Next Article in Journal
Polysaccharides Are Effective Inhibitors of Natural Gas Hydrate Formation
Next Article in Special Issue
Mechanical, Thermal, and Fire Retardant Properties of Rice Husk Biochar Reinforced Recycled High-Density Polyethylene Composite Material
Previous Article in Journal
Pressure Drop Dynamics during Filtration of Mixture Aerosol Containing Water, Oil, and Soot Particles on Nonwoven Filters
Previous Article in Special Issue
Effect of Varying Curing Conditions on the Strength of Biopolymer Modified Sand
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Polymers
Volume 15
Issue 7
10.3390/polym15071788
polymers-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Study of the Plasticization Effect of 1-Ethyl-3-methylimidazolium Acetate in TPS/PVA Biodegradable Blends Produced by Melt-Mixing

by
Jennifer M. Castro
1,2,*,
Mercedes G. Montalbán
3,
Daniel Domene-López
2,
Ignacio Martín-Gullón
1,2 and
Juan C. García-Quesada
1,2,*
1
Chemical Engineering Department, University of Alicante, Apartado 99, 03080 Alicante, Spain
2
Institute of Chemical Process Engineering, University of Alicante, Apartado 99, 03080 Alicante, Spain
3
Chemical Engineering Department, Faculty of Chemistry, Regional Campus of International Excellence “Campus Mare Nostrum”, University of Murcia, 30071 Murcia, Spain
*
Authors to whom correspondence should be addressed.
Polymers 2023, 15(7), 1788; https://doi.org/10.3390/polym15071788
Submission received: 3 February 2023 / Revised: 27 March 2023 / Accepted: 2 April 2023 / Published: 4 April 2023
(This article belongs to the Special Issue Natural-Based Biodegradable Polymeric Materials)
Browse Figures
Versions Notes

Abstract

:
The first step towards the production and marketing of bioplastics based on renewable and sustainable materials is to know their behavior at a semi-industrial scale. For this reason, in this work, the properties of thermoplastic starch (TPS)/polyvinyl alcohol (PVA) films plasticized by a green solvent, as the 1-ethyl-3-methylimidazolium acetate ([Emim+][Ac−]) ionic liquid, produced by melt-mixing were studied. These blends were prepared with a different content of [Emim+][Ac−] (27.5–42.5 %wt.) as a unique plasticizer. According to the results, this ionic liquid is an excellent plasticizer due to the transformation of the crystalline structure of the starch to an amorphous state, the increase in flexibility, and the drop in Tg, as the [Emim+][Ac−] amount increases. These findings show that the properties of these biomaterials could be modified in the function of [Emim+][Ac−] content in the formulations of TPS, depending on their final use, thus becoming a functional alternative to conventional polymers.

Graphical Abstract

1. Introduction

Ionic liquids (ILs) are gaining interest in the field of plastic production because they have the potential to act as plasticizers in polymer matrices [1] due to properties such as high thermal and chemical stability, non-flammability, low vapor pressure, tunable solubility, and good hydraulic properties [2,3,4,5,6,7]. In addition, they can be found as liquids in a wide range of temperatures because they are organic salts with melting points below 100 °C, formed by a bulky inorganic cation (with a low degree of symmetry) and as an anion resulting in a little compact structure with large and non-uniform ions [8,9]. Some authors have previously reported the use of ILs as plasticizers of different conventional polymers. Scott et al. [10] studied the properties of poly(methyl methacrylate) (PMMA) plasticized by the IL 1-butyl-3-methylimidazolium hexafluorophosphate and concluded that the material was comparable with those that contain conventional plasticizers, noting that the low volatile IL created a more flexible polymer over a long lifetime which prevented the material from brittleness. Similar conclusions were obtained by Rahman et al. [9], who reported that the addition of a variety of ILs to different PVC formulations improved mechanical properties (increasing the flexibility) at the same time that films had a longer life with a decrease of plasticizer migration.
In industry, ILs are commonly used as catalysts for the production and storage [11] of energy, or as an extracting agent for organic compounds [12]. ILs can be considered “green” solvents because they are environmentally friendly, with low explosion risk, and with easily recovered and recycled procedures [13,14]. Therefore, ILs can play an interesting role in the new environmental context, where research oriented toward the development of new materials from renewable and sustainable sources is experiencing significant growth. In this sense, the plastic industry is one of the most affected sectors and exchanging conventional fossil-based polymers with renewable polymers is a solution for some up-to-date problems due to the enormous consumption of “limited” resources, the problems related to plastic waste mismanagement [15,16,17,18], and their harmful effects on the environment [19,20,21].
In the past, some researchers have investigated the effect of ILs as a solvent in the research of biodegradable and renewable materials. However, recently, ILs have been used to study their plasticizer effect in biodegradable materials [22,23,24,25,26,27,28,29,30,31], with starch being one of the most promising materials due to its abundance, low cost, and biodegradability [15]. Starch is a biopolymer composed of two polysaccharides: amylose and amylopectin [32,33]; and the presence of plasticizers is needed in order for it to be transformed into thermoplastic starch (TPS) [34] by a gelatinization process [35]. There are a number of studies on the use of ILs as plasticizers in biodegradable starch blends. Wilpiszewska et al. [8] concluded that the presence of ILs on TPS could decrease the glass transition temperature more than when using glycerol, suggesting the better plasticization efficiency of ILs in comparison to polyols which are conventional plasticizers for these biomaterials [36,37,38,39]. These conclusions were supported by Xie et al. [40], Domene-López et al. [41], and Abera et al. [42], who studied the behavior of films prepared with maize, potato, and anchote starch, respectively, using 1-ethyl-3-methylimidazolium acetate as a plasticizer by a solution casting method in the presence of water.
The use of 1-ethyl-3-methylimidazolium acetate ([Emim+][Ac−]), among other ILs, as a TPS plasticizer is interesting because it has a more biodegradable character and is less toxic than other ILs due to its carboxylic anion [43,44]. Furthermore, it is capable of forming chemical bonds with CO2 [45]. Chen et al. [46] studied the process of atmospheric water sorption and CO2 capture in a system of [Emim+][Ac−] and biopolymers (cellulose, chitin, and chitosan). Their findings indicate that these biomaterials could be employed for food packaging and storage applications. In our research group, we have studied the prospective use of [Emim+][Ac−] with different botanical sources of starch, and have concluded that the starch characteristics are crucial in order to obtain good blend properties and the potato blend values were especially very promising [47]. Moreover, the incorporation of multi-walled carbon nanotubes (MWCNT) to the starch blends plasticized by [Emim+][Ac−] showed great electrical conductivity, proving that these types of biomaterials could be used in a wide range of applications, such as lithium batteries, fuel cells, or dye-sensitized solar cells [26,41].
The use of the casting method is common in laboratory-scale TPS research because this allows for the study of the starch films plasticized under ideal gelatinization conditions, and promoted by an excess of plasticizer. Nevertheless, for the purposes of industrial research, these materials should be processed in semi-industrial scale equipment, considering real conditions, and without an excess of plasticizer. For example, Sankri et al. [25] prepared TPS from maize starch plasticized by water, glycerol, and 1-butyl-3-methylimidazolium chloride using melt processing and they confirmed that the IL had strong plasticized effects through the mechanical property values achieved. Decaen et al. [48] studied the rheology properties of TPS from maize starch plasticized by three ILs in the presence of water by melt rheology at 120 °C. They concluded that the [Emim+][Ac−] is a promising plasticizer due to the lowest shear viscosity and limited macromolecular degradation.
TPS is usually formulated with water since it is considered the best starch plasticizer, but its use has several limitations such as the evaporation of the water during the process (temperatures above 100 °C are needed in the industrial process), and the interaction between the water and the ILs acetate anions can limit the plasticization effect of the IL studied [49,50]. TPS pure films are brittle due to the strong chain interactions of the starch polymer via hydrogen bonding which increases the cohesion forces of the matrix [51]. Therefore, the use of other adjuvant polymers such as polyvinyl alcohol (PVA) [52] is a good option to confer resistance to starch-based materials. PVA is currently employed in the food, medical, and hygiene sectors, among others [15]. PVA is a synthetic polymer with a high degree of biocompatibility, solubility in water, chemical resistance, biodegradability, and other notable physical properties by its hydroxyl groups, which promotes the formation of hydrogen bonds [53] and, in addition, this thermoplastic has remarkably superior features as an oxygen barrier, compared with the other biopolymers [54].
Thus, the aim of this work is the study of the plasticization effect of [Emim+][Ac−] in thermoplastic starch/PVA blends by melt-mixing using semi-industrial scale equipment. Samples have been prepared without water to prevent interaction with the ILs. Mechanical and hydration properties, migration degree of plasticizer, dynamic mechanical analysis, morphology, and XRD and ATR-FTIR spectra of the TPS films are discussed to determine the potential capability of these materials to replace synthetic and non-biodegradable polymers. To the best of our knowledge, no studies can be found in the literature about starch/PVA mixtures plasticized by a single plasticizer consisting in IL, without an additional water supply, and produced by melt-mixing.

2. Materials and Methods

2.1. Materials

The potato starch was provided by Across Organics (Geel, Belgium) and characterized in our previous works [47,55]. PVA hydrolyzed (Mw: 89,000–98,000 Da) was purchased from Sigma-Aldrich (Madrid, Spain). The ionic liquid 1-ethyl-3-methylimidazolium acetate ([Emim+][Ac−]) (>95% purity) was supplied by loLiTec-Ionic Liquids Technologies GmbH (Heilbronn, Germany). Zinc stearate, used as a lubricant, was also provided by Sigma-Aldrich (Madrid, Spain). All chemicals were used without further purification.

2.2. Preparation of the Starch/PVA Films Using the Ionic Liquid as Plasticized

Starch films were prepared by the method of starch melt-compounding previously described by Domene-Lopéz et al. [15], with some modifications. The processing was carried out with the HAAKE TM PolyLab TM QC Modular Torque Rheometer (ThermoFisher Scientific, Waltham, MA, USA). The samples were processed at 130 °C for 14 min; the first 8 min at 50 rpm at the rest of the time at 100 rpm. The blend obtained was then hot pressed at 160 °C for 15 min at a pressure of 10 tons obtaining a 1 mm thick sheet. Samples were stored in a controlled atmosphere of relative humidity of 50% for 48 h prior to their further characterization, making sure to avoid the TPS properties being changed by the humidity effect [56].
Starch, PVA, and ionic liquid were manually premixed at room temperature for 3 min and then introduced in the HAAKE rheometer. The weight ratio between the potato starch and PVA in the sample was 1:1, adding different amounts of ionic liquid as plasticizer: 27.5, 30, 32.5, 37.5, 40, and 42.5 %wt. of ionic liquid; the studied formulations were labeled as IL_27.5, IL_30, IL_32.5, IL_37.5, IL_40, and IL_42.5, respectively, and 0.5 %wt. of zinc stearate was also added to all blends.

2.3. Characterization of the Films

2.3.1. Scanning Electron Microscopy (SEM) Analysis

SEM images were obtained with a Hitachi Scanning Electron Microscope (Hitachi S3000N, Tokyo, Japan) using an accelerating voltage of 10 kV. To observe the microstructure and morphology, the samples were cryo-fractured by immersion in liquid nitrogen and cooled with gold.

2.3.2. Mechanical Properties

Mechanical properties of the films were determined with an Instron 3344 Universal Test Instrument (Norwood, MA, USA) equipped with a 2000 N load cell and operated at 25 mm/min following ASTM D882-12(2012) [57] standard recommendations. Each film was cut into dumbbell-shaped specimens. The tensile properties studied were Young’s Modulus (MPa), tensile strength at break (MPa), and elongation at break (%), which were calculated using the average thickness of the specimen and at least eight specimens were tested.

2.3.3. Hydration Properties

The hydration properties were determined following the method previously described in the literature [15,41,47,55,58]. The films were cut into 1 × 1 cm² specimens. On the one hand, the water content was determined by measuring the lost weight after drying the samples in an oven at 110 °C for 5 h. The moisture content was calculated using Equation (1) and was expressed as a percentage (grams of water in 100 g of sample):
H % = m 0 − m 1 m 0 × 100
where m0 is the initial mass and m1 is the mass after drying.
On the other hand, the solubility in the samples of water was determined by placing the films individually in 10 mL tubes filled with 9 mL of distilled water, which were capped and stored at 25 °C for 24 h. After that, the samples were taken out and dried again at 110 °C for 5 h. Solubility in water was calculated using Equation (2):
S o l u b i l i t y   % = m 0 − m f m 0 × 100
where mf is the final dry mass.
The water content and solubility values were taken as the average of at least five repetitions.

2.3.4. Migration Degree

The degree of migration of plasticizer to the surface of films is determined as the weight loss of the sample after the migration test, which was carried out following a modified procedure based on methods described by Marcilla et al. [59] and Rahman et al. [9]. The films were cut into small circles with dimensions of 7 mm in diameter and 1 mm thickness, which were placed between two Petri dishes with absorbent papers and kept under a pressure of 16.5 kPa in an oven at 60 °C for 1 week. The values of plasticizer migration were obtained by taking out the samples at different times (1, 2, 5, and 7 days), and then calculating the weight loss using Equation (3):
M i g r a t i o n   D e g r e e   % = m 0 − m f m 0 × 100
where m0 and mf are the initial and final weights of the sample.
The results of the migration of plasticized were obtained from an average of at least three repetitions.

2.3.5. Attenuated Total Reflection-Fourier Transform Infrared (ATR-FTIR) Spectroscopy

A Bruker Spectrometer (IFS 66/S model, Ettlingen, Germany) with an ATR accessory was used to obtain the ATR-FTIR spectra of films between 400 and 4000 cm−1. ATR-FTIR spectra were processed using the FITYK software (1.3.1 version) and the ratio of band intensities at 995 and 1022 cm−1 was determined to study the film’s molecular rearrangement.

2.3.6. X-ray Diffraction (XRD) Studies

A Bruker diffractometer (D8-Advance model, Ettlingen, Germany) was used to obtain the diffractograms of the films. This equipment has a KRISTALLOFLEX K 76080F X-Ray generator (power = 3000 W, voltage = 20–60 kV, intensity = 5–80 mA), that has an X-Ray tube with a copper anode. The dimensions of specimens were 1 × 1 cm² and the equipment was operated at 40 kV and 40 mA with 2θ varying from 4 to 50° with a step size of 0.05°.

2.3.7. Dynamic Mechanical Analysis (DMA)

The DMA analysis was carried out in a DMA 1 Instrument (Mettler-Toledo, Barcelona, Spain). The dimensions of the samples used for this analysis were 8.5 × 25 × 1 mm and the temperature range was −100 °C to 60 °C at a rate of 3 °C/min and a constant frequency of (1 Hz).

3. Results and Discussion

The visual appearance of the films is shown in Figure 1. As can be seen, all are homogeneous and transparent. However, the higher the [Emim+][Ac−] percentage, the higher the transparency of the samples. In addition, they show a yellowish color attributed to the color of the [Emim+][Ac−].

3.1. Scanning Electron Microscopy (SEM) Analysis

SEM images of the surface of the samples are shown in Figure 2. These provide useful information about the homogeneity, morphology, etc. of the films [55], features that are closely related to the final mechanical properties of the material [34].
SEM micrographs showed a heterogeneous matrix with some cracks and some readily visible starch granules that had not been dissolved during mixing and hot pressing at IL concentrations of up to 32.5%. At higher concentrations, starch is clearly destructured, dissolved, and incorporated into a continuous phase that exhibits a smooth surface in SEM images, especially in samples with 40 and 42.5% of IL.

3.2. Mechanical Properties

The mechanical properties of starch/PVA with IL as a plasticizer are shown in Figure 3. From these properties, it is possible to know the potential use of the films in future applications [47,60].
According to Figure 3, the values are heavily dependent on the content of IL; the results of Young’s modulus vary from 56.1 MPa to 0.911 MPa, and the maximum tensile strength from 9.17 MPa to 1.56 MPa. In both cases, the maximum and minimum values correspond to the IL_27.5 and IL_42.5 samples, respectively. Elongation at break ranged from 735% to 304% at IL concentrations of 37.5 and 42.5%, respectively.
Results obtained reveal a sharp drop in Young’s modulus when IL concentration is around 30%. At higher concentrations, Young’s modulus progressively decreases coinciding with a raise in elongation at break which indicates a clear plasticizing effect of the IL. Nevertheless, concentrations up to approximately 40% involve a clear excess of plasticizer, since above this value tensile strength and elongation at break markedly decrease. In fact, at these concentrations, the material starts to become a gel, extremely soft and sticky.
In order to understand this behavior, it is important to bear in mind the effect of IL in starch. As reported in the literature, ILs are good starch solvents, but at the same time they could provoke a certain degree of depolymerization, and, more specifically, those including the ion chloride. The use of acetate does not prevent this depolymerization process since it seems to occur, even to a low extent, at concentrations of around 50% of [Emim+][Ac−] [61].
Thus, the results shown in Figure 3 could be the result of the contribution of several effects. On the one hand, as the IL content increases, starch is progressively dissolved and the blend becomes more ductile [40] as expected by the presence of the plasticizer: tensile strength drops while elongation at break increases. Above 37.5% of IL content, the complete gelatinization of the material for having an excess of plasticizer contributes to a weak interaction between the starch chains which is responsible for the drop in mechanical properties.

3.3. Hydration Properties

The hydration properties are the water content and the solubility in water, which are shown in Table 1. These properties are limiting and important factors of the film to determine its use in the future [62].
On the one hand, as can be observed in the table, the values obtained of moisture of films with [Emim+][Ac−] as a plasticizer show a plateau with a value close to 10% of moisture content, but drastically increases at a 40% content of IL reaching a value of moisture around 15%. On the other hand, solubility values progressively increase with IL concentration, observing solubility changes not only attributable to the IL extraction and dissolution. When IL concentration is 27.5%, around 35% of starch formulation dissolves, but when IL concentration raises 15 units up to 42.5% (i.e., 15% more), the solubility increases to 58%. In general, this behavior could be attributed in part to the hygroscopic nature of the ILs and, in particular, [Emim+][Ac−] has a high hygroscopicity and water solubility [63]. In addition, the IL could contribute to higher and stronger water–ion interactions [41,64] and, at the same time, to a certain starch depolymerization [61] which forms monosaccharides and disaccharides at high IL contents [65]. This phenomenon is due to the alkyl chain length of cations, meaning the hydrophobicity of the ILs increases as the increase in the alkyl chain length of the cations [2,5].
It is worth mentioning that water solubility is related to the biodegradability of the material; the material’s biodegradability should increase with the solubility [58]. However, there are applications where the material has to be insoluble to preserve the integrity of the final product [66].

3.4. Migration Degree

The migration degree of plasticizers is an interesting parameter to bear in mind because it can determine the life of the material since this phenomenon is an undesirable effect that causes difficulties in its commercialization and uses in long-term applications [59]. The migration is due to starch retrogradation or recrystallization [67], which involves changes from the amorphous state of starch to new ordered structures [68]. In addition, the migration process depends on nature, molecular weight, and amount of plasticizer, and this in turn results in the loss of material properties [59] because when it is produced for plasticizer loss in TPS, this causes a decrease of elongation at break and an increase in the elastic modulus [69,70].
The values of IL migration are shown in Figure 4. These results follow a clear trend since the migration of IL increases as the plasticizer amount increases. Hence, a small content of [Emim+][Ac−] as a plasticizer in the starch/PVA blends helps to reduce this effect (IL_42.5 and IL_27.5 have 11.8% and 7.46% of migration degree of plasticizer, respectively). It must be taken into account that the superficial moisture of the samples has probably been eliminated during this test. However, this fact does not change the results or the trend obtained from the migration test. Analyzing these, the plasticizer migration mainly occurs in the early 24 h of the test.
As far as we know, there are no scientific findings in the literature on the migration of starch/PVA films plasticized by any IL. Nevertheless, Rahman et al. [9] studied the migration in samples of PVC plasticized by different ILs and concluded that the PVC with traditional plasticizers had a greater weight loss than those that use ILs as a plasticizer, which is due to the bulky structure of some ILs that hinders their migration to the surface of the material. They also carried out the study of plasticizer loss due to leaching. These can be considered similar methods and their obtained results are comparable because the aim in both cases is to quantify the plasticizer loss; the water is used as an extractant in the leaching experiment, while migration samples are subjected to a determinate pressure. The same trend was observed in the percentage of plasticizer loss to that shown in Figure 4 and they confirmed that using IL as a plasticizer reduced the leaching.
Therefore, we could conclude that the problem of plasticizer migration to the surface of the films is reduced when using a small percentage of certain ILs as plasticizers in starch/PVA blends.

3.5. Attenuated Total Reflection-Fourier Transform Infrared (ATR-FTIR) Spectroscopy

Figure 5 shows the ATR-FTIR spectra of the samples. This technique reflects the changes in molecular interactions in the starch/PVA films with [Emim+][Ac−] as a plasticizer. As can be seen, the spectra are similar and, as expected, show the corresponding peaks to IL and starch.
First of all, it is worth mentioning a wide band between 3000–3600 cm−1 where two different bands overlap: on the one hand, the stretching vibration of the –OH groups of the glucose units and water [60] and the vibration C–H of the imidazolium ring in [Emim+][Ac−] [71].
Other bands shared by both components (starch and [Emim+][Ac-]) are localized between 2800–3000 cm−1, and this is attributed to asymmetric and symmetric stretching of –CH2 and –CH3, and aliphatic asymmetric C–H stretching vibrations [47].
The infrared spectrum of the pure IL reveals two peaks at 1380 and 1580 cm−1 corresponding to symmetric and asymmetric O–C–O stretches of [Ac−] anion of the IL, respectively [72]. However, in Figure 5, those peaks are shown at 1400 and 1560 cm−1, slightly shifted to the position in the pure IL, probably due to the result of the hydrogen bonding between the IL and water molecules (which presents in the starch as moisture) [73]. In addition, the small peak around 1660 cm−1 is assigned to water [47] or the –C–H stretching of the vinyl group [74].
The band at 1148–925 cm−1 shows the stretching of –C–O– situated in –C–O–H and –C–O–C– bonds of the glucose of starch [47]. More concretely, the peaks at around 995 cm−1, 1022 cm−1, and 1047 cm−1 are related to the degree of the rearrangements of the starch after the process of plasticization. While the band at 995 cm−1 corresponds to the hydrogen bonds and the regularity given by molecular rearrangements, the peak at 1022 cm−1 is associated with the amorphous phase of the films, and a decrease in crystallinity [26,33,50,74]; the degree of order in starch can be quantified in consequence by the ratio of the areas of the bands at 995 and 1022 cm−1 [47].
The results are shown in Table 2. According to the ratio values calculated, it can be seen that R995/1022 decreases when increasing the IL content (IL_27.5 and IL_42.5 have values of 0.824 and 0.536, respectively), indicating the ability of this IL to hinder molecular rearrangements after plasticization. These results are in good agreement with the XRD and DMA, as shown below.

3.6. X-ray Diffraction (XRD) Studies

The XRD spectra of the starch/PVA blends plasticized by [Emim+][Ac−] are shown in Figure 6. This analysis allows the study of the crystalline structure of films. All samples showed a similar pattern, where it is possible to observe peaks at around 20, 23, and 40° with different intensities; the peak at 2Ɵ = 20° is less prominent as [Emim+][Ac−] content increases, so a loss of crystallinity is observed. This fact is due to the plasticization process since when the IL content increases the disruption of hydrogen bonds between the starch molecules [75,76], this increases the mobility of the starch chains and contributes to the creation of a more amorphous structure, according to the conclusions of Domene-López et al. [47,55] and Luchese et al. [32], who also studied the native starch and the starch films using [Emim+][Ac−] as a plasticizer, obtaining similar results. Xie et al. [40] concluded that using IL as a plasticizer contributed to a decrease in crystallinity, in comparison with glycerol, because the [Emim+][Ac−] decreases the B-type crystallinity and the V-type crystallinity, hindering the formation of the single-helical structure due to interaction between the hydroxyl groups of starch and acetate anion in [Emim+][Ac−].
It is worth mentioning that various authors such as Zhang et al. [26], Bhagabati et al. [77], and Domene-López et al. [47] state that the transparency of the final material is related to its crystallinity; more amorphous polymeric films had higher transparency due to the disruption of starch grains, and this effect was observed in the obtained films (see Figure 1); when increasing the IL content, the final films lose their crystalline structure, but they are more transparent.

3.7. Dynamic Mechanical Analysis (DMA)

The DMA data of the starch/PVA[Emim+][Ac−] are shown in Figure 7. The curves are similar, showing a peak corresponding to the glass transition of the system [15,78]. As can be seen, the glass transition of samples is shifted towards lower temperatures when IL content increases; for example, the Tg of IL_27.5 was −4 °C while the Tg of IL_42.5 was −30 °C. Jaramillo et al. [58] concluded that this was associated with the plasticization process. In addition, the peak is more prominent as the IL content increases, in good agreement with Xie et al. [40]. Thus, a higher content of IL resulted in a more amorphous structure, hence with greater mobility. This loss of crystallinity is also reflected in ATR-FTIR and XRD spectra, as commented above. These data are consistent with the mechanical properties since a decrease in the glass transition temperature with IL content produces less stiff samples with lower Young’s modulus (Figure 3A).
It should be kept in mind that moisture content (favored by the presence of IL) could also affect glass transition, as Madrigal et al. [78] reported, showing a relation between the moisture contents and the value of tan δ; they concluded that the curves showed a more prominent peak as the water content increased. As is possible to observe in Table 1, the highest results of moisture correspond to the samples with more prominent peaks (IL_37.5, IL_40, and IL_42.5).
It is worth mentioning that there is not much literature on the DMA of starch films plasticized by ILs. However, the DMA analysis of the TPS plasticized by glycerol among other plasticizers has been extensively studied in the literature [79,80,81,82] and all the curves of DMA showed two peaks (one attributed to a phase rich in plasticizer and the other in starch) while that in the [Emim+][Ac−] plasticized-starch films appear in only one transition. As mentioned above, water and conventional starch plasticizers do not bring about a full starch dissolution and gelation; it could be the reason for the presence of two different glass transitions readily observable in glycerol-starch compounds. In the case of the IL-starch, they seem to be fully dissolved and it could be the reason for the presence of one single glass transition.

4. Conclusions

In the present work and, for the first time, starch/PVA films have been plasticized by a single plasticizer being an ionic liquid by melt-mixing.
According to the results obtained, it is possible to conclude that the 1-ethyl-3-methylimidazolium acetate ([Emim+][Ac−]) is an efficient plasticizer to obtain these biomaterials. After the analysis of the results, it has been possible to prove that this IL provokes the disruption of hydrogen bonds between the starch molecules, changing its crystalline structure to an amorphous state, which is possible to observe in the XRD spectra. This was also confirmed by the SEM images, which show that the presence of IL involves the dissolution of the starch granules, even when the [Emim+][Ac−] content in the films was low. Furthermore, a clear trend has been found in accordance with the IL amount added to the blends that the mechanical properties were significantly changed; when there are more crystalline domains than amorphous, the samples were stiffer (increasing Young’s modulus and maximum tensile strength). By contrast, the samples showed more flexibility when the amorphous phase was predominant, due to the increase in chain movement. [Emim+][Ac−] is a good starch plasticizer as revealed by the drop in Tg when the IL content increases; the IL_27.5 sample has a glass transition temperature at −3.17 °C, while the IL_42.5 sample has −31.4 °C, finding a difference of 28.2 °C between both. The same occurs in the diffusion and hydration properties, which are higher as the IL content increases; the values of IL_27.5 and IL_42.5 for the migration degree of plasticizer and solubility in water are 7.46–11.8% and 35.2–57.6%, respectively.
For all these reasons, the [Emim+][Ac−] could be considered an interesting plasticizer to obtain biodegradable polymeric blends from starch, constituting an alternative to other conventional plasticizers such as water or polyols. The results achieved through a technique prior to industrial development, such as melt-mixing, show the high potential of these materials to be a real replacement to conventional polymer in a wide range of applications such as packaging and provide the possibility to be used in applications which previously had no place in this type of biomaterial, such as in dye-sensitized solar cells, fuel cells, among others.

Author Contributions

J.M.C.: methodology, procedures, formal analysis, writing—original draft; M.G.M.: conceptualization, formal analysis, supervision, writing; D.D.-L.: conceptualization, formal analysis, supervision, writing; I.M.-G.: project administration, funding acquisition, supervision; J.C.G.-Q.: supervision, formal analysis, writing, project administration. All authors have read and agreed to the published version of the manuscript.

Funding

This work was partially supported by the Spanish Ministry of Science and Ministry of Economy, Industry, and competitiveness (PID2019-108632RB-I00) and Generalitat Valenciana (PROMETEO CIPROM/2021/027). This work was partially supported by the TED2021-130389B-C21 research project, funded by MCIN/AEI/10.13039/501100011033 and by the European Union NextGenerationEU/PRTR.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Wypych, G. (Ed.) Plasticizers Use and Selection for Specific Polymers. In Handbook of Plasticizers; ChemTec Publishing: Scarborough, ON, Canada, 2012; pp. 307–419. [Google Scholar]
  2. Shi, W.; Damodaran, K.; Nulwala, H.B.; Luebke, D.R. Theoretical and Experimental Studies of Water Interaction in Acetate Based Ionic Liquids. Phys. Chem. Chem. Phys. 2012, 14, 15897–15908. [Google Scholar] [CrossRef] [PubMed]
  3. Ghandi, K. A Review of Ionic Liquids, Their Limits and Applications. Green Sustain. Chem. 2014, 4, 44–53. [Google Scholar] [CrossRef] [Green Version]
  4. Crowhurst, L.; Mawdsley, P.R.; Perez-Arlandis, J.M.; Salter, P.A.; Welton, T. Solvent-Solute Interactions in Ionic Liquids. Phys. Chem. Chem. Phys. 2003, 5, 2790–2794. [Google Scholar] [CrossRef]
  5. Ren, F.; Wang, J.; Xie, F.; Zan, K.; Wang, S.; Wang, S. Applications of Ionic Liquids in Starch Chemistry: A Review. Green Chem. 2020, 22, 2162–2183. [Google Scholar] [CrossRef]
  6. Montalbán, M.G.; Hidalgo, J.M.; Collado-González, M.; Díaz Baños, F.G.; Víllora, G. Assessing Chemical Toxicity of Ionic Liquids on Vibrio Fischeri: Correlation with Structure and Composition. Chemosphere 2016, 155, 405–414. [Google Scholar] [CrossRef]
  7. Díaz Alvarez, J.C.; Martínez Rey, R.; Barrero Acosta, R. Ionic Liquids: Physicochemical Properties and Potential Application in Upgrading of Heavy Crude Oils. Rev. Ion 2012, 25, 61–87. [Google Scholar]
  8. Wilpiszewska, K.; Spychaj, T. Ionic Liquids: Media for Starch Dissolution, Plasticization and Modification. Carbohydr. Polym. 2011, 86, 424–428. [Google Scholar] [CrossRef]
  9. Rahman, M.; Brazel, C.S. Ionic Liquids: New Generation Stable Plasticizers for Poly(Vinyl Chloride). Polym. Degrad. Stab. 2006, 91, 3371–3382. [Google Scholar] [CrossRef]
  10. Scott, M.P.; Brazel, C.S.; Benton, M.G.; Mays, J.W.; Holbrey, J.D.; Rogers, R.D. Application of Ionic Liquids as Plasticizers for Poly(Methyl Methacrylate). Chem. Commun. 2002, 2, 1370–1371. [Google Scholar] [CrossRef]
  11. Wong, S.I.; Lin, H.; Sunarso, J.; Wong, B.T.; Jia, B. Optimization of Ionic-Liquid Based Electrolyte Concentration for High-Energy Density Graphene Supercapacitors. Appl. Mater. Today 2020, 18, 100522. [Google Scholar] [CrossRef]
  12. Montalbán, M.G.; Collado-González, M.; Lozano-Pérez, A.A.; Díaz Baños, F.G.; Víllora, G. Extraction of Organic Compounds Involved in the Kinetic Resolution of Rac-2-Pentanol from n-Hexane by Imidazolium-Based Ionic Liquids: Liquid-Liquid Equilibrium. J. Mol. Liq. 2018, 252, 445–453. [Google Scholar] [CrossRef]
  13. Rojas, O.G.; Hall, S.R. On the Synergistic Interaction of an Ionic Liquid and Biopolymers in the Synthesis of Strontium Niobate. Mater. Chem. Phys. 2017, 202, 220–224. [Google Scholar] [CrossRef] [Green Version]
  14. Lucas, M.; MacDonald, B.A.; Wagner, G.L.; Joyce, S.A.; Rector, K.D. Ionic Liquid Pretreatment of Poplar Wood at Room Temperature: Swelling and Incorporation of Nanoparticles. ACS Appl. Mater. Interfaces 2010, 2, 2198–2205. [Google Scholar] [CrossRef] [PubMed]
  15. Domene-López, D.; Guillén, M.M.; Martin-Gullon, I.; García-Quesada, J.C.; Montalbán, M.G. Study of the Behavior of Biodegradable Starch/Polyvinyl Alcohol/Rosin Blends. Carbohydr. Polym. 2018, 202, 299–305. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  16. Geyer, R.; Jambeck, J.R.; Law, K.L. Production, Use, and Fate of All Plastics Ever Made. Sci. Adv. 2017, 3, 25–29. [Google Scholar] [CrossRef] [Green Version]
  17. Kaza, S.; Yao, L.; Bhada-Tata, P.; Van Woerden, F. What a Waste 2.0: A Global Snapshot of Solid Waste Management to 2050; World Bank Publications: Washington, DC, USA, 2018. [Google Scholar]
  18. Scaffaro, R.; Citarrella, M.C.; Gulino, E.F.; Morreale, M. Hedysarum Coronarium-Based Green Composites Prepared by Compression Molding and Fused Deposition Modeling. Materials 2022, 15, 465. [Google Scholar] [CrossRef]
  19. Kumar, M.; Xiong, X.; He, M.; Tsang, D.C.W.; Gupta, J.; Khan, E.; Harrad, S.; Hou, D.; Ok, Y.S.; Bolan, N.S. Microplastics as Pollutants in Agricultural Soils. Environ. Pollut. 2020, 265, 114980. [Google Scholar] [CrossRef]
  20. Li, W.; Wufuer, R.; Duo, J.; Wang, S.; Luo, Y.; Zhang, D.; Pan, X. Microplastics in Agricultural Soils: Extraction and Characterization after Different Periods of Polythene Film Mulching in an Arid Region. Sci. Total Environ. 2020, 749, 141420. [Google Scholar] [CrossRef]
  21. Lusher, A.L.; Bråte, I.L.N.; Munno, K.; Hurley, R.R.; Welden, N.A. Is It or Isn’t It: The Importance of Visual Classification in Microplastic Characterization. Appl. Spectrosc. 2020, 74, 1139–1153. [Google Scholar] [CrossRef] [PubMed]
  22. Park, S.; Oh, Y.; Yun, J.; Yoo, E.; Jung, D.; Park, K.S.; Oh, K.K.; Lee, S.H. Characterization of Blended Cellulose/Biopolymer Films Prepared Using Ionic Liquid. Cellulose 2020, 27, 5101–5119. [Google Scholar] [CrossRef]
  23. Zan, K.; Wang, J.; Ren, F.; Yu, J.; Wang, S.; Xie, F.; Wang, S. Structural Disorganization of Cereal, Tuber and Bean Starches in Aqueous Ionic Liquid at Room Temperature: Role of Starch Granule Surface Structure. Carbohydr. Polym. 2021, 258, 117677. [Google Scholar] [CrossRef] [PubMed]
  24. Wang, J.; Ren, F.; Yu, J.; Copeland, L.; Wang, S.; Wang, S. Toward a Better Understanding of Different Dissolution Behavior of Starches in Aqueous Ionic Liquids at Room Temperature. ACS Omega 2019, 4, 11312–11319. [Google Scholar] [CrossRef] [PubMed]
  25. Sankri, A.; Arhaliass, A.; Dez, I.; Gaumont, A.C.; Grohens, Y.; Lourdin, D.; Pillin, I.; Rolland-Sabaté, A.; Leroy, E. Thermoplastic Starch Plasticized by an Ionic Liquid. Carbohydr. Polym. 2010, 82, 256–263. [Google Scholar] [CrossRef]
  26. Zhang, B.; Xie, F.; Shamshina, J.L.; Rogers, R.D.; McNally, T.; Wang, D.K.; Halley, P.J.; Truss, R.W.; Zhao, S.; Chen, L. Facile Preparation of Starch-Based Electroconductive Films with Ionic Liquid. ACS Sustain. Chem. Eng. 2017, 5, 5457–5467. [Google Scholar] [CrossRef] [Green Version]
  27. Bendaoud, A.; Chalamet, Y. Plasticizing Effect of Ionic Liquid on Cellulose Acetate Obtained by Melt Processing. Carbohydr. Polym. 2014, 108, 75–82. [Google Scholar] [CrossRef]
  28. Mahmood, H.; Moniruzzaman, M.; Yusup, S.; Welton, T. Ionic Liquids Assisted Processing of Renewable Resources for the Fabrication of Biodegradable Composite Materials. Green Chem. 2017, 19, 2051–2075. [Google Scholar] [CrossRef] [Green Version]
  29. Mateyawa, S.; Xie, D.F.; Truss, R.W.; Halley, P.J.; Nicholson, T.M.; Shamshina, J.L.; Rogers, R.D.; Boehm, M.W.; McNally, T. Effect of the Ionic Liquid 1-Ethyl-3-Methylimidazolium Acetate on the Phase Transition of Starch: Dissolution or Gelatinization? Carbohydr. Polym. 2013, 94, 520–530. [Google Scholar] [CrossRef] [Green Version]
  30. Zdanowicz, M.; Spychaj, T. Ionic Liquids as Starch Plasticizers or Solvents. Polimery 2011, 56, 861–864. [Google Scholar] [CrossRef]
  31. Yang, X.; Qiao, C.; Li, Y.; Li, T. Dissolution and Resourcfulization of Biopolymers in Ionic Liquids. React. Funct. Polym. 2016, 100, 181–190. [Google Scholar] [CrossRef]
  32. Luchese, C.L.; Benelli, P.; Spada, J.C.; Tessaro, I.C. Impact of the Starch Source on the Physicochemical Properties and Biodegradability of Different Starch-Based Films. J. Appl. Polym. Sci. 2018, 135, 46564. [Google Scholar] [CrossRef]
  33. Lopez-Rubio, A.; Flanagan, B.M.; Shrestha, A.K.; Gidley, M.J.; Gilbert, E.P. Molecular Rearrangement of Starch during in vitro Digestion: Toward a Better Understanding of Enzyme Resistant Starch Formation in Processed Starches. Biomacromolecules 2008, 9, 1951–1958. [Google Scholar] [CrossRef] [PubMed]
  34. Lekube, B.M.; Fahrngruber, B.; Kozich, M.; Wastyn, M.; Burgstaller, C. Influence of Processing on the Mechanical Properties and Morphology of Starch-Based Blends for Film Applications. J. Appl. Polym. Sci. 2019, 136, 47990. [Google Scholar] [CrossRef]
  35. Valero-Valdivieso, M.F.; Ortegón, Y.; Uscategui, Y. Biopolímeros: Avances y Perspectivas. Dyna 2013, 80, 171–180. [Google Scholar]
  36. Biliaderis, C.G.; Lazaridou, A.; Arvanitoyannis, I. Glass Transition and Physical Properties of Polyol-Plasticized Pullulan-Starch Blends at Low Moisture. Carbohydr. Polym. 1999, 40, 29–47. [Google Scholar] [CrossRef]
  37. Talja, R.A.; Helén, H.; Roos, Y.H.; Jouppila, K. Effect of Various Polyols and Polyol Contents on Physical and Mechanical Properties of Potato Starch-Based Films. Carbohydr. Polym. 2007, 67, 288–295. [Google Scholar] [CrossRef]
  38. Sreekumar, P.A.; Al-Harthi, M.A.; De, S.K. Effect of Glycerol on Thermal and Mechanical Properties of Polyvinyl Alcohol/Starch Blends. J. Appl. Polym. Sci. 2012, 123, 135–142. [Google Scholar] [CrossRef]
  39. Da Róz, A.L.; Carvalho, A.J.F.; Gandini, A.; Curvelo, A.A.S. The Effect of Plasticizers on Thermoplastic Starch Compositions Obtained by Melt Processing. Carbohydr. Polym. 2006, 63, 417–424. [Google Scholar] [CrossRef]
  40. Xie, F.; Flanagan, B.M.; Li, M.; Sangwan, P.; Truss, R.W.; Halley, P.J.; Strounina, E.V.; Whittaker, A.K.; Gidley, M.J.; Dean, K.M.; et al. Characteristics of Starch-Based Films Plasticised by Glycerol and by the Ionic Liquid 1-Ethyl-3-Methylimidazolium Acetate: A Comparative Study. Carbohydr. Polym. 2014, 111, 841–848. [Google Scholar] [CrossRef] [Green Version]
  41. Domene-López, D.; Delgado-Marín, J.J.; García-Quesada, J.C.; Martín-Gullón, I.; Montalbán, M.G. Electroconductive Starch/Multi-Walled Carbon Nanotube Films Plasticized by 1-Ethyl-3-Methylimidazolium Acetate. Carbohydr. Polym. 2020, 229, 115545. [Google Scholar] [CrossRef]
  42. Abera, G.; Woldeyes, B.; Demash, H.D.; Miyake, G. The Effect of Plasticizers on Thermoplastic Starch Films Developed from the Indigenous Ethiopian Tuber Crop Anchote (Coccinia abyssinica) Starch. Int. J. Biol. Macromol. 2020, 155, 581–587. [Google Scholar] [CrossRef]
  43. Gomez-Coma, L.; Garea, A.; Irabien, A. Carbon Dioxide Capture by [Emim][Ac] Ionic Liquid in a Polysulfone Hollow Fiber Membrane Contactor. Int. J. Greenh. Gas Control 2016, 52, 401–409. [Google Scholar] [CrossRef] [Green Version]
  44. Ostadjoo, S.; Berton, P.; Shamshina, J.L.; Rogers, R.D. Scaling-up Ionic Liquid-Based Technologies: How Much Do We Care about Their Toxicity? Prima Facie Information on 1-Ethyl-3-Methylimidazolium Acetate. Toxicol. Sci. 2018, 161, 249–265. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  45. Gómez-Coma, L.; Garea, A.; Irabien, A. Non-Dispersive Absorption of CO2 in [Emim][EtSO4] and [Emim][Ac]: Temperature Influence. Sep. Purif. Technol. 2014, 132, 120–125. [Google Scholar] [CrossRef]
  46. Chen, Y.; Sun, X.; Yan, C.; Cao, Y.; Mu, T. The Dynamic Process of Atmospheric Water Sorption in [EMIM][Ac] and Mixtures of [EMIM][Ac] with Biopolymers and CO2 Capture in These Systems. J. Phys. Chem. B 2014, 118, 11523–11536. [Google Scholar] [CrossRef] [PubMed]
  47. Domene-López, D.; Delgado-Marín, J.J.; Martin-Gullon, I.; García-Quesada, J.C.; Montalbán, M.G. Comparative Study on Properties of Starch Films Obtained from Potato, Corn and Wheat Using 1-Ethyl-3-Methylimidazolium Acetate as Plasticizer. Int. J. Biol. Macromol. 2019, 135, 845–854. [Google Scholar] [CrossRef]
  48. Decaen, P.; Rolland-Sabaté, A.; Colomines, G.; Guilois, S.; Lourdin, D.; Della Valle, G.; Leroy, E. Influence of Ionic Plasticizers on the Processing and Viscosity of Starch Melts. Carbohydr. Polym. 2020, 230, 115591. [Google Scholar] [CrossRef]
  49. Tan, X.; Li, X.; Chen, L.; Xie, F. Solubility of Starch and Microcrystalline Cellulose in 1-Ethyl-3-Methylimidazolium Acetate Ionic Liquid and Solution Rheological Properties. Phys. Chem. Chem. Phys. 2016, 18, 27584–27593. [Google Scholar] [CrossRef]
  50. Liu, K.; Tan, X.; Li, X.; Chen, L.; Xie, F. Characterization of Regenerated Starch from 1-Ethyl-3-Methylimidazolium Acetate Ionic Liquid with Different Anti-Solvents. J. Polym. Sci. Part B Polym. Phys. 2018, 56, 1231–1238. [Google Scholar] [CrossRef]
  51. Gunawardene, O.H.P.; Amaraweera, S.M.; Wannikayaka, W.M.D.B.; Fernando, N.M.L.; Gunathilake, C.A.; Manamperi, W.A.; Kulatunga, A.K.; Manipura, A. Role of Compatibilization of Phthalic Acid in Cassava Starch/Poly Vinyl Alcohol Thin Films. In Proceedings of the 12th International Conference on Structural Engineering and Construction Management: ICSECM 2021, Kandy, Sri Lanka, 2–5 December 2021; Springer Nature: Singapore, 2022; pp. 665–689. [Google Scholar]
  52. Narancic, T.; Cerrone, F.; Beagan, N.; O’Connor, K.E. Recent Advances in Bioplastics: Application and Biodegradation. Polymers 2020, 12, 920. [Google Scholar] [CrossRef] [Green Version]
  53. Gulino, E.F.; Citarrella, M.C.; Maio, A.; Scaffaro, R. An Innovative Route to Prepare in Situ Graded Crosslinked PVA Graphene Electrospun Mats for Drug Release. Compos. Part A 2022, 155, 106827. [Google Scholar] [CrossRef]
  54. Gaaz, T.S.; Sulong, A.B.; Akhtar, M.N.; Kadhum, A.A.H.; Mohamad, A.B.; Al-amiery, A.A. Properties and Applications of Polyvinyl Alcohol, Halloysite Nanotubes and Their Nanocomposites. Molecules 2015, 20, 22833–22847. [Google Scholar] [CrossRef] [Green Version]
  55. Domene-López, D.; García-Quesada, J.C.; Martin-Gullon, I.; Montalbán, M.G. Influence of Starch Composition and Molecular Weight on Physicochemical Properties of Biodegradable Films. Polymers 2019, 11, 1084. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  56. Eaton, M.D.; Domene-López, D.; Wang, Q.; Montalbán, M.G.; Martin-Gullon, I.; Shull, K.R.; Martin-Gullon, I.; Shull, K.R. Exploring the Effect of Humidity on Thermoplastic Starch Films Using the Quartz Crystal Microbalance. Carbohydr. Polym. 2021, 261, 117727. [Google Scholar] [CrossRef] [PubMed]
  57. ASTM D882-12; Standard Test Method for Tensile Properties of Thin Plastic Sheeting. ASTM International: West Conshohocken, PA, USA, 2012. Available online: https://www.astm.org/DATABASE.CART/HISTORICAL/D882-02.htm (accessed on 28 March 2018).
  58. Jaramillo, C.M.; González Seligra, P.; Goyanes, S.; Bernal, C.; Famá, L. Biofilms Based on Cassava Starch Containing Extract of Yerba Mate as Antioxidant and Plasticizer. Starch/Staerke 2015, 67, 780–789. [Google Scholar] [CrossRef]
  59. Marcilla, A.; García, S.; García-Quesada, J.C. Study of the Migration of PVC Plasticizers. J. Anal. Appl. Pyrolysis 2004, 71, 457–463. [Google Scholar] [CrossRef]
  60. Dai, L.; Zhang, J.; Cheng, F. Effects of Starches from Different Botanical Sources and Modification Methods on Physicochemical Properties of Starch-Based Edible Films. Int. J. Biol. Macromol. 2019, 132, 897–905. [Google Scholar] [CrossRef]
  61. Sciarini, L.S.; Rolland-Sabaté, A.; Guilois, S.; Decaen, P.; Leroya, E.; Le Bail, P. Understanding the Destructuration of Starch in Water–Ionic Liquid Mixtures. Green Chem. 2015, 17, 291–299. [Google Scholar] [CrossRef]
  62. Zhong, Y.; Li, Y.; Liang, W.; Liu, L.; Li, S.; Xue, J.; Guo, D. Comparison of Gelatinization Method, Starch Concentration, and Plasticizer on Physical Properties of High-Amylose Starch Films. J. Food Process Eng. 2018, 41, 1–8. [Google Scholar] [CrossRef]
  63. Otero-Mato, J.M.; Lesch, V.; Montes-Campos, H.; Smiatek, J.; Diddens, D.; Cabeza, O.; Gallego, L.J.; Varela, L.M. Solvation in Ionic Liquid-Water Mixtures: A Computational Study. J. Mol. Liq. 2019, 292, 111273. [Google Scholar] [CrossRef]
  64. Ismail, S.; Mansor, N.; Majeed, Z.; Man, Z. Effect of Water and [Emim][OAc] as Plasticizer on Gelatinization of Starch. Procedia Eng. 2016, 148, 524–529. [Google Scholar] [CrossRef] [Green Version]
  65. Li, X.; Gao, B.; Zhang, S. Adjusting Hydrogen Bond by Lever Principle to Achieve High Performance Starch-Based Biodegradable Films with Low Migration Quantity. Carbohydr. Polym. 2022, 298, 120107. [Google Scholar] [CrossRef] [PubMed]
  66. Edhirej, A.; Sapuan, S.M.; Jawaid, M.; Zahari, N.I. Cassava/Sugar Palm Fiber Reinforced Cassava Starch Hybrid Composites: Physical, Thermal and Structural Properties. Int. J. Biol. Macromol. 2017, 101, 75–83. [Google Scholar] [CrossRef] [PubMed]
  67. Liu, H.; Xie, F.; Yu, L.; Chen, L.; Li, L. Thermal Processing of Starch-Based Polymers. Prog. Polym. Sci. 2009, 34, 1348–1368. [Google Scholar] [CrossRef]
  68. Li, C.; Hu, Y.; Li, E. Effects of Amylose and Amylopectin Chain-Length Distribution on the Kinetics of Long-Term Rice Starch Retrogradation. Food Hydrocoll. 2021, 111, 106239. [Google Scholar] [CrossRef]
  69. Schmitt, H.; Guidez, A.; Prashantha, K.; Soulestin, J.; Lacrampe, M.F.; Krawczak, P. Studies on the Effect of Storage Time and Plasticizers on the Structural Variations in Thermoplastic Starch. Carbohydr. Polym. 2015, 115, 364–372. [Google Scholar] [CrossRef]
  70. Nazrin, A.; Sapuan, S.M.; Ilyas, R.A. Water Barrier and Mechanical Properties of Sugar Palm Crystalline Nanocellulose Reinforced Thermoplastic Sugar Palm Starch (TPS)/Poly(Lactic Acid) (PLA) Blend Bionanocomposites. Nanotechnol. Rev. 2021, 10, 431–442. [Google Scholar] [CrossRef]
  71. Zhang, B.; Chen, L.; Xie, F.; Li, X.; Truss, R.W.; Halley, P.J.; Shamshina, J.L.; Rogers, R.D.; McNally, T. Understanding the Structural Disorganization of Starch in Water-Ionic Liquid Solutions. Phys. Chem. Chem. Phys. 2015, 17, 13860–13871. [Google Scholar] [CrossRef] [Green Version]
  72. Delgado, J.M.; Rodes, A.; Orts, J.M. B3LYP and in Situ ATR-SEDIRAS Study of the Infrared Behavior and Bonding Mode of Adsorbed Acetate Anions on Silver Thin-Film Electrodes. J. Phys. Chem. C 2007, 111, 14476–14483. [Google Scholar] [CrossRef]
  73. Zhang, B.; Xie, F.; Zhang, T.; Chen, L.; Li, X.; Truss, R.W.; Halley, P.J.; Shamshina, J.L.; McNally, T.; Rogers, R.D. Different Characteristic Effects of Ageing on Starch-Based Films Plasticised by 1-Ethyl-3-Methylimidazolium Acetate and by Glycerol. Carbohydr. Polym. 2016, 146, 67–79. [Google Scholar] [CrossRef] [Green Version]
  74. Das, K.; Ray, D.; Bandyopadhyay, N.R.; Gupta, A.; Sengupta, S.; Sahoo, S.; Mohanty, A.; Misra, M. Preparation and Characterization of Cross-Linked Starch/Poly(Vinyl Alcohol) Green Films with Low Moisture Absorption. Ind. Eng. Chem. Res. 2010, 49, 2176–2185. [Google Scholar] [CrossRef]
  75. Phetwarotai, W.; Potiyaraj, P.; Aht-Ong, D. Characteristics of Biodegradable Polylactide/Gelatinized Starch Films: Effects of Starch, Plasticizer, and Compatibilizer. J. Appl. Polym. Sci. 2010, 116, 2658–2667. [Google Scholar] [CrossRef]
  76. Bendaoud, A.; Chalamet, Y. Effects of Relative Humidity and Ionic Liquids on the Water Content and Glass Transition of Plasticized Starch. Carbohydr. Polym. 2013, 97, 665–675. [Google Scholar] [CrossRef] [PubMed]
  77. Bhagabati, P.; Hazarika, D.; Katiyar, V. Tailor-Made Ultra-Crystalline, High Molecular Weight Poly(ε-Caprolactone) Films with Improved Oxygen Gas Barrier and Optical Properties: A Facile and Scalable Approach. Int. J. Biol. Macromol. 2019, 124, 1040–1052. [Google Scholar] [CrossRef]
  78. Madrigal, L.; Sandoval, A.J.; Müller, A.J. Effects of Corn Oil on Glass Transition Temperatures of Cassava Starch. Carbohydr. Polym. 2011, 85, 875–884. [Google Scholar] [CrossRef]
  79. Sreekumar, P.A.; Al-Harthi, M.A.; De, S.K. Studies on Compatibility of Biodegradable Starch/Polyvinyl Alcohol Blends. Polym. Eng. Sci. 2012, 52, 2167–2172. [Google Scholar] [CrossRef]
  80. López, O.V.; Lecot, C.J.; Zaritzky, N.E.; García, M.A. Biodegradable Packages Development from Starch Based Heat Sealable Films. J. Food Eng. 2011, 105, 254–263. [Google Scholar] [CrossRef]
  81. Zhang, S.; He, Y.; Yin, Y.; Jiang, G. Fabrication of Innovative Thermoplastic Starch Bio-Elastomer to Achieve High Toughness Poly(Butylene Succinate) Composites. Carbohydr. Polym. 2019, 206, 827–836. [Google Scholar] [CrossRef]
  82. Jha, P.; Dharmalingam, K.; Nishizu, T.; Katsuno, N.; Anandalakshmi, R. Effect of Amylose–Amylopectin Ratios on Physical, Mechanical, and Thermal Properties of Starch-Based Bionanocomposite Films Incorporated with CMC and Nanoclay. Starch/Staerke 2020, 72, 1900121. [Google Scholar] [CrossRef]
Polymers 15 01788 g001 550
Figure 1. The visual aspect of starch/PVA blends plasticized by [Emim+][Ac−].
Figure 1. The visual aspect of starch/PVA blends plasticized by [Emim+][Ac−].
Polymers 15 01788 g001
Polymers 15 01788 g002 550
Figure 2. SEM images of the cryogenic fracture surface of sheets (magnification 1000×).
Figure 2. SEM images of the cryogenic fracture surface of sheets (magnification 1000×).
Polymers 15 01788 g002
Polymers 15 01788 g003 550
Figure 3. Mechanical properties of the films studied. (A) Young’s modulus; (B) Maximum Tensile Strength; and (C) Elongation at break.
Figure 3. Mechanical properties of the films studied. (A) Young’s modulus; (B) Maximum Tensile Strength; and (C) Elongation at break.
Polymers 15 01788 g003
Polymers 15 01788 g004 550
Figure 4. Migration degree as a function of time and [Emim+][Ac−] content of starch/PVA blends.
Figure 4. Migration degree as a function of time and [Emim+][Ac−] content of starch/PVA blends.
Polymers 15 01788 g004
Polymers 15 01788 g005 550
Figure 5. ATR-FTIR spectra of starch/PVA blends plasticized by [Emim+][Ac−]. (A) 500–4000 cm−1 range; (B) 800–1200 cm−1 range.
Figure 5. ATR-FTIR spectra of starch/PVA blends plasticized by [Emim+][Ac−]. (A) 500–4000 cm−1 range; (B) 800–1200 cm−1 range.
Polymers 15 01788 g005
Polymers 15 01788 g006 550
Figure 6. XRD spectra of the starch/PVA blends plasticized by [Emim+][Ac−].
Figure 6. XRD spectra of the starch/PVA blends plasticized by [Emim+][Ac−].
Polymers 15 01788 g006
Polymers 15 01788 g007 550
Figure 7. DMA spectra of the studied sheets. Dependence of loss tangent (tan δ) on the temperature at a constant frequency of 1 Hz.
Figure 7. DMA spectra of the studied sheets. Dependence of loss tangent (tan δ) on the temperature at a constant frequency of 1 Hz.
Polymers 15 01788 g007
Table
Table 1. Hydration properties of the sheets studied.
Table 1. Hydration properties of the sheets studied.
SampleWater Content (%)Solubility in Water (%)
IL_27.59.41 ± 0.2535.2 ± 0.2
IL_309.30 ± 0.2637.0 ± 0.4
IL_32.59.93 ± 0.2940.8 ± 0.2
IL_37.59.97 ± 0.1649.3 ± 1.2
IL_4011.4 ± 0.250.8 ± 1.0
IL_42.514.9 ± 0.957.6 ± 1.5
Table
Table 2. ATR-FTIR band intensity ratio (R995/1022) of the starch/PVA blends obtained.
Table 2. ATR-FTIR band intensity ratio (R995/1022) of the starch/PVA blends obtained.
Films Sample
Starch_PureIL_27.5IL_30IL_32.5IL_37.5IL_40IL_42.5
R995/10221.390.8240.6730.6590.6370.6130.536
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Castro, J.M.; Montalbán, M.G.; Domene-López, D.; Martín-Gullón, I.; García-Quesada, J.C. Study of the Plasticization Effect of 1-Ethyl-3-methylimidazolium Acetate in TPS/PVA Biodegradable Blends Produced by Melt-Mixing. Polymers 2023, 15, 1788. https://doi.org/10.3390/polym15071788

AMA Style

Castro JM, Montalbán MG, Domene-López D, Martín-Gullón I, García-Quesada JC. Study of the Plasticization Effect of 1-Ethyl-3-methylimidazolium Acetate in TPS/PVA Biodegradable Blends Produced by Melt-Mixing. Polymers. 2023; 15(7):1788. https://doi.org/10.3390/polym15071788

Chicago/Turabian Style

Castro, Jennifer M., Mercedes G. Montalbán, Daniel Domene-López, Ignacio Martín-Gullón, and Juan C. García-Quesada. 2023. "Study of the Plasticization Effect of 1-Ethyl-3-methylimidazolium Acetate in TPS/PVA Biodegradable Blends Produced by Melt-Mixing" Polymers 15, no. 7: 1788. https://doi.org/10.3390/polym15071788

APA Style

Castro, J. M., Montalbán, M. G., Domene-López, D., Martín-Gullón, I., & García-Quesada, J. C. (2023). Study of the Plasticization Effect of 1-Ethyl-3-methylimidazolium Acetate in TPS/PVA Biodegradable Blends Produced by Melt-Mixing. Polymers, 15(7), 1788. https://doi.org/10.3390/polym15071788

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop