TIME-DEPENDENT MORPHOLOGY OF POLYETHYLENE-POLYPROPYLENE BLENDS

The effect of time-temperature treatment on morphology of polyethylene-polypropylene (PE-PP) blends wasstudied to establish a relationship between thermal history, morphology and mechanical properties. Polypropylene (PP)homopolymers were used to blend with various polyethylenes (PE), including high density polyethylene (HDPE), lowdensity polyethylene (LDPE), linear low density polyethylene (LLDPE), and very and ultra low density polyethylene(VLDPE and ULDPE). The majority of the blends were prepared at a ratio of PE:PP = 80:20, while blends of PP and LLDPEwere prepared at various compositions. Thermal treatment was carried out at temperatures between the crystallizationtemperatures of PP and PEs to allow PP to crystallize first from the blends. On cooling further, PE crystallized too. A verydiffuse PP spherulite morphology in the PE matrix was formed in some partially miscible blends when PP was less than 20%by mass. Droplet-matrix structures were developed in other blends with either PP or PE as dispersed domains in a continuousmatrix, depending on the composition ratio. The scanning electron microscopy (SEM) images displayed a fibrillar structureof PP spherulite in the LLDPE-PP (80:20) and large droplets of PP in the HDPE-PP (80:20) blend, providing larger surfacearea and better bonding in the LLDPE-PP (80:20) blends. This explains why the blends with diffuse spherulite morphologyshowed greater improvement in tensile properties than droplet-matrix morphology blends after time-temperature treatment.

Influences of Reactive Compatibilizer R-Styrene-Maleic Anhydride Copolymer on PA6/PP Blends

The effect of R-styrene-maleic anhydride copolymer （R- SMA） compatibilzation on Nylon 6 （ PA6 ）/polypropylene （ PP ） blends has been investigated experimentally through Molan test, microscopic morphology, and chemical structure. Results show that the moderate R-SMA addition can promote reaction between anhydride in R-SMA and amino in PA6, and lead to a new PA6-g- R-SMA copolymer in the blends. Such PA6-g-R-SMA eopolymer in the blends can effectively reduce the interfaeial tension and PP particle size, and improve the compatibility of two immiscible phases in the blends. The crystallinity of PA6 in PA6/PP blends has greatly decreased by PP blends. The blends have the best comprehensive mechanical and thermal properties when the mass ratio of PA6/PP/ R-SMA is 90：10：2 to 90：10：4. The impact strength of the PA6/PP blends with the eompatibilizer is increased by more than 150 %.

Shear-induced Crystallization in Phase-separated Blends of Isotactic Polypropylene with Ethylene-Propylene-Diene Terpolymer

The compatibility between isotactic polypropylene（iPP） and ethylene-propylene-diene terpolymer（EPDM） in the blends was studied. SAXS analysis indicates that iPP and EPDM phases in the binary blend are incompatible. Isothermal crystallization behaviors of iPP in phase-separated iPP/EPDM were studied by in situ POM equipped with a Linkam shear hot stage. It was found that typical spherulites of iPP were formed both in neat iPP and in iPP/EPDM blends. The radial growth rate（d R/dt） of spherulites of iPP in the blend was not influenced by EPDM phases. Further investigations on isothermal crystallization of iPP in iPP/EPDM after shear with a fixed shear time showed that the crystallization rate of iPP in the blends increased with increasing shear rates, whereas, the crystallization rate was much lower than that of neat iPP. WAXD results showed that β-crystal iPP was formed in neat iPP as well as in iPP/EPDM blends after shearing and the percentage of β-crystal bore a relationship to the applied shear rate. The presence of EPDM resulted in lower percentage of β-crystal in the blends than that in neat iPP under the same constant shear conditions. SAXS experiments revealed that shear flow could induce formation of oriented lamellae in iPP and iPP in the blends, and the presence of EPDM led to a reduced fraction of oriented lamellae.