Molten Low-density Polyethylene Research Articles

Impact of gamma irradiation on physico-chemical and electromagnetic interference shielding properties of Cu2O nanoparticles reinforced LDPE nanocomposite films

In the current work, cuprous oxide (Cu2O) nanoparticles coated with Tween 80 were successfully synthesized via the chemical reduction method. Nanocomposites composed of low-density polyethylene (LDPE) and different ratios of Cu2O nanoparticles were fabricated by the melt mixing process. 10% of ethyl vinyl acetate (EVA) as a compatibilizing agent was added to the molten LDPE matrix and the mixing process continued until homogenous nanocomposites were fabricated. To study the influence of ionizing radiation on the fabricated samples, the prepared species were exposed to 50 and 100 kGy of gamma rays. The synthesized Cu2O nanoparticles were investigated by transmission electron microscopy (TEM) and X-ray diffraction (XRD). XRD and TEM analysis illustrated the successful formation of spherical Cu2O nanoparticles with an average size of 16.8 nm. The as-prepared LDPE/Cu2O nanocomposites were characterized via different techniques such as mechanical, thermal, morphological, XRD, and FTIR. Electromagnetic interference shielding (EMI) of the different nanocomposite formulations was performed as a promising application for these materials in practical life. The electromagnetic shielding effectiveness (SE) of the produced samples was measured in the X-band of the radio frequency range from 8 to 12 GHz using the vector network analyzer (VNA) and a proper waveguide. All the samples were studied before and after gamma-ray irradiation under the same conditions of pressure and temperature. The shielding effectiveness increased significantly from 25 dB for unirradiated samples to 35 dB with samples irradiated with 100 kGy, which reflects 40% enhancement in the effectiveness of the shielding.

Microwave-assisted catalytic co-pyrolysis of waste edible oil and low-density polyethylene: Synergistic enhancement of co-melt feeding

In this study, a new delayed feeding process for blending waste edible oil (WEO) as cosolvent with molten low-density polyethylene (LDPE) applied in microwave-assisted fixed bed pyrolysis was proposed. The experiment was carried out at the melting temperature of 250 ℃, the pyrolysis temperature of 550 ℃, and the catalytic temperature of 450 ℃. The co-feeding of the WEO and molten LDPE effectively promoted the formation of light aromatics, with the content of monocyclic aromatic hydrocarbons as high as 82.69 % (LDPE/WEO = 1:3) and the relative content of BTEX (benzene, toluene, ethylbenzene, xylenes) as high as 65.96 %. The proportion of feedstocks affects the distribution of pyrolysis products by adjusting the content of hydrogen radicals in the pyrolysis system. Hydrogen radicals derived from LDPE can combine with oxygen-containing intermediate from triglycerides, to promote the removal of oxygen in the form of H2O, and inhibit the decarboxylation and decarbonylation reactions. Compared with the pre-feeding process, the relative content of BTEX increased by 14.43 % and the relative content of PAHs decreased by 10.86 %. The application of downdraft reactors further improved the relative content of BTEX in pyrolysis oil. When the mass of SiC was 500 g, the peak relative content of BTEX was 69.79 %. This study provides a new process for the effective production of light aromatic hydrocarbons.

Insight into co-pyrolysis interaction of Pingshuo coal and low-density polyethylene under varied mixing configurations via in-situ Py-TOF-MS

The real-time detection of volatiles is crucial for exploring co-pyrolysis mechanisms. In this study, the co-pyrolysis interaction mechanism of Pingshuo coal (PC) and low-density polyethylene (LDPE) with three varied mixing configurations was explored based on the product distribution and stable radicals in char by using in-situ pyrolysis time-of-flight mass spectrometry with vacuum ultraviolet photoionization as well as electron paramagnetic resonance. Total ion currents results show that mixing configurations have an obvious impact on the release of volatiles. In the coal-LDPE test, the volatiles from coal promotes the cracking of long-chain branches in LDPE, resulting in high alkenes content. Meanwhile, the LDPE melts delay the release of coal volatiles causing a higher peak temperature of 478 °C. As for the LDPE-coal configuration, the LDPE volatiles has a better hydrogen-donor effect, which can interact with volatiles and char from coal pyrolysis to facilitate the formation of aromatics and phenols. Comparatively, coal/LDPE configuration prompts the molten LDPE to coat coal particles and exhibits poor synergies between coal and LDPE. In addition, LDPE-coal char has higher spin concentrations of C-, and O-centered radicals, indicating that the released ·H radicals from LDPE pyrolysis can well interact with char and unreleased volatiles in coal.

Experimental study on downward/opposed flame spread and extinction over electric wires in partial gravity environments

Downward/opposed flame spread over laboratory wire samples under varied gravity conditions were investigated in the range from 0 G to 1 G. Reduced gravity experiments are conducted by parabolic flights of an airplane. Limiting oxygen concentrations (LOCs) and flame spread rates (Vf) are obtained as a function of gravity level, with oxygen concentration, forced flow velocity, and wire characteristics such as insulation thickness and core material as experimental variables. The samples used in this study consist of low-density polyethylene (LDPE) insulation over metallic cores. Copper (Cu) and nickel-chrome (NiCr) were selected as core materials. It is found that the effect of gravity on the insulation flammability varies with the thermal conductivity of the wire core; the LOCs of the Cu sample are less affected by gravity, while those of the NiCr sample decrease with decreasing gravity level. On the other hand, Vf increase monotonically with increasing gravity level in the Cu sample, while Vf of the NiCr sample show a peak value under the low gravity conditions. It is suggested that these differences in the response of LOCs and Vf to the gravity level due to the difference in core materials are controlled by the fuel concentration in the reaction zone, which is a function of Vf. It is also found that the molten LDPE produced during the flame spread process shows unique behaviors depending on the gravity levels and wire characteristics. Some characteristics of the dynamic motion of the molten LDPE during the flame spread process, such as deformation and dripping, are also summarized in this paper. The experimental data obtained in this study provide useful information on the flammability of materials in a partial gravity environment and will serve as a database for fire safety design in future space exploration.

Functionalization of Low Density Polyethylene with Ricinol-2-oxazoline Methyl Maleate in a Twin-screw Extruder

AbstractThe grafting reaction of ricinol-2-oxazoline methyl maleate onto molten low density polyethylene was investigated in a twin-screw extruder. The influence of peroxide content, added ricinol-2-oxazoline methyl maleate and process variables such as residence time, screw speed and reaction temperature were considered. The rate and level of grafting were quantitatively measured by FTIR technique. Maximum level of grafting at constant peroxide content was obtained when concentration of ricinol-2-oxazoline methyl maleate reached 3%, above which it declined. The rate of grafting increased with increasing peroxide content. However crosslinking of polyethylene was found to have taken place as parallel competitive reaction which was intensified with increasing peroxide content. It was demonstrated that it is possible to make an optimization of the grafting reaction on the basis of experimental results. The considerable grafting yield with acceptable melt flow rate for the samples was achieved when initial ricinol-2-oxazoline methyl maleate and peroxide concentrations were 2 to 3% and 0.06 to 0.1 %, respectively.

Measurement of solubility and diffusion coefficients of ethylene in solid and molten low‐density polyethylene with different melt indices

AbstractThe diffusion behavior of ethylene in polyethylene is of great importance for the polymerization and degassing of polyethylene (PE) industry. Based on the gravimetric sorption and desorption measurement approach, an intelligent gravimetric analyzer is applied to obtain the solubility and diffusion coefficients of ethylene in solid low‐density PE (LDPE) with different melt indices at 30°C to 70°C, 0 to 4 atm and in molten LDPE at 160°C to 230°C, 0 to 4 atm, respectively. Results indicate that both the solubility and diffusion coefficients of ethylene in solid LDPE are smaller than those in molten LDPE, while the dissolution enthalpy and diffusion activation energy of ethylene in solid LDPE are higher. In addition, one‐ and two‐dimensional diffusion models are built and the effects of particle size, polymer properties, and operation conditions are systematically investigated on the diffusion behaviors of ethylene in solid and molten LDPE.

Combustion Characteristics of Municipal Solid Waste Bales

Combustion behaviour of municipal solid waste bales is a rarely studied topic hitherto. However, there is dire need to devote research on the topic because baling as a storage methodology is getting popular among waste management companies and fire episodes in such storage sites can have devastating economic, environmental and social implications. In this study, thickness of low density polyethylene (LDPE) plastic sheets (12 layers, 6 layers and no layer) and type of ignition source (pilot ignition, thermal radiation) were investigated to see their effect on combustion behaviour of bales. In total eleven tests with a single bale in each test were performed. It has been found that the bales not wrapped with LDPE plastic sheets may pose higher hazards for adjacently stored material to catch fire as the value of maximum heat release rate observed for them was higher than those wrapped with LDPE plastic sheets. Furthermore, it has been found that LDPE plastic wrapping do not contribute significantly to the combustion of bales when exposed only to thermal radiation from an adjacent fire. However, it plays a significant role in ignition of bales in case exposed to a pilot flame ignition source. Molten LDPE plastic trapped between the adjacently stored bales was found to be another important factor influencing the combustion of bales.

Mechanical strengths of molten and solidified LLDPE/LDPE blends and wood/LDPE composites under tensile deformation

AbstractThe mechanical strengths of neat low‐density polyethylene (LDPE), a blend of LDPE with linear low‐density polyethylene (LLDPE), and a composite of LDPE with wood flour (wood/LDPE) were investigated in molten and solidified states under tensile deformation. The results are discussed in terms of the effects of LLDPE and wood contents, roller speed, and volumetric flow rate. In LLDPE/LDPE blends, incorporating LLDPE from 0 to 30 wt% into LDPE caused a slight increase in drawdown force, a larger fluctuation in drawdown force, and a reduction of maximum roller speed to failure. The mechanical properties of the solidified LLDPE/LDPE corresponded to those of the molten LLDPE/LDPE with regard to the effect of LLDPE content. For wood/LDPE composites, increasing the wood flour content in molten LDPE caused considerable reductions in drawdown time and maximum roller speed to failure. The drawdown force increased with increasing wood flour up to 10 wt% before it decreased at the wood loading of 20 wt%. A number of voids and pores on the extrudate surfaces became obvious for the composites with 20 wt% of wood content. Increasing wood content enhanced the tensile modulus for the solidified LDPE but decreased its tensile strength. Unlike those of LLDPE/LDPE blends, the changes in tensile modulus and strength of solidified wood/LDPE composites with wood content did not correspond to those of the molten composites. In all cases, the drawdown force increased with increasing roller speed. The effect of volumetric flow rate from the extruder on the mechanical strengths of the solidified blends was more pronounced than on those of the molten ones. J. VINYL ADDIT. TECHNOL., 2011. © 2011 Society of Plastics Engineers

Effects of Roller Speed, Die Temperature, Volumetric Flow Rate, and Multiple Extrusions on Mechanical Strength of Molten and Solidified LDPE under Tensile Deformation

An experimental rig coupled with a high speed data-logging and recording system and a personal computer was specially designed and constructed for the real-time measurement of mechanical strength (in terms of drawdown force) as a function of volumetric flow rate and roller speed for virgin low-density polyethylene (LDPE) and reprocessed LDPE during a filament stretching process. The effect of the number of extrusion passes for the reprocessed LDPE was our main interest. The experimental rig was connected to the end of a single-screw extruder, which was used to melt and extrude the polymers. The LDPE filaments were then solidified and collected for studying the mechanical properties. The mechanical strength of the virgin LDPE and reprocessed LDPE were investigated in both molten and solidified states. The mechanical strengths of the virgin and reprocessed LDPEs under these two states are discussed and compared in terms of change in magnitude under a wide range of processing conditions (volumetric flow rate, die temperature, and roller speed). The results suggested that in the molten state the drawdown force for LDPE melts was dependent on volumetric flow rate, die temperature, roller speed, and the number of reprocessing passes. The drawdown force being affected by the number of reprocessing passes could be explained by molecular degradation and gelation effects when using high volumetric flow rates. In the solidified state, the tensile properties of the solidified LDPE increased with roller speed. The effect of the number of extrusion passes for the solidified LDPE was similar to that for the molten LDPE. In the case of volumetric flow rates, the mechanical properties of the solidified LDPE decreased with increasing volumetric flow rate, whereas those of the molten LDPE exhibited the opposite effect. Thus, the mechanical strength of the molten LDPE could not always be used to assess the mechanical properties of the solidified LDPE.

An Experimental Apparatus for Measurement of Elongational Flow Properties for LDPE Melt and the Effect of Testing Conditions

An experimental rig was designed and constructed for melt strength measurement and was assembled at the end of a single screw extruder used for the production of low-density polyethylene (LDPE) melt. The experimental rig was coupled with a high speed data logging system and a personal computer for the real-time measurement of melt strength. The molten LDPE was extruded through a capillary die, forming a continuous filament before being pulled down by speed-adjustable mechanical rollers until the filament failed. A digital camera was used for measuring the actual extrudate size at failure point. The drawdown forces as a function of volumetric flow rate from the extruder, roller speed, die temperature and take-up style were of interest in this study. It was found that the experimental rig could be used for accurate measurement of the mechanical strength for the LDPE melt. The experimental results suggested that the melt strength of LDPE was dependent upon the volumetric flow rate through the die from the screw extruder, roller speed, and the take-up style. For ladder-step take-up, increasing roller speed resulted in non-linear increases in the drawdown forces, the drawdown force changes being associated with the molecular disentanglement and elastic resistances of the branched LDPE melt. The drawdown forces of the LDPE melt measured under the rapid speed take-up method were 40–60% greater than those tested under the ladder-step speed take-up method, depending on the volumetric flow rate used in the screw extruder. The tensile viscosity of the LDPE melt was found to decrease slightly with strain rate and die temperature in the testing conditions used in this work.

Functionalization of Low Density Polyethylene with Ricinol-2-oxazoline Methyl Maleate in a Twin-screw Extruder

Abstract The grafting reaction of ricinol-2-oxazoline methyl maleate onto molten low density polyethylene was investigated in a twin-screw extruder. The influence of peroxide content, added ricinol-2-oxazoline methyl maleate and process variables such as residence time, screw speed and reaction temperature were considered. The rate and level of grafting were quantitatively measured by FTIR technique. Maximum level of grafting at constant peroxide content was obtained when concentration of ricinol-2-oxazoline methyl maleate reached 3%, above which it declined. The rate of grafting increased with increasing peroxide content. However crosslinking of polyethylene was found to have taken place as parallel competitive reaction which was intensified with increasing peroxide content. It was demonstrated that it is possible to make an optimization of the grafting reaction on the basis of experimental results. The considerable grafting yield with acceptable melt flow rate for the samples was achieved when initial r...

On the Use of a Kolsky Torsion Bar to Study the Transient Large-Strain Response of Polymer Melts at High Shear Rates

A Kolsky torsion bar is utilized successfully in a novel rheometric experiment for measuring the transient large-strain response of polymer melts under high shear-rate loading. A molten low-density polyethylene is studied with the new technique. The results show that the high-rate shear response of the material has an instantaneous rate dependence that may not be discernible at low rates and a strain-dependent hardening that saturates at large strains instead of fading. The usefulness of the technique and the significance of the findings are discussed in comparison with a modified rubberlike liquid theory and high-rate capillary measurements for low-density polyethylene melts.

Grafting of itaconic acid onto LDPE by the reactive extrusion: Effect of neutralizing agents

AbstractGrafting of itaconic acid (IA) onto low‐density polyethylene (LDPE) was performed by reactive extrusion where the initiator was dicumyl peroxide, and the neutralizing agents (NAs) were zinc oxides and hydroxides as well as magnesium oxides and hydroxides. The carboxyl groups were neutralized in molten LDPE directly in the course of acid grafting, and in prefabricated functionalized polyethylene (LDPE‐g‐IA). It was found that neutralizing agents introduced into the initial reaction mixture increase the yield of LDPE‐g‐IA while the carboxyl groups were neutralized partially or totally through chemical reactions. The physical structure of LDPE‐g‐IA did not in fact suffer any substantial changes. From the standpoint of neutralization activity, the NAs studied could be arranged as follows: Zn(OH)2 > ZnO > Mg(OH)2 > MgO. NA, added into the initial reaction mixture improved the grafting efficiency of IA onto LDPE. In case of the one‐step process (neutralization simultaneously with grafting), the neutralizing effect appears stronger than that in the two‐step process (neutralization of prepared LDPE‐g‐IA). This means that neutralization of carboxyl groups in IA was less effective when NA was introduced into LDPE‐g‐IA than for the case of the initial reactive mixture. Chemical neutralization of grafted IA results in products of improved resistance to thermal oxidation and thermal stability of melt. This result is of practical importance to the opportunities for widening the application range for PE modified by grafting IA, while preparing polymer blends to be compounded, processed, and used at elevated temperatures. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 828–836, 2003

Nonaffine network structural model for molten Low-Density polyethylene and High-Density Polyethylene in oscillatory shear

We propose molten polymer’s entanglement network deformation to be nonaffine and use transient network structural theory with the revised Liu’s kinetics rate equation and the revised upper convected Maxwell constitutive equation to establish a nonaffine network structural constitutive model for studying the rheological behavior of molten Low-Density Polyethylene (LDPE) and High-Density Polyethylene (HDPE) in oscillatory shear. As a result, when the strain amplitude or frequency increases, the shear stress amplitude increases. At the same time, the accuracy of the nonaffine network model is higher than that of affine network model. It is clear that there is a small amount of nonaffine network deformation for LDPE melts which have long-chain branches, and there is a larger amount of nonaffine network deformation in oscillatory shear for HDPE melts which has no long-chain branches. So we had better consider the network deformation nonaffine when we establish the constitutive equations of polymer melts in oscillatory shear.

Measurement and prediction of LDPE/CO2 solution viscosity

AbstractWhen CO2 is dissolved into a polymer, the viscosity of the polymer is drastically reduced. In this paper, the melt viscosities of low‐density polyethylene (LDPE)/supercritical CO2 solutions were measured with a capillary rheometer equipped at a foaming extruder, where CO2 was injected into a middle of its barrel and dissolved into the molten LDPE. The viscosity measurements were performed by varying the content of CO2 in the range of 0 to 5.0 wt% and temperature in the range of 150°C to 175°C, while monitoring the dissolved CO2 concentration on‐line by Near Infrared spectroscopy. Pressures in the capillary tube were maintained higher than an equilibrium saturation pressure so as to prevent foaming in the tube and to realize single‐phase polymer/CO2 solutions. By measuring the pressure drop and flow rate of polymer running through the tube, the melt viscosities were calculated. The experimental results indicated that the viscosity of LDPE/CO2 solution was reduced to 30% of the neat polymer by dissolving CO2 up to 5.0 wt% at temperature 150°C. A mathematical model was proposed to predict viscosity reduction owing to CO2 dissolution. The model was developed by combining the Cross‐Carreau model with Doolittle's equation in terms of the free volume concept. With the Sanchez‐Lacombe equation of state and the solubility data measured by a magnetic suspension balance, the free volume fractions of LDPE/CO2 solutions were calculated to accommodate the effects of temperature, pressure and CO2 content. The developed model can successfully predict the viscosity of LDPE/CO2 solutions from PVT data of the neat polymer and CO2 solubility data.

Solubility of nonpolar and slightly polar organic compounds in low-density polyethylene by inverse gas chromatography with open tubular column

Inverse gas chromatography (IGC) with open tubular column was used to determine low pressure solubilities of 13 organic solutes in low-density polyethylene (LDPE) for temperatures from 50 to 175°C. Based on the principle of corresponding states, two simple correlation equations were developed for estimation of the solubility of nonpolar and slightly polar solutes in rubbery and molten LDPE.

Electrical conduction in molten polymers

Measurements of the electrical conductivities and the dielectric constants of low density polyethylene (LDPE), high density polyethylene (HDPE), polystyrene (PS), and polyvinylidene fluoride (PVdF) have been carried out in their melting states. The sample polymers were sandwiched between two electrodes and were heated above their melting points up to 310°C. After application of a dc voltage, the current decayed with time until a steady current was reached for LDPE, HDPE and PS. However, the times required to reach the steady currents were shorter for the molten polymers than those for the solid polymers. On the other hand, the current of PVdF did not show monotonous decrease with time. Dielectric constants of the molten LDPE, HDPE and PS did not depend on the frequency. On the other hand, the dielectric constant of the molten PVdF decreased with increasing frequency and increased with increasing temperature in the low frequency region. These results indicate that impurity ions in PVdF may contribute to the electrical conduction. The measurements of the viscosities and the thermal analyses were also carried out.

Influence of shearing history on the rheological properties and processability of branched polymers. I

AbstractThe influence of shearing history on the viscoelastic properties of low‐density polyethylene (LDPE) is investigated. Swelling of extrudates from a melt indexer is measured for monitoring the variation in viscoelasticity. Continuous shearing of molten LDPE reduces the swelling ratio. The reduction is not due to molecular degradation, as evidenced by constancy of intrinsic viscosity. The rate of the reduction in the swelling ratio depends on the shearing conditions and characteristics of LDPE, but the swelling ratio finally attain a steady value. The swelling ratio reduced by the continuous shearing is completely recovered by solvent or heat treatment. The ratio of the completely reduced swelling ratio to the completely recovered one is defined as a new index representing the viscoelastic variation, the processing index (PI), and the relationship between PI and the primary molecular parameters of LDPE is investigated. It is concluded that the variation in the viscoelastic properties becomes more remarkable with increase in the weight‐average molecular weight. The cause of the viscoelastic variation is also discussed from the rheological and thermodynamic points of view.