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organoclay nanocomposites by melt extrusion
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Applied Clay Science 40 (2008) 38 – 44 www.elsevier.com/locate/clay
High-performance EPDM/organoclay nanocomposites by melt extrusion Peiyao Li a,b,1 , Lanlan Yin c , Guojun Song a,b,⁎, Jin Sun b , Li Wang b , Hailong Wang b a
College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing, 100029, China b Institute of Polymer Materials, Qingdao University, Qingdao, 266071, China c Haidu Institute of Laiyang Agriculture University, Laiyang, 265200, China Received 7 March 2007; received in revised form 29 June 2007; accepted 5 July 2007 Available online 14 July 2007
Abstract Ethylene-propylene-diene terpolymer (EPDM)/organoclay nanocomposites were prepared by melt extrusion in a twin-screw extruder. The organoclay was characterized by XRD and TGA. As observed by transmission electron microscopy (TEM), the organoclay particles were exfoliated in EPDM. The tensile strength of the nanocomposites increased to 12.3 MPa at the same 3.0 phr amounts of fillers, which was a five-fold increase compared to pure EPDM and 2.8 times compared to the nanocomposite prepared by direction blending; furthermore it was above that of carbon black composites with 15.0 phr. The results of coreinforcement system exploited a promising application prospect of the organoclay and the nanocomposites. The processability of the terpolymer was improved as a result of the decrease of mooney viscosity; the improvement of the thermal stability of the nanocomposite was determined by TGA. © 2007 Elsevier B.V. All rights reserved. Keywords: EPDM; Organoclay; Nanocomposites; Mechanical property
1. Introduction The most attractive aspect of reinforcement by nanoparticles is that the properties can be largely improved only by adding small amounts of organoclay. Rubber/ organoclay nanocomposites have attracted great attention in recent years, such as nitrile butadiene rubber (Kim et al., 2004), chlorobutyl rubber (Sridhar and Tripathy, 2006), hydrogenated nitrile rubber (Gatos et al., 2004), styrene-butadiene rubber (Wang et al., 2005a; Zhang ⁎ Corresponding author. Institute of Polymer Materials, Qingdao University, Qingdao, 266071, China. E-mail address: [email protected] (P. Li). 1 Tel.: +86- 532- 8595 0691; fax: +86- 532- 8595 3260. 0169-1317/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2007.07.002
et al., 2005), natural rubber (Sharifa et al., 2005; Joly et al., 2002), silicone elastomer (LeBaron and Pinnavaia, 2001), polybutadiene (Wang et al., 2005b). Ethylene/propylene/diene terpolymer (EPDM) is a typical non-polar unsaturated rubber with wide applications. It has become extensively used in making automotive tire sidewalls, cover stripes, wires, cables, hoses, belting, footwear, roofing barriers and sporting goods. As it is incompatible with the organoclay which was modified with hexadecyl trimethyl-ammonium bromide or with dodecyl ammonium ions. EPDM/ organoclay nanocomposites were prepared with the oligomer (Young et al., 2002) or EPDM-g-MAH (Sandrine et al., 2005; Gatos and Kocsis, 2005; Silva et al., 2005; Ahmadi et al., 2005a,b) as compatibilizer.
P. Li et al. / Applied Clay Science 40 (2008) 38–44
39
2.3. Preparation of composites
Fig. 1. X-ray diffraction patterns of bentonite and organoclay.
In the current paper, we focused on the development of a ‘reactive’ organoclay compatible with the EPDM without additional compatibilizer. The clay used in this study was a bentonite produced in Shandong Province of China. The organoclay was added into the EPDM by the extrusion processing without any compatilizer. 2. Experimental studies 2.1. Materials The bentonite was obtained from the clay mine in Shandong Province of China, The montmorillonite (MMT) of the bentonite has the cation exchange capacity (CEC) of 100 meq/100 g. The organoclay (FMR02-F) was produced by Institute of Polymer Materials in Qingdao University, China. EPDM (KEP-570P, granulated elastomer) with 70% ethylene and 4.5% ethylidene norbornene content having a mooney viscosity of ML(1 + 4) at 100 °C = 75 was supplied by Kumho Chemicals, Korea. High abrasion furnace carbon black (N330) was commercial product, China. The vulcanization curatives: tetramethyl thiuram disulfide (TMTD), dibenzothiazole disulfide (DM), stearic acid, zinc oxide and sulfur were also commercial products, China. The formed mixing was (in parts), rubber: 100, organoclay: various, ZnO: 5.0, stearic acid: 1.0, TMTD: 1.5, DM: 0.5 and S: 1.5.
The EPDM pellets and the organoclay were placed into the high-speed mixer. After mixed homogeneously, the samples were extruded in a twin-screw extruder (co-rotative screws, D = 35.0 mm, L/D = 32/1); the temperature was 150 °C–160 °C from feeder to extrusion-head and the screw speed was 80 rpm. The extruded materials were granulated with a hot-cutting granulating head. Then the extruded samples incorporated with the curatives and other ingredients on a two roll miller with a nip clearance of 0.8 mm and friction ratio 1.3 (22/17 rpm). Mixing was performed at room temperature for 5 to 10 min. The specimens were cured at a plate vulcanization machine with 20 ton pressure in 160 °C. This type specimen was called extruded composite. The organoclay (or carbon black) compounded with EPDM by directed blending on the twin roll miller at the same contents compared to the extruded composites. The obtained samples were called directed blended organoclay and carbon black composites, respectively. 2.4. Measurements X-ray diffraction(XRD) experiments were performed for the bentonite and the organoclay using a D/max-RB diffractometer (Rigaku, Japan),which has an X-ray generator of 12 kW, a graphite monochromator, CuKα radiation operating at 40 kV, 100 mA. The samples were scanned at a scanning speed of 5°/min at diffraction angles 2θ 1–30°. Thermogravimetric analyses (TGA) were performed on a TGA/STDA851e instrument with platinum pan using about 7 mg of material as probe. The samples were heated at 10 °C/min rate in nitrogen atmosphere under a flow rate of 50 ml/min. Nanocomposites were thin-sectioned with an ultramicrotome and collected on a copper grid and examined with a TEM (JEM1200EX, JEOL) running at an accelerating voltage of 60 kV. Vulcanized composites sheets were cut into standard samples according to standard ISO37-1994 and ISO341:1994, respectively. The tensile properties and tear strength were determined on dumbbell-shaped and crescent-shaped
2.2. Preparation of organoclay The bentonite was wetted with water, and then purified by sedimentation and washing. The fined bentonite (100 g) was dispersed into 1000 ml of distilled water at 80 °C under vigorous stirring. A mixture of 53 g dimethyl hydrogenated tallow benzyl quaternary ammonium chloride (DMHTB), 200 g distilled water and 10 ml 98% concentrated sulfuric acid was prepared at 80 °C and then slowly added into the bentonite dispersion. The reaction was maintained for 6 h. The sediment was collected by filtration and washed ten times with hot water, and then dried at 80 °C in vacuum, ground and sieved to 30 μm. The organophilic clay was designated as organoclay.
Fig. 2. TGA thermogram of bentonite and organoclay.
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P. Li et al. / Applied Clay Science 40 (2008) 38–44
Fig. 3. TEM images of directed blended composites, a1: 50,000 magnification. TEM images of directed blended composites, a2: 10,000 magnification.
specimens at a crosshead speed of 500 mm/min by using an electronic universal testing machine. All measurements were made several times and the values were averaged. Mooney viscosity ML (1 + 4) at 100 °C was measured by using a Mooney viscometer based on standard ISO289-1985. The samples were sheared with the large rotor.
3. Results and discussion 3.1. Characterization of organoclay The organoclay was prepared by using a well-chosen organic modifier. The hydrophobic organic modifier
could facilitate the intercalation of a hydrophobic polymer by reducing the surface energy. The XRD and TGA tests were used to characterize organoclay. Fig. 1 shows the XRD patterns of bentonite and organoclay. The basal spacing of the montmorillonite and the organoclay was 1.51 nm and 3.09 nm (Fig. 1), respectively. That suggests the successful preparation of organoclay. Fig. 2 shows the TGA thermogram of the bentonite and organoclay. TGA curves taken from the organoclay after being subjected to a temperature of 700 °C resulted in 70 wt.% ashes content. Therefore the total weight loss of 30 wt.% up to 700 °C (Fig. 2) could be attributed to the decomposition of organic modifier.
Fig. 4. TEM images of extruded composites, b1: 50,000 magnification. TEM images of extruded composites, b2: 15,000 magnification.
P. Li et al. / Applied Clay Science 40 (2008) 38–44
Fig. 5. Stress–strain curves for EPDM and the composites. (3.0 phr loading amount of fillers).
41
Fig. 7. Elongation at break of EPDM and the composites.
3.3. Mechanical properties 3.2. TEM observation The organo-montmorillonite layers are dispersed into nanometer size particles (Figs. 3 and 4). Single montmorillonite layers and some multi-layer stacks (shown as intercalated layers) in the case of EPDM containing 3.0 phr organoclay are seen in a1 of Fig. 3; it indicates that exfoliated and partially intercalated organo-montmorillonite layers coexisted in the directed blended EPDM/organoclay nanocomposite. On the contrary, b1 of Fig. 4 clearly reveals many exfoliated layers and a few layer stacks in the extruded composite. The a2 of Fig. 3 and b2 of Fig. 4 are the TEM images in a larger observation scales. The layers of extrusion nanocomposite dispersed more uniformly and their diameter is thinner than that of the directed blended nanocomposite. The difference is due to the higher shear force during extrusion for extruded nanocomposites.
Fig. 6. Tensile strength of EPDM and the composites.
Fig. 5 presents the dependence of stress–strain characteristics of the pure EPDM and the other three composites, which contain 3.0 phr filler (organoclay or carbon black). At the strains below about 200%, these materials behaved similarly; but from 200% to 400%, the tensile modulus of carbon black composite was higher than of the other composites; at 400% the carbon black composite and the pure EPDM sample broke. The other two nanocomposites broke when the strain was about 500%. The tensile strength of the directed blended composite was higher than of the other materials. The extruded composite broke at the strain of 700%. Thus, the extruded composite has the highest tensile strength and the longest elongation. The organoclay nanocomposites showed a strong increase in the stress behavior at the high strain approaching
Fig. 8. Tear strength of EPDM and the composites.
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P. Li et al. / Applied Clay Science 40 (2008) 38–44
Table 1 Mechanical properties of organoclay/carbon black co-reinforcement composites Pure EPDM
Hardness (shore A) Modulus 200% (MPa) Tensile strength (MPa) Elongation at break (%) Tear strength (MPa)
56.0 1.4 2.4 388.5 11.5
C.B.
C.B.
ORC./C.B.
ORC./C.B.
(20 phr)
(30 phr)
(3.0 + 17.0 phr)
(6.0 + 14.0 phr)
65.0 3.7 16.3 420.5 21.9
68.5 6.1 21.5 398.3 25.2
58.0 2.4 22.2 646.3 28.6
60.0 3.3 27.6 764.3 31.3
Note: C.B.: carbon black; ORC./C.B.: organoclay/carbon black.
break. This resulted from the macromolecular chain orientation and the resultant orientation of the clay mineral layers brought about by the rubber macromolecular orientation (Hwang et al., 2004). The effects of organoclay content on the tensile strength of the crosslinked EPDM/organoclay nanocomposites are illustrated in Fig. 6. There are some clear differences between the samples as shown in Fig. 5, the extruded nanocomposites have the highest strength. Comparing the values of tensile strength especially at the 3.0 phr loading, the tensile strength of the extruded nanocomposites increased to 12.3 MPa, which is a fivefold increase of that of pure EPDM (2.4 MPa), 3.8 times of directed blended carbon black composites (3.2 MPa) and 2.8 times of directed blended organoclay nanocomposites (4.3 MPa). It reveals the strong reinforcement by low organoclay contents. The enhancement of the tensile strength is ascribed to the special layered structures of the clay mineral which were intercalated by EPDM macromolecular chains. There was a good compatibility at the phase boundaries of the EPDM macromolecular chains and the modified clay mineral layers as shown in the TEM images. The values of elongation at break are shown in Fig. 7. The addition of carbon black changed slightly the
Fig. 9. Mooney viscosity values of three composites.
elongation at break; but the addition of organoclay remarkably increased the elongation gradually improving with the increasing organoclay. Due to the presence of the silicate layers, some macromolecular chains could not be crosslinked by sulfur. These unvulcanized macromolecular chains elongated the tensibility of nanocomposites, and then increased the elongation at break. Because the dispersion of organoclay in extruded nanocomposites was more pronounced than in the directed nanocomposites, the elongation at break was higher. The tear strength of all the composites increases monotonously (Fig. 8). Nevertheless, the tear strength of extrusion nanocomposites is higher than that of the other samples, and that of the carbon black composites is the lowest. Due to the increased dispersion, the extruded composites have the higher tear strength. 3.4. Mechanical properties of co-reinforcement composites As discussed in the previous paragraphs, the extruded nanocomposites showed high performance only with low organoclay content (such as 3.0 phr). For the manufacturing, we selected two types of extrusion nanocomposites
Fig. 10. Thermogravimetric curves of EPDM and the nanocomposites (3.0 phr loading amount of organoclay).
P. Li et al. / Applied Clay Science 40 (2008) 38–44 Table 2 Temperatures of weight loss of pure EPDM and nanocomposites (3.0 phr) Ti − 5 wt.% (°C) Ti − 10 wt.% (°C) Tmax (°C) Pure EPDM 365.8 Direction nanocomposite 383.6 Extrusion nanocomposite 390.8
399.2 400.4 411.3
434.6 432.9 437.5
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and 10 wt.% weight loss (Ti − 5 wt.% and Ti − 10 wt.%), (Table 2). Ti and Tmax of the directed blended nanocomposite are close to pure EPDM. Ti and Tmax of the extruded nanocomposites increased remarkably relative to those of the pure EPDM. The high decomposition temperature indicates the improved thermal stability of the extruded nanocomposite.
containing 3.0 and 6.0 phr organoclay; and the absent filler filled with carbon black to compare with the samples full of the carbon black at the same loading. The results are shown in Table 1. The strength of the co-reinforcement system is higher than that of the system full of carbon black at the same filler content. Even the strength of the co-reinforcement system containing 20.0 phr filler is higher than the carbon black system containing 30.0 phr. It should also be considered that the hardness of co-reinforcement system is lower than carbon black system about ten at the similar strength. It is a new approach for manufacturing products that need high strength and low hardness. Thus it can be expected that this extrusion nanocomposite has promising applications.
4. Conclusions
3.5. Mooney viscosity
The authors thank the experts in the TEM observation lab for helping in testing the samples for this study. They also wish to thank the reviewer for the critical comments to improve on this work.
The mooney viscosity is a measure of viscosity of the raw rubber, which means the processability of the rubber for manufacturing use. The values of mooney viscosity of carbon black composites are higher than that of pure EPDM; however, those of organoclay nanocomposites are clearly lower than pure EPDM (Fig. 9). The filled carbon black particles restrict the movement of EPDM macromolecular chains, which increases the viscosity. The decrease viscosity of the nanocomposites may be related to the lamellar structure of the clay minerals; the exfoliated layers space the distance of macromolecular chains and reduce the amounts of entangled macromolecular chains. This unchaining phenomenon called disentaglement effect would decrease the viscosity of the system. Because of the higher amounts of exfoliated layers, the mooney viscosity of the extruded nanocomposites was lower than that of the directed blended nanocomposites. 3.6. Thermal stability Fig. 10 shows the TGA curves of pure EPDM and EPDM/organoclay nanocomposite with 3.0 phr organoclay content. The insert figure in Fig. 10 shows the differentiated curves used to find out the temperature of maximum decomposition rate (Tmax). The initial thermal stability (Ti) is characterized by the temperatures at 5
• Melt extrusion lead to a good exfoliation of modified clay mineral particles in EPDM. • The extruded nanocomposite containing 3.0 phr organoclay had the tensile strengths up to 12.3 MPa, which was fivefold higher than that of the pure EPDM and higher than that of conventional composites with 15 phr carbon black. Co-reinforcement appeared as a promising application. • The adding of organoclay decreased the Mooney viscosity and increased the thermal stability of EPDM. Acknowledgement
References Ahmadi, S.J., Huang, Y.D., Li, W., 2005a. Fabrication and physical properties of EPDM-organoclay nanocomposites. Compos. Sci. Technol. 65, 1069–1076. Ahmadi, S.J., Huang, Y.D., Li, W., 2005b. Morphology and characterization of clay-reinforced EPDM nanocomposites. J. Compos. Mater. 39 (8), 745–754. Gatos, K.G., Sawanis, N.S., Apostolov, A.A., 2004. Nanocomposite formation in hydrogenated nitrile rubber (HNBR)/organo-montmorillonite as a function of the intercalant type. Macromol. Mater. Eng. 289 (12), 1079–1086. Gatos, K.G., Kocsis, J.K., 2005. Effects of primary and quaternary amine intercalants on the organoclay dispersion in a sulfur-cured EPDM rubber. Polymer 46, 3069–3076. Hwang, W.G., Wei, K.H., Wu, C.M., 2004. Preparation and mechanical properties of nitrile butadiene rubber/silicate nanocomposites. Polymer 45, 5731. Joly, S., Garnaud, G., Ollitrault, R., Bokobza, L., 2002. Organically modified layered silicates as reinforcing fillers for natural rubber. Chem. Mater. 14, 4202–4208. Kim, J.T., Oh, T.S., Lee, D.H., 2004. Curing and barrier properties of NBR/organo-clay nanocomposite. Polym. Int. 53 (4), 406–411. LeBaron, P.C., Pinnavaia, T.J., 2001. Clay nanolayer reinforcement of a silicone elastomer. Chem. Mater. 13, 3760–3765. Sandrine, M.T., Mailhot, B., Gardette, J.L., Silva, C.D., Haidar, B., Vidal, A., 2005. Photooxidation of ethylene-propylene-diene/ montmorillonite Nanocomposites. Polym. Degrad. Stab. 90, 78–85.
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Sharifa, J., Yunus, W.M., Dahlan, K.Z.H., Ahmad, M.H., 2005. Preparation and properties of radiation crosslinked natural rubber/ clay nanocomposites. Polym. Test. 24, 211–217. Silva, C.D., Haidar, B., Vidal, A., Brendle, J.M., Dred, R.L., Vidal, L., 2005. Preparation of EPDM/synthetic montmorillonite nanocomposites by direct compounding. J. Mater. Sci. 40, 1813–1815. Sridhar, V., Tripathy, D.K., 2006. Barrier properties of chlorobutyl nanoclay composites. J. Appl. Polym. Sci. 101, 3630–3637. Wang, Z.F., Wang, B., Qi, N., Zhang, H.F., Zhang, L.Q., 2005a. Influence of fillers on free volume and gas barrier properties in styrenebutadiene rubber studied by positrons. Polymer 46, 719–724.
Wang, S.H., Zhang, Y., Ren, W.T., Zhang, Y.X., Lin, H.F., 2005b. Morphology, mechanical and optical properties of transparent BR/ clay nanocomposites. Polym. Test. 24, 766-674. Young, W.C., Yungchul, Y., Seunghoon, R., Changwoon, N., 2002. Preparation and properties of EPDM/organomontmorillonite hybrid nanocomposites. Polym. Int. 51 (4), 319–324. Zhang, Z.J., Zhang, L.N., Li, Y., Xu, H.D., 2005. New fabricate of styrene–butadiene rubber/montmorillonite nanocomposites by anionic polymerization. Polymer 46, 129–136.
Applied Clay Science 40 (2008) 38 – 44 www.elsevier.com/locate/clay
High-performance EPDM/organoclay nanocomposites by melt extrusion Peiyao Li a,b,1 , Lanlan Yin c , Guojun Song a,b,⁎, Jin Sun b , Li Wang b , Hailong Wang b a
College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing, 100029, China b Institute of Polymer Materials, Qingdao University, Qingdao, 266071, China c Haidu Institute of Laiyang Agriculture University, Laiyang, 265200, China Received 7 March 2007; received in revised form 29 June 2007; accepted 5 July 2007 Available online 14 July 2007
Abstract Ethylene-propylene-diene terpolymer (EPDM)/organoclay nanocomposites were prepared by melt extrusion in a twin-screw extruder. The organoclay was characterized by XRD and TGA. As observed by transmission electron microscopy (TEM), the organoclay particles were exfoliated in EPDM. The tensile strength of the nanocomposites increased to 12.3 MPa at the same 3.0 phr amounts of fillers, which was a five-fold increase compared to pure EPDM and 2.8 times compared to the nanocomposite prepared by direction blending; furthermore it was above that of carbon black composites with 15.0 phr. The results of coreinforcement system exploited a promising application prospect of the organoclay and the nanocomposites. The processability of the terpolymer was improved as a result of the decrease of mooney viscosity; the improvement of the thermal stability of the nanocomposite was determined by TGA. © 2007 Elsevier B.V. All rights reserved. Keywords: EPDM; Organoclay; Nanocomposites; Mechanical property
1. Introduction The most attractive aspect of reinforcement by nanoparticles is that the properties can be largely improved only by adding small amounts of organoclay. Rubber/ organoclay nanocomposites have attracted great attention in recent years, such as nitrile butadiene rubber (Kim et al., 2004), chlorobutyl rubber (Sridhar and Tripathy, 2006), hydrogenated nitrile rubber (Gatos et al., 2004), styrene-butadiene rubber (Wang et al., 2005a; Zhang ⁎ Corresponding author. Institute of Polymer Materials, Qingdao University, Qingdao, 266071, China. E-mail address: [email protected] (P. Li). 1 Tel.: +86- 532- 8595 0691; fax: +86- 532- 8595 3260. 0169-1317/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2007.07.002
et al., 2005), natural rubber (Sharifa et al., 2005; Joly et al., 2002), silicone elastomer (LeBaron and Pinnavaia, 2001), polybutadiene (Wang et al., 2005b). Ethylene/propylene/diene terpolymer (EPDM) is a typical non-polar unsaturated rubber with wide applications. It has become extensively used in making automotive tire sidewalls, cover stripes, wires, cables, hoses, belting, footwear, roofing barriers and sporting goods. As it is incompatible with the organoclay which was modified with hexadecyl trimethyl-ammonium bromide or with dodecyl ammonium ions. EPDM/ organoclay nanocomposites were prepared with the oligomer (Young et al., 2002) or EPDM-g-MAH (Sandrine et al., 2005; Gatos and Kocsis, 2005; Silva et al., 2005; Ahmadi et al., 2005a,b) as compatibilizer.
P. Li et al. / Applied Clay Science 40 (2008) 38–44
39
2.3. Preparation of composites
Fig. 1. X-ray diffraction patterns of bentonite and organoclay.
In the current paper, we focused on the development of a ‘reactive’ organoclay compatible with the EPDM without additional compatibilizer. The clay used in this study was a bentonite produced in Shandong Province of China. The organoclay was added into the EPDM by the extrusion processing without any compatilizer. 2. Experimental studies 2.1. Materials The bentonite was obtained from the clay mine in Shandong Province of China, The montmorillonite (MMT) of the bentonite has the cation exchange capacity (CEC) of 100 meq/100 g. The organoclay (FMR02-F) was produced by Institute of Polymer Materials in Qingdao University, China. EPDM (KEP-570P, granulated elastomer) with 70% ethylene and 4.5% ethylidene norbornene content having a mooney viscosity of ML(1 + 4) at 100 °C = 75 was supplied by Kumho Chemicals, Korea. High abrasion furnace carbon black (N330) was commercial product, China. The vulcanization curatives: tetramethyl thiuram disulfide (TMTD), dibenzothiazole disulfide (DM), stearic acid, zinc oxide and sulfur were also commercial products, China. The formed mixing was (in parts), rubber: 100, organoclay: various, ZnO: 5.0, stearic acid: 1.0, TMTD: 1.5, DM: 0.5 and S: 1.5.
The EPDM pellets and the organoclay were placed into the high-speed mixer. After mixed homogeneously, the samples were extruded in a twin-screw extruder (co-rotative screws, D = 35.0 mm, L/D = 32/1); the temperature was 150 °C–160 °C from feeder to extrusion-head and the screw speed was 80 rpm. The extruded materials were granulated with a hot-cutting granulating head. Then the extruded samples incorporated with the curatives and other ingredients on a two roll miller with a nip clearance of 0.8 mm and friction ratio 1.3 (22/17 rpm). Mixing was performed at room temperature for 5 to 10 min. The specimens were cured at a plate vulcanization machine with 20 ton pressure in 160 °C. This type specimen was called extruded composite. The organoclay (or carbon black) compounded with EPDM by directed blending on the twin roll miller at the same contents compared to the extruded composites. The obtained samples were called directed blended organoclay and carbon black composites, respectively. 2.4. Measurements X-ray diffraction(XRD) experiments were performed for the bentonite and the organoclay using a D/max-RB diffractometer (Rigaku, Japan),which has an X-ray generator of 12 kW, a graphite monochromator, CuKα radiation operating at 40 kV, 100 mA. The samples were scanned at a scanning speed of 5°/min at diffraction angles 2θ 1–30°. Thermogravimetric analyses (TGA) were performed on a TGA/STDA851e instrument with platinum pan using about 7 mg of material as probe. The samples were heated at 10 °C/min rate in nitrogen atmosphere under a flow rate of 50 ml/min. Nanocomposites were thin-sectioned with an ultramicrotome and collected on a copper grid and examined with a TEM (JEM1200EX, JEOL) running at an accelerating voltage of 60 kV. Vulcanized composites sheets were cut into standard samples according to standard ISO37-1994 and ISO341:1994, respectively. The tensile properties and tear strength were determined on dumbbell-shaped and crescent-shaped
2.2. Preparation of organoclay The bentonite was wetted with water, and then purified by sedimentation and washing. The fined bentonite (100 g) was dispersed into 1000 ml of distilled water at 80 °C under vigorous stirring. A mixture of 53 g dimethyl hydrogenated tallow benzyl quaternary ammonium chloride (DMHTB), 200 g distilled water and 10 ml 98% concentrated sulfuric acid was prepared at 80 °C and then slowly added into the bentonite dispersion. The reaction was maintained for 6 h. The sediment was collected by filtration and washed ten times with hot water, and then dried at 80 °C in vacuum, ground and sieved to 30 μm. The organophilic clay was designated as organoclay.
Fig. 2. TGA thermogram of bentonite and organoclay.
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P. Li et al. / Applied Clay Science 40 (2008) 38–44
Fig. 3. TEM images of directed blended composites, a1: 50,000 magnification. TEM images of directed blended composites, a2: 10,000 magnification.
specimens at a crosshead speed of 500 mm/min by using an electronic universal testing machine. All measurements were made several times and the values were averaged. Mooney viscosity ML (1 + 4) at 100 °C was measured by using a Mooney viscometer based on standard ISO289-1985. The samples were sheared with the large rotor.
3. Results and discussion 3.1. Characterization of organoclay The organoclay was prepared by using a well-chosen organic modifier. The hydrophobic organic modifier
could facilitate the intercalation of a hydrophobic polymer by reducing the surface energy. The XRD and TGA tests were used to characterize organoclay. Fig. 1 shows the XRD patterns of bentonite and organoclay. The basal spacing of the montmorillonite and the organoclay was 1.51 nm and 3.09 nm (Fig. 1), respectively. That suggests the successful preparation of organoclay. Fig. 2 shows the TGA thermogram of the bentonite and organoclay. TGA curves taken from the organoclay after being subjected to a temperature of 700 °C resulted in 70 wt.% ashes content. Therefore the total weight loss of 30 wt.% up to 700 °C (Fig. 2) could be attributed to the decomposition of organic modifier.
Fig. 4. TEM images of extruded composites, b1: 50,000 magnification. TEM images of extruded composites, b2: 15,000 magnification.
P. Li et al. / Applied Clay Science 40 (2008) 38–44
Fig. 5. Stress–strain curves for EPDM and the composites. (3.0 phr loading amount of fillers).
41
Fig. 7. Elongation at break of EPDM and the composites.
3.3. Mechanical properties 3.2. TEM observation The organo-montmorillonite layers are dispersed into nanometer size particles (Figs. 3 and 4). Single montmorillonite layers and some multi-layer stacks (shown as intercalated layers) in the case of EPDM containing 3.0 phr organoclay are seen in a1 of Fig. 3; it indicates that exfoliated and partially intercalated organo-montmorillonite layers coexisted in the directed blended EPDM/organoclay nanocomposite. On the contrary, b1 of Fig. 4 clearly reveals many exfoliated layers and a few layer stacks in the extruded composite. The a2 of Fig. 3 and b2 of Fig. 4 are the TEM images in a larger observation scales. The layers of extrusion nanocomposite dispersed more uniformly and their diameter is thinner than that of the directed blended nanocomposite. The difference is due to the higher shear force during extrusion for extruded nanocomposites.
Fig. 6. Tensile strength of EPDM and the composites.
Fig. 5 presents the dependence of stress–strain characteristics of the pure EPDM and the other three composites, which contain 3.0 phr filler (organoclay or carbon black). At the strains below about 200%, these materials behaved similarly; but from 200% to 400%, the tensile modulus of carbon black composite was higher than of the other composites; at 400% the carbon black composite and the pure EPDM sample broke. The other two nanocomposites broke when the strain was about 500%. The tensile strength of the directed blended composite was higher than of the other materials. The extruded composite broke at the strain of 700%. Thus, the extruded composite has the highest tensile strength and the longest elongation. The organoclay nanocomposites showed a strong increase in the stress behavior at the high strain approaching
Fig. 8. Tear strength of EPDM and the composites.
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P. Li et al. / Applied Clay Science 40 (2008) 38–44
Table 1 Mechanical properties of organoclay/carbon black co-reinforcement composites Pure EPDM
Hardness (shore A) Modulus 200% (MPa) Tensile strength (MPa) Elongation at break (%) Tear strength (MPa)
56.0 1.4 2.4 388.5 11.5
C.B.
C.B.
ORC./C.B.
ORC./C.B.
(20 phr)
(30 phr)
(3.0 + 17.0 phr)
(6.0 + 14.0 phr)
65.0 3.7 16.3 420.5 21.9
68.5 6.1 21.5 398.3 25.2
58.0 2.4 22.2 646.3 28.6
60.0 3.3 27.6 764.3 31.3
Note: C.B.: carbon black; ORC./C.B.: organoclay/carbon black.
break. This resulted from the macromolecular chain orientation and the resultant orientation of the clay mineral layers brought about by the rubber macromolecular orientation (Hwang et al., 2004). The effects of organoclay content on the tensile strength of the crosslinked EPDM/organoclay nanocomposites are illustrated in Fig. 6. There are some clear differences between the samples as shown in Fig. 5, the extruded nanocomposites have the highest strength. Comparing the values of tensile strength especially at the 3.0 phr loading, the tensile strength of the extruded nanocomposites increased to 12.3 MPa, which is a fivefold increase of that of pure EPDM (2.4 MPa), 3.8 times of directed blended carbon black composites (3.2 MPa) and 2.8 times of directed blended organoclay nanocomposites (4.3 MPa). It reveals the strong reinforcement by low organoclay contents. The enhancement of the tensile strength is ascribed to the special layered structures of the clay mineral which were intercalated by EPDM macromolecular chains. There was a good compatibility at the phase boundaries of the EPDM macromolecular chains and the modified clay mineral layers as shown in the TEM images. The values of elongation at break are shown in Fig. 7. The addition of carbon black changed slightly the
Fig. 9. Mooney viscosity values of three composites.
elongation at break; but the addition of organoclay remarkably increased the elongation gradually improving with the increasing organoclay. Due to the presence of the silicate layers, some macromolecular chains could not be crosslinked by sulfur. These unvulcanized macromolecular chains elongated the tensibility of nanocomposites, and then increased the elongation at break. Because the dispersion of organoclay in extruded nanocomposites was more pronounced than in the directed nanocomposites, the elongation at break was higher. The tear strength of all the composites increases monotonously (Fig. 8). Nevertheless, the tear strength of extrusion nanocomposites is higher than that of the other samples, and that of the carbon black composites is the lowest. Due to the increased dispersion, the extruded composites have the higher tear strength. 3.4. Mechanical properties of co-reinforcement composites As discussed in the previous paragraphs, the extruded nanocomposites showed high performance only with low organoclay content (such as 3.0 phr). For the manufacturing, we selected two types of extrusion nanocomposites
Fig. 10. Thermogravimetric curves of EPDM and the nanocomposites (3.0 phr loading amount of organoclay).
P. Li et al. / Applied Clay Science 40 (2008) 38–44 Table 2 Temperatures of weight loss of pure EPDM and nanocomposites (3.0 phr) Ti − 5 wt.% (°C) Ti − 10 wt.% (°C) Tmax (°C) Pure EPDM 365.8 Direction nanocomposite 383.6 Extrusion nanocomposite 390.8
399.2 400.4 411.3
434.6 432.9 437.5
43
and 10 wt.% weight loss (Ti − 5 wt.% and Ti − 10 wt.%), (Table 2). Ti and Tmax of the directed blended nanocomposite are close to pure EPDM. Ti and Tmax of the extruded nanocomposites increased remarkably relative to those of the pure EPDM. The high decomposition temperature indicates the improved thermal stability of the extruded nanocomposite.
containing 3.0 and 6.0 phr organoclay; and the absent filler filled with carbon black to compare with the samples full of the carbon black at the same loading. The results are shown in Table 1. The strength of the co-reinforcement system is higher than that of the system full of carbon black at the same filler content. Even the strength of the co-reinforcement system containing 20.0 phr filler is higher than the carbon black system containing 30.0 phr. It should also be considered that the hardness of co-reinforcement system is lower than carbon black system about ten at the similar strength. It is a new approach for manufacturing products that need high strength and low hardness. Thus it can be expected that this extrusion nanocomposite has promising applications.
4. Conclusions
3.5. Mooney viscosity
The authors thank the experts in the TEM observation lab for helping in testing the samples for this study. They also wish to thank the reviewer for the critical comments to improve on this work.
The mooney viscosity is a measure of viscosity of the raw rubber, which means the processability of the rubber for manufacturing use. The values of mooney viscosity of carbon black composites are higher than that of pure EPDM; however, those of organoclay nanocomposites are clearly lower than pure EPDM (Fig. 9). The filled carbon black particles restrict the movement of EPDM macromolecular chains, which increases the viscosity. The decrease viscosity of the nanocomposites may be related to the lamellar structure of the clay minerals; the exfoliated layers space the distance of macromolecular chains and reduce the amounts of entangled macromolecular chains. This unchaining phenomenon called disentaglement effect would decrease the viscosity of the system. Because of the higher amounts of exfoliated layers, the mooney viscosity of the extruded nanocomposites was lower than that of the directed blended nanocomposites. 3.6. Thermal stability Fig. 10 shows the TGA curves of pure EPDM and EPDM/organoclay nanocomposite with 3.0 phr organoclay content. The insert figure in Fig. 10 shows the differentiated curves used to find out the temperature of maximum decomposition rate (Tmax). The initial thermal stability (Ti) is characterized by the temperatures at 5
• Melt extrusion lead to a good exfoliation of modified clay mineral particles in EPDM. • The extruded nanocomposite containing 3.0 phr organoclay had the tensile strengths up to 12.3 MPa, which was fivefold higher than that of the pure EPDM and higher than that of conventional composites with 15 phr carbon black. Co-reinforcement appeared as a promising application. • The adding of organoclay decreased the Mooney viscosity and increased the thermal stability of EPDM. Acknowledgement
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