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Linear Low-density Polyethylene (linear + low-density_polyethylene)
Selected AbstractsTandem Action of TpMsNiCl and Supported Cp2ZrCl2 Catalysts for the Production of Linear Low-Density PolyethyleneMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 9 2006Maria Cristina A. Kuhn Abstract Summary: Linear low-density polyethylene (LLDPE) samples with different properties were prepared from ethylene, without the addition of an , -olefin co-monomer, using a combination of the catalyst precursors TpMsNiCl (TpMs,=,hydridotris(3-mesitylpyrazol-1-yl) and Cp2ZrCl2/SMAO-4, by varying the nickel loading mole fraction (xNi). Upon activation with methylaluminoxane (MAO), this binary catalytic system showed activities varying from 12.3 to 309.1 kg of PE,·,(mol[M],·,atm,·,h),1. The properties of the polymeric materials are influenced by xNi as well as by the temperature of polymerization, affording the copolymers with a melting point (Tm) between 118 and 135,°C. The GPC results show that the molecular weight () of the polymers is sensitive to the xNi. In all of the cases studied, the GPC curves displayed monomodal molecular weight distributions (MWDs) with the average molecular weight varying from 30,000 to 507,000 g,·,mol,1. Studies using dynamic mechanical thermal analysis (DMTA) show that the formation of different polymeric materials is associated with the branching content, with the stiffness varying according to the xNi and the temperature used in the polymerization reaction. Overview of the copolymerization process, from ethylene in the presence of MAO, mediated by catalysts 1 and 2/SMAO. [source] The effect of high-pressure food processing on the sorption behaviour of selected packaging materialsPACKAGING TECHNOLOGY AND SCIENCE, Issue 3 2004C. Caner Abstract The sorption behaviour and flavour-scalping potential of selected packaging films in contact with food simulant liquids (FSLs) (ethanol and acetic acid solutions) were evaluated after high-pressure processing (HPP). The films used were monolayer polypropylene (PP), a multilayer (polyethylene/nylon/ethylene vinyl alcohol/polyethylene: PE/nylon/EVOH/PE), film and a metallized (polyethylene terephthalate/ethylene,vinyl acetate/linear low-density polyethylene: metallized PET/EVA/LLDPE) material. D-limonene was used as the sorbate and was added to each of the FSLs. After HPP treatment at 800,MPa, 10,min, 60°C, the amount of D-limonene sorbed by the packaging materials and the amount remaining in the FSL was measured. Untreated controls (1,atm, 60°C and 40°C) were also prepared. Extraction of the D-limonene from the films was performed using a purge/trap method. D-limonene was quantified in both the films and the FSL, using gas chromatography (GC). The results showed that D-limonene concentration, in both the films and the food simulants, was not significantly affected by HPP, except for the metallized PET/EVA/LLDPE. Significant differences in D-limonene sorption were found in comparison with the control pouches. The results also showed that changes in temperature significantly affected the sorption behaviour of all films. Copyright © 2004 John Wiley & Sons, Ltd. [source] Changes in carotenoid, physicochemical and sensory values of deep-fried carrot chips during storageINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 5 2003Ahmad Sulaeman Summary Deep-fried carrot chips were packaged in layered film (metallized polyester and linear low-density polyethylene) pouches under a partial vacuum of <1% O2 concentration. Packages containing chips were stored in dark chambers at three conditions: 0,1 °C, 94,98% relative humidity (r.h.) (A); 22,23 °C, 31,45% r.h. (B); and 29,31 °C, 89,93% r.h. (C) for 0,5 months. Retention of , - and , -carotene content and vitamin A activity were >82% over 5 months for all conditions. Colour values (L, a, b) were unchanged over 5 months for A and B, but decreased gradually (P < 0.05) for C. No changes in moisture content, fat content, water activity, texture values and sensory values were observed over time for A and B, but changed (P < 0.05) for C. No sensory differences were observed by condition or time in colour. Carrot chips, packaged in partially vacuumed opaque pouches, can be stored for at least 5 months at 0,1 °C, 94,98% r.h. or 22,23 °C, 31,45% r.h. [source] Cohesive-driven particle circulation in the solids conveying zone of a single-screw extruderADVANCES IN POLYMER TECHNOLOGY, Issue 2 2008Michael R. Thompson Abstract Aspects of heat transfer within the solids conveying zone of a single-screw extruder were studied by using a specially constructed drum testing apparatus. Experiments were conducted with linear low-density polyethylene, polystyrene (PS), and polypropylene (PP) samples by examining their transient temperature profile while the heated drum was stationary or moving. In accordance with classic solids conveying theory, the granular beds of PP and PS remained as plugs while the drum rotated. In such cases, the dominant modes of heat transfer for these systems are conduction through the contact area of a particle and conduction through the interstitial gas. An exception to this behavior was found with PE, in which the bed temperature increased more rapidly while the drum rotated. Visual observations of the bed showed that the particles circulated in the presence of shear and that this complex flow pattern increased in velocity as the drum temperature approached the onset temperature for melting the PE material. With strong correlation between the rate of circulation and the temperature rise in the bed, the movement of particles was assumed to act in a convective heat transfer mode bringing about more uniform heating of the polymer. The circulation phenomenon was attributed to dominant adhesive forces at the particle,drum interface overcoming the cohesive strength of the bulk. © 2009 Wiley Periodicals, Inc. Adv Polym Techn 27:74,88, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20121 [source] Small-angle neutron scattering study of the miscibility of metallocene-catalyzed octene linear low-density polyethylene and low-density polyethylene blendsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2009Tae Joo Shin Small-angle neutron scattering (SANS) analysis was performed to investigate the miscibility of blends of metallocene-catalyzed octene linear low-density polyethylene (octene-mLLDPE) and low-density polyethylene (LDPE). The quantitative SANS analysis found that the blends are miscible in both the melt and the quenched states. Moreover, this analysis confirmed that the radii of gyration of octene-mLLDPE(D) and LDPE(H) remain unchanged in the quenched state and that the two polymer components cocrystallize via fast crystallization from the melt state. [source] Simulation of heat transfer during rotational moldingADVANCES IN POLYMER TECHNOLOGY, Issue 4 2003A. Greco Abstract In rotational molding, polymer powders are subjected to heating, melting, cooling, and subsequent solidification in biaxially rotating molds. Heat transfer phenomena during rotational molding are significantly affected by the presence of endothermic and exothermic transitions. In this paper instead of using the traditional moving interface method, a new approach is presented which is applicable to semicrystalline materials like linear low-density polyethylene. Melting is described by a statistical model and crystallization by a kinetic model. The model parameters are determined from differential scanning calorimetry measurements. The one-dimensional unsteady heat conduction equation is solved by a finite difference method. The numerical predictions are in good agreement with experimental data. The overall heat transfer model can be used for process optimization purposes. © 2003 Wiley Periodicals, Inc. Adv Polym Techn 22: 271,279, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10055 [source] Rotational molding of two-layered polyethylene foamsADVANCES IN POLYMER TECHNOLOGY, Issue 2 2001Shih-Jung Liu Rotational molding of polyethylene foams has increasingly become an important process in industry because of its resultant thicker walls, low sound transfer, high stiffness, and good thermal insulation. This report assesses the rotomoldability of two-layer polyethylene foamed parts. The polymeric material used in this study was linear low-density polyethylene and the foaming material was an endothemic chemical blowing agent. Two different molding methods, by powder and by pellet, were used to mold the multilayer foamed parts. Rotational molding experiments were carried out in a laboratory scale uniaxial machine, capable of measuring internal mold temperature in the cycle. Characterization of molded part properties was performed after molding. Optical microscopy was also employed to determine the bubble distribution in foamed parts. The final goal of this study was to investigate how the blowing agent and processing conditions can influence the process of rotational molding and the final product quality. It was found that the rotational molding of two-layer polyethylene foams produced parts of better impact properties, as well as fine outside surfaces. In addition, rotational molding of foamed parts by pellets saves the cost of powder grinding, but is counteracted by uneven inner surfaces. © 2001 John Wiley & Sons, Inc. Adv Polym Techn 20: 108,115, 2001 [source] Preparation of ethylene/1-octene copolymers from ethylene stock with tandem catalytic systemJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008Tao Jiang Abstract Tandem catalysis offers a novel synthetic route to the production of linear low-density polyethylene. This article reports the use of homogeneous tandem catalytic systems for the synthesis of ethylene/1-octene copolymers from ethylene stock as the sole monomer. The reported catalytic systems involving a highly selective, bis(diphenylphosphino)cyclohexylamine/Cr(acac)3/methylaluminoxane (MAO) catalytic systems for the synthesis of 1-hexene and 1-octene, and a copolymerization metallocene catalyst, rac -Et(Ind)2ZrCl2/MAO for the synthesis of ethylene/1-octene copolymer. Analysis by means of DSC, GPC, and 13C-NMR suggests that copolymers of 1-hexene and ethylene and copolymers of 1-octene and ethylene are produced with significant selectivity towards 1-hexene and 1-octene as comonomers incorporated into the polymer backbone respectively. We have demonstrated that, by the simple manipulation of the catalyst molar ratio and polymerization conditions, a series of branched polyethylenes with melting temperatures of 101.1,134.1°C and density of 0.922,0.950 g cm,3 can be efficiently produced. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Evaluation of the crystallization kinetics and melting of polypropylene and metallocene-prepared polyethylene blendsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Mohammad Razavi-Nouri Abstract The kinetics of the isothermal crystallization of a polypropylene (PP) random copolymer containing 5 mol % ethylene, a metallocene linear low-density polyethylene (m -LLDPE) with 3.3 mol % hexene-1 as a comonomer, and three blends were studied with differential scanning calorimetry at temperatures sufficiently high to prevent any crystallization of m-LLDPE. The analysis was carried out with the Avrami equation. The overall crystallization rate and the equilibrium melting temperature of the PP copolymer decreased with increasing amounts of m-LLDPE in the blends. The former was attributed to the effect of m-LLDPE in reducing the number of primary nuclei, and the latter was attributed to a lowering of the fold surface energy due to the limited partial miscibility of the blend components. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 634,640, 2007 [source] Solid-State NMR Characterization of the Multiphase Structure of Polypropylene In-reactor AlloyMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 10 2010Haijin Zhu Abstract A variety of solid-state NMR techniques were used to characterize the chain dynamics, miscibility and the micro-phase structure of a polypropylene (PP) in-reactor alloy system. The alloy was physically separated into three fractions, and the molecular dynamics and relaxation behavior of the pure fractions was then compared with the components in the alloy to achieve comprehensive understanding of the phase structure of the PP in-reactor alloy. The miscibility among different components of the alloy was studied by the rotational frame spin-lattice relaxation time. Proton spin-diffusion methods were used to quantify the domain thicknesses of different regions in the alloy. The results show that the alloy is composed of three phases, namely, a homo-polyethylene (HPE) matrix, a homo-polypropylene (HPP) dispersed phase, and a linear low-density polyethylene (LLDPE) interphase. The thickness of the LLDPE interphase is estimated to be 7.7,nm at room temperature, and changes dramatically with temperature. Finally, based on all the solid-state NMR results, a model for the micro-phase-structure of the PP in-reactor alloy is proposed, and a correlation between the micro-phase structure and the excellent mechanical property is established. [source] Life cycle environmental performance and improvement of a yogurt product delivery systemPACKAGING TECHNOLOGY AND SCIENCE, Issue 2 2004Gregory A. Keoleian Abstract A life cycle assessment was conducted to evaluate the environmental performance of the yogurt product delivery system used by Stonyfield Farm. A life cycle model was developed which included material production, manufacturing and disposition for primary and secondary packaging, as well as the related transportation links between these stages and filling, retail and the point of consumption. Product delivery systems (PDS) that utilized 4, 6, 8 and 32,oz polypropylene (PP) cups and 2,oz linear low-density polyethylene (LLDPE) tubes were analysed. Ten strategies for improving the environmental performance of these systems were proposed and their impacts on the total life cycle burden were analysed. The life cycle energy consumption for the 2, 4, 6, 8 and 32,oz containers was 4050, 4670, 5230, 4390 and 3620,MJ/1000,lb yogurt delivered to market, respectively. Material production of the primary packaging accounted for 58% of the life cycle energy, while Distribution 3 (yogurt delivery to distributors/retailers) alone accounted for one-third of the life cycle total energy. The life cycle solid waste profile showed that as the container size decreased, the solid waste burden increased, from 27.3,kg (32,oz) to 42.8,kg (6,oz) per 1000,lb yogurt delivered to market. This relationship was even more pronounced for the 4,oz (47.5,kg) and 2,oz (56.2,kg) product delivery systems. The greatest potential improvements in the environmental performance of the PDS are achievable through redesigning the primary packaging and using alternative manufacturing techniques for the yogurt cups. Shifting from injection moulding to thermoforming of 32,oz container reduces the life cycle energy and solid waste by 18.6% and 19.5%, respectively, primarily due to light-weighting. Elimination of lids for 6,oz and 8,oz containers provided similar benefits. Consumers purchasing yogurt in 32,oz instead of 6,oz containers can save 14.5% of the life cycle energy and decrease solid waste by 27.2%. Copyright © 2004 John Wiley & Sons, Ltd. [source] Thermal, electrical, and mechanical properties of Si3N4 filled LLDPE compositePOLYMER COMPOSITES, Issue 7 2009Qunli An Silicon nitride (Si3N4) filled linear low-density polyethylene (LLDPE) composite was prepared. The effects of Si3N4 filler content, dispersion, and LLDPE particle size on the thermal conductivity, and Si3N4 filled content on the mechanical and electrical properties of Si3N4 reinforced LLDPE composites prepared using powder mixing were investigated. The results indicate that there existed a unique dispersion state of Si3N4 particles in LLDPE, shell-kernel structure, in which Si3N4 particles surrounded LLDPE matrix particles. With increasing filler content and LLDPE particles size, thermal conductivity increased, and reached 1.42 W/m K at 30 vol% of filler, seven times as that of unfilled LLDPE. Furthermore, the examinations of Agari model demonstrate that larger size LLDPE particles form thermal conductive networks easily compared with smaller ones. The values predicted by theoretical model underestimate the thermal conductivity of Si3N4/LLDPE composites. In addition, the composites still possessed rather higher electrical resistivity and dielectric properties, but the mechanical properties decreased. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers [source] Process of grafting styrene onto LLDPE by swelling and suspension copolymerizationPOLYMER ENGINEERING & SCIENCE, Issue 9 2010Jing Yan A technology of swelling and suspension copolymerization was conducted to graft styrene onto linear low-density polyethylene (LLDPE). The graft mechanism of styrene with LLDPE had been described by 1H NMR and IR. The mean particle diameter and size distribution of the products with different proportions of LLDPE to styrene monomer were calculated. The morphology and thermal behavior of copolymers were characterized by scanning electron microscopy and differential scanning calorimetry. The glass transition temperature of copolymers increased with the addition of LLDPE, which proved the existence of the polyethylene- g -polystyrene copolymer. The grafting efficiency and granulation rate of suspension copolymerization were investigated. It was found that the grafting efficiency increased and the granulation rate decreased with the addition of LLDPE. POLYM. ENG. SCI., 50:1713,1720, 2010. © 2010 Society of Plastics Engineers [source] Maleated amorphous ethylene propylene compatibilized polyethylene nanocomposites: Room temperature nonlinear creep responsePOLYMER ENGINEERING & SCIENCE, Issue 8 2010Ali Shaito Nonlinear creep of polyethylene and its nanocomposites remains an area of significant interest. Maleated polyethylene is often used as a compatibilizer to ensure enhanced dispersion. This article investigates blown films of linear low-density polyethylene and its nanocomposites with montmorillonite-layered silicate (MLS). An amorphous ethylene propylene copolymer grafted maleic anhydride (amEP) was added to enhance the interaction between the PE and the MLS. Tensile results indicate that the addition of amEP and MLS separately and together produces a synergistic effect on the mechanical properties of the neat PE. Nonlinear creep was analyzed by examining creep and recovery of the films with a Burger model and the Kohlrausch-Williams-Watts relation. A consistent decrease in unrecoverable plastic strain was obtained in the nanocomposite samples. A decreased retardation time associated with MLS presence was determined. POLYM. ENG. SCI., 50:1620,1632, 2010. © 2010 Society of Plastics Engineers [source] Thermal conductivity and mechanical properties of aluminum nitride filled linear low-density polyethylene compositesPOLYMER ENGINEERING & SCIENCE, Issue 5 2009Junwei Gu To acquire polymer composites with high thermal conductivity and mechanical properties, the aluminum nitride (AlN) microparticles modified with titanate coupling reagent of isopropyltrioleictitanate (NDZ-105) were employed to blend linear low-density polyethylene (LLDPE) via powder mixing method. Thermal conductive coefficient of the AlN/LLDPE composites was measured using hot disk thermal analyzer, and the thermal stability characteristics of AlN/LLDPE composites were mainly investigated via thermogravimetric analyzer (TGA) and differential scanning calorimeter (DSC). The results indicated that the use of AlN particles modified by NDZ-105 significantly enhanced thermal conductivity and mechanical properties of AlN/LLDPE composites. The thermal conductivity coefficient , was 1.0842 W/mk with 30% volume fraction of AlN, about three times higher than that of native LLDPE. The tensile strength of composites was maximum (17.42 MPa) with 20% mass fraction of AlN. DSC analyses results indicated that AlN had an influence on the melting temperature and the crystallinity of LLDPE. Additionally, TGA analyses showed that the thermal stability of LLDPE was significantly increased with addition of AlN. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source] Crystallization and chemi-crystallization of recycled photodegraded polyethylenesPOLYMER ENGINEERING & SCIENCE, Issue 4 2005I.H. Craig Test bars (3 mm thick) made from a high-density polyethylene (HDPE), a low-density polyethylene (LDPE), and a linear low-density polyethylene (LLDPE) were injection-molded from virgin polymer and from blends containing recycled photodegraded polymer of the same kind. The molded bars were then subjected to ultraviolet (UV) exposure. Crystallinity measurements were made at different depths from the exposed surface using differential scanning calorimetry. The effects caused by processing and photodegradation were separated by comparing thermograms obtained in the initial DSC run and in a reheating run, respectively. Chemi-crystallization was produced by UV exposure. The results are interpreted in terms of molecular scission and photo-initiated molecular defects. Scission accounts for the observed chemi-crystallization, whereas the molecular defects inhibit crystallization and eventually limit chemi-crystallization. After remelting, crystallization of the photodegraded materials is influenced both by the molecular mass distribution and by the defect content of the material. The changes in crystallization behavior caused by photodegradation are different for the three polyethylenes. The results obtained using blends that included photodegraded recyclate were consistent with this material acting as a pro-degradent. The recyclability of the materials is discussed. POLYM. ENG. SCI., 45:588,595, 2005. © 2005 Society of Plastics Engineers [source] Processing characteristics and mechanical properties of metallocene catalyzed linear low-density polyethylene foams for rotational moldingPOLYMER ENGINEERING & SCIENCE, Issue 4 2004E. Archer The object of this work is to assess the suitability of metallocene catalyzed linear low-density polyethylenes for the rotational molding of foams and to link the material and processing conditions to cell morphology and part mechanical properties (flexural and compressive strength). Through adjustments to molding conditions, the significant processing and physical material parameters that optimize metallocene catalyzed linear low-density polyethylene foam structure have been identified. The results obtained from an equivalent conventional grade of Ziegler-Natta catalyzed linear low-density polyethylene are used as a basis for comparison. The key findings of this study are that metallocene catalyzed LLDPE can be used in rotational foam molding to produce a foam that will perform as well as a Ziegler-Natta catalyzed foam and that foam density is by far the most influential factor over mechanical properties of foam. Polym. Eng. Sci. 44:638,647, 2004. © 2004 Society of Plastics Engineers. [source] Study of oxidation after monoacrylate grafting on polyethylenePOLYMER INTERNATIONAL, Issue 8 2008Ourida Iguerb Abstract BACKGROUND: The surface properties of high-density polyethylene and linear low-density polyethylene were modified by grafting urethane monoacrylate monomer under UV irradiation. This graft polymerization was carried out on native substrates and on substrates pre-treated by wet oxidation, for different oxidation times. RESULTS: As the urethane monacrylate layer is crosslinked, its grafting efficiency was checked by dissolving the polyethylene substrates in hot toluene. Grafting was evidenced by Fourier transform infrared spectroscopy of the obtained residues, which showed that both the characteristic urethane acrylate (3350 cm,1) and polyethylene (2920, 730 and 720 cm,1) bands were observable for any polyethylene oxidation time. For an oxidation time longer than 10 hours, acrylate grafting was homogeneous and the grafted surface was smooth with a roughness of less than 10 nm. In addition, X-ray photoelectron spectroscopy analysis of the residues revealed that O/C had an average value of 0.19, which is lower than the value corresponding to pure acrylate (0.42), whereas N/C had an average value of 0.068, also lower than that of pure acrylate (0.09), thus confirming the grafting. CONCLUSION: A urethane monoacrylate layer was grafted on native and oxidized polyethylene films. For highly oxidized films, the grafted surfaces are smooth and homogeneous. Copyright © 2008 Society of Chemical Industry [source] Recycled PCB flour reinforced linear low-density polyethylene composites enhanced by water cross-linking reactionASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2009Chen-Feng Kuan Abstract Recycled printed circuit board (PCB) flour reinforced linear low-density polyethylene (LLDPE) composites were prepared successfully. Water cross-linking technique was adopted to improve the physical characteristics of the composites. Composites were compounded using a twin-screw extruder and treated with a coupling agent (vinyltrimethoxysilane, VTMOS) and a compatibilizer (polyolefin elastomer grafted with melaic acid, POE-g-MA). They were then moisture-cross-linked in hot water. The composite that was cross-linked in water exhibited better mechanical properties than the noncross-linked composite because of strong chemical bonding between the filler and the polyolefin matrix. When the PCB flour content reaches 60 wt% following 4 h of water cross-linking, the tensile strength and the flexural strength are increased by 18.8% (12.8,15.2 MPa) and 13.2% (21.9,24.8 MPa) respectively. Scanning electron microscopy (SEM) images of the fracture surfaces of water cross-linked composites indicated that good interfacial strength existed between the filler and the polyolefin matrix. Thermal analyses of water cross-linked composites indicated that the thermal degradation temperature and the heat deflection temperature (HDT) of the composite increased with the increasing of water cross-linking time. The HDT of the composite rose from 55.8 to 83 °C. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source] A Grade Transition Strategy for the Prevention of Melting and Agglomeration of Particles in an Ethylene Polymerization ReactorCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 7 2005M. R. Rahimpour Abstract To satisfy the diverse product quality specifications required by the broad range of polyethylene applications, polymerization plants are forced to operate under frequent grade transition policies. During the grade transition, the reactor temperature must be kept within the narrow range between the gas dew point and the polymer melting point, otherwise the particles melt or agglomerate inside the reactor. In the present study, a dynamic well-mixed reactor model is used to develop a grade transition strategy to prevent melting and agglomeration of particles in an ethylene polymerization reactor. The model predicts the conditions under which the temperature of the reactor is outside the allowable range in continuous grade transition. Manipulation of feed flow and cooling water flow rates has shown that the reactor temperature cannot be maintained within the allowable range. Hence, a semi-continuous grade transition strategy is used for this case so that the temperature is maintained within the allowable range. In addition, several continuous and semi-continuous grade transition strategies for the production of linear low-density polyethylene (LLDPE), medium density polyethylene (MDPE), and high-density polyethylene (HDPE) are compared. [source] Processing characteristics and mechanical properties of metallocene catalyzed linear low-density polyethylene foams for rotational moldingPOLYMER ENGINEERING & SCIENCE, Issue 4 2004E. Archer The object of this work is to assess the suitability of metallocene catalyzed linear low-density polyethylenes for the rotational molding of foams and to link the material and processing conditions to cell morphology and part mechanical properties (flexural and compressive strength). Through adjustments to molding conditions, the significant processing and physical material parameters that optimize metallocene catalyzed linear low-density polyethylene foam structure have been identified. The results obtained from an equivalent conventional grade of Ziegler-Natta catalyzed linear low-density polyethylene are used as a basis for comparison. The key findings of this study are that metallocene catalyzed LLDPE can be used in rotational foam molding to produce a foam that will perform as well as a Ziegler-Natta catalyzed foam and that foam density is by far the most influential factor over mechanical properties of foam. Polym. Eng. Sci. 44:638,647, 2004. © 2004 Society of Plastics Engineers. [source] Influence of side-chain structures on the viscoelasticity and elongation viscosity of polyethylene meltsPOLYMER ENGINEERING & SCIENCE, Issue 11 2002Gwo-Geng Lin Metallocene-catalyzed, low-density and linear low-density polyethylenes with similar melt indexes were used to investigate how side-chain structures influence the elongation viscosity and viscoelastic properties. The viscoelastic properties were determined with a rotation rheometer, while the elongation viscosities were acquired by using isothermal fiber spinning. The Phan-Thien-Tanner (PTT) model was also used to understand how the side-chain structure affects the elongation behavior. Experimental results demonstrate that the log G, vs. log G, plot can qualitatively describe the effects of the side chain branch on the rheological properties of polyethylene melts. According to the results determined by the PTT model, low-density polyethylene (LDPE) has low elongation viscosities at high strain rates. This low elongation viscosity can be attributed to the fact that LDPE has high shear thinning behavior. The long-chain branching tends to increase entanglements, thereby enhancing the storage modulus, elongation viscosity and shear-thinning behaviors. Uniform side-chain distribution lowers the entanglements, which results in a low storage modulus, elongation viscosity and shear-thinning behavior. [source] | |||||||||||||