Chemical sensing materials II: Electrically conductive peroxide crosslinked SEBS copolymers systems

Chemical sensing materials based on electrically conductive styrene–ethylene butylene–styrene (SEBS) triblock‐copolymers systems were investigated. Systems based on crosslinked rather than thermoplastic SEBS systems can be exposed to a wide range of chemical environments. Composites of SEBS containing various amounts of CB and Varox DBPH (peroxide crosslinking agent) were prepared by blending at relative low temperatures, limiting the peroxide activation, and then compression molding at elevated temperatures. Samples containing CB at a level near the corresponding percolation threshold were used for the sensing experiments. Structure characterization included crosslink level and density, dynamic mechanical analysis (DMA), and calorimetry (DSC). The crosslinked SEBS composites exhibit large reversible changes in conductivity on exposure to various solvents and air drying cycles The observed electrical conductivity changes on solvent sorption/desorption is based on the polymer reversible swelling, resulting in breakdown and reconstruction of conductive CB networks, respectively. Sensing performance depends mainly on the solvents solubility parameter and volatility. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Improvement of melt spinning properties and conductivity of immiscible polypropylene/polystyrene blends containing carbon black by addition of styrene‐ethylene‐butene‐styrene block copolymer

Conducting polymeric materials prepared from immiscible blends, such as polypropylene (PP)/polystyrene (PS), together with carbon black (CB), are known to have a relatively high electrical conductivity, because of a selective distribution of CB (double percolation). Melt spinning of immiscible blends containing CB has, however, not been extensively reported on previously. An immiscible 1:1 blend of PP and PS to which 4 wt% CB was added exhibited a very low melt draw‐down ratio at rupture compared wit PP with the same content of CB. By adding 5 wt% SEBS (styrene‐ethylene‐butene‐styrene block copolymer), the ultimate melt draw‐down ratio increased about 10 times, which made the material more suitable for melt spinning. As‐extruded samples of the immiscible blends (with CB) did not have higher electrical conductivities than PP/CB. A heat treatment increased the conductivity of immiscible PP/PS/CB composites, and longer treatment times and higher temperatures promoted the conductivity. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Morphology and flame‐retardancy properties of ternary high‐impact polystyrene/elastomer/polystyrene‐encapsulated magnesium hydroxide composites

The effects of elastomer type on the morphology, flammability, and mechanical properties of high‐impact polystyrene (HIPS)/polystyrene (PS)‐encapsulated magnesium hydroxide (MH) were investigated. The ternary composites were characterized by cone calorimetry, mechanical testing, and scanning electron microscopy. Morphology was controlled with poly[styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene] (SEBS) triblock copolymer or the corresponding maleinated poly[styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene] (SEBS‐g‐MA). The HIPS/SEBS/PS‐encapsulated MH composites exhibited separation of the filler and elastomer, whereas the HIPS/SEBS‐g‐MA/PS‐encapsulated MH composites exhibited encapsulation of the filler by SEBS‐g‐MA. The flame‐retardant and mechanical properties of the ternary composites were strongly dependent on microstructure. The composites with an encapsulation structure showed higher flame‐retardant properties than those with a separation structure at the optimum use level of SEBS‐g‐MA. Furthermore, the composites with a separation structure showed a higher modulus and impact strength than those with an encapsulation structure. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

SEBS/PPy.DBSA blends: Preparation and evaluation of electromechanical and dynamic mechanical properties

In this study, the electromechanical and dynamic mechanical properties of electrically conducting polymer blends were investigated. The blends were comprised poly(styrene‐b‐butylene‐ran‐ethylene‐b‐styrene) (SEBS) containing polypyrrole doped with dodecylbenzenesulfonic acid (PPy.DBSA). The two types of PPy.DBSA (with and without an excess of DBSA) were blended with SEBS through the solution casting method at room temperature. The dynamic mechanical characterization of the SEBS/PPy.DBSA blends demonstrated that the use of PPy.DBSA with and without free DBSA molecules results in different degrees of interaction with the two phases of the SEBS copolymer matrix. The changes in the electrical conductivity of the blends during repeated pressure loading/unloading were investigated. The conducting SEBS/PPy.DBSA polymer blends exhibited an increase in the electrical conductivity on pressure loading and underwent a corresponding decrease on unloading. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and performance characteristics of short‐glass‐fiber/maleated styrene–ethylene–butylene–styrene/polypropylene hybrid composites

Eighty/twenty polypropylene (PP)/styrene–ethylene–butylene–styrene (SEBS) and 80/20 PP/maleated styrene–ethylene–butylene–styrene (SEBS‐g‐MA) blends reinforced with 30 wt % short glass fibers (SGFs) were prepared by extrusion and subsequent injection molding. The influence of the maleic anhydride (MA) functional group grafted to SEBS on the properties of SGF/SEBS/PP hybrid composites was studied. Tensile and impact tests showed that the SEBS‐g‐MA copolymer improved the yield strength and impact toughness of the hybrid composites. Extensive plastic deformation occurred at the matrix interface layer next to the fibers of the SGF/SEBS‐g‐MA/PP composites during impact testing. This was attributed to the MA functional group, which enhanced the adhesion between SEBS and SGF. Differential scanning calorimetry measurements indicated that SEBS promoted the crystallization of PP spherulites by acting as active nucleation sites. However, the MA functional group grafted to SEBS retarded the crystallization of PP. Finally, polarized optical microscopy observations confirmed the absence of transcrystallinity at the glass‐fiber surfaces of both SGF/SEBS/PP and SGF/SEBS‐g‐MA/PP hybrid composites. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1303–1311, 2002     

Phase structure and morphology of wollastonite‐reinforced polypropylene composites modified with SEBS and SEBS‐g‐MA elastomers

Supermolecular structure of isotactic polypropylene/wollastonite/styrenic rubber block copolymers composites were studied as a function of elastomeric poly‐ (styrene‐b‐ethylene‐co‐butylene‐b‐styrene) triblock copolymer (SEBS) and the SEBS grafted with maleic anhydride (SEBS‐g‐MA) content (from 0 to 20 vol%) by optical, scanning, and transmission electron microscopy, wide‐angle X‐ray diffraction and differential scanning calorimetry. Wollastonite particles disturbed the spherulitization of polypropylene matrix. Both elastomers affected the crystallization of polypropylene matrix mainly by solidification effect. Although SEBS‐g‐MA encapsulated wollastonite particles more expressive than SEBS forming thus core‐shell morphology in higher extent, scanning electron micrographs indicated more constrained wollastonite particles in fractured surfaces of composites with SEBS elastomer. Moreover, SEBS‐g‐MA disorientated wollastonite particles and affected reorientation of the polypropylene crystallites stronger than SEBS elastomer. POLYM. ENG. SCI., 47:2145–2154, 2007. © 2007 Society of Plastics Engineers     

Mechanical properties of wollastonite‐reinforced polypropylene composites modified with SEBS and SEBS‐g‐MA elastomers

Mechanical properties of isotactic polypropylene/wollastonite/styrene rubber block copolymers (iPP/wollastonite/SRBC) composites were studied as a function of elastomeric poly(styrene‐b‐ethylene‐co‐butylene‐b‐styrene) triblock copolymer (SEBS) and SEBS grafted with maleic anhydride (SEBS‐g‐MA) content from 0 to 20 vol%. Microphase morphology was stronger influenced by SRBC elastomers than by different wollastonite types. Higher encapsulation ability of SEBS‐g‐MA than SEBS caused more expressive core‐shell morphology and consequently higher notched impact strength as well as yield parameters, but lower Young's modulus. Higher ductility of the composites with SEBS than with SEBS‐g‐MA has been primarily caused by better miscibility of the polypropylene chains with SEBS molecules. Surface properties of components and adhesion parameters also indicated that adhesion at SEBS‐g‐MA/wollastonite interface, which was stronger than the one at the SEBS/wollastonite interface, influenced higher encapsulation of wollastonite particles by SEBS‐g‐MA. POLYM. ENG. SCI., 47:1873–1880, 2007. © 2007 Society of Plastics Engineers     

Tribological behavior of polyamide 66‐based binary and ternary composites

Friction and wear characteristics of polyamide 66 (PA66) and the composites of organoclay modified by styrene–ethylene/butylene–styrene triblock copolymer grafted with 1.84 wt% of maleic anhydride (SEBS‐g‐MA) were studied using an Universal Micro Tribometer reciprocating friction and wear tester. The morphologies of the wear tracks of PA66 and the composites were observed using a scanning electron microscope. The results showed that plastic deformation induced by the traction of the harder steel ball occurred on the worn surfaces of PA66 and the composite which were reinforced by SEBS‐g‐MA copolymer. It was found that the average frictional coefficient and specific wear rate of PA66/SEBS‐g‐MA binary composite are lowest under the same conditions. This indicates that toughness and wear resistance of PA66 matrix are improved with the incorporation of SEBS‐g‐MA copolymer. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Effect of maleated polypropylene and impact modifiers on the morphology and mechanical properties of PP/Mica composites

Composites of polypropylene (PP) with mica powder and impact modifiers were produced by internal mixer. A major drawback in the use of mica‐filled PP is its low impact resistance. In the present study, the effect of the maleated PP (MAPP) and impact modifiers was evaluated on the composite properties separately and together. Thus, two different styrene‐ethylene/butylene‐styrene triblock copolymers (SEBS) and one ethylene‐propylene‐diene terpolymer (EPDM) have been used as impact modifiers in the PP‐mica composites. Addition of MAPP had a negative effect on the composite notched impact strength and elongation at break but had a positive effect on tensile strength when used together with impact modifiers. All three elastomers increased the impact strength of the PP‐mica composites but the addition of maleated SEBS (SEBS‐MA) granted the greatest improvement in impact strength. It was inferred from the scanning electron microscopy that SEBS‐MA had a stronger interaction with mica surface than the other impact modifiers. POLYM. COMPOS., 27:614–620, 2006. © 2006 Society of Plastics Engineers     

Stability of electrical properties of carbon black‐filled rubbers

Conducting composites were prepared by melt mixing of ethylene–propylene–diene terpolymer (EPDM) or styrene‐butadiene rubber (SBR) and 35 wt % of carbon black (CB). Stability of electrical properties of rubber/CB composites during cyclic thermal treatment was examined and electrical conductivity was measured in situ. Significant increase of the conductivity was observed already after the first heating–cooling cycle to 85°C for both composites. The increase of conductivity of EPDM/35% CB and SBR/35% CB composites continued when cyclic heating‐cooling was extended to 105°C and 125°C. This effect can be explained by reorganization of conducting paths during the thermal treatment to the more conducting network. EPDM/35% CB and SBR/35% CB composites exhibited very good stability of electrical conductivity during storage at ambient conditions. The electrical conductivity of fresh prepared EPDM/35% CB composite was 1.7 × 10⁻² S cm⁻¹, and slightly lower conductivity value 1.1 × 10⁻² S cm⁻¹ was measured for SBR/35% CB. The values did not significantly change after three years storage. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Influence of addition of styrene–ethylene/butylene–styrene copolymer on rheological,mechanical, and tribological properties of polyamide nanocomposites

To develop new tribomaterials for mechanical sliding parts, investigations were carried out on the influence of adding styrene–ethylene/butylene–styrene block copolymer (SEBS) on the rheological, mechanical, and tribological properties of polyamide 6 (PA6) nanocomposite, which is a commercial product of layered silicate (clay) filled polyamide 6 (PA6/Clay). Two kinds of block copolymers, unmodified SEBS (SEBS) and maleic anhydride‐grafted SEBS (SEBS‐g‐MA), were added with PA6/Clay nanocomposite. Dynamic viscoelastic properties in the molten state of these nanocomposites and their tensile, impact, and tribological properties of these nanocomposites were evaluated. Dynamic viscoelastic properties were found to increase with the addition of SEBS and were influenced, in particular, by block copolymers containing SEBS‐g‐MA. Influence of the addition of SEBS on mechanical properties of these systems differed for each mechanical property. Although tensile properties decreased with SEBS, Izod impact properties were improved with the addition of SEBS‐g‐MA. Tribological properties were improved with the addition of block copolymer, and the influence of the amount of addition was higher than the type of block copolymer used. These results indicate that new tribomaterials developed have sufficient balance amongst moldability, mechanical, and tribological properties. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Effect of LCP and rPET as reinforcing materials on rheology,morphology, and thermal properties of in situ microfibrillar‐reinforced elastomer composites

Microfibrillar‐reinforced elastomer composites based on two dispersed phases, liquid crystalline polymer (LCP) and recycled poly(ethylene terephthalate)(rPET), and styrene‐(ethylene butylene)‐styrene (SEBS) were prepared using extrusion process. The rheological behavior, morphology, and thermal stability of SEBS/LCP and SEBS/rPET blends containing various dispersed phase contents were investigated. All blends and LCP exhibited shear thinning behavior, whereas Newtonian fluid behavior was observed for rPET. The incorporation of both LCP and rPET into SEBS significantly improved the processability by bringing down the melt viscosity of the blend system. The fibrillation of LCP dispersed phase was clearly observed in as‐extruded strand with addition of LCP up to 20–30 wt %. Although the viscosity ratio of SEBS/rPET system is very low (0.03), rPET domains mostly appeared as droplets in as‐extruded strand. The results obtained from thermogravimetric analysis suggested that an addition of LCP and rPET into the elastomer matrix improved the thermal resistance significantly in air but not in nitrogen. The simultaneous DSC profiles revealed that the thermal degradation of all polymers examined were endothermic and exothermic in nitrogen and in air, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effects of styrene–ethylene–butylene–styrene based additives on the mechanical properties of rice hull/polypropylene composites

The purpose of this study was to improve the mechanical properties (such as tensile, flexural, and impact strength) of rice hull/polypropylene composites, with the use of styrene–ethylene–butylene–styrene copolymer (SEBS) and maleated styrene–ethylene–butylene–styrene copolymer (SEBS-MA). The results suggested that both types of additives increased the impact strength of the composites significantly as their contents increased. However, only SEBS-MA improved the tensile and flexural strength of the composites. The results also indicated that the composites with SEBS-MA consistently showed better mechanical properties than the SEBS counterparts for all the contents. POLYM. ENG. SCI., 47:1148–1155, 2007. © 2007 Society of Plastics Engineers     

Fabrication and properties of carbon nanotube/styrene–ethylene–butylene–styrene composites via a sequential process of (electrostatic adsorption aided dispersion)‐plus‐(melt mixing)

Carbon nanotube (CNT)/styrene–ethylene–butylene–styrene (SEBS) composites were prepared via a sequential process of (electrostatic adsorption assisted dispersion)‐plus‐(melt mixing). It was found that CNTs were uniformly embedded in SEBS matrix and a low percolation threshold was achieved at the CNT concentration of 0.186 vol %. According to thermal gravimetric analysis, the temperatures of 20% and 50% weight loss were improved from 316°C and 352°C of pure SEBS to 439°C and 463°C of the 3 wt % CNT/SEBS composites, respectively. Meanwhile, the tensile strength and elastic modulus were improved by about 75% and 181.2% from 24 and 1.6 MPa of pure SEBS to 42 and 4.5 MPa of the 3 wt % CNT/SEBS composite based on the tensile tests, respectively. Importantly, this simple and low‐cost method shows the potential for the preparation of CNT/polymer composite materials with enhanced electrical, mechanical properties, and thermal stability for industrial applications. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40227.     

Thermoplastic SEBS Elastomer Nanocomposites Reinforced with Functionalized Graphene Dispersions

Blending a maleinated polystyrene‐b‐poly(ethylene‐r‐butylene)‐b‐polystyrene (SEBS) thermoplastic elastomer with functionalized graphene (FG) dispersions in tetrahydrofuran (THF) prior to the melt processing results in SEBS/FG nanocomposites with improved property profiles. According to microscopic imaging (atomic force microscopy, transmission electron microscopy, focus ion beam–scanning electron microscopy), FG dispersions derived from multilayer graphene (MLG 350) and thermally reduced graphite oxide enable uniform dispersion of single‐ and few‐layer FG within both the THF and the SEBS matrix. In contrast, high‐pressure homogenization of nonfunctionalized graphite yields larger graphene stacks together with blend of graphene stacks with micrometer‐sized graphite (GG). As opposed to SEBS/GG composites, SEBS/FG composites exhibit superior mechanical properties as well as higher Shore A hardness, electrical conductivity at a lower percolation threshold, and enhanced gas barrier resistance. Hence, SEBS/FG composites hold promise as thermoplastic elastomers, serving the needs of automotive and sealant industries.     

Influences of compatibilizers on rheology and mechanical properties of propylene random copolymer/styrene‐ethylene‐butylene‐styrene block copolymer/organic‐montmorillonite nanocomposites

Propylene random copolymer (PPR)/styrene‐ethylene‐butylene‐styrene block copolymer (SEBS)/compatibilizer/organic‐montmorillonite (OMMT) quaternary nanocomposites and PPR/compatibilizer/OMMT ternary nanocomposites were prepared via two‐stage melt blending and influences of compatibilizers, maleic anhydride (MA) grafted styrene‐ethylene‐butylene‐styrene copolymer (SEBS‐g‐MA), poly(octene‐co‐ethylene) (POE‐g‐MA), or propylene block copolymers (PPB‐g‐MA), on rheology and mechanical properties of the nanocomposites were investigated. The results of X‐ray diffraction measurement and transmission electron microscopy observation showed that OMMT layers were mainly intercalated in the nanocomposites except for the mainly exfoliated structure in the quaternary nanocomposites using POE‐g‐MA as compatibilizer. The nanocomposites exhibited pseudo‐solid like viscoelasticity in low frequencies and shear‐thinning in high shear rates. As far as OMMT dispersion was concerned, POE‐g‐MA was superior to SEBS‐g‐MA and PPB‐g‐MA, which gives rise to the highest viscosities in both the ternary and quaternary nanocomposites. The quaternary nanocomposites containing POE‐g‐MA were endowed with balanced toughness and rigidity. It was suggested that a suitable combination of compatibilizer and SEBS was an essentially important factor for adjusting the OMMT dispersion and distribution, the rheological and mechanical performances of the nanocomposites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Reactive mixing of PET and PET/PP blends with glycidyl methacrylate–modified styrene‐b‐(ethylene‐co‐olefin) block copolymers

Styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene (SEBS) and styrene‐b‐(ethylene‐co‐propylene) (SEP, SEPSEP) block copolymers with different styrene contents and different numbers of blocks in the copolymer chain were functionalized by melt radical grafting with glycidyl methacrylate (GMA) and employed as compatibilizers for PET‐based blends. Binary blends of PET with both functionalized (SEBS‐g‐GMA, SEP‐g‐GMA, SEPSEP‐g‐GMA) and neat (SEBS, SEP, SEPSEP) copolymers (75 : 25 w/w) and ternary blends of PET and PP (75 : 25 w/w) with various amounts (2.5–10 phr) of both modified and unmodified copolymers were prepared in an internal mixer, and their properties were evaluated by SEM, DSC, melt viscosimetry, and tensile and impact tests. The roles of the chemical structure, grafting degree, and concentration of the various copolymers on blend compatibilization was investigated. The blends with the grafted copolymers showed a neat improvement of phase dispersion and interfacial adhesion compared to the blends with nonfunctionalized copolymers. The addition of grafted copolymers resulted in a marked increase in melt viscosity, which was accounted for by the occurrence of chemical reactions between the epoxide groups of GMA and the carboxyl/hydroxyl end groups of PET during melt mixing. Blends with SEPSEP‐g‐GMA and SEBS‐g‐GMA, at concentrations of 5–10 phr, showed a higher compatibilizing effect with enhanced elongation at break and impact resistance. The effectiveness of GMA‐functionalized SEBS was then compared to that of maleic anhydride–grafted SEBS. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2201–2211, 2005     

Effect of different fillers on physical,mechanical, and optical properties of styrenic‐based thermoplastic elastomers

The effects of different fillers on physical, mechanical, and optical properties of styrenic‐based thermoplastic elastomers were investigated by experimental study. Poly[styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene] block copolymer (SEBS)‐based thermoplastic elastomer composites were prepared in a co‐rotating intermeshing twin‐screw extruder, using silica and calcite as filler materials with three different particle sizes. The loading ratios in the composites were varied. Hardness, density, tensile strength, tear strength, compression set, wear resistance, transmittance, and haze measurements were performed. Thermal properties and morphological structure were investigated by differential scanning calorimeter (DSC) and scanning electron microscopy (SEM), respectively. The results show that, an interaction between silica and the polymer matrix exists, whereas calcite does not show any interaction with the polymer. Therefore, it is concluded that, calcium carbonate can be used in the composite as filler for cost efficiency, whereas silica can be used as reinforcing material in SEBS‐based thermoplastic elastomer composites, when optical properties are also concerned. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Compatibilization of kraft lignin‐polyethylene composites using unreactive compatibilizers

This article presents a novel approach to compatibilize Kraft lignin with polyethylene that involves the use of modified poly (styrene‐co‐ethylene‐co‐butylene‐co‐styrene) (SEBS) as unreactive compatibilizers. As SEBS shows no compatibilizing effect on Kraft lignin‐polyethylene composites, SEBS was functionalized via nitration followed by amination to obtain nitrated (SEBS‐NO₂) and aminated (SEBS‐NH₂) SEBS. The compatibilizing effects of SEBS derivatives were studied by means of morphological and mechanical analyses. The results show that SEBS‐NO₂ is less effective than SEBS‐NH₂, the later displaying comparable compatibilizing efficiency to a commercial reactive compatibilizer based on maleated polyethylene. Overall, compatibilization was found to decrease lignin particle size. Addition of SEBS‐NH₂ varying between 1% and 10% improved the tensile strength of composites by up to 96%, elongation at break by up to 64%, and impact strength by up to 48%. Finally, the crystallinity and density of the resulting composites were also studied. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41040.     

Thermoplastic polyurethane–carbon black compounds: Structure,electrical conductivity and sensing of liquids

Thermoplastic polyurethane (TPU) copolymers are interesting host matrices for the incorporation of conductive carbon black (CB) particles. The two‐phase character of the TPU systems provides an opportunity for the CB particles to distribute nonuniformly within the phases, owing to their different characteristics. Thus, in spite of its highly polar nature, the TPU/CB system percolates at a relatively low CB content. The CB presence affects the TPU two‐phase structure, resulting in a large change of its low temperature loss modulus. CB‐containing extruded filaments produced by a capillary rheometer at various shear rates were studied as sensing materials for different alcohols. All filaments displayed an increase in resistance upon exposure to various alcohols. Filaments exposed to methanol exhibited the highest sensitivity. This behavior was related to the sorption kinetics by the TPU/CB compound, which is affected by the different characteristics of the solvents. The resistance of filaments exposed to ethanol or methanol tended to reversibility during the drying cycle, returning to the initial values. The relatively rapid recovery to the filaments' initial resistance values (for methanol and ethanol) suggests that the structural changes due to solvent sorption mainly occur in the outer skin regions of the extruded filaments, whereas the core region remains essentially intact.