Characterization
Utkarsh A. Patil; Pravin Ramchandra Kubade
Abstract
The growing need for enhanced materials has led to the development of nanocomposites, which have shown great potential in various industries. However, optimizing the composition of these materials to achieve the best mechanical performance and cost-effectiveness remains a challenge. This research addresses ...
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The growing need for enhanced materials has led to the development of nanocomposites, which have shown great potential in various industries. However, optimizing the composition of these materials to achieve the best mechanical performance and cost-effectiveness remains a challenge. This research addresses this challenge by employing a virtual experimental approach, utilizing Digimat for material modeling and CATIA for Design and Finite Element Analysis (FEA). This approach allows for the simulation and analysis of different nanocomposite compositions without the need for costly and time-consuming physical experiments. The study focuses on Polypropylene (PP) and Polyvinyl Chloride (PVC) based nanocomposites with graphene and carbon black reinforcements. The research investigates the impact of varying the weight percentages of these nanofillers on the mechanical properties of the composites. The PP/PVC blends are created in different weight ratios to provide further compositional control. The material preparation is carried out in Digimat, where the properties of the composites are defined using a micromechanical model. The FEA is then conducted in CATIA, where a standard ASTM D638 tensile specimen is simulated under controlled conditions. The results are validated by varying mesh sizes to optimize deflection and Von Mises stress predictions. Furthermore, an economic analysis is conducted to evaluate the cost-effectiveness of the different nanocomposite compositions. The study highlights the importance of virtual experimentation in material science, as it allows for efficient exploration of various material compositions and reduces the need for physical prototyping. This approach accelerates the material development process and enables the optimization of material design for specific applications. The virtual trials explored alternatives to PVC using PP-based composites reinforced with graphene/carbon black. PP/PVC 40/60 reinforced with 1.5% wt. graphene (P4V6G15) and reinforced with 7.5% wt. carbon black (P4V6C75) showed 31.6% and 31.2% deflection reductions compared to pure PP, respectively. These results show that P4V6 blends, especially those with graphene or high carbon black concentrations, serve as promising alternatives to conventional PVC. Among them, P4V6C75 stands out by offering the best overall mechanical performance. It also provides the lowest production cost. In terms of economic favorability, P4V6C75 is approximately 2.55 times more cost-effective than the graphene-based blend P4V6G15. This combination of high performance and low cost makes P4V6C75 the most suitable candidate for PVC replacement.
Characterization
Ahmed Hamdi
Abstract
Describing the solidification process is very important in polymer processing. In polypropylene (PP), the increase of viscosity, named stiffening or hardening, is determined by a rise in crystallinity. When PP flows in a channel or is stretched on a chill roll, the stress induces an anticipated crystallization ...
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Describing the solidification process is very important in polymer processing. In polypropylene (PP), the increase of viscosity, named stiffening or hardening, is determined by a rise in crystallinity. When PP flows in a channel or is stretched on a chill roll, the stress induces an anticipated crystallization and thus can lead to an unexpected solidification. This study explores how flow fields influence the crystallization behavior of PP. A controlled-stress rheometer was used to investigate the effect of short shear stress steps on crystallization kinetics. The results revealed that applying a stress step significantly increased the rate of crystallization compared to a non-stressed sample. This acceleration is attributed to the stress-induced orientation of macromolecules, which promotes nucleation. Furthermore, longer durations of applied stress led to a faster increase in viscosity, indicating a higher nucleation density with increasing stress exposure. A mastercurve approach validated the consistency of the model describing the stress-crystallization relationship. The calculated parameter relating to nucleation density confirmed a linear increase with stress duration, allowing estimation of the nucleation rate during shear.
Characterization
Masayoshi Saito; Hiroshi Kashimura; Takuo Kataoka; Masahide Murata; Yusuke Sakuda; Hiroyuki Yamada; Hideyuki Takahashi
Abstract
This report is on the characterization of active Ti center in heterogeneous Ziegler-Natta catalysts with Soft X-ray Emission Spectrometer (SXES). Since titanium in the catalyst has various chemical bonds, it is important to grasp the chemical bond state. The outermost shell electrons are very important ...
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This report is on the characterization of active Ti center in heterogeneous Ziegler-Natta catalysts with Soft X-ray Emission Spectrometer (SXES). Since titanium in the catalyst has various chemical bonds, it is important to grasp the chemical bond state. The outermost shell electrons are very important for understanding the chemical bond state. SXES is the only method that can easily observe outermost shell electrons with current analytical instruments. Here, a co-milled solid of MgCl2, TiCl4, and Phthalate was used as a catalyst precursor, and three types of catalysts with significantly different catalytic activity levels were synthesized by changing the subsequent preparation process. The correlation between catalytic activity and the signal shape of Lα,β emission, which is the outermost shell electron of Ti in SXES analysis, was investigated. Lα,β emission was detected as broad signal. It could be observed that the high active catalyst had relatively strong signal intensity at the high energy side. The shape changes were also checked when the catalyst solids were treated by triethylaluminium. By this treatment, the relative intensity of the high energy side signal was further enhanced, suggesting that triethylaluminium treatment induced the elimination of inactive Ti from the catalyst solid. By comparing with the solid 13C-NMR analyses data of the Ziegler-Natta catalyst described in our previous report, the high energy side signal of Ti Lα,β in SXES results implies the relationship with the NMR results for carbonyl function.
Characterization
Mehri Dana; Gholam Hossein Zohuri; Navid Ramezanian; Saeid Asadi Shahidi; Sohail Yazdanbakhsh
Abstract
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 ...
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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 w% 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.
Catalysis
Masayoshi Saito; Toshiya Uozumi; Masahide Murata; Takuo Kataoka; Riichiro Chujo
Abstract
Ziegler-Natta catalyst for propylene polymerization, which TiCl4 and di-alkyl phthalate were supported on MgCl2, was analyzed by solid state 13C NMR. It was confirmed that the spin-lattice relaxation time (“relaxation time” hereafter) of carbonyl group in phthalate was shortened with ...
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Ziegler-Natta catalyst for propylene polymerization, which TiCl4 and di-alkyl phthalate were supported on MgCl2, was analyzed by solid state 13C NMR. It was confirmed that the spin-lattice relaxation time (“relaxation time” hereafter) of carbonyl group in phthalate was shortened with increasing measurement temperature as a general manner because of the enhancing of molecular mobility at high temperature. The degree of the relaxation period reduction with temperature was influenced by the alkyl group size in phthalate molecule; the larger alkyl group showed a greater shorting of the relaxation period. A short relaxation time should suggest a weak interaction between the phthalate molecule and the MgCl2 support surface. The change in catalytic performance was discussed by the active site formation mechanism involving the phthalate removal step.
Characterization
Ivan Kuryndin; Sergei Kostromin; Rustam Mamalimov; Anton Chervov; Andrei Grebennikov; Sergei Bronnikov
Abstract
Swelling of high-density polyethylene (PE) in organic solvents, orthodichlorobenzene and orthoxylene, was investigated. The swelling kinetics of the PE specimen was described by the first-order equation. For the first time, the PE specimen swelling rate constant was shown to decrease with increasing ...
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Swelling of high-density polyethylene (PE) in organic solvents, orthodichlorobenzene and orthoxylene, was investigated. The swelling kinetics of the PE specimen was described by the first-order equation. For the first time, the PE specimen swelling rate constant was shown to decrease with increasing thickness of the specimens. The equilibrium swelling of the PE specimen was evaluated. It was found that equilibrium swelling is independent of the thickness of specimens. It was shown that storage of polyethylene specimens in organic solvents changes its mechanical properties (tensile strength, Young’s modulus, and elongation-at-break) due to polymer plasticization. We have shown that the increase in flexibility and elongation-at-break after relatively short-term immersion of PE samples in these organic solvents is significant. However, the tensile strength of swollen specimens remains high enough. The interaction between polymer chains and solvent molecules was not detected. The results obtained are important for the design and operation of PE coatings and PE products, such as pipes, tanks, and other accessories exposed to oil products.
Characterization
Marzie Alidadi-Shamsabadi; Shirin Shokoohi
Abstract
Melt free-radical grafting reactions between ethylene-propylene-dieneterpolymer (EPDM) and glycidyl methacrylate (GMA) were investigated in a batch mixer (170°C, 60rpm). Effect of dicumylperoxide (DCP) initiator and GMA functionalizing monomer concentrations was studied on the grafted EPDM characteristics. ...
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Melt free-radical grafting reactions between ethylene-propylene-dieneterpolymer (EPDM) and glycidyl methacrylate (GMA) were investigated in a batch mixer (170°C, 60rpm). Effect of dicumylperoxide (DCP) initiator and GMA functionalizing monomer concentrations was studied on the grafted EPDM characteristics. Titration results indicated an increase in the graft degree (GD) and gel content (GC) values with increasing DCP concentration as a result of increasing primary free radical concentration and strengthening cross-linking side reaction. FTIR spectrums confirmed that GMA functionalities have been grafted onto EPDM with appearing carbonyl (C=O) peak. After that, the resultant EPDM-g-GMA was used as compatibilizer in PS(polystyrene)/EPDM/PA6 (polyamide6) ternary blends. The effect of rubbery compatibilizer on the blend morphology and mechanical properties was studied. The ATR-FTIR spectra of ternary blends, etched to remove unreacted PA6, demonstrated that the compatibilizing reactions occurred during melt blending. By investigating the SEM micrographs it was revealed that the EPDM-g-GMA compatibilizer at the concentration range of 5 wt.% to 15 wt.% changed the size and type of the blend morphology from separated dispersed to multicore-shell morphology. The finest morphology was achieved by using 7.5 wt.% EPDM-g-GMA. Also, the presence of compatibilizer up to 7.5 wt.% could improve the tensile modulus, yield stress and impact strength, but a decreasing trend was observed at higher concentration of the compatibilizer.
Characterization
Reza Poorghasemi; Yousef Jahani
Abstract
In this work, the compatibility and crystallinity of low density polyethylene (LDPE) and polybutene-1 (PB-1) blends were studied. Various blends of LDPE/PB-1 containing 5, 10 and 20 wt.% PB-1 were prepared in a corotating twin-screw extruder and characterized by scanning electron microscopy (SEM), shear ...
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In this work, the compatibility and crystallinity of low density polyethylene (LDPE) and polybutene-1 (PB-1) blends were studied. Various blends of LDPE/PB-1 containing 5, 10 and 20 wt.% PB-1 were prepared in a corotating twin-screw extruder and characterized by scanning electron microscopy (SEM), shear oscillation rheology and wide-angle X-ray diffractometry (WAXD). A matrix-droplet morphology was observed in SEM images, indicating incompatibility of the two polymers in the solid state. Compared to neat LDPE, the relaxation spectra of the blends were broadened, and a slight increase in their relaxation times was observed. The relaxation time of the blends was enhanced by increasing PB-1 content, which was further proved by fitting rheological data in the Carreau-Yasuda model. Deviation of Cole-Cole diagrams from circular shape means that the blend samples were not miscible and the positive-deviation behavior of the complex viscosity and storage modulus from the mixing rule revealed the formation of strong interfacial interactions. The crystallinity of both LLDPE and PB-1 was decreased as a result of blending. The peaks attributed to the form II of PB-1 crystals were eliminated and the peaks related to LDPE were obviously weakened, suggesting to prevent crystallinity of polymers which is associated with a reduction in the total crystallinity percentage for the blend. The reduction of crystallinity was more pronounced in PB-1 phase.
Characterization
Afshar Alihosseini; Davood Zergani; Amir Hossein Saeedi Dehaghani
Abstract
The application of membranes in various industries is one of the most urgent needs to reduce energy consumption and environmental pollutants as well as low investment costs in the process of separation. In this investigation, the optimization of effective parameters for separation of gas mixture of CH4, ...
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The application of membranes in various industries is one of the most urgent needs to reduce energy consumption and environmental pollutants as well as low investment costs in the process of separation. In this investigation, the optimization of effective parameters for separation of gas mixture of CH4, CO2, O2 and N2 is studied by modified poly(4-methyl-1-pentane) (PMP) membrane including nanoparticles (TiO2, ZnO, Al2O3). Design expert software was used and prevailing data on membrane modeling were categorized according to the process variables such as permeability, selectivity, composition and percentage of nanoparticle, and gas pressure difference. In order to validate the model, the results predicted by the model were compared with the experimental data. Good agreement was observed between the predicted and experimental data, and it was found that nanoparticles have a considerable effect on the results. In the case of gas permeability, the best results were obtained for the nanoparticles of alumina (15 wt%) at the pressure of 3 bar. However, titanium dioxide nanoparticle (10 wt%) at the pressure of 9 bar showed the best results for gas selectivity. The optimum point for both permeability and selectivity was obtained for the membrane containing 10 wt% titanium dioxide at 5 bar.
Characterization
Behjat Tajeddin; Najmaeh Ramedani; Habibolah Mirzaei
Abstract
To apply the nanomaterial as a component in the packaging material structure, in this research, the carboxymethyl cellulose (CMC)/polyvinyl alcohol (PVA) film were prepared with three levels of nanoclay particles (0.5, 1 and 3%) using solution casting evaporation method. The incorporation of nanoclay ...
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To apply the nanomaterial as a component in the packaging material structure, in this research, the carboxymethyl cellulose (CMC)/polyvinyl alcohol (PVA) film were prepared with three levels of nanoclay particles (0.5, 1 and 3%) using solution casting evaporation method. The incorporation of nanoclay on mechanical, water vapor permeability, and oxygen barrier properties of CMC/PVA-based film was investigated. The best result was obtained through the nanocomposite film contain 3% nanoclay. In the next step, the CMC/PVA/nanoclay films were employed for walnut packaging. After 90 days storage in the environmental condition, the optimum result was found through the nanocomposite film with 3% nanoclay in terms of oil content, moisture content, acidity and peroxide indexes of walnuts. According to the overall results, the reinforcement of CMC/PVA film with 3% nanoclay could be introduced as a good candidate for the development of high barrier food packaging material against the diffusion of water vapor and oxygen permeability.
Characterization
Mina Ahsani; Meisam Dabiri Havigh; Reza Yegani
Abstract
A polypropylene microporous membrane (PPMM) was fabricated by thermally induced phase separation (TIPS) method. The effects of protein size and structure as well as filtration pressure on the membrane performance and fouling mechanisms were investigated using two different proteins, bovine serum albumin ...
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A polypropylene microporous membrane (PPMM) was fabricated by thermally induced phase separation (TIPS) method. The effects of protein size and structure as well as filtration pressure on the membrane performance and fouling mechanisms were investigated using two different proteins, bovine serum albumin (BSA) and collagen, in dead-end filtration setup. Obtained results showed that, for each protein filtration, increasing the operational pressure led to higher irreversible fouling ratio (IFR) and consequently lower flux recovery (FR). Moreover, in collagen filtration, the higher portion of the total fouling ratio (TFR) belonged to reversible fouling ratio (RFR) and the FR of membrane in collagen solution filtration was higher than that in BSA solution filtration at the same operational pressure. The FR values were about 42.48 and 56.32% at 2 bar, 52.28 and 64.53% at 1.5 bar and 65.97 and 75.83% at 0.75 bar for BSA and collagen solutions filtrations, respectively. Investigation of the fouling mechanisms using Hermia's models showed that the cake filtration mechanism of fouling turned to pore blocking mechanism in both proteins filtrations by increasing the operational pressure. Obtained results using combined fouling models for all filtration processes confirmed that the cake filtration-standard blocking model (CFSBM) was the prevailing mechanism, whilst the contribution of standard blockage increased by increasing the operational pressure.
Characterization
Setareh Heidari; Yoones Jafarzadeh; Mahdi Seyfollahi Samarin; Reza Yegani
Abstract
In this study, neat HDPE and HDPE/PE-g-MA/EVA blend membranes were fabricated via thermally induced phase separation (TIPS) method and their fouling behaviors were examined using filtration of BSA protein. Membranes were characterized using FESEM, AFM, ATR-FTIR analyses and porosity measurement. Fouling ...
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In this study, neat HDPE and HDPE/PE-g-MA/EVA blend membranes were fabricated via thermally induced phase separation (TIPS) method and their fouling behaviors were examined using filtration of BSA protein. Membranes were characterized using FESEM, AFM, ATR-FTIR analyses and porosity measurement. Fouling behavior of membranes was analyzed using the resistance-in-series (RIS), classic and combined pore blocking models. The results of RIS model revealed that the magnitude of inherent, reversible and irreversible resistances decreased from 0.611 ×1013m-1 and ,1.578 ×1013m-1 and 0.525 ×1013m-1 for the neat membrane to 0.237 ×1013m-1, 0.789 ×1013m-1 and 0.154×1013m-1 for the blend membrane, respectively. None of the classical Hermia’s models were able to accurately predict fouling during the entire filtration run. The results obtained from the combined pore blocking model indicated that the combined cake formation-intermediate blocking model provided good prediction of fouling mechanism for both the membranes. However, comparison between fitted parameters showed that much greater fouling occurred for pure HDPE membrane. The key reasons for such different fouling behaviors were mainly attributed to the difference in hydrophobicity as well as the distribution of pore size on the surface of the pure and blend membranes.
Characterization
Sampat Bhati; Tibor Macko; Robert Brüll
Abstract
Hyphenating High Temperature High Performance Liquid Chromatography (HT-HPLC) with High Temperature Size Exclusion Chromatography (HT-SEC) (High Temperature Two Dimensional Liquid Chromatography (HT-HPLC x HT-SEC or HT 2D-LC)) leads to an isocratic elution in the second dimension, which in turn enables ...
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Hyphenating High Temperature High Performance Liquid Chromatography (HT-HPLC) with High Temperature Size Exclusion Chromatography (HT-SEC) (High Temperature Two Dimensional Liquid Chromatography (HT-HPLC x HT-SEC or HT 2D-LC)) leads to an isocratic elution in the second dimension, which in turn enables to use IR detector (quantitative detection) for monitoring the eluting polymers. Experimental data obtained from HT 2D-LC with IR detector are usually presented as contour plots, which can be mathematically described in matrices. Quantitative data about chemical composition, molar mass and concentration of all the segments, which are present in a polymer, can be obtained, after calibrating the HPLC separation (HPLC elution volume vs chemical composition), SEC separation (SEC separation vs molar mass) and response of the IR detector (IR response vs mass of the polymer). A new procedure based on subtraction and addition of matrices is described, which enables quantitative comparison of different polymer materials. This procedure enables to determine, which components are present in both materials (i.e., identical components or segments) and which are present only in one from both the materials (i.e., unique segments). Moreover, molar mass distribution, as well as chemical composition distribution of both identical and unique segments is evaluated from experimental data. The procedure was applied on two different ethylene-propylene copolymer samples.
Characterization
Mostafa Ahmadi; Seyed Mohammad Mehdi Mortazavi; Saeid Ahmadjo; Majid Zahmati; Khosrow Valieghbal; Davoud Jafarifar; Reza Rashedi
Abstract
Ethylene / 1-butene copolymers at different comonomer levels were synthesized using Ziegler-Natta catalyst to evaluate the applicability of thermal fractionation methods in predicting chemical composition distribution (CCD). The continuous melting endotherms by DSC were converted to continuous CCD, and ...
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Ethylene / 1-butene copolymers at different comonomer levels were synthesized using Ziegler-Natta catalyst to evaluate the applicability of thermal fractionation methods in predicting chemical composition distribution (CCD). The continuous melting endotherms by DSC were converted to continuous CCD, and the average comonomer contents were compared with NMR results. DSC underestimated comonomer content specifically at higher levels and was more sensitive to the drawn baseline. The thermally fractionated melting endotherms by SSA method were deconvoluted and transformed into discrete CCDs. SSA method underestimated average comonomer content even more, however results were more reproducible. The main shortcoming of the thermal methods was the inability of short ethylene sequences in forming discernible lamella thicknesses at high comonomer levels. Calibration curves were created for converting the predicted comonomer contents into absolute values and used for studying industrial LLDPEs with different comonomer levels. It was shown that SSA provides more reliable results and correlates more reasonably to the measured densities.
Characterization
Tao Zheng; Qian Li; Qian Zhou; Huayi Li; Qian Xing; Liaoyun Zhang; Youliang Hu
Abstract
9,10-Dihydro-9,10-ethano-anthracene-11,12-dicarboxylic acid disodium salt (DHEAS) was synthesized and used as a nucleating agent for poly(1-butene) (iPB). The isothermal crystallization kinetics of iPB having different nucleating agents were investigated by differential scanning calorimetry (DSC) and ...
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9,10-Dihydro-9,10-ethano-anthracene-11,12-dicarboxylic acid disodium salt (DHEAS) was synthesized and used as a nucleating agent for poly(1-butene) (iPB). The isothermal crystallization kinetics of iPB having different nucleating agents were investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The results showed that the nucleating agents increased the crystallization temperature and the crystallization rate and shortened the crystallization half-time (t1/2). As well, the nucleating agents could be used as heterogeneous nuclei in the iPB matrix and decreased the size of iPB. When the nucleating agent was DHEAS, the crystallization temperature of iPB was up to 93.6°C which was higher than that of other nucleating agents for iPB and pure iPB. The crystallization half-time in the presence of DHEAS was 0.58 min which was less than that of other nucleating agents for iPB and pure iPB. In this case, the spherulitic size of iPB was the smallest and the morphology was changed, which indicated that DHEAS displayed better nucleation effect among the studied nucleating agents.
Characterization
Sepideh Gomari; Ismaeil Ghasemi; Mohammad Karrabi; Hamed Azizi
Abstract
Nanocomposites based on polyamide 6 (PA6) and poly(ethylene-co-1-butene)-graft-maleic anhydride (EB-g- MAH) blends have been prepared via melt mixing. The effect of blend ratio and organoclay concentration on the crystallization and melting behavior of specimens were studied. Three types of commercial ...
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Nanocomposites based on polyamide 6 (PA6) and poly(ethylene-co-1-butene)-graft-maleic anhydride (EB-g- MAH) blends have been prepared via melt mixing. The effect of blend ratio and organoclay concentration on the crystallization and melting behavior of specimens were studied. Three types of commercial organo-modified clay (Cloisite 30B, Cloisite 15A and Cloisite 20A) were employed to assess the importance of the nanoclay polarity and gallery distance. The crystallization behavior was investigated using differential scanning calorimetry (DSC) and wide angle X-ray diffraction spectroscopy (WAXD). The strong interactions between amine end groups of PA6 and maleic anhydride groups of EB-g-MAH led to complete inhibition of EB-g-MAH crystallization according to the DSC results. A transformation from the α form to the γ form crystals of PA6, induced by both organoclays and EB-g-MAH, was monitored by WAXD and DSC. Small angle X-ray scattering (SAXS) was used to evaluate the morphology of nanocomposites. Moreover, transmission electron microscopy (TEM) was conducted to determine the location of organoclays and indicated that the organoclays mainly present in the PA6 matrix and rarely distribute in the EB-g-MAH phase in the case of low polarity organoclays. It was also evidenced that the organoclay with the most affinity to PA6 (Cloisite 30B) had the largest effect on the thermal and crystallization behavior of this phase in the blend.
Characterization
Ning Zhao; Ruihua Cheng; Qi Dong; Xuelian He; Zhen Liu; Shiliang Zhang; Minoru Terano; Boping Liu
Abstract
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 ...
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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.
Polyolefin degradation
Abbas Kebritchi; Mehdi Nekoomanesh; Fereidoon Mohammadi; Hossein Ali Khonakdar
Abstract
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 ...
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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.
