Thermal and mechanical properties of microcellular thermoplastic SBS/PS/SBR blend: effect of crosslinking

This study investigates the effect of peroxide crosslinking on the structure and mechanical properties for SBS/PS/SBR foams composed of polystyrene (PS), poly(styrene-b-butadiene) diblock copolymer (SBR-1502), and poly(styrene-b-butadiene-b-styrene) triblock copolymer (SBS). The cell size and its distribution of SBS/PS/SBR foams were investigated by SEM images, showing the smaller and denser of hollow cells for the SBS/PS/SBR foam containing the higher concentration of DCP (dicumyl peroxide). As expected, the density of the SBS/PS/SBR foams increases with increasing the content of DCP. The high density of polymeric foams exhibits the high mechanical properties such as hardness, shrinkage, tensile strength, tear strength, elongation at break, and compression set.     

接枝改性SBS对PS/SBS/CaCO_3复合材料形态和力学性能的影响

采用马来酸酐(MAH)和苯乙烯(St)作为接枝单体,通过溶液聚合法合成接枝极性基团的苯乙烯-丁二烯-苯乙烯三嵌段共聚物(SBS),然后与聚苯乙烯(PS)基体、碳酸钙(CaCO_3)粒子复合,用傅立叶红外光谱仪表征接枝处理前后SBS表面化学结构的变化;并研究了SBS改性对复合材料微观结构和力学性能的影响.结果表明:双单体溶液聚合法成功地将极性基团接枝在SBS链上;填充SBS-g-MAH后,促进CaCO_3在PS基体中的分散、改善PS-CaCO_3粒子间界面粘接,起到良好的增容作用;SBS-g-MAH和CaCO_3粒子对PS基体具有协同增强增韧作用,同时能提高复合材料的拉伸强度和冲击强度.     

Blends of SBS triblock copolymer with poly(2,6‐dimethyl‐1,4‐phenylene oxide)/polystyrene mixture

Blends of styrene–butadiene–styrene (SBS) or styrene–ethylene/1‐butene–styrene (SEBS) triblock copolymers with a commercial mixture of polystyrene (PS) and poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) were prepared in the melt at different temperatures according to the chemical kind of the copolymer. Although solution‐cast SBS/PPO and SBS/PS blends were already known in the literature, a general and systematic study of the miscibility of the PS/PPO blend with a styrene‐based triblock copolymer in the melt was still missing. The thermal and mechanical behavior of SBS/(PPO/PS) blends was investigated by means of DSC and dynamic thermomechanical analysis (DMTA). The results were then compared to analogous SEBS/(PPO/PS) blends, for which the presence of a saturated olefinic block allowed processing at higher temperatures (220°C instead of 180°C). All the blends were further characterized by SEM and TGA to tentatively relate the observed properties with the blends' morphology and degradation temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2698–2705, 2003     

PO／PS合金的相态结构与力学性能

以氢化ＳＢＳ（ＳＥＢＳ）为增容剂的聚烯烃／聚苯乙烯（ＰＯ／ＰＳ）合金，与聚烯烃相比具有更好的力学性能，尤其是抗冲击强度随机容剂的增加而大幅度提高，应用ＴＥＭ，ＳＥＭ、ＤＳＣ、偏光显微技术对一系列合金相形态，相容程度及分散相颗粒尺的考察研究发现，合金中分散相多数呈卵石状，随ＳＥＢＳ含量增加，分散相粒径显著变小，而合金抗冲击强度增大，分散相形态结构。颗粒尺寸与材料力学性能密切相联。     

Plasticization of nano‐CaCO3 in polystyrene/nano‐CaCO3 composites

The shear rheological properties of polystyrene (PS)/nano‐CaCO₃ composites were studied to determine the plasticization of nano‐CaCO₃ to PS. The composites were prepared by melt extrusion. A poly(styrene–butadiene–styrene) triblock copolymer (SBS), a poly(styrene–isoprene–styrene) triblock copolymer (SIS), SBS‐grafted maleic anhydride (SBS–MAH), and SIS‐grafted maleic anhydride were used as modifiers or compatibilizers. Because of the weak interaction between CaCO₃ and the PS matrix, the composites with 1 and 3 phr CaCO₃ loadings exhibited apparently higher melt shear rates under the same shear stress with respect to the matrix polymer. The storage moduli for the composites increased with low CaCO₃ concentrations. The results showed that CaCO₃ had some effects on the compatibility of PS/SBS (or SBS–MAH)/CaCO₃ composites, in which SBS could effectively retard the movement of PS chain segments. The improvement of compatibility, due to the chemical interaction between CaCO₃ and the grafted maleic anhydride, had obvious effects on the rheological behavior of the composites, the melt shear rate of the composites decreased greatly, and the results showed that nano‐CaCO₃ could plasticize the PS matrix to some extent. Rheological methods provided an indirect but useful characterization of the composite structure. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Compatibilisation of polystyrene-polyolefin blends

Summary The impact properties of 1:1 polyolefin-polystyrene blends compatibilised with a series of hydrogenated styrene-butadiene block copolymers of various structures have been studied with a view to establishing a structure-property realationship. The most effective compatibiliser in this context appears to be a low molecular weight triblock (Kraton G1652). Addition of only 5% Kraton G1652 affords a ca. three-fold improvement in the impact strength for a 1:1 PP/PS blend over the uncompatibilised blend and leads to near HIPS impact strength for a 1:1 LDPE/PS blend. This compatibiliser is as effective as a high molecular weight tapered diblock and appears to be substantially more effective than either low molecular weight diblocks or a higher molecular weight triblock.     

Viscoelastic properties of heterophase blends of homopolymers and block copolymers

Stress relaxation and dynamic mechanical measurements were carried out for two types of heterophase polyblends. One is obtained by blending homopolymers of butadiene and styrene (high impact polystyrene or HIPS); the other by blending homopolymer of butadiene with a triblock copolymer of styrene-butadiene-styrene (SBS/B). It was found that for HIPS, time temperature superposition is difficult, and the shift factors cannot be adequately interpreted by a reasonable model. For SBS/B it is impossible to carry out superposition. Modulus-temperature and loss tangent curves determined by dynamic mechanical experiments indicate the presence of new transition near ?40°C. Possible mechanisms giving rise to this new transition are discussed.     

Compatibilization of polypropylene/polystyrene blends with poly(styrene-b-butadiene-b-styrene) block copolymer

The compatibilizing effect of the triblock copolymer poly(styrene-b-butadiene-b-styrene) (SBS) on the morphology and mechanical properties of immiscible polypropylene/polystyrene (PP/PS) blends were studied. Blends with three different weight ratios of PP and PS were prepared and three different concentrations of SBS were used for investigations of its compatibilizing effects. Scanning electron microscopy (SEM) showed that SBS reduced the diameter of the PS-dispersed particles as well as improved the adhesion between the matrix and the dispersed phase. Transmission electron microscopy (TEM) revealed that in the PP matrix dispersed particles were complex “honeycomblike” aggregates of PS particles enveloped and joined together with the SBS compatibilizer. Wide-angle X-ray diffraction (WAXD) analysis showed that the degree of crystallinity of PP/PS/SBS slightly exceeded the values given by the addition rule. At the same time, addition of SBS to pure PP and to PP/PS blends changed the orientation parameters A₁₁₀ and C significantly, indicating an obvious SBS influence on the crystallization process in the PP matrix. SBS interactions with PP and PS influenced the mechanical properties of the compatibilized PP/PS/SBS blends. Addition of SBS decreased the yield stress and the Young's modulus and improved the elongation at yield as well as the notched impact strength in comparison to the binary PP/PS blends. Some theoretical models for the determination of the Young's modulus of binary PP/PS blends were used for comparison with the experimental results. The experimental line was closest to the series model line. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 69: 2625–2639, 1998     

Isothermal decomposition behavior and dynamic mechanical properties of in situ‐reinforcing elastomer composites based on thermoplastic elastomers and thermotropic liquid crystalline polymer

In situ‐reinforcing composites based on two elastomer matrices very different in melt viscosity, styrene–(ethylene butylene)–styrene triblock copolymer (Kraton G1650), and styrene–(ethylene propylene) diblock copolymer (Kraton G1701), and a thermotropic liquid crystalline polymer (TLCP), Rodrun LC3000, were prepared using a twin‐screw extruder. The isothermal decomposition behavior and dynamic mechanical properties of the extruded strands were investigated by means of thermogravimetry (TG) and dynamic mechanical analysis (DMA), respectively. No significant change in the shape of TG curves for the neat matrices and their LC3000‐containing blends was observed under isothermal heating in nitrogen. In air, G1650 and G1701 showed a single weight‐loss stage and rapid decomposition whereas their blends with 30 wt % LC3000 showed different profiles of weight loss depending on isothermal temperatures. The calculated kinetic parameters indicated that the thermal stability of the polymers is much higher in nitrogen than in air and suggested an enhancement of thermal resistance of the elastomer matrices by addition of TLCP. DMA results showed a great enhancement in dynamic moduli for the blend with 10 wt % LC3000 when compared with the neat matrix. The tan δ peaks corresponding to the elastic and hard phases in both matrices mostly shifted to the lower temperature with LC3000 loading. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 917–927, 2007     

Effects of the blending sequence and interfacial agent on the morphology and mechanical properties of injection molded PC/PP Blends

Summary The effects of blending sequence and the addition of an interfacial agent (triblock copolymer styrene-butylene ethylene/styrene, Kraton G1652) on the morphology and the mechanical properties of Polycarbonate (PC)/Polypropylene (PP) blends prepared by injection molding were studied. This study presents an analysis of impact resistance, tensile properties and morphology of the raw materials and the blends at different compositions. The blends, before being injected, were prepared in a twin-screw extruder by different sequences of blending. The results indicate that the blending sequence and the presence of humidity significantly affect the properties and morphology of the blends. For ternary blends (PC/PP/Kraton), only one-step mixing before injection molding proved to be sufficient to improve mechanical properties. Increasing the amount of blending steps did not present a significant change in properties. With the addition of the interfacial agent, higher impact resistance and particle size reduction were observed.     

Selective self-assembly of surface-functionalized carbon nanotubes in block copolymer template

Microphase-separated styrene-butadiene-styrene (SBS) triblock copolymer was utilized as a template for the selective self-assembly of polystyrene (PS)-functionalized carbon nanotubes (CNTs) in the PS phase. It was also found that PS-functionalized CNTs could be accommodated in the PS phase of SBS regardless of the molecular weight of the PS ligand. This is different from the case for assembling nanoparticles or nanorods with a block copolymer, in which the ligand should be shorter than the corresponding block such that the nanoparticles or nanorods can be incorporated into that block. This phenomenon is explained based on the different chain morphologies of the ligands functionalizing the CNTs, nanoparticles and nanorods.     

影响中空玻璃微珠填充PS复合材料性能的因素

研究了中空玻璃微珠的表面改性和粒径分布,苯乙烯-丁二烯-苯乙烯弹性体(SBS)的加入对聚苯乙烯(PS)/中空玻璃微珠复合材料力学性能的影响.结果表明:硅烷偶联剂KH550对中空玻璃微珠的表面改性效果优于KH560;粒径分布窄的中空玻璃微珠填充PS复合材料具有较高的拉伸强度、弯曲强度和冲击强度:SBS的加入可以提高复合材料的力学性能,尤其可以大幅提高简支梁缺口冲击强度.     

PP／废旧橡胶／SBS复合材料的制备和力学性能研究

通过磨盘型力化学反应器制备PP/废旧橡胶(WTR)复合粉体，然后与SKS共混制备PP/WTR/SBS复合材料。研究了材料的力学性能、微观结构和共混物的加工性质。结果表明：当SBS添加量在20％～25％时，PP/WTR/SBS复合材料的力学性能较PP/WTR有了很大的提高，当SBS用量为25％时，断裂伸长率提高了365％，冲击强度提高了73．2％，而体系的拉伸强度基本不变。复合材料冲击断面的形貌和复合体系流变性能研究结果表明：磨盘碾磨可有效改善各组分间的混合性能，提高相容性并有效改善材料的加工性能。     

Morphology, structure and properties of conductive PS/CNT nanocomposite electrospun mat

The morphologies and properties of Polystyrene (PS)/Carbon Nanotube (CNT) conductive electrospun mat were studied in this paper. Nanocomposite fibers were obtained through electrospinning of PS/Di-Methyl Formamide (DMF) solution containing different concentrations and types of CNTs. The dispersion condition of CNTs was correlated to morphologies and properties of nanocomposite fibers. A copolymer as an interfacial agent (SBS, Styrene-butadiene-styrene type) was used to modify the dispersion of CNTs in PS solution before electrospinning. The results showed that the presence of the copolymer significantly enhances CNT dispersion. The fiber diameters varied between 200 nm and 800 nm depending on CNT type, polymer concentration and copolymer. The final morphological study of the fibers showed that CNT addition caused a decrease in beads formation along fiber axis before percolation threshold. However, addition of CNTs above percolation increased the beads formation, depending on the dispersion condition. The presence of SBS modified the dispersion, reduced the fiber diameter and the number of bead structures. Electrical conductivity measurements on nanocomposite mats of 15-300 μm in thickness showed an electrical percolation threshold around 4 wt% MWCNT; while the samples containing SBS showed higher values of conductivities below percolation compared to the samples with no compatibilizer. Enhancement in mechanical properties was observed by the addition of CNTs at concentrations below percolation.     

Miscibility study of polycarbonate and SBS triblock copolymer blends

Polymer blends of Polycarbonate (PC) and Styrene-Butadiene-Styrene triblock (SBS) have been investigated. SBS copolymers have four different styrenic contents, three of which are linear SBS. PC and PS blends are partially miscible as revealed by dynamic mechanical analysis with two clear Tgs near 100–150°C. On the contrary, PC/SBS blends have only one Tg with a left shoulder. Based on the PS domain model of pure SBS, we suggest a micelle model based on the structure when the micelle and absorb PC in the PC/SBS blends. The micelle plays an important role in improving the miscibility. The proposed micelle model has been empolyed to interpret the testing results, such as toughness, impact strength, dynamic mechanical property and SEM morphologies. This proposed micelle model seems a worth-while method to explain the properties of partialtly miscible blends of PC and SBS.     

Mechanical properties and morphology of crosslinked PP/PE blends and PP/PE/propylene–ethylene copolymer blends

Blending is an effective method for improving polymer properties. However, the problem of phase separation often occurs due to incompatibility of homopolymers, which deteriorates the physical properties of polyblends. In this study, isotactic polypropylene was blended with low-density polyethylene. Crosslinking agent and copolymers of propylene and ethylene (either random copolymer or block copolymer) were added to improve the interfacial adhesion of PP/LDPE blends. The tensile strength, heat deflection temperature, and impact strength of these modified PP/PE blends were investigated. The microstructures of polyblends have been studied to interpret the mechanical behavior through dynamic viscoelasticity, wide-angle X-ray diffraction, differential scanning calorimetry, picnometry, and scanning electron microscopy. The properties of crosslinked PP/PE blends were determined by the content of crosslinking agent and processing method. For the material blended by roll, a 2% concentration of peroxide corresponded to a maximum tensile strength and minimum impact strength. However, the mechanical strength of those products blended by extrusion monotonously decreased with increasing peroxide content because of serious degradation. The interfacial adhesion of PP/PE blends could be enhanced by adding random or block copolymer of propylene and ethylene, and the impact strength as well as ductility were greatly improved. Experimental data showed that the impact strength of PP/LDPE/random copolymer ternary blend could reach as high as 33.3 kg · cm/cm; however, its rigidity and tensile strength were inferior to those of PP/LDPE/block copolymer blend.     

环氧化SBS研究进展

介绍了环氧化苯乙烯-丁二烯-苯乙烯嵌段共聚物(SBS)的合成、表征、结构和性能。分析了由环氧化SBS的特殊性能带来的应用前景。SBS环氧化改性后,其结构和性能发生了变化,特别是耐油性和拉伸性能得到改善,拓宽了应用范围。目前其应用主要集中在粘合剂领域,还有很大的开拓空间。     

Effect of charge groups in polyurethane and polystyrene interpenetrating polymer networks

Opposite charges, namely tertiary amine and carboxyl groups, were introduced into polyurethane (PU) and polystyrene (PS), respectively, to prepare PU/PS interpenetrating polymer networks (IPNs) by means of simultaneous bulk polymerization. Four IPNs were synthesized: a full-IPN, two semi-IPNs and a linear blend. The effect of charge groups on the mechanical properties and morphology of the four polymer alloys was investigated. It is found that the PU/PS IPN which was incorporated with charge groups is free of any phase-separation, and sufficiently uniformly distributed, as can be seen from the corresponding scanning electron microscopy (SEM) photographs. Dynamic mechanical analysis indicates that the transition peak of the loss modulus E″ will move towards the centre between the two transition peaks of both components in the absence of charge groups, as a function of an increase in the contents of the opposite charge groups. Meanwhile the storage modulus E′ will decrease in a single-stage way from the previous two-stage mode. The tensile strength in all the four polymer alloys increased markedly along with an increase in the contents of acrylic acid (AA) in the poly(styrene-acrylic acid) (PSAA), which clearly can be seen for the PU/PSAA full-IPN.     

Dynamic and static properties of SBS triblock copolymer and their blends

By using a dynamic testing method (Rheovibron), it has been established that for a pure triblock copolymer (styrene-butadiene-styrene, SBS), the morphology is composed of a continuous phase, a dispersed phase and an interphase. The predominance of the phase depends upon whether the polymer is cast from a good or poor solvent for each block. For the blends of SBS with PS and PBd, the interphase occupies a greater fraction as indicated by the fact that its corresponding molecular relaxation temperature range is much broader (10°–80°C) than that of pure SBS (60°–80°C). If the blends of SBS with its corresponding homopolymers are heated at 140°C for 45 min, the fraction of the interphase increases significantly and the onset of molecular relaxation is lowered to ?10°C. The viscosities of SBS and their blends are measured by both dynamic and static methods. Complex viscosities calculated from the dynamic method show transitions similar to those of storage moduli. Viscosities at different temperatures from these two methods are superimposed onto master curves.     

Effect of styrene‐butadiene triblock copolymer structure on its compatibilization efficiency in PS/PB and PS/PP blends

Two styrene‐butadiene triblock copolymers differing in the length of their styrene blocks (40S‐60B‐40S and 10S‐60B‐10S) were used as compatibilizers for PS/PB (4/1) and PS/PP (4/1) blends. The supramolecular structure of the copolymers determined by small‐angle X‐ray scattering (SAXS), morphology of the blends using transmission electron microscopy (TEM), and their tensile impact strength were chosen as criteria of the compatibilization efficiency of the copolymers used. Different mechanisms of compatibilization for “symmetrical” system (PS/PB/SBS) and “asymmetrical” system (PS/PP/SBS) were proved. While for the PS/PB blend, the 40S‐60B‐40S copolymer proved to be a good compatibilizer, for the PS/PP blend, surprisingly, the 10S‐60B‐10S copolymer is more efficient.