Next Article in Journal
The Effect of d10 Precious Elements on Structural, Magnetic and Elastic Properties of MnPt Alloy: A First-Principles Study
Next Article in Special Issue
Continuous CF/PA6 Composite Aircraft Window Frame Manufactured via a Novel Winding Compression Process
Previous Article in Journal
Development of a Binderless Particleboard from Brown Seaweed Sargassum spp.
Previous Article in Special Issue
Effects of Peroxide and Sulfur Curing Systems on Physical and Mechanical Properties of Nitrile Rubber Composites: A Comparative Study
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Materials
Volume 17
Issue 3
10.3390/ma17030540
materials-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 thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Biodegradable Nanocomposites Based on Blends of Poly(Butylene Adipate–Co–Terephthalate) (PBAT) and Thermoplastic Starch Filled with Montmorillonite (MMT): Physico-Mechanical Properties

by
Hamed Peidayesh
1,
Leoš Ondriš
2,
Simona Saparová
2,
Mária Kovaľaková
2,
Oľga Fričová
2 and
Ivan Chodák
1,*
1
Polymer Institute of the Slovak Academy of Sciences, Dúbravská Cesta 9, 845 41 Bratislava, Slovakia
2
Department of Physics, Faculty of Electrical Engineering and Informatics, Technical University of Košice, Park Komenského 2, 042 00 Košice, Slovakia
*
Author to whom correspondence should be addressed.
Materials 2024, 17(3), 540; https://doi.org/10.3390/ma17030540
Submission received: 26 November 2023 / Revised: 1 January 2024 / Accepted: 8 January 2024 / Published: 23 January 2024
(This article belongs to the Special Issue Multiphase Systems with Polymeric Matrices: Polymer Blends and Composites II)
Browse Figures
Versions Notes

Abstract

:
Poly(butylene adipate–co–terephthalate) (PBAT) is widely used for production of biodegradable films due to its high elongation, excellent flexibility, and good processability properties. An effective way to develop more accessible PBAT-based bioplastics for wide application in packaging is blending of PBAT with thermoplastic starch (TPS) since PBAT is costly with prices approximately double or even triple the prices of traditional plastics like polyethylene. This study is focused on investigating the influence of TPS/PBAT blend ratio and montmorillonite (MMT) content on the physical and mechanical properties and molecular mobility of TPS–MMT/PBAT nanocomposites. Obtained TPS–MMT/PBAT nanocomposites through the melt blending process were characterized using tensile testing, dynamic mechanical thermal analysis (DMTA), and X-ray diffraction (XRD), as well as solid-state 1H and 13C NMR spectroscopy. Mechanical properties demonstrated that the addition of TPS to PBAT leads to a substantial decrease in the tensile strength as well as in the elongation at break, while Young’s modulus is rising substantially, while the effect of the MMT addition is almost negligible on the tensile stress of the blends. DMTA results confirmed the formation of TPS domains in the PBAT matrix. With increasing TPS content, mobility of starch-rich regions of TPS domains slightly increases. However, molecular mobility in glycerol-rich regions of TPS domains in the blends was slightly restricted. Moreover, the data obtained from 13C CP/MAS NMR spectra indicated that the presence of TPS in the sample decreases the mobility of the PBAT chains, mainly those located at the TPS/PBAT interfaces.

1. Introduction

Biodegradable plastics from renewable resources have attracted much attention in the last two decades due to increasing concern about the serious negative effects of fossil-based plastics on the ecological environment [1]. Starch has been considered as one of the most promising biodegradable polymers owing to its abundant availability, low cost, and production from renewable resources [2,3,4]. It is necessary to make the starch processable using standard techniques since native starch degrades before reaching melting point, which is well above 200 °C, due to strong intermolecular hydrogen bonds [5]. Therefore, thermoplastic starch (TPS) is obtained by the incorporation of plasticizers such as glycerol, sorbitol, urea, etc., at higher temperatures, applying shear force [6,7,8,9]. However, TPS exhibits poor mechanical properties caused mainly due to moisture absorption related to the hydrophilic nature of starch and recrystallization phenomena which are observed after a longer time of storing [10].
Many strategies have been developed to improve the performance of starch-based materials [11,12]. As mentioned above, TPS suffers from retrogradation and recrystallization. An effective approach to improve the mechanical properties consists of blending TPS with hydrophobic biodegradable plastics such as polyhydroxyalkanoate (PHA) [13,14], poly(lactic acid) (PLA) [15,16], poly(ε–caprolactone) (PCL) [17,18], and poly(butylene adipate–co–terephthalate) (PBAT) [19,20,21,22]. Among all of these polymers which are mixed with TPS, a biodegradable copolyester, PBAT, has attracted great attention since its physical and mechanical properties are similar to those of polyethylene [23,24]. However, the poor compatibility between the hydrophilic TPS and hydrophobic PBAT makes the PBAT/TPS blends not so easy to prepare, and especially, their application properties are changing in many cases [25]. Interestingly, some studies reported that inorganic fillers such as sodium montmorillonite (NaMMT) and zeolite could enhance the compatibility between TPS and hydrophobic plastics such as PLA [26] and PE [27], which avoids some of the drawbacks of using compatibilizers containing maleic anhydride due to its potential toxicity.
On the other hand, another common approach to increase the mechanical strength and stiffness is the addition of reinforcing nanoparticles [28,29,30]. In this regard, reinforcing fillers not only could enhance the mechanical properties but also act as compatibilizers between the polymers. The most recent research is focused on montmorillonite (MMT) due to its well-controlled chemical properties, availability, and versatility towards the environment and health. MMT, a layered silicate, forms an intercalated structure by penetration of large organic molecules inside the interlayer space of the nanofiller forming so-called organomodified nanoparticles [31]. During further processing, applying shear stress, the organomodified MMT particles decompose to individual layers with an extremely high surface area [8,32,33] which can be dispersed in the TPS matrix independently, forming exfoliated MMT nanoparticles [34]. A high surface area is the basis for the extensive changes in physical properties. The incorporation of inorganic fillers such as MMT and sepiolite nanoclays into TPS/PBAT blends has been reported in the literature [35,36]. However, these studies have investigated only the tensile and thermal properties of the nanocomposites. To the best of our knowledge, there are no reports on investigating the physical and mechanical properties, structure, and molecular mobility of nanocomposites based on blends of PBAT and TPS filled with MMT. By appropriate blending of PBAT with TPS, a material with desired properties and a competitive price can be achieved [37].
The main goal of the present work was to evaluate the influence of the TPS/PBAT blend ratio and MMT content on the physical and mechanical properties and molecular mobility of TPS–MMT/PBAT nanocomposites. In the context of this work, the TPS–MMT/PBAT nanocomposites were characterized using tensile testing, dynamic mechanical thermal analysis (DMTA), and X-ray diffraction (XRD), as well as solid-state 1H and 13C NMR spectroscopy. The aim of this publication is to obtain general information on possibilities to modify properties of the PBAT/TPS mixture by modification of the TPS. The hypothesis assumes that if one of the major components will improve its ultimate properties, this should also positively affect the performance of the final blend. Since the tensile strength of the PBAT/TPS mixture is decreasing compared to the virgin PBAT material, the introduction of reinforcing fillers to the TPS should contribute to higher strength and, possibly, also to other parameters, e.g., water/moisture uptake and stability of the properties during storage. Moreover, the addition of TPS as an inexpensive biodegradable component results in a substantial decrease in the price of the final mixture, making the biodegradable blend economically more competitive compared to, e.g., polyethylene, in spite of the necessity to accept a certain decrease in the ultimate properties of the product.

2. Materials and Methods

2.1. Materials

Native corn starch Meritena® 100 was provided by Brenntag (Bratislava, Slovakia). Its water content was around 12 wt% as determined by drying in the oven at 100 °C for 5 h. Poly(butylene adipate–co–terephthalate) (PBAT), grade Ecoworld™ 003 with MFI < 5 (according to DIN ISO 1133 [38] at 190 °C and 2.16 kg), was supplied by Jinhui Zhaolong Co. (Shanxi Xiaoyi, China). Natrified montmorillonite (Cloisite® Na+) with a cationic exchange capacity range of 80–95 mequiv/100 g was purchased from Southern Clay Products (Gonzales, TX, USA). Glycerol was obtained from Centralchem, Ltd. (Bratislava, Slovakia). Double distilled water was used for the preparation of all solutions.

2.2. Preparation of TPS–MMT/PBAT Nanocomposites

First, TPS–MMT samples were prepared as follows. Cloisite Na (MMT) particles at content of 2 and 5 php (parts per 100 parts of polymer, based on the dry weight of starch) were dispersed in a mixture of water and glycerol by mechanical mixing at ambient temperature for 5 min. The suspension of starch, MMT, glycerol, and water was continuously mechanically stirred at 80 °C for 10 min. The weight ratio of starch/glycerol/water was 1.0:0.5:2.3. Then, the suspension was dried in the oven at 100 °C for 5 h, and it was left overnight at 60 °C to prevent moisture absorption. Then, TPS–MMT materials (containing MMT when appropriate) were processed in a laboratory mixer Plastograph Brabender PLE 331 for 10 min at 130 °C and 100 rpm (rounds per minute). Afterward, the obtained TPS–MMT materials were blended with PBAT in different ratios 10/90, 20/80, and 30/70 in another chamber for 10 min at 130 °C and 100 rpm. The slabs around 1 mm thick were prepared through compression molding (laboratory press, Fontijne TP 50, Delft, The Netherlands) at 130 °C using 2 min preheating without pressure and an additional 2 min at a pressure of 2.65 MPa. The obtained samples were stored in airtight plastic containers for 48 h at ambient conditions before performing characterizations.

2.3. Mechanical Properties

The tensile properties of the nanocomposites were measured at room temperature using an Instron 3365 universal testing machine (Instron, Norwood, MA, USA) at cross-head speed of 50 mm·min−1 in uniaxial deformation. According to the standard ASTM D638 [39], the dog-bone testing specimens with the dimensions of the deformed area 3.5 × 30 mm2 and thickness of approximately 1 mm (exactly measured by micrometer before testing) were used. The mean values and standard deviations were calculated from seven specimens for all parameters.

2.4. Dynamic Mechanical Thermal Analysis (DMTA)

DMA measurements of the nanocomposites were carried out using a DMA Q800 (TA Instruments, New Castle, DE, USA). The samples (ca. 30 × 6 × 1 mm3) were measured at a frequency of 5 Hz and an amplitude of 5 μm in tensile mode with a heating rate of 2 °C·min−1.

2.5. X-ray Diffraction (XRD)

XRD measurements were taken on a MiniFlex600 XRD analyzer (Rigaku, Tokyo, Japan). The XRD was performed using the theta–2theta method at a voltage of 40 kV and a current of 15 mA. Cu Kα X-rays with wavelength λ = 0.154 nm were used. The sample and the detector rotated at 2.5°/min and 5°/min, respectively.

2.6. Nuclear Magnetic Resonance (NMR)

The samples were cut into small pieces and filled into 4 mm ZrO2 rotors. NMR spectra were acquired on a 400 MHz Varian spectrometer (Palo Alto, CA, USA) at room temperature. 1H NMR spectra were performed on static samples as well as using the magic angle spinning technique (MAS NMR spectra) with a MAS rate of 10 kHz. The π/2 pulse duration was 2.9 μs, the spectra were detected with a delay of 10 s and acquisition time of 20 ms, and 32 scans were accumulated for the final spectra. 1H BL NMR spectra were measured using Chen’s method [40]. 13C CP/MAS NMR measurements were performed using cross-polarization (CP) and MAS techniques simultaneously with a MAS rate of 10 kHz. Cross-polarization contact time was 2 ms, acquisition time 40 ms, power heteronuclear decoupling 52 kHz, delay time was 10 s, and 10,000 scans were accumulated. Adamantane was used for the calibration of 1H and 13C chemical shifts. The measured spectra were processed using Mestrelab Research Mnova 9.0 software.

3. Results and Discussion

3.1. X-ray Diffraction (XRD)

XRD measurements were carried out to detect crystalline features in the sample structure and their changes during storage. Figure 1a shows the diffractogram of samples without nanofiller and pure TPS and PBAT samples. The PBAT diffractogram (Figure 1a; black curve) shows diffraction maxima at 2theta ≈ 16°, 17.1°, 20.1°, 22.8°, and 24.5°, which correspond to the crystalline domains of PBAT [41]. In the diffractogram of the TPS sample (Figure 1a; pink curve), a small peak at position 2theta ≈ 13.2° and a pronounced maximum at 2theta ≈ 20.4° appear corresponding to the TPS crystalline structures of the VA-type [42,43]. As the TPS content in the investigated blends increases, the peak for the VA-type TPS crystalline structures at 2theta ≈ 20.4° becomes more pronounced. Comparing the TPS/PBAT blends (Figure 1a; red, green, and blue curves), a decrease in the intensities of PBAT diffraction maxima are observed with decreasing PBAT content. Higher and narrower peaks at higher PBAT contents indicate better ordering of the PBAT crystalline domains since TPS can limit formation of crystalline domains in blends. The diffractograms for TPS/PBAT blends are more similar to the diffractogram of PBAT than TPS, which is due to the prevailing PBAT content.
Figure 1b shows diffractograms of a 10 TPS to 90 PBAT mixture without MMT (black curve) and with 2% MMT (red curve) and 5% MMT (green curve). Diffractograms do not differ much from each other. The addition of MMT nanoparticles (at low TPS content) has no significant effect on the crystalline phase in the blends.
Diffractograms of TPS/PBAT mixtures at a 20 to 80 ratio show almost identical diffractograms (Figure 1c) regardless of whether they are without MMT or containing 2 or 5 parts of MMT (related to the starch content). The sample containing 5 php of MMT was measured up to 4 days after preparation and may partially crystallize during that time. The fact that the maxima at 2theta ≈ 22.8° and 24.5° show higher intensities compared to the samples without MMT or containing 2 php of MMT supports this assumption. At the same time, a new diffraction maximum at position 2theta ≈ 4.8° corresponding to the intercalated MMT appears in the diffractogram of the sample with 5 php of MMT [44]. The fact that this maximum was not observed with 2 php MMT and in samples with a TPS/PBAT ratio 10 to 90 may indicate that MMT particles were exfoliated, or (more likely) that due to a low TPS/PBAT ratio and resulting low MMT content, XRD could not detect the MMT structure due to the insufficient size of crystalline structures [45].
A slightly different pattern is observed in the diffractogram of samples with a 30/70 TPS/PBAT ratio (Figure 1d). Similar to the 20/80 ratio sample, we also observe a diffraction maximum for the 2theta ≈ 4.8° position related to the intercalated MMT. This maximum is higher and broader compared to the 20/80 TPS/PBAT ratio with the 5 php of MMT sample, probably due to the higher MMT content in the blend.

3.2. Mechanical Properties

Standard mechanical properties are the most important data regarding any application of plastic-based materials. Generally, by the addition of TPS to PBAT, an increase in brittleness and a decrease in elongation at break can be expected. The ultimate mechanical properties of the TPS–MMT/PBAT nanocomposites are presented in Table 1. It is seen that the tensile strength and elongation at break of the blends exhibit a significant decrease with the addition and rising amount of TPS. This indication is ascribed to low tensile strength and elongation at break of TPS. Moreover, the increase in TPS content results in a monotonous increase in Young’s modulus, indicating the hard and brittle nature of the TPS [46]. The tendency of the modulus to increase is confirmed also by data from DMTA which were taken from curves of storage modulus (E′) at the temperature of 20 °C corresponding roughly to the conditions of tensile properties determination (Table 2).
Considering the incorporation of MMT, the tensile strength of the nanocomposites is decreasing by the addition of 2% MMT, while the tensile strength of the blends with 5% MMT are more or less the same as the samples containing 2% MMT. This observation can be explained by the formation of an exfoliated structure at higher MMT contents [47]. On the other hand, Young’s modulus is increasing with the increase in the MMT content. This increase in modulus may be caused by the increase in the number of exfoliated MMT sheets and, consequently, the reinforcing effect. As expected, the elongation at break of the blends decreased with the addition of MMT nanoparticles.
The more detailed analysis of the data in Table 1 is supported by Figure 2, where stress–strain curves are shown. Except for neat TPS, all curves have the same shape, without local maximum, indicating a yield point in the region after the initial Hookean-type of deformation (straight line at the beginning of stress–strain curve corresponding to the Hooke law stating that the force is proportional to the extension). This is somewhat unusual, especially for neat PBAT, which would be expected to behave similarly to polyethylene with a clear peak at the yield point.
Neat TPS behaves as a typical brittle material with a plasticizer content, exhibiting high Young’s modulus and low deformation at break. Mixtures of PBAT with TPS demonstrate a similar tendency, showing a decrease in elongation at break with rising TPS content. At the same time, the tensile strength also decreases, especially because of the lower elongation so that considering a similarity in the stress–strain curves, breaking the specimen at lower deformation, at break results also in lower tensile stress. However, considering the ratio ε/σ of elongation and tensile stress, it is seen that the data for a particular TPS/PBAT ratio ε/σ are the same when changing the MMT content from 0 to 5, but the ε/σ is rising if the composition of the polymers is increasing from TPS/PBAT 10/90 to 20/80, and 30/70 (ε/σ = 33 ± 0.3, 36.3 ± 1.1, and 43.7 ± 0.6, respectively). This indicates that the effect of the MMT addition is almost negligible on the tensile stress. Similar behavior is observed also for the addition of MMT to starch on Young’s modulus values. The effect is only marginal, if any. The reason may consist in the way of mixing, where the MMT is dispersed in the plasticizer before being mixed into the starch. By using such a method, it was expected that MMT particles would exfoliate to a greater extent but, obviously, at the same time, they created interactions with the plasticizer so that the surface of reinforcing MMT was be deactivated to certain extent.

3.3. Dynamic Mechanical Thermal Analysis (DMTA)

DMA analysis detects temperature-induced transitions in the investigated materials demonstrated as a distinct decrease in the temperature dependence of storage modulus E′, representing stored energy in one cycle of sample deformation, and as local maxima in the temperature dependences of the loss modulus E″ determining the dissipated energy in one cycle of sample deformation and the loss factor tanδ equal to E″/E′.
Relaxation transitions in polymers are associated with an increase in the molecular mobility. When the polymer system is in the glassy state, only vibrational and rotational motions of atoms and short segments can take place, while with increasing temperature, adjacent group motion is activated, then segmental motion is allowed, and at a sufficiently high temperature, a large-scale chain slippage occurs. During relaxation transitions, the energy is dissipated into the polymer system which results in thermal motion accompanied by the decrease in storage modulus and local maxima in the tanδ temperature dependence indicating a significant rearrangement of the polymer chains [48,49].
The loss factor tanδ temperature dependence of the PBAT sample (Figure 3a; black curve) shows a maximum at −19.6 °C [50], corresponding to a glass transition in the amorphous PBAT domains. Below this temperature, the movement of the macromolecule segments consists only in vibration or rotation, while at temperatures above Tg, the segments can also change their position. Therefore, the polymeric material changes from a hard and brittle substance (in the glassy state) to a highly elastic one (in the rubbery state) as movement of the chain segments is promoted with the temperature increase. Another relaxation transition is observed above 120 °C when overall chain mobility is enhanced due to melting of PBAT crystalline domains. In the case of the TPS sample (Figure 3a; pink curve), two distinct maxima related to the glass transitions in the plasticizer (glycerol)-rich (at −46 °C) and in the starch-rich regions (above 0 °C) are evident. Two separate relaxation transitions, present within the broad maximum above 0 °C, can be assigned to segmental motion of the linear amylose chains (at 40 °C) and the branched amylopectin chains (at 63 °C) [51,52]. In these domains, segmental motion of the amylose and amylopectin chains take place, respectively. The glass transition temperature for the segmental motion of amylose chains is observed (usually) at lower temperatures than in the case of amylopectin. If we observe only one wide maximum for starch-rich domains on the temperature dependence of the loss factor tanδ, this may indicate a possible overlap of the glass transitions of the segmental motion of the amylose and amylopectin chains [52]. We see such a possible scenario in the graphs of Figure 3a,c,d. The most pronounced maximum for starch-rich domains is for blends with a 30/70 TPS/PBAT ratio (Figure 3d). In general, PBAT and TPS are immiscible polymers, and therefore, four relaxation transitions can be expected for the TPS/PBAT blends. The loss factor tanδ temperature dependence of all investigated blends (Figure 3a–d) shows a maximum around −20 °C, corresponding to glass transition in amorphous PBAT domains. Differences in the glass transition temperatures for PBAT in TPS/PBAT blends are in the range of ±1 °C, which is within the scatter of the measurements. In the case of TPS/PBAT blends, melting at lower temperatures was observed compared to the virgin PBAT sample, probably due to the continuous PBAT matrix being distorted by the presence of the TPS domains.
Comparing the blends with different TPS/PBAT ratios (Figure 3a), two relaxation transitions (at −41 °C and 30 °C) can be clearly seen for the blend of a TPS/PBAT ratio of 30/70 (Figure 3a; blue curve), related to glycerol-rich and starch-rich regions, respectively. These maxima are less pronounced and shifted to slightly lower temperatures (at −44 °C and 20 °C) for the ratio of 20/80 (Figure 3a; green curve). This indicates a slightly higher mobility of the chains in the TPS domains. Relaxation transitions in TPS domains are not seen at the temperature dependence on the loss factor tanδ for the TPS/PBAT ratio of 10 to 90 (Figure 3a, red curve) due to the lower TPS content.
By comparing the temperature dependences of TPS/PBAT blends (Figure 3b–d) with the same TPS/PBAT ratio (10/90, 20/80 and 30/70) and different MMT content, it is seen that the curves are (almost) identical. In the case of blends with a ratio of 10/90 (Figure 3b), only glass transition and melting of PBAT chains are observed due to the low TPS content. In the case of the blends with a 20/80 TPS/PBAT ratio (Figure 3c), glass transition for glycerol-rich domains and starch-rich domains can already be observed. As the MMT content increases, minor changes also occur. The glass transition temperature for starch-rich domains decrease from about 20 °C to 15 °C for a TPS/PBAT ratio of 20/80 without MMT and with 5 php MMT, respectively. For TPS containing 2 php MMT, the glass transition temperature cannot be accurately determined. The glass transition temperature for the glycerol-rich regions also decrease to lower temperatures. The temperature dropped from −42 °C, through −45 °C to −49 °C for rising MMT content in the TPS/PBAT mixture of 20/80. A similar trend as in the case of the blends with a TPS/PBAT ratio of 20/80 (Figure 3c) is also observed for the blends with a TPS/PBAT ratio of 30/70 (Figure 3d), where the glass transition temperature of starch-rich domains decreased from 30 °C to 26 °C for the samples with 0% MMT and 5% MMT, respectively. The changes in glass transition temperature for the glycerol-rich regions were small (±2 °C). These transitions took place at about −42 °C. The lowering of the glass transition temperature is related to the higher mobility of starch chains.
In Figure 4, the temperature dependences of the storage modulus E′ of all the samples are shown. By comparing the samples within and between graphs, it can be concluded that the TPS sample appears to be the stiffest material. This corresponds to the high values of storage modulus at negative temperatures as well as the value of the storage modulus at room temperature (Table 2). Samples with the same TPS/PBAT ratio do not differ much in the temperature dependences and values of storage modulus at room temperature.

3.4. Nuclear Magnetic Resonance (NMR)

The widths of signals in 1H BL NMR spectra provide information on the molecular mobility in polymer materials since 1H nuclei in rigid and mobile chains produce broad and narrow signals, respectively [53]. The 1H BL NMR spectra of studied samples (Figure 5) consist of one broad (BS) and one narrow signal (NS). The broad signal originates from 1H nuclei in rigid starch chains, immobile PBAT chains, and bound water. The narrow signal comes from the 1H nuclei in more mobile glycerol molecules, free water molecules (for samples containing TPS), and more mobile PBAT chains (for samples containing PBAT). The apparent chemical shift of this signal ranges from 4.2 to 2.1 ppm. With the changing TPS/PBAT ratio (Figure 5) in the samples, the chemical shift of the narrow signal also changes.
The narrow signal of the TPS/PBAT blends is a superposition of the two signals—one from 1H nuclei in CH2 groups in PBAT at a chemical shift of 1.7 ppm (NS1) and one from 1H nuclei in glycerol, water, and OCH2 groups in PBAT at a chemical shift of 4.4 ppm (NS2) [54].
By deconvolution of 1H BL NMR spectra (Figure 6), it is possible to obtain information about the width and intensity of individual signals (Table 3). With increasing TPS content in the studied samples, the relative intensity of the broad signal increases (Figure 7), which indicates an increase in the rigid fraction in TPS/PBAT blends. However, the line width of NS2 signals decreases (Figure 8) which points to the enhanced mobility of water and glycerol molecules in TPS domains probably due to the hydrophobic nature of the PBAT matrix. This effect is more pronounced for samples containing MMT, and it may be related to the size of TPS domains since larger TPS domains provide better conditions for the motion of water and glycerol molecules.
With the increase in MMT content in the samples with particular TPS content, the relative intensity of the broad signal decreases (Figure 7), which indicates the increasing number of intercalated species in the MMT interlayer space which are less mobile than those that are free but more mobile than those that could be entrapped in the TPS structure [29]. The width of NS2 signals for samples with a particular TPS content increases with the increasing MMT content (Figure 8), indicating decreased molecular mobility due to the interaction of relevant species with MMT layers.
1H MAS NMR spectrum of the TPS sample consists of two well-resolved signals with chemical shift values of 5.2 ppm and 3.7 ppm from the 1H nuclei in glycerol (Figure 9). The signal from the 1H nuclei in the starch molecules is found in the broad signal and in the rotational signals (not shown in Figure 9). The 1H MAS NMR spectrum of the PBAT sample contains three signals with chemical shift values of 8.0 ppm, 4.0 ppm, and 1.6 ppm, which originate from the 1H nuclei in the terephthalate unit, OCH2, and CH2/CH group in PBAT, respectively. The signal with a chemical shift of 1.6 ppm is a superposition of three signals from p4, p5, and p6 hydrogens. In the 1H MAS NMR spectra of TPS/PBAT blends, there are four signals, with chemical shift values of 8.0 ppm, 5.2 ppm, 3.8 ppm, and 1.6 ppm, which originate from the 1H nuclei in PBAT and glycerol within the TPS component [55]. The signal with a chemical shift value of 3.8 ppm is a superposition of signals from p2, p3 PBAT hydrogen nuclei, and 1H nuclei in CH2/CH groups in glycerol. In these spectra, another signal with a chemical shift value of 4.7 ppm is observed, which is attributed to 1H nuclei in mobile water molecules [45,54]. This signal is not observed in the spectrum of the TPS sample. It may mean that the hydrophobic PBAT matrix surrounding TPS domains is able to displace water molecules located in the TPS domains of TPS/PBAT blends and thereby increases their molecular mobility.
The 1H MAS NMR spectra of TPS/PBAT blends containing MMT do not differ much from those for samples without MMT (Figure 9). With increasing MMT content, a small difference is seen in decreasing the intensity of the mobile water signal with a chemical shift of 4.7 ppm, which is the most conspicuous for samples with the highest TPS content (Figure 10), due to the lower mobility of water molecules, as was detected in BL spectra as the NS2 linewidth increases (Figure 8).
Figure 11 shows the measured 13C CP/MAS NMR spectra of TPS, PBAT, and TPS/PBAT blends. The chemical shifts of the individual signals and the functional groups from which they originate are listed in Table 4, assigned in Figure 11 according to [56,57]. The resonance from the C1 carbons in starch in the spectra for TPS and TPS/PBAT samples shows only one broad signal with an amplitude at the 103 ppm chemical shift. The shape of this signal indicates that TPS chains are disordered in the studied samples. The signal from C6 carbons in starch is not observed in the spectra for TPS/PBAT blends probably due to a low intensity, a large line width, and an overlap with the p3 signal of the PBAT component [58].
The presence of TPS in studied blends affects the molecular mobility of PBAT chains. This effect can be deduced from the comparison of the spectra for PBAT and TPS/PBAT 10/90 (Figure 11). The intensities of signals from p5 in the spectrum of the TPS/PBAT 10/90 blend and for neat PBAT are almost the same (despite the lower content of PBAT in the sample). The same effect is observed for signals of p1, p3, and p6 carbons of PBAT and also for blends containing MMT (Figure 12) This may be due to the fact that signals from less mobile parts in the sample are enhanced in 1H-13C CP/MAS NMR spectra. The presence of 10 wt% of TPS in the sample decreases the mobility of the PBAT chains, mainly those located at the TPS/PBAT interfaces.

4. Conclusions

The investigation of mixtures of PBAT with thermoplastic starch indicates that TPS addition results in a substantial decrease in tensile strength and an increase in the brittleness of the blends with rising TPS content. This tendency is even more visible after the addition of montmorillonite particles as the reinforcing filler indicated by the significant increase in the Young’s modulus and further decrease in the elongation at break. However, even the addition of 30% of TPS results in maintaining sufficiently high values of elongation at break, i.e., the blend is still quite tough in spite of the presence of 30% highly brittle TPS.
DMTA results reveal the formation of TPS domains in the PBAT matrix. The two relaxation transitions correspond to a presence of glycerol-rich and starch-rich regions, respectively. These conclusions are convincingly supported by the NMR measurement of chain mobility, which is higher in the glycerol-rich compared to starch-rich regions.
The effect of the MMT addition is almost negligible on the tensile stress of the blends due to interactions between MMT and plasticizer molecules. The reason is seen in the way of the mixture preparation where the MMT is dispersed in the plasticizer before mixing into the starch, so that the reinforcing effect of the MMT nanoparticles through the interactions of MMT with starch macromolecules are not prevailing; although, MMT has been intercalated and partially exfoliated according to XRD measurements supported by mechanical parameters evaluation.
The presented data suggest the possibility of applications of the mixtures of PBAT with TPS up to 20 and in some cases 30 wt% for less demanding applications, which makes the price of the biodegradable plastics material competitive with common polyolefins, if accepting a certain decrease in mechanical parameters of the final mixture.
All conclusions mentioned above are fully supported by measurements of the polymer chain mobilities performed with NMR, making the conclusions much more understandable and reliable.

Author Contributions

Conceptualization, H.P., I.C., O.F. and M.K.; writing—original draft, H.P.; methodology, H.P., L.O., S.S., O.F. and M.K.; software, H.P. and O.F.; investigation, H.P., L.O., S.S., O.F. and M.K.; writing—review and editing, H.P., O.F., M.K. and I.C.; supervision, I.C.; funding acquisition, I.C., H.P. and M.K. All authors have read and agreed to the published version of the manuscript.

Funding

The authors appreciate the support from the Slovak Research and Development Agency under project APVV 19-0487 and the Slovak Grant Agency VEGA 2/0109/23 and VEGA 1/0751/21.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The datasets presented in this article are not readily available because the data are part of an ongoing study.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Ferreira, F.; Pinheiro, I.; Gouveia, R.; Thim, G.; Lona, L. Functionalized cellulose nanocrystals as reinforcement in biodegradable polymer nanocomposites. Polym. Compos. 2018, 39, E9–E29. [Google Scholar] [CrossRef]
  2. Peidayesh, H.; Heydari, A.; Mosnáčková, K.; Chodák, I. In situ dual crosslinking strategy to improve the physico-chemical properties of thermoplastic starch. Carbohydr. Polym. 2021, 269, 118250. [Google Scholar] [CrossRef]
  3. Saparová, S.; Ondriš, L.; Kovaľaková, M.; Fričová, O.; Peidayesh, H.; Baran, A.; Hutníková, M.; Chodák, I. Effects of glycerol content on structure and molecular motion in thermoplastic starch-based nanocomposites during long storage. Int. J. Biol. Macromol. 2023, 253, 126911. [Google Scholar] [CrossRef] [PubMed]
  4. Drakopoulos, S.; Karger-Kocsis, J.; Kmetty, Á.; Lendvai, L.; Psarras, G. Thermoplastic starch modified with microfibrillated cellulose and natural rubber latex: A broadband dielectric spectroscopy study. Carbohydr. Polym. 2017, 157, 711–718. [Google Scholar] [CrossRef] [PubMed]
  5. Chivrac, F.; Pollet, E.; Avérous, L. Progress in nano-biocomposites based on polysaccharides and nanoclays. Mater. Sci. Eng. R Rep. 2009, 67, 1–17. [Google Scholar] [CrossRef]
  6. Dang, K.M.; Yoksan, R.; Pollet, E.; Avérous, L. Morphology and properties of thermoplastic starch blended with biodegradable polyester and filled with halloysite nanoclay. Carbohydr. Polym. 2020, 242, 116392. [Google Scholar] [CrossRef]
  7. Peidayesh, H.; Mosnáčková, K.; Špitalský, Z.; Heydari, A.; Šišková, A.O.; Chodák, I. Thermoplastic starch–based composite reinforced by conductive filler networks: Physical properties and electrical conductivity changes during cyclic deformation. Polymers 2021, 13, 3819. [Google Scholar] [CrossRef] [PubMed]
  8. Šmídová, N.; Peidayesh, H.; Baran, A.; Fričová, O.; Kovaľaková, M.; Králiková, R.; Chodák, I. Influence of Air Humidity Level on the Structure and Mechanical Properties of Thermoplastic Starch-Montmorillonite Nanocomposite during Storage. Materials 2023, 16, 900. [Google Scholar] [CrossRef]
  9. Drakopoulos, S.X.; Špitalský, Z.; Peidayesh, H.; Lendvai, L. The Effect of Drying of Glycerol-Plasticized Starch upon Its Dielectric Relaxation Dynamics and Charge Transport. J. Polym. Environ. 2023, 31, 5389–5400. [Google Scholar] [CrossRef]
  10. Lendvai, L.; Sajó, I.; Karger-Kocsis, J. Effect of storage time on the structure and mechanical properties of starch/bentonite nanocomposites. Starch-Stärke 2019, 71, 1800123. [Google Scholar] [CrossRef]
  11. Khan, B.; Bilal Khan Niazi, M.; Samin, G.; Jahan, Z. Thermoplastic starch: A possible biodegradable food packaging material—A review. J. Food Process Eng. 2017, 40, e12447. [Google Scholar] [CrossRef]
  12. Lendvai, L.; Karger-Kocsis, J.; Kmetty, Á.; Drakopoulos, S.X. Production and characterization of microfibrillated cellulose-reinforced thermoplastic starch composites. J. Appl. Polym. Sci. 2016, 133, 42397. [Google Scholar] [CrossRef]
  13. Sun, S.; Liu, P.; Ji, N.; Hou, H.; Dong, H. Effects of various cross-linking agents on the physicochemical properties of starch/PHA composite films produced by extrusion blowing. Food Hydrocoll. 2018, 77, 964–975. [Google Scholar] [CrossRef]
  14. Zhang, M.; Thomas, N.L. Preparation and properties of polyhydroxybutyrate blended with different types of starch. J. Appl. Polym. Sci. 2010, 116, 688–694. [Google Scholar] [CrossRef]
  15. Palai, B.; Biswal, M.; Mohanty, S.; Nayak, S.K. In situ reactive compatibilization of polylactic acid (PLA) and thermoplastic starch (TPS) blends; synthesis and evaluation of extrusion blown films thereof. Ind. Crops Prod. 2019, 141, 111748. [Google Scholar] [CrossRef]
  16. Martinez Villadiego, K.; Arias Tapia, M.J.; Useche, J.; Escobar Macías, D. Thermoplastic starch (TPS)/polylactic acid (PLA) blending methodologies: A review. J. Polym. Environ. 2022, 30, 75–91. [Google Scholar] [CrossRef]
  17. Cai, J.; Xiong, Z.; Zhou, M.; Tan, J.; Zeng, F.; Lin, S.; Xiong, H. Thermal properties and crystallization behavior of thermoplastic starch/poly (ɛ-caprolactone) composites. Carbohydr. Polym. 2014, 102, 746–754. [Google Scholar] [CrossRef] [PubMed]
  18. de Campos, A.; Tonoli, G.H.; Marconcini, J.M.; Mattoso, L.H.; Klamczynski, A.; Gregorski, K.S.; Wood, D.; Williams, T.; Chiou, B.-S.; Imam, S.H. TPS/PCL composite reinforced with treated sisal fibers: Property, biodegradation and water-absorption. J. Polym. Environ. 2013, 21, 1–7. [Google Scholar] [CrossRef]
  19. Olivato, J.; Müller, C.; Carvalho, G.; Yamashita, F.; Grossmann, M.V.E. Physical and structural characterisation of starch/polyester blends with tartaric acid. Mater. Sci. Eng. C 2014, 39, 35–39. [Google Scholar] [CrossRef]
  20. Lendvai, L.; Apostolov, A.; Karger-Kocsis, J. Characterization of layered silicate-reinforced blends of thermoplastic starch (TPS) and poly (butylene adipate-co-terephthalate). Carbohydr. Polym. 2017, 173, 566–572. [Google Scholar] [CrossRef]
  21. Dammak, M.; Fourati, Y.; Tarrés, Q.; Delgado-Aguilar, M.; Mutjé, P.; Boufi, S. Blends of PBAT with plasticized starch for packaging applications: Mechanical properties, rheological behaviour and biodegradability. Ind. Crops Prod. 2020, 144, 112061. [Google Scholar] [CrossRef]
  22. Bumbudsanpharoke, N.; Harnkarnsujarit, N.; Chongcharoenyanon, B.; Kwon, S.; Ko, S. Enhanced properties of PBAT/TPS biopolymer blend with CuO nanoparticles for promising active packaging. Food Packag. Shelf Life 2023, 37, 101072. [Google Scholar] [CrossRef]
  23. Wei, D.; Wang, H.; Xiao, H.; Zheng, A.; Yang, Y. Morphology and mechanical properties of poly (butylene adipate-co-terephthalate)/potato starch blends in the presence of synthesized reactive compatibilizer or modified poly (butylene adipate-co-terephthalate). Carbohydr. Polym. 2015, 123, 275–282. [Google Scholar] [CrossRef] [PubMed]
  24. Jian, J.; Xiangbin, Z.; Xianbo, H. An overview on synthesis, properties and applications of poly (butylene-adipate-co-terephthalate)–PBAT. Adv. Ind. Eng. Polym. Res. 2020, 3, 19–26. [Google Scholar] [CrossRef]
  25. Li, Z.; Li, H.; Wang, M.; Zhang, Z.; Yang, L.; Ma, L.; Liu, H. Preparation and Properties of Poly (butylene adipate-co-terephthalate)/thermoplastic Hydroxypropyl Starch Composite Films Reinforced with Nano-Silica. Polymers 2023, 15, 2026. [Google Scholar] [CrossRef]
  26. Ayana, B.; Suin, S.; Khatua, B. Highly exfoliated eco-friendly thermoplastic starch (TPS)/poly (lactic acid)(PLA)/clay nanocomposites using unmodified nanoclay. Carbohydr. Polym. 2014, 110, 430–439. [Google Scholar]
  27. Thipmanee, R.; Sane, A. Effect of zeolite 5A on compatibility and properties of linear low-density polyethylene/thermoplastic starch blend. J. Appl. Polym. Sci. 2012, 126, E252–E259. [Google Scholar] [CrossRef]
  28. Dufresne, A.; Castaño, J. Polysaccharide nanomaterial reinforced starch nanocomposites: A review. Starch-Stärke 2017, 69, 1500307. [Google Scholar] [CrossRef]
  29. Baran, A.; Fričová, O.; Vrábel, P.; Popovič, Ľ.; Peidayesh, H.; Chodák, I.; Hutníková, M.; Kovaľaková, M. Effects of urea and glycerol mixture on morphology and molecular mobility in thermoplastic starch/montmorillonite-type nanofiller composites studied using XRD and NMR. J. Polym. Res. 2022, 29, 257. [Google Scholar] [CrossRef]
  30. Chung, Y.-L.; Ansari, S.; Estevez, L.; Hayrapetyan, S.; Giannelis, E.P.; Lai, H.-M. Preparation and properties of biodegradable starch–clay nanocomposites. Carbohydr. Polym. 2010, 79, 391–396. [Google Scholar] [CrossRef]
  31. Yang, F.; Chen, G.; Li, J.; Zhang, C.; Ma, Z.; Zhao, M.; Yang, Y.; Han, Y.; Huang, Z.; Weng, Y. Effects of quercetin and organically modified montmorillonite on the properties of poly (butylene adipate-co-terephthalate)/thermoplastic starch active packaging films. ACS Omega 2022, 8, 663–672. [Google Scholar] [CrossRef] [PubMed]
  32. El Nokab, M.E.H.; Lasorsa, A.; Sebakhy, K.O.; Picchioni, F.; van der Wel, P.C. Solid-state NMR spectroscopy insights for resolving different water pools in alginate hydrogels. Food Hydrocoll. 2022, 127, 107500. [Google Scholar] [CrossRef]
  33. Camargo, P.H.C.; Satyanarayana, K.G.; Wypych, F. Nanocomposites: Synthesis, structure, properties and new application opportunities. Mater. Res. 2009, 12, 1–39. [Google Scholar] [CrossRef]
  34. Madhumitha, G.; Fowsiya, J.; Mohana Roopan, S.; Thakur, V.K. Recent advances in starch–clay nanocomposites. Int. J. Polym. Anal. Charact. 2018, 23, 331–345. [Google Scholar] [CrossRef]
  35. Santos, R.A.; Muller, C.M.; Grossmann, M.V.; Mali, S.; Yamashita, F. Starch/poly (butylene adipate-co-terephthalate)/montmorillonite films produced by blow extrusion. Quim. Nova 2014, 37, 937–942. [Google Scholar] [CrossRef]
  36. Olivato, J.; Marini, J.; Pollet, E.; Yamashita, F.; Grossmann, M.; Avérous, L. Elaboration, morphology and properties of starch/polyester nano-biocomposites based on sepiolite clay. Carbohydr. Polym. 2015, 118, 250–256. [Google Scholar] [CrossRef]
  37. Guo, M.; Jin, Y.; Han, X.; Sun, J.; Yuan, J.; Tian, H. Biodegradable Poly (Butylene Adipate-Co-Terephthalate) and Thermoplastic Starch Sustainable Blends Modified by Epoxy-Terminated Hyperbranched Polyester with Excellent Mechanical Properties and High Transparency. Starch-Stärke 2023, 75, 2200169. [Google Scholar] [CrossRef]
  38. ISO 1133-1; Plastics—Determination of the Melt Mass-Flow Rate (MFR) and Melt Volume-Flow Rate (MVR) of Thermoplastics—Part 1: Standard Method. ISO: Geneva, Switzerland, 2011.
  39. ASTM, D638-14; Standard Test Method for Tensile Properties of Plastics. ASTM International: West Conshohocken, PA, USA, 2014.
  40. Chen, Q.; Hou, S.; Schmidt-Rohr, K. A simple scheme for probehead background suppression in one-pulse 1H NMR. Solid State Nucl. Magn. Reson. 2004, 26, 11–15. [Google Scholar] [CrossRef]
  41. Garalde, R.A.; Thipmanee, R.; Jariyasakoolroj, P.; Sane, A. The effects of blend ratio and storage time on thermoplastic starch/poly (butylene adipate-co-terephthalate) films. Heliyon 2019, 5, e01251. [Google Scholar] [CrossRef]
  42. Van Soest, J.J.; Hulleman, S.; De Wit, D.; Vliegenthart, J. Crystallinity in starch bioplastics. Ind. Crops Prod. 1996, 5, 11–22. [Google Scholar] [CrossRef]
  43. Lopez-Rubio, A.; Flanagan, B.M.; Gilbert, E.P.; Gidley, M.J. A novel approach for calculating starch crystallinity and its correlation with double helix content: A combined XRD and NMR study. Biopolymers 2008, 89, 761–768. [Google Scholar] [CrossRef]
  44. Aouada, F.A.; Mattoso, L.H.; Longo, E. New strategies in the preparation of exfoliated thermoplastic starch–montmorillonite nanocomposites. Ind. Crops Prod. 2011, 34, 1502–1508. [Google Scholar] [CrossRef]
  45. Šmídová, N.; Šoltýs, A.; Hronský, V.; Olčák, D.; Popovič, Ľ.; Chodák, I. Aging-induced structural relaxation in cornstarch plasticized with urea and glycerol. J. Appl. Polym. Sci. 2021, 138, 50218. [Google Scholar] [CrossRef]
  46. Liu, W.; Liu, S.; Wang, Z.; Dai, B.; Liu, J.; Chen, Y.; Zeng, G.; He, Y.; Liu, Y.; Liu, R. Preparation and characterization of reinforced starch-based composites with compatibilizer by simple extrusion. Carbohydr. Polym. 2019, 223, 115122. [Google Scholar] [CrossRef]
  47. Jalalvandi, E.; Majid, R.; Ghanbari, T.; Ilbeygi, H. Effects of montmorillonite (MMT) on morphological, tensile, physical barrier properties and biodegradability of polylactic acid/starch/MMT nanocomposites. J. Thermoplast. Compos. Mater. 2015, 28, 496–509. [Google Scholar] [CrossRef]
  48. Menard, K.P. Dynamic Mechanical Analysis: A Practical Introduction, 2nd ed.; CRC Press: Boca Raton, FL, USA, 2008; pp. 95–122. [Google Scholar]
  49. Bashir, M.A. Use of dynamic mechanical analysis (DMA) for characterizing interfacial interactions in filled polymers. Solids 2021, 2, 108–120. [Google Scholar] [CrossRef]
  50. Fourati, Y.; Tarrés, Q.; Mutjé, P.; Boufi, S. PBAT/thermoplastic starch blends: Effect of compatibilizers on the rheological, mechanical and morphological properties. Carbohydr. Polym. 2018, 199, 51–57. [Google Scholar] [CrossRef] [PubMed]
  51. Schmitt, H.; Guidez, A.; Prashantha, K.; Soulestin, J.; Lacrampe, M.; 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]
  52. Fričová, O.; Hutníková, M. Viscoelastic behavior of starch plasticized with urea and glycerol. AIP Conf. Proc. 2019, 2131, 020011. [Google Scholar]
  53. Kou, Y.; Dickinson, L.; Chinachoti, P. Mobility characterization of waxy corn starch using wide-line 1H nuclear magnetic resonance. J. Agric. Food Chem. 2000, 48, 5489–5495. [Google Scholar] [CrossRef]
  54. Šmídová, N.; Fričová, O.; Chodák, I.; Kovaľaková, M. Structural characterization of poly (butylene-adipate-co-terephthalate)(PBAT)/thermoplastic starch blends. AIP Conf. Proc. 2023, 2778, 040026. [Google Scholar]
  55. Kijchavengkul, T.; Auras, R.; Rubino, M.; Selke, S.; Ngouajio, M.; Fernandez, R.T. Biodegradation and hydrolysis rate of aliphatic aromatic polyester. Polym. Degrad. Stab. 2010, 95, 2641–2647. [Google Scholar] [CrossRef]
  56. Mutungi, C.; Passauer, L.; Onyango, C.; Jaros, D.; Rohm, H. Debranched cassava starch crystallinity determination by Raman spectroscopy: Correlation of features in Raman spectra with X-ray diffraction and 13C CP/MAS NMR spectroscopy. Carbohydr. Polym. 2012, 87, 598–606. [Google Scholar] [CrossRef] [PubMed]
  57. Cranston, E.; Kawada, J.; Raymond, S.; Morin, F.G.; Marchessault, R.H. Cocrystallization model for synthetic biodegradable poly (butylene adipate-co-butylene terephthalate). Biomacromolecules 2003, 4, 995–999. [Google Scholar] [CrossRef] [PubMed]
  58. Kuwabara, K.; Gan, Z.; Nakamura, T.; Abe, H.; Doi, Y. Crystalline/Amorphous Phase Structure and Molecular Mobility of Biodegradable Poly (butylene adipate-c o-butylene terephthalate) and Related Polyesters. Biomacromolecules 2002, 3, 390–396. [Google Scholar] [CrossRef]
Materials 17 00540 g001
Figure 1. X-ray diffractogram of pure TPS (pink curve) and PBAT (black) and TPS/PBAT blends (10/90—red; 20/80—green; and 30/70—blue) without MMT (a) and TPS/PBAT blends with MMT content for blend ratios of 10/90 (b) 20/80 (c), and 30/70 (d). The contents of MMT are 0 (black curves), 2 (red), and 5 parts per 100 parts of starch (green).
Figure 1. X-ray diffractogram of pure TPS (pink curve) and PBAT (black) and TPS/PBAT blends (10/90—red; 20/80—green; and 30/70—blue) without MMT (a) and TPS/PBAT blends with MMT content for blend ratios of 10/90 (b) 20/80 (c), and 30/70 (d). The contents of MMT are 0 (black curves), 2 (red), and 5 parts per 100 parts of starch (green).
Materials 17 00540 g001
Materials 17 00540 g002
Figure 2. Stress–strain curves for the neat TPS (black line) and PBAT (orange), as well as TPS/PBAT blends of the ratios 10/90 (red), 20/80 (green), and 30/70 (blue). The content of MMT was 0 (full line ―), 2 (dashed line – – –), and 5 (dotted line …) parts per 100 parts of starch.
Figure 2. Stress–strain curves for the neat TPS (black line) and PBAT (orange), as well as TPS/PBAT blends of the ratios 10/90 (red), 20/80 (green), and 30/70 (blue). The content of MMT was 0 (full line ―), 2 (dashed line – – –), and 5 (dotted line …) parts per 100 parts of starch.
Materials 17 00540 g002
Materials 17 00540 g003
Figure 3. Temperature dependences of tan δ for pure TPS (pink curve) and PBAT (black) and TPS/PBAT blends (10/90—red; 20/80—green; and 30/70—blue) without MMT (a), and TPS/PBAT blends with MMT content for blend ratios of 10/90 (b), 20/80 (c), and 30/70 (d). The contents of MMT are 0 (black curves), 2 (red), and 5 parts per 100 parts of starch (green).
Figure 3. Temperature dependences of tan δ for pure TPS (pink curve) and PBAT (black) and TPS/PBAT blends (10/90—red; 20/80—green; and 30/70—blue) without MMT (a), and TPS/PBAT blends with MMT content for blend ratios of 10/90 (b), 20/80 (c), and 30/70 (d). The contents of MMT are 0 (black curves), 2 (red), and 5 parts per 100 parts of starch (green).
Materials 17 00540 g003
Materials 17 00540 g004
Figure 4. Temperature dependences of storage modulus for pure TPS (pink curve) and PBAT (black) and TPS/PBAT blends (10/90—red; 20/80—green; and 30/70—blue) without MMT (a), and TPS/PBAT blends with MMT content for blend ratio 10/90 (b), 20/80 (c), and 30/70 (d). The contents of MMT are 0 (black curves), 2 (red), and 5 parts per 100 parts of starch (green).
Figure 4. Temperature dependences of storage modulus for pure TPS (pink curve) and PBAT (black) and TPS/PBAT blends (10/90—red; 20/80—green; and 30/70—blue) without MMT (a), and TPS/PBAT blends with MMT content for blend ratio 10/90 (b), 20/80 (c), and 30/70 (d). The contents of MMT are 0 (black curves), 2 (red), and 5 parts per 100 parts of starch (green).
Materials 17 00540 g004
Materials 17 00540 g005
Figure 5. Figure on the top, 1H BL NMR spectra of pure TPS (light blue), PBAT (dark blue), and the blends of TPS/PBAT ratios 10/90 (magenta), 20/80 (orange), and 30/70 (green). Figure on the bottom, 1H BL NMR spectra of samples TPS/PBAT containing 2 (left) and 5 (right) parts of MMT per 100 parts of starch. The samples from top to bottom: neat PBAT (dark blue), TPS/PBAT ratios 10/90 (purple), 20/80 (olive), and 30/70 (dark green).
Figure 5. Figure on the top, 1H BL NMR spectra of pure TPS (light blue), PBAT (dark blue), and the blends of TPS/PBAT ratios 10/90 (magenta), 20/80 (orange), and 30/70 (green). Figure on the bottom, 1H BL NMR spectra of samples TPS/PBAT containing 2 (left) and 5 (right) parts of MMT per 100 parts of starch. The samples from top to bottom: neat PBAT (dark blue), TPS/PBAT ratios 10/90 (purple), 20/80 (olive), and 30/70 (dark green).
Materials 17 00540 g005
Materials 17 00540 g006
Figure 6. Deconvolution of 1H BL NMR spectrum of the sample TPS/PBAT ratio of 10/90, with addition of 2 parts of MMT per 100 parts of starch. Black curve represents the measured spectrum, and blue curves are the curves obtained by the deconvolution of the measured spectra to individual processes, described in the discussion part.
Figure 6. Deconvolution of 1H BL NMR spectrum of the sample TPS/PBAT ratio of 10/90, with addition of 2 parts of MMT per 100 parts of starch. Black curve represents the measured spectrum, and blue curves are the curves obtained by the deconvolution of the measured spectra to individual processes, described in the discussion part.
Materials 17 00540 g006
Materials 17 00540 g007
Figure 7. Relative intensity of broad signal (BS) in 1H BL NMR spectra for mixtures TPS/PBAT with varying content of MMT in php (parts per 100 parts of starch); ratios of the components are shown inside the figure.
Figure 7. Relative intensity of broad signal (BS) in 1H BL NMR spectra for mixtures TPS/PBAT with varying content of MMT in php (parts per 100 parts of starch); ratios of the components are shown inside the figure.
Materials 17 00540 g007
Materials 17 00540 g008
Figure 8. Linewidth of narrow signal NS2 in 1H BL NMR spectra for mixtures of TPS/PBAT with varying content of MMT in php (parts per 100 parts of starch); the composition of TPS/PBAT ratios are shown inside the figure.
Figure 8. Linewidth of narrow signal NS2 in 1H BL NMR spectra for mixtures of TPS/PBAT with varying content of MMT in php (parts per 100 parts of starch); the composition of TPS/PBAT ratios are shown inside the figure.
Materials 17 00540 g008
Materials 17 00540 g009
Figure 9. 1H MAS NMR spectra of studied samples, showing signals for particular hydrogens. Composition of polymeric matrices: TPS—light blue; PBAT—dark blue; TPS/PBAT 10/90—magenta; 20/80—orange; 30/70—green.
Figure 9. 1H MAS NMR spectra of studied samples, showing signals for particular hydrogens. Composition of polymeric matrices: TPS—light blue; PBAT—dark blue; TPS/PBAT 10/90—magenta; 20/80—orange; 30/70—green.
Materials 17 00540 g009
Materials 17 00540 g010
Figure 10. 1H MAS NMR spectra for samples of TPS/PBAT with ratios of 30/70 and 0, 2, and 5 parts of MMT per 100 parts of starch (php). The samples from top to bottom: 0 (dark blue), 2 (purple), and 5 (green) php of MMT.
Figure 10. 1H MAS NMR spectra for samples of TPS/PBAT with ratios of 30/70 and 0, 2, and 5 parts of MMT per 100 parts of starch (php). The samples from top to bottom: 0 (dark blue), 2 (purple), and 5 (green) php of MMT.
Materials 17 00540 g010
Materials 17 00540 g011
Figure 11. 13C CP/MAS NMR spectra of TPS—light blue; PBAT—dark blue; TPS/PBAT 10/90—magenta; 20/80—orange; 30/70—green.
Figure 11. 13C CP/MAS NMR spectra of TPS—light blue; PBAT—dark blue; TPS/PBAT 10/90—magenta; 20/80—orange; 30/70—green.
Materials 17 00540 g011
Materials 17 00540 g012
Figure 12. 13C CP/MAS NMR spectra of studied samples, showing signals for particular carbon atoms. Figure on the top, MMT content 2 php (parts per 100 parts of starch); on the bottom, MMT content 5 php in each sample; composition of polymeric matrices: PBAT—dark blue; TPS/PBAT 10/90—purple; 20/80—olive; 30/70—green.
Figure 12. 13C CP/MAS NMR spectra of studied samples, showing signals for particular carbon atoms. Figure on the top, MMT content 2 php (parts per 100 parts of starch); on the bottom, MMT content 5 php in each sample; composition of polymeric matrices: PBAT—dark blue; TPS/PBAT 10/90—purple; 20/80—olive; 30/70—green.
Materials 17 00540 g012
Table 1. Mechanical properties of the TPS–MMT/PBAT nanocomposites depend on the blend composition; TPS—thermoplastic starch; PBAT—Poly(butylene adipate–co–terephthalate); MMT—montmorillonite.
Table 1. Mechanical properties of the TPS–MMT/PBAT nanocomposites depend on the blend composition; TPS—thermoplastic starch; PBAT—Poly(butylene adipate–co–terephthalate); MMT—montmorillonite.
TPS
wt% 		PBAT
wt%		MMT
php *		Tensile Stress
(MPa)		Tensile Strain
(%)		Young’s Modulus
(MPa)
0100029.6 ± 3.3845 ± 9642.8 ± 3.4
1090021.3 ± 0.9696 ± 4468.7 ± 2.9
1090218.7 ± 1.4627 ± 5776.0 ± 2.6
1090518.8 ± 0.8629 ± 3573.0 ± 5.0
2080017.2 ± 1.8641 ± 5863.3 ± 1.4
2080213.0 ± 2.1500 ± 10159.6 ± 4.1
2080511.2 ± 2.0380 ± 13463.9 ± 1.3
3070013.1 ± 1.4586 ± 6150.2 ± 2.0
3070210.7 ± 2.0469 ± 12852.6 ± 3.7
3070510.3 ± 1.5429 ± 10053.0 ± 2.0
100007.2 ± 0.533.7 ± 8.6363 ± 20
* php—parts per hundred parts of starch.
Table 2. Storage modulus values (GPa) at room temperature (20 °C) of the TPS–MMT/PBAT nanocomposites depend on the blend composition; TPS—thermoplastic starch; PBAT—Poly(butylene adipate–co–terephthalate); MMT—montmorillonite.
Table 2. Storage modulus values (GPa) at room temperature (20 °C) of the TPS–MMT/PBAT nanocomposites depend on the blend composition; TPS—thermoplastic starch; PBAT—Poly(butylene adipate–co–terephthalate); MMT—montmorillonite.
TPS
wt% 		PBAT
wt%		MMT
php *		Storage Modulus (GPa)
0100070
1090084.7
1090282.3
1090578.3
2080094.2
2080285.3
2080585.8
30700125
30702103.7
30705123.2
10000395
* php—parts per hundred parts of starch.
Table 3. Deconvolution of 1H BL NMR spectra of studied PBAT/TPS mixtures into broad (BS) and two narrow signals (NS1 and NS2) as seen in Figure 6, dependent on the composition of blend components, thermoplastic starch (TPS, wt%), poly(butylene adipate–co–terephthalate) (PBAT, wt%), and montmorillonite (MMT, parts per hundred parts of starch) are given.
Table 3. Deconvolution of 1H BL NMR spectra of studied PBAT/TPS mixtures into broad (BS) and two narrow signals (NS1 and NS2) as seen in Figure 6, dependent on the composition of blend components, thermoplastic starch (TPS, wt%), poly(butylene adipate–co–terephthalate) (PBAT, wt%), and montmorillonite (MMT, parts per hundred parts of starch) are given.
NS1NS2BS
TPS
wt% 		PBAT
wt%		MMT
php *		Linewidth (Hz)Rel. Int. (%)Linewidth (Hz)Rel. Int. (%)Linewidth (Hz)Rel. Int. (%)
01000170027.2310022.717,00050.1
10900190028.3350026.122,00045.6
10902195031.6390025.722,50042.7
10905205034.640002423,00041.4
20800170019.5260033.620,00046.9
20802180021.8280032.921,00045.3
20805190025.7300029.822,50044.5
30700190017.6210032.321,00050.1
30702215021.8245030.122,00048.1
30705220026.2260029.923,00043.9
10000190060.2--26,00039.8
* php—parts per hundred parts of starch.
Table 4. Overview of chemical shifts in 13C CP/MAS NMR spectra of studied samples.
Table 4. Overview of chemical shifts in 13C CP/MAS NMR spectra of studied samples.
ComponentFunctional GroupChemical Shift (ppm)
PBAT–COOR (p1, p5)173.2
164.6
–C6H4– (p2)134.2
129.6
–CH2–COOR (p6)34.2
–CH2– (p4)25.9
–O–CH2 (p3)65.2
TPSC1103
C2–C565.5–78.8
C482.1
C661.4
GlycerolCH2 (g2)63.6
CH (g1)73
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

Peidayesh, H.; Ondriš, L.; Saparová, S.; Kovaľaková, M.; Fričová, O.; Chodák, I. Biodegradable Nanocomposites Based on Blends of Poly(Butylene Adipate–Co–Terephthalate) (PBAT) and Thermoplastic Starch Filled with Montmorillonite (MMT): Physico-Mechanical Properties. Materials 2024, 17, 540. https://doi.org/10.3390/ma17030540

AMA Style

Peidayesh H, Ondriš L, Saparová S, Kovaľaková M, Fričová O, Chodák I. Biodegradable Nanocomposites Based on Blends of Poly(Butylene Adipate–Co–Terephthalate) (PBAT) and Thermoplastic Starch Filled with Montmorillonite (MMT): Physico-Mechanical Properties. Materials. 2024; 17(3):540. https://doi.org/10.3390/ma17030540

Chicago/Turabian Style

Peidayesh, Hamed, Leoš Ondriš, Simona Saparová, Mária Kovaľaková, Oľga Fričová, and Ivan Chodák. 2024. "Biodegradable Nanocomposites Based on Blends of Poly(Butylene Adipate–Co–Terephthalate) (PBAT) and Thermoplastic Starch Filled with Montmorillonite (MMT): Physico-Mechanical Properties" Materials 17, no. 3: 540. https://doi.org/10.3390/ma17030540

APA Style

Peidayesh, H., Ondriš, L., Saparová, S., Kovaľaková, M., Fričová, O., & Chodák, I. (2024). Biodegradable Nanocomposites Based on Blends of Poly(Butylene Adipate–Co–Terephthalate) (PBAT) and Thermoplastic Starch Filled with Montmorillonite (MMT): Physico-Mechanical Properties. Materials, 17(3), 540. https://doi.org/10.3390/ma17030540

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