Microstructural characteristics of ternary polymer composites
10.1002/spepro.002573
Microstructural characteristics of ternary polymer composites Onur Balkan, Ayhan Ezdes¸ir, and Halil Demirer
The possible formation pathways of separate and core-shell microstructures of dispersed rigid filler and elastomer particles depend on the elastomer’s polarity. Using a suitable melt-mixing method, isotactic polypropylene (iPP) can be modified readily by adding rigid fillers and soft elastomers, thus producing a ternary polymer composite (composed of three constituents). (In isotactic chain molecules, all substituents are located on the same side of the main macromolecular structure.) The reinforcing fillers improve stiffness, while polar elastomers enhance toughness. Therefore, their addition generates a microstructure with a specific stiffnesstoughness balance. Ternary composites can generate both separate and core-shell microstructures. In the former, rigid filler and elastomer particles disperse separately throughout the polymer matrix, while the elastomer phase encapsulates filler particles in the core-shell configuration. Certain mismatches of rigid-filler and polymer-matrix properties introduce stresses. This results in debonding and pre-crack at the filler-matrix interface, thus causing a decline in the strength of the composites. However, the presence of a soft interlayer can partially relieve the stresses by deforming without breaking. In 1967, Matonis and Small1, 2 proposed a hypothetical ternary composite containing rigid, spherical core-shell particles encapsulated in a thin elastomer interlayer, leading to improvements in toughness without sacrificing stiffness. We employed spherical glass beads (GBs) and acicular wollastonite (W: calcium metasilicate or CaSiO3 ) as isotropic (extender) and anisotropic filler (reinforcing agent), respectively. We also used poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS) copolymer and its functionalized maleic anhydride-grafted variant (SEBS-gMA, here referred to as SEBS-MA) as thermoplastic elastomers. We filled the iPP with GBs and W using a co-rotating twin-screw extruder, producing iPP/GB and iPP/W binary composites (80/20% by volume). We then incorporated SEBS and SEBS-MA elastomers into the binary composites to produce the ternary composites (iPP/GB)/SEBS, (iPP/GB)/SEBS-MA, (iPP/W)/SEBS, and (iPP/W)/SEBS-MA. We investigated the microstructural, thermal, and molecular characteristics of the iPP-based composites using scanning-electron microscopy
Figure 1. Scanning-electron microscopy (SEM) of ternary composites (magnification 3000), (80/20)/10 by volume, exhibiting separate microstructures with poly(styrene-b-ethylene-co-butylene-bstyrene) (SEBS) copolymer. (a) Unetched. (b) Etched. iPP: Isotactic polypropylene. GB: Glass bead. W: Acicular wollastonite. (SEM), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA) and Fourier-transform IR (FTIR) approaches, respectively. Typical SEM micrographs of the ternary composites containing SEBS showed separate microstructures without interfacial adhesion (see Figure 1). We detected elastomer particles as small, dark holes after etching: see Figures 1(b) and 2(b). For SEBS-MA, the filler particles were very diffuse—see Figure 2(a)—suggesting strong interfacial adhesion. After etching, we clearly observed both the filler particles and their surrounding cavities, as shown in Figure 2(b), exhibiting clear evidence of core-shell microstructures. The SEBS-MA interlayer was 0.5–1.0m thick. Our DSC analysis revealed that the crystallization temperature of the binary composites decreased more significantly for SEBS-MA than for SEBS. This suggests that the rigid filler and SEBS particles each Continued on next page
10.1002/spepro.002573 Page 2/3
Figure 2. SEM micrographs of ternary composites, (80/20)/10 by volume, exhibiting core-shell microstructures with maleic anhydridegrafted SEBS (SEBS-MA). (a) Unetched. (b) Etched.
influenced the crystallization behavior of the iPP matrix (as a separate microstructure), while the SEBS-MA interlayer suppressed the nucleating effects of the fillers on the iPP matrix (resulting in a core-shell microstructure).3, 4 The storage modulus (E0 , an elasticity measurement) of the binary composites decreased most strongly for the SEBS-MA copolymer, despite strong interfacial adhesion (see Figure 3), suggesting that core-shell particles acted like elastomer. Our ternary composites showed two damping-factor (tan ı) peaks, corresponding to the glassy transition of the elastomer phase and the iPP matrix, respectively. For SEBS-MA, we found that the tan ı peaks were much higher and broader than their SEBS-related counterparts because of the thick elastomer interlayer.4 We explain the strong interfacial adhesion for SEBS-MA by the specific affinity of its polar MA groups with polar hydroxyl (-OH) groups on the filler surfaces and a similar chemical structure of the iPP matrix as that of the ethylene-co-butylene midblock of SEBS-MA.5 Our FTIR analysis revealed an esterification reaction between MA groups of the SEBS-MA phase and hydroxyl groups on the filler surfaces (see Figure 4).3, 4 In summary, our SEM analysis showed that SEBS particles dispersed separately throughout the iPP matrix, while SEBS-MA both encapsulated spherical GBs and acicular W particles completely with strong interfacial adhesion (i.e., core-shell microstructure). DSC and DMA also revealed (quantitatively) that the rigid filler and SEBS particles in the iPP matrix acted individually, while rigid fillers in the presence of SEBS-MA acted like elastomer because of the thick elastomer
Figure 3. Variations in storage modulus (E0 ) and damping factor (tan ı) of ternary composites as a function of temperature.
Figure 4. Interfacial interactions between SEBS-MA and the inorganic-particle surface.4, 6
interlayer. The esterification reaction uncovered by our FTIR analysis induces strong interfacial adhesion between SEBS-MA and filler particles. We will report on the mechanical properties of the blends and composites in a forthcoming article.7 Following Matonis and Small,1, 2 we will further investigate the effects of much thinner elastomer interlayers (which can probably be obtained using a more specific technique) on the mechanical properties of the composites. Continued on next page
10.1002/spepro.002573 Page 3/3
We thank the Marmara University Scientific Research Committee ¨ u Y{lmazer, for financial support (grant FEN-BGS-100105-0076), Ulk¨ ¨ ¨ G¨uralp Ozkoc¸, Ozcan K¨oys¨uren, Sertan Yes¸il, and Mert K{l{nc¸ (all at the Middle East Technical University) for their kind help during the extrusion process, Sinan Kara (Kraton Polymers LLC) for the elastomers, Sema Akkartal (Prosim Kimya Ltd.) for providing wollastonite, Burak Ero˘glu (Akay Plastik Inc.) for injection molding, and H¨useyin Y{ld{r{m and G¨okhan Temel (Y{ld{z Technical University) for their help with DMA.
Author Information Onur Balkan Department of Materials Institute of Pure and Applied Sciences Marmara University Istanbul, Turkey
References 1. V. A. Matonis, An Analytical Evaluation of a Hypothetical Three-Phase Material, PhD thesis, The University of Connecticut, CT, 1967. 2. V. A. Matonis and N. C. Small, A macroscopic analysis of composites containing layered spherical inclusions, Polym. Eng. Sci. 9 (2), pp. 90–99, 1969. 3. O. Balkan, The Effect of Thermoplastic Elastomers on the Mechanical Properties of Polypropylene Composites, PhD thesis, Marmara University, Turkey, 2006. 4. O. Balkan, A. Ezdes¸ir, and H. Demirer, Microstructural characteristics of glass beadand wollastonite-filled isotactic-polypropylene composites modified with thermoplastic elastomers, Polym. Compos. in press, doi:10.1002/pc.20948 5. S. Setz, F. Stricker, J. Kressler, T. Duschek, and R. M¨ulhaupt, Morphology and mechanical properties of blends of isotactic or syndiotactic polypropylene with SEBS block copolymers, J. Appl. Polym. Sci. 59 (7), pp. 1117–1128, 1996. 6. N. G. Gaylord, Compatibilization of hydroxyl-containing fillers and thermoplastic polymers, 1972. UK patent 1, 300, 640. 7. O. Balkan and H. Demirer, Mechanical properties of glass bead- and wollastonite-filled isotactic-polypropylene composites modified with thermoplastic elastomers, Polym. Compos. In press, doi:10.1002/pc.20953
Onur Balkan received BS on ‘metalworking’ from Technical Education Faculty in 1994, MS on ‘welding of polymer-products’ in 1999, and PhD on ‘polymer composites’ in 2006 from Institute of Pure and Applied Sciences, Marmara University. His current research interests include microstructural, mechanical and rheological characteristics of polymer blends and composites. Ayhan Ezdes¸ir Experimental Design and Application Department Research and Development Center Petkim Petrochemical Holding Inc. Izmir, Turkey Halil Demirer Department of Materials Technical Education Faculty, Marmara University, G¨oztepe Campus 34722 Kadık¨oy-˙Istanbul, T¨urkiye
c 2010 Society of Plastics Engineers (SPE)
Microstructural characteristics of ternary polymer composites Onur Balkan, Ayhan Ezdes¸ir, and Halil Demirer
The possible formation pathways of separate and core-shell microstructures of dispersed rigid filler and elastomer particles depend on the elastomer’s polarity. Using a suitable melt-mixing method, isotactic polypropylene (iPP) can be modified readily by adding rigid fillers and soft elastomers, thus producing a ternary polymer composite (composed of three constituents). (In isotactic chain molecules, all substituents are located on the same side of the main macromolecular structure.) The reinforcing fillers improve stiffness, while polar elastomers enhance toughness. Therefore, their addition generates a microstructure with a specific stiffnesstoughness balance. Ternary composites can generate both separate and core-shell microstructures. In the former, rigid filler and elastomer particles disperse separately throughout the polymer matrix, while the elastomer phase encapsulates filler particles in the core-shell configuration. Certain mismatches of rigid-filler and polymer-matrix properties introduce stresses. This results in debonding and pre-crack at the filler-matrix interface, thus causing a decline in the strength of the composites. However, the presence of a soft interlayer can partially relieve the stresses by deforming without breaking. In 1967, Matonis and Small1, 2 proposed a hypothetical ternary composite containing rigid, spherical core-shell particles encapsulated in a thin elastomer interlayer, leading to improvements in toughness without sacrificing stiffness. We employed spherical glass beads (GBs) and acicular wollastonite (W: calcium metasilicate or CaSiO3 ) as isotropic (extender) and anisotropic filler (reinforcing agent), respectively. We also used poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS) copolymer and its functionalized maleic anhydride-grafted variant (SEBS-gMA, here referred to as SEBS-MA) as thermoplastic elastomers. We filled the iPP with GBs and W using a co-rotating twin-screw extruder, producing iPP/GB and iPP/W binary composites (80/20% by volume). We then incorporated SEBS and SEBS-MA elastomers into the binary composites to produce the ternary composites (iPP/GB)/SEBS, (iPP/GB)/SEBS-MA, (iPP/W)/SEBS, and (iPP/W)/SEBS-MA. We investigated the microstructural, thermal, and molecular characteristics of the iPP-based composites using scanning-electron microscopy
Figure 1. Scanning-electron microscopy (SEM) of ternary composites (magnification 3000), (80/20)/10 by volume, exhibiting separate microstructures with poly(styrene-b-ethylene-co-butylene-bstyrene) (SEBS) copolymer. (a) Unetched. (b) Etched. iPP: Isotactic polypropylene. GB: Glass bead. W: Acicular wollastonite. (SEM), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA) and Fourier-transform IR (FTIR) approaches, respectively. Typical SEM micrographs of the ternary composites containing SEBS showed separate microstructures without interfacial adhesion (see Figure 1). We detected elastomer particles as small, dark holes after etching: see Figures 1(b) and 2(b). For SEBS-MA, the filler particles were very diffuse—see Figure 2(a)—suggesting strong interfacial adhesion. After etching, we clearly observed both the filler particles and their surrounding cavities, as shown in Figure 2(b), exhibiting clear evidence of core-shell microstructures. The SEBS-MA interlayer was 0.5–1.0m thick. Our DSC analysis revealed that the crystallization temperature of the binary composites decreased more significantly for SEBS-MA than for SEBS. This suggests that the rigid filler and SEBS particles each Continued on next page
10.1002/spepro.002573 Page 2/3
Figure 2. SEM micrographs of ternary composites, (80/20)/10 by volume, exhibiting core-shell microstructures with maleic anhydridegrafted SEBS (SEBS-MA). (a) Unetched. (b) Etched.
influenced the crystallization behavior of the iPP matrix (as a separate microstructure), while the SEBS-MA interlayer suppressed the nucleating effects of the fillers on the iPP matrix (resulting in a core-shell microstructure).3, 4 The storage modulus (E0 , an elasticity measurement) of the binary composites decreased most strongly for the SEBS-MA copolymer, despite strong interfacial adhesion (see Figure 3), suggesting that core-shell particles acted like elastomer. Our ternary composites showed two damping-factor (tan ı) peaks, corresponding to the glassy transition of the elastomer phase and the iPP matrix, respectively. For SEBS-MA, we found that the tan ı peaks were much higher and broader than their SEBS-related counterparts because of the thick elastomer interlayer.4 We explain the strong interfacial adhesion for SEBS-MA by the specific affinity of its polar MA groups with polar hydroxyl (-OH) groups on the filler surfaces and a similar chemical structure of the iPP matrix as that of the ethylene-co-butylene midblock of SEBS-MA.5 Our FTIR analysis revealed an esterification reaction between MA groups of the SEBS-MA phase and hydroxyl groups on the filler surfaces (see Figure 4).3, 4 In summary, our SEM analysis showed that SEBS particles dispersed separately throughout the iPP matrix, while SEBS-MA both encapsulated spherical GBs and acicular W particles completely with strong interfacial adhesion (i.e., core-shell microstructure). DSC and DMA also revealed (quantitatively) that the rigid filler and SEBS particles in the iPP matrix acted individually, while rigid fillers in the presence of SEBS-MA acted like elastomer because of the thick elastomer
Figure 3. Variations in storage modulus (E0 ) and damping factor (tan ı) of ternary composites as a function of temperature.
Figure 4. Interfacial interactions between SEBS-MA and the inorganic-particle surface.4, 6
interlayer. The esterification reaction uncovered by our FTIR analysis induces strong interfacial adhesion between SEBS-MA and filler particles. We will report on the mechanical properties of the blends and composites in a forthcoming article.7 Following Matonis and Small,1, 2 we will further investigate the effects of much thinner elastomer interlayers (which can probably be obtained using a more specific technique) on the mechanical properties of the composites. Continued on next page
10.1002/spepro.002573 Page 3/3
We thank the Marmara University Scientific Research Committee ¨ u Y{lmazer, for financial support (grant FEN-BGS-100105-0076), Ulk¨ ¨ ¨ G¨uralp Ozkoc¸, Ozcan K¨oys¨uren, Sertan Yes¸il, and Mert K{l{nc¸ (all at the Middle East Technical University) for their kind help during the extrusion process, Sinan Kara (Kraton Polymers LLC) for the elastomers, Sema Akkartal (Prosim Kimya Ltd.) for providing wollastonite, Burak Ero˘glu (Akay Plastik Inc.) for injection molding, and H¨useyin Y{ld{r{m and G¨okhan Temel (Y{ld{z Technical University) for their help with DMA.
Author Information Onur Balkan Department of Materials Institute of Pure and Applied Sciences Marmara University Istanbul, Turkey
References 1. V. A. Matonis, An Analytical Evaluation of a Hypothetical Three-Phase Material, PhD thesis, The University of Connecticut, CT, 1967. 2. V. A. Matonis and N. C. Small, A macroscopic analysis of composites containing layered spherical inclusions, Polym. Eng. Sci. 9 (2), pp. 90–99, 1969. 3. O. Balkan, The Effect of Thermoplastic Elastomers on the Mechanical Properties of Polypropylene Composites, PhD thesis, Marmara University, Turkey, 2006. 4. O. Balkan, A. Ezdes¸ir, and H. Demirer, Microstructural characteristics of glass beadand wollastonite-filled isotactic-polypropylene composites modified with thermoplastic elastomers, Polym. Compos. in press, doi:10.1002/pc.20948 5. S. Setz, F. Stricker, J. Kressler, T. Duschek, and R. M¨ulhaupt, Morphology and mechanical properties of blends of isotactic or syndiotactic polypropylene with SEBS block copolymers, J. Appl. Polym. Sci. 59 (7), pp. 1117–1128, 1996. 6. N. G. Gaylord, Compatibilization of hydroxyl-containing fillers and thermoplastic polymers, 1972. UK patent 1, 300, 640. 7. O. Balkan and H. Demirer, Mechanical properties of glass bead- and wollastonite-filled isotactic-polypropylene composites modified with thermoplastic elastomers, Polym. Compos. In press, doi:10.1002/pc.20953
Onur Balkan received BS on ‘metalworking’ from Technical Education Faculty in 1994, MS on ‘welding of polymer-products’ in 1999, and PhD on ‘polymer composites’ in 2006 from Institute of Pure and Applied Sciences, Marmara University. His current research interests include microstructural, mechanical and rheological characteristics of polymer blends and composites. Ayhan Ezdes¸ir Experimental Design and Application Department Research and Development Center Petkim Petrochemical Holding Inc. Izmir, Turkey Halil Demirer Department of Materials Technical Education Faculty, Marmara University, G¨oztepe Campus 34722 Kadık¨oy-˙Istanbul, T¨urkiye
c 2010 Society of Plastics Engineers (SPE)
