Phase Behavior and Thermo-Mechanical Properties of IF-WS2 Reinforced PP–PET Blend-Based Nanocomposites

The industrial advancement of high-performance technologies directly depends on the thermo-mechanical properties of materials. Here we give an account of a facile approach for the bulk production of a polyethylene terephthalate (PET)/polypropylene (PP)-based nanocomposite blend with Inorganic Fullerene Tungsten Sulfide (IF-WS2) nanofiller using a single extruder. Nanofiller IF-WS2 was produced by the rotary chemical vapor deposition (RCVD) method. Subsequently, IF-WS2 nanoparticles were dispersed in PET and PP in different loadings to access impact and their dispersion behavior in polymer matrices. As-prepared blend nanocomposites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), dynamic differential scanning (DSC), dynamic mechanical analysis (DMA), and X-ray diffraction (XRD). In this work, the tensile strength of the PP/PET matrix with 1% IF-WS2 increased by 31.8%, and the thermal stability of the sample PP/PET matrix with 2% increased by 18 °C. There was an extraordinary decrease in weight loss at elevated temperature for the nanocomposites in TGA analysis, which confirms the role of IF-WS2 on thermal stability versus plain nanocomposites. In addition, this method can also be used for the large-scale production of such materials used in high-temperature environments.

. Summary of recent work about IF-WS 2 -based polymer nanomaterials to reinforce properties.

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Blending Partner Focused Study Ref.

Materials
Polypropylene (PP, model specification, M2500E) with MFI = 2.5 g/10 min at 200 • C/5 Kg was purchased in this study from Shanghai Petrochemical Co. Ltd. (Shanghai, China), as white transparent. PET (model specification, Dupont 530) was supplied from E. I. DuPont de Nemours and Company, Wilmington, DE, USA. The IF-WS 2 nanoparticles were synthesized by Xu Fang's rotary furnace reaction method [19]. The average size is 90 nm (80-110 nm).

Characterization of IF-WS 2 /PP/PET Nanocomposites
Scanning Electron Microscopy (SEM, Hitachi SU8220, Chiyoda, Tokyo, Japan) was used for observing the morphology of IF-WS 2 /PP/PET nanocomposites, 15 kV operational voltage, and the samples were pre-coated with a thin gold layer. X-ray diffraction (XRD, Rigaku D/MAX 2500V, Matsubara-cho, Akishima-shi, Tokyo, Japan) was operated to appraise the crystal structure analysis, a step size of 0.03 • , over a 2θ range of 10-80 • . Transmission electron microscopy (TEM, FEI TECNAI G2 F30, Hillsboro, OR, USA) was performed to study the micrographs of the IF-WS 2 nanoparticles and the actual particle distribution of the matrix. Also, the test nanocomposite sample was prepared into 0.3 × 0.3 mm by a diamond razor blade, with a sample thickness of 100 nm during the TEM test. The mechanical properties of nanocomposites (Dumbbell shape) were tested by material mechanics experimental system (British model specification 8801, INSTRON, Norwood, MA, USA), with test speed of 50 mm/min at room temperature and the specimen. At least 5 samples were tested for each concentrate of materials. Thermogravimetric analysis (TGA, Perkin Elmer-4000, Waltham, MA, USA) of neat blends and nanocomposites were carried out under a dried nitrogen atmosphere at a scan rate 10 • C/min in the temperature range 30-800 • C. The melting temperature and crystallization temperature curves of the nanocomposite were obtained from dynamic differential scanning (DSC, model specification, TA instruments-Model 25, New Castle, DE, USA). Dynamic mechanical analysis (DMA, TA instruments-Model 850, New Castle, DE, USA) was characterized in the tensile mode at a frequency of 1 Hz, with rectangular geometry films, at temperatures from 30-200 • C. Specimens of the storage modulus (E') and as a function of the temperature were appraised using a heating rate of 3 • C/min.

Structure and Morphology Analysis of IF-WS 2 Nanoparticles
The morphology and structure of IF-WS 2 nanoparticles were characterized by SEM and TEM in Figure 2. As shown in Figure 2a,b, the IF-WS 2 nanoparticles presented spherical and hemispherical nanostructures with a size of about 90-110 nm. The hollow-cage configuration of nanoparticles is clearly shown in Figure 2c,d. Meanwhile, it can be noticed that there are multiple closed-ring structures at the edges of the nanoparticles in Figure 2d.

SEM Analysis
The SEM images of the fractured surface of neat blend and nanocomposites are presented in Figure 3. These images demonstrate an imaginable mechanism for reinforcement owing to the incorporation of IF-WS2 as a nanofiller in nanocomposites. The pure PP-PET blend with clear droplet and cracked structure is signified, which is owing to the immiscibility controlled by the viscosity hysteresis between PP and PET. Furthermore, it is believed that the droplet is a form of PET due to the high shear pressure extracted from PP during the melting and compounding process. The droplets can be seen clearly. Meanwhile, the cracks and open-ring structures (as indicated by the circle) can be seen more clearly in the magnified SEM image of the pure PP-PET blend. Indeed, a very highly incompatible property of PP and PET blend was confirmed by SEM observation reported elsewhere [17]. Moreover, with the addition of IF-WS2 into PP-PET by 0.1%, an indistinctive change in surface morphologies of nanocomposite was exhibited in Figure 3 (PP/PET0.1). In addition, little decrease in the size of PP phase along with the collapsing of droplets (coalescence phenomenon) into the surface can be observed in the same picture. The exact reason for coalescence of the polymer blends in the presence of IF-WS2 has been elaborated on elsewhere [18]. However, even in this case, cracking, droplets, and phase separation is quite observable and similar to the pure PP-PET system. Upon further loading, the same surface morphology was observed in the blend with 0.1% of IF-WS2. The degree of compatibility seems much better in the case of 0.5% loading owing to the nanosizing effect, decrease in droplet size, and increased miscibility (Figure 3 PP/PET0.5). Interestingly, 1% of IF-WS2 (Figure 3 PP/PET1.0) was loaded into the PP-PET blend, showing a high degree of compatibility, no cracks at the interface, and huge coalescence. In this case, the SEM image of blend nanocomposite shows no individual phases of PP and PET, which is an unswerving sign for sufficient loading of nanofiller to the blend system. In this case, the separate phases of PP and PET were not

SEM Analysis
The SEM images of the fractured surface of neat blend and nanocomposites are presented in Figure 3. These images demonstrate an imaginable mechanism for reinforcement owing to the incorporation of IF-WS 2 as a nanofiller in nanocomposites. The pure PP-PET blend with clear droplet and cracked structure is signified, which is owing to the immiscibility controlled by the viscosity hysteresis between PP and PET. Furthermore, it is believed that the droplet is a form of PET due to the high shear pressure extracted from PP during the melting and compounding process. The droplets can be seen clearly. Meanwhile, the cracks and open-ring structures (as indicated by the circle) can be seen more clearly in the magnified SEM image of the pure PP-PET blend. Indeed, a very highly incompatible property of PP and PET blend was confirmed by SEM observation reported elsewhere [17]. Moreover, with the addition of IF-WS 2 into PP-PET by 0.1%, an indistinctive change in surface morphologies of nanocomposite was exhibited in Figure 3 (PP/PET0.1). In addition, little decrease in the size of PP phase along with the collapsing of droplets (coalescence phenomenon) into the surface can be observed in the same picture. The exact reason for coalescence of the polymer blends in the presence of IF-WS 2 has been elaborated on elsewhere [18]. However, even in this case, cracking, droplets, and phase separation is quite observable and similar to the pure PP-PET system. Upon further loading, the same surface morphology was observed in the blend with 0.1% of IF-WS 2 . The degree of compatibility seems much better in the case of 0.5% loading owing to the nanosizing effect, decrease in droplet was loaded into the PP-PET blend, showing a high degree of compatibility, no cracks at the interface, and huge coalescence. In this case, the SEM image of blend nanocomposite shows no individual phases of PP and PET, which is an unswerving sign for sufficient loading of nanofiller to the blend system. In this case, the separate phases of PP and PET were not displayed. This is an unwavering sign that the nanofiller is sufficient to be loaded into the blended system. Moreover, the roughness of the surface in the case of 1% of IF loading suggests better adhesion at the PET-PP interface and better thermo-mechanical properties (Figure 3 PP/PET1.0). Therefore, the 1% IF-WS 2 loading showed a complete change in the obvious aggregation morphology of the PP-PET phase, which may be due to the nucleation of IF nanoparticles in PET and promote the collapse of the droplets. Surprisingly, droplet formation, cracking, and diminished coalescence phenomenon are described with the further increase of IF-WS 2 loading (such as 1.5% and 2% loading) in Figure 3 (PP/PET1.5, PP/PET2.0). This is mainly due to the aggregation of nanofillers in the blend matrix, which is related to the decrease in the mechanical properties of blend PP/PET1.5 and PPPET2.0 [28].
Polymers 2020, 12, x FOR PEER REVIEW 6 of 15 collapse of the droplets. Surprisingly, droplet formation, cracking, and diminished coalescence phenomenon are described with the further increase of IF-WS2 loading (such as 1.5% and 2% loading) in Figure 3 (PP/PET1.5, PP/PET2.0). This is mainly due to the aggregation of nanofillers in the blend matrix, which is related to the decrease in the mechanical properties of blend PP/PET1.5 and PPPET2.0 [28].

TEM Analysis
The exact distribution of IF-WS2 in PP-PET was auxiliary deliberated using the high resolution transmission electron microscope (HRTEM) technique. Here we are only presenting TEM images of polymer blends with 1% and 2% of IF-WS2 instead of all samples. The logic behind selecting only these two samples is similar to the SEM morphology remaining samples. Figure 4 (PP/PET1.0) shows typical TEM pictures of the PP-PET sample containing 1% IF-WS2, and nanofillers can be seen at the interfaces of PP and PET. Moreover, IF-WS2 is well dispersed in both phases, and IF-WS2 nanoparticles can be seen in microtome slice sample. The light gray and dark gray parts in the TEM image correspond to PP and PET blends, respectively. The uniform dispersion of IF-WS2 may be due to the positive interaction between the oxygen functional groups of the nanofiller and the polar groups of PET. If pragmatic, all IF-WS2 were mostly localized in the PET polymer due to its viscoelastic property along with significant amount rapped on PP polymer chains. The TEM images of blend consisting of 2% of IF-WS2 and highly aggregated IF-WS2 can be seen in PET along with a few portions of interfaces as well ( Figure 4, PP/PET2.0).

TEM Analysis
The exact distribution of IF-WS 2 in PP-PET was auxiliary deliberated using the high resolution transmission electron microscope (HRTEM) technique. Here we are only presenting TEM images of polymer blends with 1% and 2% of IF-WS 2 instead of all samples. The logic behind selecting only these two samples is similar to the SEM morphology remaining samples. Figure 4 (PP/PET1.0) shows typical TEM pictures of the PP-PET sample containing 1% IF-WS 2 , and nanofillers can be seen at the interfaces of PP and PET. Moreover, IF-WS 2 is well dispersed in both phases, and IF-WS 2 nanoparticles can be seen in microtome slice sample. The light gray and dark gray parts in the TEM image correspond to PP and PET blends, respectively. The uniform dispersion of IF-WS 2 may be due to the positive interaction between the oxygen functional groups of the nanofiller and the polar groups of PET. If pragmatic, all IF-WS 2 were mostly localized in the PET polymer due to its viscoelastic property along with significant amount rapped on PP polymer chains. The TEM images of blend consisting of 2% of IF-WS 2 and highly aggregated IF-WS 2 can be seen in PET along with a few portions of interfaces as well (Figure 4, PP/PET2.0).

Tensile Properties
The tensile strength and elongation at break (%) of pure blend and nanocomposites with different amounts of IF-WS2 (0.1 wt% to 2 wt%) are shown in Figure 5. Typical tensile strength curves of the neat blend and nanocomposites clearly demonstrate a distinct improvement in tensile strength on the appropriate addition of IF-WS2 owing to the nucleation and nanosizing effect. The value of tensile strength of samples very clearly implies a role of different loading of IF-WS2, and as a result was against the plain blend sample. The 1 wt% composite presented a 31.8% improvement in the ultimate tensile strength, which increased from 13.06 MPa to 17.22 MPa in Table 3. This can be attributed to the bridging effect of IF-WS2 which functions as a stress-transferring medium between the blending partners and agrees with previous studies [24,26]. Here, outcomes show the nanocomposite with 1% of IF-WS2 had the highest value of tensile modulus compared to all other samples, and a further increase in loading to 2% shows a declined trend in the tensile strength, which may be due to agglomeration (due to excess loading) of IF-WS2 in the blend matrix and hence the appropriate loading is crucial to enhancing thermo-mechanical properties. It mostly happened due to preferential dispersion of IF-WS2 in the minor PET phase and controlled by polar-polar interaction at optimum loading. The role of different loading of IF-WS2 is also discussed in detail in the TGA and DSC section.

Tensile Properties
The tensile strength and elongation at break (%) of pure blend and nanocomposites with different amounts of IF-WS 2 (0.1 wt% to 2 wt%) are shown in Figure 5. Typical tensile strength curves of the neat blend and nanocomposites clearly demonstrate a distinct improvement in tensile strength on the appropriate addition of IF-WS 2 owing to the nucleation and nanosizing effect. The value of tensile strength of samples very clearly implies a role of different loading of IF-WS 2 , and as a result was against the plain blend sample. The 1 wt% composite presented a 31.8% improvement in the ultimate tensile strength, which increased from 13.06 MPa to 17.22 MPa in Table 3. This can be attributed to the bridging effect of IF-WS 2 which functions as a stress-transferring medium between the blending partners and agrees with previous studies [24,26]. Here, outcomes show the nanocomposite with 1% of IF-WS 2 had the highest value of tensile modulus compared to all other samples, and a further increase in loading to 2% shows a declined trend in the tensile strength, which may be due to agglomeration (due to excess loading) of IF-WS 2 in the blend matrix and hence the appropriate loading is crucial to enhancing thermo-mechanical properties. It mostly happened due to preferential dispersion of IF-WS 2 in the minor PET phase and controlled by polar-polar interaction at optimum loading. The role of different loading of IF-WS 2 is also discussed in detail in the TGA and DSC section.

XRD Analysis
The impact of different loadings of IF-WS2 on crystallinity of prepared polymer nanocomposites was investigated using XRD and plots are presented in Figure 6. The effect of different loadings of IF-WS2 on the crystallinity of the fabricated nanocomposites was observed using XRD technology. The semi-crystalline property of the pure blend and nanocomposite materials was different due to the shift of the IF-WS2 loading in Figure 6. In the XRD plot, the characteristic diffraction peak for the PP and PET agree well with previous results [39]. However, a slight change in the peak position (especially in change in width) in the case of the blends containing IF-WS2 can be perceived when equated to the pure blend. As a semi-crystalline plastic, PP matrix has characteristic diffraction peaks of 2θ = 14.1°, 17.1° and 18.6°, corresponding to the planes (110), (040), and (130), which are typical reflections of α-crystals. In addition, it can be seen that the characteristic diffraction peak of the pure copolymer matrix with the content of IF-WS2 has a significant shift to the (002) characteristic diffraction peak of IF-WS2. The analysis suggests that this may be due to the interaction of the peak of IF-WS2 and the blend. Interestingly, most of the well-defined peak positions in the figure for assynthesized nanocomposites are closer to peaks for PET and PP, either merged or very tiny. The blends indicate a semi-crystalline property, and a new bond structure is clearly expected from the observations of different peak positions of the newly fabricated materials. The XRD peaks for 0.1% and 0.5% IF-WS2 loading are very similar to each other and it is very difficult to see any measure of impact of the nanofiller. This result is consistent with SEM and tensile results. On the other hand, in the case of 1.5 and 2% IF-WS2 loading, sharpness in one of two prominent XRD peaks get pronounced, which may be attributed to the aggregation of IF-WS2 perennially in the PET phase, while PP is strapped outside and result low thermal stability as discussed in TGA/DSC section. Undeniably, both prominent peaks get equally sharp and intense in the case of 1% of IF-WS2 loading. It implies 1% IF-WS2 is sufficient and could be the best content for PP-PET-based polymer nanocomposites. Moreover, predominant deposition of IF-WS2 in only the PET phase can disrupt the non-bonding

XRD Analysis
The impact of different loadings of IF-WS 2 on crystallinity of prepared polymer nanocomposites was investigated using XRD and plots are presented in Figure 6. The effect of different loadings of IF-WS 2 on the crystallinity of the fabricated nanocomposites was observed using XRD technology. The semi-crystalline property of the pure blend and nanocomposite materials was different due to the shift of the IF-WS 2 loading in Figure 6. In the XRD plot, the characteristic diffraction peak for the PP and PET agree well with previous results [39]. However, a slight change in the peak position (especially in change in width) in the case of the blends containing IF-WS 2 can be perceived when equated to the pure blend. As a semi-crystalline plastic, PP matrix has characteristic diffraction peaks of 2θ = 14.1 • , 17.1 • and 18.6 • , corresponding to the planes (110), (040), and (130), which are typical reflections of α-crystals. In addition, it can be seen that the characteristic diffraction peak of the pure copolymer matrix with the content of IF-WS 2 has a significant shift to the (002) characteristic diffraction peak of IF-WS 2 . The analysis suggests that this may be due to the interaction of the peak of IF-WS 2 and the blend. Interestingly, most of the well-defined peak positions in the figure for as-synthesized nanocomposites are closer to peaks for PET and PP, either merged or very tiny. The blends indicate a semi-crystalline property, and a new bond structure is clearly expected from the observations of different peak positions of the newly fabricated materials. The XRD peaks for 0.1% and 0.5% IF-WS 2 loading are very similar to each other and it is very difficult to see any measure of impact of the nanofiller. This result is consistent with SEM and tensile results. On the other hand, in the case of 1.5 and 2% IF-WS 2 loading, sharpness in one of two prominent XRD peaks get pronounced, which may be attributed to the aggregation of IF-WS 2 perennially in the PET phase, while PP is strapped outside and result low thermal stability as discussed in TGA/DSC section. Undeniably, both prominent peaks get equally sharp and intense in the case of 1% of IF-WS 2 loading. It implies 1% IF-WS 2 is sufficient and could be the best content for PP-PET-based polymer nanocomposites. Moreover, predominant deposition of IF-WS 2 in only the PET phase can disrupt the non-bonding interactions among polymer chains acting as a barrier between two chains [40]. The excess dispersion of IF-WS 2 in PET phase could be due to lower viscosity of PP as compared to PP at melting conditions. interactions among polymer chains acting as a barrier between two chains [40]. The excess dispersion of IF-WS2 in PET phase could be due to lower viscosity of PP as compared to PP at melting conditions.

TGA Analysis
To examine thermal properties and weight loss of neat blend and nanocomposites, TGA was conducted and a TG thermogram is presented in Figure 7. The data obtained from TGA is presented in Table 2. The data reveals that due to the incorporation of IF-WS2, Ts (onset degradation) was shifted toward a higher temperature. From Figure 7, it is also clear that the 1% IF-WS2 loading is enough for its homogeneous dispersion and greatly affects phase behavior of polymer nanocomposites, as discussed in the SEM section. It is well established that PP and PET start gigantic thermal decomposition above 280 °C and 250 °C, respectively, and its pure blend beyond 310 °C, as reported in [41,42]. However, in the present study, pure blend showed weight loss as expected, while weight loss of nanocomposites with IF-WS2 is significantly increased and can be observed in the graph. This reflection might be accredited to cross-liking between the PP and PET governed to the incorporation of IF-WS2 as discussed in the SEM and tensile properties sections. Thus, the nucleation and crossliking nanosizing effect of IF-WS2 offers a combined response of both blending allies toward the uniform heat distribution during heating in TG testing. With the increase of IF-WS2 loading, the loading of IF-WS2 nanoparticles leads to enhanced crosslinking of the interface, delays the unfavorable enthalpy (increase of molecular motion) conditions, and leads to enhanced thermal stability. Under a load of 0.1% and 0.5%, the phase separation and crosslinking is weakened due to insufficient nanofillers. Although the thermal stability has increased under 1.5% and 2.0% loads, the enhancement was not obvious. Meanwhile, the char residue of different mass of IF-WS2/PP/PET nanocomposite can be clearly obtained in Table 4. In this study, the nanocomposite loaded with 1% IF-WS2 has the highest char residue, which is further confirmed when the nanocomposite has better thermal stability with 1% IF-WS2 loading. Therefore, the 1% load can make the nanocomposite have good thermal stability and economic efficiency.

TGA Analysis
To examine thermal properties and weight loss of neat blend and nanocomposites, TGA was conducted and a TG thermogram is presented in Figure 7. The data obtained from TGA is presented in Table 2. The data reveals that due to the incorporation of IF-WS 2 , T s (onset degradation) was shifted toward a higher temperature. From Figure 7, it is also clear that the 1% IF-WS 2 loading is enough for its homogeneous dispersion and greatly affects phase behavior of polymer nanocomposites, as discussed in the SEM section. It is well established that PP and PET start gigantic thermal decomposition above 280 • C and 250 • C, respectively, and its pure blend beyond 310 • C, as reported in [41,42]. However, in the present study, pure blend showed weight loss as expected, while weight loss of nanocomposites with IF-WS 2 is significantly increased and can be observed in the graph. This reflection might be accredited to cross-liking between the PP and PET governed to the incorporation of IF-WS 2 as discussed in the SEM and tensile properties sections. Thus, the nucleation and cross-liking nanosizing effect of IF-WS 2 offers a combined response of both blending allies toward the uniform heat distribution during heating in TG testing. With the increase of IF-WS 2 loading, the loading of IF-WS 2 nanoparticles leads to enhanced crosslinking of the interface, delays the unfavorable enthalpy (increase of molecular motion) conditions, and leads to enhanced thermal stability. Under a load of 0.1% and 0.5%, the phase separation and crosslinking is weakened due to insufficient nanofillers. Although the thermal stability has increased under 1.5% and 2.0% loads, the enhancement was not obvious. Meanwhile, the char residue of different mass of IF-WS 2 /PP/PET nanocomposite can be clearly obtained in Table 4. In this study, the nanocomposite loaded with 1% IF-WS 2 has the highest char residue, which is further confirmed when the nanocomposite has better thermal stability with 1% IF-WS 2 loading. Therefore, the 1% load can make the nanocomposite have good thermal stability and economic efficiency.  Table 4. Thermogravimetric analysis (TGA) critical points of IF-WS2/PP/PET nanocomposites under nitrogen flow at a heating rate of 10 °C/min (TS represents the onset temperature of degradation, Tm represents the maximum temperature of decomposition, and T50 represents the decomposition temperature of the nanocomposite when the mass loss was 50%).

DSC Analysis
The DSC curves of pure blend and nanocomposites is shown in Figure 8. the melting temperature of the nanocomposites is presented in Table 5. Since melting temperature of PP and glass transition temperature of PET comes near each other at around 80 °C, this region is analyzed for thermal characterization of fabricated systems. Similarly, merging of melting temperature and glass transition temperature of two different polymer has also been previously reported [7]. In the present case there is no peak in DSC thermogram instead of melting region 145-155 °C.  Table 4. Thermogravimetric analysis (TGA) critical points of IF-WS 2 /PP/PET nanocomposites under nitrogen flow at a heating rate of 10 • C/min (T S represents the onset temperature of degradation, T m represents the maximum temperature of decomposition, and T 50 represents the decomposition temperature of the nanocomposite when the mass loss was 50%).

DSC Analysis
The DSC curves of pure blend and nanocomposites is shown in Figure 8. the melting temperature of the nanocomposites is presented in Table 5. Since melting temperature of PP and glass transition temperature of PET comes near each other at around 80 • C, this region is analyzed for thermal characterization of fabricated systems. Similarly, merging of melting temperature and glass transition temperature of two different polymer has also been previously reported [7]. In the present case there is no peak in DSC thermogram instead of melting region 145-155 • C. From the DSC graph, it is clear that the assimilation of IF-WS2 into PP-PET matrices made significant changes in thermal stability. The results shown that at a lower loading (0.1% and 0.5%) there is a diminutive increase in the melting point of PP, which recommends that the maximum nanofiller distributed in the PET is due to better interaction and its high viscosity at melting condition restrict migration of IF-WS2 as previously reported. On the other hand, higher loading (1.5% and 2%) decreased melting temperature, which is attributed to phase separation. Among the PP and PET, PET is quite polar while PP is non-polar. During melt-compounding, polar-polar interaction among PET and IF-WS2 might influence its dispersion in a PP-PET blending system. Such interaction of IF-WS2 first migrates to the PET phase and then to PP. However, in the case of higher loading, this migration is badly restricted by the higher viscosity of the PET phase, and results in the aggregation of nanofiller, as shown in the TEM section. Thus, the migration and uniform dispersion of IF-WS2 into polymer matrices is controlled by kinetic (viscosity lag between PP and PET) and thermodynamic effects (polar and non-polar interaction of PET with IF-WS2).

Storage Modulus Analysis
Variation in the storage modulus as a function of temperature for the as-fabricated polymeric systems is presented in Figure 9. A linear decrease in storage modulus with increase of temperature can be observed of up to 1% IF-WS2 loading and vice versa beyond the 1% of loading. This alteration can be attributed to the increase in molecular motion of the blend partners, owing to rapid thermal  From the DSC graph, it is clear that the assimilation of IF-WS 2 into PP-PET matrices made significant changes in thermal stability. The results shown that at a lower loading (0.1% and 0.5%) there is a diminutive increase in the melting point of PP, which recommends that the maximum nanofiller distributed in the PET is due to better interaction and its high viscosity at melting condition restrict migration of IF-WS 2 as previously reported. On the other hand, higher loading (1.5% and 2%) decreased melting temperature, which is attributed to phase separation. Among the PP and PET, PET is quite polar while PP is non-polar. During melt-compounding, polar-polar interaction among PET and IF-WS 2 might influence its dispersion in a PP-PET blending system. Such interaction of IF-WS 2 first migrates to the PET phase and then to PP. However, in the case of higher loading, this migration is badly restricted by the higher viscosity of the PET phase, and results in the aggregation of nanofiller, as shown in the TEM section. Thus, the migration and uniform dispersion of IF-WS 2 into polymer matrices is controlled by kinetic (viscosity lag between PP and PET) and thermodynamic effects (polar and non-polar interaction of PET with IF-WS 2 ).

Storage Modulus Analysis
Variation in the storage modulus as a function of temperature for the as-fabricated polymeric systems is presented in Figure 9. A linear decrease in storage modulus with increase of temperature can be observed of up to 1% IF-WS 2 loading and vice versa beyond the 1% of loading. This alteration can be attributed to the increase in molecular motion of the blend partners, owing to rapid thermal conduction and a resulting decrease in rigidity. This observation is in well in accordance with DSC results.
attributed to the uninform dispersion of IF-WS2 in both PP and PET phases as discussed in the DSC and tensile testing sections. Also, a high aspect ratio of IF-WS2 increases the polymer-nanoparticle interaction area and hence the smooth stress transfers to enhance the storage modulus. However, increase in IF-WS2 loading to 2% expressions lowers the storage modulus as compared to PPPET1.0 blend nanocomposite, which can be attributed to the agglomeration of IF-WS2 as presented in the TEM section.

Conclusions
In summary, the uniform distribution of IF-WS2 in PP-PET composites has been efficaciously realized using melt-compounding methodology. Thermal stabilities and strengths of as-fabricated blend systems with increased loading of IF-WS2 were examined using DSC, TGA, DMA, and tensile instruments. This examination confirms improved compatibility between immiscible blending partners and facilitates enhanced stress transfer at the interface during thermo-mechanical testing. Thus, a strategy was extended to increase the compatibility of PP and PET wherein IF-WS2 localized at the interface enhanced the interaction between the blend components. Furthermore, selective dispersion of IF-WS2 and its effect on PP-PET morphological properties was observed for nanocomposites, signifying better stress transfer at the interface. A diagram exemplifying the formation of droplets on the surface of nanocomposites and the aggregation of IF-WS2 is also presented as a graphical abstract.
Author Contributions: D.C. is mainly responsible for the fabrication of IF-WS2 and the entire experimental performance analysis of the nanocomposite. J.L., Z.M., J.W., F.W., S.L. contributed to the preparation of polymer nanocomposites. S.K.T., K.T., and Z.Y. assisted in the analysis of the experimental results, and N.W. and Y.Z. gave many detailed instructions on the idea and process of the whole experiment. All authors have read and agreed to the published version of the manuscript.  A notable increase in storage modulus for the PPPET1.0 in the elastomeric region due to the incorporation of IF-WS 2 can be observed. The maximum increase in storage modulus for 1% can be attributed to the uninform dispersion of IF-WS 2 in both PP and PET phases as discussed in the DSC and tensile testing sections. Also, a high aspect ratio of IF-WS 2 increases the polymer-nanoparticle interaction area and hence the smooth stress transfers to enhance the storage modulus. However, increase in IF-WS 2 loading to 2% expressions lowers the storage modulus as compared to PPPET1.0 blend nanocomposite, which can be attributed to the agglomeration of IF-WS 2 as presented in the TEM section.

Conclusions
In summary, the uniform distribution of IF-WS 2 in PP-PET composites has been efficaciously realized using melt-compounding methodology. Thermal stabilities and strengths of as-fabricated blend systems with increased loading of IF-WS 2 were examined using DSC, TGA, DMA, and tensile instruments. This examination confirms improved compatibility between immiscible blending partners and facilitates enhanced stress transfer at the interface during thermo-mechanical testing. Thus, a strategy was extended to increase the compatibility of PP and PET wherein IF-WS 2 localized at the interface enhanced the interaction between the blend components. Furthermore, selective dispersion of IF-WS 2 and its effect on PP-PET morphological properties was observed for nanocomposites, signifying better stress transfer at the interface. A diagram exemplifying the formation of droplets on the surface of nanocomposites and the aggregation of IF-WS 2 is also presented as a graphical abstract.
Author Contributions: D.C. is mainly responsible for the fabrication of IF-WS 2 and the entire experimental performance analysis of the nanocomposite. J.L., Z.M., J.W., F.W., S.L. contributed to the preparation of polymer nanocomposites. S.K.T., K.T., and Z.Y. assisted in the analysis of the experimental results, and N.W. and Y.Z. gave many detailed instructions on the idea and process of the whole experiment. All authors have read and agreed to the published version of the manuscript.
Funding: This study was supported by grants from the National Natural Science Foundation (Grant NO:51972068) and Key Laboratory of New Processing Technology for Nonferrous Metals and Materials.