasticizer may have provoked a certain disarrangement and breakage of the intra and intermolecular interactions of the polymeric material that caused the chains to move away, which was manifested as an increase in the thickness of the films 3.4 Water vapor transmission rate (WVTR) The addition of glycerol to the cellulose acetate film at concentrations of 10 and 30% caused an increase in WVTR as compared to the control film (Table 2) Jost et al (Jost, Kobsik, Schmid, & Noller, 2014) also observed that alginate films incorporating glycerol had their rate of oxygen permeability and water increased However, in this work, the concentrations of 20 and 50% of glycerol caused a reduction in the water vapor permeability This must have occurred due to the antiplasticizing effect caused by the incorporated glycerol, which even decreased the intermolecular bonds in the chain and may still create possibilities for other bonds Shimazu et al (Shimazu et al., 2007) evaluated the antiplasticizing effect of glycerol on the moisture sorption properties of cassava starch films The authors reported that, depending on the concentration of the plasticizer, it may cause a contrary effect, instead of increasing the hydrophilicity of the material Therefore, the interactions between the additives and the polymer matrix may have provided less polar characteristics, which may have been caused due to the low concentration of hydrogen-like bonds in the polymeric network added The barrier properties of the polymeric materials can be influenced by the type and concentration of plasticizer Studies were conducted on 193 Carbohydrate Polymers 209 (2019) 190197 S.M Gonỗalves et al Fig SEM of the surface (left column with 500 and 5000x) and fracture region (right column with 500 and 5000x) of the CA films (CA0% (A and B)) and CA films with glycerol (CA5% (C and D); CA10% (E and F); CA20% (G and H); CA30% (I and J) and CA50% (L and M)) 3.6 Scanning electron microscopy (SEM) (Fig 2B) From the addition of glycerol, the surface images (Fig 2C, E, and G) for films with 5, 10, and 20% of glycerol, respectively, are already presented small and uniform depressions Moreover, the films incorporating 30 and 50% of glycerol (Fig 2I and L), respectively, SEM images (Fig 2) for the control film (0% glycerol) are smooth and homogeneous for the surface (Fig 2A) and fracture regions 194 Carbohydrate Polymers 209 (2019) 190197 S.M Gonỗalves et al the presence of glycerol caused a slight increase of RC in this region, being the highest values for the films with 30 and 50% of glycerol The presence of glycerol may have caused a slight rearrangement of the chains, via hydrogen bonds between plasticizer and CA that increased crystallinity Table Average values of the thickness and water vapor transmission rate (WVTR) of the CA films (CA0%) and CA films with glycerol (CA5%, CA10%, CA20%, CA30%, or CA50% w/v) Treatments Thickness (μm) WVTR (g.m-2 day−1) CA0% Glycerol CA5% Glycerol CA10% Glycerol CA20% Glycerol CA30% Glycerol CA50% Glycerol 41.3 ± 4.64 b 52,43 ± 337 a 50.17 ± 6.28 ab 56.07 ± 3.52 a 55.47 ± 1.66 a 54.07 ± 1.53 a 258.09 270.18 316.64 257.83 308.26 238.16 ± ± ± ± ± ± 5.9 bc 28.69 31.34 20.86 37.17 17 c 3.8 Differential scanning calorimetry (DSC) abc a Fig shows DSC curves for CA (CA0%) films and CA films with different concentrations of glycerol (CA 5, 10, 20, 30, and 50%) The curves representing the first heating (Cycle 1) have endothermic peaks at 148.16, 117.57, 109.37, 147.27, 146.20, and 132.59 °C for the CA0%, CA5%, CA10%, CA20%, CA30%, and CA50% films, respectively (Cycle 1) According to De Freitas et al (De Freitas, Senna, & Botaro, 2017), such endothermic events between 77.5 and 91.1 °C are related to the water adsorption capacity of each polymer material, which depends on the degree of CA substitution The authors also report the occurrence of endothermic peak at 123.5 °C for cellulose Thus, as with acetyl, the plasticizers also have the ability to modify the arrangement of the CA chains, thereby altering their water adsorption capacity The glass transition temperature of the films was observed in Cycle and confirmed in Cycle (second heating) (Fig 4) The CA0%, CA5%, CA10%, CA20%, CA30%, and CA50% films had Tg at 229.02, 223.74, 224.10, 218.73, 211.09, and 207.34 °C, respectively (Cycle 2) The literature reports that the Tg of CA with a replacement grade of 1.48° is concentrated around 223.45 °C (De Freitas et al., 2017), close to that found for the CA0% film (229.02 °C) (Fig 4) However, for the other films, the presence of the glycerol in different concentrations must have caused a reduction of the intermolecular forces of the polymer chains, causing a reduction of the Tg of the CA films bc ab * Average followed by the same letters not differ from each other (p > 0.05) by the Tukey test at the 5% level of significance Table Mechanical properties of CA films Treatments Tensile Strength (N) CA0% Glycerol CA5% Glycerol CA10% Glycerol CA20% Glycerol CA30% Glycerol CA50% Glycerol 46.56 51.16 56.28 57.57 51.28 39.04 ± ± ± ± ± ± 2.08 2.69 2.31 1.69 7.03 0.63 b ab a a ab c Young's Modulus (MPa) 5± 5.51 6.42 6.62 5.78 3.87 0.28 c ± 0.61 ± 0.24 ± 0.21 ± 0.56 ± 0.68 bc ab a abc d Elongation at break (%) 6.8 ± 0.63 a 8.99 ± 1.48 a 8.18 ± 1.7 a 7.83 ± 0.71 a 8.49 ± 2.46 a 6.86 ± 1.23 a Average ± standard deviation Average in columns followed by the same letters not differ from each other (p > 0.05) by the Tukey test already show surface containing micropores of different diameters and depth It is observed that these pores present similarity in number and diameter in both films containing 30 and 50% of glycerol, while it was also noted that there was a slight increase in relation to the amount of pores for the film with 50% of the plasticizer As can be seen in Fig the fracture images of the films with glycerol (D, F, H, J and M), present small pores start to appear Hence, the presence of glycerol possibly modified the polymer network, which caused internal morphological changes reflected with the appearance of micropores According to the results presented in the mechanical evaluation (Table 3), the film incorporating 30% glycerol presented numerical reduction of the values for tensile strength (but in relation to the control film is still higher), while the films with 5, 10, and 20% of glycerol showed higher resistance For the tensile strength analysis, the concentration of 50% glycerol presented a difference (p < 0.05) in relation to the other concentrations This evidences a film with lower resistance, which may have been influenced by the porous structure Therefore, the presence of these micropores on the surface and fracture region may be a reflection of the lack of interfacial interaction between the cellulose acetate and glycerol, making the material more vulnerable to forces in the mechanical test, resulting in a decrease in tensile strength 3.9 Principal component analysis (PCA) and Pearson’s correlation The first two components explained approximately 70% of total variability of the experimental data (Fig 5) (PC1 = 44.5% and PC2 = 25.5%), and this value was adequate Opacity (Abs), L*, and Thickness (Fig 5) showed greater influence on the differentiation of the treatments (variables with reddish colors presents high influence) Abs and L* (Table 4) had a positive correlation (r = 0.958), as well as the variables a* and b* (r = 0.987) and between TS and YM (r = 0.997) As mentioned previously, according to Table 1, the variables a* and b* behave in a similar manner against different concentrations of glycerol Likewise, the same was observed in Table 3, which corroborates the similarity of the mechanical analyses (TS and YM) in the presence of different concentrations of glycerol on the CA film The control and 50% glycerol films were the most differentiated (Fig 5b) The 50% Glycerol treatment showed higher values for opacity, L*, and thickness (Tables and 2) This shows that the addition of glycerol caused changes in certain properties of the CA film Conclusion According to the results of this study, the cellulose acetate films incorporated with different glycerol concentrations underwent changes in the polymer matrix and were reflected by the majority of the evaluated parameters This confirms that the chemical structure of the additives and the polymer matrix is of fundamental importance in defining the functional properties of the polymer films The films incorporating glycerol proved to be thicker, opaque, luminous, yellowish and reddish, semi-crystalline, and with higher water vapor transmission rate for most treatments, in addition to presenting morphological change and alteration of the mechanical properties Such alterations can be confirmed by the FTIR spectra that demonstrated possible chemical interaction between the polymer matrix and the additive Therefore, given the properties shown, most of the films incorporated with glycerol are particularly suitable for packaging foods 3.7 X-ray diffraction (XRD) XRD revealed (Fig 3) materials with low crystallinity that had little distinction between different treatments The diffractograms present small peaks in the region of 2θ = 8.8° and 23° According to Wan Daud et al (Wan Daud & Djuned, 2015), the region corresponding to 2θ = 8° indicates possible disturbances caused by acetylation of cellulose for CA production The presence of acetyl may cause disruption in the cellulose chains and consequent breakage of its microfibrillar structure Chen, Xu, Wang, Cao, and Sun, (2016) reported that the crystalline diffractions of CA occur at approximately 2θ = 8, 10, and 13° The values of relative crystallinity (RC) (Fig 3) for the control film (CA0%), CA5%, CA10%, CA20%, CA30%, and CA50% were 10.5%, 10.8%, 11.4%, 11.8%, 18.3%, and 18.2%, respectively It is noted that 195 Carbohydrate Polymers 209 (2019) 190–197 S.M Gonỗalves et al Fig XRD diractograms of cellulose acetate film (CA0%) and CA films incorporating with glycerol (CA5%, CA10%, CA20%, CA30%, or CA50% w/v) Fig DSC thermograms of CA film (CA0%) and CA films with glycerol (CA5%, CA10%, CA20%, CA30% and CA50%) Fig Bi-plot distribution (PCA- PC1 and PC2); (a) PCA response variables and (b) score plot of for treatments 196 Carbohydrate Polymers 209 (2019) 190–197 S.M Gonỗalves et al Table Pearsons correlation for dependent variables Variables Thickness L* a* b* Abs Young's modulus Tensile strength Elongation at break WVTR Thickness L* a* b* Abs Young modulus Tensile strength Elongation at break WVTR 0.547 0.709 0.596 0.307 0.215 0.210 0.463 0.321 −0.001 −0.109 0.958 −0.013 0.002 0.008 −0.146 0.987 −0.183 0.450 0.407 0.246 0.309 −0.258 0.451 0.404 0.153 0.306 −0.122 −0.108 −0.231 −0.293 0.997 0.586 0.570 0.616 0.616 0.674 Values in bold are different from with a significance level alpha = 0.05 that require greater protection against mechanical forces, greater moisture exchanges, and protection against light Soon, such films could be used to pack fresh 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