Types Of High-density Polyethylene Research Articles

Attenuated Total Reflection-Far-Ultraviolet Spectroscopy and Quantum Chemical Calculations of the Electronic Structure of the Top Surface and Bulk of Polyethylenes with Different Crystallinities.

In this study, we explored the electronic structure of the surfaces of polyethylene samples having different crystallinities using attenuated total reflection (ATR) far-ultraviolet (FUV) spectroscopy and quantum chemical calculations. Specifically, the ATR-FUV spectra of five types of high-density polyethylene (HDPE), six types of linear low-density PE (LLDPE), and seven types of low-density PE (LDPE) were obtained. All the spectra contained an intense band near 156 nm and a broad band between 180 and 190 nm. Transmission spectra were obtained for the thin-film (30 µm) PE samples between 165 and 250 nm. In this region, the HDPE films show very low-intensity bands. In contrast, the transmission spectra of the LLDPE and LDPE samples yielded weak-to-medium and medium-intensity bands around 180-190 nm, respectively. In addition, to understand the differences in the absorption spectra among the PEs observed, we simulated the spectra of n-pentane as a PE crystal model using time-dependent density functional theory and found that the common intense band at 156 nm is due to the σ (C(2p)-H)→Rydberg 3s, 3p transition. The absorption bands near 180-190 nm may correspond to aggregates of numerous molecular chains in the amorphous parts of the LLDPE and LDPE samples.

Physical stabilization of expansive subgrade soil using locally produced geogrid material

This paper illustrates application of a locally produced geogrid material for strength improvement of expansive subgrade soil. Samples of black, soft soil predominating the study area were collected from south western parts of Modjo town, inside the rift valley region of central parts of Ethiopia. X-Ray diffraction as well as index property tests were executed to identify and categorize the expansiveness of the highly plastic soft soil. The effects of two locally manufactured geogrid reinforcement materials; namely, polypropylene (PP) and high density polyethylene (HDPE) on the California bearing ratio (CBR) values of the expansive soil have been investigated. The test results indicated that the use of the geogrid reinforcement can significantly improve the bearing capacity of weak subgrade soil. The soaked CBR of the untreated soil sample, which was about 2.98%, was able to be raised to 10.16% and 7.48% by the application of PP and HDPE type of geogrid respectively, that were placed at 0.35H from the top of specimen. The research demonstrated the potential of using locally produced geogrid material for the improvement of weak subgrade soil.

Creep of high density polyethylene filled with multiwall carbon nanotubes

The creep-recovery behaviour of two types of high density polyethylene (HDPE) filled with multiwall carbon nanotubes (MWCNT) is investigated. Nanocomposites with various contents of MWCNT were produced by using a commercially available masterbatch aimed to transfer the gained knowledge to an assessment of properties of industrial-scale products. Nanocomposites are characterized by the improved creep resistance compared to the neat polymers. Incorporation of 10 wt.% of MWCNT into the polymers resulted in a decrease of creep and residual strains for more than 3 and 5 times, respectively. The reinforcing effect of the nanofiller appeared also in a great increase of the elastic modulus (up to 100%) and ultimate strength (up to 60%) as well as a decrease of the coefficient of linear thermal expansion (down to 17%) of HDPE. Carbon nanotubes, being also good heat conductors, greatly contributed to the improvement of polyethylene’s thermal conductivity (up to 60%). Electrical percolation is determined below 2 wt.% of MWCNT. The electrical resistance changes monitored during creep-recovery tests are well correlated with the overall strain changes and residual strains in nanocomposites, that approve their in situ strain sensing capability during inelastic and long-term deformation.

Laboratory Investigation of Shear Behavior of High-Density Polyethylene Geomembrane Interfaces.

As a product of polymeric materials, geomembranes (GMs) are widely used in engineered systems as impervious barriers due to their low permeability. In this study, a large-scale composite shear test apparatus was developed to investigate the shear behaviors of various GM interfaces. A series of direct shear tests were conducted on GM–soil, GM–geotextile, and GM–concrete interfaces. Two types of high-density polyethylene (HDPE) GMs, a smooth GM and a textured GM, were used to evaluate the effect of GM-texturing on the shear properties of these interfaces. Based on the experimental data, the friction angles and adhesions of GM interfaces were calculated using the Mohr–Coulomb criterion. Test results describing the behavior of GM–soil and GM–geotextile interfaces from the current study were then compared with results from previous studies. The test results are shown to verify the reliability of the new large-scale composite shear apparatus. In addition, this paper presents preliminary experimental results of the GM–concrete interface shear tests.

Effect of PET functionalization in composites of rubber–PET–HDPE type

The functionalization of polyethylene terephthalate (PET) from tire rubber–PET–high density polyethylene (HDPE) composites represents a key strategy for improving the composite properties. This is a practical and effective method to improve the interface between matrix (waste tire rubber) and fillers (waste PET and HDPE). By PET functionalization, adherence and surface properties of composite materials can be controlled. PET functionalization was performed with polyethylene glycol (PEG 400, 1%) and sodium dodecyl sulphate (SDS 1%). The characterization of the components and composite are discussed in terms of surface energy values (evaluated from water contact angle measurements) and surface morphology by using scanning electron microscopy (SEM). The structural and conformational changes were investigated by Fourier Transform Infrared (FTIR) Spectroscopy while the crystalline structure was studied by X-ray diffraction (XRD). The improved interfacial adhesion, thermal stability and mechanical properties (stress–strain, compression and impact resistance) of the composites are correlated with the PET functionalization, with non-ionic (PEG) and an anionic surfactant (SDS). The results proved that the interface properties are improved by functionalization of PET. The best mechanical properties were recorded at 30min moulding. The samples with 45% PET–SDS showed the best combination of mechanical properties: tensile strength (1.56N/mm2), impact strength (43.72kJ/m2) and compression (158.78N/mm2).

Effect of High-Density Polyethylene Nanocomposite Compatibilizer Type on the Interfacial Adhesion and Mechanical Properties of Polyethylene Nano-Homocomposites

In this paper, the effect of nanocomposite compatibilizer type on the interfacial adhesion and mechanical properties of new class of polyethylene (PE) homocomposites, comprising PE/clay nanocomposites as matrix and ultra high molecular weight polyethylene (UHMWPE) fibers as reinforcement, was investigated. These were manufactured by a combination of powder impregnation and film stacking methods, introduced in previous research. Three types of high-density polyethylene (HDPE) Nanocomposites were prepared based on the various compatibilizers used: (i) nanocomposites containing HDPE-grafted maleic anhydride (HDPE-g-MA) as compatibilizer of clay and HDPE matrix, (ii) linear low-density polyethylene-grafted maleic anhydride (LLDPE-g-MA) used as compatibilizer, and (iii) nanocomposites without any compatibilizer. The effects of the presence and compatibilizer type on the quality of clay dispersion, and also the interface features of HDPE-nanocomposite and UHMWPE fibers were investigated and compared with each other. The results demonstrated that the kind of compatibilizer was an important factor determining the dispersion state of clay platelets, and influenced the UHMWPE fiber–PE matrix interface adhesion and the mechanical properties of the PE nano-homocomposites.

Flow-induced crystallization of high-density polyethylene: the effects of shear and uniaxial extension

The effects of shear, uniaxial extension and temperature on the flow-induced crystallization of two different types of high-density polyethylene (a metallocene and a ZN-HDPE) are examined using rheometry. Shear and uniaxial extension experiments were performed at temperatures below and well above the peak melting point of the polyethylenes in order to characterize their flow-induced crystallization behavior at rates relevant to processing (elongational rates up to 30 s − 1 and shear rates 1 to 1,000 s − 1 depending on the application). Generally, strain and strain rate found to enhance crystallization in both shear and elongation. In particular, extensional flow was found to be a much stronger stimulus for polymer crystallization compared to shear. At temperatures well above the melting peak point (up to 25°C), polymer crystallized under elongational flow, while there was no sign of crystallization under simple shear. A modified Kolmogorov crystallization model (Kolmogorov, Bull Akad Sci USSR, Class Sci, Math Nat 1:355–359, 1937) proposed by Tanner and Qi (Chem Eng Sci 64:4576–4579, 2009) was used to describe the crystallization kinetics under both shear and elongational flow at different temperatures.

Segregation behavior of polyethylene with broad molecular weight distribution by annealing procedure in temperature gradient

An annealing treatment in a molten state, in which temperature of the top plate is different from that of the bottom one in a compression-molding, leads to molecular weight segregation of high-density polyethylene (HDPE) prepared by mixture of two types of HDPE with different molecular weights (Mw = 1.8 × 105 and 2.9 × 104). Low molecular weight fraction tends to localize at the surface attached to the higher temperature and vice versa. The segregation behavior is obvious at a large temperature gradient. Although the accuracy and mechanism of the phenomenon have not been clarified yet, this could be applied as a new fractionation method, which does not use a solvent.

Effects of matrix molecular weight on structure and reinforcement of high density polyethylene/mica composites

Three types of high-density polyethylene (HDPE) with different molecular weights (high, medium and low) were adopted to evaluate the influence of matrix molecular weight on the structure-property relation of injection-molded HDPE/mica composites through a combination of SEM, 2d-WAXS, DSC, DMA and tensile testing. Various structural factors including orientation, filler dispersion, interfacial interaction between HDPE and mica, etc., which can impact the macroscopic mechanics, were compared in detail among the three HDPE/mica composites. The transcrystallization of HDPE on the mica surface was observed and it exhibited strong matrix molecular weight dependence. Obvious transcrystalline structure was found in the composite with low molecular weight HDPE, whereas it was hard to be detected in the composites with increased HDPE molecular weight. The best reinforcement effect in the composite with low molecular weight HDPE can be understood as mainly due to substantially improved interfacial adhesion between matrix and mica filler, which arises from the transcrystallization mechanism.

Effect of aspect ratio on large deformation and necking of polyethylene

Objective of the study is to examine influence of aspect ratio of rectangular cross-section on the tri-axial stress state developed by necking in tensile specimens of polyethylene. The first part of the paper presents an experimental study that used two types of high-density polyethylene (HDPE) as sample material to identify the thickness-dependent relationship between engineering stress and elongation from tensile tests. The experimental study also shows that thinner specimens, i.e. higher aspect ratio, have lower neck propagation speed and higher flow stress, thus higher rate of energy consumption for the neck propagation. The second part of the paper presents finite element simulation of large deformation and necking in HDPE when subjected to uni-axial tension. True stress–strain relationship and governing equation for visco-plastic deformation are determined from the finite element simulation based on experimental data for the two HDPEs, which reveals influence of aspect ratio of cross-section on the stress state during the necking process. Results from the study indicate that plane-stress condition prevails when the aspect ratio increases, i.e. by decreasing the specimen thickness. The finite element simulation also supports the observation that necking in specimens with higher aspect ratio, i.e. thinner specimens, generates higher percentage of reduction in the thickness direction but lower in the width direction. The overall capability for the deformation endurance was found to improve by reducing the specimen thickness. The paper concludes that finite element simulation has successfully demonstrated the influence of aspect ratio of the cross-section on the stress state in the necking process. The paper also concludes that by combining experimental testing and finite element simulation, time-dependent deformation behaviour can be separated from the time-independent deformation behaviour, which is almost impossible to achieve based on the experimental techniques that rely purely on measurement only.

Die Kinetik und Mechanismus der direkten Fluorinierung von Polyethylenen

Two types of low-density polyethylene (LDPE), five types of high-density polyethylene (HDPE), poly(vinyl fluoride) (PVF) and poly(vinylidene fluoride) (PVDF) were studied. The fluorination of LDPE and HDPE is a diffusion-controlled process and proceeds via a branched chain mechanism following an induction period. Initiation of the reaction takes place via the reaction of molecular fluorine with the C-H bond. The rate of fluorination of HDPE exceeds that of LDPE. PVDF cannot be fluorinated even at temperatures as high as 430K and/or under UV irradiation. The kinetics associated with the formation and termination of peroxy RO 2 • and fluorocarbon long-lifetime radicals was studied. It is mainly middle peroxy radicals that are formed at treatment conditions close to those used in industrial processes.

The role of chain scission and chain branching in high density polyethylene during thermo-mechanical degradation

The mechanical and thermo-oxidative degradation of high density polyethylene (HDPE) was measured in a twin-screw extruder using various processing conditions. Two types of HDPE, Phillips and Ziegler-Natta, having different levels of terminal vinyl unsaturation were analysed. Mild screw profiles, having mainly conveying elements, have short mean residence times then profiles with kneading discs and left hand elements. Carbonyl and trans-vinylene group concentrations increased, whereas vinyl group concentration decreased with number of extrusions. Higher temperature profiles intensified these effects. The thermo-mechanical degradation mechanism begins with chain scission in the longer chains due to their higher probability of entanglements. These macroradicals then react with the vinyl terminal unsaturations of other chains producing chain branching. Shorter chains are more mobile, not suffering scission but instead are used for grafting the macroradicals, increasing the molecular weight. Increase in the levels of extrusion temperature, shear and vinyl end groups content facilitates the thermo-mechanical degradation reducing the amount of both, longer chains via chain scission and shorter chains via chain branching, narrowing the polydispersity. Phillips HDPE produces a higher level of chain branching than does the Ziegler-Natta type.

Effect of combining boron nitride with fluoroelastomer on the melt fracture of HDPE in extrusion blow molding

Boron nitride (BN) is a new polymer processing aid which not only eliminates surface melt fracture in the extrusion of molten polymers, but also postpones the critical shear rate for the onset of gross melt fracture to significantly higher values that depend on resin type and additive concentration. In this work, the influence of BN as a polymer processing additive is first examined in the extrusion blow molding of high-density polyethylene (HDPE) resins in order to evaluate its usefulness and performance in operations other than continuous extrusion. The equipment used includes both a Battenfeld/Fisher 50-mm extrusion blow molding machine and a parallel-plate rheometer. Two types of HDPE, which are blended with boron nitride at various concentration levels, are tested accordingly. It is found that the degree of BN dispersion, characteristics of the HDPE resins, extrusion temperature, and induction time play an important role in eliminating melt fracture. Finally, the influence of combining BN with fluoroelastomer, as an enhanced and potentially better processing aid on the melt fracture of a third HDPE is examined. It is found that such a combination is a superior processing aid that allows extrusion blow molding at very high shear rates.

Effect of Resin Types and Antioxidants on Release of Off-Flavor From HDPE Bottles

Abstract The effects of three types of high-density polyethylene (HDPE) resins (A, B, and C) and three antioxidants (vitamin E, Irganox 1010, and BHT) on the release of off-flavor (including off-odor and off-taste) from blow-molded HDPE bottles were investigated using sensory analysis and gas chromatography/mass spectrometry (GC/MS) analysis. Overall the sensory study showed that off- flavor intensity was affected by both resin type and antioxidant. Resin A bottles yielded less off-flavor compared to resin B or C bottles. Vitamin E containing bottles yielded less off-flavor compared to Irganox 1010 or BHT containing bottles for resins A and B; however, the antioxidants have almost the same effect on resin C. The GC/MS study identified more than 60 volatile compounds released from the bottles, ranging from C5 to C20, which belonged to the groups of n-alkane, 1-alkene, aldehyde, ketone, phenolic, olefin, and paraffin—among them aldehydes and ketones were the most important due to their very low odor thresho...

'Phosphite-Free' Stabilization of Polyolefins

Deficiencies of present anti-oxidant (AO) systems led to our initiating a series of studies with 'phosphite-free' AO systems based on catocopherol (vitamin E) formulations. This study evaluated the effects of several AO systems on the yellowness index (YI), melt flow rate (MFR) and on gel formation after five to eight passes of two types of high density polyethylene (HDPE) and four types of polypropylene (PP) resins through an extruder. It was demonstrated that the a-tocopherol can replace phenolic/phosphite combination as the primary AO system; or the a-tocopherol formulations can simply replace the phosphite portion to achieve better performance. In either case, the problems associated with phosphites can be eliminated or minimized by the ca-tocopherol AO; and usually at a lower cost.

Comparative study of the structural, morphological and oxidative characteristics of high-density polyethylene and poly(ethylene oxide)

A comparative study was made of the thermo-oxidative stabilities of high-density polyethylene (HDPE) and poly(ethylene oxide) (PEO) aged in air at 90 and 60°. The PEO was a commercially available grade and two types of HDPE were produced using organo-chromium catalysts supported on a porous silica substrate. Examination of the silica by scanning electron microscopy (SEM) showed it to consist of spherically shaped particles with rough, irregular particulates adhering to their surfaces. Fractured silica particles reveal a system of voids which influences the ultimate mechanical strength of the silica and hence determines the stage at which the silica particles shatter during the polymerization process. The particle size distribution of each silica support was determined by laser light scattering. It was found that the silica support which had the higher effective surface area to weight ratio increased the reactivity and productivity of the catalyst system, thus affecting the morphological characteristics of the nascent polymer particles. The SEM examination of nascent PEO showed ductile, drawn cobweb structures. Since HDPE catalysed using a bis(triphenylsilyl)chromate shows a similar cobweb morphology and is known to have an induction period proceeding steady-state polymerization, it can be inferred that PEO polymerizes after an induction period. The rate of polymer oxidation was assessed by carbonyl index measurements obtained by Fourier transform i.r. spectroscopy. The rate of oxidation correlates with the specific surface area of the polymer, which is determined by the nascent morphology. Polarized optical microscopy showed that isothermally crystallized films of the oxidized polymers display an axialitic morphology. After oxidation, it appears that the calcium oxide residue [ ca 0.8% (w/w)] in the commercial grade of PEO can act as an efficient nucleating agent for axialitic growth, when the surfaces of the residue particles are wetted by oligomeric oxidation products.

The optical birefringence of injection-moulded polystyrene and polyethylene

Injection-moulded plaques of polystyrene and of two types of high-density polyethylene have been produced under different moulding conditions. Microscopic examination coupled with birefringence measurements on polystyrene and polyethylene show that the plaques contain a flow-induced molecularly ordered structure together with, in the case of polyethylene, a thin (∼4µm) disordered surface layer. Thermal annealing of the polystyrene birefringence and “frozen-in” strain distribution have been measured and interpreted in terms of phenyl group reorientation and molecular rearrangement, respectively.

The microhardness of injection moulded polystyrene and polyethylene

Injection moulded plaques of polystyrene and of two types of high density polyethylene have been produced under different moulding conditions. The mean densityϱ of each plaque together with its surface microhardnessV H have been measured. Polystyrene shows only a slight increase inϱ with increasing mould temperatureT m together with a reduced spread inϱ andV H values. In polyethylene, however,ϱ andV H both increase linearly withT m, giving a usefulV H againstϱ relation, which is attributed to increased percentage crystallinity.

Energy criterion for modelling creep rupture of high-density polyethylene

A technique involving the use of a three-element mechanical model with a critical stored energy criterion modelled accurately the creep rupture time of two types of high-density polyethylene (HDPE) specimens. The upper stress limit where the specimen ruptured immediately on application of load and the lower stress limit where the specimen sustained the load indefinitely were also features of the model. These two limits were found to depend on the resilience, elastic modulus and anelastic modulus of the HDPE.

The oscillating shear phenomenon in high density polyethylenes

AbstractStudies of capillary extrusion measurements using an Instron rheometer show that certain types of high density polyethylene exhibit a discontinuity in the shear stress/shear rate curve. This behavior which is separate and distinct from the phenomenon of melt fracture is caused by a change in the flow regime. It is manifested by oscillation of the recorded load while the rheometer piston is operated at a constant rate. Therefore, this behavior has been termed “oscillating shear phenomenon”. The location and magnitude of the fluctuations are functions of the molecular parameters of the polymer as well as the melt temperature, capillary geometry, and other rheometer variables. Evidence is presented which indicates that the change in flow regime could result from the orientation of the melt as it enters the capillary.