Composite Interfaces 16 (2009) 337 346 www.brill.nl/ci Effect of Rubber Content of ABS on the Mechanical Properties of ABS/Clay Nanocomposites Hyun-Kyo Kim a, Gue-Hyun Kim b,, Byung-Mook Cho b and Chang-Sik Ha a, a Department of Polymer Science and Engineering, Pusan National University, Busan 609-735, South Korea b Division of Applied Bio Engineering, Dongseo University, Busan 617-716, South Korea Received 18 February 2008; accepted 2 June 2008 Abstract One approach to improve the impact strength of acrylonitrile butadiene styrene (ABS)/clay nanocomposites is to increase rubber content. To investigate the effect of the rubber content of ABS on the mechanical properties of the ABS/clay nanocomposites, other parameters were fixed and ABS/clay nanocomposites containing various rubber contents were prepared in this study. Also the effect of the UV stabilizer on the mechanical properties of ABS/clay nanocomposite was studied. For addition of 3 wt% clay, ABS nanocomposite with 35 wt% content of rubber displayed the highest reinforcement ratio for tensile properties and impact strength. Koninklijke Brill NV, Leiden, 2009 Keywords Nanocomposites, ABS, impact strength, rubber content 1. Introduction In recent years polymer/clay nanocomposites have attracted considerable attention from both the field of fundamental research and applications due to their remarkable improvement in materials properties. Owing to the nanometer thickness and extremely high aspect ratio of silicate layers, these nanocomposites exhibit dramatic improvements in the mechanical, thermal and barrier properties of composites [1 4]. Acrylonitrile butadiene styrene (ABS) is one of the most commonly used engineering plastics because of its excellent mechanical properties, chemical resistance and convenient processibility [5]. ABS is generally prepared by the copolymerization of styrene and acrylonitrile in the presence of polybutadiene (PB) latex. * To whom correspondence should be addressed. E-mails: csha@pusan.ac.kr or guehyun@gdsu.dongseo.ac.kr Koninklijke Brill NV, Leiden, 2009 DOI:10.1163/156855409X447156
338 H.-K. Kim et al. / Composite Interfaces 16 (2009) 337 346 Even though there have been some studies about ABS/clay nanocomposites, most works have concentrated on their thermal and flammability properties [6 9]. In a recent study, detailed mechanical properties of ABS/clay nanocomposites were reported by Stretz et al. [10]. Since the impact strength of ABS/clay nanocomposites was reported to significantly decrease and impact strength is a very important mechanical property for the application of ABS, the optimization of the formulation is needed. One approach to improve the impact strength is to increase rubber content in ABS/clay nanocomposites. According to continuum-based micromechanical models, the modulus enhancement of nanocomposites is much more dramatic for a compliant matrix such as elastomers than a stiff matrix such as glassy and semicrystalline polymers. Therefore it is very interesting to study the extent of enhancement of modulus for ABS/clay nanocomposites over the various rubber contents compared with corresponding ABS. To investigate the effect of the rubber content of ABS on the mechanical properties of the ABS/clay nanocomposites, other parameters were fixed and ABS/clay nanocomposites containing various rubber contents were prepared in this study. Also the effect of the UV stabilizer on the mechanical properties of ABS/clay nanocomposites was investigated in this study. 2. Experimental 2.1. Materials and Preparation of ABS/Clay Nanocomposites Important characteristics of the materials used in this study are summarized in Table 1. Three types of ABS prepared with the same styrene acrylonitrile copolymer (SAN) and same polybutadiene impact modifier were provided by LG Chemical Company named ABS25 (rubber content: 25 wt%), ABS30 (30 wt%) and ABS35 (35 wt%), respectively. Clay was purchased from Southern Clay Products (USA) under the trade name of Cloisite 20A. The organic modifier of Cloisite 20A is dimethyl, dihydrogenated tallow, quaternary ammonium. ABS, clay and other additives were mixed in a Prism co-rotating, intermeshing twin screw extruder (L/D = 40) at 200 rpm, 220 C and a feed rate of 40 kg/h. The recipes of the compounds are described in Table 2. Test specimens for tensile and Izod impact experiments were prepared using an Arburg 370M injection molding machine (barrel temperature: 220 C and mold temperature: 50 C). 2.2. Nanocomposite Testing X-ray diffraction (XRD) patterns were taken with a Rigaku D/max 2200H X-ray diffractometer (40 kv, 50 ma). The scanning rate was 0.5 /min. The basal spacing of the silicate layer, d, was calculated using the Bragg s equation, nλ = 2d sin θ.
H.-K. Kim et al. / Composite Interfaces 16 (2009) 337 346 339 Table 1. Important characteristics of the materials used in this study Class of materials Materials Supplier Characteristics Polymer Acrylonitrile butadiene LG Chemical Co., Korea Rubber content: 25 wt% styrene (ABS25) Acrylonitrile butadiene LG Chemical Co., Korea Rubber content: 30 wt% styrene (ABS30) Acrylonitrile butadiene LG Chemical Co., Korea Rubber content: 35 wt% styrene (ABS35) Clay Cloisite 20A Southern Clay, USA Modifier concentration: 95 mequiv/100 g Lubricant N,N-ethylene bis Choyang Chemical, Korea Melting point: stearamide (EBA) 141.5 146.5 C Anti-oxidant Distearyl pentaerythritol Asahi Denka, Japan Melting point: 45 60 C diphosphite (PEP-8) Specific gravity: 0.925 UV Stabilizer 2(2 -Hydroxy-3-5 -di- Ciba Geigy, Japan Melting point: 154 158 C t-butylphenyl)-5-chloro Specific gravity: 1.26 benzotriazole (UV Hisorb 327) Bis (2,2,6,6-tetramethyl- Ciba Geigy, Japan Melting point: 128 132 C 4-piperidyl) sebaceate Specific gravity: 0.873 (UV Hisorb 770) Table 2. Recipes (in phr) of the compounds Materials Code ABS25/ ABS25/ ABS30/ ABS30/ ABS35/ ABS35/ Clay3 Clay6 Clay3 Clay6 Clay3 Clay6 ABS25 100 100 ABS30 100 100 ABS35 100 100 Clay 3 6 3 6 3 6 EBA 2 2 2 2 2 2 PEP-8 0.2 0.2 0.2 0.2 0.2 0.2 The tensile properties at room temperatue were measured according to ASTM D638 using a Universal Testing Machine (Instron 4202). All measurements were performed for five replicates of dog-bone shaped specimens and averaged to get the final result. The notched Izod impact test (ASTM D256) was measured using a Tinius olsen tester at room temperature.
340 H.-K. Kim et al. / Composite Interfaces 16 (2009) 337 346 3. Results and Discussion 3.1. Characterization of ABS/Clay Nanocomposites Figure 1 shows the XRD patterns of ABS/clay nanocomposites. For ABS25/Clay3 nanocomposites a peak at 3.62 nm (2θ = 2.44 ), for ABS30/Clay3 nanocomposites a peak at 3.42 nm (2θ = 2.58 ), and for ABS35/Clay3 nanocomposites a peak at 3.09 nm (2θ = 2.86 ) are observed. Also for ABS25/Clay6 nanocomposites a peak at 3.47 nm (2θ = 2.54 ), for ABS30/Clay6 nanocomposites a peak at 3.37 nm (2θ = 2.62 ), and for ABS 35/Clay6 nanocomposites a peak at 3.34 nm (2θ = 2.64 )are observed. Compared with the peak at 2θ = 3.54 for the original clay (Cloisite 20A), the peaks at lower angle for all ABS/clay nanocomposites indicate the intercalation of ABS molecules into the interlayer of clay resulting in the expansion of the interlayer distance. However, the degree of expansion of the interlayer distance for ABS25/Clay3 (2.49 nm 3.62 nm) is larger than that for ABS30/Clay3 (2.49 nm 3.42 nm) and ABS35/Clay3 (2.49 nm 3.09 nm). Also, the degree of expansion of the interlayer distance for ABS25/Clay6 (2.49 nm 3.47 nm) is larger than that for ABS30/Clay6 (2.49 nm 3.37 nm) and ABS35/Clay6 (2.49 nm 3.34 nm). From XRD results, it may be concluded that ABS nanocomposites with 30, 35% rubber content (ABS30 and ABS35) lead to a lower degree of dispersion of clay than ABS nanocomposites with 25% rubber content (ABS25). 3.2. Mechanical Properties To investigate the effect of the rubber content of ABS on the mechanical properties of the ABS/clay nanocomposites, the mechanical properties of ABS/clay nanocom- Figure 1. XRD patterns of ABS/clay nanocomposites.
H.-K. Kim et al. / Composite Interfaces 16 (2009) 337 346 341 posites containing various rubber contents (25%, 30% and 35%) were examined in this study. Since ABS matrix polymers with different rubber contents were used for the preparation of ABS/clay nanocomposites, it is convenient to introduce a new variable a relative ratio allowing for the direct comparison of the efficiency of mechanical properties enhancement of nanocomposites. For example, the relative tensile modulus is defined as follows: Tensile modulus of nanocomposite Relative tensile modulus = Tensile modulus of its matrix polymer. (1) The matrix polymer for ABS25/Clay3, ABS30/Clay3 and ABS35/Clay3 nanocomposites is ABS25, ABS30 and ABS35, respectively. Figure 2 shows the relative tensile modulus of ABS/clay nanocomposites. Since the value is higher than 1, tensile modulus slightly increases with addition of clay. For 3% of clay addition, the ABS nanocomposite with 35% rubber content displays the highest relative tensile modulus. According to Stretz et al. [10], predictions from the Halpin Tsai theory indicate that the modulus enhancement of nanocomposites is much more dramatic for a compliant matrix such as elastomers than with a stiff matrix such as glassy and semicrystalline polymers. ABS nanocomposite with 35% rubber content has the most compliant matrix. However, as the aspect ratio of filler is smaller, the difference in modulus enhancement between a compliant matrix and a stiff matrix is smaller. Since for 6% clay addition, ABS nanocomposites with 30% and 35% rubber content display lower relative tensile modulus than with 25% rubber content, the aspect ratio of clay in nanocomposites with 30% and 35% rubber content may be lower than nanocomposites with 25%. TEM results are needed to prove the lower aspect ratio of clay in nanocomposites with 30% and 35% rubber content. Lower aspect ratio indicates a Figure 2. Relative tensile modulus of ABS/clay nanocomposites.
342 H.-K. Kim et al. / Composite Interfaces 16 (2009) 337 346 Figure 3. Relative tensile strength of ABS/clay nanocomposites. lower degree of dispersion of the fillers and/or lower degree of orientation. According to Stretz et al. [10], the clay particles reside in the SAN matrix phase, with some accumulation of particles at the rubber surface and no clay particles were found in the rubber phase. Because of the less effective clay particle dispersion, the level of reinforcement in ABS was somewhat lower than in SAN. In our study, we found that increasing rubber content may lead to a lower degree of dispersion of clay and/or lower degree of orientation. Generally, this effect increases with increasing clay content. This lower degree of dispersion for ABS/clay nanocomposites with higher rubber content was supported by our XRD results (Fig. 1). Tensile strength slightly increases with addition of clay (Fig. 3). Relative elongations at break for ABS nanocomposites are shown in Fig. 4. Since the value is lower than 1, the elongation at break decreases with addition of clay. However, with increasing rubber content, relative elongation at break increases. Impact strength of ABS is one of the most important properties for various applications. Generally the impact strength of polymer/clay nanocomposites has been reported to decrease. In this study, the impact strength of ABS also decreases with addition of clay. However, ABS nanocomposite with higher content of rubber displays the higher relative Izod impact strength (Fig. 5). The impact strength of ABS nanocomposite (clay: 3%) with 25% rubber content is only 1/3 of the impact strength of ABS25. However, the impact strength of ABS nanocomposite (clay: 3%) with 35% rubber content is 1/2 of the impact strength of ABS30. Therefore, to optimize the mechanical properties, the content of rubber should be optimized. 3.3. Effect of UV Stabilizer To investigate the effect of UV stabilizer on the mechanical properties of ABS/clay nanocomposites, a mixture of UV stabilizers (0.5 phr UV Hisorb 770 + 0.5 phr
H.-K. Kim et al. / Composite Interfaces 16 (2009) 337 346 343 Figure 4. Relative elongation at break of ABS/clay nanocomposites. Figure 5. Relative Izod impact strength of ABS/clay nanocomposites. UV Hisorb 327) was used to prepare ABS/clay nanocomposites. Since the mixture also protects polymers from thermal degradation, the mechanical properties of ABS with UV stabilizers are improved compared with ABS without UV stabilizers. Compared with relative Izod impact strength of ABS/clay nanocomposites without UV stabilizers (Fig. 5), the relative Izod impact strength of ABS/clay nanocomposites with UV stabilizers (Fig. 6) is increased significantly. The relative Izod impact strength of ABS/clay nanocomposites increases with increasing rubber content. The
344 H.-K. Kim et al. / Composite Interfaces 16 (2009) 337 346 Figure 6. Relative Izod impact strength of ABS/clay nanocomposites with UV stabilizer. Figure 7. Relative tensile modulus of ABS/clay nanocomposites with UV stabilizer. impact strength of ABS/clay nanocomposite (clay: 3%) with 35% rubber content is about 70% of the impact strength of ABS35. Since the relative tensile modulus is higher than 1, the tensile modulus slightly increases with addition of clay (Fig. 7). However, tensile strength and elongation at break of ABS decrease with addition of clay (Figs 8 and 9). For 3% of clay addition, the ABS nanocomposite with 35% rubber content displays the highest relative Izod impact strength and relative tensile modulus.
H.-K. Kim et al. / Composite Interfaces 16 (2009) 337 346 345 Figure 8. Relative tensile strength of ABS/clay nanocomposites with UV stabilizer. Figure 9. Relative elongation at break of ABS/clay nanocomposites with UV stabilizer. 4. Conclusions Even though the improved physical properties of ABS/clay nanocomposites have been reported, the significant reduction of impact strength was a big obstacle to their practical applications. The optimization of mechanical properties is very important for the applications. In this study, to optimize the mechanical properties, ABS/clay nanocomposites with different rubber contents were prepared. For 3% of clay addition, the relative Izod impact strength and relative tensile properties in-
346 H.-K. Kim et al. / Composite Interfaces 16 (2009) 337 346 crease with increasing rubber content. When the clay content is increased from 3% to 6%, there is a significant reduction in impact strength. For addition of 3 wt% clay, the ABS nanocomposite with 35 wt% content of rubber (ABS35/Clay3) displayed the highest reinforcement ratio for tensile properties and impact strength. Also the addition of UV stabilizer significantly improves the impact strength of ABS35/Clay3 nanocomposites. Acknowledgements This study was financially supported for two years by the Pusan National University, Korea and the Brain Korea 21 project. References 1. M. Alexandre and P. Dubois, Polymer-layered silicate nanocomposites: preparation, properties and uses of new class of materials, Mater. Sci. Engng 28, 1 63 (2000). 2. A. M. Showkat, K. P. Lee, A. I. Gopalan and S. H. Kim, Synthesis and chiroptical properties of water processable conducting poly(diphenylamine) nanocomposite, Macromol. Res. 15, 575 580 (2007). 3. J. U. Park, J. L. Kim, D. H. Kim, K. H. Ahn and S. J. Lee, Rheological behavior of polymer/layered silicate nanocomposites under uniaxial extensional flow, Macromol. Res. 14, 318 323 (2006). 4. S. S. Ray and M. Okamoto, Polymer/layered silicate nanocomposite: a review from preparation to processing, Prog. Polym. Sci. 28, 1539 1641 (2003). 5. J. H. Hong, K. H. Song, H. G. Lee, M. S. Han and Y. H. Kim, Morphological and rheological properties of poly(acrylonitrile butadiene styrene)/polycarbonate/poly(ε-caprolactone) ternary blends, Macromol. Res. 15, 520 526 (2007). 6. S. Wang, Y. Hu, L. Song, Z. Wang, Z. Chen and W. Fan, Preparation and thermal properties of ABS/montmorillonite nanocomposite, Polym. Degrad. Stab. 77, 423 426 (2002). 7. S. Wang, Y. Hu, Z. Lin, Z. Gui, Z. Wang, Z. Chen and W. Fan, Flammability and thermal stability studies of ABS/nanocomposite, Polym. Intl 52, 1045 1049 (2003). 8. S. Wang, Y. Hu, R. Zong, Y. Tang, Z. Chen and W. Fan, Preparation and characterization of flame retardant ABS/montmorillonite nanocomposite, Appl. Clay Sci. 25, 49 55 (2004). 9. A. P. Patiňo-soto, S. Sănchez-Valdes and L. F. Ramos-deValle, Morphological and thermal properties of ABS/montmorillonite nanocomposite using ABS with different AN contents, Macromol. Mater. Engng 292, 302 309 (2007). 10. H. A. Stretz, D. R. Paul and P. E. Cassidy, Poly(styrene-co-acrylonitrile)/montmorillonite oganoclay mixtures: a model system for ABS nanocomposite, Polymer 46, 3818 3830 (2005).