Molecular Dynamics-Based Simulation of Polyethylene Pipe Degradation in High Temperature and High Pressure Conditions

High-density polyethylene(HDPE)pipes have gradually become the first choice for gas networks because of their excellent characteristics.As the use of pipes increases,there will unavoidably be a significant amount of waste generated when the pipes cease their operation life,which,if improperly handled,might result in major environmental contamination issues.In this study,the thermal degradation of polyethylene materials is simulated for different pressures(10,50,100,and 150 MPa)and temperatures(2300,2500,2700,and 2900 K)in the framework of Reactive Force Field(ReaxFF)molecular dynamics simulation.The main gas products,density,energy,and the mean square displacement with temperature and pressure are also calculated.The findings indicate that raising the temperature leads to an increase in the production of gas products,while changing the pressure has an impact on the direction in which the products are generated;the faster the temperature drops,the less dense the air;both temperature and pressure increase impact the system’s energy conversion or distribution mechanism,changing the system’s potential energy as well as its total energy;the rate at which molecules diffuse increases with temperature,and decreases with pressure.The results of this investigation provide a theoretical basis for the development of the pyrolytic treatment of polyethylene waste materials.

Fracture Characterization of High-Density Polyethylene Materials Using the Energetic Criterias

Impact behavior of polymers has received considerable attention in recent years,and much work based on fracture mechanic approaches has been carried out.In this paper,fracture behavior in large deformation of a high density polyethylene(HDPE)materials was investigated through experimental impact testing on single edge notched specimen(SENB)and by using theoretical and analytical fracture criteria concepts.Moreover,a review of the main fracture criteria is given in order to characterize the toughness of this polymer in the both cases(static and dynamic).The fractured specimens obtained from the Charpy impact test were characterized with respect to their fracture surfaces.Characteristic zones of the fracture surface can be assigned to different stages and mechanisms of the fracture process.Finally,for a better understanding of fracture and damage mechanisms and to provide the best estimation of fracture toughness in impact,an experimental approach based on microscopic observations(SEM)was used.

Micromechanical analysis on tensile properties prediction of discontinuous randomized zalacca fibre/high-density polyethylene composites under critical fibre length

In this research,the tensile properties'performance of compression moulded discontinuous randomized zalacca fibre/high-density polyethylene under critical fibre length was analysed by means of experimental method and micromechanical models.These investigations were used to verify the tensile properties models toward the effect of fibre length and volume fraction on the composites.The experimental results showed that the tensile properties of composites had significantly increased due to the enhancement of fibre length.On the contrary,a decline in the tensile properties was observed with the increase of volume fraction.A comparison was made between the available experimental results and the performances of Tsai-Pagano,Christensen and Cox-Krechel models in their prediction of composites elastic modulus.The results showed that the consideration of fibre's elastic anisotropy in the Cox-Krenchel model had yielded a good prediction of the composites modulus,nevertheless the models could not accurately predict the composites modulus for fibre length study.

Characterization and Comparison of Rheological Properties of Agro Fiber Filled High-Density Polyethylene Bio-Composites

The rheological behavior of composites made with high-density polyethylene (HDPE) and different agro fiber by-products such as corncob (CCF), Rice hull (RHF), Flax shives (FSF) and Walnut shell (WSF) flour of 60 - 100 mesh were studied. The experimental results were obtained from samples containing 65 vol.% agro fiber and 3 wt.% lubricant. Particle sizes distribution of the agro fibers was in the range of 0.295 mm to ?0.125 mm. SEM showed evidence of complete matrix/fiber impregnation or wetting. The melt rheological data in terms of complex viscosity (η*), storage modulus (G'), loss modulus (G"), and loss tangent (tanδ) were evaluated and compared for different samples. Due to higher probability of agglomeration formation in the samples containing 65 vol.% of agro fillers, the storage modulus, loss modulus and complex viscosity of these samples were high. The unique change in all the samples is due to the particle size distribution of the agro fibers. The storage and loss modulus increased with increasing shear rates for all the composites, except for Walnut shell composite which exhibited unusual decrease in storage modulus with increasing shear rate. Damping factor (tanδ) decreased with increasing shear rate for all the composites at 65 vol.% filler load although there were differences among the composites. Maximum torque tended to increase at the 65 vol.% agro fiber load for all composites. Corncob and Walnut shell composites gave higher torque and steady state torque values in comparison with Flax shives and Rice hull composites due to differences in particle sizes distribution of the agro fibers.

Accurate detection method of high-density polyethylene fi lm leakage location based on secondary electric potential difference

High-density polyethylene(HDPE)film leakage location detection is frequently accomplished using the double-electrode technique.The electric potential and potential difference are the main physical parameters in the double-electrode approach.Due to the impact of the complex geoelectric environment,the electric potential and the electric potential difference are not sensitive enough to respond to minimal leakage.The tiny leaking area cannot be precisely located using the electric potential and electric potential difference.Using the COMSOL Multiphysics software,this study created a standard geoelectric model of the double-electrode method.We calculated a new parameter—the G parameter through secondary electric potential difference—based on the response characteristics of the electric potential and the electric potential difference while the HDPEfilm is leaking.The experiment demonstrates that the G parameter is more sensitive than the electric potential and electric potential difference for detecting the leaking area of HDPE film.The G parameter is more effective at detecting leakage than the electric potential and electric potential difference.The results of this study can be used to locate HDPEfilm leakage areas in a landfill.

A New Selective Neural Network Ensemble Method Based on Error Vectorization and Its Application in High-density Polyethylene (HDPE) Cascade Reaction Process

Chemical processes are complex, for which traditional neural network models usually can not lead to satisfactory accuracy. Selective neural network ensemble is an effective way to enhance the generalization accuracy of networks, but there are some problems, e.g., lacking of unified definition of diversity among component neural networks and difficult to improve the accuracy by selecting if the diversities of available networks are small. In this study, the output errors of networks are vectorized, the diversity of networks is defined based on the error vectors, and the size of ensemble is analyzed. Then an error vectorization based selective neural network ensemble (EVSNE) is proposed, in which the error vector of each network can offset that of the other networks by training the component networks orderly. Thus the component networks have large diversity. Experiments and comparisons over standard data sets and actual chemical process data set for production of high-density polyethylene demonstrate that EVSNE performs better in generalization ability.

Decorative Wood Fiber/High-Density Polyethylene Composite with Canvas or Polyester Fabric

Wood-plastic composite is an environmentally friendly material,due to its use of recycled thermoplastics and plant fibers.However,its surface lacks attractive aesthetic qualities.In this paper,a method of decorating wood fiber/high-density polyethylene(WF/HDPE)without adding adhesive was explored.Canvas or polyester fabrics were selected as the surface decoration materials.The influence of hot-pressing temperature and WF/HDPE ratio on the adhesion was studied.The surface bonding strength,water resistance,and surface color were evaluated,and observation within the infrared spectrum and under scanning electron microscopy was used to analyze the bonding process.The results showed that the fabric and WF/HDPE substrate could be closely laminated together depending on the HDPE layer accumulated on the WF/HDPE surface.The molten HDPE matrix penetrates canvas more easily than polyester fabric,and the canvasveneered composite shows a greater bonding strength than does the polyester fabric-veneered composite.A higher proportion of the thermoplastic component in the substrate improved the bonding.When the hot-pressing temperature exceeded 160°C,the fabric-veneered WF/HDPE panels had greater water resistance,although the canvas fabric changed more obviously in terms of fiber shape and color,compared with the polyester fabric.For the canvas fabric,140°C–160°C was a suitable hot-pressing temperature,whereas 160°C–180°C was more suitable for polyester fabric.The proportion of the thermoplastic component in the composite should be not less than 30%to achieve adequate bonding strength.

Studies on the Effects of Bentonite (Nanoclay) on the Mechanical Properties of High-Density Polyethylene

In this work, the effect of Bentonite (Nanoclay) on the mechanical and mor-phology properties of HDPE/Nanoclay composite pipe material was investi-gated. This led to the development of a composite material with improved me-chanical properties. The HDPE/nanoclay composites were produced using an injection moulding machine at 200?C and rotor speed of 50 rpm. The compati-bilizer used in this study was Polyethylene-graft-Maleic Anhydride. Different compositions of nanoclay reinforcements were prepared and added to HDPE resin. A particle size of 425 μm was used in proportions of 0%, 5%, 10%, 15%, and 20% on weight fraction basis. All the composites samples were characterized by Zwick Roell tensile testing machine and Scanning Election Microscopy (SEM). Experimental results obtained showed improvements in the tensile strength, and modulus at the expense of elongation. The maximum tensile strength and modulus was obtained at 10% filler composition. These enhanced properties are due to the homogenous dispersion of nanoclay in HDPE matrix, which is evident from the structure that was evaluated using SEM.

High-Density Polyethylene Based on Exfoliated Graphite Nanoplatelets/Nano-Magnesium Oxide: An Investigation of Thermal Properties and Morphology

In this study, high-density polyethylene (HDPE)/exfoliated graphite nanoplatelet (xGnP) composites reinforced with a 2 wt.% concentration of nano-magnesia (n-MgO) were fabricated using an injection moulding machine. The thermal properties and morphological structures of the composites were investigated. The XRD results showed the peaks of xGnP and n-MgO, where the intensity of the xGnP peaks became stronger with adding increasing amounts of xGnP into the polymermatrix. In terms of morphology, some agglomeration of particles was observed within the matrix, and the agglomeration decreased the thermal properties of the composites. The nanocomposites showed less thermal stability than the pristine polymer. The reduction in the onset temperature compared to that of neat HDPE was attributed to less adhesion between the fillers and the matrix. In addition, the crystallinity was reduced by the addition of fillers.

Anatomic Anteversion of the Acetabular Component Correlates with Polyethylene Linear Wear in Total Hip Arthroplasty: The Three-Dimensional Numerical Analysis

Background: Although abduction of the acetabular component is considered to predict factors for polyethylene wear attributable to osteolysis, other radiographic factors have yet to be elucidated. The purpose of the present study was to evaluate whether anteversion or change in implantation angle of the acetabular component influences polyethylene linear wear by using standing and supine radiographs of the hip joint. Methods: Standing and supine plain anteroposterior radiographs of 62 hip joints in which cementless total hip arthroplasty was performed were examined for polyethylene linear wear rate (mm/year), pelvic inclination, and radiological inclination and anatomic anteversion of the acetabular component. Results: All correlation coefficients of measurements of polyethylene linear wear, pelvic inclination angle, anatomical anteversion angle and radiological inclination angle were calculated highly. And by the three-dimensional numerical analysis, anatomic anteversion of the acetabular component had at least some effect on the degree of polyethylene wear. Conclusion: This study suggests that increased anteversion of the acetabular component reduces polyethylene linear wear in metal-on-polyethylene total hiparthroplasty.

Flame retardancy effect of surface-modified metal hydroxides on linear low density polyethylene

Metal hydroxides （MAH） consisting of magnesium hydroxide and aluminum hydroxide with a mass ratio of 1：2 were surface-modified by y-diethoxyphosphorous ester propyldiethoxymethylsilane, boric acid and diphenylsilanediol in xylene under dibutyl tin dilaurate catalyst at 140 ℃. Phosphorus, silicon and boron elements covalently bonded to metal hydroxide particles were detected by X-ray photoelectron spectroscopy. The degradation behavior of the surface-modified MAH was characterized by thermogravimetric analysis. The results show that linear low density polyethylene （LLDPE） composite, filled with 50% （mass fraction） of MAH modified by 5.0% （mass fraction） of modifiers, passes the V-0 rating of UL-94 test and shows the limited oxygen index of 34%, and its heat release rate and average effective heat combustion in a cone calorimeter measurement decrease obviously; The mechanical properties of MAH can be improved by surface-modification. The uniform dispersion of particles and strong interfacial bonding between particles and matrix are obtained.

Low Density Linear Polyethylene Reinforced with Alkali and MAPE Treated Fibers from Coffee Pulp

In this work fibers derived from coffee, hulls have been incorporated into Linear Low Density Polyethylene (LLDPE). The influence of the filler content on the thermal and physicomechanical properties of the composites obtained was assessed. The results showed that the incorporation of fibers was able to improve the thermostability of LLDPE/Coffee hulls fibers;comparing the treated fiber composite with untreated fiber composites, the chemical treatment reduces by 58.3% the water absorption, while increasing the elongation and tensile strength by about 48% and 17% respectively. Moreover, due to better interfacial interaction induced by MAPE, the corresponding composite exhibited better properties compared to the untreated fiber composite. Results are indicative of the fact that both mercerization and MAPE (coupling agent) have significant positive effects on the fiber-matrix interaction in terms of adhesion, wetting and dispersion, this treatment produced a better fiber distribution and consequently a more uniform composite morphology without voids and gaps between the fibers and the matrix, allowing the possibility to use higher fiber contents (up to 30% wt.) with acceptable mechanical properties.

High temperature and high pressure rheological properties of high-density water-based drilling fluids for deep wells

To maintain tight control over rheological properties of high-density water-based drilling fluids, it is essential to understand the factors influencing the theology of water-based drilling fluids. This paper examines temperature effects on the rheological properties of two types of high-density water-based drilling fluids （fresh water-based and brine-based） under high temperature and high pressure （HTHP） with a Fann 50SL rheometer. On the basis of the water-based drilling fluid systems formulated in laboratory, this paper mainly describes the influences of different types and concentration of clay, the content of a colloid stabilizer named GHJ-1 and fluid density on the rheological parameters such as viscosity and shear stress. In addition, the effects of aging temperature and aging time of the drilling fluid on these parameters were also examined. Clay content and proportions for different densities of brine-based fluids were recommended to effectively regulate the rheological properties. Four theological models, the Bingham, power law, Casson and H-B models, were employed to fit the rheological parameters. It turns out that the H-B model was the best one to describe the rheological properties of the high-density drilling fluid under HTHP conditions and power law model produced the worst fit. In addition, a new mathematical model that describes the apparent viscosity as a function of temperature and pressure was established and has been applied on site.

EFFECT OF PAN-MILLING STRESS ON CRYSTAL STRUCTURES OF HIGH DENSITY POLYETHYLENE

A detailed study was performed on the crystal structures of pan-milled high-density polyethylene (HDPE) using differential scanning calorimetry (DSC) and X-ray diffraction. The crystallinity of HDPE first decreased slightly, followed by a gradual increase with increasing milling times. Monoclinic crystals appeared after 4 cycles of milling. With increasing times of milling, the proportion of monoclinic crystals increased significantly while the proportion of orthorhombic crystals decreased gradually. With increasing times of milling, the crystallite size of orthorhombic form decreased greatly, while the size of monoclinic crystallites kept almost constant during milling.

Effect of substrates on crystallization of high density polyethylene

The experimental observations about remarkable influence of the substrates on the isothermal crystallization rate of a high density polyethylene(HDPE) were presented.Two methods were used to characterize the crystallization rate:the change of turbidity of the HDPE specimen and the changes of the complex viscosity and storage modulus measured by a rotational rheometer,which gave consistent results showing that the isothermal crystallization rate decreased in sequence as the specimen contacted with aluminum,brass and stainless steel plates,respectively.As to the dominant influence factor,the chemical composition of the substrates can be excluded via insulating the plate by an aluminum foil.Instead,we propose the plate's ability of removing the latent heat of crystallization from the specimen.Rheological measurement is sensitive to the crystallization process.The colloid like model proposed by BOUTAHAR et al for the crystallization of HDPE gives reasonable predictions of the crystallized fraction from the measured storage modulus.

Optimum Combination of Femoral Head Size, Femoral Head Material, and Acetabular Cup Liner’s Highly-Cross-Linked Polyethylene Brand for Hip Implant

Clinical two-dimensional linear wear rate data for acetabular cup liners fabricated using approved brands of highly cross-linked ultra-high-molecular-weight polyethylene, as reported in 39 articles in the literature, were analyzed using a statistical technique called response surface methodology. The output was a series comprising16 acceptable combinations of femoral head diameter (HD), femoral head material (HM), and HXLPE brand (PB), each of which would yield the optimum wear rate (herein taken to be a wear rate of practically zero). An example of such a combination is 28- mm-diameter Oxinium? femoral head articulated against an acetabular cup liner fabricated from ReflectionTM HXLPE. The findings in this work may guide an orthopaedic surgeon’s selection of the combination of HD, HM, and PB to use in a primary total hip joint replacement.

Selection of Thickness of High Density Polyethylene Film for Mulching in Paddy Rice

In water deficit area, judicious use of water is essential for increasing area under crop production with limited water supply. Film Mulching has been advocated as an effective means for conserving soil moisture in rice production. The effects of high density polyethylene (HDPE) film on increasing rice production, controlling weeds and residue amount of plastic were studied under five treatments, including 5, 10, 15 and 20 μm thickness as well as bare cultivation (CK). The results indicated that the HDPE film mulching mode had significant effects on weed control, soil temperature, soil moisture, photosynthetic rate, seedling biomass, yield and residues of plastic film. Combined with economic effect, it showed that the HDPE film of 10 μm is the best option for rice production.

Physical and Thermo-Oxidative Characterization of Asphalt Modified with High Density Polyethylene and Recycled Engine Oil

Modification of asphalt using polymers, oils and other additives has been an option to improve asphalt pavement performance and extend its lifespan. The present work aims to evaluate the influence of the addition of engine oil on the consistency and thermal properties of HDPE-modified asphalt. For this study, compositions containing asphalt, engine oil and high-density polyethylene (HDPE) were prepared, varying the concentration of engine oil by 2.5 wt%, 5 wt%, 7.5 wt% and 10 wt% and keeping the concentration of HDPE at 5 wt%. The samples were characterized by conventional tests of penetration, softening point and viscosity, aging in a Rotational Thin Film Oven (RTFO), Thermogravimetric Analysis (TGA). According to the results, the addition of HDPE to virgin asphalt causes an increase in the consistency of the virgin asphalt, which then decreases linearly as the engine oil is added into the matrix. Conventional tests showed improvements in the applicability of the asphalt in terms of resistance to cracks and permanent deformation. TGA showed a slight increase in stability for the modified asphalt samples at elevated temperatures. The RTFO showed mass gain and loss for samples with and without engine oil, respectively.

LDPE/MLLDPE共混改性及发泡性能

以低密度聚乙烯(LDPE)为基体树脂、4,4'-氧代双苯磺酰肼(OBSH)为发泡剂、茂金属线性低密度聚乙烯(MLLDPE)为改性剂,采用化学发泡法和辐照交联技术制备一系列LDPE/MLLDPE发泡材料。研究不同MLLDPE含量对LDPE/MLLDPE复合材料的熔体流动速率、热性能、发泡行为及力学性能的影响。结果表明,MLLDPE能提高LDPE/MLLDPE复合体系的结晶度,降低其熔体流动速率。随着MLLDPE含量的增加,LDPE/MLLDPE复合发泡材料的拉伸强度、撕裂强度和压缩永久变形呈现先上升后下降的趋势,而断裂伸长率、回弹率逐渐提高。当MLLDPE含量为15份时,LDPE/MLLDPE复合发泡材料的表观密度、拉伸强度、撕裂强度和压缩永久变形量分别提高了6.8%、24.4%、11.4%和24.2%。当辐照剂量为80 kGy、LDPE∶MLLDPE=85∶15时,LDPE/MLLDPE复合发泡材料的力学性能和泡孔结构更佳,满足胶带型片材的综合性能要求。

聚乙烯共混体系流变行为对吹塑薄膜雾度的影响

研究了线型低密度聚乙烯(LLDPE)/低密度聚乙烯(LDPE)共混体系的吹塑薄膜雾度与流变行为之间的关系。利用DSC、光散射和WLI等方法对吹塑薄膜制品的内部结晶情况及表面形貌进行表征,利用GPC和流变学方法对单组分及共混物熔体的结构进行表征。实验结果表明,LLDPE/LDPE共混体系吹塑薄膜的总雾度主要取决于薄膜的表面粗糙度;薄膜的表面粗糙度与可恢复剪切应变参数(γ_(∞))呈开口向上抛物线函数关系,选择具有合适γ_(∞)的LDPE树脂以及添加量是控制LLDPE/LDPE共混体系吹塑薄膜雾度的关键。