Ke Wang

Radial growth rate of spherulites in polypropylene/barium sulfate composites

Abstract The effect of barium sulfate (BaSO4) on the spherulite radial growth rates of isotactic polypropylene (PP) was studied by means of optical microscopy. The PP–BaSO4 interface was modified by treating the fillers with different couple agents. The addition of BaSO4 depresses the spherulite growth rate, and the effect is more dramatic when the interfacial interaction between the PP and BaSO4 was enhanced. The data were analyzed with the Lauritzen–Hoffmann secondary nucleation theory, and the results demonstrated that the enhanced PP–BaSO4 interaction promotes the particles to serve as physical crosslinking points, which hinder the movement of the polymer chains and results in a decrease of the pre-exponential factor, G0.

Microstructures and fracture behavior of glass-fiber reinforced PBT/PC/E-GMA elastomer blends: 1 : Microstructures

Abstract A group of glass-fiber-reinforced polymer composites with controlled morphology were designed and prepared by sequential compounding of poly(butylene terephthalate)/glass-fiber (PBT/GF) composite with a reactive elastomer, ethylene-co-glycidyl methacrylate (E-GMA), and/or polycarbonate (PC). The microstructures of the composites were characterized by means of AFM, SEM and thermal analysis. The results indicate that the glass fiber was surrounded by a dead layer of PBT. In the matrix, the E-GMA particles, of sizes varying between 0.5 and 1 μm, were encapsulated by the PBT phase. The PBT and PC formed an interconnected phase structure with a PBT domain thickness of about 1 μm and the PC domain thickness of less than 0.5 μm. It was found that when the PBT/GF was mixed with the E-GMA in the first step of the sequential blending, the epoxide groups in the E-GMA tended to homo-polymerize through ring-opening rather than to react with the carboxyl and/or hydroxyl groups of the PBT. Consequently, a slightly cross-linked structure formed in the E-GMA phase, which kept the E-GMA domains to stay in the PBT phase during the second step of the sequential blending with the PC. On the other hand, the transesterification between the PBT and the PC resulted in a decrease in the PBT chain regularity, leading to a lower crystallization rate and formation of crystallites with low perfection.

Low density polyethylene-polypropylene blends: Part 2 - Strengthening and toughening with copolymer

Abstract The strengthening and toughening of low density polyethylene (LDPE)-polypropylene (PP) blends with a commercial ethylene/propylene block copolymer (CO) have been investigated. It is shown that the addition of the copolymer improved the ductility of the LDPE-PP blends without any loss of elastic modulus. Particularly for the PP rich LDPE-PP blends, the copolymer can improve the ductility, tensile strength and impact strength simultaneously. It was found that the copolymer has no obvious influence on the crystallisation behaviour of the LDPE and PP phases, whereas the interfacial adhesion was enhanced significantly. The results suggested that the ethylene/propylene block copolymer is a suitable compatibiliser for LDPE-PP blends, which can be used as an effective additive for the recycling of the polyalkene mixtures, especially the PP rich LDPE-PP mixtures.

Low density polyethylene-polypropylene blends: Part 1 - Ductility and tensile properties

Abstract The composition-property relationships of LDPE-PP binary blends have been investigated. Youngs modulus, yield strength and flexural strength of the blends varied monotonically with composition, whereas the elongation at failure and the true ultimate tensile strength for the blends with 30-50 wt-% PP exhibited synergetic effects. These blends showed strong cold draw hardening, and their elongations at failure and the true ultimate tensile strengths were much higher than those of the neat components. Meanwhile, impact strength showed an abrupt reduction with increasing PP content and the failure mode changed from ductile to brittle in the composition range of 30-50 wt-% PP. Failure mechanisms are discussed, addressing interfacial adhesion between LDPE and PP and the non-uniform shrinkage of the component domains upon cooling.

Effect of interfacial modification on the rheological properties and nucleation behaviour of PP-BaSO4 composites

Polypropylene-barium sulfate (PP-BaSO4) composites were prepared by pretreating the filler with stearic acid, silane and polypropylene-g-maleic anhydride, respectively. The effects of the PP-BaSO4 interfacial interaction on the rheological properties and nucleation behaviour of the composites were studied. Surface treatment with reactive coupling agents enhanced the matrix-filler interfacial interaction and caused an increase in the melt viscosity, whereas the use of non-reactive coupling agents reduced the particle-particle interaction and led to a decrease in melt viscosity. The plain BaSO4 had a weak nucleating effect on PP. When the PP-BaSO4 interaction was enhanced, a remarkable increase in nucleation activity of the filler was observed. It is suggested that the enhanced adsorption of PP molecules onto the BaSO4 surface is of benefit in lowering the thermodynamic potential barrier for the formation of primary nuclei.