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1.
Mohammed A. Bahattab 《应用聚合物科学杂志》2006,101(1):756-759
Ethylene polymer was synthesized by the treatment of a metallocene catalyst Zr(CP)2Cl2 solution with ultrasonic energy. Ultrasonic energy irradiation was used to change the polymer structure of the formed polymer. Different ultrasonic energy irradiation times were applied to the metallocene catalyst solution. The ultrasonic energy had an effect on the average molecular weight, molecular weight distribution, and polymer productivity. A lower average molecular weight and a narrower molecular weight distribution were produced with a longer ultrasonic irradiation time. The polymer productivity was almost constant when the metallocene catalyst was treated with ultrasonic energy. Finer polyethylene particles were produced with longer ultrasonic irradiation times. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 756–759, 2006 相似文献
2.
The leaching of the catalyst zirconocene dichloride (Cp2ZrCl2) from an SBA‐15 silica support during ethylene polymerization was studied; severe leaching was observed when commercial methylaluminoxane (MAO) was used as the cocatalyst. However, the removal of free trimethylaluminum (TMA) from an MAO solution with a sterically hindered phenol reduced the catalyst leaching by 97–100%. The results obtained from the leaching experiments with TMA‐free MAO suggested that the major reason for catalyst leaching was the free TMA in the commercial MAO solution, not the pure MAO itself. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4632–4635, 2006 相似文献
3.
The effects of branch content (BC) and comonomer type on the mechanical properties of metallocene linear low‐density polyethylene (m‐LLDPEs) were studied by means of a stress–strain experiment at room temperature. A total of 16 samples with different BCs and comonomer types were used. In addition, the effect of crosshead speed on the mechanical properties of m‐LLDPEs with different BCs was examined. The degree of crystallinity (Xt) of these copolymers was determined by differential scanning calorimetry. In addition, Ziegler–Natta linear low‐density polyethylenes (ZN‐LLDPEs) were also studied for comparison purposes. The increase in BC of m‐LLDPEs decreased Xt and the modulus. However, the ZN‐LLDPEs showed higher small‐strain properties but lower ultimate properties than the m‐LLDPEs with similar weight‐average molecular weights and BCs. In comparison with low‐BC resins, m‐LLDPEs with high BCs exhibited a stronger strain hardening during the stress–strain experiments. Strain hardening was modeled by a modified Avrami equation, and the order of the mechanically induced crystal growth was in the range of 1–2, which suggested athermal nucleation. The crosshead speed was varied in the range 10–500 mm/min. For low‐BC m‐LLDPEs, there existed a narrow crosshead speed window within which the maxima in modulus and ultimate properties were observed. The location of the maxima were independent of BC. The effect of the crosshead speed on the mechanical properties of the m‐LLDPEs was a strong function of BC. However, highly branched m‐LLDPE in this experiment showed a weak dependence on the crosshead speed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 5019–5033, 2006 相似文献
4.
Effect of polymerizable montmorillonites (P‐MMTs) on the morphology of polyethylene/montmorillonites (PE/MMTs) nanocomposites during filling polymerization was studied. The microstructure analysis showed that the P‐MMTs were more exfoliatable than nonpolymerizable MMTs in the preparation of PE/MMTs nanocomposites. By examining the influence of the polymerization condition on the microstructure of the resultant nanocomposites, it was confirmed that the shear force formed by the mechanical stirring was the driving force of the exfoliation dispersion of MMT sheets during the filling polymerization. Comparatively, the shear force on MMT sheets might be increased due to strong interaction between PE chains linked to the surface of P‐MMTs and the solvents molecules, which is the reason that polymerizable clay is more exfoliatable than nonpolymerizable clay. The copolymerization between polymerizable modifier and ethylene was confirmed by NMR measurements. Furthermore, the morphology of the resultant nanocomposites was influenced by the concentration of the dispersed P‐MMTs. The degree of exfoliation of the resultant nanocomposites at a relatively low concentration was higher than that at a high concentration. This is because of the multiscale organization of the organoclay dispersed in the organic medium. High exfoliation degree of MMTs and improved interaction between PE matrix and P‐MMTs in PE/P‐MMTs nanocomposites led to significant improvements in mechanical properties and barrier properties. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
5.
The effects of support friability (Φ) and ethylene/comonomer ratios were investigated over supported metallocene/methylaluminoxane catalysts prepared with nine different porous polymeric supports and various comonomer concentrations with a 2‐L reactor operated in the semibatch gas‐phase mode at 80°C and 1.4 MPa. Φ of the supports was measured with a newly devised method. The performance of the supported catalysts depended on support Φ as follows. The average homopolymerization activities varied from less than 6 t of polyethylene (PE) (mol of Zr)?1 h?1 for low‐Φ catalysts to 10–20 t of PE (mol of Zr)?1 h?1 for moderate‐Φ catalysts and up to 100 t of PE (mol of Zr)?1 h?1 for the high‐Φ catalysts. The presence of 1‐hexene and propylene comonomers increased the activity of the low‐Φ catalysts by up to 20‐fold and 50‐fold, respectively; that is, there were very marked comonomer effects. Activity enhancement by 1‐hexene was less than 3‐fold for the moderate‐Φ catalysts, whereas the high‐Φ catalysts showed little activity enhancement. Sometimes, 1‐hexene even resulted in activity reductions. Very different particle morphologies were obtained with the catalysts of different Φ's. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 514–527, 2007 相似文献
6.
Flow performance of metallocene linear low‐density polyethylene (mLLDPE) containing small amounts of polyethylene glycol (PEG) diatomite and diatomite/PEG binary processing aids respectively was investigated. The mLLDPE melt viscosity is increased by the addition of diatomite, but is decreased by addition of PEG or the diatomite/PEG binary processing aids. It was also found that the viscosity reduction of mLLDPE with the addition of diatomite/PEG binary processing aid was significantly greater than that obtained with the addition of only PEG. The flow curves of mLLDPE containing diatomite/PEG binary processing aid show extremely lower value and stronger dependence on shear rate than the others. It is suggested that the rheological improvement of mLLDPE with diatomite/PEG binary processing aids resulted not entirely from the wall slip promoted by PEG; the intrinsic structure may have changed under the application of shear flow. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1546–1552, 2004 相似文献
7.
In this work, fibrous very high molar mass polyethylene was prepared by Cp2TiCl2, which was supported on methylaluminoxane (MAO) pretreated mesoporous silica fiber. After the polymerization, an “ordinary” washing procedure was not sufficient to remove the aluminum residues of the cocatalyst MAO from the polymerization product. When hydrochloric acid was used in the termination of the polymerization, the aluminum existed as [Al(H2O)6]Cl3, the presence of which causes additional signals to DSC and XRD grams of the polyethylene. These signals have previously been interpreted to be attributed to the extended chain crystal structure of the polyethylene. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1812–1815, 2004 相似文献
8.
This work reports the synthesis of a series of reactor blends of linear and branched polyethylene materials using a combination of [1,4‐bis(2,6‐diisopropylphenyl) acenaphthene diimine nickel(II) dibromide] ( 1 )/MMAO, known as an active catalyst for the production of branched polyethylene, and [rac‐ethylenebis(indenyl) zirconium dichloride] ( 2 )/MMAO, which is active for the production of linear polyethylene. The polymerization runs were performed at various levels of temperature, pressure, and catalyst 2 molar fractions. At 5°C, there was very low influence of catalyst 2 molar fraction on the overall catalyst activity. However, at 30°C and 50°C, the overall catalyst activity increased linearly with catalyst 2 molar fraction. The same linear dependency was also found for the polymerization reactions carried out at 60°C and 100°C. At various levels of temperature and ethylene pressure, higher melting temperature and crystallinity were observed with an increase in catalyst 2 molar fraction. At 60°C and 100 psig, the DSC thermograms of the polymers produced with 1 / 2 /MMAO exhibited two distinct peaks with melting temperatures closely corresponding to the melting temperatures of the polymers produced with the individual catalysts, 1 /MMAO and 2 /MMAO. The GPCV analysis of all polyethylene samples showed monomodal molecular weight distributions with low polydispersities. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2212–2217, 2005 相似文献
9.
Marlene J. Cran Peter K. Fearon Norman C. Billingham Stephen W. Bigger 《应用聚合物科学杂志》2003,89(11):3006-3015
Chemiluminescence (CL) monitoring has successfully been applied to the study of the oxidative degradation of two‐component polyethylene blends made with commercially available low‐density polyethylene, linear low‐density polyethylene, high‐density polyethylene, and metallocene‐catalyzed linear low‐density polyethylene (mLLDPE) formulations. The emphasis in the analysis of the results is placed on blends containing mLLDPE to address the lack of CL information on these blends. The CL data are consistent with the thermal and physicomechanical properties of the blends, with a decreased blend miscibility being reflected in the CL data as a departure from the idealized behavior observed for more miscible blends. Furthermore, the results suggest that immiscibility in the solid state is reflected to some extent in the behavior of the melt. Preliminary experiments conducted to determine the level of consistency of CL results with respect to both variability between instruments and variability between techniques indicate a high degree of correlation in each case. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3006–3015, 2003 相似文献
10.
In situ intercalative polymerization for ethylene monomers was carried out to produce PE‐based hybrids through a slurry polymerization method. In this approach, organic solvent for olefin polymerization was found to be one of the most significant factors for the dispersion of the OMMT‐intercalated Et[Ind]2ZrCl2 catalysts, which determines that whether olefin monomers polymerize is in a well‐defined confinement environment or not. Understanding the olefin polymerization occurring in between the nanoscale silicate layers of OMMT as well as the corresponding structure of OMMT in an organic polymerization solvent is a critical step toward tailoring and characterizing nanocomposites formed by OMMT in a polyolefin matrix. As we know, the Et[Ind]2ZrCl2 catalyst and MAO are both better dissolved in toluene than that in hexane because of the larger polarity of toluene. Thus, in hexane the active sites of the OMMT/Et[Ind]2ZrCl2 catalyst exist in the silicate layers of OMMT and the PE chains grow in the middle of them, while in toluene the active specimens are exposed in the gel formed by the OMMT‐intercalated catalyst with MAO, which cause that the PE chains propagated in the mixture liquids. Consequently, when hexane is selected as the polymerization solvent, the formed PE‐based nanocomposites have a good dispersion of OMMT and the nanofiller content (TGA measurement residue at 600°C) is thus higher (>7.0 wt %). However, in toluene, most of the silicate layers of OMMT are agglomerated in the PE matrix. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 相似文献
11.
Prashant S. Umare Karumanchi Rao Gopal L. Tembe Deepa A. Dhoble Bhavna Trivedi 《应用聚合物科学杂志》2007,104(3):1531-1539
Soluble complexes of titanium(IV) bearing sterically hindered biphenols, such as biphenol, 1,1′‐methylene di‐2‐naphthol, 2,2′‐methylene bis(4‐chlorophenol), 2,2′‐methylene bis(6‐tert‐butyl‐4‐ethyl phenol), and 2,2′ ethylidene bis(4,6‐di‐tert‐butyl phenol), were prepared and characterized. These catalyst precursors, formulated as [Ti(O∧O)X2], were active in the polymerization of ethylene at high temperatures in combination with ethylaluminum sesquichloride as a cocatalyst. The ultra‐low‐molecular‐weight polyethylenes (PEs) were linear and crystalline and displayed narrow polydispersities. The catalytic polymerization leading to PE waxes in this reaction exhibited unique properties that have potential applications in surface coatings and adhesive formulations. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1531–1539, 2007 相似文献
12.
Maleated polyethylene/silicate nanocomposite and maleated polyethylene/SiO2 blown films were prepared by melt extrusion. The silicate and SiO2 significantly affected the physical properties of the films. The former films showed higher tensile strength than the latter films. This high reinforcement effect seemed to be attributable to the strong interaction between the matrix and silicate as well as the uniform dispersion of silicate layers in the polymer matrix. The addition of silicate beyond a certain content gave a worse Elmendorf tear strength than SiO2. The silicate did not increase the falling dart impact strength at all. The worst Elmendorf strength apparently originated from the orientation of anisotropic silicate rather than the orientation of lamellae of the polymer matrix, and the silicate made the films more brittle. The well‐dispersed silicate layers in the polymer matrix gave almost the same optical properties as the pure polymer despite the increase in the silicate content. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2131–2136, 2003 相似文献
13.
The yield behavior of melt‐mixed nanocomposites containing 5 wt % organically modified montmorillonite in matrices of a linear low‐density polyethylene (LLDPE) or a modified polyethylene was studied as a function of the temperature and strain rate. In the melt‐mixed LLDPE nanocomposite, the montmorillonite showed a slight increase in the clay spacing, which suggested that the clay was at best intercalated. Transmission electron microscopy (TEM) images showed that the dispersion in this nanocomposite was poor. The use of the modified polyethylene promoted exfoliation of the clay tactoids in the nanocomposite, as assessed by X‐ray diffraction and TEM. In both nanocomposites, the yield mechanisms were insensitive to the addition of the organoclay, even though modest increases in the modulus were produced. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3044–3049, 2006 相似文献
14.
Several carbon blacks with surface areas from 105 to 1353 m2/g were used to produce composites through melt compounding with a high‐density polyethylene matrix. The electrical behavior of the obtained composites was investigated by the measurement of their resistivity as a function of the carbon black content and type at various temperatures and times during isothermal annealing treatments. The percolation threshold markedly decreased as the carbon black surface area increased, reaching a minimum value of 1.8 vol % for the carbon black with a surface area of 1353 m2/g. The resistivity passed through a maximum as the test temperature increased. Moreover, the analysis of the experimental data evidenced that the host high‐density polyethylene matrix and the conductive carbon black network rearranged during the isothermal thermal treatments, causing a resistivity decrease. This rearrangement became less and less important as the carbon black surface area increased. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 相似文献
15.
The coarsening rates of the two‐phase morphologies of linear polyethylene/poly(ethylene‐co‐1‐octene) blends were determined as functions of molecular weight. Samples with cocontinuous morphologies that were prepared through solution blending were annealed in the melt state for various times, and, subsequently the length scales of the morphologies were determined with a line‐intersection method. Length‐scale data were multiplied by a function that normalized for the effects of differences in zero‐shear‐rate viscosity and thermal energy; after normalization, the data largely fell on one trend line within the bounds of experimental error. This indicated that the principal effect of increasing molecular weight was to slow the coarsening rate through an increase in melt viscosity, with little effect from the thermodynamic compatibility of the two polymers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1655–1661, 2003 相似文献
16.
Sven Kselau Saskia Scheel Linnea Petersson Chau‐Hon Ho Gerrit A Luinstra 《Polymer International》2019,68(5):946-954
Nanocomposites of isotactic polypropylene (iPP) with 0.5 wt% filler of MgO@Mg(OH)2 (35 nm) or silicon dioxide (20–60 nm) or barium titanate (50 nm) nanoparticles were obtained from melt compounding of filler masterbatches with commercial iPP. The masterbatches with 5 wt% nanofiller were prepared in an in situ polymerization procedure using a metallocene/methylaluminoxane (MAO) catalyst system that was supported on the respective oxides. The original agglomerates of the nanoparticles were broken up by treatment with dibutylmagnesium for MgO@Mg(OH)2, and with ultrasound in the presence of MAO for SiO2 and BaTiO3. The tacticity (98% mmmm) of the in situ formed PP was not influenced by the presence of the nanofillers. Scanning electron microscopy and energy‐dispersive X‐ray spectroscopy mapping show a fine dispersion of single particles and small clouds or clusters. The primary nanoparticles appear to be surrounded by polymer. The elongation at break was decreased to 50, 17 and 9% for MgO@Mg(OH)2), SiO2 and BaTiO3, respectively. After melt compounding with iPP, a homogeneous single‐particle distribution of the oxidic nanoparticles was found in the resulting composites with 0.5 wt% filler content. © 2019 Society of Chemical Industry 相似文献
17.
Ibnelwaleed A. Hussein 《应用聚合物科学杂志》2008,107(5):2802-2809
The effect of weight‐average molecular weight (Mw) on the nonisothermal crystallization kinetics of linear metallocene polyethylene (m‐PE) was studied with modulated differential scanning calorimetry. Six linear m‐PEs of molecular weights in the range 122–934 kg/mol were prepared by gas‐phase polymerization. The cooling rate (R) was varied in the range 2–20°C/min, and it significantly affected the crystallization behavior. Mw had a weak influence on both the peak crystallization temperature and the crystallization onset temperature. All m‐PEs showed primary and secondary crystallizations. At both low and high R's, the crystallinity showed a significant drop (～ 30%) when Mw was increased from 122 to 934 kg/mol. At low R's (< 10°C/min), the rate parameters in the modified Avrami method [primary rate constant (kR)] and Mo method [F(T)] of analyses agreed in suggesting that an increased Mw slowed the rate of crystallization. The Mw dependency of kR followed the Arrhenius type (kR = kRoe281/Mw, where kRo is a rate‐dependent constant). However, at higher R's, kR approached a constant value. The order parameters obtained by the different methods of analysis (n and α) were independent of Mw, which suggests that the crystal type remained the same. Hoffman–Lauritzen theory was used for data analysis, and activation energy per segment showed a significant decrease, from 225.0 to 11.8 kJ/mol, when Mw was increased from 152 to 934 kg/mol. Finally, all methods of analysis suggested a significant effect of Mw on slowing the overall crystallization process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
18.
In this study, saline water was used as a preintercalating agent for pristine clay surface to assist clay dispersion in one‐step melt state process. The solution contains dodecyl trimethyl ammonium chloride salt in distilled water and was injected into the twin‐screw extruder using a high pressure dosing pump. To investigate the effect of dissolution of alkyl salt on clay dispersion, two samples with the same compositions were prepared through both salt solution and pure water injection which was compared with organo‐modified prepared sample. The resultant compounds were characterized using x‐ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and dynamic rheological measurements (RMS). Tensile and notched‐Izod impact properties of the samples were measured as well. The XRD results showed no peak for the sample containing 2 wt % pristine clay, prepared via injection of salt solution representing exfoliated microstructure. In addition, TEM images showed proper dispersion and distribution of clay platelets in the matrix. Furthermore, RMS results showed that the slop of the storage modulus has been declined and for the sample using saline, the variation was prominent as a result of network structure formation. Tensile results also showed an increase of tensile modulus in the range of about 22% for the sample containing 2 wt % clay. Izod impact strength in the sample prepared via injection of salt solution showed fracture energy comparable to neat polyethylene. Additionally, the crystallization data in terms of degree of crystallinity, melting, and crystallization temperatures of samples represented no noticeable change compared to neat polyethylene. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献
19.
Nano‐ZnO/high‐density polyethylene (HDPE) composite films were prepared via melt blending and a hot compression‐molding process. The properties, including ultraviolet absorption, mechanical and antibacterial properties of the films, and plasticizing behavior of the composites, were investigated. The results show that the absorbance in the ultraviolet region of the HDPE films was enhanced after the addition of modified nano‐ZnO to the HDPE matrix. Also, we found that improvement in the HDPE films of the tensile strength and elongation at break was achieved by the incorporation of modified ZnO nanoparticles up to 0.5 wt % in contrast with the original nano‐ZnO/HDPE composite films. Antibacterial testing was carried out via plate counting, and the results indicate that the HDPE films doped with modified ZnO nanoparticles showed favorable antibacterial activity, especially for Staphylococcus aureus. However, the low doped content of modified nano‐ZnO in the HDPE matrix made the balance torque of the composites increase slightly. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
20.
北京化工研究院合成了50余种新型茂金属化合物,在茂金属催化剂均相乙烯聚合的系统研究基础上,深入研究了载体茂金属催化剂的制备方法和制备条件等因素与载体催化剂性能的关系,研制出性能优异的载体茂金属催化剂。采用载体茂金属催化剂进行了浆液法和气相法乙烯聚合中试研究,还进行了茂金属聚乙烯树脂的加工应用研究,树脂性能与国外同类产品相当。 相似文献