Susceptibility to scratch damage of high density polyethylene coating

The scratch behaviour of a polymeric coating, based on high density polyethylene (HDPE), used for pipeline application was investigated in this work. Instrumented scratch testing was used for the characterization of the friction and wear behaviour of such materials. Static contact of a diamond conical indenter against the polyethylene (PE) coating was experimentally studied. Normal and tangential forces are measured during the scratch experiments using various scratch parameters (such as sliding velocity, attack angle, applied normal load). All the experiments were performed under unlubricated conditions and at room temperature. Moreover, some hygrothermally aged coating samples were considered in order to analyze the effect of immersion aging on their scratch behaviour. Before being subjected to scratch experiments, these samples were immersed in synthetic sea water at a set temperature of 70 °C and for 6 months. The scratch behaviour of the polymeric coating was discussed in terms of friction coefficient, wear resistance and wear mechanisms. Thus, scratch tracks were analyzed qualitatively and quantitatively. To characterize the scratch process, three-dimensional topography of the scratched surfaces was measured. In fact, wear morphologies of the PE coating were observed after scratching by tactile profilometer and laser interferometer. Friction response was correlated to wear mechanisms. Wear volume can be considered relevant responses to describe the material's scratch resistance. It was found that friction and wear behaviours are significantly affected by scratch parameters. Hygrothermal aging considerably affects the wear resistance of the studied coating. In terms of wear mechanisms, the ploughing controls the wear of such PE coating whole the retained test conditions.     

DOP对高密度聚乙烯/石墨复合材料PTC特性及力学性能的影响

以邻苯二甲酸二辛酯（DOP）为石墨填充高密度聚乙烯（HDPE）复合体系的增塑剂，借助SEC和弯曲实验等手段研究了增塑剂的引入对HDPE/石墨导电复合体系的结晶行为、石墨聚集态结构及PTC特性、力学性能的影响．结果表明，少量增塑剂的引入可以使得基体的微晶尺寸变小，从而改善了导电复合物的PTC特性，提高了材料的力学性能。     

Toughening effect of maleic anhydride grafted linear low density polyethylene on linear low density polyethylene

The blend of linear low density polyethylene (LLDPE) and maleic-anhydride grafted LLDPE with the grafting degree of 1.3% and the gel content of 27.0% (designated as LLDPE/MA-PE) was melt-compounded. Their thermal, rheological, and mechanical properties were studied. The crystallization temperature and crystallization rate of LLDPE/MA-PE blends increase due to the nucleation of MA-PE, their crystallinity is between those of LLDPE and MA-PE due to the balance between the nucleation of MA-PE and simultaneously produced more defects. The addition of MA-PE increases the apparent viscosity of blend melts, but the shear-sensitivity of blends provides them with melting processing. Interestingly, the lamellar crystallites induced by MA-PE decrease the tensile yielding strength of LLDPE/MA-PE blends. During the impact fracture, the formation of oriented crystalline lamellae parallel to the crack front and perpendicular to the crack flank, leads to the deformation and microstriations in LLDPE/MA-PE blends. Subsequently, toughness of LLDPE/MA-PE blends is improved.     

Effects of gamma irradiation on polypropylene, polypropylene + high density polyethylene and polypropylene + high density polyethylene + wood flour

The effect of the gamma-irradiation on the mechanical properties of the composites, Polypropylene (PP), PP+high density Polyethylene (HDPE), PP+ HDPE+wood flour, where HDPE is virgin and recycled, was studied. This paper discusses the behavior of the composites after exposure to various doses of gamma irradiation (1–7 MRads) in the presence of oxygen. The dependence of mechanical properties on the integral dose for a constant dose rate of 0.48 MRads/h confirms the influence of the irradiation. Strong effects on the elongation at break and break strength is noticed. The mathematical analysis suggests for the PP+r-HDPE a bimolecular process of the elongation at break. On the order hand, for the PP+HDPE a complex process is represented for a three exponential equation. Received: 9 October 2000 / Reviewed and accepted: 10 October 2000     

The effect of gamma radiation on hardness evolution in high density polyethylene at elevated temperatures

This research focuses on characterizing hardness evolution in irradiated high density polyethylene (HDPE) at elevated temperatures. Hardness increases with increasing gamma ray dose, annealing temperature and annealing time. The hardness change is attributed to the variation of defects in microstructure and molecular structure. The kinetics of defects that control the hardness are assumed to follow the first order structure relaxation. The experimental data are in good agreement with the predicted model. The rate constant follows the Arrhenius equation, and the corresponding activation energy decreases with increasing dose. The defects that control hardness in post-annealed HDPE increase with increasing dose and annealing temperature. The structure relaxation of HDPE has a lower energy of mixing in crystalline regions than in amorphous regions. Further, the energy of mixing for defects that influence hardness in HDPE is lower than those observed in polycarbonate (PC), poly(methyl methacrylate) (PMMA) and poly (hydroxyethyl methacrylate) (HEMA). This is due to the fact that polyethylene is a semi-crystalline material, while PC, PMMA and PHEMA are amorphous.     

Influence of a fine talc on the properties of composites with high density polyethylene and polyethylene/polystyrene blends

Fine talc filled high density polyethylene (HDPE) and HDPE/polystyrene (PS) blends were extruded, injection moulded and characterized. Some of the mechanical properties of the talc filled HDPE and talc filled 75/25 HDPE/PS blend were deduced from stress–strain measurements. A comparison between the effect of the talc on the properties of the filled HDPE and filled 75/25 HDPE/PS blend showed that the mineral filler had the same effect on both systems provided that its array in the organic matrix is almost the same in both cases. In fact, the rheological results proved that the dispersion of talc in the HDPE matrix was not really affected by the presence of PS. The study particularly focused on the effect of talc on the ultimate tensile strength of the filled HDPE and that of the filled blend. It has been noted that the brittle nature of PS neutralizes, to a certain extent, the degrading effect of talc on this property. Furthermore, both PS and talc have a complementary effect on the stiffness and the resilience of HDPE/PS/talc blend composites.     

J-integral studies of crack initiation of a tough high density polyethylene

The J-integral is applied to characterise the fracture initiation of a tough high density polyethylene for which the concepts of linear elastic fracture mechanics (LEFM) are inapplicable for reasonably sized specimens due to extensive plasticity. The multiple specimen resistance curve technique recommended by the ASTM is the basic method employed. A formulation based on the finite difference in crack area between two otherwise identical specimens is used to determine J _Ic for comparison with the result obtained from the basic method. A comparison is also made with the results obtained from the Bilby, Cottrell & Swinden (BCS) model of yielding ahead of a crack.Tests are performed in the temperature range from +23°C to –80°C.

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Résumé On applique l'intégrale J à la caractérisation de l'amorçage d'une rupture dans un polyéthilène tenace à haute densité pour lequel les concepts de la théorie linéaire élastique de la mécanique de rupture sont inapplicables dans le cas d'éprouvette de dimension raisonnable, en raison d'une plasticité étendue. La méthode de base utilisée est la technique de la courbe de résistance d'une éprouvette multiple, telle que recommandée par l'ASTM. Une formulation basée sur les différences finies dans la zone de fissuration entre deux éprouvettes identiques par ailleurs, est utilisée à la détermination de J_Ic en vue d'une comparaison avec les résultats obtenus à partir de la méthode de base. Une comparaison est également effectuée avec les résultats obtenus par l'utilisation du modèle de Bilby, Cottrell et Swinden relatif à l'écoulement plastique en avant de la fissure.Les essais ont été effectués dans une gamme de températures comprise entre +23°C et –80°C.

     

Shrinkage as a measure of the deformation efficiency of ultra-oriented high density polyethylene

A simple test is described that allows the evaluation of the molecular extension in solid state extruded high density polyethylene at maximum extrusion draw ratio 36. The samples, which were prepared by shaving the extrudates to films of average thickness 0.4 mm, were melted very rapidly and shrunk at 160° C. Experimental evidence shows that at high heating rates (800° C min⁻¹) all the molecular extension is recovered elastically. The variation of shrinkage with molecular weight indicates a difference in the molecular extension produced during the extrusion, and a simple relationship between molecular draw ratio and modulus is considered.     

Influence of joining on the tensile behaviour of high density polyethylene pipe

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Influence of joining on the tensile behaviour of high density polyethylene pipe

Abstracts are not published in this journal     

Product distribution modelling in the thermal pyrolysis of high density polyethylene

The thermal fast pyrolysis of high density polyethylene (HDPE) has been carried out in a conical spouted bed reactor in the 450-715 degrees C range, and individual products have been monitored with the aim of obtaining kinetic data for the design and simulation of this process at large scale. Kinetic schemes have been proposed in order to explain both the results obtained in the laboratory plant and those obtained in the literature by other authors operating at laboratory and larger scale. Discrimination has been carried out based on the contribution of the variance of model parameters (stepwise regression) to the total variance explained by the model. The models based on that of Westerhout et al. [R.W.J. Westerhout, J. Waanders, W.P.M. Van Swaaij, Recycling of polyethene and polypropene in a novel bench-scale rotating cone reactor by high-temperature pyrolysis. Ind. Eng. Chem. Res. 37 (6) (1998) 2293-2300] do not adequately predict the experimental results, especially those corresponding to aromatics and char, which is probably due to the very short residence times attained in the conical spouted bed and, consequently, to the lower yields of aromatics and char. The model of best fit is the one where polyethylene degrades to give gas, liquid (oil) and wax fractions. Furthermore, the latter undergoes secondary reactions to give liquid and aromatics, which in turn produce more char.     

Effect of high energy ball milling on the structure and mechanical properties of cross-linked high density polyethylene

The effects of high energy ball milling (HEBM) on the structure and some key-properties of crosslinked high density polyethylene (PEX) have been thoroughly examined with a combination of X-ray diffraction analysis, IR and Raman spectroscopy, differential scanning calorimetry, gel content measurements, and tensile properties tests. A structure–property relationship, which provides a reasonable explanation for the studied case has been developed based on the experimental results and their analysis. It is proposed that the HEBM provides some of the silane-grafted macromolecular chains, which have a specific orientation, with sufficient energy in order to crosslink and form small crystalline-like areas. The arrangement of chains in the “reformed” domains leads to a total increase of the overall crystallinity, but also a decrease of the crystalline size. The proposed model can also support the fact that by increasing the milling time, the overall crystallinity of PEX and some important mechanical properties are found to increase.     

Effects of modified and non-modified clay on the rheological behavior of high density polyethylene

HDPE nanocomposites containing 2.5, 5 and 10 wt.% of non-modified and modified clays (NMC and MC) were prepared by melt extrusion in a twin screw extruder. Compression molded samples were prepared. Transmission electron microscopy (TEM) indicated a partial intercalation of the modified clay nanofiller within the HDPE matrix comparing to that of non-modified clay. The moduli of nanocomposites increased with increase in nanofiller concentration; but this increase was greater in the low frequency region. The non-modified clay had a greater increase in the elastic behavior, while the modified clay increased viscose behavior because of more interactions with the matrix and partial intercalation. The rheological behaviors of both HDPE/NMC and HDPE/MC nanocomposites are more sensitive to nanoparticles’ concentration at low frequencies. The HDPE/MC nanocomposites showed semi-circle shapes comparing to HDPE/NMC nanocomposites. While the Cole–Cole plot of HDPE/NMC nanocomposite had more departure of semi-circle shape. The agglomerated particles could concentrate the imposed stress so the yield stress reached at lower shear rates comparing to pure HDPE and HDPE filled 2.5 wt.% NMC nanocomposite. Study of suspension models showed that the Eilers-Van Dijck and Einsten models fitted to almost experimental data satisfactorily.     

等离子体处理聚乙烯表面官能团的研究

利用Ar等离子体射频放电,在不同功率和时间下处理高密聚乙烯(HDPE),通过X光电子能谱(XPS)及化学诱导法进行测定和分析处理后样品表面引入含氧基团的性质.结果表明:Ar等离子体处理后表面存在含氧基团,且随着表面深度不同,氧含量有所变化,在近表面氧含量较高.进一步分析表明:经Ar等离子体处理的高密聚乙烯表面羟基(-OH)和羧基(-COOH)均存在,且表面-COOH的含量大于-OH的含量.     

Influence of the stretching temperature on an alumina filled microporous high density polyethylene membrane

The effects of the stretching temperature on the properties of an alumina filled high density polyethylene (HDPE) membrane were investigated. As the stretching temperature increases up to 120 °C, the porosities of the alumina filled HDPE membrane were increased. The crystallinity of the microporous alumina filled HDPE membranes was increased steadily with an increasing stretching temperature up to 120 °C. The pores of the alumina filled HDPE film was easily formed at the interface between the alumina particles and HDPE, and the lamellae separation of HDPE was enhanced as the crystallinity of the alumina filled HDPE film was increased. The tensile strength at a stretching temperature of 80 °C was a little larger than those at a stretching temperature of 100 °C and 120 °C. The electrolyte uptake and the ionic conductivity were increased in proportion to the porosity. When the stretching temperature was 120 °C, the ionic conductivity of the microporous alumina filled HDPE membrane reached 4.56 × 10⁻³ S/cm.     

On the use of nanoscale indentation with the AFM in the identification of phases in blends of linear low density polyethylene and high density polyethylene

The microstructures generated by blends of linear low density polyethylene (LLDPE) and high density polyethylene (HDPE) following isothermal crystallization from the melt have been studied using several techniques. The traditional methods of electron microscopy, wide angle X-ray scattering, and differential scanning calorimetry were used to examine the superstructures, lattice spacings, and thermal properties, respectively. In addition, nanoindentation of specific moieties within the microstructure was performed using the atomic force microscope (AFM). The indentation measurements were used to generate values for the relative elastic moduli of the crystalline features and to identify phases within the superstructures. The AFM results were compared to results obtained from the aforementioned techniques and to microhardness measurements.