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Composites and nanocomposites of ABS: Synergy between glass fiber and nano-sepiolite
Composites: Part B 47 (2013) 42–47
Contents lists available at SciVerse ScienceDirect
Composites: Part B journal homepage: www.elsevier.com/locate/compositesb
Composites and nanocomposites of ABS: Synergy between glass fiber and nano-sepiolite F.C. Basurto a,⇑, D. García-López b, N. Villarreal-Bastardo b, J.C. Merino a,b, J.M. Pastor a,b a b
Department of Condensed Matter Physics, EII, University of Valladolid, Paseo del Cauce 59, 47011 Valladolid, Spain CIDAUT – Foundation for Research and Development in Transport and Energy, Parque Tecnológico de Boecillo, Boecillo, 47151 Valladolid, Spain
a r t i c l e
i n f o
Article history: Received 20 February 2012 Received in revised form 20 August 2012 Accepted 31 August 2012 Available online 3 December 2012 Keywords: A. Glass fibers A. Polymer–Matrix Composites (PMCs) B. Mechanical properties E. Extrusion Sepiolite
a b s t r a c t One of the latest steps in polymer nano-technology is polymer/clay/glass fiber composites because of the synergistic effects of both reinforcing particles. Acrylonitrile–butadiene–styrene (ABS) – sepiolite nanocomposites have been developed, and glass fiber has been added to this system in order to study a synergistic behavior between both reinforcing particles. Properties such as Young modulus, impact strength and heat deflection temperature have been measured to characterize the nanocomposites. Morphology has been studied by means of optical and electron microscopy. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction Glass fiber (GF) composites have received great attention in the field of polymer technology in the last years. It is well known that the addition of GF to a thermoplastic matrix is able to improve the mechanical properties of the matrix [1–4]. The final properties depend not only on the reinforcing effect of the load, but also on the interaction between both phases. Traditionally, polymers typically used in the automotive industry are reinforced by adding fillers like GF at a high loading level, increasing the weight and hence the fuel consumption and CO2 emissions. The use of GF as a reinforcing agent in polymer technology leads also to processing and reusing related problems. On one hand, GF is usually employed at high percentages, so it is harder to process and recycle industrial pieces made of GF composites. On the other hand, as the reinforcing percentage is increased, a geometrical deformation or warping appears in those pieces, loosing their dimensional stability and deteriorating the surface finish. Due to these reasons, it is recommendable to reduce the GF percentage. One of the most recent alternatives to this type of filler is the use of nano-clays, particles in the nanometric range. This reinforcement added to the GF at a very low amount (less than 10% by weight) is capable of increasing mechanical properties of polymers, ⇑ Corresponding author. Tel.: +34 983 54 80 35; fax: +34 983 14 82 01. E-mail address: [email protected] (F.C. Basurto). 1359-8368/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.compositesb.2012.08.026
such as Young’s modulus and heat deflection temperature (HDT), but usually with a reduction of the toughness [5]. Theoretically, a synergistic reinforcement is achieved when the working together of two or more loads produces an effect greater than the sum of their individual effects. In this case, sepiolite would be used as a partial replacement of the GF. Therefore, if it is possible to obtain a synergy between GF and clay in at least one property, not only the processing and reusing related problems will be reduced, but also it would be possible to obtain an industrial piece that satisfies the same requirements (in stiffness for example), reducing the total amount of particle reinforcement. In that sense, it is the aim of this research to obtain a synergy between GF and clay, and show that nanosepiolite is a serious complement to GF reinforcement. For example, Clifford and Wan [6] demonstrated that the Halpin–Tsai theory was acceptable to estimate the Young’s modulus in a hybrid composite. In this paper, they explained that the synergistic effect could be understood considering a polymer with reinforcement in two scales: microscopic fiber reinforcement combined with exfoliated nanoscale particles. Acosta et al. [7] studied the incorporation and substitution of part of GF by sepiolite in a polypropylene composite. With 30 wt.% of GF, they found an increment of 228% in flexural modulus, but in a hybrid composite with 20 wt.% of GF and 10 wt.% of sepiolite, the modulus increased up to 263%. Concerning processing conditions for GF, Ozkoc et al. [8] studied the influence of temperature and screw speed on the mechanical
F.C. Basurto et al. / Composites: Part B 47 (2013) 42–47
properties of ABS–GF composites elaborated in a co-rotating twinscrew extruder. It was concluded that a better balance in mechanical properties was achieved when screw speed was reduced and extrusion temperature was slightly increased, because these modifications in the processing conditions reduced the breaking of the glass fibers. Particularly, they stated that new stress-concentrated zones were generated by the breaking of fibers, with a negative effect on the impact strength. In another article [9], Ozkoc et al. found an increment of 190% in Young modulus and a reduction of 83% in impact strength in composites with 30 wt.% of GF. The improvement in stiffness was related to the presence of the fiber, which also was the responsible for the reduction in toughness, associated to the restricted deformation ability of matrix. In our previous work [10], we described the processing and characterization of ABS nanocomposites with 5 wt.% of sepiolite. In that work, an optimal methodology to obtain those nanocomposites was developed. It was concluded that: (1) 200 rpm (rpm) was the most favorable extrusion screw speed, and (2) quaternary ammonium salts were the best surfactant agents for sepiolite in ABS nanocomposites. In the present work, the previous conclusions were used to elaborate new nanocomposites with a high amount of sepiolite, in order to find out how the thermal and mechanical properties were modified. Moreover, hybrid nanocomposites made of GF and sepiolite were processed and characterized, with the purpose of evaluating the synergistic effects of both reinforcements. 2. Materials and methods 2.1. Materials Two different types of ABS polymers have been selected in this work. Although the real amount of polybutadiene (PB) was not provided by the polymer compounders, it could be inferred, from technical data sheets, that HI-100, supplied by LG Chem. has a higher PB content than G-360, supplied by GE Plastics. Modified sepiolite was prepared from pristine sepiolite named Pangel S9, supplied and modified by Tolsa S.A. The organic surfactants were two quaternary ammonium salts: BM2TH (bencylmethyl-dihydrogenated tallow) and 3MTH (trimethyl-hydrogenated tallow). The selection of the modifier used for each grade of ABS was based on the polarity of the matrix and the agent. Type E glass fiber (typically employed in automotive composites) was supplied by Saint-Gobain Vetrovex S.A., with a diameter of 17 lm and a mean length of 6 mm. Its density is very similar to sepiolite (2.54 g/cm3). Fibers were sized with a silane coupling agent, typically used in the automotive industry with polymer matrixes such as ABS, PC or PA 6.
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2.3. Characterization The morphologies of the ABS matrix and the nanocomposites were examined by scanning electron microscopy (SEM) using a Hitachi 3200 SN apparatus, operating at an accelerating voltage of 20 kV. The cryogenic fracture surface was subjected to a selective extraction technique, according to Shenavar and Abbasi [11], with a solution of CrO3 and H2SO4 during 5 min at 65 °C. This technique allowed us to observe the gaps left by the PB particles, and hence, explore their size and distribution. Transmission electron microscopy (TEM) images were obtained on a Jeol 2010 with an accelerating voltage of 120 kV. Samples for TEM were sectioned using a RMC PowerTome XL cryogenic ultramicrotome to a thickness of 60 nm with a diamond knife at 40 °C. Knife speed was 0.4 mm/s. Sectioned samples were stained in order to improve the contrast between PB particles and acrylonitrile-styrene (SAN) continuous phase. This process consisted of a selective staining technique [12], exposing the samples to OsO4 vapors during 24 h. In TEM images, the gray continuous region corresponds to SAN phase, and PB particles appear as black islands. In addition, in the GF-sepiolite hybrid nanocomposites, optical microscopy (OM) was conducted using an Olympus BX60M-KPM1E/K microscope, with a magnification of 10. This technique was employed to observe the distribution of both reinforcements, and measure the fiber length. After dissolving the ABS matrix in xylene, fibers were observed and measured by means of Omnimet Enterprise software, using a special routine designed specifically for this purpose. Thermogravimetric analysis was carried out using a Mettler Toledo 851e analyzer under inert atmosphere from 50 °C to 550 °C, and under oxidant atmosphere from 550 °C to 850 °C, at a rate of 20 °C/min, to determine the real amount of clay in the nanocomposites. The Young modulus of the nanocomposites was tested in a MTS model 831-59 testing machine, according to UNE-EN ISO 527-1, with a crosshead speed of 1 mm/min. The notched Izod impact test results were measured in a Resil Impact 6957 impact pendulum at room temperature, according to UNE-EN-ISO 180. Heat deflection temperature (HDT) was measured in a CEAST HDT-3-VICAT P/N 6911/000), using 1.8 MPa load, according to UNE-EN ISO 75-1180.
3. Results and discussion In our previous article [10], it was concluded that quaternary ammonium salts were good surfactants for the ABS-sepiolite nanocomposites. In that investigation, a clay percentage of 5 wt.% was used; now the percentage was increased to 10 wt.%, in order to analyze how the final properties were modified.
2.2. Processing
3.1. Increasing clay percentage
Raw materials were previously dried in order to avoid possible degradation due to an excess of moisture during extrusion according to our previous work [10]. Composites and nanocomposites were processed in a co-rotating twin-screw extruder, model Leistritz 27 GL. ABS-sepiolite nanocomposites were extruded at 230 °C and 200 rpm. GF were added at the same temperature reducing screw speed at 100 rpm, in order to minimize the fiber breakage, according to Ozkoc et al. [8]. After that, to obtain the mechanical experiment bars the pelletized materials were dried again under the same conditions as before and then injected using a Krauss Maffei KM 200 injection molding machine. The temperature of the cylinders was 220– 230 °C and the mold temperature was 60 °C.
TEM microphotographs of nanocomposites with 10 wt.% of clay are shown in Fig. 1. From the examination of the morphology, two different PB particle size distributions can be observed: particles of around 0.2 lm in HI-100, and particles of 0.2 lm and less than 0.1 lm in G-360, which is indicative of two different polymerization processes [13]. Moreover, a ‘‘salami structure’’ [14] of PB particles can be seen, that is, SAN inclusions embedded in a larger PB particle. On the other hand, sepiolite fibers are in a nanometric scale, with a length of 200 nm and a diameter of 30–50 nm approximately. Fibers of sepiolite are homogeneously dispersed in the SAN phase, not inside the PB particles, due to the higher polarity of SAN. In addition, random aggregates of sepiolite fibers were found in Fig. 1b, due to the higher amount of clay.
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F.C. Basurto et al. / Composites: Part B 47 (2013) 42–47
Fig. 1. TEM microphotographs of ABS nanocomposites: (a) HI-100 + 10% BM2TH; (b) G-360 + 10% 3MTH.
Table 1 Mechanical properties of ABS nanocomposites with different clay percentage. Material
% Clay
Young modulus (MPa)
HDT (°C)
Impact strength (kJ/m2)
HI-100 HI-100 + 5% BM2TH HI-100 + 10% BM2TH G-360 G-360 + 5% 3MTH G-360 + 10% 3MTH
0 3.7 7.4 0 3.6 7.4
1810 ± 11 2740 ± 19 3530 ± 25 2390 ± 15 3310 ± 26 4500 ± 45
76.5 ± 0.8 80.0 ± 0.1 83.6 ± 0.5 79.2 ± 0.3 79.9 ± 0.1 89.1 ± 1.3
26.8 ± 0.9 5.5 ± 0.5 2.5 ± 0.1 19.7 ± 0.9 4.2 ± 0.6 2.0 ± 0.1
Fig. 2. OM microphotographs of ABS–GF composites: (a) HI-100 + 20% GF; (b) G-360 + 20% GF; (c) HI-100 + 30% GF; (d) G-360 + 30% GF.
Mechanical properties of these nanocomposites are summarized in Table 1. Properties of neat ABS and nanocomposites with 5 wt.% of sepiolite from our previous article [10] were included
with the purpose of comparison. First of all, the clay amount is lower than the original, due to the degradation of the organic component of the surfactant during TGA experiment.
F.C. Basurto et al. / Composites: Part B 47 (2013) 42–47
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Fig. 3. OM microphotographs of ABS hybrid nanocomposites: (a) HI-100 + 10% GF + 10% BM2TH; (b) G-360 + 10% GF + 10% 3MTH.
Fig. 4. Distribution of measured fiber length: (a) HI-100 + 10% GF + 10% BM2TH; (b) G-360 + 10% GF + 10% 3MTH.
The reinforcing effect of sepiolite was reflected in the increment of the stiffness, and it was greater when higher the percentage of clay. With 10 wt.% of clay, modulus was increased around 90% from neat ABS. This behavior could be explained in terms of: (1) a good distribution of sepiolite and interaction between nanofibers and matrix, as seen in Fig. 1, (2) a high aspect ratio of sepiolite, and (3) the difference between matrix modulus (2 GPa) and clay modulus (86 GPa) [15]. Furthermore, G-360 matrix showed a lower increment in modulus than HI-100, probably related to the presence of aggregates seen in Fig. 1b. It is quite remarkable that the enhancement in HDT is very low, with an increment around 10–12%. As it was explained in our previous work [10], the amorphous character of the ABS matrix can be related to the low increase in the deflection temperature. On the other hand, the impact strength decreased, being the drop with 10 wt.% of clay not so prominent compared with the one observed with 5 wt.% of sepiolite. It could be assumed that sepiolite fibers represented ‘‘stress-concentrated zones’’, similarly to GF ends, acting as crack initiators [8] that could justify the loss of toughness. 3.2. Adding glass fiber: synergy GF was employed with the purpose of looking for a synergistic effect between both reinforcing agents. To analyze this phenomenon, two composites with 20 and 30 wt.% of GF respectively, and another hybrid nanocomposite with 10 wt.% of GF and 10 wt.% of
sepiolite were elaborated. When the GF was added in the extruder in any of the three composites, the screw speed was reduced from 200 to 100 rpm in order to minimize its breaking [8], but keeping the extrusion and injection temperatures constant. Morphological characterization was carried out by means of OM and SEM. OM images of composites and hybrid nanocomposites are collected in Figs. 2 and 3, respectively. The mean length was reduced to less than 0.35 mm (from 6 mm originally), due to the shear effect of the extruder screws. The analysis of the fiber distribution is represented in Fig. 4. These short fibers will not increase the mechanical properties as much as if they were of higher length, but they will have a positive effect on the dimensional stability and surface finish. In Fig. 3, GF and sepiolite cannot be distinguished, but it is possible to conclude that both types of particles are well dispersed in the ABS matrix, taking into account that sepiolite was extruded twice, and GF can be helpful to disperse it. The morphology of the PB particles was studied by means of SEM microscopy (Figs. 5 and 6). Again, in these microphotographs two different size distributions of PB particles can be observed. Moreover, size and distribution of PB particles are homogeneous and any remarkable change in morphology can be detected after the incorporation of GF. Fig. 7 shows a SEM microphotograph of the cryogenically fractured surface of the composite HI-100 + 20 wt.% GF, where it is possible to observe a dark ring around the debonded fibers, due to a local deformation of the matrix during the breaking similar to the one reported by Ozkoc et al. [9]. In addition, a smooth fiber
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F.C. Basurto et al. / Composites: Part B 47 (2013) 42–47
Fig. 5. SEM microphotographs of ABS–GF composites: (a) HI-100 + 20% GF; (b) G-360 + 20% GF; (c) HI-100 + 30% GF; (d) G-360 + 30% GF.
Fig. 6. SEM microphotographs of ABS hybrid nanocomposites: (a) HI-100 + 10% GF + 10% BM2TH; (b) G-360 + 10% GF + 10% 3MTH.
Fig. 7. SEM microphotograph of an ABS–GF composite.
is shown, indicating a poor adhesion of matrix to glass fibers. This phenomenon will affect the mechanical properties of hybrid nanocomposites, specially, toughness. The variations in mechanical properties compared to neat ABS are summarized in Table 2. It is interesting to note that load percentages in ABS–GF composites are very close to the original value: the sizing of the GF needs more aggressive conditions than those of the extrusion to disappear, and it usually represents around 1 wt.% of the fiber. As before, the load percentage in nanocomposites is lower than the original, again due to degradation of the organic component of sepiolite during TGA experiment. The reinforcing effect of GF was clearly demonstrated in the Young modulus of composites. The increment in this value was higher for HI-100: it was increased around 190% and 280%, and 135% and 218% for G-360 with 20 and 30 wt.% of GF, respectively. But the main result was achieved when analyzing the replacement of 10 wt.% of GF by sepiolite: a similar value was achieved in HI100 nanocomposites, but the modulus of the hybrid G-360 nanocomposite was higher than that of the composite with the same fil-
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F.C. Basurto et al. / Composites: Part B 47 (2013) 42–47 Table 2 Mechanical properties of ABS composites and hybrid nanocomposites. Material
% Clay
Young modulus (MPa)
HDT (°C)
Impact strength (kJ/m2)
HI-100 HI-100 + 20% GF HI-100 + 30% GF HI-100 + 10% GF + 10% BM2TH G-360 G-360 + 20% GF G-360 + 30% GF G-360 + 10% GF + 10% 3MTH
0 20.3 28.9 17.7 0 19.1 29.5 16.8
1810 ± 11 5250 ± 89 6890 ± 64 5150 ± 52 2390 ± 15 5630 ± 30 7590 ± 45 6250 ± 32
76.5 ± 0.8 94.9 ± 0.1 96.2 ± 0.2 92.3 ± 0.1 79.2 ± 0.3 100.4 ± 0.2 101.7 ± 0.1 96.7 ± 0.1
26.8 ± 0.9 4.8 ± 0.2 4.7 ± 0.2 1.3 ± 0.1 19.7 ± 0.9 3.9 ± 0.1 4.2 ± 0.2 1.1 ± 0.1
ler percentage. So it could be concluded that a synergistic effect was managed between GF and sepiolite in stiffness. Regarding the HDT results, an increment around 25% was reached in both matrices with the addition of GF, but the value of the hybrid nanocomposite was lower than the composites with 20 wt.% of GF. So it could be assumed that GF is the main responsible for the improvement of the deflection temperature, and the effect of sepiolite in HDT values was not the expected, not achieving a synergy between both reinforcements. Finally, the toughness of the GF composites decreased around 80%, and around 95% in hybrid nanocomposites. The pronounced drop in impact strength could be related to the poor adhesion of GF seen in SEM microphotographs, and the appearance of ‘‘stress-concentrated zones’’ due to the combined presence of GF and sepiolite. Consequently, only the Young modulus was improved with the combination of both fillers.
4. Conclusions Composites and hybrid nanocomposites of ABS, GF and sepiolite were elaborated and morphological and mechanical properties were analyzed. A poor adhesion between fibers and matrix was reflected, with a good dispersion of both reinforcing particles. The addition of both types of reinforcement led to an improvement of stiffness, obtaining a synergistic effect in Young modulus between GF and sepiolite. The drop of toughness is associated to the stress-zones generated by GF and sepiolite. As seen before, the amorphous behavior of ABS matrix and the presence of GF play an important role in the improvement of the HDT. Acknowledgements The authors would like to sincerely thank Dr. D.R. Paul for his support and valuable assistance, and Ministerio de Educación y Ciencia (Programme MAT 2008-06379-C02) and Consejería de
Educación de la Junta de Castilla y León (GIE 104) for the financial support. References [1] Laura DM, Keskkula H, Barlow JW, Paul DR. Effect of glass fiber surface chemistry on the mechanical properties of glass fiber reinforced, rubbertoughened nylon 6. Polymer 2002;43:4673–87. [2] Wang W, Tang L, Qu B. Mechanical properties and morphological structures of short glass fiber reinforced PP/EPDM composite. Eur Polym J 2003;39:2129–34. [3] Yilmazer U. Tensile, flexural and impact properties of a thermoplastic matrix reinforced by glass fiber and glass bead hybrids. Compos Sci Technol 1992;44:119–25. [4] Fu S-Y, Lauke B. Fracture resistance of unfilled and calcite-particle-filled ABS composites reinforced by short glass fiber (SGF) under impact load. Composites Part A 1998;29A:631–41. [5] Tiwari RR, Natarajan U. Effect of organic modifiers and silicate type on filler dispersion, thermal and mechanical properties of ABS-clay nanocomposites. J Appl Polym Sci 2008;110:2374–83. [6] Clifford MJ, Wan T. Fibre reinforced nanocomposites: mechanical properties of PA6/clay and glass fibre/PA6/clay nanocomposites. Polymer 2010;51:535–9. [7] Acosta JL, Morales E, Ojeda MC, Linares A. Effect of addition of sepiolite on the mechanical properties of glass fiber reinforced polypropylene. Angew Makromol Chem 1986;138:103–10. [8] Ozkoc G, Bayram G, Bayramli E. Short glass fiber reinforced ABS and ABS/PA6 composites: processing and characterization. Polym Compos 2005;26:745–55. [9] Ozkoc G, Bayram G, Bayramli E. Effects of polyamide 6 incorporation to the short glass fiber reinforced ABS composites: and interfacial approach. Polymer 2004;45:8957–66. [10] Basurto FC, García-López D, Villarreal-Bastardo N, Merino JC, Pastor JM. Nanocomposites of ABS and sepiolite: study of different clay modification processes. Composites Part B 2012;43:2222–9. [11] Shenavar A, Abbasi F. Morphology, thermal and mechanical properties of acrylonitrile-butadiene-styrene/carbon black composites. J Appl Polym Sci 2007;105:2236–44. [12] Stretz HA, Paul DR, Cassidy PE. Poly(styrene-co-acrylonitrile)/montmorillonite organoclay mixtures: a model system for ABS nanocomposites. Polymer 2005;46:3818–30. [13] Mark HF, Bikales NM, Overberger CG, Menges G. Encyclopedia of polymer science and engineering, vol. 1. John Wiley & Sons; 1985. [14] Castellani L, Frassine R, Pavan A, Rink M. Rate and temperature dependence of fracture toughness in ABS resins in relation to dispersed-phase structure. Polymer 1996;37:1329–38. [15] Vlasveld DPN, Jong M, Bersee HEN, Gotsis AD, Picken SJ. The relation between rheological and mechanical properties of PA6 nano- and micro-composites. Polymer 2005;46:10279–89.
Contents lists available at SciVerse ScienceDirect
Composites: Part B journal homepage: www.elsevier.com/locate/compositesb
Composites and nanocomposites of ABS: Synergy between glass fiber and nano-sepiolite F.C. Basurto a,⇑, D. García-López b, N. Villarreal-Bastardo b, J.C. Merino a,b, J.M. Pastor a,b a b
Department of Condensed Matter Physics, EII, University of Valladolid, Paseo del Cauce 59, 47011 Valladolid, Spain CIDAUT – Foundation for Research and Development in Transport and Energy, Parque Tecnológico de Boecillo, Boecillo, 47151 Valladolid, Spain
a r t i c l e
i n f o
Article history: Received 20 February 2012 Received in revised form 20 August 2012 Accepted 31 August 2012 Available online 3 December 2012 Keywords: A. Glass fibers A. Polymer–Matrix Composites (PMCs) B. Mechanical properties E. Extrusion Sepiolite
a b s t r a c t One of the latest steps in polymer nano-technology is polymer/clay/glass fiber composites because of the synergistic effects of both reinforcing particles. Acrylonitrile–butadiene–styrene (ABS) – sepiolite nanocomposites have been developed, and glass fiber has been added to this system in order to study a synergistic behavior between both reinforcing particles. Properties such as Young modulus, impact strength and heat deflection temperature have been measured to characterize the nanocomposites. Morphology has been studied by means of optical and electron microscopy. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction Glass fiber (GF) composites have received great attention in the field of polymer technology in the last years. It is well known that the addition of GF to a thermoplastic matrix is able to improve the mechanical properties of the matrix [1–4]. The final properties depend not only on the reinforcing effect of the load, but also on the interaction between both phases. Traditionally, polymers typically used in the automotive industry are reinforced by adding fillers like GF at a high loading level, increasing the weight and hence the fuel consumption and CO2 emissions. The use of GF as a reinforcing agent in polymer technology leads also to processing and reusing related problems. On one hand, GF is usually employed at high percentages, so it is harder to process and recycle industrial pieces made of GF composites. On the other hand, as the reinforcing percentage is increased, a geometrical deformation or warping appears in those pieces, loosing their dimensional stability and deteriorating the surface finish. Due to these reasons, it is recommendable to reduce the GF percentage. One of the most recent alternatives to this type of filler is the use of nano-clays, particles in the nanometric range. This reinforcement added to the GF at a very low amount (less than 10% by weight) is capable of increasing mechanical properties of polymers, ⇑ Corresponding author. Tel.: +34 983 54 80 35; fax: +34 983 14 82 01. E-mail address: [email protected] (F.C. Basurto). 1359-8368/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.compositesb.2012.08.026
such as Young’s modulus and heat deflection temperature (HDT), but usually with a reduction of the toughness [5]. Theoretically, a synergistic reinforcement is achieved when the working together of two or more loads produces an effect greater than the sum of their individual effects. In this case, sepiolite would be used as a partial replacement of the GF. Therefore, if it is possible to obtain a synergy between GF and clay in at least one property, not only the processing and reusing related problems will be reduced, but also it would be possible to obtain an industrial piece that satisfies the same requirements (in stiffness for example), reducing the total amount of particle reinforcement. In that sense, it is the aim of this research to obtain a synergy between GF and clay, and show that nanosepiolite is a serious complement to GF reinforcement. For example, Clifford and Wan [6] demonstrated that the Halpin–Tsai theory was acceptable to estimate the Young’s modulus in a hybrid composite. In this paper, they explained that the synergistic effect could be understood considering a polymer with reinforcement in two scales: microscopic fiber reinforcement combined with exfoliated nanoscale particles. Acosta et al. [7] studied the incorporation and substitution of part of GF by sepiolite in a polypropylene composite. With 30 wt.% of GF, they found an increment of 228% in flexural modulus, but in a hybrid composite with 20 wt.% of GF and 10 wt.% of sepiolite, the modulus increased up to 263%. Concerning processing conditions for GF, Ozkoc et al. [8] studied the influence of temperature and screw speed on the mechanical
F.C. Basurto et al. / Composites: Part B 47 (2013) 42–47
properties of ABS–GF composites elaborated in a co-rotating twinscrew extruder. It was concluded that a better balance in mechanical properties was achieved when screw speed was reduced and extrusion temperature was slightly increased, because these modifications in the processing conditions reduced the breaking of the glass fibers. Particularly, they stated that new stress-concentrated zones were generated by the breaking of fibers, with a negative effect on the impact strength. In another article [9], Ozkoc et al. found an increment of 190% in Young modulus and a reduction of 83% in impact strength in composites with 30 wt.% of GF. The improvement in stiffness was related to the presence of the fiber, which also was the responsible for the reduction in toughness, associated to the restricted deformation ability of matrix. In our previous work [10], we described the processing and characterization of ABS nanocomposites with 5 wt.% of sepiolite. In that work, an optimal methodology to obtain those nanocomposites was developed. It was concluded that: (1) 200 rpm (rpm) was the most favorable extrusion screw speed, and (2) quaternary ammonium salts were the best surfactant agents for sepiolite in ABS nanocomposites. In the present work, the previous conclusions were used to elaborate new nanocomposites with a high amount of sepiolite, in order to find out how the thermal and mechanical properties were modified. Moreover, hybrid nanocomposites made of GF and sepiolite were processed and characterized, with the purpose of evaluating the synergistic effects of both reinforcements. 2. Materials and methods 2.1. Materials Two different types of ABS polymers have been selected in this work. Although the real amount of polybutadiene (PB) was not provided by the polymer compounders, it could be inferred, from technical data sheets, that HI-100, supplied by LG Chem. has a higher PB content than G-360, supplied by GE Plastics. Modified sepiolite was prepared from pristine sepiolite named Pangel S9, supplied and modified by Tolsa S.A. The organic surfactants were two quaternary ammonium salts: BM2TH (bencylmethyl-dihydrogenated tallow) and 3MTH (trimethyl-hydrogenated tallow). The selection of the modifier used for each grade of ABS was based on the polarity of the matrix and the agent. Type E glass fiber (typically employed in automotive composites) was supplied by Saint-Gobain Vetrovex S.A., with a diameter of 17 lm and a mean length of 6 mm. Its density is very similar to sepiolite (2.54 g/cm3). Fibers were sized with a silane coupling agent, typically used in the automotive industry with polymer matrixes such as ABS, PC or PA 6.
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2.3. Characterization The morphologies of the ABS matrix and the nanocomposites were examined by scanning electron microscopy (SEM) using a Hitachi 3200 SN apparatus, operating at an accelerating voltage of 20 kV. The cryogenic fracture surface was subjected to a selective extraction technique, according to Shenavar and Abbasi [11], with a solution of CrO3 and H2SO4 during 5 min at 65 °C. This technique allowed us to observe the gaps left by the PB particles, and hence, explore their size and distribution. Transmission electron microscopy (TEM) images were obtained on a Jeol 2010 with an accelerating voltage of 120 kV. Samples for TEM were sectioned using a RMC PowerTome XL cryogenic ultramicrotome to a thickness of 60 nm with a diamond knife at 40 °C. Knife speed was 0.4 mm/s. Sectioned samples were stained in order to improve the contrast between PB particles and acrylonitrile-styrene (SAN) continuous phase. This process consisted of a selective staining technique [12], exposing the samples to OsO4 vapors during 24 h. In TEM images, the gray continuous region corresponds to SAN phase, and PB particles appear as black islands. In addition, in the GF-sepiolite hybrid nanocomposites, optical microscopy (OM) was conducted using an Olympus BX60M-KPM1E/K microscope, with a magnification of 10. This technique was employed to observe the distribution of both reinforcements, and measure the fiber length. After dissolving the ABS matrix in xylene, fibers were observed and measured by means of Omnimet Enterprise software, using a special routine designed specifically for this purpose. Thermogravimetric analysis was carried out using a Mettler Toledo 851e analyzer under inert atmosphere from 50 °C to 550 °C, and under oxidant atmosphere from 550 °C to 850 °C, at a rate of 20 °C/min, to determine the real amount of clay in the nanocomposites. The Young modulus of the nanocomposites was tested in a MTS model 831-59 testing machine, according to UNE-EN ISO 527-1, with a crosshead speed of 1 mm/min. The notched Izod impact test results were measured in a Resil Impact 6957 impact pendulum at room temperature, according to UNE-EN-ISO 180. Heat deflection temperature (HDT) was measured in a CEAST HDT-3-VICAT P/N 6911/000), using 1.8 MPa load, according to UNE-EN ISO 75-1180.
3. Results and discussion In our previous article [10], it was concluded that quaternary ammonium salts were good surfactants for the ABS-sepiolite nanocomposites. In that investigation, a clay percentage of 5 wt.% was used; now the percentage was increased to 10 wt.%, in order to analyze how the final properties were modified.
2.2. Processing
3.1. Increasing clay percentage
Raw materials were previously dried in order to avoid possible degradation due to an excess of moisture during extrusion according to our previous work [10]. Composites and nanocomposites were processed in a co-rotating twin-screw extruder, model Leistritz 27 GL. ABS-sepiolite nanocomposites were extruded at 230 °C and 200 rpm. GF were added at the same temperature reducing screw speed at 100 rpm, in order to minimize the fiber breakage, according to Ozkoc et al. [8]. After that, to obtain the mechanical experiment bars the pelletized materials were dried again under the same conditions as before and then injected using a Krauss Maffei KM 200 injection molding machine. The temperature of the cylinders was 220– 230 °C and the mold temperature was 60 °C.
TEM microphotographs of nanocomposites with 10 wt.% of clay are shown in Fig. 1. From the examination of the morphology, two different PB particle size distributions can be observed: particles of around 0.2 lm in HI-100, and particles of 0.2 lm and less than 0.1 lm in G-360, which is indicative of two different polymerization processes [13]. Moreover, a ‘‘salami structure’’ [14] of PB particles can be seen, that is, SAN inclusions embedded in a larger PB particle. On the other hand, sepiolite fibers are in a nanometric scale, with a length of 200 nm and a diameter of 30–50 nm approximately. Fibers of sepiolite are homogeneously dispersed in the SAN phase, not inside the PB particles, due to the higher polarity of SAN. In addition, random aggregates of sepiolite fibers were found in Fig. 1b, due to the higher amount of clay.
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Fig. 1. TEM microphotographs of ABS nanocomposites: (a) HI-100 + 10% BM2TH; (b) G-360 + 10% 3MTH.
Table 1 Mechanical properties of ABS nanocomposites with different clay percentage. Material
% Clay
Young modulus (MPa)
HDT (°C)
Impact strength (kJ/m2)
HI-100 HI-100 + 5% BM2TH HI-100 + 10% BM2TH G-360 G-360 + 5% 3MTH G-360 + 10% 3MTH
0 3.7 7.4 0 3.6 7.4
1810 ± 11 2740 ± 19 3530 ± 25 2390 ± 15 3310 ± 26 4500 ± 45
76.5 ± 0.8 80.0 ± 0.1 83.6 ± 0.5 79.2 ± 0.3 79.9 ± 0.1 89.1 ± 1.3
26.8 ± 0.9 5.5 ± 0.5 2.5 ± 0.1 19.7 ± 0.9 4.2 ± 0.6 2.0 ± 0.1
Fig. 2. OM microphotographs of ABS–GF composites: (a) HI-100 + 20% GF; (b) G-360 + 20% GF; (c) HI-100 + 30% GF; (d) G-360 + 30% GF.
Mechanical properties of these nanocomposites are summarized in Table 1. Properties of neat ABS and nanocomposites with 5 wt.% of sepiolite from our previous article [10] were included
with the purpose of comparison. First of all, the clay amount is lower than the original, due to the degradation of the organic component of the surfactant during TGA experiment.
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Fig. 3. OM microphotographs of ABS hybrid nanocomposites: (a) HI-100 + 10% GF + 10% BM2TH; (b) G-360 + 10% GF + 10% 3MTH.
Fig. 4. Distribution of measured fiber length: (a) HI-100 + 10% GF + 10% BM2TH; (b) G-360 + 10% GF + 10% 3MTH.
The reinforcing effect of sepiolite was reflected in the increment of the stiffness, and it was greater when higher the percentage of clay. With 10 wt.% of clay, modulus was increased around 90% from neat ABS. This behavior could be explained in terms of: (1) a good distribution of sepiolite and interaction between nanofibers and matrix, as seen in Fig. 1, (2) a high aspect ratio of sepiolite, and (3) the difference between matrix modulus (2 GPa) and clay modulus (86 GPa) [15]. Furthermore, G-360 matrix showed a lower increment in modulus than HI-100, probably related to the presence of aggregates seen in Fig. 1b. It is quite remarkable that the enhancement in HDT is very low, with an increment around 10–12%. As it was explained in our previous work [10], the amorphous character of the ABS matrix can be related to the low increase in the deflection temperature. On the other hand, the impact strength decreased, being the drop with 10 wt.% of clay not so prominent compared with the one observed with 5 wt.% of sepiolite. It could be assumed that sepiolite fibers represented ‘‘stress-concentrated zones’’, similarly to GF ends, acting as crack initiators [8] that could justify the loss of toughness. 3.2. Adding glass fiber: synergy GF was employed with the purpose of looking for a synergistic effect between both reinforcing agents. To analyze this phenomenon, two composites with 20 and 30 wt.% of GF respectively, and another hybrid nanocomposite with 10 wt.% of GF and 10 wt.% of
sepiolite were elaborated. When the GF was added in the extruder in any of the three composites, the screw speed was reduced from 200 to 100 rpm in order to minimize its breaking [8], but keeping the extrusion and injection temperatures constant. Morphological characterization was carried out by means of OM and SEM. OM images of composites and hybrid nanocomposites are collected in Figs. 2 and 3, respectively. The mean length was reduced to less than 0.35 mm (from 6 mm originally), due to the shear effect of the extruder screws. The analysis of the fiber distribution is represented in Fig. 4. These short fibers will not increase the mechanical properties as much as if they were of higher length, but they will have a positive effect on the dimensional stability and surface finish. In Fig. 3, GF and sepiolite cannot be distinguished, but it is possible to conclude that both types of particles are well dispersed in the ABS matrix, taking into account that sepiolite was extruded twice, and GF can be helpful to disperse it. The morphology of the PB particles was studied by means of SEM microscopy (Figs. 5 and 6). Again, in these microphotographs two different size distributions of PB particles can be observed. Moreover, size and distribution of PB particles are homogeneous and any remarkable change in morphology can be detected after the incorporation of GF. Fig. 7 shows a SEM microphotograph of the cryogenically fractured surface of the composite HI-100 + 20 wt.% GF, where it is possible to observe a dark ring around the debonded fibers, due to a local deformation of the matrix during the breaking similar to the one reported by Ozkoc et al. [9]. In addition, a smooth fiber
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Fig. 5. SEM microphotographs of ABS–GF composites: (a) HI-100 + 20% GF; (b) G-360 + 20% GF; (c) HI-100 + 30% GF; (d) G-360 + 30% GF.
Fig. 6. SEM microphotographs of ABS hybrid nanocomposites: (a) HI-100 + 10% GF + 10% BM2TH; (b) G-360 + 10% GF + 10% 3MTH.
Fig. 7. SEM microphotograph of an ABS–GF composite.
is shown, indicating a poor adhesion of matrix to glass fibers. This phenomenon will affect the mechanical properties of hybrid nanocomposites, specially, toughness. The variations in mechanical properties compared to neat ABS are summarized in Table 2. It is interesting to note that load percentages in ABS–GF composites are very close to the original value: the sizing of the GF needs more aggressive conditions than those of the extrusion to disappear, and it usually represents around 1 wt.% of the fiber. As before, the load percentage in nanocomposites is lower than the original, again due to degradation of the organic component of sepiolite during TGA experiment. The reinforcing effect of GF was clearly demonstrated in the Young modulus of composites. The increment in this value was higher for HI-100: it was increased around 190% and 280%, and 135% and 218% for G-360 with 20 and 30 wt.% of GF, respectively. But the main result was achieved when analyzing the replacement of 10 wt.% of GF by sepiolite: a similar value was achieved in HI100 nanocomposites, but the modulus of the hybrid G-360 nanocomposite was higher than that of the composite with the same fil-
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F.C. Basurto et al. / Composites: Part B 47 (2013) 42–47 Table 2 Mechanical properties of ABS composites and hybrid nanocomposites. Material
% Clay
Young modulus (MPa)
HDT (°C)
Impact strength (kJ/m2)
HI-100 HI-100 + 20% GF HI-100 + 30% GF HI-100 + 10% GF + 10% BM2TH G-360 G-360 + 20% GF G-360 + 30% GF G-360 + 10% GF + 10% 3MTH
0 20.3 28.9 17.7 0 19.1 29.5 16.8
1810 ± 11 5250 ± 89 6890 ± 64 5150 ± 52 2390 ± 15 5630 ± 30 7590 ± 45 6250 ± 32
76.5 ± 0.8 94.9 ± 0.1 96.2 ± 0.2 92.3 ± 0.1 79.2 ± 0.3 100.4 ± 0.2 101.7 ± 0.1 96.7 ± 0.1
26.8 ± 0.9 4.8 ± 0.2 4.7 ± 0.2 1.3 ± 0.1 19.7 ± 0.9 3.9 ± 0.1 4.2 ± 0.2 1.1 ± 0.1
ler percentage. So it could be concluded that a synergistic effect was managed between GF and sepiolite in stiffness. Regarding the HDT results, an increment around 25% was reached in both matrices with the addition of GF, but the value of the hybrid nanocomposite was lower than the composites with 20 wt.% of GF. So it could be assumed that GF is the main responsible for the improvement of the deflection temperature, and the effect of sepiolite in HDT values was not the expected, not achieving a synergy between both reinforcements. Finally, the toughness of the GF composites decreased around 80%, and around 95% in hybrid nanocomposites. The pronounced drop in impact strength could be related to the poor adhesion of GF seen in SEM microphotographs, and the appearance of ‘‘stress-concentrated zones’’ due to the combined presence of GF and sepiolite. Consequently, only the Young modulus was improved with the combination of both fillers.
4. Conclusions Composites and hybrid nanocomposites of ABS, GF and sepiolite were elaborated and morphological and mechanical properties were analyzed. A poor adhesion between fibers and matrix was reflected, with a good dispersion of both reinforcing particles. The addition of both types of reinforcement led to an improvement of stiffness, obtaining a synergistic effect in Young modulus between GF and sepiolite. The drop of toughness is associated to the stress-zones generated by GF and sepiolite. As seen before, the amorphous behavior of ABS matrix and the presence of GF play an important role in the improvement of the HDT. Acknowledgements The authors would like to sincerely thank Dr. D.R. Paul for his support and valuable assistance, and Ministerio de Educación y Ciencia (Programme MAT 2008-06379-C02) and Consejería de
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