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Polyolefins - Volume:5 Issue: 1, Winter 2018

Polyolefins Journal
Volume:5 Issue: 1, Winter 2018

  • تاریخ انتشار: 1396/11/16
  • تعداد عناوین: 8
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  • Liang Zhu, Xuelian He *, Ruihua Cheng, Zhen Liu, Ning Zhao, Boping Liu Pages 1-13
    SiO2/MgCl2 (ethoxide type)/TiCl4 Ziegler-Natta catalysts for use in ethylene polymerization and ethylene/1-hexene copolymerization have been prepared using silica with a supported layer of magnesium ethoxide (Mg(OEt)2) as a catalyst precursor, followed by treating with TiCl4 at different Ti/Mg molar ratios, which showed significant effects on the active centers and pore structures of the catalysts. The formation amount of β-MgCl2 carrier increased to a maximum with increasing the Ti/Mg molar ratio from 1.50 to 2.25, and then decreased with the further increasing of Ti/Mg molar to 2.50. When the Ti/Mg molar ratio reached 2.25, the catalyst showed the best performance of polymerization, which could be attributed to the most active centers, high surface area and loose surface structure, mainly owing to the high conversion of Mg(OEt)2 to β-MgCl2. The polymers obtained showed medium and high molecular weight (Mw) with medium molecular weight distribution (MWD). In contrast to the conventional Mg(OEt)2-based ZN catalysts, the sphericity of particles was easy to control in this bi-supported catalyst. Furthermore, the prepared catalysts exhibited rather high activity, good copolymerization ability and hydrogen response.
    Keywords: Polyethylene, magnesium ethoxide, Ti, Mg molar ratio, Ziegler-Natta catalyst, pore structure
  • Lei Cui, Ji-Xing Yang, Yan-Guo Li *, Yue-Sheng Li Pages 15-22
    Novel cyclic olefin polymers (COPs) derived from bulky cyclic olefins, tricyclodipentadiene (TCPD) and tricyclo[6.4.0.19,12]-tridec-10-ene (TTE), with high glass transition temperature (Tg), excellent thermal stability, and high transparency, have been synthesized by ring-opening metathesis polymerization (ROMP) and subsequent hydrogenation. ROMP of TCPD and TTE was carried out successfully without gel formation using a WCl6/i-Bu3Al/Et-OH/hexene catalyst system at room temperature. By changing the TCPD/TTE molar ratio, the optimized catalyst component ratio for the polymerization varied. Chemical structures of the unsaturated and hydrogenated polymers were characterized by 1H NMR technique. Thermal properties of these newly synthesized polymers were determined using TGA and DSC measurements. The degradation temperatures (Td) were all above 420°C in N2, indicating that all these copolymers had excellent thermal stability. After hydrogenation, Tg of ROMP polymers was decreased by 30-60°C. The Tg of h-pTCPD reached as high as about 230°C. The light transmittances of these polymer films were also analyzed using UV-Vis absorption spectroscopy. A high light transmittance of up to 92% was found by UV-Vis absorption spectra for these polymer films.
    Keywords: Ring-opening metathesis polymerization, cyclic olefin polymer, norbornene derivatives, tungsten, glass transition temperature
  • Hafez Maghsoudi * Pages 23-30
    In this paper, the performances of potential zeolite membranes were estimated by the Maxwell-Stefan model and then they were placed in Robeson plot of propylene/propane separation. Additionally, the effects of feed pressure and the mole fraction of propylene in the feed on both the propylene permeabilities and membrane permselectivities were investigated. The results showed that zeolite membranes had better performances than carbon and polymer membranes. However, the performances of carbon membranes were better than those of zeolites 4A and ITQ-3. Also, among various zeolites studied, a DD3R zeolite membrane had the highest propylene permselectivity. According to the minimum requirement needed for membranes (i.e., a minimum selectivity of 35 and a permeability of 1 Barrer) for propylene/propane separation, it was found that the zeolite membranes of DD3R, SAPO-34, Si-CHA and ITQ-12 had this performance requirement. However, DD3R and SAPO-34 zeolite membranes were more preferred than the polymer, carbon and composite membranes due to their higher performances.
    Keywords: Propylene, membrane, zeolite, Maxwell-Stefan model, gas separation
  • Ting Fu, Ruihua Cheng, Xuelian He, Zhen Liu, Zhou Tian, Boping Liu * Pages 31-45
    Vanadium-modified (SiO2/MgO/MgCl2)•TiClx Ziegler-Natta catalysts were prepared through co-impregnation of water-soluble magnesium and vanadium salts under different pH values. Several key factors such as pH value of co-impregnation solution during catalyst preparation, catalyst performances including catalytic activity, ethylene/1-hexene copolymerization and hydrogen response were investigated. It is found that the components, structures and performance of the catalysts are obviously affected by changing the pH value (pH=5, 7 and 9) of co-impregnation solution. An appropriate pH value (pH=7) can maximize catalytic activity and hydrogen response, while lower pH value (pH=5) is beneficial to the 1-hexene incorporation. The GPC results show that the polymers obtained have high average molecular weight.
    Keywords: Ziegler-Natta catalysts, Polyethylene, polymerization kinetics
  • Mehdi Hajiabdolrasouli *, Amir Babaei Pages 47-58
    The effects of three different mixers, two different feeding orders and nanoclay content on the structure development and rheological properties of PE/nanoclay nanocomposite samples were investigated. Fractional Zener and Carreau–Yasuda models were applied to discuss the melt linear viscoelastic properties of the samples. Moreover, scaling law for fractal networks was used to quantify clay dispersion depended on the PE matrix structure. The simultaneous feeding resulted in better dispersion and melt intercalation for the nanoclay as compared to the compatibilizer/nanoclay masterbatch feeding. The twin screw extruder (Brabender DSE 25 model) showed greater potential for melt intercalation of PE/nanoclay as compared to the internal mixers (Brabender W50 and Haake Rheomix 3000 batch mixer) . Comparing the thermal Analysis of PE, PE/PE-g-MA and PE/nanoclay samples by DSC technique showed the opposite effect of the compatibilizer and the nanoclay to crystallization behavior of PE. PE/nanoclay cast film samples were produced with three different draw ratios. X-ray diffraction structural analysis in conjunction with the melt linear viscoelastic measurements confirmed that the PE/nanoclay cast film produced at higher draw ratio showed the more effective melt intercalation. Tensile test showed the machine direction modulus and yield strength of both PE and PE/nanoclay cast film samples reduced with increase of draw ratio
    Keywords: Polyethylene, nanocomposite, film, rheology, tensile test
  • Mohammad Rostamizadeh *, Fereydoon Yaripour, Hossein Hazrati Pages 59-70
    Highly siliceous ZSM-5 nanocatalysts can dehydrate methanol to a wide range of hydrocarbons. In this study, the development of hierarchical H-ZSM-5 nanocatalysts (Si/Al=200) were reported for the methanol-toolefins (MTO) reaction. The nanocatalysts were prepared through a hydrothermal technique and treated by NaOH desilication. The parent and desilicated nanocatalysts were characterized using FE-SEM, XRD, FTIR, NH3-TPD and N2 adsorption-desorption techniques. The mesoporosity increased five times without significant collapse of the crystalline framework as a result of the appropriate desilication of H-ZSM-5 nanocatalyst. For the nanocatalyst, a high surface area of 189.5 m2 g-1, mesopore volume of 0.35 cm3 g-1 and well-adjusted strong acidity of 0.16 mmol NH3 g-1 resulted in a high methanol conversion of 100%, high propylene selectivity of 43% and low light paraffins selectivity of
    Keywords: Hierarchical zeolites, ZSM-5, desilication, nanocatalyst, MTO
  • Leticia Pereira, Maria Marques * Pages 71-84
    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 catalytically active center, but only acted as an alkyd transfer agent.
    Keywords: Homogeneous catalyst, bis(imino)pyridine iron complex, ethylene-norbornene copolymerization, alkyd transfer agent
  • Qian Li, Yongjie Zhang, Huayi Li *, Zhongchuan Peng, Yu Zhang, Youliang Hu Pages 85-95
    PP-g-PS copolymer is a typical compatilizer used in polypropylene and polystyrene immiscible blends. PP-g-PS copolymers with different side chain lengths were synthesized, and their thermal and mechanical properties were characterized by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and dynamic mechanical analysis (DMA), respectively. The DSC and POM results show that the introduction of PS side chain dramatically accelerates the crystallization rate of the PP main chain due to the covalent bond in the PP and PS copolymer. Furthermore, the copolymers become more rigid as the PS component content increases. Blend of PP with PP-g-PS copolymer was prepared to investigate the compatibility between PP and PS. The properties of five PP/PP-g-PS binary blends were characterized by DSC, DMA, scanning electron microscopy (SEM) and mechanical testing. Well dispersion of PS and small PS particle size are detected in the binary blends. The formation of covalent bond between PP and PS also increases the compatibility and interfacial adhesion between these two phases.
    Keywords: polypropylene, polypropylene-graft-polystyrene, binary blends, covalent bond, morphology