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Article

Influence of Urea Content in Deep Eutectic Solvents on Thermoplastic Starch Films’ Properties

by
Magdalena Zdanowicz
Center of Bioimmobilisation and Innovative Packaging Materials, Faculty of Food Sciences and Fisheries, West Pomeranian University of Technology, Janickiego 35, 71-270 Szczecin, Poland
Appl. Sci. 2023, 13(3), 1383; https://doi.org/10.3390/app13031383
Submission received: 18 December 2022 / Revised: 2 January 2023 / Accepted: 3 January 2023 / Published: 20 January 2023
(This article belongs to the Section Materials Science and Engineering)
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Abstract

:

Featured Application

Thermoplastic starch (TPS) materials with urea-rich eutectic mixtures are obtained from cheap, available and abundant sources. They can be used as ecofriendly agricultural plastics because urea-based DESs act not only as starch plasticizers, but they also constitute sources of fertilizer, which can be released from the materials.

Abstract

The goal of the study was to prepare deep eutectic solvents (DESs) with different urea (U) contents and apply them as potato-starch plasticizers to investigate the influence of various DES compositions on the physicochemical properties of thermoplastic starch (TPS) obtained via thermocompression. As hydrogen bond acceptors, quaternary ammonium compounds, choline chloride (CC) and betaine (B-anhydrous and monohydrate) were used. The molar ratios of CC or B to U were 1:2, 1:3, 1:4 and 1:5. Before starch processing, the DESs were thermally characterized (DSC, TGA). The increase in U content in the eutectics led to higher phase-transition temperatures and lower thermal stability. The influence of the DESs on thermocompressed TPS mechanical (tensile test) and thermal–mechanical (DMTA) properties, morphology (XRD and FTIR), sorption/dissolution behavior and surface contact angle was investigated. The mechanical tests revealed that the increase in U led to higher elongation at break and a highly amorphous structure. The FTIR results indicated that the starch underwent some carbamation derivatization with the presence of B. The DESs with high U content plasticized starch effectively; therefore, preliminary extrusion tests for starch were performed with selected CC and B-based DES with the molar ratio of 1:5.

1. Introduction

Starch is one of the most abundant biopolymers and is used in many areas of industry [1]. It can be used as a biodegradable ecofriendly alternative to the conventional oil-based polymers, applied for example, in food packaging, agriculture and pharmacy. Due to the high glass temperature (Tg) of starch close to its degradation, caused by strong H-bonding, its thermal processing is impossible. This polysaccharide, which consists of two polymer fractions, amylose and amylopectin, needs some additives that facilitate their processing. Small-molecule polar additives that decrease Tg, called plasticizers, disrupt H bonds between OH groups of polysaccharide chains. Newly formed H bonds between small plasticizers’ molecules and OH groups of the polysaccharide lead to the production of thermoplastic starch (TPS). This process can be performed via starch gelatinization in water or via thermal–pressure processes, such as extrusion or thermocompression. Starch plasticizers, i.e., polyols (the most common being glycerol), sugars, amides or amines, ionic liquids or deep eutectic solvents (DESs) [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16] can be applied. Urea (U) is amide compound that can be used for starch plasticization. However, when used as a single component as a starch plasticizer, U tends to recrystallize in the polymer matrix [17,18,19]; thus, it is mixed with other co-plasticizers [5,13,20,21,22,23,24,25,26]. It can form deep eutectic solvents with, for example, choline chloride (CC) [5,21,27], betaine (B) [28] and polyalcohols [22] and also melts with sugars [29]. Deep eutectic solvents are mixtures with much lower phase-transition temperatures than their individual components [27]. Due to the application of urea as a fertilizer (nitrogen source), TPS plasticized with U can be used as agricultural bioplastics, facilitating fertilization [30,31,32,33]. Versino et al. prepared TPS films (from cassava), plasticized with U and glycerol with bagasse as a filler, via the casting method [31]. They studied, for example, the influence of the U content on the biodegradation rate, revealing that higher U content was correlated with higher biodegradability. The films with 50 wt% urea showed a total weight loss of 57% and a 95% release of the active compound after ca. 2 weeks. Rychter et al. prepared TPS/U via extrusion [32]. In their work, the influence of the TPS/U materials on plant growth (including the determination of such parameters as the fresh and dry matter of plants and their visual evaluation) was examined. The study revealed that the materials exhibited a stimulating effect on the growth and development of the cultivated model plants.
Most of the urea-based DESs used for starch plasticization have a low molar ratio with the second component and there are no studies related to TPS with mixtures containing excessive U. Additionally, B (anhydrous and monohydrate) was chosen because there are few works related to B-based eutectic mixtures for polysaccharide processing [5,34,35,36]. In this work, two types of DES, based on CC and B, with molar ratios CC or B to U up to 1:5, were prepared, thermally characterized (DSC, TGA) and used for potato-starch plasticization. The influence of the U content in the DESs on the TPS’s mechanical properties (tensile test), morphology (XRD and FTIR) and sorption/dissolution behavior were investigated. Moreover, a dynamic thermal–mechanical analysis (DMTA) was performed on the TPS films. The DESs with the highest U content were selected for the preliminary test of extrusion. The TPS extrudates were characterized via mechanical tests, XRD and sorption behavior. The aim of these tests was to investigate whether U-rich DESs are able to plasticize starch via a more industrially acceptable continuous method of functional TPS-material production that could be used for agriculture or horticulture.

2. Materials and Methods

2.1. Materials

Potato starch, with a moisture content of 15 wt% (average molecular weight 4.37 × 107 g/mol; 29.7 wt% amylose content), was supplied by Nowamyl SA (Nowogard, Poland). Urea—U (≥98%)—was purchased from Chempur (Poland). Anhydrous betaine (Ba (99%)), betaine monohydrate (Bh (99%)) and choline chloride (CC (≥98%)) were purchased from Alfa Aesar (Kandel, Germany).

2.2. Eutectic-Mixture Preparation

Eutectic mixtures were prepared as follows. Selected components (B or CC with different molar ratio to U) were placed in a glass reactor immersed in a water bath, heated up to 95 °C, and stirred until a homogenous pellucid liquid was obtained. Next, the mixture was poured into glass vials and these were placed in a vacuum chamber (105 °C, 250 mbar, 1 h) to remove remaining moisture. The mixtures intended for starch plasticization were kept in sealed vials. Only CCU 1:2 was liquid at room temperature; the rest of the systems crystallized after cooling.

2.3. Differential Scanning Calorymetric Analysis of Eutectic Mixtures

Phase transitions of plasticizing mixtures were investigated using the DSC technique (Q100 TA Instruments, New Castle, DE, USA). The DESs were analyzed in aluminum hermetic pans with nitrogen as the cooling agent at a heating rate of 5 °C/min. Standard runs at the temperature range from −90 to 250 °C. First run (heating I) from −90 to 250 °C, second one from 250 to 250 °C (cooling) and third run from −90 to 250 °C (heating II).

2.4. Preparation of TPS Films via Thermocompression (Test 1)

TPS/DES films were prepared as follows: starch and U-based mixture (35 pph per dry starch) were placed in a mortar and mixed to obtain a homogenous composition and then placed into polypropylene vial, where they were sealed and stored for 24 h at ambient conditions. The premixtures were thermocompressed with a hydraulic press (RemiPlast S.C., Czerwonak, Poland) at 140 °C and 12 tons (153 bars) for 5 min; they were then cooled down to 85 °C under pressure, after which the obtained films were stored in a climate chamber for 7 days (25 °C, RH 50%). The methodology is presented in Scheme 1 as test 1.

2.5. Preparation of TPS Films via Extrusion and Thermocompression (Test 2)

The preparation of TPS extrudates (eTPS) was performed as follows: premixtures of starch and selected plasticizing U-based eutectics were processed after 24 h storage. The systems were extruded a with laboratory twin-screw co-rotational extruder with L/D ratio 40:1, screw diameter 16 mm (PRISM Eurolab Digital). The temperature profile from the feed throat to the nozzle was 80/100 × 6/110 °Cx and the screw speed was maintained at 150 or 200 rpm. After processing, the extrudates were pelletized (granulator Prism Varicut), yielding ca. 3 mm pellets. After 14 days of storage at ambient conditions in sealed PE bags, pellets were thermocompressed at 120 °C, 12 tons, after which they were cooled down under pressure to ca. 85 °C and stored in a climate chamber (25 °C, RH 50%) for 48 h before testing. The methodology is presented in Scheme 1 as test 2.

2.6. Mechanical Tests

Mechanical tests for the films were performed using Instron 5982 (load cell 1 kN). The films (thickness 0.50–0.65 mm) were cut into 10 mm wide, 120 mm long stripes. The initial grip separation was 50 mm and the crosshead speed was set to 10 mm/min. At least eight replicated samples for each system were tested and the mechanical parameters (EB—elongation at break, TS—tensile strength and YM—Young’s modulus) were calculated with the Bluehill 3 software.

2.7. DMTA of TPS Films

The measurements of thermocompressed TPS films were carried with a film tension clamp at a frequency of 1 Hz, heating rate 3 °C/min, and a temperature range from −90 to 140 °C using Dynamic Mechanical Analyzer Q800 (TA Instruments, New Castle, DE, USA).

2.8. X-ray Diffraction Analysis of the Films

Crystallinity of the TPS films, obtained via test 1 and 2 methods, was analyzed using XRD (X’pert Pro, PANalytical, Almelo, The Netherland, operated at the CuK(alfa) wavelength 1.54 Å). The XRD analysis of the samples was repeated after 4 and 12 months of storage in ambient conditions.

2.9. FTIR-ATR Spectroscopy of the Films

FTIR analysis of films obtained via test 1 method was performed using the Nexus (Thermo-Nicolet) technique equipped with ATR. For each sample, 32 scans were taken from 4000–400 cm−1. Obtained spectra were analyzed using the OMNIC software.

2.10. Moisture Sorption and Water Sorption Degrees

For moisture sorption and swelling tests, samples with dimensions of 20 × 20 mm were prepared. The test was performed as in the previous work [37]. Samples were placed in a vacuum dryer (250 milibar) at 65 °C/24 h. The masses of dried samples, stored in a climate chamber and kept at 25 °C/50% and 75% RH (for moisture sorption evaluation) or otherwise immersed in distilled water for 24 h (for swelling behavior investigation), were determined.

2.11. Surface Contact Angle Measurements of the Films

The contact angle measurement was carried out by direct observation of a distilled water drop (2 μL) on TPS surfaces. The measurements were conducted at room temperature using Drop Shape Analyzer (DSA 100, KRÜSS GmbH—Hamburg, Germany). Values of angles were registered after 5 s (2 μL drop deposited on evaluated material surface).

2.12. Statistical Analysis

Statistical analysis of the mechanical test data for extruded samples was subjected to a one-way analysis of variance and the significant difference was determined by the significance difference test (Student’s t-test).

3. Results and Discussion

3.1. Thermal Characteristic of Urea-Based Mixtures

Before using the U-based mixtures as plasticizers, their thermal properties i.e., phase transitions (Tg—glass temperature, Tm—melting temperature, Tdeg—decomposition temperature) were investigated via the DSC technique and thermal stability was assessed via TGA. Results are presented in Table 1. The DSC results present temperatures of phase transitions for the cooling and second heating run. For mixtures with CC, increasing urea content led to an increase in Tg and Tm as well as to a decrease in the thermal stability of the DESs (Table 1, Figure 1). A similar trend was obtained when Zeng and coworkers studied DESs made with betaine and urea [28]. In Figure 1, it can be noticed that, for the DESs with higher U content, degradation runs in two steps. The first, main weight loss at range (180–200 °C), can be related to the degradation of a dissolved urea due to its lower thermal stability in the eutectic mixture [38,39]. Comparing two types of betaines monohydrate (Bh) is more thermally stable than anhydrous betaine (Ba) (Supplementary Information; Figure S1).

3.2. Mechanical Test Results for the Films Obtained via Thermocompression as Well as via Extrusion and Thermcompression

Table 2 lists results of the tensile test for the films. For choline chloride and anhydrous betaine-based plasticizing mixtures, the higher the U content in the DES is, the lower TS and YM and the higher EB values will be. It means that the higher content of urea leads to more elastic films. Generally, U-based DESs lead to highly elastic TPS films with lower TS and higher EB than starch films plasticized with a conventional plasticizer like glycerol or polyol-based DESs [5,12]. Similar results were obtained also in the work where mixtures of urea and glycerol were used as starch plasticizers [22,32]. In the case of BhU eutectics, there is decrease in mechanical properties with the increase in U content in the plasticizer. This could be caused by the lower thermal stability of these systems (Table 1). Comparing the type of ammonium compound, films with Ba-based DESs exhibited slightly better mechanical properties. This can be caused by Ba forming stronger interactions with the polymer matrix than CC.
Due to fact that the mechanical properties of TPS/BhU were the worst amongst three selected systems, as well as the fact that Bh is more expensive than Ba, CCU 1:5 and BaU 1:5 were selected for the preliminary extrusion test of starch processing in the presence of U-rich DES. The modification was performed with two screw rotation speeds: 100 and 200 rpm. The results of mechanical properties of extruded (and thermocompressed) samples are shown in Table 3. Mechanical properties of starch, plasticized with DES at the highest molar ratio of urea, were similar to samples obtained only via the direct thermocompression of starch/DES premixtures (Table 2). A slight difference in decrease in EB values can be caused by shearing forces, leading to a lower molecular weight of the polymer [40]. However, for higher rotational speeds, slightly better mechanical properties were obtained. This can be a result of the better mixing of TPS components and a good distribution of the plasticizer in the polysaccharide matrix.

3.3. DMTA Results for TPS Films Obtained via Thermocompression (Test 1)

The values of the storage modulus (E’) and the tangent of the loss angle (tanδ), depending on the temperature, were determined via DMTA. Tan δ curves for TPS/CCU (Figure 2A) and for the TPS/BaU films revealed three relaxation effects. The first, attained at the low temperature range (from −60 to 0 °C), is related to β-relaxation of the movement of a small size-plasticizer that is bonded with the polysaccharide chains via hydrogen bonds. The second region (for TPS/CCU ca. 30 °C and for TPS/BaU for max tan δ peak) is assigned to α-relaxation of more mobile, thermally modified starch chains. Analyzing the TPS, the third α’-relaxation (ca. 120 °C for max tan δ peak) is only observed for TPS films with the presence of dissolving plasticizers (DES based on U) so that it can be associated with a dissolved fraction of the polysaccharide by DES [5,22,41]. For CCU, the intensity of this peak increased with the increase in U content, and it also seems that α-relaxation is shifted towards α’-relaxation. This could be related to increased dissolving activity of this DES with higher U content [22]. In the case of TPS/CCU films, the temperature of β-relaxation increased with the increase in U content in the DES (peak maximum for TPS/CCU 1:2 is at ca. −39 °C and for TPS/CCU 1:5 at ca. −23 °C). This can be related to greater differences in Tg for CCU than for BaU (Table 1).
Comparing the storage modulus curves, there are also differences between TPS with different plasticizers, and they are more visible for samples with CCU. The higher the content of U in the film is, the higher the temperature of a drop of E’ for TPS/CCU value will be (Figure 2B). The drop of E’ value for TPS/CCU 1:2 is at 6 °C and for TPS/CCU 1:5 is at 32 °C. The differences in drop of E’ during heating are not so distinctive and all samples exhibited decreasing E’ at ca. 20 °C. This drop in E’ is related to glass transition of starch-rich fraction. A low storage modulus at higher temperatures indicated that the TPS materials, plasticized with the eutectics, are susceptible to thermoformation via e.g., compression molding, independently of the urea content.

3.4. XRD Results for TPS/DES Films Obtained via Thermocompression and Extrusion and Thermocompression (Test 1 and 2)

The starch structure was modified dramatically after thermal processing in the presence of plasticizing mixtures. Native potato starch granules exhibit characteristic peaks at 5.4, 17.1, 19.5, 22.5, 24.0 and 26.0°, forming B-type semi-crystallinity [5]. As we can observe from Figure 3 after processing in the presence of the DESs, all these peaks were flattened, indicating a highly amorphous structure independently of the processing method. It corresponds with high EB values (Table 2) related to a higher mobility of the amorphous structure of the polysaccharide. In the case of CCU mixtures, there is a slight difference in the diffractograms regarding the dependence of U content it can be noticed whereby the higher urea content is, the smoother the pattern of the sample becomes. The analysis was repeated after a certain time period of storage at ambient conditions. After 4 months of storage, there was no difference in the diffractogram. However, after 1 year, there was a barely noticeable peak at 16.8° that came from B-type crystals corresponding to the {1 2 1} crystal face (Figure 3B) [19,42]. Comparing types of DES, for TPS with CCU eutectics, there is also a barely visible peak at ca. 17°. However, this peak is not present in the extruded sample (eTPS), meaning that extrusion led to a more amorphous structure due to the presence of mixing and shear forces during processing. It corresponds with mechanical tests, where higher EB values indicated higher mobility of polysaccharide chains due to their highly amorphous structure.

3.5. FTIR-ATR Results for TPS/DES Films Obtained via Thermocompression (Test 1)

FTIR-ATR spectroscopy results for DES, starch and thermoplasticized starch with DES are presented in Figure 3. The analysis was performed to investigate if some derivatization of starch occurred. In Figure 4A, there is a comparison of the TPS plasticized with CCU 1:5 with the unmodified starch. For the TPS there is a band of bending N-H (amide-II region) with a peak at 1624 cm−1 and stretching C-N (amide-II region) groups at 1458 cm−1, originating from U in DES. In the TPS, there is a shift in these peaks towards higher wave numbers in comparison with the DES due to a weakening of hydrogen bonds between DES component and the formation of new bonds with the polysaccharide OH groups [5]. There are no new peaks for TPS plasticized with all the CC-based eutectics with different U contents (data not shown). Figure 4B shows the comparison of TPS plasticized with anhydrous betaine and urea with native starch and the plasticizing eutectic.
Starch, thermoplasticized with BaU mixture, exhibits a band of bending N-H (amide-II region) with a peak at 1618 cm−1 and stretching C-N (amide-II region) groups at 1456 cm−1, originating from U in DES. Moreover, there is a new band at 1732 cm−1 for DES at 1:3, 1:4 and 1:5 molar ratios of Ba and U associated with a formation of stretching carbamate groups in the base of urethane [35]. Thus, the polysaccharide underwent derivatization with urea from BaU mixtures during thermoprocessing.

3.6. Behavior in Water and Contact Angle Determination Results for TPS Films Obtained via Thermocompression and Extrusion and Thermocompression (Test 1 and 2)

The behavior in water of starch plasticized with U-based DES is different than the TPS prepared with a conventional plasticizer like glycerol (Table 4).
Due to the highly amorphous structure of TPS/DES materials, their dissolving ability towards polysaccharide and the hygroscopic character of plasticizer, their swelling degree is much higher than that of, e.g., TPS/glycerol, or TPS a with non-dissolving DES [5]. The swelling degree of TPS with CC is lower (154–253%) than that with Ba (371–589%). It can be caused by the presence of a carboxyl group in betaine [37]. Moreover, as FTIR results reveal the occurrence of starch, carbamation can increase the polysaccharide hydrophilicity [43,44]. For CCU mixtures there is no relation between swelling or dissolving degree. However, for BaU the higher urea content in the material is, the higher the swelling and dissolving degrees will be. The samples obtained via extrusion (eTPS) defragmented in water, due to their higher hydrophilicity than thermocompressed TPS, caused there to be a higher amorphous structure and better distribution of the plasticizer in the polymer matrix.
Surface contact angle measurement results indicate that both types of ammonium salt, as well as urea content in the DES, affect the parameter. For TPS with CC, the higher U content is, the higher contact angle of the film surface will be. Similar results were also obtained for TPS with U/glycerol mixtures [22]. However, for samples with Ba, there is no linear relation with the urea content. Comparing thermocompressed and extruded samples, eTPS exhibits higher values of the parameter.

4. Conclusions

Thermoplastic starch with urea-rich eutectic mixtures was obtained via thermal processing. DESs prepared with choline chloride or betaine with different U content were thermally characterized before starch modification. DSC and TGA analyses indicated that the higher U content in the eutectic mixture is, the higher the phase transition temperature (glass and melting temperatures) and the lower the thermal stability of the DESs will be. The larger the increase in U content in the plasticizer, the lower the tensile strength and higher the elongation at break will be, as the mechanical test results showed. XRD analysis of the TPS indicated that the tested plasticizing mixtures led to highly amorphous structure of the polysaccharide. FTIR results indicated that starch underwent the derivatization via carbamate formation with U in the mixtures with betaine, which could lead to higher sorption degree of TPS with B-based DESs. TPS presented in this work was obtained from cheap and abundant sources and can be used as an ecofriendly alternative for agricultural plastics. Moreover, due to the use of urea-based DESs as a plasticizer, it can be the source of the fertilizer in the multifunctional materials.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/app13031383/s1, Figure S1: TGA and DTG curves for DESs: CCU 1:5, BaU 1:5, BhU 1:5.

Funding

This research was funded by The National Centre of Science and Development (Poland), TANGO-V-A/0047/2021-00. Project’s title: “Development of multifunctional biodegradable polysaccharides-based materials intended for plants cultivation”.

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.

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Applsci 13 01383 sch001 550
Scheme 1. TPS plasticized with U-rich DES via thermocompression (test 1) and extrusion and then thermocompression (test 2).
Scheme 1. TPS plasticized with U-rich DES via thermocompression (test 1) and extrusion and then thermocompression (test 2).
Applsci 13 01383 sch001
Applsci 13 01383 g001 550
Figure 1. DMTA curves (A) Tan δ for TPS/CCU; (B) Tan δ for TPS/BaU and (C) Storage modulus − E’ for TPS/CCU; (D) Storage modulus − E’ for TPS/CCU; The analysis was performed on thermocompressed TPS films.
Figure 1. DMTA curves (A) Tan δ for TPS/CCU; (B) Tan δ for TPS/BaU and (C) Storage modulus − E’ for TPS/CCU; (D) Storage modulus − E’ for TPS/CCU; The analysis was performed on thermocompressed TPS films.
Applsci 13 01383 g001
Applsci 13 01383 g002 550
Figure 2. DMTA curves (A) Tan δ for TPS/CCU; (B) Tan δ for TPS/BaU and (C) Storage modulus − E’ for TPS/CCU; (D) Storage modulus − E’ for TPS/CCU; The analysis was performed on thermocompressed TPS films.
Figure 2. DMTA curves (A) Tan δ for TPS/CCU; (B) Tan δ for TPS/BaU and (C) Storage modulus − E’ for TPS/CCU; (D) Storage modulus − E’ for TPS/CCU; The analysis was performed on thermocompressed TPS films.
Applsci 13 01383 g002
Applsci 13 01383 g003 550
Figure 3. XRD patterns for the films plasticized with DESs: (A) based on CC with different U content; (B) TPS/CCU 1:5 after storage at ambient conditions; (C) based on Ba with different U content.
Figure 3. XRD patterns for the films plasticized with DESs: (A) based on CC with different U content; (B) TPS/CCU 1:5 after storage at ambient conditions; (C) based on Ba with different U content.
Applsci 13 01383 g003
Applsci 13 01383 g004 550
Figure 4. FTIR-ATR spectra for potato granular starch, DES and: (A) DES CCU 1:5 and TPS plasticized with this DES; (B) DES BaU at 1:2 and 1:5 molar ratio and TPS plasticized with BaU 1:5.
Figure 4. FTIR-ATR spectra for potato granular starch, DES and: (A) DES CCU 1:5 and TPS plasticized with this DES; (B) DES BaU at 1:2 and 1:5 molar ratio and TPS plasticized with BaU 1:5.
Applsci 13 01383 g004
Table
Table 1. Thermal properties of DESs with different urea content.
Table 1. Thermal properties of DESs with different urea content.
SampleAmmonium Compund: U Molar RatioDSCTGA
Tf [°C]Tdeg [°C]TdegDTAmax
TPS/CCU 1:21:2Tg -67; Tm 5; 169182260
TPS/CCU 1:31:3Tg -48; Tm 12168144254
TPS/CCU 1:41:4Tg Tm 62; Tcc -14186138250
TPS/CCU 1:51:5Tg -11; 86; Tc 31171125244
TPS/BaU 1:21:2Tg -19; Tm 106, Tcc 37167180254
TPS/BaU 1:31:3Tg -22; Tm 100; Tcc 51166150245
TPS/BaU 1:41:4Tg -30; Tm 88 Tcc 55166148241
TPS/BaU 1:51:5Tg -20; Tm 107; Tcc 57168131237
TPS/BhU 1:21:2Tm 91147177246
TPS/BhU 1:31:3Tg -22; Tm 76130161245
TPS/BhU 1:41:4Tg -24; Tm 88136155245
TPS/BhU 1:51:5Tg -18; Tm 101139144247
Tc—crystallization temperature, Tcc—cold crystallization temperature, Tg—glass temperature, Tm—melting temperature.
Table
Table 2. Mechanical properties of TPS films obtained via thermocompression directly from the premixture (test 1) plasticized with U-based eutectics (YM—Young’s modulus, TS—tensile strength, EB—elongation at break).
Table 2. Mechanical properties of TPS films obtained via thermocompression directly from the premixture (test 1) plasticized with U-based eutectics (YM—Young’s modulus, TS—tensile strength, EB—elongation at break).
SampleYM
[MPa]		TS
[MPa]		EB
[%]		Thickness
[mm]
TPS/CCU 1:232 (±1.6)2.2 (±0.1)119 (±2.2)0.62 (±0.01)
TPS/CCU 1:312 (±0.6)1.7 (±0.3)131 (±9.2)0.58 (±0.02)
TPS/CCU 1:415 (±4.0)1.6 (±0.2)125 (±8.4)0.60 (±0.02)
TPS/CCU 1:522 (±6.9)1.8 (±0.3)190 (±27.0)0.63 (±0.05)
TPS/BhU 1:2156 (±22.7)3.8 (±0.09)74 (±11.6)0.60 (±0.02)
TPS/BhU 1:380 (±22.3)3.2 (±0.29)80 (±9.8)0.57 (±0.01)
TPS/BhU 1:477 (±7.8)2.3 (±0.30)64 (±17.6)0.55 (±0.03)
TPS/BhU 1:574 (±22.6)2.0 (±0.28)49 (±9.3)0.57 (±0.00)
TPS/BaU 1:270 (±15.8)3.3 (±0.20)117 (±2.8)0.56 (±0.06)
TPS/BaU 1:330 (±8.9)2.2 (±0.17)141 (±24.1)0.56 (±0.04)
TPS/BaU 1:440 (±9.8)2.5 (±0.21)159 (±5.0)0.54 (±0.02)
TPS/BaU 1:562 (±9.4)3.0 (±0.38)181 (±8.8)0.60 (±0.06)
Table
Table 3. Mechanical properties of TPS films obtained via extrusion and thermocompression (test 2).
Table 3. Mechanical properties of TPS films obtained via extrusion and thermocompression (test 2).
SampleExtrusion Parameters
[°C/rpm]		YM
[MPa]		TS
[MPa]		EB
[%]
eTPS/CCU 1:5110/10022 (±2.3)1.8 (±0.10)170 (±12.2)
eTPS/CCU 1:5110/20024 (±2.1)2.0 (±0.10)188 (±9.3)
eTPS/BaU 1:5110/10062 (±13.1)2.5 (±0.24)96 (±23.9)
eTPS/BaU 1:5110/20091 (±14.5)2.9 (±0.17)166 (±17.6)
Table
Table 4. Swelling and solubility degrees as well as surface contact angle values of TPS films obtained via thermocompression (TPS) and extrusion and then thermocompression (eTPS).
Table 4. Swelling and solubility degrees as well as surface contact angle values of TPS films obtained via thermocompression (TPS) and extrusion and then thermocompression (eTPS).
SampleSwelling
Degree [%]		Solubility Degree
[%]		Contact Angle
[°]
TPS/CCU 1:2253 (±30.6)23.7 (±0.4)69 (±2.9)
TPS/CCU 1:3154 (±11.7)22.3 (±1.2)66 (±2.7)
TPS/CCU 1:4165 (±8.5)22.6 (±1.2)72 (±3.6)
TPS/CCU 1:5209 (±30.1)21.4 (±1.1)76 (±4.3)
TPS/BaU 1:2371 (±34.4)24.7 (±5.8)60 (±4.3)
TPS/BaU 1:3436 (±30.9)27.2 (±1.3)90 (±6.7)
TPS/BaU 1:4589 (±30.9)32.0 (±4.2)82 (±7.8)
TPS/BaU 1:5426 (±33.8)32.5 (±5.0)68 (±7.4)
eTPS/CCU 1:5 110/100gelled/defragemented95 (±4.0)
eTPS/CCU 1:5 110/20097 (±8.5)
eTPS/BaU 1:5 110/10093 (±4.2)
eTPS/BaU 1:5 110/20072 (±8.2)
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Zdanowicz, M. Influence of Urea Content in Deep Eutectic Solvents on Thermoplastic Starch Films’ Properties. Appl. Sci. 2023, 13, 1383. https://doi.org/10.3390/app13031383

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Zdanowicz M. Influence of Urea Content in Deep Eutectic Solvents on Thermoplastic Starch Films’ Properties. Applied Sciences. 2023; 13(3):1383. https://doi.org/10.3390/app13031383

Chicago/Turabian Style

Zdanowicz, Magdalena. 2023. "Influence of Urea Content in Deep Eutectic Solvents on Thermoplastic Starch Films’ Properties" Applied Sciences 13, no. 3: 1383. https://doi.org/10.3390/app13031383

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