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organoclay nanocomposite using maleic anhydride functionalized polypropylene as a compatibilizer
Materials Letters 58 (2004) 3481 – 3485 www.elsevier.com/locate/matlet
Preparation and properties of a new thermoplastic vulcanizate (TPV)/organoclay nanocomposite using maleic anhydride functionalized polypropylene as a compatibilizer Joy K. Mishraa, Jin-Ho Ryoub, Gue-Hyun Kimc, Kun-Jun Hwanga, Il Kima, Chang-Sik Haa,* a
Department of Polymer Science and Engineering, Pusan National University, Keumgjung ku, Pusan 609-735, South Korea b Coal Research Team, Iron-making Research Group, POSCO, Pohang 790-735, South Korea c Department of Chemical Engineering, Applied Engineering Division, Dongseo University, Pusan 617-716, South Korea Received 12 March 2004; received in revised form 12 June 2004; accepted 5 July 2004 Available online 28 July 2004
Abstract A new thermoplastic vulcanizate (TPV) /organoclay nanocomposite was prepared using maleic anhydride functionalized polypropylene (PP) as a compatibilizer. The X-ray diffraction (XRD) and transmission electron microscope indicated the intercalation of polymer chains inside the clay layer. The tensile modulus of the only 5 wt.% clay-based nanocomposite is much higher than that of the 20 wt.% talc-based microcomposite. Dynamic mechanical analysis showed that the glass transition temperature of the ethylene–propylene–diene terpolymer phase of the nanocomposite remains the same, whereas that of PP phase is increased compared to the pristine counterpart of the nanocomposite. D 2004 Elsevier B.V. All rights reserved. Keywords: Nanocomposite; Polymer; Thermoplastic vulcanizate; Organoclay; Maleic anhydride functionalized polypropylene; Properties
1. Introduction Polymer-layered silicate (PLS) nanocomposites exhibit outstanding properties that are synergistically derived from their organic and inorganic components. PLS nanocomposites exhibit good mechanical and biochemical properties [1–4]. In an intercalated nanocomposite, extended polymer chains remain between the host layers, whereas in an exfoliated hybrid, silicate layers are randomly dispersed in a continuous polymer matrix such that the interlayer distance is comparable to the radius of gyration of the polymer [5]. Thermoplastic elastomers based on the blends of uncured ethylene–propylene–diene terpolymer (EPDM) rubber and polypropylene (PP) are referred to as thermoplastic polyolefin (TPO), whereas the blends of PP and dynamically
* Corresponding author. Tel.: +82 51 510 2407; fax: +82 51 514 3331. E-mail address: [email protected] (C.-S. Ha). 0167-577X/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2004.07.003
vulcanized EPDM rubber are termed as thermoplastic vulcanizates (TPV). TPO as well as TPV are witnessing a wide range of applications in the automotive industry. Reinforcing fillers are generally mixed with TPO and TPV to increase the stiffness. However, conventional fillers such as talc, mica, and calcium carbonate introduce higher stiffness but increase weight and melt viscosity and decrease toughness. Glass-fiber reinforcement provides high stiffness with corresponding increased difficulty of fabrication. The traditional reinforcements and fillers must be used at high loading levels, which increase the weight and cause an adverse effect. A small amount of nanofiller (2–5 wt.%) is generally sufficient to increase the stiffness of the material, and nanofillers are thus cost-effective for automotive applications. Moreover, they are more easily recyclable. Until now, though, there is very little information available regarding TPO-based nanocomposites [6] and on the TPVbased nanocomposite. In this article, we report the preparation and properties of a TPV-based nanocomposite
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Table 1 Compositions of various TPV-based samples Sample codea
TPV (gm)
Talc (gm)
MA functionalized PP (gm)
Cloisite 20A (gm)
TPV (wt.%):MA functionalized PP (wt.%)
TVN5 TVE5 TV/20A TVt20
40 42.1 47.5 40
– – – 10
7.5 7.9 – –
2.5 – 2.5 –
5.33 5.33 – –
a For TVN5, the organoclay (20A) and the compatibilizer (m-PP) ratio are kept 1:3 [8] and the hybrid contains 5 wt.% of organoclay. For TVE5, TPV and m-PP were mixed with the same weight ratio as was used for the sample TVN5. Thus, this sample is equivalent to the sample TVN5 as far as the weight ratio of the TPV and the m-PP is concerned. This sample is the pristine equivalent of the sample TVN5 and is necessary for the comparison of the various properties of TPV/organoclay hybrids with its pristine counterpart. The TPV/20A hybrid is a 5 wt.% clay-based hybrid (without any compatibilizer). Finally, the TVt20 denotes 20% talc-based TPV microcomposite.
containing 5 wt.% of organoclays. As TPV is not polar, to improve the dispersibility of filler, polar maleic anhydride functionalized polypropylene is used as a compatibilizer [7,8] in the nanocomposite preparation.
2. Experimental The TPV used here was SantopreneR-like TPV with specific gravity 0.97 with hardness 80A. It was kindly
obtained from Kwangsung Plastic, Korea. Maleic anhydride (MA) functionalized PP [hereafter referred to as m-PP; melt flow index (MFI) of 50 and % functionality of 0.5] as a compatibilizer was supplied by Uniroyal Chemical [8]. Organically modified clay Cloisite 20A was procured from Southern Clay, Texas, USA. Four samples were prepared for this work. The compositions of the prepared samples are listed Table 1. The samples were prepared by the meltintercalation method [9]. Before being used, the organoclay was dried overnight in a vacuum oven at 80 8C. Mixing was carried out in a Haake Rheocorder mixer at 190 8C and 50 rpm rotor speed for 10 min. X-ray diffraction (XRD) studies of the samples were carried out using a Rigaku D/max 2200 H X-ray diffractometer operating at 40 kV and 50 mA (Cu Ka radiation). The scanning rate was 0.58/min. The microstructure of the nanocomposite was examined by Phillips CM-20 transmission electron microscope (TEM). The accelerating voltage was 120 kV. Tensile properties of the samples were measured with a Universal Tester (H.T.E, H 25 km and 500Lm extensometer) at a strain rate of 100 mm/min. At least six dog bone shape replica of each samples were used. Dynamic mechanical analysis of samples was carried out using a dynamic mechanical analyzer (Rhevibron DDV-25 F; Orientec) in tension mode with the following parameters: frequency 1 Hz; scan rate 58/min, in the temperature range of 100 to +160 8C. For the solvent uptake measurement, samples (circular films prepared by compression molding)
Fig. 1. XRD patterns of TPV/organoclay nanocomposites and organoclay.
J.K. Mishra et al. / Materials Letters 58 (2004) 3481–3485
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were immersed in toluene for 3 days at 25 8C and 1 h for 100 8C.
3. Results and discussion 3.1. Characterization of nanocomposites Evidence of intercalation of polymer chains into the silicate galleries is obtained from the XRD patterns in the range of 2h=1.5–128, as shown in Fig. 1. The peak corresponding to the basal spacing (d001) of the organoclay 20A appears at 2h=3.488 (corresponding d-spacing 2.47 nm). The d001 peak of the organoclay has been shifted to a low angle corresponding to an increase in the d spacing from 2.47 to 4.5 nm for the sample TVN5 and 3.8 nm for the sample TV/20A. Again, there is a decrease in the peak intensity for TVN5 and TV/20A as compared to pure Cloisite 20A, which indicates a decrease in the coherent layer scattering. The increase in basal spacing in case of TVN5 and TV/20A (compared to the organoclay) is due to the intercalation of polymers inside the layered silicate. The larger is the basal spacing, the easier the intercalation will be. More intercalation of the polymer chains is expected in the case of the TVN5 as compared to the TV/20A hybrid. This is due to the effect of compatibilizer (m-PP), which is used for TVN5. The polar compatibilizer molecules initially diffuse inside the polar clay galleries (due to the polar–polar interaction) and increase the basal spacing of the organoclays, which decreases the attraction between two silicate layers. Then, nonpolar PP and EPDM molecules also can be easily intercalated into silicate layers with enlarged spacings. In this way, the dispersion becomes better in the presence of a compatibilizer [10]. The intercalation of the polymer leads to the disordering of layered clay structure, which is responsible for the decrease in the XRD coherent scattering intensity in the
Fig. 2. TEM micrograph of the TVN5 nanocomposite; labels A and B show intercalated and exfoliated states, respectively.
Fig. 3. Dynamic storage modulus of the nanocomposite and its pristine counterpart as a function of temperature.
samples as compared to the organoclay. The TVN5 nanocomposite was further characterized by TEM (shown in Fig. 2). The dark lines in the TEM image are silicate layers. It is revealed that an overwhelming majority of silicate layers are in intercalated state (label dAT). However, few silicate layers are in exfoliated state (label dBT). The average thickness of the clay layers are ~1 nm. The average distance between the two silicate layers is 4.3 nm. 3.2. Dynamic mechanical properties The storage modulus and the loss modulus of the samples over a wide temperature range of 100–160 8C are displayed in Figs. 3 and 4, respectively. The storage modulus data are given in Table 2. There is a significant increase in the storage modulus for the TVN5 over its pristine equivalent TVE5 over all the temperatures. At 25 8C, the storage modulus of the TVN5 is 70% higher than the TVE5. The significant improvement of the storage modulus of the nanocomposite is due to the intercalation of polymer
Fig. 4. Loss modulus of the nanocomposite and its pristine counterpart as a function of temperature.
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Table 2 Mechanical and dynamic mechanical properties of various TPV-based samples Sample code
Tensile modulus (kgf/cm2)
Tensile strength (kgf/cm2)
Elongation at break (%)
Storage modulus (25 8C) (MPa)
TVN5 TVE5 TVt20 TV/20A TPV
294 149.5 227 195 120
128 88 98.5 53.5 39.7
208 198 247 240 268
28.6106 18.1106 – – –
chains inside the silicate layer as well as the high aspect ratio of the organoclay. The variation of tan d with temperature, which is shown in Fig. 5, is quite interesting. For the TVE5, two peaks appear at 37.7 and 7.2 8C, which are attributed to the glass transition temperature (T g) of EPDM and PP phase, respectively. In the nanocomposite TVN5, the T g of the hard PP phase has been shifted to 20.6 8C (which is 13.4 8C higher than its pristine equivalent), but the T g of EPDM remains almost the same. The increase of T g of PP in the nanocomposite is due to the hindered cooperative motion of the polymer chains in the constrained environment [11]. Laus et al. [12] studied a thermoplastic elastomer (TPE) nanocomposite system, where the thermoplastic elastomer generates from poly(styrene-b-butadiene) block copolymer. They observed that the T g of the hard polystyrene phase increases, whereas the T g of the soft polybutadiene phase remains the same. In this case, the TPE system generates from an elastomer-plastic blend. Here also the T g of hard PP phase increases and soft EPDM phase remains the same. The reason is not clear at this moment and it needs more experimentation on various TPE nanocomposite systems based on elastomer-plastic blends. 3.3. Mechanical and solvent uptake properties
Table 3 Solvent resistance properties (measured in toluene)a Sample code
Solvent uptake rate (at 25 8C) (%)
Solvent uptake rate (at 100 8C) (%)
TVN5 TVE5
18.1 29.3
24.3 36.1
a
The solvent uptake rate was calculated as the formula (solvent uptake rate=W 2 W 1/W 1100%, where W 2 is the weight of the wet sample and W 1 is the weight of the dry sample, respectively).
the TVN5 are higher than those of either TVE5 or TVt20. The tensile modulus of the TVN5 nanocomposite is 97% higher than its unfilled pristine equivalent TVE5. The TV/ 20A nanocomposite (without a compatibilizer) shows 60% higher modulus compared to the virgin TPV. Thus, the increment of tensile modulus (compared to their pristine counterpart) is more when compatibilizer is used. Again, as observed from Table 2, the TVN5 shows 29% higher modulus than the 20% talc-filled microcomposite TVt20. The intercalation of the polymer chains inside the clay gallery produces enormous surface area between clay and polymer chains, which results in a tremendous enhancement of interactions between them. These increased interactions are responsible for the dramatic improvement of the mechanical properties of the nanocomposite over its pristine equivalent as well as the talc-based microcomposite. The results of the solvent uptake measurements are shown in Table 3. The solvent uptake rate (at 25 8C) of the TVN5 is 18.1% and the TVE5 is 29.3%. Solvent uptake rate of the nanocomposite as well as its pristine equivalent are higher at 100 8C than that of 25 8C. This decrease in the solvent uptake in the nanocomposite is due to the interaction between the filler (Cloisite 20A) and TPVs. This interaction leads to the formation of dbound polymerT in the close proximity to the reinforcing filler, which is restricting the solvent uptake.
The tensile properties of the samples are summarized in Table 2. The tensile modulus as well as tensile strength of 4. Conclusion
Fig. 5. The tan d behaviour of the nanocomposite and its pristine counterpart as a function of temperature.
We have successfully prepared the thermoplastic vulcanizate/organoclay nanocomposite by using maleic anhydride functionalized PP as a compatibilizer. The nanocomposite was found to be an intercalated one as evidenced by XRD and TEM measurements. The tensile modulus of the only 5 wt.% clay-based TPV nanocomposite is 97% higher than that of its pristine counterpart. The tensile modulus of the 5 wt.% clay-based nanocomposite is higher than the 20 wt.% talc-based microcomposite. The storage modulus of the nanocomposite is higher than that of its pristine counterpart. The most noteworthy observation was obtained from a dynamic mechanical analysis, which reveals that the glass transition temperature of the EPDM phase of the thermoplastic vulcanizate nanocomposite remained the same, whereas that of the PP phase increased.
J.K. Mishra et al. / Materials Letters 58 (2004) 3481–3485
Acknowledgements The work was supported by the National Research Laboratory Program, the Center for Integrated Molecular System, and the Brain Korea 21 project.
References [1] M. Kojima, A. Usuki, A. Okada, Kagimato, O. Kagimoto, J. Mater. Res. 8 (1993) 1185. [2] M. Pramanik, S.K. Srivastava, B.K. Samantaray, A.K. Bhowmick, Macromol. Res. 11 (4) (2003) 260. [3] M.S. Wang, T.J. Pinnavia, Chem. Mater. 6 (1994) 468. [4] M. Xu, Y.S. Choi, K.H. Wang, J.H. Kim, I.J. Chung, Macromol. Res. 11 (6) (2003) 410.
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[5] E.P. Giannelis, R. Krishnamoorti, E. Manius, Adv. Polym. Sci. 138 (1999) 108. [6] M. Oldenbo, TPO-nanocomposites for automotive exterior body panels—potentials and experiences from evaluations of commercial materials, Nanocomposite 2001 Proceedings, June 25–27, Chicago, Illinois, USA, 2001. [7] P. Reichert, H. Nitz, S. Klinke, R. Brandrch, R. Thomann, R. Mulfhaupt, Macromol. Mater. Eng. 8 (2000) 275. [8] M. Kawasumi, N. Hasegawa, M. Kato, A. Usuki, A. Okada, Macromolecules 30 (1997) 6333. [9] R.A. Vaia, H. Ishii, E.P. Giannelis, Chem. Mater. 5 (1993) 694. [10] H. Zheng, H.Y. Zhang, Z. Peng, Y. Zhang, J. Appl. Polym. Sci. 92 (2004) 638. [11] R.A. Via, B.B. Saure, O.K. Tse, E.P. Giannelis, J. Polym. Sci., Polym. Phys. 35 (1997) 59. [12] M. Laus, O. Francescangeli, F. Sandrolini, J. Mater. Res. 31 (1997) 34.
Preparation and properties of a new thermoplastic vulcanizate (TPV)/organoclay nanocomposite using maleic anhydride functionalized polypropylene as a compatibilizer Joy K. Mishraa, Jin-Ho Ryoub, Gue-Hyun Kimc, Kun-Jun Hwanga, Il Kima, Chang-Sik Haa,* a
Department of Polymer Science and Engineering, Pusan National University, Keumgjung ku, Pusan 609-735, South Korea b Coal Research Team, Iron-making Research Group, POSCO, Pohang 790-735, South Korea c Department of Chemical Engineering, Applied Engineering Division, Dongseo University, Pusan 617-716, South Korea Received 12 March 2004; received in revised form 12 June 2004; accepted 5 July 2004 Available online 28 July 2004
Abstract A new thermoplastic vulcanizate (TPV) /organoclay nanocomposite was prepared using maleic anhydride functionalized polypropylene (PP) as a compatibilizer. The X-ray diffraction (XRD) and transmission electron microscope indicated the intercalation of polymer chains inside the clay layer. The tensile modulus of the only 5 wt.% clay-based nanocomposite is much higher than that of the 20 wt.% talc-based microcomposite. Dynamic mechanical analysis showed that the glass transition temperature of the ethylene–propylene–diene terpolymer phase of the nanocomposite remains the same, whereas that of PP phase is increased compared to the pristine counterpart of the nanocomposite. D 2004 Elsevier B.V. All rights reserved. Keywords: Nanocomposite; Polymer; Thermoplastic vulcanizate; Organoclay; Maleic anhydride functionalized polypropylene; Properties
1. Introduction Polymer-layered silicate (PLS) nanocomposites exhibit outstanding properties that are synergistically derived from their organic and inorganic components. PLS nanocomposites exhibit good mechanical and biochemical properties [1–4]. In an intercalated nanocomposite, extended polymer chains remain between the host layers, whereas in an exfoliated hybrid, silicate layers are randomly dispersed in a continuous polymer matrix such that the interlayer distance is comparable to the radius of gyration of the polymer [5]. Thermoplastic elastomers based on the blends of uncured ethylene–propylene–diene terpolymer (EPDM) rubber and polypropylene (PP) are referred to as thermoplastic polyolefin (TPO), whereas the blends of PP and dynamically
* Corresponding author. Tel.: +82 51 510 2407; fax: +82 51 514 3331. E-mail address: [email protected] (C.-S. Ha). 0167-577X/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2004.07.003
vulcanized EPDM rubber are termed as thermoplastic vulcanizates (TPV). TPO as well as TPV are witnessing a wide range of applications in the automotive industry. Reinforcing fillers are generally mixed with TPO and TPV to increase the stiffness. However, conventional fillers such as talc, mica, and calcium carbonate introduce higher stiffness but increase weight and melt viscosity and decrease toughness. Glass-fiber reinforcement provides high stiffness with corresponding increased difficulty of fabrication. The traditional reinforcements and fillers must be used at high loading levels, which increase the weight and cause an adverse effect. A small amount of nanofiller (2–5 wt.%) is generally sufficient to increase the stiffness of the material, and nanofillers are thus cost-effective for automotive applications. Moreover, they are more easily recyclable. Until now, though, there is very little information available regarding TPO-based nanocomposites [6] and on the TPVbased nanocomposite. In this article, we report the preparation and properties of a TPV-based nanocomposite
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Table 1 Compositions of various TPV-based samples Sample codea
TPV (gm)
Talc (gm)
MA functionalized PP (gm)
Cloisite 20A (gm)
TPV (wt.%):MA functionalized PP (wt.%)
TVN5 TVE5 TV/20A TVt20
40 42.1 47.5 40
– – – 10
7.5 7.9 – –
2.5 – 2.5 –
5.33 5.33 – –
a For TVN5, the organoclay (20A) and the compatibilizer (m-PP) ratio are kept 1:3 [8] and the hybrid contains 5 wt.% of organoclay. For TVE5, TPV and m-PP were mixed with the same weight ratio as was used for the sample TVN5. Thus, this sample is equivalent to the sample TVN5 as far as the weight ratio of the TPV and the m-PP is concerned. This sample is the pristine equivalent of the sample TVN5 and is necessary for the comparison of the various properties of TPV/organoclay hybrids with its pristine counterpart. The TPV/20A hybrid is a 5 wt.% clay-based hybrid (without any compatibilizer). Finally, the TVt20 denotes 20% talc-based TPV microcomposite.
containing 5 wt.% of organoclays. As TPV is not polar, to improve the dispersibility of filler, polar maleic anhydride functionalized polypropylene is used as a compatibilizer [7,8] in the nanocomposite preparation.
2. Experimental The TPV used here was SantopreneR-like TPV with specific gravity 0.97 with hardness 80A. It was kindly
obtained from Kwangsung Plastic, Korea. Maleic anhydride (MA) functionalized PP [hereafter referred to as m-PP; melt flow index (MFI) of 50 and % functionality of 0.5] as a compatibilizer was supplied by Uniroyal Chemical [8]. Organically modified clay Cloisite 20A was procured from Southern Clay, Texas, USA. Four samples were prepared for this work. The compositions of the prepared samples are listed Table 1. The samples were prepared by the meltintercalation method [9]. Before being used, the organoclay was dried overnight in a vacuum oven at 80 8C. Mixing was carried out in a Haake Rheocorder mixer at 190 8C and 50 rpm rotor speed for 10 min. X-ray diffraction (XRD) studies of the samples were carried out using a Rigaku D/max 2200 H X-ray diffractometer operating at 40 kV and 50 mA (Cu Ka radiation). The scanning rate was 0.58/min. The microstructure of the nanocomposite was examined by Phillips CM-20 transmission electron microscope (TEM). The accelerating voltage was 120 kV. Tensile properties of the samples were measured with a Universal Tester (H.T.E, H 25 km and 500Lm extensometer) at a strain rate of 100 mm/min. At least six dog bone shape replica of each samples were used. Dynamic mechanical analysis of samples was carried out using a dynamic mechanical analyzer (Rhevibron DDV-25 F; Orientec) in tension mode with the following parameters: frequency 1 Hz; scan rate 58/min, in the temperature range of 100 to +160 8C. For the solvent uptake measurement, samples (circular films prepared by compression molding)
Fig. 1. XRD patterns of TPV/organoclay nanocomposites and organoclay.
J.K. Mishra et al. / Materials Letters 58 (2004) 3481–3485
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were immersed in toluene for 3 days at 25 8C and 1 h for 100 8C.
3. Results and discussion 3.1. Characterization of nanocomposites Evidence of intercalation of polymer chains into the silicate galleries is obtained from the XRD patterns in the range of 2h=1.5–128, as shown in Fig. 1. The peak corresponding to the basal spacing (d001) of the organoclay 20A appears at 2h=3.488 (corresponding d-spacing 2.47 nm). The d001 peak of the organoclay has been shifted to a low angle corresponding to an increase in the d spacing from 2.47 to 4.5 nm for the sample TVN5 and 3.8 nm for the sample TV/20A. Again, there is a decrease in the peak intensity for TVN5 and TV/20A as compared to pure Cloisite 20A, which indicates a decrease in the coherent layer scattering. The increase in basal spacing in case of TVN5 and TV/20A (compared to the organoclay) is due to the intercalation of polymers inside the layered silicate. The larger is the basal spacing, the easier the intercalation will be. More intercalation of the polymer chains is expected in the case of the TVN5 as compared to the TV/20A hybrid. This is due to the effect of compatibilizer (m-PP), which is used for TVN5. The polar compatibilizer molecules initially diffuse inside the polar clay galleries (due to the polar–polar interaction) and increase the basal spacing of the organoclays, which decreases the attraction between two silicate layers. Then, nonpolar PP and EPDM molecules also can be easily intercalated into silicate layers with enlarged spacings. In this way, the dispersion becomes better in the presence of a compatibilizer [10]. The intercalation of the polymer leads to the disordering of layered clay structure, which is responsible for the decrease in the XRD coherent scattering intensity in the
Fig. 2. TEM micrograph of the TVN5 nanocomposite; labels A and B show intercalated and exfoliated states, respectively.
Fig. 3. Dynamic storage modulus of the nanocomposite and its pristine counterpart as a function of temperature.
samples as compared to the organoclay. The TVN5 nanocomposite was further characterized by TEM (shown in Fig. 2). The dark lines in the TEM image are silicate layers. It is revealed that an overwhelming majority of silicate layers are in intercalated state (label dAT). However, few silicate layers are in exfoliated state (label dBT). The average thickness of the clay layers are ~1 nm. The average distance between the two silicate layers is 4.3 nm. 3.2. Dynamic mechanical properties The storage modulus and the loss modulus of the samples over a wide temperature range of 100–160 8C are displayed in Figs. 3 and 4, respectively. The storage modulus data are given in Table 2. There is a significant increase in the storage modulus for the TVN5 over its pristine equivalent TVE5 over all the temperatures. At 25 8C, the storage modulus of the TVN5 is 70% higher than the TVE5. The significant improvement of the storage modulus of the nanocomposite is due to the intercalation of polymer
Fig. 4. Loss modulus of the nanocomposite and its pristine counterpart as a function of temperature.
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Table 2 Mechanical and dynamic mechanical properties of various TPV-based samples Sample code
Tensile modulus (kgf/cm2)
Tensile strength (kgf/cm2)
Elongation at break (%)
Storage modulus (25 8C) (MPa)
TVN5 TVE5 TVt20 TV/20A TPV
294 149.5 227 195 120
128 88 98.5 53.5 39.7
208 198 247 240 268
28.6106 18.1106 – – –
chains inside the silicate layer as well as the high aspect ratio of the organoclay. The variation of tan d with temperature, which is shown in Fig. 5, is quite interesting. For the TVE5, two peaks appear at 37.7 and 7.2 8C, which are attributed to the glass transition temperature (T g) of EPDM and PP phase, respectively. In the nanocomposite TVN5, the T g of the hard PP phase has been shifted to 20.6 8C (which is 13.4 8C higher than its pristine equivalent), but the T g of EPDM remains almost the same. The increase of T g of PP in the nanocomposite is due to the hindered cooperative motion of the polymer chains in the constrained environment [11]. Laus et al. [12] studied a thermoplastic elastomer (TPE) nanocomposite system, where the thermoplastic elastomer generates from poly(styrene-b-butadiene) block copolymer. They observed that the T g of the hard polystyrene phase increases, whereas the T g of the soft polybutadiene phase remains the same. In this case, the TPE system generates from an elastomer-plastic blend. Here also the T g of hard PP phase increases and soft EPDM phase remains the same. The reason is not clear at this moment and it needs more experimentation on various TPE nanocomposite systems based on elastomer-plastic blends. 3.3. Mechanical and solvent uptake properties
Table 3 Solvent resistance properties (measured in toluene)a Sample code
Solvent uptake rate (at 25 8C) (%)
Solvent uptake rate (at 100 8C) (%)
TVN5 TVE5
18.1 29.3
24.3 36.1
a
The solvent uptake rate was calculated as the formula (solvent uptake rate=W 2 W 1/W 1100%, where W 2 is the weight of the wet sample and W 1 is the weight of the dry sample, respectively).
the TVN5 are higher than those of either TVE5 or TVt20. The tensile modulus of the TVN5 nanocomposite is 97% higher than its unfilled pristine equivalent TVE5. The TV/ 20A nanocomposite (without a compatibilizer) shows 60% higher modulus compared to the virgin TPV. Thus, the increment of tensile modulus (compared to their pristine counterpart) is more when compatibilizer is used. Again, as observed from Table 2, the TVN5 shows 29% higher modulus than the 20% talc-filled microcomposite TVt20. The intercalation of the polymer chains inside the clay gallery produces enormous surface area between clay and polymer chains, which results in a tremendous enhancement of interactions between them. These increased interactions are responsible for the dramatic improvement of the mechanical properties of the nanocomposite over its pristine equivalent as well as the talc-based microcomposite. The results of the solvent uptake measurements are shown in Table 3. The solvent uptake rate (at 25 8C) of the TVN5 is 18.1% and the TVE5 is 29.3%. Solvent uptake rate of the nanocomposite as well as its pristine equivalent are higher at 100 8C than that of 25 8C. This decrease in the solvent uptake in the nanocomposite is due to the interaction between the filler (Cloisite 20A) and TPVs. This interaction leads to the formation of dbound polymerT in the close proximity to the reinforcing filler, which is restricting the solvent uptake.
The tensile properties of the samples are summarized in Table 2. The tensile modulus as well as tensile strength of 4. Conclusion
Fig. 5. The tan d behaviour of the nanocomposite and its pristine counterpart as a function of temperature.
We have successfully prepared the thermoplastic vulcanizate/organoclay nanocomposite by using maleic anhydride functionalized PP as a compatibilizer. The nanocomposite was found to be an intercalated one as evidenced by XRD and TEM measurements. The tensile modulus of the only 5 wt.% clay-based TPV nanocomposite is 97% higher than that of its pristine counterpart. The tensile modulus of the 5 wt.% clay-based nanocomposite is higher than the 20 wt.% talc-based microcomposite. The storage modulus of the nanocomposite is higher than that of its pristine counterpart. The most noteworthy observation was obtained from a dynamic mechanical analysis, which reveals that the glass transition temperature of the EPDM phase of the thermoplastic vulcanizate nanocomposite remained the same, whereas that of the PP phase increased.
J.K. Mishra et al. / Materials Letters 58 (2004) 3481–3485
Acknowledgements The work was supported by the National Research Laboratory Program, the Center for Integrated Molecular System, and the Brain Korea 21 project.
References [1] M. Kojima, A. Usuki, A. Okada, Kagimato, O. Kagimoto, J. Mater. Res. 8 (1993) 1185. [2] M. Pramanik, S.K. Srivastava, B.K. Samantaray, A.K. Bhowmick, Macromol. Res. 11 (4) (2003) 260. [3] M.S. Wang, T.J. Pinnavia, Chem. Mater. 6 (1994) 468. [4] M. Xu, Y.S. Choi, K.H. Wang, J.H. Kim, I.J. Chung, Macromol. Res. 11 (6) (2003) 410.
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