Clay Nanocomposites

Article pubs.acs.org/IECR

Investigation of Mechanical Properties of PP/Clay Nanocomposites Based on Network Cross-Linked Compatibilizers Catalina G. Sanporean (previously Potarniche),*,†,§ Zina Vuluga,*,‡,§ Jesper deClaville Christiansen,† Constantin Radovici,‡ Erik A. Jensen,† and Horia Paven‡ †

Department of Mechanical and Manufacturing Engineering, Aalborg University, Fibigerstraede 16 DK-9220 Aalborg, Denmark National Research and Developement Institute for Chemistry and Petrochemistry-ICECHIM, Bucharest, Romania

‡

S Supporting Information *

ABSTRACT: Nanocomposites of polypropylene with organically modified clay were obtained on a corotating extruder. The modification of clay was done by swelling with a polyetherdiamine which undergoes cross-linking reaction with maleated polypropylene. The effect of clay concentration and of thermal treatment was studied from a morphological and mechanical point of view. The structure was analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and dynamic-mechanical thermal analyses (DMTA). Nanocomposites with 1 and 2 wt% silicate concentration presented improvement in mechanical properties. The improvements observed were: 20% increase in tensile strength, 21% increase in Young modulus, 34% reduction in creep strain and 30% decrease in tensile strain after cyclic loading, meaning improved fatigue.

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INTRODUCTION Polymer nanocomposites have attracted great interest from researchers since these materials exhibit improved properties. Generally speaking, the mechanical properties of polymer reinforced at the nanoscale level are determined by the complex relations between the nature and the size of the filler, the hybrid interface and the type of the interactions between the organic and inorganic components.1−9 The use of the silicate layered particles as nanofillers in polymer-based nanocomposites has mostly been focused on the cationic exchange capacity. However, Jiang-Jen Lin et al. reported the intercalation of poly(propylene oxide)amino acid by keeping the Na+ cations which forms a chelation structure with the modifier.10 Polypropylene (PP) is one of the most widely used nonpolar polyolefins. In the case of nonpolar polymers such as PP, exfoliation or delamination occurs only when the organoclay is further treated with compatibilizers.11 The most representative compatibilizer used for obtaining PP/clay nanocomposites is maleated polypropylene (PPMA).12,13 Researchers have found that surfactant containing active hydrogen atoms can interact with the PPMA in the interlayers.14−16 Therefore, the structure of surfactant probably influences the intercalation of PPMA. The three methods frequently used to obtain polymeric nanocomposites are intercalation of monomer followed by in situ polymerization, polymer intercalation from solution, and melt intercalation using a polymer mixer or extrusion.17−19 In this work, PP/organoclay nanocomposites were obtained by extrusion of PP with organic montmorillonite (MMT) in the presence of PPMA. The purposes of this work are: - to modify the clay with a polyetherdiamine by swelling - to thermally treat the obtained nanocomposites in order to obtain a cross-linked network - to improve the mechanical properties of polypropylene. © 2013 American Chemical Society

Polyetheramines are suitable for modifying the silicate surface due to their structure which can give dipole−dipole interaction between the backbone of the polymer and the clay surface.20 Another reason for using polyetheramines for obtaining PP nanocomposites is that these substances are compatible with PP21 and they can also react with PPMA. The objectives of this study are to investigate the effect of clay dispersion in a PP matrix, and the effect of thermal treatment on the structure and mechanical properties of nanocomposites.

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EXPERIMENTAL SECTION Materials. The PP matrix used for this study was a homopolymer produced by LyondellBasell. The grade name is HP400R, and the density = 0.905 g/cm3, melt flow rate = 25 g/ 10 min at 230 °C, 2.16 kg load. The Na-Cloisite (ClNa) was purchased from Southern Clay Products, Inc. Water content was about 7 wt % in the original state, and the particle size of the agglomerates was less than 13 μm. The polyetherdiamine which was used has the trade name Jeffamine ED 600. This compatibilizer was provided by Huntsman Co. and is a hydrophilic polyetherdiamine of approximately 600 g/mol molecular weight, with a propylene oxide/ethylene oxide (PO/ EO) mole ratio of about 3.6:9. Maleated polypropylene G-3015 was purchased from Eastman Chemical Company. It contains 1 wt % maleic anhydride, presents an acidic number of 15 mg KOH/g, and has a molecular weight of 47.000 g/mol. Preparation of PP/Clay Nanocomposites. The Jeffamine can be used to modify the layered silicates either by cationic Received: Revised: Accepted: Published: 3773

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Dynamic mechanical thermal analysis measurements in shear mode were performed using a Paar-Physica MCR500 modular compact rheometer fitted with SRF20 fixtures for rectangular solid torsion bars and a CTD600 convection oven. The tests were run in a temperature range of 25−160 °C with a frequency of 1 Hz, a strain of 0.01%, and a constant heating rate of 1 °C/min. During heating time the samples were subjected to a tensile load of 0.5 N to allow for thermal expansion of the material. Tensile, creep, and cyclic tests were carried out at room temperature on a universal tensile machine, INSTRON 5944, equipped with a static extensometer with the gauge length of 25 mm (series 2630-107) to control the tensile strain in the active zone. The tensile force was measured by a 2 kN load cell. Dog bone specimens for tensile tests (according to ASTM standard D-638), with the cross-sectional area 4 mm × 2 mm, were molded using a Thermo Scientific HAAKE MiniJet miniinjection molder. The error domain was computed for strength and stiffness, taking into account the results obtained on five different specimens.

exchange reactions if it is protonated or by dipole−dipole reactions.10 The modification of Cloisite-Na with Jeffamine (ClNa/Jeff) was done at a 1:1 wt ratio by mixing the silicate with the amine into a mortar for 10 min.22 After mixing, the components were allowed to swell for 24 h. This modification was made by keeping the Na+ between the silicate platelets and considering the dipole−dipole interactions which can occur between components.10 Nanocomposites were prepared by dispersing the modified Cloisite into the polypropylene matrix with 5 wt % PPMA. A Prism Eurolab 16 corotating twin-screw extruder was used for preparation of the nanocomposites. The temperature of the extruder was 200 °C from hopper to die. The screw speed was maintained at 300 rpm. The screws were set in a strong configuration with three mixing zones having mixing disks spaced at 90°. The final nanocomposites contain 1, 2, and 4 wt % unmodified silicate. Dried pellets of the nanocomposites were injection-molded into test bars for following mechanical tests using a Haakeminijet from Thermo Scientific. The temperature of the cylinder was 200 °C, the temperature of the mold was 70 °C, and the injection pressure was 800 bar. Even though the mixing was done in severe conditions of temperature and shear, we supposed that the residence time was too short for the reaction between the amine and the maleated group to finish;23,24 thus, three sets of nanocomposites were obtained. Accordingly, some of the obtained tensile bars were thermally treated in an oven for 24 h at 90 °C or at 120 °C, but some of them were kept untreated. The nanocomposites were denoted JXGY, J being from Jeffamine, X being the concentration of clay at 1, 2, or 4 wt %, while Y was the temperature of the thermal treatment. The polypropylene sample was noted MM, while the mixture of polypropylene with maleated polypropylene was noted MG. Characterization. The basal spacing, d001, was determined by means of X-ray diffraction (XRD) on a DRON diffractometer; the Co Kα radiation source (λ = 1.79021 Å) was used, filtered with Fe for removing the Kβ component in the Bragg−Brentano system (by reflection); the patterns were automatically recorded at small angles (2θ: 1.3 ÷ 12°). The samples were scanned at a scanning rate of 0.02°/5 s from 2θ values of 1.3−12° and 0.05°/ 5 s from 12° to 30°. DSC-TG analyses were carried out using a Netzsch DSC-TG type STA 449 C Jupiter differential scanning calorimeter− thermal analyzer. About 5 mg of each nanocomposite was weighed in the Al2O3 DSC pan and placed in the DSC cell. The samples were heated in the temperature range 25−550 °C, at a heating rate of 10 °C/min and under a current of air of 50 cm3/ min. The % of crystalline phase (X) was estimated using the following equation: X=

ΔH 100 w*ΔH100

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RESULTS AND DISCUSSION X-ray Diffraction Analyses. X-ray diffraction was performed on the Cloisite-Na, the Jeffamine modified with Cloisite-Na, and on the PP nanocomposites. Figure 1 illustrates

Figure 1. XRD patterns for (a) Cloisite Na and modified cloisite Na and (b) nanocomposites with 4 wt % cloisite Na, thermally treated and untreated.

the XRD patterns in the silicate region. As can be seen, during modification of ClNa, the Jeffamine intercalated between the silicate platelets as a bilayer, increasing the height of gallery with 8 Å, reported to the dehydrated silicate (Figure 1a). The excess of Jeffamine remained on the surface of silicate layers. In the nanocomposites, the intensity of the silicate characteristic peak increased when samples were subjected to thermal treatment, and a more ordered structure was formed. Delamination tendencies cannot be observed in the nanocomposites. FT-IR Spectroscopy. Figure 2 shows a schematic representation of the interactions and possible reactions that can occur between Jeffamine and PPMA after thermal treatment. Figure 3 shows the range of the spectral region between 1800 and 1500 cm−1 for the nanocomposites with and without

(1)

where ΔH is the enthalpy of melting of the analyzed sample, ΔH100 is the reference value for the enthalpy of melting of 100% crystalline polymer, and w is the weight fraction of PP in nanocomposite. For isotactic polypropylene, ΔH100 is 209 J/ g.25 Fourier transform infrared spectroscopy was performed on a Perkin Elmer spectrophotometer with selenium ATR crystal at a resolution of 4 cm−1. 3774

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After the thermal treatment at 90 °C, the intensity of the absorption bands at 1744 and 1560 cm−1 diminished, while the intensity of the absorption band at 1665 cm−1 increased and shifted toward a higher wavelength ∼1673 cm−1 (Figure 3b). This band corresponds to the CO of the imide link formed during thermal treatment.17,27,28 The nanocomposites treated at 120 °C presented the two increased bands at 1665 and 1560 cm−1 which are characteristic for the CO group from polyamic acid (Figure 3c). In the case of the nanocomposites with 4% layered silicate it can be noticed that the absorption band at 1560 cm−1 decreased in intensity, while the adsorption band at 1665 cm−1 increased and shifted toward a higher wavelength. This may be due to the formation of both types of imide and polyamic acid links in the same material (Figure 2). Regardless of the amount of silicate, the same reactions occur during the thermal treatment; at a high content of modified silicate, the reactions are more visible. Correlating XRD with FTIR, it can be said that the reaction occurred with the excess of Jeffamine found on the surface of silicate layers. Crystallization and Melting Behavior. Table 1 summarizes the corresponding melting temperature and the

Figure 2. Schematic representation of silicate Jeffamine interactions and possible reactions between Jeffamine and PPMA.

Table 1. Influence of Thermal Treatment on Melting Temperature and Degree of Crystallinity

Figure 3. FTIR spectra for PP nanocomposites (a) thermally untreated, (b) thermally treated at 90 °C, and (c) thermally treated at 120 °C.

a

sample name

Tma (°C)

Xmb (%)

MM MM90 MM120 J1G J1G90 J1G120 J2G J2G90 J2G120 J4G J4G90 J4G120

166.8 169 168.8 171.5 169.6 170.5 170.5 172.2 172.7 169.5 171.3 172.2

32.5 30.4 30.5 41.9 46.1 47.6 42.2 46.8 49.3 43.5 48.0 51.2

Melting temperature from DSC measurements. crystallinity from DSC measurements.

b

Degree of

crystallinity percentage computed using formula 1, taking into consideration the percent of additives incorporated into the polypropylene matrix. The increase of silicate concentration showed a small effect on the melting temperature. Probably, a concentration of ClNa higher than 4 wt % will decrease the melting peak below the PP value. However, it was observed that the thermal treatment increased both the melting temperature and the degree of crystallinity. These changes can be attributed to cross-linking which affected the materials structure. FTIR correlates with DSC results; the obtained imide and/or polyamic acid links increased the degree of crystallinity for thermally treated samples as well as for those treated at 120 °C. Thus, correlating XRD, FT-IR, and DSC, it can be said that the increase in the cross-linking degree reflected an increase of the melting temperature and the degree of crystallinity. The DMTA performed in shear mode revealed differences in the mechanical behavior of the nanocomposites (Figure 4). Materials behavior is strongly related to different amorphous and crystalline microstructure phases between PP and nanofiller. All nanocomposites presented a lower tan δ, probably due to increase of rigidity. However, in thermally untreated

thermal treatment. Thermally untreated nanocomposites presented two bands at 1665 and 1560 cm−1 (Figure 3a). The first one corresponds to the stretching vibration of the C O group from the amide, while the second one corresponds to the trans configuration of N−H and CO from secondary amides.26 The secondary amide formed in this case has the general name of polyamic acid. Usually this polymer is unstable and tends to convert to the fully cyclized imide link.27 It is possible that the reaction stopped due to the presence of the silicate layers. Untreated samples of polymeric nanocomposites presented a band at 1744 cm−1 which can be attributed to carbonyl groups of anhydride. Cyclic anhydrides are characterized by two CO stretching vibration bands 1778 and 1716 cm−1, the one at the lower wavenumber being usually more intense than the CO band at the higher wavenumber. However, in the mixture of PP with PPMA and in the nanocomposites, the CO stretching vibration from the maleic group was found to be a single band at 1744 cm−1. Thus, it can be said that during processing, the reaction between the amine and maleic group was not complete. 3775

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Figure 5. Loss factor (tan δ) for 2% layered silicate nanocomposites treated at different temperatures.

Figure 6. Storage modulus for thermally treated nanocomposites at 90 °C.

Figure 4. Loss factor tan δ as function of temperature for: (a) untreated nanocomposites, (b) thermally treated nanocomposites at 90 °C, and (c) thermally treated nanocomposites at 120 °C.

Mechanical Properties. Tensile Properties. The mechanical properties of PP nanocomposites are summarized in Table 2. The tensile strength increased with 15% for untreated nanocomposites when 1 wt % silicate was added and then started to decrease as the concentration of the silicate increased. This may suggest that during the obtaining process the reaction between the amine and maleic group was not finished. When thermally treated at 90 °C, the nanocomposites presented a tensile strength of approximately 37 MPa, and no influence of the silicate concentration can be noticed, meaning that a cross-linking network was formed and the silicate platelets may be locked inside the network. Nanocomposites treated at 120 °C presented a small reduction in tensile strength as the concentration of silicate increased. As FTIR results show, this reduction can be attributed to the fact that at 120 °C the polyamic acid was formed and acts as a defect in the network causing a reduction in strength. Another interesting observation is Young’s modulus standard deviation, which was ±5% for the untreated samples, while for the samples thermally treated at 90 °C the standard deviation was only ±0.5−1%. This reflected a more stable behavior of thermally treated samples which can be attributed to the imide link formation. Figure 7 illustrates the effect of thermal treatment upon nanocomposite necking points. The formation of a cross-linked network shifted the necking point of thermally treated nanocomposites at 90 °C with 10%, whereas in those thermally treated at 120 °C, it almost disappeared. However, a significant improvement can be noticed in Young’s modulus. As was expected, Young’s modulus increased with 21% for the thermally treated nanocomposites as compared to PP. Secant modulus at 1% was also computed and shows that thermally treated nanocomposites presented higher values of modulus compared to PP (Table 3).

nanocomposites α′ relaxation can be noticed at 72 °C (Figure 4a). Furthermore, for the thermally treated materials at 120 °C, α′ relaxation shifted to 83 °C. Cerrada et al.29,30 argue that this shift is related to the molecular orientation, caused either by the relaxation of hydrogen bonds or by the movement close to the silicate surface. Another phenomenon, α, was observed when annealing materials at 90 and 120 °C, respectively. At 90 °C, PP presented a new shoulder at 110 °C, which may be attributed to the type of packing and orientation of the polymer chains (Figure 4b). For the nanocomposites treated at 90 °C, this shoulder was shifted at 104 °C and became broader. The same phenomenon was found in the materials treated at 120 °C, except in this case the shoulder shifted toward 130 °C (Figure 4c). For a better illustration of the nanocomposites mechanical behavior function of thermal treatment, the loss factor function of temperature for the nanocomposite with 2% layered silicate is presented in Figure 5. As can be seen in Figure 5, α′ relaxation shifted toward higher temperatures in nanocomposites. Lower values of the tan δ, observed for the nanocomposites in the α′ relaxation temperature range, can be related to different crystalline morphologies with lower molecular mobility, i.e., an improved crystalline phase, as pointed out by DSC.1 Loss factor (tan δ) decreased for the nanocomposites, due to an increase of G′ in nanocomposites, meaning that crosslinking increased rigidity (stiffness) at high temperatures (Figure 6). Moreover, a higher amount of silicate will tend to increase stiffness, too. 3776

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Table 2. Influence of Thermal Treatment on Nanocomposites Tensile Properties sample name MM J1G J2G J4G MM90 J1G90 J2G90 J4G90 MM120 J1G120 J2G120 J4G120 a

tensile stress at yield (MPa) 31 35.5 34.2 32.4 36.7 36.9 36.5 36.9 37.1 36.8 36.3 36.2

± ± ± ± ± ± ± ± ± ± ± ±

0.6 0.3 0.3 0.3 0.2 0.6 0.2 0.1 0.1 0.2 0.5 0.1

tensile stress at break (MPa)

tensile strain at breaka (%)

± ± ± ± ± ± ± ± ± ± ± ±

>50 >50 >50 >50 >50 29 >50 45 >50 30 38 34

16.9 20.5 20.1 19.6 21.7 29.8 20.7 31 22.9 30.5 24 25.6

0.5 0.2 0.3 0.3 0.2 3.1 0.3 0.5 0.2 2 0.5 2.5

tensile modulus at 1% secantb (MPa) 1334 1569 1592 1498 1448 1585 1596 1565 1495 1572 1555 1562

± ± ± ± ± ± ± ± ± ± ± ±

77 109 50 34 18 16 4 8 25 85 122 26

young tensile modulus (MPa) 1675 1988 1961 1873 1773 1984 2033 1978 1887 2029 2018 1990

± ± ± ± ± ± ± ± ± ± ± ±

87 111 107 37 38 10 7 1 40 117 230 58

Tensile strain was measured up to 50% bComputed at 1% strain from tensile test.

Figure 9. Tensile strain after 10 cycles for nanocomposites with or without thermal treatment.

Figure 7. Stress−strain curves for nanocomposites with 2 wt % cloisite Na.

Creep and Cyclic Loading. Figure 8 presents strain at creep values for thermally treated and untreated nanocomposites.

attributed to the formation of the polyamic acid in nanocomposites treated at 120 °C, which acted as a defect in the network. Surprisingly, the untreated nanocomposites presented the highest value of tensile strain resistance after 10 cycles. The best results were observed in the nanocomposites with 1 and 2 wt % silicate concentration, corresponding to an improvement of 30% in tensile strain resistance.

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CONCLUSIONS The use of Jeffamine as intercalating agents allowed the preparation of highly ordered bilayer intercalated nanocomposites through a dipole−dipole mechanism. The curing reaction between Jeffamine and PPMA improved the interaction between the filler and polymer matrix. The incorporation of the modified silicate increased the storage modulus (stiffness), proving the reinforcing effect of the modified clay. Tensile strength and Young’s modulus were significantly improved by thermal treatment. A more effective stress transfer was achieved in thermally treated nanocomposites, resulting in the improvement of the neck propagation. Resistance to failure which was measured by fatigue tests was improved by 34%. Considering the structure properties characteristics for the obtained nanocomposites, the nanocomposites which were thermally treated at 90 °C showed the best balanced properties.

Figure 8. Strain at creep for nanocomposites with or without thermal treatment.

A decrease of 34% in creep strain can be noticed for the untreated nanocomposites. As the thermal treatment increased, creep strain decreased, which can be interpreted as a higher resistance to failure. Although the cross-linked network was formed, in this case it can be seen that the influence of the silicate concentration improved the resistance to failure. Zhang et al.31 conclude that the reduction of the creep strain is more important since it relates to the dimensional stability of the materials, which is defined as the ability of a material to maintain its size and shape under various temperatures and stresses. In order to observe the homogeneous deformation (before necking) of the materials obtained, short time fatigue tests were performed. For thermally treated nanocomposites it can be noticed that, as the silicate concentration increased, the samples presented decreased tensile strain (Figure 9). However, nanocomposites treated at 120 °C presented an increase in tensile strain as compared to those treated at 90 °C, regardless the silicate concentration. This increase can be

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ASSOCIATED CONTENT

S Supporting Information *

Structural changes observed in PP nanocomposites after thermal treatment (Table S1), Full FTIR spectra for PP nanocomposites (a) thermally untreated; (b) thermally treated at 90 °C, and (c) thermally treated at 120 °C (Figure S1) and detailed description of tensile, creep, and cyclic tests. This 3777

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(15) Meng, X.; Wang, Z.; Du, X.; Wang, Y.; Tang, T. Exfoliation of Organically Modified MontmorilloniteDriven by Molecular Diffusion in Maleated Polypropylene. J. Appl. Polym. Sci. 2009, 113, 678. (16) Zhao, Z.; Tang, T.; Qin, Y.; Huang, B. Relationship between the Continually Expanded Interlayer Distance of Layered Silicates and Excess Intercalation of Cationic Surfactants. Langmuir 2003, 19, 9260. (17) Rohlmann, C. O.; Failla, M. D.; Quinzani, L. M. Linear Viscoelasticity and Structure of Polypropylene Montmorillonite Nanocomposites . Polymer 2006, 47, 7795. (18) Lee, J. Y.; Lee, H. K. Characterization of Organobentonite Used for Polymer Nanocomposites. Mater. Chem. Phys. 2004, 85, 410. (19) Mungray, A. K.; Mungray, A. A.; Singala, K. Degradation Behavior of Polypropylene Organically Modified Clay Nanocomposites. Ind. Eng. Chem. Res. 2012, online. (20) Potarniche, C.-G.; Vuluga, Z.; Christiansen, J. deC.; Radovici, C.; Kristensen, P. K. Influence of Two Compatibilizers on Clay/PP Nanocomposites Properties. Polym. Eng. Sci. 2012, online early view. (21) Evans, R. K.; Dominguez, R. J. G.; Clark, R. J. Polyether amine modification of polypropylene.U.S. Pat. Appl. US/2001/0039312 A1, 2001. (22) Yoshimoto, S.; Ohashi, F.; Ohnishi, Y.; Nonami, T. Synthesis of Polyaniline−Montmorillonite Nanocomposites by the Mechanochemical Intercalation Method. Synth. Met. 2004, 145, 265. (23) Tyan, H.-L.; Liu, Y.-C.; Wei, K.-H. Enhancement of Imidization of Poly(amic acid) through Forming Poly(amic acid)/Organoclay Nanocomposites. Polymer 1999, 40, 4877. (24) Zhang, Y.; Tan, K. L.; Liaw, B. Y.; Liaw, D. J.; Kang, E. T. Thermal Imidization of Poly(amic acid) Precursors on Glycidyl Methacrylate (GMA) Graft-Polymerized Si(100) Surface. Thin Solid Films. 2000, 374, 70. (25) Roy, S. B.; Ramaraj, B.; Shit, S. C.; Nayak, S. K. Polypropylene and Potato Starch Biocomposites: Physicomechanical and Thermal Properties. J. Appl. Polym. Sci. 2011, 120, 3078. (26) Ebisawa, S.; Ishii, J.; Sato, M.; Vladimirov, L.; Hasegawa, M. Spontaneous Molecular Orientation of Polyimides Induced by Thermal Imidization (5). Effect of Ordered Structure Formation in Polyimide Precursors on CTE. Eur. Polym. J. 2010, 46, 283. (27) Wiley, V. C. H. Ullmann’s Encyclopedia of Industrial Chemistry; John Wiley: New York, 2002. (28) Silverstein, R. M.; Bassler, G. C.; Morrill, T. C. Spectrometric Identification of Organic Compounds; John Wiley: New York, 1991. (29) Cerrada, M. L.; Benavente, R.; Perez, E.; Perena, J. M. The Effect of Tensile Drawing on the Structure and Relaxation Processes in Vinyl Alcohol-Ethylene Copolymers. Polymer 2001, 42, 3127. (30) Franco-Urquiza, E.; Santana, O. O.; Gamez-Perez, J.; Martinez, A. B.; Maspoch, M. L. Influence of Processing on the Ethylene-Vinyl Alcohol (EVOH) Properties: Application of the Successive SelfNucleation and Annealing (SSA) Technique. eXPRESSPolym. Lett. 2010, 4, 153. (31) Zhang, Z.; Yang, J. L.; Friedrich, K. Creep Resistant Polymeric Nanocomposites. Polymer 2004, 45, 3481.

material is available free of charge via the Internet at http:// pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (C.G.S.); [email protected] (Z.V.). Author Contributions §

C.G.S. and Z.V. contributed equally.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support by the European Commission through project Nanotough -213436 is gratefully acknowledged.

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REFERENCES

(1) Ardanuy, M.; Velasco, J. I.; Antunes, M.; Rodriguez-Perez, M. A.; de Saja, J. A. Structure and Properties of Polypropylene/Hydrotalcite Nanocomposites. Polym. Compos. 2010, 31, 870. (2) Orolinova, Z.; Mockovciakova, A. Structural Study of Bentonite/ Iron Oxide Composites. Mater. Chem. Phys. 2009, 114, 956. (3) Rama, M. S.; Swaminathan, S. Polycarbonate/Clay Nanocomposites via in Situ Melt Polycondensation. Ind. Eng. Chem. Res. 2010, 49, 2217. (4) Mammeri, F.; Le Bourhis, E.; Rozesa, L.; Sanchez, C. J. Mechanical Properties of Hybrid Organic−Inorganic Materials. J. Mater. Chem. 2005, 15, 3787. (5) Ianchis, R.; Cinteza, L. O.; Donescu, D.; Petcu, C.; Corobea, M. C.; Somoghi, R.; Ghiurea, M.; Spataru, C. Implications of Silylated Montmorillonite on Montmorillonite-Polyacrylate Nanocomposites. Appl. Clay Sci. 2011, 52, 96. (6) Manias, E.; Touny, A.; Wu, L.; Strawhecker, K.; Lu, B.; Chung, T. C. Polypropylene/Montmorillonite Nanocomposites. Review of the Synthetic Routes and Materials Properties. Chem. Mater. 2001, 13, 3516. (7) Borthakur, L. J.; Das, D.; Dolui, S. K. Development of Core− Shell Nanocomposite of Poly(styrene-co-methyl acrylate) and Bentonite Clay by Ultrasonic Assisted Mini-Emulsion Polymerization. Mater. Chem. Phys. 2010, 124, 1182. (8) Zhang, J.; Qiu, Z. Morphology, Crystallization Behavior, and Dynamic Mechanical Properties of Biodegradable Poly(ε-caprolactone)/Thermally Reduced Graphene Nanocomposites. Ind. Eng. Chem. Res. 2011, 50, 13885. (9) Donescu, D.; Somoghi, R.; Nistor, C. L.; Ianchis, R.; Ghiurea, M.; Prodan, G.; Radovici, C. Copolymerization in Dispersion of Divinylbenzene-Maleic Anhydride in the Presence of Silylated Montmorilonite Clay. Polym. Bull. 2012, 68, 993. (10) Lin, J. J.; Chang, Y. C.; Cheng, I. J. Novel Mechanism for Layered Silicate Clay Intercalation by Poly(propylene oxide) Segmented Carboxylic Acid. Macromol. Rapid Commun. 2004, 25, 508. (11) Hong, C. H.; Lee, Y. B.; Bae, J. W.; Jho, J. Y.; Nam, B. U.; Hwang, T. W. Preparation and Mechanical Properties of Polypropylene/Clay Nanocomposites for Automotive Parts Application. J. Appl. Polym. Sci. 2005, 98, 427. (12) Chrissopoulou, K.; Anastasiadis, S. H. Polyolefin/Layered Silicate Nanocomposites with Functional Compatibilizers. Eur. Polym. J. 2011, 47, 600. (13) Zhai, W.; Park, C. B.; Kontopoulou, M. Nanosilica Addition Dramatically Improves the Cell Morphology and Expansion Ratio of Polypropylene Heterophasic Copolymer Foams Blown in Continuous Extrusion. Ind. Eng. Chem. Res. 2011, 50, 7282. (14) Szazdi, L.; Pukanszky, B., Jr.; Foldes, E.; Pukanszky, B. Possible Mechanism of Interaction among the Components in MAPP Modified Layered Silicate PP Nanocomposites. Polymer 2005, 46, 8001. 3778

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