Showing papers by "Rosario Benavente published in 2012"

Tailoring the Formation Rate of the Mesophase in Random Propylene-co-1-pentene Copolymers

Abstract: The mesophase structuring has been studied by fast scanning calorimetry in a series of random propylene-co-1-pentene copolymers, up to 7.9 mol % of 1-pentene units. It was found that the formation ...

Quality assessment of recycled and modified LDPE/PP blends

Abstract: An experimental study was conducted to investigate the morphology, thermal and mechanical properties of recycled polyolefin blends with different prehistory modified with ethylene propylene rubber (ethylene-propylene diene monomer (EPDM)) using the differential scanning calorimetry (DSC), wide angle X-ray scattering, Fourier transform infrared spectroscopy (FTIR), scanning electron microscope and mechanical methods. The efficiency of the modification was investigated as a function of the modifier content in the range from 7 wt% to 15 wt%. DSC results show that the single polymers are not clean material and contain some quantity of another polyolefins. In the processing and exploitation conditions, there is an increase in imperfect crystals in the postconsumer waste polypropylene. FTIR provides clear evidence about the oxidative processes and mechanical destruction during exploitation and blending. The obtained results proved that the technological and postconsumer wastes could be successfully reused as bl...

Electrical conductivity of new zinc phosphate glass/metal composites

Abstract: Zinc phosphate–glass/metal composites have been successfully prepared. Glass with composition of 45 mol% ZnO–55 mol% P 2 O 5 (ZP) has been filled with metallic powders (nickel and cobalt). The glass matrix thermal stability has been assessed by differential thermal analysis technique. The morphology has been examined by scanning electronic microscopy, showing almost homogenous composites. Comparison between the measured and calculated densities as a function of metallic content exhibits a good coherence and allows the estimation of porosity inside the composites. X-ray diffraction analysis has revealed that the ZP-matrix phase is amorphous when the temperature treatment is below the glass transition temperature T g . However, the principal peaks observed in the case of the composites have been assigned to the metallic crystals of nickel or cobalt fillers. It has been found that the phosphate glass phase is not affected by the growing of the metallic network. The electronic conductivity measurements versus filler volume fraction have been investigated for the first time on phosphate–glass/metal composites. This study has shown the occurrence of a conducting transition at around 30% filler volume fraction. The obtained result has been interpreted on the basis of the statistical percolation theory frame.

Vibration-assisted melt compounding of polypropylene/carbon black composites: Processability, filler dispersion and mechanical properties

Abstract: Composites of polypropylene and carbon black were melt compounded by a vibration-assisted process. For comparison, conventional extrusion was also used for preparation of the same composites. A throughput of the vibration-assisted process was established to be higher than that of conventional extrusion. Microscopic images of the extrudates demonstrated better dispersion of the fillers when the vibration force field was applied. The mechanical properties and viscoelastic behavior of the composites were studied and the results were discussed in the context of the reinforcing action of the fillers and the higher level of polypropylene chain scission accompanying the vibration-assisted process.

Influence of β-nucleation on polymorphism and properties in random copolymers and terpolymers of propylene

Abstract: The competition between α, β, and γ polymorphs has been studied in several random copolymers and terpolymers of propylene, by performing X-ray diffraction and differential scanning calorimetry experiments. Formation of β-crystals, achieved by the addition of a β-nucleating agent, was found to be highly dependent on comonomer type and crystallization conditions. Additionally, the mechanical properties have been evaluated from stress-strain, microhardness and dynamic-mechanical thermal analyses. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

Morphology, thermal properties and mechanical relaxations of metallocene syndiotactic polypropylenes

Abstract: The complex polymorphic behaviour of four syndiotactic polypropylene (sPP) samples have been analysed by means of DSC and WAXD techniques. Two samples (sPP1, sPP2) were synthesised via metallocene polymerization by using the ansa-zirconocene Ph2C(Cp)(9-Flu)ZrCl2 as catalyst. Finally, two additional specimens with different molar masses (sPP1-Fr1, sPP1-Fr2) were prepared from the most syndiotactic sPP1 sample by temperature gradient extraction. The WAXD analysis shows that together with the orthorhombic form I, form II can coexist in a variable but small proportion depending on both the chain features and the processing conditions. The relative contribution of the disordered and the ordered types of form I is also dictated by molar mass, configurational microstructure as well as processing conditions. The observed changes in the thermal properties as measured by DSC and in the mechanic-dynamical relaxations of the samples, on slowing the crystallisation rate down, can be rationalised in terms of two concurrent processes, namely the perfection undergone by the crystals and the segregation of the amorphous phase.

Conductive Composites Based on Metallocene Isotactic Poly(propylene): Preparation and Properties

Abstract: Summary: The research deals with the preparation and the further comprehensive characterization of metallocene polypropylene-based composite materials by incorporation of carbon black nanoparticles. Composites containing up to 10 wt% of carbon black were prepared by direct melt mixing in a single screw extruder Brabender Extrusiograph type 30/25D with attached static mixer at melt temperature of 200 °C and a screw speed of 30 rpm, according to a two-step process. Some composites were treated with 3 wt% maleic anhydride grafted polypropylene (MAH-PP). The rheological behaviour of the miPP nanocomposites was determined by cone/plate rheological measurements at 180 °C. The composites were characterized by SEM for morphological details and uniaxial stress-strain measurements for determining the mechanical parameters. Electric conductivity of injection molded plates from these composites was investigated. The different miPPs studied are ranked in an ascending order according to their increasing molecular weight concerning the magnitude of their rheological parameters. The maleic anhydride compatibilizer leads to lower viscosity values even at high shear gradients and to better homogenization of the nanofiller in the polymer matrix. The processing conditions, carbon black concentration and viscosity of the virgin polymer have an impact on the final conductivity of the miPP/carbon black composites.