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Effects of Mixing Sequence on the Morphological and Rheological Properties of Polymer-Clay Nanocomposites of Poly(Butylene Adipate-co-Terephthalate) and Poly(Lactic Acid) Blend
Written By
Mahin Shahlari, Bahareh Baheri and Sunggyu Lee
Submitted: 21 January 2024Reviewed: 15 February 2024Published: 29 March 2024
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The effect of sequential mixing of poly(butylene adipate-co-terephthalate) (PBAT) and poly(lactic acid) (PLA) with organically modified silicate layers on the dispersion of the organoclay particles and its effect on the morphology of the blended polymer clay nanocomposite (BPCN) was examined. The dispersion of the organoclay platelets, morphology of the blend composite, and rheological and thermomechanical properties of these composites with 50/50 ratio of PLA to PBAT were investigated using X-Ray diffraction analysis, scanning and transmission electron microscopy, dynamic mechanical shear test, and thermogravimetric analysis. The morphology of blends with 70/30 ratio of PLA to PBAT was also examined and compared. The sequential mixing of the organoclay with this BPCN enhanced the level of clay dispersion when compared to the simultaneously blended nanocomposites. Larger PLA domains and better clay dispersion in PLA phase were observed when clay was first mixed with PLA and then subsequently mixed with PBAT.
Northern Technologies International Corporation, Circle Pines, MN, USA
Bahareh Baheri
Chemtech Innovators, LLC, Athens, OH, USA
Sunggyu Lee*
Chemtech Innovators, LLC, Athens, OH, USA
*Address all correspondence to: drkblee@gmail.com
1. Introduction
In response to the escalating global demand for sustainable alternatives and the imperative to reduce the environmental impact of traditional commodity plastics, there has been a pronounced surge in interest in biodegradable polymers. These polymers, designed to naturally break down over time, offer a promising solution to mitigate the persistent environmental issues associated with nondegradable plastics. As industries and consumers increasingly recognize the importance of eco-friendly materials, there is a compelling need and motivation to further develop and refine the properties of existing biodegradable polymers. Traditional plastics, notorious for their prolonged persistence in the environment, have triggered a paradigm shift in consumer preferences and industry practices. Biodegradable polymers present a sustainable pathway forward, but for their widespread adoption, they must surpass the performance benchmarks set by conventional plastics [1, 2].
Among the extensively studied biodegradable polymers, poly(lactic acid) (PLA) has gained significant attention due to its production from renewable resources such as corn-starch, sugar, and wheat, along with its relatively high modulus [3, 4, 5, 6, 7, 8]. However, PLA is hindered by brittleness and a lack of flexibility. To address these shortcomings, blending PLA with other biodegradable polymers has been explored as a viable solution [9, 10, 11, 12].
Poly(butylene adipate-co-terephthalate) (PBAT), a biodegradable polymer with high elasticity, is one of the polymers whose blend with PLA has been studied by several researchers [13, 14, 15, 16]. The resulting blends of PLA and PBAT exhibited an increased elongation at break compared to PLA alone. Nevertheless, the blends demonstrated lower values for both modulus and strength in comparison to pure PLA [14]. Blends of unmodified PLA and PBAT are poorly miscible without an aid of a compatibilizing effect, thus exhibiting a tendency of macro-separation. Properly functionalized nanoparticles such as organically modified nanoclay could provide a needed compatibilizing effect for blends of PLA and PBAT while rendering reinforcements of polymeric matrix.
Incorporating functional nanoparticles, a well-documented method for fortifying the modulus and strength of polymers [3, 17, 18, 19], including PLA [20], emerges as a strategic intervention. Therefore, to regain a high modulus for the PLA composite despite the softening effect of PBAT addition, nanoparticles have been compounded with PLA and PBAT blends [21, 22, 23, 24].
Numerous potential applications for PBAT could find advantages in utilizing PBAT and PLA blend, resulting in an enhanced modulus and renewable content. Introducing nanoparticles not only serves to increase the blend’s modulus but also has the potential to increase the heat deflection temperature, thermomechanical properties, and barrier properties of the blend. Organoclay has been found to be effective to improve these properties in PLA composites [25, 26, 27, 28, 29].
In composites of polymer blends, the location of the nanoparticles can impart a significant effect on the final properties, therefore controlling the location of these particles in a blend can be a great tool in tailoring polymers with desired properties.
Principally, the dispersed location of organoclay depends on the interaction between the two polymers as well as the interaction of each polymer with the organoclay particles. However, the high viscosity of the polymers does not allow the systems to always reach a thermodynamic equilibrium state, and the kinetic factors involved in the mixing process could influence and determine the location of the particles in the polymer. When the polymers and the particles are added simultaneously, regardless of the real affinity between the polymer and the organoclay, the polymer with a lower melting temperature typically exhibits better interaction with particles [30]. Therefore, the mixing sequence of the components could have a significant effect on how organoclay platelets are dispersed in the blend and ultimately affect the characteristics of the blend [31].
The effects of the mixing sequence on the properties of blends have been different from case to case. Kim et al. showed an increased degree of exfoliation of the clay when poly(ε-caprolactone) was initially mixed with clay and then blended with poly(styrene-co-acrylonitrile) [32]. Increased heat deflection temperature and flexural modulus were reported when ethylene vinyl acetate (EVA) was mixed with organoclay and Cloisite 20A and then mixed with propylene-(ethylene-propylene) copolymer (PP–EP) [33]. Dasari et al. observed that for a blend of Nylon66 and maleated styrene-ethylene/butylene-styrene block copolymer (SEBS-g-MA), the best impact strength was achieved when Cloisite 30B was mixed with Nylon66 first [34]. Tao et al. studied the migration behavior of carbon nanotubes (CNTs) within a co-continuous poly(lactic acid)/poly(ε-caprolactone) (PLA/PCL) blend when pre-compounding CNTs in one phase and controlling the mixing time. Enhanced viscosity compatibility between the two polymer phases led to a reduction in the size of the respective phases. Specifically, composites subjected to premixing of PCL/CNT followed by the introduction of PLA under low shear stress conditions demonstrated a reduction in the size of the individual phases [35].
On the other hand, some studies showed better properties were achieved by the simultaneously blended composites [36, 37]. Vo et al. reported the highest mechanical properties for Cloisite 30B simultaneously compounded with polyvinylidenefluoride (PVDF) and nylon 6 with Cloisite 30B mostly dispersed in Nylon 6 and some located at interface. The location of the particles was claimed to be responsible for inhibited coalescence of the dispersed phase [36]. In some studies, the mixing order did not cause a significant effect [38, 39, 40].
To investigate the interaction of the organically modified clays with the PBAT and PLA blends and to study the effect of the mixing sequence on the dispersed location of the nanoclay particles, a series of experiments were designed that considered the mixing sequence to be a main factor. Clay was first mixed with either PBAT or PLA; then, the second polymer was blended with the compound. In one set of samples, clay was dry-mixed with the two polymers prior to melt-mixing. The morphology and rheological properties of the blends were analyzed to determine any significant changes that may occur because of varying the mixing order. The transition of the particles from one polymer to the other was studied as well.
The PLA used in this study was a product of NatureWorks LLC (United States), PLA 4042, with a density of 1.24 g/cm3, glass transition temperature of 52–58°C, and melting temperature of 150°C. The structure of this polymer is shown in Figure 1.
Figure 1.
PLA structure.
The PBAT was a BASF product marketed as Ecoflex® FBX 7011, with a mass density of 1.25–1.27 g/cm3, glass transition temperature of about −29°C, melting temperature of 115°C, and melt flow rate of 3.3–6.6 g/10 min at 190°C and 2.16 Kg [41]. The structure of this polymer is shown in Figure 2.
Figure 2.
PBAT structure.
The organically modified nanoclay, Cloisite 30B, was supplied by Southern Clay Products Corporation. Cloisite 30B is montmorillonite (MMT)-type clay. Based on the technical data sheets of Southern Clay Products, Inc., Cloisite 30B was modified by methyl, tallow, bis-2-hydroxyethyl, and quaternary ammoniums. The amount of surfactant for Cloisite 30B is 90 meq/100 g. Tallow is a mixture of octadecyl, hexadecyl, and tetradecyl with octadecyl as the major component [42].
2.2 Sample preparations
Both the polymer pellets and the organoclay particles were dried in a vacuum oven for 12 hours at 65°C to reduce the chance of hydrolytic degradation during processing. The compounds were prepared in a Rheomix batch mixer (Haake Inc.) at a constant speed of 30 rpm at 190°C.
For one set of samples, clay was mixed with PBAT or PLA for 5 minutes before the second polymer was added and melt-blended for an additional 5 minutes. Another set was prepared by mixing clay for 10 minutes with the melt of the two polymers, which had been dry-mixed prior to melt mixing. The PBAT/PLA ratios considered here were 50/50 and 70/30. This work carried out the sequential mixing in a batch system; however, the process is transferable to an extrusion system by first compounding each polymer separately with organoclay and then blending the pelletized composite with the neat blend in the extruder.
The samples are named by the ratio of the first polymer mixed with organoclay followed by the letter B representing Cloisite 30B and its weight percentage in the blend. Therefore, 50PLA/B3 would be a blend in which the ratio of PLA to PBAT is 50/50 and PLA is first mixed with 3 wt.% Cloisite 30B and 70PLA/B3 would be a blend with the ratio of PLA to PBAT of 70/30 with similar clay content and mixing procedure.
2.3 Characterization
The X-ray Diffraction (XRD) analyses were carried out using a Philips X-Pert diffractometer at ambient temperature with Cu Kα radiation with wavelength of 0.154 nm, voltage of 45 kV, and current of 40 mA. The scanning step was 0.03 degrees, and the time per step was 10 seconds. The samples used for XRD were molded using a hydraulic hot-press. The interlayer spacing (d-spacing) of each sample was determined from the angular location of the peaks caused by the basal reflection of the repetitive 22 structure of the silicate layers using the Bragg’s relationship [43]. In case of complete exfoliation of the silicate layers, no peak should be observed. However, the lack of a peak is not a certain indication of exfoliation. The shift of the characteristic peak to lower angles results in higher calculated d-spacing for the clay and is attributable to the intercalation of the silicate layers [43].
The thermomechanical properties of the molded compounds were tested using a Dynamic Mechanical Thermal Analyzer (DMTA) IV from Rheometric Scientific Inc., and Rheometric Orchestrator software was used to operate the instrument and analyze the data. A dynamic strain sweep test was conducted prior to these tests to ensure that the applied strain was within the linear viscoelastic region for the blends. Dynamic temperature ramp tests were then conducted using a three-point bending fixture at a frequency of 1 s−1 and a constant strain of 0.1%. The storage and loss moduli were acquired while the specimens were heated from 30–100°C at a rate of 2°C/min. Five specimens were tested for each sample set.
Scanning Electron Microscopy (SEM) was performed using a Hitachi S4700 FESEM. The samples were immersed in liquid nitrogen and then fractured. Subsequently, they were sputter-coated with gold-palladium. An accelerating voltage of 5 kV was used to avoid charging accumulation on the sample surface, and a short working distance of 3–5 mm at ultra-high resolution mode was adopted to ensure vivid images. The lack of a selective solvent for these two polymers prevented etching the samples prior to SEM imaging [42].
Transmission Electron Microscopy (TEM) analysis was performed using a JEOL JEM-1400 with an accelerating voltage of 120KV. Specimens were cryomicrotomed to an average thickness of 70 nm. The TEM pictures were taken using a Gatan 2K×2K digital camera. The images were analyzed using Image J software. TEM images make it possible to evaluate the dispersion of silicate layers in the blend and to identify their location.
The Thermogravimetric Analysis (TGA) was performed using Netzsch STA 409C/CD with a nitrogen flow rate of 20 ml/min. The samples were heated to 500°C at a linear rate of 10°C/min. Approximately 100 mg of grinded compound was used as a sample.
An X-ray diffractometry (XRD) analysis was used to investigate the dispersion of the organoclay within the blends. The basal reflection of the repetitive structure of the silicate layers (if the latter are not completely exfoliated) creates low-angle peaks corresponding to the interlayer spacing of the silicate layers.
Figure 3 shows the XRD diffraction pattern of the sequentially mixed blends. The interlayer spacing of the samples is determined from the angular location of the peaks using the Bragg’s law. The XRD peak positions and interlayer spacing of 5050premixed/B3, 50PLA/B3, and 50PBAT/B3 samples are shown in Table 1. If the peaks are assumed to be related to (001) plane, n = 1, the spacings for all three compounds would be lower than 1.88 nm, the original d-spacing of the Cloisite 30B. This decrease in the space between the layers, although less likely, can be attributed to the degradation of some of the methyl, tallow, bis-2-hydroxyethyl, and quaternary ammonium present as the organic modifiers in Cloisite 30B.
Figure 3.
XRD patterns of (a) 5050premixed/B3, (b) 50PBAT/B3, and (c) 50PLA/B3.
Sample
2θ°
Interlayer spacing(nm)
5050premixed/B3
5.271
3.35
50PLA/B3
5.167
3.42
50PBAT/B3
5.141
3.44
Table 1.
XRD peak positions and interlayer spacing of 5050premixed/B3, 50PLA/B3, and 50PBAT/B3 samples.
The interlayer spacing of the samples did not indicate a significant difference between the two sequentially mixed samples, but the premixed sample showed a smaller d-spacing compared to the other two samples. As will be explained later in the TEM analysis section, the premixed samples showed a higher content of organoclay tactoids and agglomerates. The agglomerates could locally concentrate the heat and expedite the degradation of the organic modification in the premixed blend.
3.2 Rheological analysis
The rheological behavior of a polymer system is directly affected by the microstructure and properties of the particles that compounded with the polymer. Due to this fact, it is possible to evaluate the particle’s relative dispersion state in the matrix [44, 45].
As shown in Figure 4, at low frequencies, the shear storage modulus (G’) and shear loss modulus (G”) of clay-containing blends showed a large increase compared to those of the neat blend. The lowest storage and loss moduli among clay-composites were observed for the premixed samples, as the storage modulus of 50PBAT/B3 and 50PLA/B3 at lowest frequency were 205% and 123% higher than that of the premixed composite. The higher storage and loss modulus in the sequentially mixed blends could be due to the greater level of clay dispersion in this blend. The rheological properties are highly dependent on the population (i.e., number) of particles dispersed per volume of the matrix.
Figure 4.
Storage modulus (G’) and loss modulus (G”): 5050PBAT/PLA, 5050premixed/B3, 50PBAT/B3, and 50PLA/B3 composites.
In general, polymers in a melt state show a storage modulus larger than their loss modulus. As shown in Figure 4, unlike the neat blend, the loss moduli of the clay-containing blends were lower than the storage moduli at low frequencies. In addition, at lower frequencies, the slopes of the storage moduli graphs were reduced significantly, indicating less dependence on frequency. In nanocomposites, the storage modulus higher than loss modulus, in addition to a plateau for storage modulus at low frequencies, indicates solid-like behavior [46].
The storage modulus for both sequentially mixed samples had a higher value than the loss modulus at any frequency. The 5050premixed/B3 sample showed a G’/G” crossover point indicating transition to liquid-like behavior at higher frequencies for this melt. This observation in addition to larger dependence of the storage modulus on frequency (larger slope) for the premixed blend is an indication of the lower number of particles dispersed in this blend and higher level of agglomeration as mentioned above. At high frequencies, different samples showed similar moduli due to the short response time [45].
3.3 Organoclay dispersion
To determine the clay dispersion degree, and study the morphology of the blends, the TEM images of the samples were analyzed. In these images, PLA appears as the lighter phase and PBAT is the darker one (Figure 5). In all the blends with 50/50 ratio, exfoliated, intercalated, and agglomerated clay platelets were observed. However, in the premixed blend, large clay tactoids and agglomerates and fewer exfoliated/intercalated clay platelets were detected than the sequentially mixed samples.
Figure 5.
TEM micrographs of the sequentially mixed blends, (a) and (b): 50PLA/B3, (c) and (d): 50PBAT/B3, and (e) and (f): 5050premixed/B3. (b), (d), and (f) images have higher magnification. The lighter phase is PLA and the darker phase is PBAT [42].
The large clay tactoids observed in the premixed samples were mainly located in the PLA phase. This could be due to the low affinity of PLA to the organoclay [21]. On the other hand, since PBAT is being processed at a temperature more than 50°C above its melting temperature, it has a lower viscosity than PLA in this blend. Therefore, PBAT forms the matrix in 50/50 ratio as is generally known for polymer blends with large viscosity differences [6]. Therefore, the shear applied is significantly different for each phase. As the premixed polymers melt, some of the tactoids originally located in the PLA phase might not get exposed to a large enough shear. As PLA phase goes through successive breakups, some of the tactoids are broken and dispersed, but there is a chance that a few tactoids would be preserved in the PLA phase.
In the sequentially mixed samples, clay particles were located at the blend’s interface as well as in both phases of the blend despite organoclay’s initial mixing solely with one of the phases. This indicates the transition of the particles from one phase to the other.
Due to the large contrast between the two phases in the TEM images, it is difficult to detect the clay platelets in the PBAT phase, and only agglomerates are detectable in PBAT matrix, which itself is an indication of the migration of the particles form PLA phase to PBAT. Due to this limitation in addition to the key role the organoclay particles can have on the PLA phase properties, the TEM study was focused on the dispersion of the clay platelets in the PLA.
Only few groups have studied the mechanisms of particles’ transition from one phase to another [30, 47]. The migration of particles from matrix to the droplets occurs through the collision of the particles with the droplets. The solidity and the small size of the particles help the drainage of the matrix polymer between the particle and the droplets. Also based on their studies, the transition of the particles from the droplets to the matrix is possible as the particles can be moved by the internal flow inside the dispersed phase to the boundary and pass through the interface if the interfacial forces are in favor for the transition. Another possibility for particles transfer is through coalescence of the dispersed phase droplets. However, this mechanism has not been studied specifically [47].
In considering the transition of the organoclay particles from PBAT to PLA droplets in the 50PBAT/B3 composites, the uneven accumulation of particles in the PLA phase could be an indication of the coalescence as the main mechanism for migration of the particles from the PBAT phase to PLA (Figure 6). As the PLA droplets collide, the organoclay concentrated at the interface gets trapped between the droplets and locates inside the bigger droplet that is formed (Figure 6a). The schematic illustration of the organoclay transfer from PBAT matrix to the PLA phase is shown in Figure 7.
Figure 6.
Dispersion of the organoclay particles in the PLA phase. (a) 50PBAT/B3 and (b) 50PLA/B3. The lighter phase is PLA and the darker phase is PBAT [42].
Figure 7.
Schematic illustration of organoclay transfer from the PBAT matrix to the PLA dispersed phase.
In 50PLA/B3, since clay was first mixed with PLA, the organoclay platelets were more evenly dispersed in the PLA phase compared to the 50PBAT/B3 blends (Figure 6(b)). However, organoclay aggregates were observed in both phases and at the interface.
The overall better dispersion of the silicate layers in the 50PLA/B3 and 50PBAT/B3 than the premixed blend suggests that higher level of dispersion for clay can be achieved when it is mixed with a single polymer at a time than mixed with two polymers simultaneously.
3.4 Morphology
To compare the dispersed phase sizes of the three samples, the area of the PLA domains was measured, and the measurements were divided into 4 ranges. The fraction of area in each range was calculated in order to better illustrate the size distribution of the PLA domains in each sample. These data are reported in Table 2, and the size distribution of the PLA phase is illustrated in Figure 8. Among the three sets of samples, the largest PLA domains were observed in 50PLA/B3, whereas the smallest PLA phase sizes were observed for the premixed samples. The kinetic factors involved in the 50PLA/B3 system and the effect of the organoclay particles in hindering the breakup of the PLA phase resulted in large and partially continuous PLA domains. The organoclay platelets can obstruct the breakup process by creating a network structure inside the dispersed phase, which would resist breakup of the droplet [48]. The clay platelets can also reduce the mobility of the polymer chains [49].
Maximum PLA Domain (area) (μm2)
Overall Average (μm2)
50PLA/B3
123.94
5.26
50PBAT/B3
13.24
1.59
5050premixed/B3
9.16
0.95
Table 2.
Effect of mixing sequence on the PLA domain size. Maximum and overall average of the PLA phase area in the 50PLA/B3, 50PBAT/B3, and 5050premixed/B3 (obtained from TEM images).
Figure 8.
Size distribution of PLA particles in the 50PLA/B3 (PLA), 50PBAT/B3 (PBAT), and 5050premixed/B3 (premixed). The units for size ranges are μm2.
The SEM images of the 70PLA/B3 and 30PBAT/B3 are shown in Figure 9. A semicontinuous structure for PLA was observed for 70PLA/B3 blend unlike the 30PBAT/B3 one. To further detect the level of co-continuity in the 70PLA/B3 blend, TEM images of the former blend were acquired, which showed the continuity of each phase to be considerable (Figure 10).
Figure 9.
SEM images of blends with PLA/PBAT ratio of 70 to 30: (a) 70PLA/B3, (b) 30PBAT/B3 [42].
Figure 10.
TEM images of 70PLA/B3 at two magnifications. (a): 1 μm and (b) 200 nm. The lighter phase is PLA and the darker phase is PBAT [42].
Since the numerical ratio of the two polymers was kept the same in the 70PLA/B3 and 30PLA/B3 samples but the continuity was not observed in the latter samples, the ratio of the two polymers is not a significant factor in forming the semi-co-continuous morphology. The effect of organoclay’s presence on the morphology of the PLA phase, as was explained for the 50PLA/B3 samples, and the effect of the particles in stabilizing the kinetic factors introduced through the mixing procedure are likely the reasons for the observed continuity. Figure 10b shows the TEM image of 70PLA/B3 in a larger magnification, which makes it possible to observe some of the clay platelets forming a network structure in this phase. Several studies have shown formation of a co-continuous morphology with assistance of organoclay particles [48, 50]. A schematic morphology of 70PLA/B3 blend and the effect of clay network on formation of co-continuous morphology has been illustrated in Figure 11.
Figure 11.
Schematic illustration of the effect of clay network on the morphology of 70PLA/B3 sample. Organoclay network enhances the continuity of the phase. The lighter phase is PLA and the darker phase is PBAT.
3.5 Thermal analysis
Thermal stabilities of the samples with a 50/50 ratio were analyzed using TGA instrument. Figure 12 shows the weight loss of these samples when heated to 500°C as well as the degradation graphs of neat PLA and PBAT for comparison. As shown, the PLA degradation occurs prior to PBAT. Therefore, the temperatures reported for up to 10% weight loss in Table 3 should be explained with regard to PLA’s degradation. A 1% weight loss did not occur till the temperature reached 272.53°C for 50PLA/B3, 279.89°C for 50PBAT/B3, and 287.1°C for the 5050premixed/B3 sample. A similar trend was observed in the 5 and 10% weight loss temperatures as the lowest stability was observed for the 50PLA/B3, and the 5050premixed/B3 blend showed the highest temperature for the onset of degradation.
Figure 12.
Thermal degradation of PLA, PBAT, 50PBAT/B3, 50PLA/B3, and the 5050premixed/B3 samples.
Weight Loss %
Temperature (°C)
50PBAT/B3
50PLA/B3
5050Premixed/B3
1
279.89
272.53
287.10
5
334.46
331.74
338.73
10
346.19
345.63
348.89
Table 3.
Thermal degradation of 50PBAT/B3, 50PLA/B3 and the 5050premixed/B3 samples.
The degradation trend of the samples relates directly to the level of clay dispersion in the PLA phase. As it was explained earlier, the premixed samples showed the lowest clay dispersion, which shows the highest temperature for the onset of the degradation. The PLA phase of the 50PLA/B3 sample contained the largest content of dispersed organoclay and showed the lowest thermal stability.
Paul et al. [51] evaluated the hydrolytic degradation of PLA nanocomposites and observed the presence of organoclay accelerated the degradation of PLA. The highest degradation was observed in samples containing unmodified clay, which could be explained by the higher hydrophilicity of the particles. This could lead to an overall conclusion that clay’s role in the acceleration of the degradation of PLA could be from the greater absorption of water by these particles [52, 53].
The increasing global demand for sustainable alternatives has led to a growing interest in biodegradable polymers as a solution to mitigate the environmental impact of traditional plastics. However, the field faces significant challenges, especially in enhancing the performance of biodegradable polymers to exceed conventional plastic benchmarks. Among these, poly(lactic acid) (PLA) stands out for its renewable sourcing but is hindered by brittleness, prompting study into blending with other biodegradable polymers such as poly(butylene adipate-co-terephthalate) (PBAT). Despite promising results in increased elongation, challenges persist, with blends demonstrating lower modulus and strength than pure PLA. The incorporation of organically modified nanoclay as a compatibilizing agent suggests a practical solution to overcome these limitations. However, the dispersion of nanoparticles within the blend, influenced by polymer–polymer interactions and mixing sequences, poses a significant challenge. Achieving a thermodynamic equilibrium state becomes difficult due to the high viscosity of polymers, affecting the location of organoclay particles and, consequently, the final properties of the blend. Understanding the complicated dynamics of mixing sequences is crucial for tailoring polymers with desired properties, making this an important area for further research in the field.
This work investigated the effect of sequential mixing of organically modified silicate layers on the rheology, morphology, and thermal properties of PBAT and PLA blends. The TEM results exhibited partial dispersion of the silicate layers in the blend. The premixed samples achieved the lowest level of clay dispersion among the samples studied. Better dispersion of the silicate layers in the 50PLA/B3 and 50PBAT/B3 indicates that a higher level of dispersion for clay can be achieved when it is mixed with a single polymer than when mixed with a blend of two polymers.
For blends with 50/50 ratio, solid-like behavior was observed in the melt state for the sequentially mixed composites but not for the premixed one. The rheological data are consistent with the quality of dispersion observed in the TEM images as the premixed blend showed the worst dispersion of the clay platelets and the lowest storage and loss modulus with highest dependence on the frequency.
Larger PLA domain sizes were detected in the 50PLA/B3 sample among the 50/50 ratio blends due to its partial continuity of the PLA phase dispersed in the PBAT matrix. Both phases were partially continuous in the 70PLA/B3 sample.
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Written By
Mahin Shahlari, Bahareh Baheri and Sunggyu Lee
Submitted: 21 January 2024Reviewed: 15 February 2024Published: 29 March 2024
Open access peer-reviewed chapter
