Grades Of Polyethylene Research Articles

Effect Of Starch Addition On The Properties Of Low Density Polyethylene For Developing Environmentally Degradable Plastic Bags

Starch is an inexpensive abundant product and is totally biodegradable in a wide variety of environments and allows the development of totally degradable products for specific market needs. We study the influence of starch on the degradation behavior of plastic films prepared by mixing the film grade polyethylene pellets with different amounts of starch. The mechanical strength of the polymer films were measured by Instron 5560 Tensile Testing Machine and observed that with the addition of starch mechanical strength decreases. As biodegradation rate increases with starch addition, 25 to 35% starch can be added safely in the plastic shopping bag without changing its strength significantly. DOI: http://dx.doi.org/10.3329/jce.v26i1.10180 JCE 2011; 26(1): 38-40

Resistance of UHMWPE to plastic deformation and wear and the possibility of its enhancement through modification by radiation

AbstractThe operational durability of a kinematical polymer–metal system, required in many applications, including endoprostheses used for the total knee or hip joint arthoplasty, depends largely on high resistance to wear and permanent deformation of the polymer cup, especially in its near‐surface layer, contacting with the metal part. In this study, the wear and deformation resistance of two ultra high molecular weight polyethylene (UHMWPE) grades used in arthoplasty, GUR1020 and GUR1050, as well as the possibilities of its enhancement by radiation treatment were studied in detail. An influence of the molecular characteristic of these grades on functional properties, including permanent plastic deformation, microhardness, elastic modulus, coefficient of the micromechanical wear were studied. The properties of GUR 1050 of higher molecular weight were found advantageous over GUR 1020 grade. It was also confirmed that irradiation with electron beam is an effective method of modification, resulting in an improvement of both resistance to permanent deformation and wear of UHMWPE. It was demonstrated that microhardness, Young's modulus, and wear resistance coefficient increase proportionally to the irradiation dose applied. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Numerical Simulation of Crack Growth in Polyethylene Composites by Means of the Cohesive Zone Model

AbstractSummary: The cohesive zone model is used for the numerical simulation of crack growth in homogeneous specimens made of two different grades of polyethylene (PE) as well as in PE‐bimaterials. The material data and the shapes of the cohesive function are deduced from experimental data by Ivankovic et al., Eng. Fract. Mech. 71, 2004, 657–668 and Ting et al., Polym. Eng. Sci. 46, 2006, 763–777. Fracture toughness parameters are evaluated from the simulated load versus displacement curves. The results show a significant influence of the arrangement of the two PE‐grades in the bimaterial specimens, caused by both the different material properties and the different characteristic parameters of the cohesive function.

Hyperbranched polyethylenes by chain walking polymerization: synthesis, properties, functionalization, and applications

Structurally different from existing polyethylene grades, hyperbranched polyethylenes (HBPEs) synthesized by Pd–diimine-catalyzed chain walking polymerization represent a novel class of polyethylene materials with unprecedented chain architectures and unique physical properties. A large number of research investigations have been carried out in the area in the past decade, and have led to the successful synthesis of a broad range HBPEs of various controlled chain topologies, molecular weights, and functionalities by tuning polymerization parameters and/or catalyst structures. Meanwhile, some new specialty applications of these materials have also been demonstrated in various fields ranging from lubricant additives to polymer building blocks to nanoencapsulation, with some interesting performance properties discovered. This review aims to summarize the developments in this area.

A quantitative assessment of the chemical variation in food grade polyethylene cling film, a common wrapping material for illicit drugs, using attenuated total reflection-Fourier transform infrared spectroscopy

Cling film is commonly encountered in forensic investigations as a wrapping for drugs of abuse. The evidential value of a match between a known and a questioned piece of cling film is directly related to the level of the chemical variation both within and between samples. However, little is known about the chemical variation in cling film. To address this, attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) was used to quantitatively assess the chemical variation in food grade low-density polyethylene (LDPE) cling film. Following acquisition of full scan IR spectra between 4000 and 650 cm−1, a spectral region of potential discrimination between 1560 and 1200 cm−1 was identified. The complex series of weak, overlapping absorption bands in this region were deconvoluted and peaks fitted. Bivariate plots comparing each pair of normalised peak areas showed significant overlap of the data points for the different samples, indicating no between-sample chemical variation. Further, the same plots demonstrated that the extent of within-sample chemical variation was at least as great as that between samples. Thus, in the sample set evaluated in this study, it was not possible to discriminate between food grade LDPE cling films using ATR-FTIR spectroscopy due to a lack of quantifiable chemical variation. The study therefore highlights the possibility of false positive matches in the analysis of LDPE cling films and provides a methodology to evaluate the extent of chemical variation in a relevant reference population prior to undertaking casework.

Characterization of the mechanical properties of a new grade of ultra high molecular weight polyethylene and modeling with the viscoplasticity based on overstress

Enhancements to the service life and performance of orthopedic implants used in total knee and hip replacement procedures can be achieved through optimization of design and the development of superior biocompatible polymeric materials. The introduction of a new or modified polymer must, naturally, be preceded by a rigorous testing program. This paper presents the assessment of the mechanical properties of a new filled grade of ultra high molecular weight polyethylene (UHMWPE) designated AOXTM and developed by DePuy Orthopaedics Inc. The deformation behavior was investigated through a series of tensile and compressive tests including strain rate sensitivity, creep, relaxation, and recovery. The polymer was found to exhibit rate-reversal behavior for certain loading histories: strain rate during creep with a compressive stress can be negative, positive, or change between the two during a test. Analogous behavior occurs during relaxation as well. This behavior lies beyond the realm of most numerical models used to computationally investigate and improve part geometry through finite element analysis of components. To address this shortcoming, the viscoplasticity theory based on overstress (VBO) has been suitably modified to capture these trends. VBO is a state variable based model in a differential formulation. Numerical simulation and prediction of all of the aforementioned tests, including good reproduction of the rate reversal behavior, is presented in this study.

Simulation of an Industrial Linear Low Density Polyethylene Plant

In this paper, an industrial linear low density polyethylene (LLDPE) production process including two serried fluidized bed reactors (FBR) and other process equipment was completely simulated in steady state mode. Both of FBRs were considered like two serried continuous stirred tank reactors (CSTR). In this simulation, a kinetic model that is based on a multiple active site heterogeneous Ziegler-Natta catalyst was used for simulation of reactions in two FBRs. Simulator by using this model is able to predict the important attributes of LLDPE like melt flow index (MFI), density (ρ), polydispersity (PDI), numerical and weight average molecular weight (Mn, Mw) and co-polymer molar fraction (SFRAC). On the other hand, this simulator can be applied in wide range of changing in inlet operating conditions. The results of the simulation are compared with industrial data of LLDPE plant. A good agreement is observed between the simulator predictions and actual plant data. Finally, by using of the simulator, the steady state operating conditions for producing different grades of polyethylene are obtained.

Correlation between molecular structure parameters and network properties of silane‐grafted and moisture cross‐linked polyethylenes

AbstractThe degree of silane grafting and cross‐linking of several high‐density polyethylenes (HDPE) was studied. The results are compared with those of a low‐density polyethylene (LDPE) and a linear low‐density polyethylene (LLDPE). Molecular characterization was done by gel permeation chromatography. The differences in grafting and cross‐linking performance are correlated to the different structural parameters of the polymers such as molecular weight, molecular weight distribution, polydispersity index (PDI), and branching. The results show that molecular weight plays the main role in silane‐grafting and cross‐linking performance. For samples with approximately similar PDI, the grafting level increased with both increasing number average molecular weight and weight average molecular weight, whereas the gel content increased with increasing weight average molecular weight. However, a zigzag relation was observed for the variation of grafting and cross‐linking performances with PDI. The presence of long‐chain branching affects the size of molecules and reduces the grafting efficiency due to coil contraction and more intramolecular entanglements. The order of the degree of grafting for the different polyethylenes investigated was LLDPE > HDPE > LDPE, whereas the order for the gel content was LDPE > LLDPE > HDPE. The presence of unsaturated groups led to increase in the grafting level. However, there is no overall rule based on the density of polyethylene. Different grades of polyethylene show different behaviors depending on the silane and peroxide concentration. © 2011 Wiley Periodicals, Inc. Adv Polym Techn 30: 286–300, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.20224

Study of the PENT test conditions for reducing failure times in high-resistance polyethylene resins for pipe applications

A thorough study of the physical conditions in the Pennsylvania Edge Notch Tensile (PENT) test, such as stress and temperature, is carried out in order to reduce the long test times observed in new bimodal and multimodal polyethylene grades (third and fourth generation grades) which may withstand hundreds or thousands of hours at the standard conditions (80○C, 2.4 MPa). The results show how on increasing the temperature up to 90○C and the applied stress up to 2.8 MPa, the failure time may be reduced by a factor of 6. Special attention should be paid to the n and Q parameters of the Brown and Lu equation, because variations in those parameters could dramatically change the result of the comparison between different systems depending on the temperature and stress value.

Comparison between Material Parameters of Polyethylene Grades and the Test Performance Behaviour of Packaging for the Transport of Dangerous Goods

For the characterization and the comparison of polyethylene grades used for the manufacture of packaging and intermediate bulk container, the following parameters are required: melt flow rate (MFR), density (D), low‐temperature notched impact strength, full notch creep test (FNCT) and increase of MFR by molecular degradation (resistance to oxidative degradation). The relationship between these material parameters determined on the basis of specimens prepared from compression‐moulded sheets of polyethylene grades and the test behaviour of packaging has been investigated in several tests. The environmental stress crack resistance determined by FNCT represents the impacts from the stacking tests performed with standard liquid wetting solution (without pre‐storage) and with normal butyl‐acetate‐saturated wetting solution (pre‐storage with normal butyl acetate). Resistance to molecular degradation by the determination of MFR increase is related to the impacts in drop tests and stacking tests performed after pre‐storage for 21 days with standard liquid 55% nitric acid at 40°C. The low‐temperature impact strength is directly comparable with the impacts in drop tests at −18°C performed without pre‐storage and after pre‐storage with 55% nitric acid. A partly good relationship was found between the test results and the material parameters. Conditioning the design types with 55% nitric acid for 21 days causes an increase in the marginal drop heights of the design types in drop tests at −18°C when compared with design types without pre‐storage. Post‐cross‐linking of the grades increases stiffness because of the acidic influence. Copyright © 2011 John Wiley & Sons, Ltd.

Study of the degradation mechanisms of polyethylene during reprocessing

The present work aims at evaluating the behaviour of various grades of high and low density polyethylene subjected to continuous injection moulding operations. It is based on a wide range of experimental techniques that allowed the establishment of relationships between the observed property changes and the structural modifications developed in the polymers. The study confirmed the coexistence of two distinct degradation mechanisms, crosslinking and chain scission, that occur due to thermo-oxidative reactions arising during the different injection moulding stages. The relative importance of these two mechanisms depends on the material structure and on the processing conditions used. It was also possible to confirm that the polyethylenes with lower molecular mass show low sensitivity to degradation during reprocessing. Furthermore, the more branched polymers (as is the case of LDPE) also proved to be less sensitive to thermo-degradation phenomena. Overall, it was concluded that the primary recycling of polyethylene, if performed under well controlled conditions, will lead to only minor material property losses.

On the action of ozone at high concentration on various grades of polyethylene and certain straight chain paraffins

The surface functionalisation of UHMWPE (ultra high molecular weight polyethylene) was successfully achieved by the action of ozone (10% by weight in oxygen) under mild conditions. The kinetics of the gas–solid reaction between O 3 and UHMWPE in powder form were measured in an IR gas cell and the pseudo-first-order rate constant was k′ UHMWPE = 1.9 × 10 −4 s −1. The resulting surface-oxidized UHMWPE was studied by FT-IR spectroscopy and the nature of the surface functionalities was determined. Furthermore, the surface-oxidized UHMWPE was studied by DSC (differential scanning calorimetry). It was evident that ozone attacks and oxidizes the amorphous phase of UHMWPE preserving the crystalline phase because after the ozone treatment there was an increase in the % of crystallinity. Two other polyethylene grades having respectively M w = 15,000 Da (defined as LMWPE = low molecular weight polyethylene) and M w = 4000 Da (defined as VLMWPE = very low molecular weight polyethylene) were studied as model compounds in comparison to UHMWPE in their reaction with ozone. Commercial liquid paraffin and n-dodecane were used as model compounds to study the reaction between high ozone concentration and alkanes.

Molecular Modification and Compatibilization of Collected Polyethylene

The increasing use of plastics in packaging materials leads to growing amounts of plastic waste. Recycling material is generally regarded as advantageous. But in fact very few products are made from plastic waste, partly this can be explained by that little is known about the recycling process and the properties of collected materials. There is a need for injection moulding grades of recycled polyethylene, while large amounts of extrusion grades are available from packaging waste. A controlled way of de-branching or partly degrading PE would be desirable. Peroxides are commonly used to crosslink polyolefins, but under certain conditions a chain scission reaction occur. Another problem encountered with recycling of polyethylene are the poor miscibility of low amounts contaminations, i. e. polypropylene. A compatibilizer can improve properties of such polymer blends, in this work EPDM is used as compatibilzer. Studies of mechanical properties and viscosity measurements show that it is possible to partly degrade PE with peroxide exposing it to high temperature and oxygen. The properties of PE/PP blends were improved with EPDM as compatibilizer.

Isothermal crystallization of high density polyethylene with monomodal and bimodal molar mass distribution

AbstractThe isothermal crystallization behavior of two different high density polyethylene grades with monomodal and bimodal molar mass distribution was investigated by means of differential scanning calorimetry. The results indicate that extensive cocrystallization between linear short chains and long chains with short branches in bimodal polyethylene grade occurred. In contrast, polymer chains of different lengths in monomodal polyethylene exhibit different tendency to crystallize. This finding was explained qualitatively based on a general discussion of the effect of molar mass and branch content/length on crystallization tendency of polymeric chains.

Sorting Mixed Polyolefins from End-of-Life Product by a Selective Grinding Process

European policy on waste and market demand for material are driving the development of sorting techniques adapted to automobiles and electric products at the end of their lifetimes. In this article, we present work on polymer sorting using selective grinding. Selective grinding is an operation that consists in sorting polymers after shredding. Specific particle size distributions characterize each polymer in the output stream and these differences are used to recover certain polymers by sifting. This process is based on the brittle or ductile properties of polymers. The first results presented in this work concern the sorting of a mixture of polymers and polyolefins, which are chemically incompatible. The working method adopted includes three parts. In the first part, a stream of mixed polymers from the shredder residue (SR) of a treatment chain was characterized. The mixed stream was composed of different grades of polypropylene and different grades of polyethylene. Afterwards, based on the characterization data, selective grinding tests were carried out on a model mixture with virgin materials. Once the selective grinding conditions were validated, other tests were carried out with SRs. The conclusion of this study is that selective grinding can be an efficient technology to sort incompatible polymers, which are not sorted by other processes, such as density separation or automated near infrared sorting.

Extrudate swell of linear and branched polyethylenes: ALE simulations and comparison with experiments

Extrudate swell is a common phenomenon observed in the polymer extrusion industry. Accurate prediction of the dimensions of an extrudate is important for appropriate design of dies for profile extrusion applications. Prediction of extrudate swell has been challenging due to (i) difficulties associated with accurate representation of the constitutive behavior of polymer melts, and (ii) difficulties associated with the simulation of free surfaces, which requires special techniques in the traditionally used Eulerian framework. In a previous work we had argued that an Arbitrary Lagrangian Eulerian (ALE) based finite element formulation may have advantages in simulating free surface deformations such as in extrudate swell. In the present work we reinforce this argument by comparing our ALE simulations with experimental data on the extrudate swell of commercial grades of linear polyethylene (LLDPE) and branched polyethylene (LDPE). Rheological behavior of the polymers was characterized in shear and uniaxial extensional deformations, and the data was modeled using either the Phan–Thien Tanner (PTT) model or the eXtended Pom–Pom (XPP) model. Additionally, flow birefringence and pressure drop measurements were done using a 10:1 contraction–expansion (CE) slit geometry in a MultiPass Rheometer. Simulated pressure drop and contours of the principal stress difference were compared with experimental data and were found to match well. This provided an independent test for the accuracy of the ALE code and the constitutive equations for simulating a processing-like flow. The polymers were extruded from long ( L/ D = 30) and short ( L/ D = 10) capillaries dies at 190 °C. ALE simulations were performed for the same extrusion conditions and the simulated extrudate swell showed good agreement with the experimental data.

Effect of selected residual Ziegler–Natta and metallocene catalysts on the UV-induced degradation of unstabilized ethylene homopolymer films

Catalyst creates new grades of polyethylenes while their degradation phenomena determine the resulting application profiles. The resins and the end-products eventually contain residual catalysts. Therefore, the effects of the following two residual catalysts—one Ziegler–Natta [PQ Silica/Bu 2Mg/ tBuCl/TiCl 4], and the other metallocene [PQ Silica/MAO/( nBuCp) 2ZrCl 2]—on the UV-induced degradation of the resulting unstabilized ethylene homopolymer films were studied. The MetCat HomoPE film was found to be more susceptible to UV-induced degradation degradation than the Z–N HomoPE one despite the residual Zr level was 1/15th of the Ti content. Therefore, the zirconocene residual catalyst better (i) facilitated the UV-initiated reaction, and (ii) decreased the activation energy required for the decomposition of the resulting hydroperoxide. These findings were explained from the differences in (i) electronic configuration and atomic radius, and (ii) surface chemistry and solid-state electronic environment of these catalyst systems. In both films, T pm and T pc did not significantly vary with the exposure time. The change of % crystallinity showed to be irregular and disturbed. As a function of carbonyl index, T pm and T pc,varied in a similar fashion in the MetCat HomoPE film. However, they significantly differed for the Z–N HomoPE film. Here, T pm did not appreciably change whereas T pc initially increased very mildly; then it did not essentially differ.

Compounding fibre grade polyethylene terephthalate with a hyperbranched additive and studying its dyeability with a disperse dye

A hyperbranched polymer which comprised a polyesteramide structure was used to study improvements in dyeability of fibre grade polyethylene terephthalate films. The optical measurements of the dyed samples showed that, by increasing the percentages of the dendritic additive, K/S as a dye uptake parameter changed in the presence or absence of a carrier. The amount of chroma increased while the hue did not change significantly. The dyeability of the prepared samples was attributed to the decrease in glass transition temperature and the lower crystallinity of the polymer, as studied by differential scanning calorimetry. Thus, a new fibre grade polyethylene terephthalate, which is dyeable, could be obtained, with less need to use a toxic carrier compound.

Effect of long‐term natural aging on the thermal, mechanical, and viscoelastic behavior of biomedical grade of ultra high molecular weight polyethylene

AbstractIn the total joint prostheses, Ultra High Molecular Weight Polyethylene (UHMWPE) may undergo an oxidative degradation in the long term. The overall properties of UHMWPE are expected to be altered due to the oxidative degradation. The goal of this study is to investigate the effects of natural aging up to 6 years in air on the thermal, mechanical, and viscoelastic properties of UHMWPE that was used in total joint replacement. The changes in UHMWPE properties due to aging are determined using Differential Scanning Calorimetry (DSC), uniaxial tensile tests, and Dynamic Mechanical Analysis (DMA). The DSC results show that the lamellar thickness and degree of crystallinity of UHMWPE specimens increase by 38% and 12% due to aging. A small shoulder region in the DSC thermograms is remarked for aged specimens, which is an indication of formation of new crystalline forms within their amorphous region. The tensile properties of aged and nonaged UHMWPE specimens show a significant decrease in the elastic modulus, yield, fracture stresses, and strain at break due to aging. The DM testing results indicate that the storage modulus and creep resistance of UHMWPE specimens decrease significantly due to aging. Also, it is remarked that the α relaxation peak for aged UHMWPE specimens occurs at lower temperature compared to nonaged ones. The significant reduction in the strength and creep resistance of UHMWPE specimens due to aging would affect the long‐term clinical performance of the total joint replacement and should be taken into consideration during artificial joint design. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Oscillating Flow in Capillary Dies for a Hdpe Melt: Effects of Extrusion Parameters

The study of the instability phenomena of polymer melts in capillary flows is of great technical relevance since, during an industrial die forming operation, these instabilities can give origin to a transition from a defect-free to a highly-defective extrudate. In this work, the instability phenomena exhibited in capillary flow by a blow moulding grade of high-density polyethylene (HDPE) were analyzed. In particular, by means of a capillary rheometer, which mimics polymer extrusion, the effects of specific extrusion parameters (temperature and imposed flow rate) on the oscillating flow, that takes place when “stick-slip” instabilities occur, were investigated.