SHOKOUFEH HAKIM | Iran Polymer Inistitute (original) (raw)

Papers by SHOKOUFEH HAKIM

International Symposium on Algorithms and Computation, May 12, 2013

علوم و تکنولوژی پلیمر, 2008

Ethylene was polymerized in slurry phase over a TiCl4/Mg(OC2H5)2 catalyst activated by Al(C2H5)3.... more Ethylene was polymerized in slurry phase over a TiCl4/Mg(OC2H5)2 catalyst activated by Al(C2H5)3. It was shown experimentally that mass transfer resistance has no effect on polymerization kinetics. After estimation ofthe active site concentration by inhibition method with carbon monoxide, the effects of polymerization temperature, monomer and cocatalyst oncentrations and hydrogen were investigated. By determination of the average rate of polymerization at 13 min and 50 min of reaction times it was observed that the polymerization rate was first order with respect to the monomer concentration and the dependence of the polymerization rate on the concentration of Al(C2H5)3 could be described by the Langmuir-Hinshelwood mechanism. The polymerization rate decreased with the increase of hydrogen partial pressure. Polymerization rate as a function of polymerization temperature showed a maximum point.

T he molecular weight and molecular weight distribution were adjusted by controlling polymerizati... more T he molecular weight and molecular weight distribution were adjusted by controlling polymerization process to meet bimodal poly(ethylene-co-1-butene) using Ziegler-Natta catalyst. The process was carried out through two-step polymerization in a semi-batch reactor where in the first step, a low molecular weight homopolymer of ethylene was produced in the presence of hydrogen and in the next step, the high molecular weight copolymer of ethylene with 1-butene was produced after the hydrogen was removed from the reactor. The effects of hydrogen and comonomer concentrations and the polymerization time for the first and second steps were investigated. Although, the second step was run in the absence of hydrogen, the results indicate that shifting the reaction from the first step to the second step leaves potentially some effects on the active centres. The higher hydrogen concentration decreased the rate of polymerization and molecular weight in the first step while, it indirectly raised the rate of polymerization and consequently the yield of reaction at the second step considerably. Increased comonomer concentration in the second step reduced the average molecular weight and increased the melt flow rate while slightly increased the rate of polymerization. It is found that the effect of comonomer concentration on the rate of copolymerization in the second step is lowered by the increase of hydrogen concentration at the first step.

Research subject: Magnesium ethoxide is a metal alkoxide used as a support for preparation of Zie... more Research subject: Magnesium ethoxide is a metal alkoxide used as a support for preparation of Ziegler-Natta catalyst. This important material which is used in HDPE production plants is not produced in Iran. It forms a complex with the catalyst that results in increase of the number of the reacting transition metal atoms inside it. Therefore the catalyst activity increases. The chemical reaction between magnesium and ethanol, in presence of iodine, results in magnesium ethoxide production. Research approach: In this work, by performing analyses such as thermal gravimetric analysis (TGA), BET and scanning electron microscopy (SEM), the effects of reaction conditions such as iodine/ magnesium, ethanol/magnesium, temperature and mixer speed on morphology and characteristics of magnesium ethoxide were investigated. Main results: By using Iodine, proper morphology of product was obtained. The mixer rotation speed didn›t affect the reaction time. The particle size of the product was depend...

MgCl 2 support, dealcoholation, Ziegler-Natta catalyst, polymerization, polypropylene A primary a... more MgCl 2 support, dealcoholation, Ziegler-Natta catalyst, polymerization, polypropylene A primary adduct of MgCl 2 .3.3EtOH (A0) was prepared by melt quenching and then it was further dealcoholated by thermal and chemical methods. In thermal dealcoholation, two different support samples with MgCl 2 .2.7 EtOH (A1) and MgCl 2 .1.8EtOH (A2) formulas were prepared using a controlled temperature-pressure program. XRD spectra of A0, A1 and A2 supports were similar, except with the peaks at 2θ = 8.9 and 9.7 which decreased by moving from A0 to A2. After preparation of support samples, final catalysts were prepared by reacting support samples with TiCl 4 in the presence of diisobutylphthalate as internal electron donor and examined in slurry phase propylene polymerization using TEA as cocatalyst and diphenyldimethoxysilane as external electron donor. The results showed that in the catalysts prepared using thermal dealcoholated supports, surface area and Ti content increase by moving from A0 t...

The rheological behavior, morphology, mechanical and thermal properties and also molecular struct... more The rheological behavior, morphology, mechanical and thermal properties and also molecular structure of in-reactor alloy of Polypropylene (PP)/Ethylene Propylene Rubber (EPR) synthesized by multi-stage sequential polymerization were investigated. The alloys were characterized by RMS, SEM, mechanical testing, DSC, NMR and GPC. The electron microscopy of samples showed that as the switch frequency increased, the size of dispersed phase decreased. Mechanical measurements revealed that impact strength increased when the size of dispersed phase decreased. The small amplitude oscillation rheometry showed that storage modulus and viscosity shifted to higher values when switch frequency increased. NMR results were used for the evaluation of compatibility between the two phases, when switch frequency is changed. DSC results showed that Tm and Tc were almost independent of switch frequency but crystal content in the alloy was be high and ?H increased about 13% when the size of dispersed phase...

Key Words: Investigating the Behaviour of a Bi-supportedSiO 2 /TiCl 4 /THF/MgCl 2 Catalyst inSlur... more Key Words: Investigating the Behaviour of a Bi-supportedSiO 2 /TiCl 4 /THF/MgCl 2 Catalyst inSlurry Ethylene Polymerization: Activity and Molecular Weight Shokoufeh Hakim * , Mehdi Nekoomanesh, and Mehrdad Aghaei Nieat Iran Polymer and Petrochemical Institute, P.O. Box: 14965/115, Tehran, IranReceived 15 September 2007; accepted 16 February 2008 B i-supported catalyst SiO 2 /TiCl 4 /THF/MgCl 2 was prepared via four steps includ-ing, (i) heat activation of silica at 600oC, (ii) preparation of precursor composi-tion, (iii) impregnation of catalyst components on silica, and (iv) catalyst prere-duction with alkyl-aluminium. Homopolymerization was carried out at 3-15 bar pres-sure and 65-85oC temperature. The GPC data was analyzed using the concept ofmultincentre catalysis and four types of active centres detected that differ in molecu-lar weight. The constancy of molecular weight of each active centre with respect tomonomer concentration showed that a bimolecular chain transfer mechanis...

Primary MgCl 2 .3.3EtOH adduct (PCT1) was prepared by melt quenching method and then submitted in... more Primary MgCl 2 .3.3EtOH adduct (PCT1) was prepared by melt quenching method and then submitted into a programmed thermal dealcoholation process using a fluidized bed reactor. During thermal dealcoholation program, different MgCl 2 .nEtOH support samples with n= 3.0, 2.7, 2.4, and 2.1 were selected and named as PCT2 to PCT5, respectively. Structural analysis of the support samples, by moving from PCT1 to PCT5, showed a significant increase in the surface area from 7.4 m 2 /g to 12.8 m 2 /g, together with reduced peak heights at 2θ ≈ 8.9 and 9.7°. After characterization of support samples, the final catalysts were prepared by reaction of the samples with TiCl 4 and tested in slurry phase propylene polymerization. The prepared catalysts showed similar stereospecificities but different activities in polymerization tests, so that, with progression of dealcoholation from PCT1 to PCT2 the catalyst activity was reached its maximum value of 2.9 kgPP/g Cat.h, and then by further dealcoholatio...

sing electron donors in Ziegler Natta catalyst system in propylene polymerization influences the ... more sing electron donors in Ziegler Natta catalyst system in propylene polymerization influences the final properties of polymer's microstructure. This paper is a review which gives an account on the effect of internal and external electron donors on propylene polymerization using Ziegler-Natta catalyst. At first, the mechanism of propylene polymerization is introduced. The internal electron donors are discussed with respect to their interaction with the surface of catalyst support and the resulting polypropylene properties, like molecular weight distribution. Subsequently, the importance of external donors, especially in the third and fourth generations of Ziegler-Natta catalyst is shown. The review further extends the discussion on the effect of alkoxysilanes as external donors in relation to propylene polymerization and activity of catalyst and properties of polypropylene like isospecificity and weight average molecular weight.

Poly(ethylene-g-maleic anhydride) (PEMA)/graphene nanoplatelets (xGn) (PEMA-xGn) composites were ... more Poly(ethylene-g-maleic anhydride) (PEMA)/graphene nanoplatelets (xGn) (PEMA-xGn) composites were prepared by melt dispersion in an internal shear mixer. By adding dicumyl peroxide (DCP), cured poly(ethylene-g-maleic anhydride) C-PEMA was also produced. Different amounts of xGn were introduced into the PEMA in range of 0.5–5 wt. %. The effects of the sequence of feeding additives into the mixer on gel content, morphology, and mechanical properties allowed thermal, dynamic mechanical, and rheological behaviors to be studied. Results demonstrated that the incorporation of graphene into the polymer matrix decreased gel content and the rate of crosslinking. Scanning electron microscopy micrographs of the PEMA and C-PEMA nanocomposites showed that below 1 wt. % graphene, its dispersion in the matrix was desirable with no agglomerates.. Crystallization temperature increased due to heterogeneous nucleation by xGn. By curing the nanocomposites with DCP, crystallization temperatures decrease ...

Three polypropylene samples (1-3) were synthesized with a 4th generation Ziegler-Natta catalyst i... more Three polypropylene samples (1-3) were synthesized with a 4th generation Ziegler-Natta catalyst in the presence of cyclohexyldimethoxymethylsilane (donor c), dicyclopenthyldimethoxysilane (donor d) and diisopropyldimethoxysilane (donor p), respectively, as external electron donors. The physical properties of the synthesized polypropylenes were determined. For samples 1 to 3, Successive self-nucleation and annealing (SSA) and Fourier transform infrared spectroscopy (FT-IR) analyses indicated that the relative content of the fraction with high isotacticity and regularity in conformational structure decreased in contrast with the fraction of low isotacticity and low uniformity in stereo-defect distribution from sample 1 to 3. The results demonstrated that the longer the isotactic sequence length and the less uniform the stereo-defect distribution, the greater the conformational order. Deconvolution of the molecular weight distribution curves indicated that the stability of the active c...

Polymer Composites, 2017

PA-6/PVB blends and related nanocomposites with organoclay were prepared via melt-processing and ... more PA-6/PVB blends and related nanocomposites with organoclay were prepared via melt-processing and structure-property relationships were comprehensively investigated. The SEM observations showed that blend composition and organoclay content play significant roles in the development of morphology. The differential scanning calorimetry results revealed occurrence of fractionated crystallization in the blends due to development of co-continuous morphology. In contrast, the degree of fractionated crystallization decreased in the nanocomposites owing to role of the nanoclay as heterogeneous nucleating agent. It was found that there is an interesting relationship between morphology development and dynamic mechanical properties of the blends. Furthermore, the effects of the morphology development and nanoclay on the viscoelastic behavior of the nanocomposites were synergistic and/or counteracting depending on the Cloisite 30B content. The PA-6/PVB blends with co-continuous morphology showed outstanding toughness. In addition, the PA-6/PVB50 blend with low nanoclay concentration exhibited high impact strength, which was originated from low interparticle distance between PVB domains in the matrix.

Journal of Polymers and the Environment, 2019

Various PVA/nanoclay hydrogel nanocomposites with different weight fractions of nanoclay (0, 0.25... more Various PVA/nanoclay hydrogel nanocomposites with different weight fractions of nanoclay (0, 0.25, 0.5, 0.75 and 1) were prepared, characterized and their performances were investigated. The structures of the synthesized hydrogel nanocomposites and the samples loaded with a potassium phosphate fertilizer were proved by FTIR spectroscopy method. The interactions between the hydrogels and nanoclay and also the effect of fertilizer loading capacity on the nanocomposites were investigated using TGA method. TGA showed that the loading of the fertilizer decreased the hydrogel weight loss which was affected by the nanoclay weight percent. In addition, the effects of glutaraldehyde as crosslinking agent and incorporation of the nanoclay and fertilizer on the glass transition temperature of the prepared hydrogels were studied using DSC method. The Tg of the hydrogels increased by adding the nanoclay and decreased with the loading of the fertilizer. The SEM images showed that the microstructure and morphology of the hydrogel changed in the presence of the nanoclay and fertilizer. The increase of the nanoclay decreased the porosity of the hydrogel and made it denser. Furthermore, the EDX spectroscopy images of the samples proved the uniform dispersion of the fertilizer and nanoclay in the prepared hybrid hydrogels. The swelling of the hydrogels decreased with increasing of the nanoclay weight percent. The results showed that the swelling under load was the highest for the hydrogel nanocomposite with 0.5 wt% of the nanoclay. The increase of the nanoclay led to increasing of the physical networking that caused more desirable controlled release of the fertilizer.

Polymer Bulletin, 2018

This work reports migration and distribution of the plasticizer of PVB phase during processing of... more This work reports migration and distribution of the plasticizer of PVB phase during processing of the PP/waste PVB blends. Storage modulus of the blends and glass transition temperature of the PP and PVB phases revealed that some part of the plasticizer of the waste PVB migrated to PP matrix and interface. This observation was further investigated from thermodynamic points of view. The calculations of solubility parameter, surface tension, and interfacial tension for the blend components helped to interpret the migration phenomenon. The obtained data confirmed relative tendency of the plasticizer to migrate to PP phase and interface. Furthermore, the effects of plasticizer migration on behavior of the blends were studied. It was shown that plasticizer can significantly affect the rheological properties of the compatibilized PP/PVB blends.

Iranian Polymer Journal, 2017

~30 °C higher than 480 °C of the unmodified one). Such increase was not observed for the NH 3 /MA... more ~30 °C higher than 480 °C of the unmodified one). Such increase was not observed for the NH 3 /MAO/DDA treatment system. Dynamic mechanical analysis showed an increase in the elastic modulus of the nanocomposite samples prepared by modified nanoclay particles, as well. Meanwhile, modification of the nanoclay particles by NH 3 led to the highest elastic behavior compared to the other modification systems. It was about 4.6 GPa which was 28% higher than the elastic modulus of the nanocomposite prepared by unmodified nanoclay particles.

Polymer Science Series A, 2015

Polypropylene was synthesized with a fourth generation of Ziegler—Natta catalyst and in the prese... more Polypropylene was synthesized with a fourth generation of Ziegler—Natta catalyst and in the presence of mixed and individual external donors, namely cyclohexyl dimethoxymethylsilane and dicyclopenthyl dimethoxysilane. A synergic effect on molecular weight and polydispersity index and changes in crystallinity and crystallization peak temperature with change in molar ratio of donor C to D were observed. The SSA results and related statistical parameters showed that in spite of close average stereo-regularity, the stereodefect distribution differences among the samples obtained with mixed external donors were so vast. The influence of mixed and individual external donors on active site distribution was studied and the results are discussed. The relationship between the crystallinity, molecular weight, stereo-defect distribution and dynamic and mechanical properties of samples was investigated.

Polymer Science Series A, 2016

The interfacial adhesion and molecular structure of an in-reactor polypropylene/ethylene propylen... more The interfacial adhesion and molecular structure of an in-reactor polypropylene/ethylene propylene rubber alloy were studied with respect to the rheological behavior and final properties of the alloy. The polymer alloys have similar structural parameters but different impact properties. The samples were characterized by gel permeation chromatography, thermal analysis, rheological analysis and mechanical testing. Fractionation of samples showed that the quantities of components are the same. Gel permeation chromatography results showed that molecular weight distribution of all components were similar. Thermal analysis results showed that the crystal size of two samples was the same but the crystal contents were different. In studying the impact strength, it was revealed that a large difference exists between the two samples. The small amplitude oscillation rheometry indicates that the rheological parameters have a glaring difference in both samples that can be an evidence of interfacial adhesion in the in-reactor alloys having so many similar structural parameters.

RSC Advances, 2016

In this study, compatibilized PP/PVB blends were prepared and their morphological, dynamic mechan... more In this study, compatibilized PP/PVB blends were prepared and their morphological, dynamic mechanical, rheological and Izod impact strength properties were investigated.