POLYOLEFINS JOURNALS
Year:2015 | Volume:2 | Issue:2|Papers Count:7

Since November 2012, when Polyolefins Journal (POJ) first accepted submissions, and subsequently on January 2013, when it published its first issue, the Journal has grown and the number of submitted articles has increased steadily during the two years period from 2013-2015. The positive response to the Journal’s launch, and relative increase in issue - by - issue submission/ publication, speak for the cautious acceptance of the Journal in the established field of polyolefins.Nonetheless, we are still quite a distance away from the ideal situation where, the number of acceptable submissions would secure, after the stringent peer-reviewing selection process, a sufficient number of accepted research and review articles needed for each issue’s publication.To review and discuss all topics related to current and foreseeable shortcomings of the Polyolefins Journal, during a two- hour meeting, a restricted editorial board was held on Sunday 22/04/2015 at the IPPI site in Tehran.

In Ziegler-Natta olefin polymerization, the pore architecture of catalysts plays a crucial role in catalytic performances and polymer properties. While the type of preparation routes (such as chemical reaction and solution precipitation) greatly affects the catalyst pore architecture as a result of different solidification mechanisms, the modification of the pore architecture within a given route has been hardly achieved. In this study, we propose a simple way to vary the pore architecture of Mg (OEt)2-based Ziegler-Natta catalysts by the addition of a second alcohol. It was found that the addition of a second alcohol during Mg (OEt)2 synthesis affected not only the morphology of Mg (OEt)2 macroparticles but also the shape of building units. The degree of alternation was found to be sensitive to the molecular structure of a second alcohol. Noticeable influences were observed in the case of branched alcohols, where the transformation of plate-like building units to cylindrical ones led to the generation of totally different pore size distributions of resultant catalysts.

Several types of hybrid catalysts are made through mixing of 4th generation Ziegler-Natta (ZN) and (2-PhInd) 2ZrCl2 metallocene catalysts using triethylaluminum (TEA) as coupling agent. Response surface methodology (RSM) is used to evaluate the interactive effects of different parameters including amounts of metallocene and TEA and temperature on metallocene loading. Analyzing the amounts of Al and Zr elements in the hybrid catalysts through ICP-OES and EDXA reveals that temperature plays a crucial role on anchoring of the metallocene catalyst on ZN while TEA has the least determining effect. The ICP analysis shows that as the concentration of Al goes up in the hybrid catalyst the concentration of Zr passes a maximum, while EDXA shows a direct relationship between the Al and Zr contents. Using triisobutylaluminum (TIBA) and methylaluminoxane (MAO) as the coupling agents, almost similar metallocene loadings are observed. Finally, the performance of hybrid catalysts is investigated in propylene polymerization and the obtained polymers are characterized using DSC and DMTA through which the presence of two types of polymers in the final product are confirmed.

The olefins polymerization process in a slurry reactor is discussed. The reaction rate dynamics was analyzed and the contributions of feed flow, gas-liquid mass transfer, polymerization reaction, and catalyst deactivation were estimated. The propylene solubility in a solvent mixture “heptane” was calculated using Soave-Redlich-Kwong equation of state. These data were then approximated by Henry-like equation and the results were verified in experiments. The influence of propylene dissolving in ”heptane which was examined in special experiments without catalyst has provided the independent estimation of gas-liquid mass transfer coefficient. It has been shown that the reaction rate during the first 20-30 min of test is much lower (or higher) than total monomer consumption, depending on reactant addition sequence. The method of kinetic experiments interpretation and corresponding mathematical model are proposed. The method enables to estimate the kinetic parameter of monomer dissolution, the reaction rate constant of polymerization, as well as the parameters of active centers transformation-activation, deactivation and self-regeneration. An adequacy of model was proved by the description of experiments at two different pressures but with the same parameters values.

Nanocomposites based on polyamide 6 (PA6) and poly (ethylene-co-1-butene) -graft-maleic anhydride (EB- g -MAH) blends have been prepared via melt mixing. The effect of blend ratio and organoclay concentration on the crystallization and melting behavior of specimens were studied. Three types of commercial organo-modified clay (Cloisite 30B, Cloisite 15A and Cloisite 20A) were employed to assess the importance of the nanoclay polarity and gallery distance. The crystallization behavior was investigated using differential scanning calorimetry (DSC) and wide angle X-ray diffraction spectroscopy (WAXD). The strong interactions between amine end groups of PA6 and maleic anhydride groups of EB-g-MAH led to complete inhibition of EB-g-MAH crystallization according to the DSC results. A transformation from the α form to the γ form crystals of PA6, induced by both organoclays and EB-g-MAH, was monitored by WAXD and DSC. Small angle X-ray scattering (SAXS) was used to evaluate the morphology of nanocomposites. Moreover, transmission electron microscopy (TEM) was conducted to determine the location of organoclays and indicated that the organoclays mainly present in the PA6 matrix and rarely distribute in the EB-g-MAH phase in the case of low polarity organoclays. It was also evidenced that the organoclay with the most affinity to PA6 (Cloisite 30B) had the largest effect on the thermal and crystallization behavior of this phase in the blend.

HDPE monofilaments were obtained using different extruders and drawn by post-extruder equipments. After solidification, drawn and undrawn monofilaments (draw ratio 7: 1) were irradiated with 10 MeV electron beams in air at room temperature at 25, 50, 75, 100 and 125 kGy doses to induce a network structure. The phenomenon of the HDPE crosslinking was studied on the basis of gel content measurements. The fibers were examined by differential scanning calorimetry (DSC) and mechanical properties measurements. It was noted that the gel fraction increased with the irradiation dose up to 75 kGy and showed a significant increase with draw ratio, but at higher doses remained without considerable change. Melting temperature of drawn fiber increased with raising irradiation dose but decreased in undrawn sample. Also a bimodal endotherm peak was observed for drawn polyethylene irradiated in air. The changes in melting temperature and appearance of bimodal endotherm were related to the radiation chemistry of polyethylene in the presence of oxygen and interlamellar interactions. Heat of fusion and degree of crystallinity slightly increased for undrawn and drawn samples but, heat of crystallization was reduced by increasing irradiation dose due to the increase in the degree of crosslinking. The results of mechanical properties revealed that no significant changes occurred in Young’s modulus by increasing irradiation dose. As a result of oxidative degradation happened by the presence of the oxygen molecules during the irradiation process, the tensile properties of irradiated fibers decreased but elongation-at-yield for undrawn and elongation-at-break for drawn fibers boosted by increasing irradiation dose up to 125 kGy.

Atwo-dimensional (2D) single particle model for the copolymerization of propylene-ethylene with heterogeneous Ziegler-Natta catalyst is developed. The model accounts for the effects of the initial shape of the catalyst and carck/ pore patterns on the copolymer composition, polymerization rate and average molecular weight properties.The spherical and oblate ellipsoidal shapes of catalyst particle and four different pattern distributions of cracks and pores in a growing particle are studied in this simulation. It is assumed that the diffusion coefficient of monomers in the cracks/pores is 10 times higher than that in the compact zone of the particle. In other word, the cracks are distinguished from the parts with higher monomer diffusion coefficient. The dynamic 2D monomer diffusionreaction equation is solved together with a two-site catalyst kinetic mechanism using the finite element method.The simulation results indicate that the initial shape of catalyst changes the average copolymer composition only in the early stage of polymerization, but the crack/pore patterns in the growing particle have a strong impact on the copolymer composition in the polymer particles due to the change of mass transfer limitations.