Behavior Of Low-density Polyethylene Research Articles

Effect of thermal-oxidative and mechanical degradation of recycled LDPE on foaming

In this study, we investigated the effect of recycling process on the molecular structure, viscoelasticity and foaming behavior of low density polyethylene (LDPE). A series of LDPE samples with different recycling process was prepared by multiple extrusion using a twin-screw extruder. The molecular weight distribution (MWD) was characterized by gel permeation chromatography (GPC). Wider MWD indicated the generation of higher molecular weight products. Small-amplitude oscillation rheology showed reduced loss factors, indicating that the chain entanglement was more difficult to relax. Moreover, nonlinear viscoelasticity was investigated using elongational rheology and molecular stress function (MSF) model. The results showed a steeper strain hardening exhibited in recycled LDPE. The correlated parameter β in the MSF model indicated that the recycling did not significantly change the branches regularity in LDPE, while the increasing [Formula: see text], the other correlated parameter, indicated that the chain entanglement was enhanced, which was corresponded to the improvement of high molecular weight component. The foaming results revealed that the recycled LDPE had finer cellular structure and higher nucleation density. Moreover, despite adding PP and active CaCO3 to simulate the impurities, the foamability loss of these mixed samples was well restricted and still valuable. Recycled LDPE is instead better than its corresponding virgin one in foaming performance, exhibiting the application potential for further developments.

Investigating the sustainability of agricultural plastic products, combined influence of polymer characteristics and environmental conditions on microplastics aging

The accelerated use of plastic products for agricultural practices has raised global concern regarding their negative impacts on soil health. This study aims to better understand the combined influence of polymer characteristics and environmental conditions on microplastic photodegradation within the agricultural soil system. For this purpose, the photodegradation behavior of low density polyethylene (LDPE) microplastics was studied through accelerated UVA radiation experiments under two different relative humidity (RH10 and RH70) and soil deposition conditions. The variations of plastics' surface physiochemistry due to the accelerated photodegradation were studied using Attenuated Total Reflectance-Fourier Transform Infrared spectroscopy (ATR-FTIR), X-ray Photoelectron Spectroscopy (XPS), and Field Emission Scanning Electron Microscopy (FE-SEM). The carbonyl and vinyl indices were calculated using the ATR-FTIR information to compare the degree of microplastics' photodegradation. The plastics' bulk characteristics, including the percentage of crystallinity and molecular weight distributions, were examined using the Differential Scanning Calorimetry (DSC) and Gel Permeation Chromatography (GPC). Furthermore, the extent of UVA light interaction with the microplastics was studied by determining spectral quantum yield. The results demonstrated that new LDPE microplastics with a lower molecular weight (Mw = 233 kD) were subjected to a greater extent of photodegradation than those with greater molecular weight (Mw = 515 kD). Elevated relative humidity (RH70) limited the photooxidation process of microplastics and consequently reduced the surface chemistry alterations. Deposition of soil particles with respect to the plastic particles impacted the photodegradation behavior. The microplastics covered by soil particles were not degraded, unlike those deposited next to the soil particles. The knowledge developed through this study could encourage the farmers and agricultural stakeholders to apply more efficient practices to remove plastic residuals after harvesting and conduct proper plastic disposal practices to protect soil health.

Evaluation of Low-Density Polyethylene Thermomechanical and Fractographic Behavior after Ultraviolet Radiation Exposure

Polyethylene (PE) has an exclusive set of properties, such as good toughness and mechanical resistance as well as high flexibility, and ease conformation. However, when exposed to degrading agents, such as heat, humidity and radiation, macromolecular changes can be observed and consequently affect the PE. This work evaluated for the first time the thermomechanical and fracture behavior of low-density polyethylene (LDPE) subjected to degradation at different times of exposure to ultraviolet (UV) radiation. The changes induced in the chemical structure and the highlighted behavior were investigated through thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier-transformed infrared spectroscopy (FTIR), reticulation content, tensile test, and scanning electron microscopy (SEM). The results suggest that UV radiation modify the failure of the polymer by reducing its crystallinity and dramatically increasing its degree of crosslinking. These modifications impair the LDPE mechanical performance as well as its thermal stability.

Effect of UV-aging on the mechanical and fracture behavior of low density polyethylene

In polyethylene, a transient, oxidation-induced strengthening is often observed over a narrow range of UV radiation dose. In addition, plastic deformation may not be volume-preserving due to cavitation. Here, we employ a suite of analytical experiments and mechanical testing on pristine and oxidized low-density polyethylene films in order to investigate the transient strengthening behavior as well as the propensity for cavitation to fracture. Emphasis is laid on connecting macroscopically observed behavior with microscopic information involving the competition between multi-scale phenomena: chain scission and cross linking at a fine scale, chemi-crystallization, oxidation-induced cracking and mechanical damage at the meso and coarse scales. The results provide an insight into the role of cavitation in the oxidative embrittlement of semicrystalline polymers.

Rheological and kinetic studies of low density polyetyhlene (LDPE) – chitosan biocomposite film

The amount of plastic waste has always increased over the years and caused many problems in the environment because of its poor degradation rate characteristics. Recently, the interest in biodegradable polymer to substitute these synthetic plastic materials has been increased. Biocomposite materials have better biodegradability rate and can be utilized for several applications, such as packaging, agriculture, biomedical and healthcare. Chitosan as natural polymer that has good biodegradability can be combined with low density polyethylene (LDPE) to improve its mechanical properties. The LDPE-chitosan biocomposites were made by mixing chitosan and LDPE with maleic anhydride as compatibilizer and perbutyl Z as an initiator. In this study, the decomposition kinetic and thermal behavior of low density polyethylene (LDPE)-chitosan biocomposites were investigated by thermogravimetric analysis (TGA). The residual weight of biocomposites after decomposition process was analyzed. The samples were heated in the range of temperature from 25 °C to 500 °C and at different heating rates of 5, 10, 15, 20 °C/min, respectively. The result shows that activation energy decreased along with the increasing of chitosan concentration. This result indicates that the LDPE-chitosan biocomposite is a promising candidate for substitution of synthetic plastic.

Swift Heavy Ion Irradiated Low-Density Polyethylene: Structural and Optical Investigations

The structural and optical effects of copper (50 MeV) and carbon (70 MeV) ion irradiation of low density polyethylene (LDPE) are described. X-ray diffraction (XRD) and differential scanning calorimetric (DSC) techniques were used to explore the structural behavior, while Fourier transform infrared (FTIR) and UV-visible spectroscopies were used to collect the optical data. Structural parameters, such as interplanar separation, distortion factor, crystallite size and degree of crystallinity, were measured to understand the change in the structural behavior of LDPE caused by the swift heavy ion irradiation. In the irradiated polymeric samples, the formation and growth of new carbon enriched species were revealed by the FTIR and UV-visible analysis, which led to the decrease of their optical bandgap energy with the increase of ion fluence.

Scratch behavior of low density polyethylene film: Effects of pre-stretch and aging

To investigate the influences of pre-stretch and aging on the scratch behavior of low density polyethylene (LDPE) film, the scratch tests were conducted with the linearly increasing normal load. The scratch process was recorded using a high-speed camera and the scratched surface morphology was microscopically investigated. Three typical film scratch deformation/damage modes, i.e., smooth sliding, folding over and tension induced puncture were identified. Their mechanisms and evolution processes were analyzed. It was found that the pre-stretch could improve the scratch performance of LDPE film in the same direction while the scratch resistance perpendicular to the pre-stretch direction declines. While the thermal aging tends to diminish this anisotropic scratch performance, a long thermal aging time causes poor scratch resistance. A good correlation was found between the critical load of tension induced puncture and the elongation at break of LDPE film. Thus, the elongation at break can be one of the good indexes to evaluate the scratch resistance. Those findings provide a fundamental insight for material scientists to design LDPE film with better scratch performance and longer service lifetime.

Electrically and Thermally Conductive Low Density Polyethylene-Based Nanocomposites Reinforced by MWCNT or Hybrid MWCNT/Graphene Nanoplatelets with Improved Thermo-Oxidative Stability.

In this paper, the electrical and thermal conductivity and morphological behavior of low density polyethylene (LDPE)/multi-walled carbon nanotubes (MWCNTs) + graphene nanoplatelets (GNPs) hybrid nanocomposites (HNCs) have been studied. The distribution of MWCNTs and the hybrid of MWCNTs/GNPs within the polymer matrix has been investigated with scanning electron microscopy (SEM). The results showed that the thermal and electrical conductivity of the LDPE-based nanocomposites increased along with the increasing content of carbon nanofillers. However, one could observe greater improvement in the thermal and electrical conductivity when only MWCNTs have been incorporated. Moreover, the improvement in tensile properties and thermal stability has been observed when carbon nanofillers have been mixed with LDPE. At the same time, the increasing content of MWCNTs and MWCNTs/GNPs caused an increase in the melt viscosity with only little effect on phase transition temperatures.

Efficient enhancement in polyethylene biodegradation as a consequence of oxidative fragmentation promoted by pro-oxidant/pro-degradant metal stearate

Abstract We report an investigation on the effect of iron and cobalt stearates as pro-degradants and their synergetic effect on the oxidation and subsequently the biodegradation behavior of low density polyethylene (LDPE) film. For this, LDPE films containing different amounts of these additives were prepared and characterized upon exposure to accelerated thermal and photo-oxidation. The analysis shows that the films underwent a significant degradation as monitored by carbonyl index, changes in the crystallinity, in the onset of decomposition temperature and hydrophobicity. The tendency to biodegradation of the oxidized LDPE, with and without pro-oxidant/pro-degradant, was then assessed through the soil burial and the aqueous medium techniques. After an incubation period of 120 days, samples were characterized by means of structural changes and cumulative CO2 emissions. During the incubation in both soil and aqueous medium, the fragmented films with pro-oxidant/pro-degradant showed a significant decrease in oxygenated moieties present initially in the polymer and formed during the accelerated ageing when compared with LDPE without pro-oxidant/pro-degradant, and the biodegradation in the different environment was highly effective following the order LDPE/Co>LDPE/Co/Fe>LDPE/Fe>LDPE and in the range of 13–45% of mineralization after 120 days in aqueous medium and 13–29% in solid medium. These results suggest the role of pro-oxidant/pro-degradant and specially their mixture and the natural environment in oxidation and degradation of LDPE samples and in the mineralization process of oxidized fragments.

Modeling and nonlinearity studies of low density polyethylene (LDPE) tubular reactor

One of the constraints in developing a successful model based control scheme is the selection of an appropriate model structure. Typically, the selected model should be able to capture the dynamics and nonlinearity behavior of the process. However, the model selection task can become challenging when the nature and behavior of the process is not fully comprehended. The aim of this study is to observe the nonlinearity behavior of Low Density Polyethylene (LDPE) Process in a Tubular Reactor. In order to study these behaviors, several nonlinearity tests based on Pearson [1] work have been adopted. The tests are asymmetric response, harmonic response, input multiplicity and output multiplicity. These tests have been conducted on steady state and dynamic simulation model of the process, which was developed using Aspen Plus software. Based on these tests, the LDPE process shown the existences of asymmetric response, super-harmonic response, input multiplicity and output multiplicity. It is shown that the process could be classified as strong nonlinearity system. Therefore, the application of nonlinear model is suggested to be more feasible for model based control application in the LDPE tubular reactor.

Influence of Nanoclay Addition on the Fatigue Behavior of Polymer Nanocomposites

The addition of nanoparticle with low strength matrix material is a well-known technique to improve the mechanical properties. Several researchers and industrial people have done many works and same has been published in the recent years. But only a limited number of studies have been made focusing on the fatigue behaviour. The objective of this study is to analyse the fatigue behaviour of low density polyethylene (LDPE)/clay nanocomposites with the help of experimental fatigue analysis. LDPE/Montmorillonite nanoclay based composites were prepared by simple melt compounding technique. The nanocomposites were prepared by adding nanoclay of different wt.% in to the LDPE matrix. The nanocomposites were analyzed for nanoclay dispersion by using scanning electron microscope (SEM) and transmission electron microscope (TEM). The prepared nanocomposites were subjected to bending fatigue on the standard specimen. The S-N curves were drawn for different percentage of nanoclay added polymer nanocomposites. The results demonstrated that the fatigue life of the nanocomposites is depending upon the magnitude of stress, dispersion of the clay particle and percentage of nanoparticle as well.

Preparation and Assessment of Phase Morphology, Rheological Properties, and Thermal Behavior of Low-Density Polyethylene/Polyhexene-1 Blends

ABSTRACTIn this work, polyhexene-1 (PH-1) is synthesized by polymerization of hexane-1 with Ziegler–Natta catalyst and melt blended with low-density polyethylene (LDPE). The phase morphology, rheology, crystallization, and thermal behavior of (LDPE)/PH-1 blends are investigated. A good compatibility is observed in the blends up to 10 wt% PH-1 and the most of the droplets in the fractured surface are covered with and buried in the LDPE matrix and at higher percentage the droplet particle size significantly increased. The effect of microstructure of the blends on the flow behavior is studied by small amplitude oscillation rheology. By decreasing the compatibility and increasing the particle size, the Cole–Cole plots are deviated from the semi-circular shape at higher percentages than 10 wt% of PH-1. The change in the crystallization and melting behavior of LDPE in the blends are studied by differential scanning calorimetry and X-ray diffraction (XRD). It is found that by increasing the PH-1 the melting temperature of LDPE decreased from 112.5 to 110.8°C and crystallization temperature increased from 95.2 to 97.7°C which is evident of the nucleation effect. The intensity of (110) peak in XRD test declined as a remake of amorphous part of LDPE and the degree of crystallinity of LDPE decreased from 28 to 22% at 20 wt% PH-1.

Studies of the effect of temperature on the charge trapping and de-trapping processes of polymeric insulators through depolarization current measurements

Formation of space charge in polymeric insulation is a critical issue in the design of high voltage electric systems. Accumulation of space charge accelerates the material aging and may lead to premature breakdown of the insulation. Therefore, it becomes increasingly important to understand the charge injection, trapping and de-trapping processes in dielectric under application of high voltage. However analysis of charge trapping and de-trapping is very difficult due to material properties and also the fact that the measurement of space charge itself is a very complicated issue. Most of the trapping and de-trapping investigation in literature has been performed through indirect means, by measuring the space charge distribution in a dielectric specimen under charging and discharging conditions. The effect of temperature on the trapping and de-trapping properties of polymeric insulating materials has also received limited attention. In this paper, the charge trapping and de-trapping behavior of low density polyethylene (LDPE), a widely used polymeric material for electrical insulation purpose, have been investigated using a direct method based on the depolarization characteristics of a stressed sample. A model has been developed to obtain the trapped charge distribution according to their energy level in the sample directly from the depolarization current. The measurements were performed at different temperature to study the effect of temperature. It was observed that temperature plays a critical role in charge injection, trap formation, trapping and de-trapping.

Effect of Flow Induced Orientation of Carbon Nanotubes on the Capillary Extrusion Behavior of Low-Density Polyethylene

Abstract The effect of carbon nanotubes (CNTs) on the capillary extrusion behavior of low-density polyethylene (PE) was investigated. From the linear viscoelasticity and the morphology observation, it was found that the CNTs were well dispersed throughout the PE matrix and our system belonged to the semi-dilute regime. The strain hardening, which quantifies the extension of the PE chain, decreased by presence of CNTs in the uniaxial elongational deformation. In contrast, the normal stress difference was almost unaffected by CNTs in the shear deformation. The capillary extrusion behavior revealed that swell ratio decreased with increasing the CNT content although melt fracture was promoted. We summarize that the suppression of swell and promotion of melt fracture are attributable to the orientation of CNTs.

Investigations on charge trapping and de-trapping properties of polymeric insulators through discharge current measurements

It is generally accepted that formation and accumulation of space charge in polymeric insulation is a critical issue in the design of high voltage electric systems, as it leads to insulation degradation and premature failure under high voltage surges and polarity reversals. Even at service stress level, accumulation of space charge may cause electrothermal aging. The insulation degradation and aging is reflected in the trapping and detrapping characteristics of the insulation, making it a useful aging marker. Space charge measurement methods are frequently used for trapping and de-trapping analysis. However, estimation of charge trapping and de-trapping behavior is very difficult due to the involvement of material properties and also partly due to the fact that proper measurement of space charge is itself a very complicated issue, requiring very sophisticated experimental arrangement and signal processing techniques. Moreover, application of these methods is limited to polymeric insulations of certain geometries (planar or radial). In this paper, the charge trapping and de-trapping behavior of low density polyethylene (LDPE), a widely used polymeric material for electrical insulation purpose, have been investigated employing a direct method based on the discharge characteristics obtained after the sample was stressed for short durations. A relationship is established between the de-trapped charge and the extracted charge measured from the discharge current. From this relationship a relative distribution of trapped charges across different trap depths was obtained. It was noticed that the trapped charge distribution is of exponential nature in the trap depth range of 0.93–1.11 eV. The presented method facilitates direct estimation of trap distribution independent of the insulation geometry. It was also observed that the trapped charge is highly dependent on the applied field.

Surface flashover performance of phenolphthalein modified LDPE in vacuum

Since surface flashover of insulators in vacuum restricts the operation of the power equipment, improvement of surface flashover performance is of considerable importance in various fields. Previous studies show that surface flashover performance is closely related to the trap parameters of materials. In this paper, the crystallization behavior of low density polyethylene (LDPE) is modified by phenolphthalein. It results in the change of the trap parameters, leading to the enhancements in surface flashover performance. Results of differential scanning calorimeter (DSC) and scanning electron microscope (SEM) show that the crystallization behavior of LDPE is greatly changed by phenolphthalein. The crystallinity increases initially and then decreases with the increase of phenolphthalein concentration, and its maximum value occurs at 0.4 wt%. The spherulite size of LDPE composites decreases obviously with the increasing phenolphthalein concentration. The results of thermally stimulated current (TSC) show that both the shallow trap (γ peak) and the deep trap (α peak) become deeper with the increase of phenolphthalein concentration. Furthermore, the impulse and dc surface flashover voltages present the optimum values at 1 wt% phenolphthalein concentration, which can be enhanced by 30.8% and 48.4%, respectively. It is concluded that LDPE with the smaller spherulite size indicates the deeper trap and the better surface flashover performance. This paper reveals the relationship between surface flashover performance and crystallization behavior of LDPE, and proposes a new method to enhance the surface flashover performance of semi-crystalline polymers in vacuum.

An effective intumescent flame retardancy of LDPE induced by the combination of APP and CNCO‐HA

ABSTRACTA char‐forming agent poly(4,6‐dichloro‐N‐hydroxyethyl−1,3,5‐triazin‐2‐amine‐1,6‐diaminohexane) (CNCO‐HA) containing triazine rings was chosen for improving the flame retardant of low density polyethylene (LDPE). The synergistic effect of CNCO‐HA and Ammonium polyphosphate (APP) on the flame retardancy and char‐forming behavior of LDPE were investigated. The limited oxygen index (LOI) and vertical burning test (UL‐94) results indicated the optimal weight ratio of APP to CNCO‐HA was 3:1, and the LOI value of composite reached 31.0% with 30% intumescent flame retardant (IFR) loading. The cone calorimeter test analysis revealed that IFR presented excellent char forming and smoke suppression ability, and resulted in the efficient decrease of combustibility parameters. The thermogravimetric analysis results demonstrated that IFR reduced the thermal degradation rate at main stage of degradation. Scanning electron microscopy observed that IFR promoted to form a compact and continuous intumescent char layer. The Laser Raman spectroscopy spectra showed that larger graphitization degree was formed to enhance the strength of char, and Fourier transform infrared results presented that P‐O‐C and P‐O‐P structures in the residue char were formed to improve shield performance of the char layer to obtain better flame retardant properties of the composite. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43950.

LDPE Filled with LLDPE/Starch Masterbatch: Rheology, Morphology and Thermal Analysis

This paper reported the effect of starch-based additive (PSN), on the rheology, morphology and thermal behavior of low-density polyethylene (LDPE). PSN was a commercial masterbatch of corn starch and linear low-density polyethylene (LLDPE) in the ratio of 45/55. Compositions of LDPE/PSN blend ratios at 100/0, 80/20, 70/30 and 60/40 were prepared by melt blending. It was found that addition of PSN to LDPE decreased its storage modulus (G′), loss modulus (G′′) and dynamic viscosity (η′) especially at low frequency. Results of the loss tangent (tan δ) measurements indicated a tendency of forming a maximum in the low-frequency region for the samples with high PSN content. Effect of temperature on the viscosity indicated that Arrhenius-type relation with a single slope was followed by neat LDPE, while the LDPE filled with PSN followed a non-Arrhenius-type relation with multiple slopes. Differential scanning calorimeter results indicated that the blend was partially compatible. Thermogravimetric measurement results confirmed that no degradation could happen at the temperature of rheology tests. Scanning electron microscopy studies revealed that starch was uniformly distributed in the blend of LDPE and LLDPE.

INFLUENCE OF ELECTRON BEAM TREATMENT ON THE CRYSTALLIZATION AND THERMAL STABILITY OF LDPE/EPDM BLENDS

The effect of blend composition and Electron Beam (EB) irradiation on the crystallization and thermal behavior of Low Density Polyethylene (LDPE)/Ethylene-Propylene-Diene elastomer (EPDM) blends had been studied. Melting temperatures were found to remain unchanged upon variation of blend composition as well as irradiation dose. But the degree of crystallinity and Tc (crystallization temperature) were decreased with increase in EPDM content and EB dose. On the other hand, thermal stability (in terms of onset temperature and degradation temperature) and activation energy were increased with increase in EPDM content and irradiation dose. But the speed of degradation slowed down with increasing EPDM content and EB dose. Interestingly, once Trimethylolpropane Triacrylate (TMPTA) and Triallyl Cynuerate (TAC) were incorporated into the blends, the degrees of change of these properties were more in same direction upon irradiation. At higher irradiation dose properties were demoted due to chain scission.

Sealability and Seal Characteristics of PE/EVA and PLA/PCL Blends

Abstract Seal strength behavior of low density polyethylene and ethylene vinyl acetate copolymer (PE/EVA) blends as well as that of blends of a seal grade PLA with aliphatic polyester (PCL) was studied. Polyethylene is commonly used for seal application in packaging multilayer structures and amorphous PLA is considered to be its counterpart for compostable and/or biodegradables ones. Incorporation of EVA in polyethylene improves its sealability in terms of a decrease in seal initiation temperature and broadness of sealability plateau. This was interpreted as due to the formation of finer crystals, a decrease in the melting point and presence of vinyl acetate polar group. These were supported by results obtained from differential scanning calorimetry (DSC) and Scanning electron microscopy (SEM). For the PLA/PCL system, the dispersed phase was stretched into elongated ellipsoidal domains. This type of morphology affected the mechanical and seal properties of the blends. As a result of blending, both hot-tack initiation temperature and strength as well as seal initiation temperature were enhanced. The enhancement in these seal properties was significant when the concentration of the dispersed phase exceeded 20 wt% in the blend. Hot-tack strength of up to twice of pure PLA was achieved through blending. This was attributed to the lower glass transition temperature of PCL, resulting in enhanced mobility of PLA chains and also the high aspect ratio of the dispersed phase. The maximum obtained hot-tack strength (1 200 g/25 mm) at 40 % dispersed content compared advantageously to commercially available polyolefin based sealant resins. The seal and hot-tack initiation temperatures were shifted to lower temperatures by as much as 30 °C, which can allow faster and more energy efficient sealing process.