Laboratory accelerated and natural weathering of styrene-ethylene-butylene-styrene (SEBS) block copolymer

Indoor accelerated and outdoor weathering of polystyrene-b-(ethylene-co-butylene)-b-styrene (SEBS) was studied by infrared spectroscopy. Accelerated conditions involved simultaneous exposure of specimens to ultraviolet-visible radiation between 295 nm and 450 nm and each of four temperature/relative humidity (RH) environments, i.e., (a) 30 °C ± 1 °C at <1% RH, (b) 30 °C ± 1 °C at 80% RH, (c) 55 °C ± 1 °C at <1% RH, and (d) 55 °C ± 1 °C at 80% RH. Outdoor exposure was conducted in Gaithersburg, MD, in two different time periods. Similar photooxidative mechanisms were operative under all conditions. In the case of indoor accelerated exposure, the rate of photooxidation was found to depend strongly on temperature. Unlike the exposure at 55 °C, moisture-assisted photooxidation was insignificant at 30 °C. A quantitative study on the synergistic effect of environmental stressors revealed that the degrading effect of combined temperature and moisture on photooxidation was greater than the sum of the two effects exerted independently. Outdoor weathered specimens exhibited significantly slower photooxidation. Acceleration of photooxidation ranged from 2.5 to 10 times in comparison to the outdoor exposure, depending on the indoor accelerated conditions.     

A Rheotens-based setup for the constant strain rate uniaxial extension of uncured elastomers

A novel experimental setup for the uniaxial extension of uncured elastomers is presented, and room temperature experiments at constant Hencky strain rate are performed by means of a commercial Rheotens tensile tester originally designed for the determination of the melt strength of polymer melts. Successful results are obtained for materials related to many aspects of the elastomers production, namely, gum elastomers and carbon black compounds. Stress growth experiments are reported for filled and unfilled high-cis-polybutadiene, and the extensional behavior is related to the carbon black dispersion. Although originally thought as an experimental tool for polymer melts, the proposed Rheotens setup can also perform constant strain rate tensile testing on thermoplastic rubbers. Stress-strain experiments are performed on a microphase separated polystyrene-b-poly(ethylene butylene)-b-polystyrene (SEBS) copolymer and related blends with polypropylene, showing the effect of a constant deformation rate on the network response. Relaxation experiments after cessation of extensional flow are also reported for the investigated materials. With respect to commonly used tensile testing procedures for elastomers at constant elongation rate and time decreasing strain rate, a complete and accurate investigation of the extensional behavior of many uncured elastomers can be carried out with the additional advantage of using a reduced amount of material.     

Flame-retarded mechanism of SEBS/PPO composites modified with mica and resorcinol bis(diphenyl phosphate)

The flame retardancy of styrene-b-ethylene/butylene-b-styrene triblock polymer (SEBS)/poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) blends was greatly improved by the combined use of mica and resorcinol bis(diphenyl phosphate) (RDP). The limiting oxygen index (LOI), vertical burning and cone calorimeter test were performed to evaluate the flame-retarded effect. The composite of SEBS/PPO/maleic anhydride grafted SEBS (SEBS-g-MAH) with a mass ratio of 11/11/3 passed a V-0 rating in the UL94 test by the addition of 10–15 wt% mica and 15–10 wt% RDP with total amount of 25 wt%. The synergism was confirmed by the mathematical evaluation of the synergistic effect index (SE) in LOI, the residue, the peak heat release rate (PHRR) and the total heat evolved (THE) per mass loss (THE/ML). The flame-retarded mechanism of the composite was also proposed on the results of cone calorimeter test, TGA-FTIR, SEM micrographs and SEM/EDS analysis of the residues. It was found that the degradation rate of SEBS/PPO/SEBS-g-MAH matrix was slowed down, a more consolidated char layer with higher residue was promoted by the combination of RDP and mica. The flame-retardancy of RDP with mica in SEBS/PPO/SEBS-g-MAH matrix was synergistic through gas and condensed phase action.     

Long-Range Processing Correlation and Morphological Fractality of Compatibilized Blends of PS/ HDPE/ SEBS Block Copolymer

Summary: Processing and compatibilization effects of a commercially available styrene/ ethylene-butylene/ styrene (SEBS) compatibilizer on the morphological structure, rheological and mechanical properties of blends of polystyrene (PS) and high density polyethylene (HDPE) were investigated. The rheological behaviour of the blends melt during processing was followed by measuring torque; extrusion capacity output and melts back-pressure in a twin screw extruder. The processing parameters were decreased with the HDPE content. The results show that SEBS compatibilizer can yield compatibilization by substantially reducing torque and increasing the back-pressure. However, the Hurst indices of melt processing parameters are increased with compatibilization. Near-infrared spectra had been described by the Hurst index H_NIR which is then related to HDPE content in the blends. The correlation between the blend compositions, morphological structure, mechanical and rheological properties and processing parameters was established and discussed on base of correlation with the fractal indices obtained from the SEM microphotographs of PS/HDPE/SEBS blends.     

Influence of extender oil composition on flowing property,thermal stability,and morphology of styrene‐b‐ethylene‐co‐butylene‐b‐styrene copolymer/polypropylene/oil blends

In this study, a series of styrene‐b‐ethylene‐co‐butylene‐b‐styrene copolymer (SEBS)/polypropylene (PP)/oil blends with different kinds of oil composition was developed through melt blending. The effect of oil with different composition and properties on its phase equilibrium and “redistribution” in multiphasic SEBS elastomer was systematically studied for the first time. Moreover, an integral influencing mechanism of oil composition on the structure and properties of SEBS/PP/oil blends was also put forward. The mineral oil was mainly distributed in ethylene/butylene (EB)/PP phase, which greatly enhanced the processing flowability of SEBS/PP/oil blends. With increasing oil C_N content, a redistribution of oil appeared and excess naphthenic oil (NO) entered the interphase of soft and hard phases. The dynamic mechanical thermal analysis (DMTA) analysis indicated that the polystyrene (PS) phase was plasticized, which also helped to improve the processing fluidity of blends. However, the plasticizing of physical cross‐linking point PS resulted in a decrease in mechanical strength and thermal stability. Small‐angle X‐ray scattering (SAXS) and transmission electron microscope (TEM) results showed that PS phase (45 nm to 55 nm) cylindrically distributed in EB/PP/oil matrix, the excess NO in the interphase enlarged the distance between PS phase and widen the escape channel for oil migration. At over 45% oil C_N content, the electron density difference between soft and hard phases reduced to the minimum, same as T_gPS, indicating a deeper plasticizing effect. The PS phase swelled and exhibited elastic behavior; thus, the force could be uniformly transferred between two phases. Importantly, a recover in strength and thermal stability was observed in O‐5 blend. This work significantly filled the gap of studies in oil‐extended thermoplastic elastomers (TPEs), exhibiting great theoretical guiding significance and application value.     

Effect of composition on the properties of SEBS modified asphalts

We characterised, from both a morphological and a rheological point of view, polymer modified asphalts prepared by the addition of styrene-(ethylene-co-butylene)-styrene block copolymer to a soft base asphalt. It was found that, even if the two components showed poor compatibility and interfacial adhesion, storage-stable mixtures could be obtained if the polymer content was maintained below about 4 wt%, with respect to the total mass. In this case, the more polar part of asphalt stabilises the dispersed polymer-rich domains, which act similarly to a filler and do not change significantly the viscoelastic behaviour of the base asphalt. On the contrary, at higher polymer concentrations, a swelled polymer-rich phase creates a network that strongly influences the viscoelastic properties. In this case the material becomes unstable and tends to give macroscopic phase separation if stored at high temperature without stirring.     

Processing, characterization and properties of conducting polyaniline-sulfonated SEBS block copolymers

Incorporation of polyaniline (PAni) into thermoplastic elastomers can be used to produce materials that potentially combine the good mechanical properties and processability of thermoplastic elastomers with electrical, magnetic and optical characteristics of PAni. In this work, a polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene copolymer (SEBS) was chemically modified by grafting a sulfonic group onto the chain backbone in order to promote higher levels of compatibility between the thermoplastic elastomer and polyaniline. The sulfonation process was performed by reacting SEBS with acetyl sulfate. Infrared spectroscopy and titration were used to monitor the amount of sulfonic groups successfully grafted on SEBS. Mechanical tests performed in sulfonated SEBS showed that sulfonation levels lower than 15% did not reduce substantially the mechanical properties of SEBS. PAni doped with dodecylbenzenesulfonic acid (PAni·DBSA), used in the preparation of the blends, was prepared by the “in situ doping polymerization” method. PAni·DBSA was then blended in solution with SEBS having different levels of sulfonation. The introduction of sulfonic group into the structure of SEBS improved coulombic interactions between the phases in the blend and enhanced compatibility. As a consequence, higher values of electrical conductivity (measured by the four-probe method) were achieved in blends with sulfonic groups grafted onto polymer chains. Concentrations as low as 20 wt% of PAni were able to lead to electrical conductivities of PAni·DBSA/sulfonated SEBS blends close to 1.2 S/cm. Optical micrographs of the blends showed that PAni·DBSA/sulfonated SEBS microstructure is composed of a very disperse group of small conducting particles. This type of microstructure would then be responsible for the enhanced electrical conductivity and low percolation threshold of PAni·DBSA/sulfonated SEBS, when compared to PAni·DBSA/SEBS blends.     

Effect of in situ oxidization with potassium permanganate on the morphologies of SEBS membranes

The morphologies of the asymmetric membranes of polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) prepared and simultaneously oxidized with different substrate solutions were investigated with atomic force microscopy (AFM), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance infrared spectroscopy (ATR-FTIR). We used the KMnO₄ aqueous solution and KMnO₄/H₂SO₄ mixture solution as solvent-casting substrates, as well as oxidized reagents. The surface composition and functional groups of membranes were also measured. The effect of casting substrates on morphological changes was discussed through possible chemical reactions. It was found that the SEBS membranes were transformed from an ordered microphase-separated structure to disordered nodular or sponge-like structures. The former might be contributed to MnO₂ depositions while the latter was caused by the bond interruption, after KMnO₄ or KMnO₄/H₂SO₄ oxidizing.     

Studies of the solution properties of sulfonated-(styrene-(ethyrene-CO-butylene)-styrene) block copolymer

The dilute solution properties of lightly sulfonated hydrogenated styrene-butadiene-styrene block copolymer (S-SEBS) dissolved in tetrahydrofunan (THF) were studied by viscometry. The ring conformation in dilute regime can be deduced from the intrinsic viscosity data. It is believed that this special conformation results from the location of ionic group at both two-end blocks. The intermolecular aggregation can be observed when the solutions undergo the freezing–thawing process in the same concentration region. The extent of aggregation is affected by the freezing–thawing cycle times, water content in THF, and the counterion radii, etc. The properties of the aggregation equilibrium are also discussed. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2677–2681, 1998     

Synthesis and Characterization of Crystalline Styrene‐b‐(Ethylene‐co‐Butylene)‐b‐Styrene Triblock Copolymers

By merit of dual catalysis of the cationic rare‐earth complex [(η⁵‐Flu‐CH₂‐Py)Ho(CH₂SiMe₃)₂(THF) (Flu = fluorenyl, Py = pyridyl) for the living polymerizations of butadiene (BD) and styrene (St), the crystalline styrene‐butadiene‐styrene (SBS) triblock copolymers consisting of elastic polybutadiene (PBD) sequences with suitable 1,4 regularity (about 70%) and crystalline syndiotactic polystyrene (sPS, [rrrr] > 99%) sequences were successfully synthesized through sequential addition of St, BD, and St monomers. The catalytic system showed high polymerization activities for St and BD in a controlled manner. The crystalline styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene (SEBS) triblock copolymers were obtained by hydrogenation of the above SBS copolymers. The observation of a strong endothermic peak at 266 °C in their differential scanning calorimetry (DSC) curves confirmed the existence of the sPS blocks in the crystalline SEBS different from the industrial product Kraton SEBS‐1652. Thermal degradation temperature of the crystalline SEBS (418 ± 2 °C) indicated the well thermostability and process window of this polymer. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 55, 1243–1249