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Article

Effect of the Processing Conditions on the Supercritical Extraction and Impregnation of Rosemary Essential Oil in Linear Low-Density Polyethylene Films

by
Nadia Esfandiari
1,
Adrián Rojas
2,3,
Arman Babhadiashar
4,
María José Galotto
2,3,5,
Nedasadat Saadati Ardestani
6 and
Seyed Ali Sajadian
7,8,*
1
Department of Chemical Engineering, Marvdasht Branch, Islamic Azad University, Marvdasht 73711-13119, Iran
2
Packaging Innovation Center (LABEN), University of Santiago of Chile (USACH), Santiago 9170201, Chile
3
Center for the Development of Nanoscience and Nanotechnology (CEDENNA), University of Santiago of Chile (USACH), Santiago 9170124, Chile
4
Department of Petroleum and Chemical Engineering, Science and Research Branch, Islamic Azad University, Tehran 14778-93855, Iran
5
Department of Food Science and Technology, Technological Faculty, University of Santiago of Chile (USACH), Santiago 9170201, Chile
6
Nanotechnology Research Center, Research Institute of Petroleum Industry (RIPI), Tehran 14778-93855, Iran
7
Department of Chemical Engineering, Faculty of Engineering, University of Kashan, Kashan 87317-53153, Iran
8
South Zagros Oil and Gas Production, National Iranian Oil Company, Shiraz 71357-17991, Iran
*
Author to whom correspondence should be addressed.
Processes 2023, 11(1), 11; https://doi.org/10.3390/pr11010011
Submission received: 18 November 2022 / Revised: 10 December 2022 / Accepted: 16 December 2022 / Published: 21 December 2022
(This article belongs to the Section Chemical Processes and Systems)
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Abstract

:
The supercritical fluid extraction of essential oil from rosemary leaves and its subsequent impregnation in linear low-density polyethylene (LLDPE) films were studied. The effects of temperature (318 and 338 K), pressure (15 and 25 MPa) and rosemary particle size (0.9 and 0.15 mm) on the extraction yield were investigated. Impregnation assays were developed at two different values of pressure (12 and 20 MPa), temperature (308 and 328 K), and impregnation time (1 and 5 h). The extraction yield of rosemary essential oil was increased by increasing pressure and decreasing particle size and temperature. ANOVA results showed that temperature, pressure, and time significantly impacted the essential oil impregnation yield in LLDPE films. The maximum impregnation yield (1.87 wt. %) was obtained at 12 MPa, 328 K, and 5 h. The antioxidant activity and the physical-mechanical properties of impregnated films were analyzed. The IC50 values for all the impregnated LLDPE samples were close to the IC50 value of the extract showing that the impregnated films have a significant antioxidant activity.

1. Introduction

Essential oils extracted from plants have always been of interest for pharmaceutical and food applications due to the highly attractive antimicrobial and antioxidant properties of some of their derivative compounds [1]. The antioxidant properties of essential oils extracted from plants belonging to the Labiatae family such as rosemary have been the most studied [2,3,4,5]. Particularly, the capacity of rosemary essential oil to delay the fat oxidation in foods such as meat, salmon, and fruits has been related to the presence of phenolic compounds with powerful antioxidant activity such as carvacrol, thymol, carnosol, carnosic acid, rosmanol, rosmadial, epirosmanol, rosmadiphenol, rosmarinic acid, among others [6].
In the last decades, green technologies based on supercritical fluids (SCF) have attracted great interest in many food and pharmaceutical applications [7,8]. Particularly, carbon dioxide (CO2) has been the most used fluid for these applications because it has a low critical temperature (Tc = 31.1 °C) and moderate critical pressure (Pc = 7.38 MPa). Other properties such as tunable density, viscosity, nontoxicity, non-flammability, and inexpensiveness have led to special attention towards supercritical carbon dioxide (SC-CO2) [9]. The extraction of active ingredients from plants through Supercritical Fluid Extraction (SFE) [10,11,12] has been one of the most widely explored techniques. Particularly, the supercritical fluid extraction of rosemary essential oil has been extensively studied. Ahmed et al. (2012) investigated the effect of the operational conditions of temperature (308 to 333 K) and pressure (10 and 22 MPa) over the essential oil extraction from Algerian rosemary [13]. Meanwhile, Bensebia et al. (2009) determined that particle size, pressure, and temperature are the main parameters impacting the rosemary essential oil extraction yield [14]. In other work, Conde-Hernández found that the rosemary essential oil obtained by extraction with SC-CO2 had higher extraction yield and antioxidant activity when compared with the extracts obtained by hydrodistillation and steam distillation [15]. Other interesting SCF-based techniques allowed both nanoparticle production or encapsulation using different techniques such as RESS [16], SAS [17], GAS [18,19], PGSS [20], SFEE and SSI.
The Supercritical Solvent Impregnation (SSI) process is a modern technique with many applications on pharmaceutics that allows the incorporation of bioactive substances, such as nutraceuticals and drugs, inside polymers taking advantage of the excellent mass transport properties of SC-CO2 that include high diffusivity and a surface tension close to zero [21]. The advantages of SSI include short processing time, no use of organic solvents, no waste generation, and low energy consumption [22,23,24]. Particularly, the SSI process has been used during the last decades as an alternative process to develop active ingredients for food packaging through the combination of antimicrobial or antioxidant substances in polymeric matrices for food packaging [25,26].
The impregnation process has been studied for the incorporation of clove essential oil in linear low-density polyethylene (LLDPE) films [27], cinnamaldehyde in poly(lactic acid) (PLA) films [28], thymol in poly(lactic acid) /Polycaprolactone (PLA/PCL) films [29], lycopene in hydrolyzed collagen [30], lavandin essential oil in octenyl succinic anhydride (OSA) modified starch produced from waxy maize [31], chia oil in soy protein [32], Pulicaria jaubertii in gum arabic [33], eugenol in LLDPE films [34], carvone in PLA films [35], a mixture of two terpene ketones in low density polyethylene (LDPE) films [36], cinnamaldehyde into cassava starch films [37], terpene ketones with insecticidal properties in LDPE/sepiolite nanocomposite films [38], antioxidant mango polyphenols into polyethylene terephthalate (PET)/Polypropylene (PP) films [39], olive leaf extract polyphenols charged into PET/PP films [40], eugenol into polyamide fibers [41], LDPE films loaded with carvone [42], PLA films with thymol [43], ibuprofen into poly(methyl methacrylate) (PMMA) films [44], mefenamic acid in PMMA [45], carvacrol in composite PCL [46], and Zataria multiflora Impregnation in PLA films [47]. In all the conducted studies pressure, temperature, time, and depressurization rate were considered as the parameters affecting the SSI process efficiency.
This study aimed to develop antioxidant LLDPE films functionalized with rosemary essential oil extract. LLDPE was used as model polymer due to its common use in food packaging. Rosemary essential oil was extracted by SFE technology and subsequently incorporated in LLDPE films using the SSI process. The effects of the different operating conditions on the extraction yield of essential oil from rosemary (pressure, temperature, and particle size) and on its impregnation yield in LLDPE films (pressure, temperature, and time) were investigated. Full factorial design (FFD) was used to optimize the parameters of both SFE and SSI processes. To our knowledge, this is the first study on the incorporation of a multicomponent antioxidant mixture obtained by SFE from rosemary leaves in LLDPE films aimed for food packaging applications.

2. Material and Methods

2.1. Materials

Rosemary leaves were obtained from Eram Botanical Garden, located in the city of Shiraz in Fars province (Iran), and dried at room temperature. Linear low-density polyethylene (LLDPE) films (thickness < 1.0 mm), were provided by Aliyan Tajhiz (Shiraz, Iran). Carbon dioxide (99.99% purity) was purchased from Aboghadareh Co. (Shiraz, Iran). Analytical-grade ethanol (99.9% HPLC grade) and methanol were purchased from Merck (Darmstadt, Germany), and 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical, was purchased from Sigma–Aldrich Chemie (Steinheim, German).

2.2. Method

2.2.1. Design of Experiments

In this study, FFD was used to optimize the operational parameters of the supercritical fluid extraction of essential oil from rosemary (pressure, temperature, and particle size) and the operational parameters of the supercritical solvent impregnation of the essential oil in LLDPE films (pressure, temperature, and time). A 23 factorial design considering two levels (high and low) for each parameter was applied to evaluate both SFE and SSI processes. For SFE assays, pressure was used at 12 and 20 MPa, temperature at 308 and 328 K, and impregnation time at 1 and 5 h. Meanwhile, for SSI assays, pressure (X1) was used at 15 and 25 MPa, temperature (X2) at 318 and 338 K, and particle size (X3) at 0.9 and 0.15 mm. Moreover, all tests were developed in duplicate. The effect of the operational parameters on the extraction yield and impregnation yield of the rosemary essential oil in LLDPE was statistically investigated through an analysis of variance (ANOVA) using the design expert software.

2.2.2. Supercritical Fluid Extraction Procedure

The equipment used to obtain the rosemary essential oil is shown in Figure 1. The main components were E-1: CO2 cylinder, E-2: Needle valve, E-3: Filter, E-4: Refrigerator unit, E-5: High-pressure pump, E-6: Compressor, E-7: Oven, E-8: Automation system, E-9: Extraction cell, E-10: Back pressure, E-11: Micrometering valve, E-12: sampler. In these assays, 2 g of dried rosemary powder was loaded in the extraction cell (stainless steel, outer diameter = 0.02 m, inner diameter = 0.01 m, length = 0.12 m). Glass beads were used to improve the mass transfer through the increase of the contact surface between the dried rosemary powder and SC-CO2. First, the back-pressure regulator (Xi’an Shelok Instrument Technology Co., Shaanxi, China) was closed. Then, CO2 was passed through a molecular sieve in order to remove moisture and impurities. Then, CO2 was entered into the refrigerator to hold the CO2 flow in liquid state (<−10 °C). A liquid pump (air driven liquid pump, type-M64, Shineeast Co., Shandong, China) was used to increase CO2 pressure. Then CO2 entered into the extraction cell placed inside an oven. When the system reached the desired temperature and pressure, the static extraction process began during 150 min. The back pressure valve was opened to return the dynamic conditions to the initial state. During the dynamic extraction time, the sampling temperature was kept below 0 °C The amount of each extracted sample was measured gravimetrically. Until the samples were analyzed, the samples were stored in a sealed dark container in the freezer. The yield of extraction was calculated by the following equation:
Y i e l d   ( % ) = A m o u n t   o f   e x t r a c t e d   o i l   ( g )   A m o u n t   o f   t o t a l   s a m p l e   ( g ) × 100

2.2.3. Supercritical Solvent Impregnation Process

Figure 2 shows the apparatus used in the SC-CO2-assisted impregnation of rosemary essential oil in LLDPE films. The accuracy of the pressure transmitter was ±0.1 MPa. An oven was used to adjust the temperature with a temperature accuracy of ±0.1 K. The mass ratio of rosemary essential oil to LLDPE was fixed and equal to 1:1. For each experiment, 3 mL of rosemary essential oil extract was placed at the bottom of the impregnation cell and LLDPE was incorporated at its upper side, a metal mesh separated both sides of the cell. First, CO2 gas was passed through a microfilter and was liquefied by the refrigerator unit. Then, CO2 reached the appropriate pressure using the pump and entered the cell. A pressure gauge was employed to control the pressure of the system. By using magnetic stirring at 100 rpm, active substances were mixed with SC-CO2. After the considered impregnation time, the impregnation process was performed and the system was manually depressurized regulating the micrometering valve. After each experiment, the impregnated film was taken from the cell. Then, to preserve their properties, the impregnated films were stored in glass flasks at 4 °C until their analyses. The amounts of impregnated oil in the LLDPE films were gravimetrically determined using a precision digital balance (±0.0001 g). The impregnation yields were defined by:
I m p r e g n a t i o n   y i e l d   ( % ) = m f − m i m i × 100
where m i and m f represent the mass of the LLDPE film before and after the impregnation process, respectively.

2.2.4. Gas Chromatography-Mass Spectrometry (GC-MS)

A GC-MS analysis of the rosemary essential oil extract was performed using an Agilent 7890A chromatograph, coupled with an Agilent 5975C mass spectrometer (Agilent Technologies, Santa Clara, CA, USA), operating at 70 eV ionization energy, 0.5 s/scan and the mass range: 35–400, equipped with an HP-5MS capillary column (phenyl methyl siloxane, 30 × 0.25 mm; 0.25 µm film thickness) (Agilent Technologies, USA). The oven temperature increased from 60 to 240 °C at a rate of 3 °C/min. The injector and detector temperatures were set at 240 and 250 °C, respectively. The carrier gas was Helium with a flow rate and split ratios of 0.9 mL/min and 1:50, respectively. The ChemStation software was used to handle mass spectra and chromatograms. To determine the retention indices, the retention time of normal alkanes under the same chromatographic conditions was used according to the van Den Dool and Kratz method [48]. The compounds were detected through a comparison of their mass spectra with the Wiley library or with the published mass spectra.

2.2.5. Antioxidant Activity of Impregnated Films

The hydrogen atom or electron donation ability of rosemary essential oil extract was measured from the bleaching of purple-colored methanol solution of DPPH. This spectrophotometer assay uses stable radical DPPH as a reagent [49]. A total of 5 mL of a solution of 0.004% DPPH in methanol was added to the 50 µL of rosemary essential oil solution at various concentrations. This mixture was maintained in a dark room and, after 30 min, the absorption was measured against a blank at 517 nm with a UV-visible spectrophotometer (Jenway 6800, Keison, Chelmsford, UK).
The DPPH inhibition (I%) was calculated with Equation (4):
I% = (Ablank − Asample/Ablank) × 100
In Equation (4), Ablank is the absorption of the control reaction and Asample indicates the absorption of the rosemary essential oil extract sample. The half maximal inhibitory concentration (IC50) is defined as the potency of a substance for inhibiting a specific biological function. The inhibition percentage against essential oil extract concentration was plotted. Then, the rosemary essential oil extract concentration providing 50% inhibition (IC50) was determined from this plot. The antioxidant activity of the rosemary essential oil was measured three times and the mean IC50 value was reported. In addition, for the determination of the IC50 values of the impregnated LLDPE films, 1000 mg of the different film samples were immersed in 25 mL of methanol for 24 h to extract the essential oil from the polymeric structures and generate a stock solution. After that, five samples with different concentrations of the essential oil extract were prepared using each stock solution. In the next step, each sample was introduced into 4 mL of a 6 × 10−5 M DPPH solution and the absorbance of each sample was measured at 515 nm.

2.3. Physical Characterization of the Impregnated Samples

Using FTIR spectroscopy, the chemical structure of the impregnated bioactive compounds and their intermolecular interactions with the LLDPE structure were studied. The crystalline properties of the neat and the impregnated LLDPE samples were evaluated with a Philips X pert Pro MPD diffractometer (PANalytical, Almelo, The Netherlands) based on Cu-Kα radiation (λ = 0.154 nm) within a 2θ range of 10−80° at room temperature. The thermal properties of the samples were carried out by DSC analysis (DSC 404 F3 Pegasus, Netzsch Co., Hanau, Germany). FESEM (TESCAN, Brno, Czech Republic) was used to investigate the particle size and morphology of the impregnated samples.

2.4. Mechanical Properties

The tensile properties of the LLDPE films were determined by ASTM D 882-18 with the aim to evaluate the effect of the supercritical impregnation process on the mechanical properties of the films. This test method covers the determination of tensile properties of plastics in the form of thin sheeting and films (less than 1.0 mm in thickness). The tensile strength and elongation at break were determined along each test. For each sample, the test was repeated five times and the average was reported as mean value ± standard deviation. Before the analyses, the film samples were kept for 24 h at 23 ± 2   °C and a humidity of 50 ± 10 % and the thickness of each sample was measured using a micrometer A1073/A1073M.

3. Results and Discussion

3.1. Supercritical Fluid Extraction of EO from Rosemary

Table 1 shows the results of extraction yield of rosemary essential oil for each of the six experimental runs carried out using the different values of pressure (15 and 25 MPa), temperature (318 and 338 K), and particle size (0.15 and 0.9 mm). Figure 3 shows a good distribution of the experimental data near the straight line corresponding to the values predicted by the model. The results of ANOVA analysis, considering R2, adjusted R2, predicted R2, and p-values are presented in Table 2. R2, adjusted R2, and predicted R2 values were 0.9846, 0.9731, and 0.9386, respectively. According to the ANOVA results, the three input variables (pressure, temperature, and particle diameter) impacted significatively (p < 0.05) over the rosemary essential oil extraction yield. The F value of 85.46 indicates that the model is meaningful. Furthermore, Prob > F values were less than 0.0500 showing that the terms of the model were significant.
Figure 4 shows the individual effects of temperature, pressure, and particle size on the rosemary essential oil extraction yield. As indicated in Figure 4a, the yield of rosemary extraction was increased by increasing pressure due to the concomitant increase of CO2 density which allowed to increase the solubility of the rosemary essential oil extract in SC-CO2. The positive effect of increasing the essential oil solubility seems to be dominant over the negative effect of reducing the essential oil diffusivity as pressure increases. Similar results were obtained by other researchers [10,15,50,51]. Figure 4b shows the effect of temperature on the extraction yield of rosemary essential oil. As seen in Figure 4b, the yield of extraction was decreased by increasing temperature from 318 to 338 K. In this way, the negative effect of decreasing CO2 density as temperature increases seems to prevail over the negative effect of increasing the essential oil vapor pressure as temperature increases [15,52]. Figure 4c shows the effect of the particle diameter on the extraction yield of rosemary essential oil. Particularly, the essential oil extraction yield was increased as the particle size decreased from 0.9 to 0.15 mm. This behavior has been previously reported by other researchers and related to the increase in the surface area available for the essential oil extraction as particle size decreases [14,53,54,55]. The highest rosemary extraction yield was 2.43% at 25 MPa, 318 K, and particle diameter of 0.15 mm.

3.2. Gas Chromatography Results

The chemical composition of the rosemary essential oil extract obtained by SC-CO2 extraction at the optimal conditions (25 MPa, 318 K, and 0.15 mm) is listed in Table 3. As shown in Table 3, the main components are α-pinene (22.66%), 1,8 cinole (16.2%), camphor (9.33%), bornyl acetate (8.33%), and borneoil (8.09%). α-pinene, bornyl acetate, and camphor are the main responsible of the antimicrobial activity of the rosemary essential oil [56]. The rosemary essential oil is composed mostly by monoterpenes: α-pinene, 1,8-cineole, camphor, bornyl acetate, limonene, camphene, and linalool. The rosemary essential oil composition depended on the essential oil obtaining method, rosemary harvest time, and genotype. Previous studies showed that the oil extracted from rosemary can be divided into two types. In one type, the concentration of α-pinene was higher than that of 1,8-cineole such as this work, [57,58,59], and in the other type, it was the opposite [60,61,62]. The highest percentage of α-pinene has been found in the essential oil of dried rosemary when compared to fresh rosemary [63]. The rosemary essential oil used by Nowak et al. [60] also consisted mostly of monoterpenes such as 1,8-cineole, limonene, and α-pinene. The rosemary essential oil used by Szumny et al. [57] contained α-pinene (33.3%) and 1,8-cineole (12.3%). Presti et al. reported to α-pinene (8.14%) and 1,8-cineole (45.75%) as the main components of the rosemary essential oil [61]. Meanwhile, Pintore et al. reported to α-pinene, 1,8-cineole, and camphor as the main components of a rosemary essential oil extract [59].

3.3. Supercritical Solvent Impregnation of Rosemary Essential Oil in LLDPE Films

The rosemary essential oil impregnation yield in LLDPE films at the different conditions of pressure (12 and 20 MPa), temperature (308 and 328 K), and impregnation time (1 and 5 h) is shown in Table 4. The maximum impregnation yield (1.87 wt. %) was obtained at 12 MPa, 328 K, and 5 h. Goñi et al. studied the effect of pressure and depressurization rate on the impregnation yield. They reported 1–6% of impregnation yield of clove in LLDPE [34]. The maximum clove essential oil loading in LLDPE with different operating conditions was 40.2 mg/g by Medeiros et al. [27]. Goñi et al. investigated the effect of pressure, temperature, time and depressurization rate in the SC-CO2-assisted impregnation of terpene ketones in LDPE/sepiolite nanocomposite films, reporting the highest impregnation (9.73 wt.%) at 9 MPa, 45 °C, 4 h, and 0.5 MPa/min [38]. Figure 5 shows the results for the rosemary essential oil extract impregnation predicted by the model versus the experimental values. Meanwhile, Table 5 presents the ANOVA results for the model fitted to the SSI process. Particularly, the values of R2, Adjusted R2 and Predicted R2 were 0.9782, 0.9618 and 0.9127, respectively, which shows that the experimental data and predicted values are in good agreement. According to its R2 coefficient, it can be said that an acceptable model has been achieved to predict the impregnation data. ANOVA was also used to investigate the importance of each independent variable (pressure, temperature and impregnation time) on the response (essential oil impregnation yield) through the determination of the p-values. By checking the p-values for pressure, temperature and time, it can be concluded that all of them have significant effects over the rosemary impregnation yield. Using the experimental design, an equation was obtained to calculate the impregnation yield (y) based on the parameters of temperature ( X 1 ), pressure ( X 2 ) and impregnation time ( X 3 ), as shown below:
y = 1.09 + 0.24 X 1 − 0.089 X 2 + 0.4 X 3

3.4. Effect of the Operational Conditions on the Impregnation of Rosemary Essential Oil in LLDPE Films

As shown in Figure 6a, increasing temperature from 308 to 328 K, at constant pressure (12 MPa) and impregnation time (1 h), increased the rosemary essential oil impregnation yield from 0.59 to 0.89 wt.%. By examining the results of impregnation yield in Table 4, the same behavior was seen at a pressure of 12 MPa for an impregnation time of 5 h, and for a pressure of 15 MPa for the two impregnation times (1 and 5 h). This trend can be explained in terms of the increase of the diffusion rate of carbon dioxide and rosemary essential oil in the polymeric matrix as temperature rises [27,64,65].
Figure 6b shows the positive effect of increasing the impregnation time on the impregnation yield of rosemary essential oil in LLDPE films at constant pressure and temperature due to the increase of the swelling and flexibility of the polymer by increasing the impregnation time. A comparable behavior has been seen for the impregnation of styrene in LDPE films [66], thymoquinone and R-(+)- pulegone in LDPE/sepiolite films [38], clove essential oil in LLDPE films [27], an active mixture of thymoquinone and R-(+)-pulegone in LDPE films [36], and for the impregnation of mango polyphenols in a multilayer PET/PP food-grade film [39]. This behavior can be related to the increase of swelling and flexibility of the polymer by increasing the impregnation time, which improves the diffusion of CO2 and the bioactive molecules through the polymeric structure.
Figure 6c shows that increasing pressure from 12 to 20 MPa, at constant temperature (308 K) and impregnation time (1 h), leads to a decrease on the impregnation yield of rosemary essential oil. Goñi et al. [36] reported a decrease on the impregnation yield of terpenic ketones when pressure was increased from 10 to 15 MPa at a constant temperature of 45 °C. Medeiros et al. [27], Almeida et al. [67], and Rojas et al. [68] reported the same trend for the impregnation of clove essential oil in LLDPE films, oregano essential oil incorporation in starch, and 2-nonanone incorporation in LLDPE films, respectively. The carbon dioxide phase can be unsaturated or saturated with the active substances during the impregnation process. For unsaturated supercritical solutions, the increase of pressure dilutes the active substances in the carbon dioxide phase, decreasing the concentration gradient of the active substances between the carbon dioxide phase and the polymeric matrix.

3.5. Characterization of the Rosemary Essential Oil and Impregnated LLDPE Films

3.5.1. Fourier Transform Infrared (FTIR) Spectroscopy

Figure 7 shows the FTIR spectra of the neat LLDPE, pure rosemary essential oil extract, and the impregnated LLDPE sample. This analysis was used to determine and identify the interaction between the polymer and the bioactive components of the rosemary essential oil. The spectrum of the neat LLDPE shows the characteristic C-H stretching bands with two peaks at 2915 cm−1 and 2847 cm−1, and the peaks at 1465.57 and 718.67 cm−1 ascribed to the stretching of C-H and C-H out of plane bending bands [69]. Meanwhile, pure rosemary presented the following key bands at 3409.62, 2928.13, 2869.12, 1725.23, 1680.47, 1453.31, 1385.13, and 1027.39 cm−1. These bands were attributed to the hydroxyl group (OH), Aliphatic saturated hydrocarbon chain (CH3, CH2), Aldehyde group (-CHO), Carbonyl group (C = O), Aliphatic unsaturated hydrocarbon chains (-C = C-), C-O, CH3(CO), and (C-O-C), respectively [60,70,71]. The impregnated LLDPE films presented the previously mentioned characteristic peaks of the neat LLDPE as well as some of the representative bands of the rosemary essential oil extract such as 2915, 2847.9, 1462.79 and 718.67 cm−1. Considering that there is no significant displacement of the peaks from impregnated LLDPE films compared to those from neat LLDPE and pure rosemary essential oil, it can be said that there was no chemical interaction between LLDPE and the rosemary essential oil components.

3.5.2. Thermal Properties

The impregnated LLDPE film at the optimal processing conditions was analyzed by DSC and compared to the neat LLDPE film to evaluate the impact of the supercritical impregnation process over the thermal properties of the films. Figure 8 shows the thermograms of the neat and impregnated LLDPE. The impregnation process caused no important change on the melting temperature (Tm), the melting temperature of neat LLDPE and impregnated LLDPE were 120.1 and 120.4 °C, respectively. However, the melting enthalpy of the film was decreased by the impregnation with rosemary essential oil from 57.81 to 25.78 J/g. This result could be explained with the plasticizing effect on the LLDPE structure caused by the incorporation of the rosemary essential oil. The same behavior has been observed for different systems such as LLDPE-thymol, LDPE-carvacrol, PP-thymol, and PP- carvacrol [72,73,74].

3.5.3. X-ray Diffraction

Figure 9 shows the X-ray diffraction patterns of the neat LLDPE, and impregnated LLDPE at the optimal processing conditions. The single peaks of the neat LLDPE film were observed at 21.46°, 23.8°, and 36.22°. These characteristic signals are in agreement with the XRD pattern of LLDPE reported by Oliani et al. [75]. The XRD pattern of the impregnated LLDPE showed the same signals than the neat LLDPE, indicating no changes in the crystalline structure of LLDPE due to the incorporation of the rosemary essential oil. This result is consistent with the findings of DSC.

3.5.4. Scanning Electron Microscopy (SEM)

The SEM analysis was used to investigate the morphology of LLDPE before and after the impregnation with the rosemary essential oil. SEM images of the neat and impregnated LLDPE are shown in Figure 10a,b. SEM images showed that the essential oil of rosemary was deposited on the LLDPE film, and its distribution was homogeneous.

3.6. Antioxidant Activity of Impregnated Films

In this work, (1,1-diphenl-2-picryhdrazl) DDPH inhibition assays and calculation of IC50 values were carried out to evaluate the antioxidant activity of the rosemary essential oil and the impregnated LLDPE films at the different processing conditions. Table 6 shows the determined IC50 values for each sample, which represents the concentration of essential oil required to obtain a 50% inhibition of DPPH radical. IC50 values were estimated through linear regression analyses from the obtained radical scavenger capacity (RSC) values and were expressed in μL of essential oil per mL of solution. In this work, the IC50 value for the rosemary essential oil was 64.04 μL/mL, demonstrating that the essential oil had a strong radical scavenging activity. The obtained results are in good agreement with the reported by other researchers. Raskovic et al. and Kadri et al. reported IC50 values of 77.6 and 69.09 μL/mL, respectively, for rosemary essential oil extracts obtained using hydrodistillation [76,77,78]. Many authors relate the antioxidant properties of rosemary essential oil extracts to their volatile constituents [79,80,81]. Del Baño et al. [82] studied the antioxidant properties and flavonoid compounds present in the root and aerial parts of rosemary plants. In addition, Inatani et al. [83] and other authors [84,85,86] reported that generally the antioxidant effectiveness of natural extracts is higher than those obtained for synthetic antioxidants such as tert-butyl-4-hydroxyanisol (BHA) and tert-butyl-4-hdroxtoluene (BHT). The IC50 values for all the impregnated LLDPE samples were close to the IC50 value of the extract showing that the impregnated films have a significant antioxidant activity. In addition, runs 1 and 4 showed the highest antioxidant activity while the neat LLDPE film (control) did not show any antioxidant activity. In the literature, many authors have used LLDPE films for the incorporation of plant extracts, and in all cases, the LLDPE polymer was able to exert antioxidant properties [34,87].

3.7. Mechanical Properties

Tensile properties are very important in the selection and application of polymeric materials. Table 7 shows the mechanical properties (yield strength (MPa), tensile strength (MPa), and elongation at break (%)) of the neat LLDPE film and the LLDPE film impregnated at the optimal processing conditions. The determination of p-values was carried out to evaluate significant changes of these properties after the supercritical impregnation process. The calculation of p-values for both yield and tensile strength showed that the changes of these two parameters after supercritical processing were not significant. Meanwhile, the elongation at break suffered significant changes after the supercritical processing. The same trend was seen in researches made by Goñi et al. [34] and Medeiros et al. [27,65]. From these results, it can be observed that both the yield strength and tensile strength remain almost unalterable after the supercritical impregnation of the rosemary essential oil. These results agree with those previously reported for LLDPE. These researches [42,43,44] show that the thermal and mechanical properties of LLDPE are not modified by the exposure to supercritical carbon dioxide at constant pressure. It has been noticed that the plasticizing effect of supercritical carbon dioxide on a polymer could be reversible once the exposure is terminated [45]. Meanwhile, a reduction in the elongation at break was obtained due to the addition of the rosemary essential oil. By adding rosemary essential oil, the intermolecular forces between the polymer chains decrease due to the plasticizing effect of the rosemary essential oil. Figure 11 shows stress-strain curves of neat LLDPE and LLDPE impregnated with rosemary essential oil.

4. Conclusions

The supercritical fluid extraction of essential oil from rosemary was studied. The main components of the essential oil extract determined by GC mass spectroscopy were α-pinene (22.66%), 1,8 cinole (16.2%), camphor (9.33%), bornyl acetate (8.33%), and borneoil (8.09%). The yield of rosemary extraction was increased by increasing pressure and decreasing temperature and particle size. The optimal conditions for the rosemary essential oil extraction were 25 MPa, 318 K, and a particle size of 0.15 mm. The effects of pressure, temperature, and time on the impregnation yield of rosemary essential oil in LLDPE were investigated. The yield of impregnation was increased by increasing temperature and time and decreasing pressure. The optimal conditions for the impregnation of LLDPE were 20 MPa, 328 K, and 5 h. Physical properties of the LLDPE films impregnated with rosemary essential oil were analyzed by FTIR, DSC, SEM, and XRD. SEM images showed that the rosemary essential oil was homogeneously deposited on the surface of the LLDPE film. Meanwhile, XRD results showed that the rosemary essential oil addition did not change the crystallographic properties of the impregnated LLDPE in comparison with the neat LLDPE. This result agrees with the DSC findings. The DDPH inhibition assay and calculation of IC50 were applied to evaluate the antioxidant activity of extracted rosemary and impregnated LLDPE films. The observed IC50 values for all samples showed that the impregnated films have a significant antioxidant activity.

Author Contributions

Conceptualization, S.A.S. and A.R.; methodology, S.A.S., N.E., N.S.A., A.R., A.B. and M.J.G.; validation, S.A.S., A.R., N.S.A. and N.E.; writing—original draft preparation, N.E., N.S.A., S.A.S., A.R. and A.B.; writing—review and editing, N.E., S.A.S., A.R., A.B. and M.J.G.; visualization, S.A.S. and N.E.; supervision, S.A.S. and M.J.G.; project administration, S.A.S.; funding acquisition, A.R. and M.J.G. All authors have read and agreed to the published version of the manuscript.

Funding

M.J.G. and A.R. thanks the support of Agencia Nacional de Investigación y Desarrollo through the Fondecyt regular project N°1201301 and to the “Programa de Financiamiento Basal para Centros Científicos y Tecnológicos de Excelencia” (Project AFB180001).

Acknowledgments

The authors gratefully acknowledge the support provided by S. A. Sajadian.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Schematic diagram of the supercritical CO2 extraction set-up used for rosemary essential oil extraction. E-1: CO2 cylinder, E-2: Needle valve, E-3: Filter, E-4: Refrigerator unit, E-5: High-pressure pump, E-6: Compressor, E-7: Oven, E-8: Automation system, E-9: Extraction cell, E-10: Back pressure, E-11: Micrometering valve, E-12: sampler.
Figure 1. Schematic diagram of the supercritical CO2 extraction set-up used for rosemary essential oil extraction. E-1: CO2 cylinder, E-2: Needle valve, E-3: Filter, E-4: Refrigerator unit, E-5: High-pressure pump, E-6: Compressor, E-7: Oven, E-8: Automation system, E-9: Extraction cell, E-10: Back pressure, E-11: Micrometering valve, E-12: sampler.
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Figure 2. Schematic representation of the SC-CO2-assisted impregnation apparatus. E-1: CO2 cylinder, E-2: Needle valve, E-3: Filter, E-4: Refrigerator unit, E-5: High-pressure pump, E-6: Compressor, E-7: Oven, E-8: Magnetic stirrer, E-9: Impregnation cell, E-10: Pressure gauge, E-11: Micrometering valve, E-12: Back pressure, E-13: Automation system.
Figure 2. Schematic representation of the SC-CO2-assisted impregnation apparatus. E-1: CO2 cylinder, E-2: Needle valve, E-3: Filter, E-4: Refrigerator unit, E-5: High-pressure pump, E-6: Compressor, E-7: Oven, E-8: Magnetic stirrer, E-9: Impregnation cell, E-10: Pressure gauge, E-11: Micrometering valve, E-12: Back pressure, E-13: Automation system.
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Figure 3. Diagnostic plots (predicted vs. actual) of model adequacy for the extraction.
Figure 3. Diagnostic plots (predicted vs. actual) of model adequacy for the extraction.
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Figure 4. The effect of (a) pressure at a constant temperature of 318 K and particle diameter 0.15 mm (b) temperature at a constant pressure of 15 MPa and particle diameter 0.15 mm, and (c) Particle diameter at a constant pressure of 15 MPa and temperature of 318 K, on the yield of rosemary essential oil extraction.
Figure 4. The effect of (a) pressure at a constant temperature of 318 K and particle diameter 0.15 mm (b) temperature at a constant pressure of 15 MPa and particle diameter 0.15 mm, and (c) Particle diameter at a constant pressure of 15 MPa and temperature of 318 K, on the yield of rosemary essential oil extraction.
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Figure 5. Diagnostic plots (predicted vs. actual) of model adequacy for the extraction.
Figure 5. Diagnostic plots (predicted vs. actual) of model adequacy for the extraction.
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Figure 6. The effect of (a) temperature at a constant pressure of 12 MPa and impregnation time of 1 h (b) time at a constant pressure of 12 MPa and temperature of 308 K, and (c) pressure at a constant temperature of 308 K and time of 1 h, on the loading of rosemary essential oil in LLDPE films.
Figure 6. The effect of (a) temperature at a constant pressure of 12 MPa and impregnation time of 1 h (b) time at a constant pressure of 12 MPa and temperature of 308 K, and (c) pressure at a constant temperature of 308 K and time of 1 h, on the loading of rosemary essential oil in LLDPE films.
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Figure 7. FTIR spectrum of the neat LLDPE, extracted oil from rosemary, and impregnated LLDPE film.
Figure 7. FTIR spectrum of the neat LLDPE, extracted oil from rosemary, and impregnated LLDPE film.
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Figure 8. DSC spectra of the neat and impregnated LLDPE films.
Figure 8. DSC spectra of the neat and impregnated LLDPE films.
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Figure 9. XRD patterns of the neat and impregnated LLDPE films.
Figure 9. XRD patterns of the neat and impregnated LLDPE films.
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Figure 10. SEM images of (a) neat LLDPE, and (b) LLDPE impregnated with rosemary essential oil.
Figure 10. SEM images of (a) neat LLDPE, and (b) LLDPE impregnated with rosemary essential oil.
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Figure 11. Stress-strain curves of neat LLDPE and LLDPE impregnated with rosemary essential oil.
Figure 11. Stress-strain curves of neat LLDPE and LLDPE impregnated with rosemary essential oil.
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Table
Table 1. Yield of extraction of rosemary essential oil by supercritical fluid extraction.
Table 1. Yield of extraction of rosemary essential oil by supercritical fluid extraction.
RunPressure (MPa)Temperature (K)Particle Diameter (mm)Extraction Yield (%)
1153180.151.87 ± 0.06
5153380.151.12 ± 0.04
4153180.901.19 ± 0.05
3153380.900.73 ± 0.03
2253180.152.43 ± 0.11
8253380.151.97 ± 0.10
7253180.901.89 ± 0.09
6253380.901.45 ± 0.05
Table
Table 2. Analysis of variance (ANOVA) for the model fitted to the SC-CO2 extraction process of rosemary essential oil.
Table 2. Analysis of variance (ANOVA) for the model fitted to the SC-CO2 extraction process of rosemary essential oil.
SourceSum of SquaresDegree of FreedomMean SquareF Valuep-Value Prob > F
Model2.1230.7185.460.0004
A-P1.0011.00120.800.0004
B-T0.5610.5667.150.0012
C-Dp0.5710.5768.430.0012
Residual0.03340.0082
Cor Total2.167
R²Adjusted R²Predicted R²
0.98460.97310.9386
Table
Table 3. Chemical composition of rosemary essential oil by GC/MS.
Table 3. Chemical composition of rosemary essential oil by GC/MS.
No.Compound%Retention Index
1α-Pinene22.66941
2Camphene6.52953
3Sabinene0.25969
4β-Pinene5.17979
5β-Myrcene0.49987
6α-phellandrene0.741007
7α-Terpinene01016
8p-cymene1.471021
9Limonene4.81030
101, 8-Cineole16.121033
11trance-Ocimenet1040
12α-Terpinenet1057
13α-Terpinolene0.491080
14Linalool2.71094
15Chrysthenonet1120
16Camphor9.331136
17Verbenolt1138
18Borneoil8.091162
19Terpine-4-ol0.491179
20α-Terpineol2.71184
21Verbenonet1195
22cis-Myrtanol0.11244
23Trans-Myrtanol0.11251
24Bornyl acetate8.331281
25Methyl eugenol0.611401
26α-Caryophyllene0.841408
27β-Caryophyllene5.051422
28α-Humulene0.111443
29trance-beta-Farnesene0.11457
Table
Table 4. The effect of impregnation parameters on impregnation yields of rosemary essential oil in LLDPE films.
Table 4. The effect of impregnation parameters on impregnation yields of rosemary essential oil in LLDPE films.
RunPressure (P),
X1 (MPa)		Temperature (T),
X2 (K)		Impregnation Time,
X3 (h)		Actual Impregnation Yield
(wt.%)
12030851.05 ± 0.04
22032810.79 ± 0.03
32030810.41 ± 0.02
42032851.67 ± 0.09
51230810.59 ± 0.02
61232810.89 ± 0.04
71230851.28 ± 0.08
81232851.87 ± 0.09
Table
Table 5. Analysis of variance (ANOVA) for the model fitted to the SSI process.
Table 5. Analysis of variance (ANOVA) for the model fitted to the SSI process.
SourceSum of SquaresD.F. (Degree of Freedom)Mean SquareF-Valuep-Value
Model1.7830.5959.760.0009
A-T0.4510.4544.930.0026
B-P0.06310.0636.340.0655
C-Time1.2711.271280.0003
Residual0.0440.009938
Cor Total1.827
R²Adjusted R²Predicted R²
0.97820.96180.9127
Table
Table 6. IC50 values using the DPPH method for rosemary essential oil and the impregnated LLDPE films. The results are presented as means ± SD (standard deviation) for triplicate assays.
Table 6. IC50 values using the DPPH method for rosemary essential oil and the impregnated LLDPE films. The results are presented as means ± SD (standard deviation) for triplicate assays.
SampleIC50
Rosemary essential oil 76.44 ± 2.87
Neat LLDPE0.00
Impregnated LLDPE
Run 169.55 ± 1.80
Run 258.68 ± 1.24
Run 360.50 ± 1.29
Run 469.82 ± 1.72
Run 560.69 ± 1.92
Run 675.07 ± 2.34
Run 775.33 ± 2.65
Run 875.40 ± 2.56
Table
Table 7. Mechanical properties of the neat LLDPE film, and impregnated LLDPE film.
Table 7. Mechanical properties of the neat LLDPE film, and impregnated LLDPE film.
Yield Strength (MPa)Tensile Strength (MPa)Elongation at Break (%)
Neat LLDPE14.9 ± 0.62 a19.5 ± 3.21 a421 ±   32.6 a
Impregnated LLDPE film 14.7 ±   0.3 a18.5 ±   2.3 a375 ±   31.4 b
Lower case letters a,b indicate significant statistical difference.
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MDPI and ACS Style

Esfandiari, N.; Rojas, A.; Babhadiashar, A.; Galotto, M.J.; Saadati Ardestani, N.; Sajadian, S.A. Effect of the Processing Conditions on the Supercritical Extraction and Impregnation of Rosemary Essential Oil in Linear Low-Density Polyethylene Films. Processes 2023, 11, 11. https://doi.org/10.3390/pr11010011

AMA Style

Esfandiari N, Rojas A, Babhadiashar A, Galotto MJ, Saadati Ardestani N, Sajadian SA. Effect of the Processing Conditions on the Supercritical Extraction and Impregnation of Rosemary Essential Oil in Linear Low-Density Polyethylene Films. Processes. 2023; 11(1):11. https://doi.org/10.3390/pr11010011

Chicago/Turabian Style

Esfandiari, Nadia, Adrián Rojas, Arman Babhadiashar, María José Galotto, Nedasadat Saadati Ardestani, and Seyed Ali Sajadian. 2023. "Effect of the Processing Conditions on the Supercritical Extraction and Impregnation of Rosemary Essential Oil in Linear Low-Density Polyethylene Films" Processes 11, no. 1: 11. https://doi.org/10.3390/pr11010011

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