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Polyolefins Journal
  • Polymerization Engineering Department

    Iran Polymer and Petrochemical Institute

    P.O. Box:  14975-122

    Tehran

    I.R. IRAN

    Postal Code: 1497713115
  • 0098 21 48662479
Beside Ziegler-Natta and Phillips catalysts the development of methylaluminoxane (MAO) as cocatalyst in combination with metallocenes or other transition metal complexes for the polymerization of olefins has widely increased the... more
Beside Ziegler-Natta and Phillips catalysts the development of methylaluminoxane (MAO) as cocatalyst in combination with metallocenes or other transition metal complexes for the polymerization of olefins has widely increased the possibilities in controlling the polymer composition, polymer structure, tacticity and special properties with high precision. These catalysts allow the synthesis of isotactic, isoblock, syndiotactic, stereoblockor atactic polymers, as well as polyolefin composite materials with superior properties such as film clarity, tensile strength and lower content of extractables. Metallocene and other single site catalysts are able to copolymerize ethene and propene with short and long chained a-olefins, cyclic olefins, or polar vinyl monomers such as ethers, alcohols or esters, especially, if the polar monomers are protected by aluminum alkyls. Different vinyl ethers such as vinyl-ethyl ether, vinyl-propyl ether, vinyl-hexyl ether, and 2,7-octadienyl methyl ether (M...
Ultra-high molecular weight polyethylene (UHMWPE) was synthesized using Bi-supported SiO 2 /MgCl 2 /TiCl 4 (Si-Mg-Ti) Ziegler-Natta catalyst in conjugation with triethyl aluminum (TEA). The impact of temperature and the presence of a... more
Ultra-high molecular weight polyethylene (UHMWPE) was synthesized using Bi-supported SiO 2 /MgCl 2 /TiCl 4 (Si-Mg-Ti) Ziegler-Natta catalyst in conjugation with triethyl aluminum (TEA). The impact of temperature and the presence of a chain-terminating agent were examined in the context of ethylene polymerization. The findings showed that as temperature decreases, the activity of the polymerization decreases, and the molecular weight of the polymer increases. Conversely, in the presence of a chain-terminating agent, the molecular weight of the polymer decreases. The introduction of triethyl borate (TEB) and tetraethoxy silane (TEOS) as an external donor has a pronounced effect on the catalyst activity, causing a significant decrease, while simultaneously leading to a substantial increase in the viscosity average molecular weight (M v). Additionally, when a chain-terminating agent is added along with triethyl borate (TEB) in the system, it results in a significant decrease in molecular weight, albeit with a slight increase in activity compared to a system without a donor. The crystallinity, particle size and bulk density of the polymer synthesized with and without external donor have been also investigated.
In this study, polypropylene (PP) was blended with polylactic acid (PLA) to enhance PP's mechanical properties, such as tensile strength and modulus, and to encourage the adoption of eco-friendly, renewable resource based material in... more
In this study, polypropylene (PP) was blended with polylactic acid (PLA) to enhance PP's mechanical properties, such as tensile strength and modulus, and to encourage the adoption of eco-friendly, renewable resource based material in polymer production. Even though PLA's biodegradability cannot be fully utilized in PP/PLA blends, but PLA can still improve PP's mechanical properties and provide an alternative resource for biobased raw materials. To meet the requirement, PP and PLA were blended in a 70:30 ratios with a compatibilizer and nanosilica at different loading levels by melt-blending. Blends of PP and PLA materials were processed without any problems, since both materials have melting points in the range of 170°C. Despite this, the properties of polymer blends are limited by the immiscibility between these neat polymers. To solve this problem, compatibilizers like polypropylene-graftedmaleic anhydride (PP-g-MA) were added to blends to improve their compatibility. Nanosilica was also added to this compatibilizer to study the system's compatibility and modify the hydrophobicity of PLA. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), tensile strength, and field emission scanning electron microscopy (FESEM) were used to analyze the polymer blend. Results indicate that compatibilizers play a significant role in improving tensile properties, thermal stability, and blend dispersion in the system, mainly in 5 parts compatibilizer-based systems. Composition with 5 parts compatibilizer increases tensile strength of 70/30 blend from 19.7 to 27 MPa, while elongation increases from 2.2 to 3.6 %. Additionally, a composition with 0.7 parts of nanosilica increases the modulus from 1488 to 1732 MPa when compared to the 70/30 blend.
The effect of calcium lactate (CL) and epoxidized soil bean (ESO) on the crystallization kinetics of polypropylene (PP) was investigated by using polarized optical microscopy (POM) and differential scanning calorimetry (DSC) techniques.... more
The effect of calcium lactate (CL) and epoxidized soil bean (ESO) on the crystallization kinetics of polypropylene (PP) was investigated by using polarized optical microscopy (POM) and differential scanning calorimetry (DSC) techniques. The experiments were performed under both non-isothermal and isothermal conditions. The development of spherulitic microstructure and crystallization kinetics were influenced by both CL and ESO. CL is an efficient nucleating agent for the crystallization of PP. The addition of CL facilitated faster spherulite growth and crystallization rate, while reduced the spherulite size. An opposite performance was discovered with the incorporation of ESO. Nucleation effect of CL on the PP crystallization was less effective with the presence of ESO. Compared with PP/CL, PP/CL/ESO provided a large spherulite size, slow spherulite growth, and a low crystallization rate. This is attributed to the ESO inhibiting the nucleation site of CL. However, the degree of crystallinity and the Avrami exponents remained unchanged with the inclusion of both CL and ESO.
Ultra-high molecular weight polyolefin (UHMWPO) has enormous potential applications due to its excellent mechanical properties such as tensile strength, flexural modulus, toughness and outstanding chemical resistance. But the processing... more
Ultra-high molecular weight polyolefin (UHMWPO) has enormous potential applications due to its excellent mechanical properties such as tensile strength, flexural modulus, toughness and outstanding chemical resistance. But the processing of polyolefin, in particular UHMWPO fibers, cannot be processed by conventional methods due to its very high melt viscosity. In this work, we synthesized isotactic ultra-high molecular weight polypropylene (UHMWPP) resin and studied the processability of UHMWPP fibers using gel spinning and investigated physicomechanical properties. UHMWPP gel was made at various concentrations in decalin solvent at 150°C to produce consistent spinning dope solutions. The 7 wt.% concentration of UHMWPP was deemed best for fiber creation, compared to 3 wt.% and 5 wt.%. A rheological time sweep was done to ensure the gel's stability at 170°C before the spinning process. The UHMWPP's gelation and fiber formation were studied by tweaking the gel concentration and adjusting the processing temperature. The resulting UHMWPP monofilament had a measure of 220-250 denier. The hot stretched fibers were analyzed with scanning electron microscopy (SEM) to understand the surface morphology of the fibers. The crystal morphology of UHMWPP fibers was measured with wide-angle X-ray diffractometry (WAXS) and DSC. The X-ray patterns of hot stretched UHMWPP fibers showed crystalline peaks compared to those without stretched fibers.
Polypropylene (PP) is a strong, tough, crystalline thermoplastic material with high performance. Because of its diverse thermo-physical and mechanical properties, it is utilized in a wide variety of disciplines. In this study, the impact... more
Polypropylene (PP) is a strong, tough, crystalline thermoplastic material with high performance. Because of its diverse thermo-physical and mechanical properties, it is utilized in a wide variety of disciplines. In this study, the impact of free quenching on the thermo-physical characteristics of PP/calcium carbonate (CaCO 3) composites was examined. Three distinct heating procedures were used. First, composites were cooled from their melting phase temperature to ambient temperature. Second, composites were cooled from 130°C to a predetermined and controlled temperature (T: 0°, 20°, 30°, 40°, 50°, 60°, 70°, 80°C). Third, composites were temperature-tested using annealing. The findings suggest that the elongation-at-break and impact strength may be improved following an initial quenching process from the melting phase to ambient temperature. On the other hand, a second quenching process at 0°C produces superior results, and a correlation between mechanical and thermal characteristics is noted; however, while these qualities are increased, others, such as flexibility, density, Vicat softening temperature (VST), and heat distortion temperature (HDT) are negatively impacted.
Silane cross-linking of metallocene-based polyethylene-octene elastomer (POE)/linear low density polyethylene (LLDPE) blend was carried out using two-step Sioplas process in an industrial scale twin-screw extruder. In the study, grafting... more
Silane cross-linking of metallocene-based polyethylene-octene elastomer (POE)/linear low density polyethylene (LLDPE) blend was carried out using two-step Sioplas process in an industrial scale twin-screw extruder. In the study, grafting and cross-linking reactions of vinyl trimethoxy silane (VTMS) were analyzed using FTIR technique. It was found that the cured compound showed absorption peaks at 1078 cm-1 and 955 cm-1 related to Si-O-Si bonds. A peak was also observed at 3405 cm-1 of hydroxyl group produced from hydrolysis of methoxyethylene group during of curing process, reflecting that curing reaction was not completed. The samples were cured at different time intervals (15 min-16 hours). The gel content values determined by solvent extraction and FTIR were in good agreement at curing times more than 4 hours. The efficiency of the silane grafting reaction was determined using the ratio of the absorption peak at 1092 cm-1 characteristic of methoxy to the transmittance peak at 1378 cm-1 characteristic of methyl group, which is considered as the internal standard. The results showed the highest efficiency of silane grafting reaction at 5 wt.% of VTMS with the least amount of internal standard ratio (0.029), at which the lowest MFI value, and the highest values for gel content, tear strength, compression set and hot set 200°C were obtained.
The concentration of ethylene and 1-butene in n-hexane as polymerization media was calculated at five different pressure levels (4, 6, 8, 10, and 12 bar) and four different 1-butene concentrations (0.13, 0.26, 0.39, and 0.52 mol/L) in... more
The concentration of ethylene and 1-butene in n-hexane as polymerization media was calculated at five different pressure levels (4, 6, 8, 10, and 12 bar) and four different 1-butene concentrations (0.13, 0.26, 0.39, and 0.52 mol/L) in n-hexane at T= 80°C using the Peng-Robinson thermodynamic equation of state. Some combinations of conditions were selected to perform the copolymerization reaction in the presence of an industrial TiCl 4 /MgCl 2 Ziegler-Natta catalyst. The forms of the synthesized products were visually and qualitatively classified as either powder or sticky. The percentage of incorporated 1-butene comonomer into the polyethylene chains was analyzed using calibrated FTIR tests. It was shown that for ethylene/1-butene concentration ratios (β) in n-hexane above approximately 1.80, the product forms as a powder. For values below 1.30 threshold, the product was sticky. Thus, this ratio could be used as a criterion for selecting the proper combination of copolymerization pressure and 1-butene concentration when aiming to achieve a powdered form of the product. It was shown that β has a strong correlation with the weight percentage of 1-butene in the final LLDPE polymer. Therefore it can be used as an accurate prediction for wt.% of incorporated 1-butene into the LLDPE chain within the studied concentration ranges with the specific catalyst system utilized.
The copolymerization of methyl acrylate (MA) and glycidyl methacrylate (GMA) with 1-hexene was carried out using activator regenerator by electron transfer atom transfer radical polymerization (ARGET ATRP) employing Cu(0)/CuBr 2 as a... more
The copolymerization of methyl acrylate (MA) and glycidyl methacrylate (GMA) with 1-hexene was carried out using activator regenerator by electron transfer atom transfer radical polymerization (ARGET ATRP) employing Cu(0)/CuBr 2 as a catalyst, pentamethyl diethylenetriamine (PMDETA) as a ligand, and ethyl 2-bromoisopropionate (EBriP) as the initiator, all at a reaction temperature of 70°C. This process resulted in the production of viscous and transparent copolymers, namely poly (methyl acrylate-co-1-hexene) or PMH and poly (glycidyl methacrylateco-1-hexene) or PGMH. For the MA/1-Hex copolymer, conversion rates ranged from a maximum of 31 wt.% to a minimum of 12 wt.%, while the GMA/1-hexene copolymer exhibited conversion rates ranging from a maximum of 42 wt.% to a minimum of 12 wt.%. It was observed that increasing the amount of 1-hexene during the synthesis led to a higher incorporation of 1-hexene content in both the MA and GMA polymer backbones, with a maximum of 15 wt.% and 18 wt.% of 1-hexene being incorporated into PMH and PGMH, respectively. The incorporation of 1-hexene was confirmed through Nuclear Magnetic Resonance (NMR) studies, including 1 H, 13 C, and DEPT 135 studies. Additionally, the copolymer PMH and PGMH exhibited monomodal molecular weight distribution curves when evaluated using the size exclusion chromatography (SEC) high-performance liquid chromatography (HPLC) technique, with polydispersity values in the range of 1.19-1.37 and 1.07-1.11, respectively. These findings indicate that the copolymerization process was well-controlled and followed a radical polymerization mechanism.
Date palm tree leaf-reinforced polymer composites have important advantages, such as sustainability and low-cost. In the present study, ternary blend composites of polyvinyl chloride (PVC), low-density polyethylene (LDPE), and... more
Date palm tree leaf-reinforced polymer composites have important advantages, such as sustainability and low-cost. In the present study, ternary blend composites of polyvinyl chloride (PVC), low-density polyethylene (LDPE), and acrylonitrile butadiene rubber (NBR) copolymer (LDPE/PVC: C0, LDPE/PVC/NBR:C1) as well as reinforced composites with 10, 20, and 30 wt.% of alkali treated date palm fiber (TDPF) (C2, C3 and C4 respectively) were fabricated using a melt blending extrusion process. TDPF and the NBR copolymer were used to improve the interfacial bonding, compatibility, and thermo-mechanical properties of the composite, yielding the highest tensile strength of 32 MPa for the composite containing 10 wt.% TDPF. Moreover, the morphological analysis showed that the incorporation of the NBR copolymer enhanced the compatibility of the blend. Mechanical tests revealed that the hardness of the TDPF/PVC/LDPE/NBR composite increased in the order C2 (450 MPa) < C3 < C4 (540 MPa). In addition, the flexural and tensile moduli of the composite increased with increasing TDPF content, with the highest values (534 and 1585 MPa, respectively) observed for composite C4. Thermal analysis revealed increased T onset and T 10% values, indicating an improved thermal stability of the composite. This study clearly demonstrates that the (DPF/PVC/LDPE/NBR) composites can be used in various high-tech engineering applications, which require excellent properties.
Novel EPDM-based polymer foams were prepared using a combination of nanomaterials, namely nano silica, nano clay, and graphene nanoplatelets. In order to achieve optimal acoustic performance, the Taguchi design (TD) technique was applied... more
Novel EPDM-based polymer foams were prepared using a combination of nanomaterials, namely nano silica, nano clay, and graphene nanoplatelets. In order to achieve optimal acoustic performance, the Taguchi design (TD) technique was applied to reduce the number of experiments and optimize the formulation. By employing an orthogonal array of L9(3 4), four controlled factors, including content of the three nanomaterials and the blowing agent (Unicell D200A), were chosen. In practice, the acoustic properties of the nine suggested experiments with TD were examined with an impedance tube, and the signal-to-noise ratio analysis revealed two more optimal formulations for foam composites. Further experiments for the last two formulations compared to the nine Taguchi tests, showed an improvement of 13.04 and 19.68%, respectively, for noise reduction coefficient (NRC) and average transmission loss (ATL). It seemed that the idea of using multiple nanomaterials simultaneously is to be an effective way. Besides, the SEM images of nine samples proved that the smaller cell size of the foam were achieved using the higher concentration of nanoparticles. These findings are in accordance with the acoustic results, as the sample with larger cell size and more open cells (C 3) showed higher NRC and the sample with larger cell size and closed cells (B 2) showed higher ATL values. To complete the study, some blank samples with zero level or only one type of the nanomaterial were also investigated. Interestingly, the obtained results indicated that the formula should contain more than one type of nanoparticle to achieve a better acoustic performance. Comparing the result obtained in this study for EPDM foam with the same EVA foam in our previous work, it can be seen that EPDM showed an increase of 15.56% in NRC and a slight decrease of 2.5% in ATL. This behavior could be due to the difference in their morphology, in which the EPDM has probably more open cells and thinner cell walls.
Ethylene-propylene copolymerization reactions were carried out using rac-Et(2-MeInd) 2 ZrMe 2 catalyst and (2,6-t Bu 2 PhO-)Al i Bu 2 as activator under varying reaction conditions. We demonstrate that reaction conditions such as monomer... more
Ethylene-propylene copolymerization reactions were carried out using rac-Et(2-MeInd) 2 ZrMe 2 catalyst and (2,6-t Bu 2 PhO-)Al i Bu 2 as activator under varying reaction conditions. We demonstrate that reaction conditions such as monomer concentration, Al/Zr molar ratio and solvent type (toluene and heptane) all have significant effect on activity of the system and copolymers composition. The decrease in reaction pressure from 11 to 3 atm leads to: a) 1.6-fold increase in specific activity (from 3030 to 4840 kg copolymer/(mol Zr•h•atm)), b) increase of M n value from 38 to 89 kg/mol, and c) increase of ethylene content in copolymer from 87 to 92 mol %. The increase of ethylene/propylene molar ratio from 0.7 to 2 does not significantly affect activity but leads to the rise in the ethylene content in copolymer from 92 to 97 mol % and, correspondingly, to the increase of copolymer crystallinity from 43 to 48%. As a result, thermal and mechanical properties of the obtained polymers also change, according to the shifts in copolymers composition. The change in Al/Zr molar ratio is confirmed to have great effect on the catalytic activity of our systems. In a row of Al/Zr= 100, 150, 200, 300 mol/mol, the lowest activity of 80 and the highest one of 8550 kg copolymer/(mol Zr•h•atm) are observed at 100 and 150 molar ratios correspondingly. We have also demonstrated the ability of catalytic systems with isobutylaluminum aryloxide activators to operate in aliphatic medium (heptane). On another note, during the reaction quenching, aryloxide activator hydrolyzes the polymer infused with 2,6-di-tert-butylphenol antioxidant. This results in the increased resistance of copolymers to the thermal-oxidative degradation. The presence of 4 wt.% phenol in the copolymer leads to an increase in the 5% mass loss temperature by 67°C. Moreover, increasing the residual phenol content from 2 to 4 wt.% affects the mechanical properties of the copolymers: the elongation-at-break increases from 500 to 600%, and the tensile strength decreases from 10 to 8 MPa.
The time available for proper casting of the polyurethane (PU) system after isocyanate addition (called pot life) affects the macrodiol microstructure. In this research, the effect of molecular weight (Mn) of hydroxyl terminated... more
The time available for proper casting of the polyurethane (PU) system after isocyanate addition (called pot life) affects the macrodiol microstructure. In this research, the effect of molecular weight (Mn) of hydroxyl terminated polybutadiene (HTPB) as an important macrodiol on the pot life of polyurethane system was rheologically investigated. The chemorheological behavior of polyurethane systems based on five different HTPBs with Mn ranging from 2810 to 4450 g/mol and two common diisocyantes (TDI and IPDI) were studied in situ. The results showed that by increasing Mn , the rotational viscosity as well as the constant reaction rate of urethane formation increases; whereas the pot life of the polyurethane system decreases. The pseudoplastic behavior of the samples showed the minimum rate constant/longest pot life at a critical molecular weight (Mc) of about 3100 g/mol, which may be due to physical chain entanglements. Rheomechanical spectrometry interestingly depicted that tan δ originated-gel point occurs before the intersection of stored modulus (G') and loss modulus (G") (t gel < t G'=G"). The kinetic model developed by Hsich showed excellent agreement with the cross-linking data of three polyurethane systems.
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.... more
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.
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... more
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.
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)... more
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.
Heterogeneous Ziegler-Natta and homogeneous metallocene catalysts exhibit greatly different active site nature in olefin polymerization. In our previous study, it was reported that MgCl2-supported titanocene catalysts can generate both... more
Heterogeneous Ziegler-Natta and homogeneous metallocene catalysts exhibit greatly different active site nature in olefin polymerization. In our previous study, it was reported that MgCl2-supported titanocene catalysts can generate both Ziegler-Natta-type and metallocene-type active sites according to the type of activators.The dual active site nature of the supported titanocene catalysts was further explored in the present study: The influence of the ligand structure of titanocene precursors was studied on the nature of active sites when supported on MgCl2 in ethylene and propylene homopolymerization, and ethylene/1-hexene copolymerization. It was found that the reducibility of titanocene precursors by alkylaluminum is closely related to the appearance of the dual active site nature, while the kind of olefin did not affect the type of active sites formed during polymerization. The Ziegler-Natta-type active sites produced poorly isotactic polypropylene and less branched polyethylene, while the metallocene-type active sites produced atactic polypropylene and exhibited much higher incorporation efficiency for 1-hexene.
Monolithic aerogels of high molecular weight polyethylene (Mw= 3x106- 6x106 g/mol) have been prepared by solvent extraction with supercritical carbon dioxide from thermoreversible gels prepared in decalin. These low density and highly... more
Monolithic aerogels of high molecular weight polyethylene (Mw= 3x106- 6x106 g/mol) have been prepared by solvent extraction with supercritical carbon dioxide from thermoreversible gels prepared in decalin. These low density and highly porous aerogels present an apparent porosity up to 90%. The aerogel morphology observed by scanning electron microscopy (SEM) is characterized by spherulitic structures being interconnected by fibers. X-ray diffraction experiments show that PE aerogels are highly crystalline with a degree of crystallinity of c.a. 80% and PE chains being packed into the typical orthorombic unit cell. Combined SEM and N2 sorption investigations show that PE aerogels are essentially macroporous with a small amount of mesopores. The oil-sorption performance of polyethylene aerogels has been also evaluated in this study in order to assess a possible use of these materials for oil spillage recovery and results show that aerogel macropores allow a very fast sorption kinetics with a 100% oil weight uptake obtained in less than 1 minute.
Pyrolysis of low density polyethylene (LDPE) by equilibrium fluid catalytic cracking (FCC) was studied in a stirred reactor under different process parameters. In this work, the effect of process parameters such as degradation temperature... more
Pyrolysis of low density polyethylene (LDPE) by equilibrium fluid catalytic cracking (FCC) was studied in a stirred reactor under different process parameters. In this work, the effect of process parameters such as degradation temperature (420-510°C), catalyst/polymer ratio (0-60%), carrier gas type (H2, N2, ethylene, propylene, Ar and He), residence time and agitator speed (0-300 rpm) on the condensate yield (liquid, gas and coke) and product composition were considered. Reaction products were determined by GC analysis and shown to contain naphthenes (cycloalkanes), paraffins (alkanes), olefins (alkenes) and aromatics. Higher temperature and more catalyst amount enhanced LDPE cracking. The maximum “fuel like” condensed product yield was attained at 450°C and 10% catalyst, respectively and gaseous products increased with increases in temperature. Hydrogen as a reactive carrier gas increased the condensed and paraffinic product yield. Appropriate heat transfer (by stirring) increased the catalyst efficiency in a stirred reactor.
The data on the effect of ethylene concentration on polymerization rate for several modifications of modern highly active titanium–magnesium catalysts TiCl4/MgCl2 are presented. These catalysts differ in titanium content and conditions of... more
The data on the effect of ethylene concentration on polymerization rate for several modifications of modern highly active titanium–magnesium catalysts TiCl4/MgCl2 are presented. These catalysts differ in titanium content and conditions of support preparation, activities, and the shape of kinetic curves. It is found that the observed order of polymerization rate with respect to ethylene in the range of ethylene pressures of 0.5–6 bar is 1.8-2.1 for all catalysts used (polymerization at 80°C, AlEt3 used as a cocatalyst). When AlEt3 was replaced with Al(i-Bu)3, the reaction order decreased to 1.3-1.4. In order to elucidate the possible reasons for the observed high order with respect to ethylene, we analyzed the data on the effect of monomer concentration on the molecular weight of polyethylene. The results gave grounds for suggesting that the observed order with respect to monomer is attributable to the effect of ethylene concentration on the number of active sites. The possible reaction scheme explaining the nonlinear dependence of the polymerization rate on monomer concentration was proposed based on these data.
EEthylene polymerization catalysts became available in an enormous variety. The challenge in this research is to find catalysts that are able to connect ethylene molecules in such a way that not only linear chains are produced but... more
EEthylene polymerization catalysts became available in an enormous variety. The challenge in this research is to find catalysts that are able to connect ethylene molecules in such a way that not only linear chains are produced but variations like branched materials that possess very interesting mechanical properties like linear low density polyethylene (LLDPE). In this contribution, three different types of catalysts are presented that are able to do not only one job at a time but three. These are “intelligent catalysts”. Catalysts of type 1 are homogeneous metallocene complexes that can be activated with methylaluminoxane (MAO).With ethylene they produce their own support and they become heterogeneous catalysts (self-immobilization) and they prevent fouling in polymerization reactors. The produced resin has evenly distributed ethyl branches (without a comonomer) with unique properties and the MAO that is necessary in the activation step can be recycled. Catalysts of type 2 are dinuclear complexes with two different active sites. One centre can oligomerize ethylene and the other one can copolymerize the in statu nascendi produced oligomers with ethylene to give branched LLDPE (a molecule as the smallest reactor for LLDPE) and/or bimodal resins.
Catalysts of type 3 are MAO activated iron di (imino) pyridine complexes that are able to oligomerize ethylene to give not only oligomers with even numbered carbon atoms but also odd numbered ones. In this reaction, one catalyst does three jobs at a time: oligomerization, isomerization and metathesis of ethylene.
Beside Ziegler-Natta and Phillips catalysts the development of methylaluminoxane (MAO) as cocatalyst in combination with metallocenes or other transition metal complexes for the polymerization of olefins has widely increased the... more
Beside Ziegler-Natta and Phillips catalysts the development of methylaluminoxane (MAO) as cocatalyst in combination with metallocenes or other transition metal complexes for the polymerization of olefins has widely increased the possibilities in controlling the polymer composition, polymer structure, tacticity and special properties with high precision. These catalysts allow the synthesis of isotactic, isoblock, syndiotactic, stereoblockor atactic polymers, as well as polyolefin composite materials with superior properties such as film clarity, tensile strength and lower content of extractables. Metallocene and other single site catalysts are able to copolymerize ethene and propene with short and long chained a-olefins, cyclic olefins, or polar vinyl monomers such as ethers, alcohols or esters, especially, if the polar monomers are protected by aluminum alkyls. Different vinyl ethers such as vinyl-ethyl ether, vinyl-propyl ether, vinyl-hexyl ether, and 2,7-octadienyl methyl ether (MODE) were copolymerized with olefins using triisobutyl aluminum as protecting agents. Polar monomers could be incorporated into the polymer chain by up to 16 mol%. Such copolymers show better gas barrier and surface properties, as well as solvent resistance and they are suitable for blends of polyolefins with polyethers and other polar polymers because of an excellent adhesion of the two polymers.
In this study we have tested the ability of a standard DFT computational protocol to reproduce the experimentally obtained stereoselectivity of 26 different C2-symmetric zirconocene catalysts active in propylene polymerization. The... more
In this study we have tested the ability of a standard DFT computational protocol to reproduce the experimentally obtained stereoselectivity of 26 different C2-symmetric zirconocene catalysts active in propylene polymerization. The catalysts were chosen for their relevance in metallocene catalyzed polymerization of propylene. To this end, primary insertion of both si- and re-propylene enantiofaces into the Zr-CH2-CH(CH3)2 bond was considered to simulate the growing chains step. The energy difference between these two transition states, ΔEre-si, was taken as a measure of the stereoselectivity (pentad: mmmm%) of different catalysts. The results clearly indicated that there was a good agreement between ΔEre-si and the mmmm% values, so that greater ΔEre-si could correspond to higher mmmm%. A model was fitted to the experimentally obtained mmmm% against theoretical ΔEre-si. The coefficient of determination (R2) of the resultant plot was 0.9793, which indicated a good accuracy of the model. Finally, to quantify the steric role of the studied ligands in the observed stereoselectivity, the analysis of the buried volume (VBur) and of the steric maps was performed for two representative complexes. The images revealed that a greater asymmetric localization of the %VBur around the metal center led to a higher mmmm% in the resultant polymer.
The commercial profile of the Amoco CD MgCl2 supported polypropylene catalyst is presented. The development, the unique method of preparation/production, with emphasis on particle morphology, and the parameters affecting particle size... more
The commercial profile of the Amoco CD MgCl2 supported polypropylene catalyst is presented. The development, the unique method of preparation/production, with emphasis on particle morphology, and the parameters affecting particle size (PS), particle size distribution (PSD), and particle shape are discussed in detail. The outstanding performance of the catalyst, tailoredmade for the Amoco-Chisso gas phase process, is attributable to synergistic effects, originating from catalyst and process design factors. Catalyst median particle size (d50) may be controlled in the 7-100 microns range. Parameters affecting PS and PSD during catalyst support preparation include: agitation speed, temperature, organic reagent to Mg ratios, morphology controlling agents, and deliberate spiking of the aromatic solvent used with appropriate contaminants. Particle shape variation between the cubic and spheroidal is affected by the types of reagents used, the ratios of these reagents to Mg, the time/temperature profile of the procedure, and the sequence of reagent addition during catalyst support preparation. Catalyst activation takes place in several steps by thermal treatment of the support with TiCl4/toluene solutions. Cost-effective TiCl4/toluene reuse system from the activation streams has been put in place to reduce waste material considerably. There is an optimum temperature of activation close to 120˚C. The progress of activation as well as catalyst quality may be monitored by IR spectroscopy, expressed in easily identifiable IR fingerprint patterns, which correlate well with the catalyst performance. More recently a new concept of supported catalysts based on the CD technology has been developed. It features organometallic complexes instead of just TiCl4 as the polymerization active centers. The new catalysts show improved performance and advantageous polymer product properties. We suggest that the newly invented organometallic complexes may open a new era in polyolefin catalysis, including polyethylene copolymers. The success of the CD and Amoco-Chisso process is illustrated by the two dozen commercial plants worldwide that use the technology, and the recent licensing advances by Ineos, the successor of Amoco, for this polypropylene technology.
In this work, the role of comonomer content of 1-hexene-medium density polyethylene (MDPE) copolymer, synthesized using Phillips catalyst, on thermal behavior parameters such as: crystallization, melting temperature and thermal... more
In this work, the role of comonomer content of 1-hexene-medium density polyethylene (MDPE) copolymer, synthesized using Phillips catalyst, on thermal behavior parameters such as: crystallization, melting temperature and thermal degradation was investigated in detail. The copolymer was fractionated to homogenous short-chain branching (SCB) fractions by "preparative temperature rising elution fractionation" (P-TREF) method and then it was subjected to thermal analyses. A broad chemical composition distribution (CCD) in terms of SCB content and molecular weight (Mw) was observed by P-TREF and gel permeation chromatography (GPC), respectively. Based on P-TREF results, a parabolic relationship between methylene sequence length (MSL) and elution temperature (ET) was presented. Differential scanning calorimetry (DSC) showed distinct, well-defined melting peaks over a 22 °C temperature range for SCB contents of about 3-12 (br/1000 C). The variations in physical characteristics such as melting temperature (Tm), crystallinity (Xc), crystallization temperature (Tc) and lamellae thickness (Lc) against SCB content were correlated. Thermogravimetric analysis (TGA) suggested linear relationships between the temperature at maximum degradation rate (Tmax) as well as the degradation initiation temperature (T5%) versus SCB content. Moreover, the TGA curves exhibited distinct differences at both initiation and propagation stages of thermal degradation at dissimilar comonomer contents.
A series of dissymmetric dinuclear complexes were synthesized, as dual site catalysts in ethylene polymerization, by coupling the allylated a-diimine complexes of the metals Ti, Zr, V, Ni and Pd with the ansa-zirconocene complex... more
A series of dissymmetric dinuclear complexes were synthesized, as dual site catalysts in ethylene polymerization, by coupling the allylated a-diimine complexes of the metals Ti, Zr, V, Ni and Pd with the ansa-zirconocene complex [C5H4-SiH(Me)-C5H4]ZrCl2 possessing a hydride silane moiety. The different stages of syntheses included the formation of bis(cyclopentadienide)methyl silane which was utilized to prepare the silyl-bridged zirconocene complexes. The dinuclear complexes were prepared by mixing the latter complexes with allylated alpha-diimine via a hydrosilylation reaction using the Karstedt catalyst, platinum (0)1,3 divinyl-1,1,3,3,-tetramethyldisiloxane to react at room temperature for 40 h. These dinuclear complexes were activated with methylaluminoxane (MAO) and tested for the polymerization of ethylene. The dinuclear catalysts showed various activities depending on the nature of the metals and produced polyethylenes with broad or bimodal molecular weight distributions. The trend in polymerization activities was: Ni>Pd>V>Zr>Ti. The ethylene polymerization activities of the dinuclear catalysts were almost double the activities of their analogous alpha-diimine precursors.
SiO2-supported silyl chromate catalyst is an important industrial catalyst for production of high grade HDPE pipe materials. The control of the short chain branch (SCB) distribution using this catalyst system is still a great challenge.... more
SiO2-supported silyl chromate catalyst is an important industrial catalyst for production of high grade HDPE pipe materials. The control of the short chain branch (SCB) distribution using this catalyst system is still a great challenge. In this work, ethylene and 1-hexene copolymers were synthesized using SiO2-supported silyl chromate catalyst combined with triisobutylaluminium (TIBA), triethylaluminium (TEA) and mixed TIBA/TEA at molar ratio 1:1 (TIBA/TEA/1:1) as three different Al-alkyl co-catalysts.The temperature rising elution fractionation (TREF) and successive self-nucleation and annealing (SSA, by DSC) methods were combined to analyze the short chain branch distribution (SCBD) of these ethylene/1-hexene copolymers. The results showed that different types of co-catalyst had a great influence on SCBD of ethylene/1-hexene copolymers. The copolymer produced with TIBA showed better SCBD than the copolymer produced with TEA, and the copolymer produced with TIBA/ TEA/1:1 showed a SCBD in between those with TIBA and TEA.
A two-dimensional single particle finite element model was used to examine the effects of particle fragmental pattern on the average molecular weights, polymerization rate and particle overheating in heterogeneous Ziegler-Natta olefin... more
A two-dimensional single particle finite element model was used to examine the effects of particle fragmental pattern on the average molecular weights, polymerization rate and particle overheating in heterogeneous Ziegler-Natta olefin polymerization. A two-site catalyst kinetic mechanism was employed together with a dynamic two-dimensional molecular species in diffusion-reaction equation. The initial catalyst active sites distribution was assumed to be uniform, while the monomer diffusion coefficient was considered to be different inside the fragments and cracks. In other words, the cracks were distinguished from fragments with higher monomer diffusion coefficient. To model the particle temperature a lumped heat transfer model was used. The fragmentation pattern was considered to remain unchanged during the polymerization. A Galerkin finite element method was used to solve the resulting two-dimensional (2-D) moving boundary value, diffusion-reaction problem. A two-dimensional polymeric flow model (PFM) was implemented on the finite element meshes. The simulation results showed that the fragmentation pattern had effects on the molecular properties, reaction rate and the particle temperature at early stages of polymerization.
Highly active metallocenes and other single site catalysts have opened up the possibility of polymerizing cycloolefins such as norbornene (N) or of copolymerizing them with ethene (E) or propene (P). The polymers obtained show exciting... more
Highly active metallocenes and other single site catalysts have opened up the possibility of polymerizing cycloolefins such as norbornene (N) or of copolymerizing them with ethene (E) or propene (P). The polymers obtained show exciting structures and properties. E-N copolymers are industrially produced materials, with variable and high glass transitions depending on the wide range of their microstructures. By realizing the possibility in great variety of stereoregularity of propene and norbornene units and the difference in comonomer distribution, P-N copolymers were expected to have fine tuned microstructures and properties. Moreover, P-N copolymers should be characterized by higher Tg-values than E-N copolymers with the same norbornene content and molar mass. A review of the state of the art of P-N copolymerization by ansa-metallocenes of C2 symmetry, namely rac-Et(Ind)2ZrCl2 (I-I) and rac-Me2Si(Ind)2ZrCl2 (I-II), and rac-Me2Si(2-Me-Ind)2ZrCl2 (I-III), and of catalysts of Cssymmetry, namely (tBuNSiMe2Flu)TiMe2 (IV-I) and derivatives, is given here. Special emphasis is given to microstructural studies of P-N copolymers, including stereo- and regioregularity of propene units as well as of comonomer distribution, stereoregularity of norbornene units, and the structure of chain end-groups. This information allows us to find a rationale for the catalytic activities and the copolymer properties.
The stereospecific polymerization of conjugated dienes began in 1954 with the first catalysts obtained by combining TiCl4 or TiCl3 with aluminum-alkyls, i.e. the catalytic systems previously employed for ethylene and propylene... more
The stereospecific polymerization of conjugated dienes began in 1954 with the first catalysts obtained by combining TiCl4 or TiCl3 with aluminum-alkyls, i.e. the catalytic systems previously employed for ethylene and propylene polymerizations. Subsequently, many other catalytic systems were obtained and examined by a combination of transition metal or lanthanide compounds with appropriate alkylating agents. With the advent of MAO as alkylating agent, at the beginning of the 1980s, new catalytic systems were introduced, in some cases much more active and stereospecific than those based on common aluminum-alkyls. Starting from the 2000s, in the wake of what happened in the case of mono-olefins, a new generation of catalysts based on complexes of transition ,metals and lanthanides with various ligands containing donor atoms such as P, N, O (e.g., phosphines, imines imino-pyridines, cheto-imines) has been introduced. These systems have proved particularly active and able to (provide polymers with controlled microstructure (i.e., cis-1,4; 1,2; mixed cis-1,4/1,2 with a variable 1,2 content ,from several types of 1,3-dienes, permitting indeed to establish new correlations between the catalyst structure the monomer structure and the polymer microstructure, and to improve our knowledge on the polymerization mechanism of 1,3-dienes. This paper provides an exhaustive overview of the latest developments in the field of stereospecific polymerization of 1,3-butadiene.
Primary MgCl2.3.3EtOH adduct (PCT1) was prepared by melt quenching method and then submitted into a programmed thermal dealcoholation project using a fluidized bed reactor. During thermal dealcoholation program, different MgCl2.nEtOH... more
Primary MgCl2.3.3EtOH adduct (PCT1) was prepared by melt quenching method and then submitted into a programmed thermal dealcoholation project using a fluidized bed reactor. During thermal dealcoholation program, different MgCl2.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 showed a significant increase in the surface area, from 7.4 m2/g to 12.8 m2/g, together with the decrease in peaks height at 2θ≈ 8.9 and 9.7˚ by moving from PCT1 to PCT5. After characterization of support samples, final catalysts were prepared by reacting these samples with TiCl4 and examined in slurry phase propylene polymerization. Prepared catalysts showed similar stereospecifities but different activities in the polymerization experiments, so that, with proceeding dealcoholation from PCT1 to PCT2 catalyst activity was reached a maximum amount of 2.9 kgPP/g Cat.h, and then by further dealcoholation, from PCT2 to PCT5, catalyst activity decreased gradually. In the last section, effect of time interval between thermal dealcoholation and catalyst preparation, which is called storage time, on the crystal and morphological characteristics of the two of the best adduct samples, namely MgCl2.2.4EtOH and MgCl2.3.0EtOH, was studied, as well. Storage time greatly affected the characteristics of the adducts together with resulted catalysts, and the best catalyst activity was achieved for the ones prepared immediately after adduct preparation.
A FI Zr-based catalyst of bis[N-(3,5-dicumylsalicylidene)-2′,6′­diisopropylanilinato]zirconium(IV) dichloride was prepared and used for polymerization of ethylene. The effects of reaction conditions on the polymerization were examined in... more
A FI Zr-based catalyst of bis[N-(3,5-dicumylsalicylidene)-2′,6′­diisopropylanilinato]zirconium(IV) dichloride was prepared and used for polymerization of ethylene. The effects of reaction conditions on the polymerization were examined in detail. The increase in ethylene pressure and rise in polymerization temperature up to 35 oC were favorable for catalyst/MAO to raise the catalytic activity as well as the viscosity-average molecular weight (Mv) of polyethylene. The activity of the catalyst was linearly increased with increasing MAO concentration and no optimum activity was observed in the range studied. Although introduction of the bulky cumyl and 2′,6′-diisopropyl alkyl substitution groups on ortho positions to the phenoxy-oxygen and on phenyl ring on the N, respectively enhanced the viscosity average molecular weight (Mv) of the obtained polymer strongly, diminished the activity of the catalyst. Neither the activity of the catalyst nor the (Mv) of the obtained polymer were sensitive to hydrogen concentration. However, higher amount of hydrogen could slightly increase the activity of the catalyst. The (Mv) of polyethylene ranged from 2.14×106 to 2.77×106 at the monomer pressure of 3 and 5 bar respectively which are much higher than that of the reported FI Zr-based catalysts.
A fourth-generation Ziegler-Natta catalyst was prepared to synthesize polypropylene (PP), which was stabilized by in situpolymerization employing lignin as antioxidant. The antioxidant properties of lignin were compared with those of the... more
A fourth-generation Ziegler-Natta catalyst was prepared to synthesize polypropylene (PP), which was stabilized by in situpolymerization employing lignin as antioxidant. The antioxidant properties of lignin were compared with those of the commercial antioxidant Irganox 1010. The presence of lignin in the reaction medium slightly decreased the catalytic activity of the reaction. The isotacticity index (I.I.) of PP synthesized with lignin (PP-lig) was not affected by the presence of the additive in the reaction medium. The thermal properties, characterized by differential scanning calorimetry, showed slightly decreased degree of crystallinity (Xc), but the melting temperature (Tm) and crystallization temperature (Tc) were not affected when compared with the neat polymer. Lignin showed good activity as a stabilizer by thermogravimetry. The initial temperature of degradation (Tonset) increased when compared to the pure PP and PP stabilized with the commercial antioxidant. The lower carbonyl index of the PP, evaluated by infrared spectroscopy (FTIR) after thermo-oxidative treatment, also revealed the stabilizing action of lignin.
T he automotive industry has a significant need for composites made of high impact strength polymer blends. Melt-mixing was used in this work to reinforce hollow glass microspheres (HGMs) with 50:50 polypropylene/ polyamide 6 (PP/PA6)... more
T he automotive industry has a significant need for composites made of high impact strength polymer blends. Melt-mixing was used in this work to reinforce hollow glass microspheres (HGMs) with 50:50 polypropylene/ polyamide 6 (PP/PA6) blends. Using FTIR spectroscopy, it is observed that the 50PP50PA6 blend is compatibilized with maleated PP, producing a reactively compatible blend. The compatibilization process has refined the morphology of the 50PP50PA6 blend. Additionally, the incorporation of HGMs into the 50PP50PA6 blend produced a finer blend morphology, which helped to enhance the crystallinity of the polymer phase and mechanical properties to the maximum. The tensile modulus and impact strength of a 50PP50PA6 blend with maleated PP that contains 3 wt.% HGMs are better than those of a neat blend by 15.6% and 90.1%, respectively. Fractography was used to identify the fracture mechanism which reveals the retention of droplets over the surface of impact specimens of HGMs-filled compatibilized PP/PA6 blend. When 50PP50PA6 blend with and without maleated PP is filled with HGMs, rheological characterization shows that the blend viscosity has decreased, indicating improved processability. Dynamic mechanical analysis (DMA) revealed that the incorporation of HGMs into the 50PP50PA6 blend enhances the storage modulus.
In this particular study, shear stability, pour point temperature and cold cranking simulation viscosity of different poly (alkyl methacrylate) homopolymers were investigated. The successful synthesis of the homopolymers was verified... more
In this particular study, shear stability, pour point temperature and cold cranking simulation viscosity of different poly (alkyl methacrylate) homopolymers were investigated. The successful synthesis of the homopolymers was verified using FTIR and 1 H NMR spectroscopy. From the experimental results, it was perceived that shear stability and low-temperature performance of the modified oil are strongly dependent on alkyl length and synthesis reaction conditions. Higher shear stability was observed for the samples possessing shorter alkyl chain lengths. An increase in initiator concentration and reaction temperature led to a decrease in molecular weight and an increase in shear stability. Moreover, poly(alkyl methacrylate) homopolymers containing longer alkyl chain lengths represented better influence in the reduction of the size and cohesiveness of the crystal structure of paraffin wax. The results also revealed that the synthesized homopolymers with lower molecular weight play a greater performance in controlling friction at low temperatures.
T he suitability of a polymer to be processed by injection molding is called moldability. The technicians in injection molding companies tend to estimate moldability by using a parameter named Melt Flow Index (MFI), which however can be... more
T he suitability of a polymer to be processed by injection molding is called moldability. The technicians in injection molding companies tend to estimate moldability by using a parameter named Melt Flow Index (MFI), which however can be often misleading since it represents the ability of a melt to flow in specific conditions, very different from the ones that the polymer encounters during injection molding. A much significant parameter is the so-called flow-length, which is the length reached by a polymer during injection molding in a thin cold cavity. In this work, three commercial grades of polypropylene were injection molded in a cold thin cavity and the flowlengths were measured in function of injection pressure and temperature. The results obtained were correlated with the rheological parameters. The results demonstrate that the MFI is misleading as a technical parameter for the moldability of polypropylene. An empirical equation is proposed to describe the flow-length of polypropylene in function of injection pressure.
I n the present study, the thermal oxidation behaviour of high-density polyethylene (HDPE) containing each of two types of oxidized polyethylene (OPE), one prepared using 500 ppm of iron (III) stearate as pro-oxidant and the other without... more
I n the present study, the thermal oxidation behaviour of high-density polyethylene (HDPE) containing each of two types of oxidized polyethylene (OPE), one prepared using 500 ppm of iron (III) stearate as pro-oxidant and the other without the pro-oxidant, was investigated. Fourier-transform infrared spectroscopy (FTIR) showed that the carbonyl index of the HDPE increased from 1.03 to 6.37 upon the addition of 5.0 wt.% of OPE containing the pro-oxidant after 100 h of thermo-oxidative aging at 90°C. Moreover, it was observed that the rate of changes in retained tensile strength and retained elongation-at-break of the HDPE during the thermal oxidation increased in the presence of 5.0 wt.% of each type of OPE, especially, the one containing iron (III) stearate, which was consistent with the obtained data from gel content measurements. Lastly, the evolution in crystallinity of the film samples was monitored by density measurements as well as differential scanning calorimetry (DSC). It was revealed that the crystallinity of the tested films during thermo-oxidative degradation grows faster in the presence of OPE. Overall, the findings indicated that the utilization of OPE containing trace amounts of iron (III) stearate can accelerate the thermal oxidation of HDPE films and facilitate entering the final biodegradation stage, while resolving the need to use high concentrations of harmful heavy metal salts.
I n this study, reversible addition-fragmentation chain transfer (RAFT) polymerization was used to synthesize hydrophobic polystyrene (PS), poly(methyl acrylate) (PMA), and poly(methyl acrylate-b-styrene) (PMA-b-PS) block copolymers with... more
I n this study, reversible addition-fragmentation chain transfer (RAFT) polymerization was used to synthesize hydrophobic polystyrene (PS), poly(methyl acrylate) (PMA), and poly(methyl acrylate-b-styrene) (PMA-b-PS) block copolymers with three distinct molecular weights. Polyaniline (PANI) was synthesized by electrochemical method. Proton nuclear magnetic resonance (1 H NMR) and gel permeation chromatography (GPC) have both been used to examine the properties of the polymers synthesized. In aqueous media at room temperature, PANI has been co-assembled with PS, PMA, and PMA-b-PS. The size and morphology of the co-assembled structures have been examined using transmission electron microscopy (TEM), dynamic light scattering (DLS), and field emission scanning electron microscopy (FE-SEM). According to the findings, polymers hydrophobicity increased with increasing molecular weight, causing faster precipitation in aqueous solution and a reduction in particle size. The results demonstrated that adding conductive polymer produced core-shell morphologies, while the core morphologies are different. Thermodynamic principles governed morphology, and the most likely morphology to develop was the one that minimized the total surface free energy. The polymers caused the surface tension between the polymers with water and the surface tension between the primary polymer and the secondary polymer to be reduced by overlapping each other and precipitation.
T his work focuses on the damage of two thermoplastic materials; high density polyethylene "(HDPE)" and high impact polystyrene "(HIPS)". The contribution of this work is to determine the lifetime of these polymers by proposing a new... more
T his work focuses on the damage of two thermoplastic materials; high density polyethylene "(HDPE)" and high impact polystyrene "(HIPS)". The contribution of this work is to determine the lifetime of these polymers by proposing a new static method, including different notches with different opening lengths instead of depth change, to predict the damage behavior of HDPE and HIPS. Three damage models were used to predict the lifetime of these polymers by a proposed simple method compared to the old complex methods. Chemical and microscopic analyses including Fourier transform infrared spectrometry (FTIR) and scanning electron microscopy (SEM) were performed. The results indicated that the shape of the notch and the morphological nature of the polymer influence the mechanical behavior of these polymers. The proposed experimental factors (life fraction as a function of notches) are in very good agreement with the experimental results.
Membrane bioreactors (MBRs) are high-tech systems for water recycling and reusing of unconventional water resources such as municipal wastewater. However, the fouling of polymeric membranes is the main impediment to the market development... more
Membrane bioreactors (MBRs) are high-tech systems for water recycling and reusing of unconventional water resources such as municipal wastewater. However, the fouling of polymeric membranes is the main impediment to the market development of MBR. The polyolefin-based membranes are subjected to more severe organic fouling than other hydrophilic membranes due to their inherent strong hydrophobic properties, therefore, proposing efficient, fast, and economic fouling mitigation methods is vital for durable and long-standing performance. In this research, the hydrodynamics of a lab-scale membrane bioreactor with different configurations of aerators and nozzle sizes were used to investigate the air scouring efficiency. It was gained that aerators with higher air flow rates, e.g., 5.5 m/s can produce slug bubbles which are capable of foulant removal from the membrane surface. In comparison with a non-central aerator, the satisfactory scouring zone of the central aerator is narrow and the edge nozzles on both sides of the aerator are blocked. Under constant air flow rate, when the inlet air is injected into the aerator from two and three points, not only the end nozzles are blocked but also the liquid is penetrated into the aerator and the shear stress on the membrane surface decreased to 0.765 Pa. In the case of the non-central aerator, the satisfactory scouring zone becomes wider and neither nozzle blockage nor liquid penetration down to the aerator has occurred. The distribution of bubbles was optically evaluated by video imaging through the transparent plexiglass tank using aerators with different inlet flow rates and various configurations. Numerical simulations and related experimental analyses demonstrated that air inlet velocity has an important role in creating larger slug bubbles. It was shown that a non-central aerator in which the central nozzle in front of the inlet air stream is blocked, produces slug bubbles and sufficient air scoring on the flat sheet membrane. Configuration of a non-central aerator with 4 nozzles not only increased the satisfactory zone of each aerator without blockage of edge nozzles and liquid penetration into the aerator but also provided a higher shear rate over 1.104 Pa under a constant flow rate, which consequently removed the foulant from the membrane surface.
The effect of structural defects on graphene interaction with other molecules is of high interest. In this study, the interaction of ethylene molecules with pristine graphene (PG) and defective graphenes including single (SVG) and double... more
The effect of structural defects on graphene interaction with other molecules is of high interest. In this study, the interaction of ethylene molecules with pristine graphene (PG) and defective graphenes including single (SVG) and double (DVG) vacancies, were investigated using dispersion-corrected periodic density functional theory (DFT). We used various pairs of pseudopotentials and dispersion-corrected methods to calculate the exchange-correlation energies and long-range energies, respectively. We conducted the calculations in the ethylene-graphene equilibrium distance where vdW interaction as a long-range interaction was dominant. Both adsorption and deformation energies were calculated to examine the possibility of ethylene chemisorption. It was found that there is a critical distance from the graphene surface, where the nature of adsorption of adsorbate molecule changes from physisorption to the possible chemisorption depending on the energetical costly distortion induced in adsorbate molecule. In the case of ethylene adsorption on the graphene structures studied here, the mentioned critical distances follow the order SVG < DVG < PG. However, in the range of vdW domination and in comparison with PG, ethylene interacts more with SVG due to the presence of a dangling bond and interacts less with DVG due to the presence of a hole. Furthermore, the interactions of ethylene with reconstructed trivacancy were studied. Moreover, all possible orientations for ethylene adsorption on graphene structures were considered and energetically compared. All calculations were done on fully optimized reconstructed geometries of vacancies with structural characteristics, i.e., reconstruction length and formation energies comparable to those reported in the literature.
Due to the large ionic radius and high electro-positivity nature, rare earth metal complexes are difficult to stabilize and undergo pathways like ligand redistribution and intramolecular C-H activation. To solve such problems and retain... more
Due to the large ionic radius and high electro-positivity nature, rare earth metal complexes are difficult to stabilize and undergo pathways like ligand redistribution and intramolecular C-H activation. To solve such problems and retain reactive versatility, rare earth complexes supported by a variety of tridentate PNP pincer ligands have been explored. Such complexes can serve as perfect precursors for preparing ultra-active rare earth species containing two metal-carbon bands, let alone Ln=N and Ln=P multiple bonds. In addition, the combined stability and activity of the cation rare earth mediates made them the best catalysts for the polymerization of olefins and other non-polar hydrocarbon monomers, especially conjugated dienes. The practical utilization of rare earth metal catalysts for new materials production have also extensively explored by experts from the academic and industries.
A mono-nuclear catalyst of bis-imine cobalt (MC) was synthesized with using 2,6-dibenzhydryl-4-ethoxy phenyl as a ligand. The so huge ligand was prepared via the reaction of 2,6-dibenzhydryl-4-ethoxy phenyl)-N=(CH 3)-C(CH 3)=O with... more
A mono-nuclear catalyst of bis-imine cobalt (MC) was synthesized with using 2,6-dibenzhydryl-4-ethoxy phenyl as a ligand. The so huge ligand was prepared via the reaction of 2,6-dibenzhydryl-4-ethoxy phenyl)-N=(CH 3)-C(CH 3)=O with diacetyl with equal mole stoichiometry in presence of formic acid catalysis. The catalyst was synthesized via a reaction between the ligands and cobalt salt (CoCl 2). The catalyst was used for polymerization of methyl methacrylate (MMA), (a polar monomer) in the presence of modified methylaluminoxane (MMAO). The highest polymerization activity (8.6 g PMMA/mmol cat. h) was obtained at [cocatalyst]/[catalyst]=1000:1 molar ratio and at room temperature reaction. For the prepared PMMA, Polymer with branching density of 263/1000C was obtained using 1 H NMR technique calculation. The microstructure of one of the produced PMMA was as follow: 48% syndiotactic, 29% isotactic and 23% atactic. GPC analysis of the polymer showed a number average molecular weight of about 5.7 × 10 5 g/mol and a narrow molecular weight distribution of 1.57.
Cyclic olefin copolymer is a type of high performance polyolefin material, which is prepared by using a single-site catalyst in solution polymerization. The common activator of this system is alkyl aluminoxane or organic boron/ aluminum... more
Cyclic olefin copolymer is a type of high performance polyolefin material, which is prepared by using a single-site catalyst in solution polymerization. The common activator of this system is alkyl aluminoxane or organic boron/ aluminum system. Among them, organic boron is mostly triphenylcarbenium tetrakis(pentafluorophenyl)borate or dimethylanilinium tetrakis(pentafluorophenyl)borate. In this study, ethylene and norbornene were copolymerized with metallocene catalyst activated with the combination of tris(pentafluorophenyl)boron and triisobutylaluminium. Compared with homopolymerization of ethylene, copolymerization shows high activity. The molecular weight of the polymer increased significantly with the increase of the insertion rate of norbornene. Fineman-Ross method was used to calculate the reactivity ratio, which showed that the reactivity ratio of norbornene was much lower than that of ethylene. The high copolymerization activity may indicate that, although norbornene has a lower coordination probability, its insertion rate is higher than ethylene. The copolymer with higher norbornene incorporation has a higher glass transition temperature, and the relationship between them is linear.
Certain cyclic olefin copolymers (COCs) are known as promising amorphous materials with high transparency in the UV-vis region, thermal and humidity resistance, low dielectric constant, low water absorption, and dimensional stability.... more
Certain cyclic olefin copolymers (COCs) are known as promising amorphous materials with high transparency in the UV-vis region, thermal and humidity resistance, low dielectric constant, low water absorption, and dimensional stability. This short review focuses on the synthesis of (new) cyclic olefin copolymers by designed (nonbridged) half-titanocene catalysts, which enabled to proceed synthesis of the amorphous polymers by ethylene/ propylene copolymerization not only with norbornene (NBE), and tetracyclododecene (TCD), but also with so called low strained cyclic olefins (cyclopentene, cyclohexene, cycloheptene, and cyclooctene). Their thermal properties (glass transition temperature, Tg values) are affected by structure of the cyclic olefin employed and the contents, whereas linear relationships between Tg values and the contents were observed in all cases.
Ethylene-norbornene copolymers were synthesized with a homogeneous catalyst system based on bis(imino) pyridine iron with the addition of diethyl zinc (DEZ) as alkyd transfer agent to promote immortal copolymerization. The addition of DEZ... more
Ethylene-norbornene copolymers were synthesized with a homogeneous catalyst system based on bis(imino) pyridine iron with the addition of diethyl zinc (DEZ) as alkyd transfer agent to promote immortal copolymerization. The addition of DEZ did not influence the catalytic activity in copolymerization with 7.5 mmol of norbornene (NB), but in the reactions with 70 mmol, the comonomer promoted an increase of activity. We observed by thermal analysis that the norbornene inserted in the chains promoted an increase in thermal stability of the synthesized material with higher amounts of comonomer, since the temperature of initial degradation was much higher for these copolymers compared to polyethylene. In addition, for the copolymers with 7.5 mmol of norbornene, the DEZ served as alkyd transfer agent, as shown by the gel permeation chromatography analysis, leading to a decrease in both molar mass and polydispersity. The UV-Vis spectra showed that the diethyl zinc did not change the catalyti...
This study presents methods for treating a kind of nanoclay and investigates the effects of methylaluminoxane (MAO) exposure time and or dodecylamine (DDA) reflux time on in-situ polymerization of ethylene in the presence of nanoclay and... more
This study presents methods for treating a kind of nanoclay and investigates the effects of methylaluminoxane (MAO) exposure time and or dodecylamine (DDA) reflux time on in-situ polymerization of ethylene in the presence of nanoclay and examines the morphology and properties of the prepared polyethylene/clay nanocomposites. The results revealed that by increasing MAO exposure time productivity decreased. Modification of nanoclay by NH3/MAO led to formation of exfoliated structures. In treatment with NH3/DDA, the change in reflux time resulted in different structures. SEM demonstrated that the morphology of the nanocomposites strongly depended on the modification method and treatment time. Dynamic mechanical analysis indicated that the elastic modulus of the nanocomposites increased by increasing MAO exposure time. The nanocomposites treated with different MAO exposure times showed similar thermal degradation behavior. The nanocomposite modified under the condition of 24 h DDA reflu...
Methanol dehydration is a high potential route for the production of light olefins (C2-C4). In this study, hierarchical Si-rich [B]-ZSM-5 catalysts (Si/Al=200) were prepared through one-pot hydrothermal synthesis, including boron as a... more
Methanol dehydration is a high potential route for the production of light olefins (C2-C4). In this study, hierarchical Si-rich [B]-ZSM-5 catalysts (Si/Al=200) were prepared through one-pot hydrothermal synthesis, including boron as a promoter and ethanol as a low-cost secondary template. N2 adsorption-desorption, XRD, FE-SEM, and FT-IR techniques were applied to characterize the catalysts. The effect of different amounts of ethanol and different operating conditions was studied on the ZSM-5 catalyst preparation and performance in methanol to olefins (MTO) reaction. The results showed that the optimum amount of ethanol (ethanol/TPABr=5) led to the highest crystallinity (91.2%), the highest specific surface area (&gt;400 m2g-1), and total pore volume (0.19 cm3g-1). The best catalytic performance was obtained at temperature of 480°C and methanol hourly space velocity (WHSV) of 7.2 h-1. The optimum catalyst had the highest propylene selectivity (58%) and light olefin selectivity (85%)....
The present study investigates the hydrophilic properties of acrylonitrile/acrylic acid P(AN/AA) copolymer films with various acrylic acid (AA) contents dendrigrafted with citric acid from zero to fourth generation numbers. It was found... more
The present study investigates the hydrophilic properties of acrylonitrile/acrylic acid P(AN/AA) copolymer films with various acrylic acid (AA) contents dendrigrafted with citric acid from zero to fourth generation numbers. It was found that the hydrophilicity of the dendrigrafted films was a complicated phenomenon. Various parameters such as intermolecular hydrogen bonding, roughness and active functional groups affected the wettability of the film samples measured via static contact angle. The results revealed that the hydrophilicity decreased with increasing the generation number owing to the steric hindrance of terminal groups. However, active functional group increased by rising generation numbers which was confirmed using zeta potential measurement. Furthermore, the percentage conversion of the reactions showed a reduction with increasing generation number and AA content which was in agreement with the reduction in wettability corresponding to the higher contact angle. On the ...

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