Mechanical,Thermal, and Surface Properties of Ultrahigh Molecular Weight Polyethylene/Polypropylene Blends

Various compositions of ultrahigh molecular weight polyethylene/polypropylene (UHMWPE/PP) blends were prepared in decalin, with the rheological, mechanical, thermal, and surface properties of the blends being determined using the solution cast film. Viscosity and mechanical properties of the blends decreased below the additivity value with increasing PP content implying that PP molecules disturb the entanglement of UHMWPE. Contact angle of the blend films with a water drop increased with increasing content of PP. The atomic force microscope (AFM) images showed that the surface of cast UHMWPE was very smooth whereas that of cast PP was very uneven. For blends, the surface became rough and uneven with increasing content of PP. The melting temperature of PP (T _mP) decreased in the blends with increasing UHMWPE content while that of UHMWPE (T _mU) remained almost constant in blends.     

Polyethylene Structure as a Function of Temperature: An EDXD Investigation

Polyethylene structure has been investigated by energy dispersive X‐ray diffraction (EDXD) as a function of temperature below the melting point, via Rietveld refinement. The behavior was studied at four temperatures, namely 25, 40, 70, and 88°C. In this range the structure undergoes a regular volume expansion that may be expressed in terms of specific volume ratio as V_E/V_25°C=0.991(2)+4.0(5)×10^?4×T(°C). The variation is almost completely taken up by the a cell parameter and results, apart for minor intrachain arrangements, in an increased distance between polymer chains.     

Investigation of the Morphological and Mechanical Properties of Polyethylene Terephthalate (PET)/Ethylene Propylene Diene Rubber (EPDM) Blends in the Presence of Multi-Walled Carbon Nanotubes

In this study the blends of polyethylene terephthalate (PET)/ethylene propylene diene rubber (EPDM) in the presence of multi-walled carbon nanotubes (MWCNT) (1 and 3?wt %) were prepared by melt compounding in an internal mixer. Mechanical and morphological properties of the nanocomposites were investigated. The thermal behaviors of the PET/EPDM nanocomposites were also investigated, by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The results of the mechanical tests showed that the tensile strength, elastic modulus and the hardness of the blends were increased with increasing CNT, while the impact strength and elongation at break decreased. The DSC and TGA results showed an increase of melting temperature (T_m) and degradation temperature of the nanocomposites with the addition of the carbon nanotubes, because the carbon nanotubes serve both as nucleating agents to increase T_m and prevent the composite from degradation to increase the thermal stability. The microstructure of the composites was evaluated through field emission scanning electron microscopy (FESEM) and the results showed a good distribution of the MWCNT within the polymer blend.     

Melt Strength and Extensional Viscosity of Low-Density Polyethylene and Poly(butylene succinate) Blends Using a Melt-Spinning Technique

The melt strength (MS) and extensional viscosity of low-density polyethylene/poly(butylene succinate) (LDPE/PBS) blends were measured using a melt-spinning technique to investigate the effects of extrusion conditions and mixing ratios on the extensional flow. The experimental results indicated that maximal extensional length and MS of the LDPE/PBS blends decreased with an increase of PBS content. The response of the MS to the extrusion rate depended on the components of the blends. The extensional viscosity of the LDPE/PBS blends decreased with the increases of PBS content, extrusion rate, and extensional strain rate. Extensional master curves were suitable for the LDPE/PBS blends, and the scaling factor decreased with the increase of extrusion rate according to a power law. When the PBS content was not more than 40%, with the further increase of the PBS content, the sensitivity of the scaling factor to the extrusion rate decreased. However, when the PBS content was 60%, the sensitivity of the scaling factor to the extrusion rate increased, and was close to the sensitivity of the LDPE melt. Based on the extensional master curve and the back propagation (BP) neural network model, predicted extensional viscosities were compared with the experimental results.     

Statistical Analysis of Morphology of Low Density Polyethylene/Polyamide 6 Blends with Addition of Organoclay and Maleic Anhydride-Grafted Polystyrene-b-Poly(Ethylene-co-Butene-1)-b-Polystyrene Copolymer As Compatibilizers

Statistical analysis of the size distribution of a polymer minor phase droplets was successfully applied for the characterization of the morphology in a LDPE/PA6 blend (75/25 wt/wt) obtained after mixing with added SEBS-g-MA(S) compatibilizer and/or organoclay 20A. It was shown that the developed approach provided detailed analysis of the morphology development in the polymer blends, including the primary droplets formation of the minor polymer phase and their break-up and coalescence. The introduction of organoclay increased the break-up of primary droplets and completely suppressed their coalescence. The addition of compatibilizer S, in contrast to nanoclay, did not suppress coalescence but the mean size of the primary droplets as well as the droplets formed at coalescence was strongly reduced. The combined addition of compatibilizer S and nanoclay did not change the morphology development of the LDPE/PA6 blend. Both processes of the droplet transformation were accelerated, similar to the system with addition of compatibilizer S only. However, an increase of nanoclay amount disturbed the break-up of the primary droplets, and the mean size of these droplets increases. Thereafter, the mean size of droplets formed at coalescence also increased. The results of statistical analysis of the phase morphology were found to correlate with the mechanical properties of the polymer blends. The fine dispersion of the minor polymer phase improved the stiffness of the polymer blends. For enhanced impact properties, the presence of relatively broad distribution of the minor polymer phase was necessary.     

Rheological Properties of Polyethylene Glycol (PEG 35000): An Interpretation of a Negative Intrinsic Viscosity and a High Huggins Coefficient Value

The effect of temperature on the intrinsic viscosity and the Huggins coefficient of polyethylene glycol (PEG 35000) in aqueous solution was studied. The intrinsic viscosity became negative for temperatures higher than 45°C. Two hypotheses are given to explain this tendency. We demonstrated that the mobility and size of the PEG molecules did not give full information concerning the causes of the negative intrinsic viscosity values. The Huggins coefficient variation was also studied. A peak around 45°C was observed where only the hydrodynamic interactions were present, confirming the transition from a soft to a hard sphere conformation. Above 45°C, the decrease of the Hugging coefficient showed that attractive interactions were responsible for the negative intrinsic viscosity values.     

Interaction of Ga<Subscript>3</Subscript> cluster with molecular hydrogen: combined DFT and CCSD(T) theoretical study

We have explored the lowest doublet and quartet potential energy surfaces (PES) for the reaction of gallium trimer with H₂. This reaction was studied experimentally by Margrave and co-workers in a noble gas matrix. The detailed reaction paths ending up with the low-energy Ga₃H₂ hydride isomers have been predicted based on the high level ab initio coupled-cluster calculations (CCSD(T)) with large basis set. We have found that the reaction occuring on the lowest doublet PES is described by the activation barrier for H₂ cleavage of about 15 kcal/mol, consistent with experiment. In the most stable Ga₃H₂ hydride structure, whose formation is exothermic by 15 kcal/mol, both H atoms assume three-fold bridged positions. The diterminal planar structure of Ga₃H₂, proposed experimentally from the observed IR spectra, is found to be only 1 kcal/mol less stable than the dibridged form.