Florian Stricker

Morphology and mechanical properties of blends of isotactic or syndiotactic polypropylene with SEBS block copolymers

Blends of poly(styrene)-block-poly(ethene-co-but-1-ene)-block-poly(styrene) (SEBS) with isotactic polypropylene (PP) and syndiotactic PP, respectively, were investigated. The morphology was observed by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The cryofracture surfaces studied by SEM did not show any particles that were pulled out, so that a good compatibility between SEBS and different PPs could be assumed. The multiphase character of the blends could be well detected by TEM of RuO4 stained samples. TEM micrographs of two-layer specimens revealed that SEBS tends to diffuse into the PP phase under formation of micelles. The block copolymer shows a reorientation phenomenon of large domains at the interface before the diffusion into the PP phase occurs. The interfacial strength as a function of annealing time was measured by a peel test of two-layer specimens. Mechanical properties are studied and related to the blend morphology.

Influence of rubber particle size on mechanical properties of polypropylene–SEBS blends

Isotactic polypropylene blends with 0–20 vol % thermoplastic elastomers were prepared to study the influence of elastomer particle size on mechanical properties. Polystyrene-block-poly(ethene-co-but-1-ene)-block-polystyrene (SEBS) was used as thermoplastic elastomer. SEBS particle size, determined by means of transmission electron and atomic force microscopy, was varied by using polypropylene and SEBS of different molecular weight. With increasing polypropylene molecular weight and, consequently, melt viscosity and decreasing SEBS molecular weight, SEBS particle size decreases. Impact strength of pure polypropylene is almost independent of molecular weight, whereas impact strength of polypropylene blends increases strongly with increasing polypropylene molecular weight. The observed sharp brittle–tough transition is caused by micromechanical processes, mostly shear yielding, especially occurring below a critical interparticle distance. The interparticle distance is decreasing with decreasing SEBS particle size and increasing volume fraction. If the polypropylene matrix ligament between the SEBS particles is thinner than 0.27 μm, the blends become ductile. Stiffness and yield stress of polypropylene and polypropylene blends increase with increasing polypropylene molecular weight in the same extent, and are consequently only dependent on matrix properties and not on SEBS particle size.

Mechanical and thermal properties of syndiotactic polypropene filled with glass beads and talcum

Glass bead- and talcum-reinforced polypropene composites based on syndiotactic polypropene (s-PP) and isotactic polypropene (i-PP) were prepared to study mechanical and thermal properties and to identify influence of PP type and stereoregularity. Composites based on s-PP gave higher notched Izod impact strength than those based on i-PP, accompanied by lower Youngs modulus and yield stress. The experimental Youngs moduli and yield stresses of composites based on highly stereoregular s-PP and i-PP were in good agreement with theoretical predictions according to Kerner and Nicolais-Narkis, respectively. The higher relative Youngs modulus and yield stress of composites based on s-PP of low stereoregularity were attributed to strong interfacial adhesion and can be described by the theory of Jancar. Lap shear tests confirmed strong glass polymer interactions. Investigations of crystallization show the nucleating effect of glass beads and talcum in the case of i-PP as well as s-PP. With increasing filler volume fraction, PP degree of crystallinity decreases. Dynamic mechanical analysis of glass bead-reinforced s-PP composites show an unexpected relaxation occurring at 55°C.

Compatibilized Polypropylene Hybrid Composites: Influence of Elastomeric Interlayers on Mechanical Properties and Nucleation Behaviour

Two families of polypropylene hybrid composites were prepared by simultaneously compounding polypropylene at 240°C together with SEBS thermoplastic elastomers and filler particles, for example, anisotropic talc and isotropic glass beads. Addition of SEBS was compared with that of maleic-anhydride-grafted SEBS (SEBS-g-MA) to study the role of SEBS compatibility with fillers, especially formation of elastomeric interlayers, on mechanical properties, morphology and nucleation behaviour. At a constant filler volume fraction of 10 vol.%, SEBS and SEBS-g-MA addition were varied between 0 and 20 vol.%. Due to coupling of amino groups at the glass-bead surface with succinic anhydride side chains of SEBS-g-MA, filler particles were encapsulated in a SEBS shell. The improved interfacial adhesion of SEBS-g-MA with respect to SEBS was reflected by higher yield stresses of the compatibilized hybrid composites. Such interlayers were detected by means of transmission electron microscopic imaging of thin sections of talc-based hybrid composites. Investigation of crystallization by means of polarized light microscopy revealed that elastomeric interlayer formation via in situ filler encapsulation markedly reduced filler-induced nucleation of polypropylene crystallization.

Influence of glass bead fillers on phase transitions of syndiotactic polypropene

Abstract The influence of glass beads on the phase transition of syndiotactic polypropene has been investigated. The glass transition at 4°C, detected by means of dynamic mechanical analysis, and multiple melt behaviour, detected by means of differential scanning calorimetry (DSC), does not depend upon the presence of glass bead fillers. However, dynamic mechanical analysis shows an unexpected phase transition at 55°C. This transition, which is not found for neat syndiotactic polypropene, can be also detected by DSC and pressure–volume–temperature (PVT) measurements. The signal detected by PVT appears at higher temperatures, due to higher pressure during measurement. Wide angle X-ray scattering (WAXS) measurements reveal that neat syndiotactic polypropene crystallizes in unit cell II, whereas glass bead-filled syndiotactic polypropene crystallizes in unit cells I and II. Glass bead-filled syndiotactic polypropene, heated up above 60°C, shows a WAXS pattern corresponding to unit cell II. From these results, it can be concluded, that glass beads can nucleate the formation of unit cell type I, which transforms into unit cell type II upon heating at 55°C.

The influence of metallocene-based LLDPE on polypropene compounds in the presence of SEBS and talcum

The influence of metallocene-based poly(ethene-co-1-butene) (linear low-density polyethylene; LLDPE) containing 10 wt.-% of 1-butene on the compounding of polypropene (PP) in the presence of polystyrene-block-poly(ethylene-co-1-butene)-block-polystyrene (SEBS) and talcum was studied. With increasing LLDPE and SEBS volume fraction, the stiffness and yield stress of PP decrease, due to the low stiffness and tensile strength of the dispersed components. The low impact strength of PP/LLDPE blends, due to weak interfacial interactions, can be improved significantly by simultaneously blending with SEBS. This is due to the compatibilizer function of SEBS, as demonstrated by transmission electron microscopy. The stiffness of the terblends can be enhanced remarkably by addition of talcum, which also acts as nucleating agent for the PP crystallization. So, a new family of compounds was obtained, exhibiting an improved stiffness/toughness balance. Der Einflus von Poly(ethylen-co-1-buten) (lineares Polyethylen niedriger Dichte, LLDPE) mit 10 Gew.-% 1-Buten, das mittels Metallocen-Katalysatoren hergestellt wurde, auf die Compoundierung von Polypropylen (PP) in Anwesenheit von Polystyrol-block-Poly(ethylen-co-1-buten)-block-Polystyrol (SEBS) und Talkum wurde untersucht. Mit steigenden LLDPE- und SEBS-Volumengehalten nehmen Steifigkeit und Fliesspannung von PP aufgrund der geringen Steifigkeit und Festigkeit der dispergierten Komponenten ab. Die wegen geringer Grenzflachenwechselwirkungen niedrige Schlagzahigkeit von PP/LLDPE-Blends kann durch Zugabe von SEBS deutlich erhoht werden. Ursache hierfur ist die kompatibilisierende Wirkung von SEBS, wie transmissionselektronenmikroskopische Untersuchungen zeigen. Die durch den SEBS-Zusatz verursachten Steifigkeitverluste konnen durch Zusatz von Talkum, das gleichzeitig als Nukleierungsmittel fur PP wirkt, kompensiert werden. Die gefullten PP/LLDPE/SEBS-Terblends zeichnen sich gegenuber PP durch erhohte Schlagzahigkeit ohne Steifigkeitsverlust aus.

Rubber-toughened cycloolefin copolymers

The influence of polystyrene-block-poly(ethene-co-but-1-ene)-block-polystyrene (SEBS) on the mechanical properties of metallocene-based cycloolefin copolymers (COC) was studied. COC is an amorphous polymer with very high stiffness and yield stress, but poor impact strength. With increasing SEBS volume fraction the notched impact strength is increasing. Low-molecular-weight SEBS (Mw = 90 000 g mol–1) is more effective as impact modifier than high-molecular-weight SEBS (Mw = 272 000 g mol–1). This is due to smaller particle size obtained when dispersing low-molecular-weight SEBS. With reduced particle size the amount of particles and, consequently, the probability of initiation of micromechanical processes, such as crazes, is increasing. The stiffness and yield stress of COC are decreasing with increasing SEBS volume fraction, due to low stiffness and tensile strength of SEBS. Addition of ultrahigh-molecular-weight polyethene (UHMWPE) does not improve the stiffness/toughness balance. Der Einflus von Polystyrol-block-Poly(ethen-co-but-1-en)-block-Polystyrol (SEBS) auf die mechanischen Eigenschaften von durch Metallocen-Katalyse hergestellten Cycloolefin-Copolymeren (COC) wurde untersucht. COC ist ein amorphes Polymeres mit sehr hoher Steifigkeit und Fliesspannung, jedoch sehr geringer Schlagzahigkeit. Mit steigendem SEBS-Volumengehalt nimmt die Kerbschlagzahigkeit zu. Niedermolekulareres SEBS (Mw = 90 000 g mol–1) ist ein effektiverer Zahmodifikator als hochmolekulareres SEBS (Mw = 272 000 g mol–1). Dies ist auf eine geringere Partikelgrose der dispergierten niedermolekularen SEBS-Phase zuruckzufuhren. Bei reduzierter Partikelgrose nimmt die Anzahl der dispergierten Partikel sowie die Wahrscheinlichkeit einer Crazeinitiierung zu. Steifigkeit und Fliesspannung von COC nehmen mit steigendem SEBS-Volumengehalt wegen der geringen Steifigkeit und Festigkeit des SEBS ab. Durch Zusatz von ultrahochmolekularem Polyethylen (UHMWPE) wurde keine Verbesserung des Steifigkeits/Zahigkeits-Verhaltnisses bewirkt.