High-density Polyethylene Specimens Research Articles

Cover Image, Volume 141, Issue 18

The cover designed by Kelly Walker shows the use of maleic anhydride (MAH) interfacial grafting improves the compatibility of 3D printed dual material specimens containing high‐density polyethylene (HDPE) and acrylonitrile‐butadiene‐styrene (ABS). Using a custom‐made die affording the core‐shell structure, the ABS‐g‐MAH is shown to improve the impact resistance by 253% and 16% compared to neat HDPE and ABS specimens, respectively. Additionally, a 10% increase compared to the unmodified ABS‐HDPE core‐shell configuration is observed. DOI: 10.1002/app.55301 image

Dual material fused filament fabrication of composite core‐shell structures with improved impact resistance and interfacial adhesion

AbstractThe mechanical performance of parts produced by fused filament fabrication (FFF) has been limited due to the presence of voids and poor interlayer welding. Recent advancements in FFF have enabled the fabrication of void‐free objects with strong interlayer welding through the use of semicrystalline polymer shells such as high‐density polyethylene (HDPE) along with a high viscosity core polymer like acrylonitrile‐butadiene‐styrene (ABS). The zero‐shear viscosity (η0) of ABS is three orders of magnitude higher than HDPE making the ABS‐HDPE core‐shell configuration preferable. ABS holds the shape by preventing bulk flow and part bending while HDPE promotes full surface contact across the layers. Most polymers, however, are immiscible which causes a weak weld line along the core‐shell interface. Herein, maleic anhydride (MAH) is grafted to the butadiene segment of the ABS core thereby compatibilizing the interface with HDPE, improving the interfacial adhesion. Attenuated total reflectance‐Fourier transform infrared spectroscopy was employed to confirm successful grafting. Using a custom‐made die affording the core‐shell structure, the ABS‐g‐MAH is shown to improve the impact resistance by 253% and 16% compared to neat HDPE and ABS specimens, respectively. Additionally, a 10% increase compared to the unmodified ABS‐HDPE core‐shell configuration is observed.

Effect of the Slit on the Mechanical Tearing Behavior of High-Density Polyethylene and Polyester Geocell Strips

Geocells are widely applied in numerous infrastructure constructions, like heavy-haul railways and ports. The mechanical tearing behavior of a geocell strip is crucial to the stability of the geocell-reinforced soil structures. At present, extensive studies have been conducted on the tensile characteristics of geocell strips, while limited research has been performed to investigate the post-damage mechanical tearing behavior of geocell strips. Meanwhile, there is also a lack of research on the comparison of performance of strips before and after damage. In this paper, a series of trapezoidal tearing tests were performed on high-density polyethylene (HDPE) and polyester (PET) geocell strips. The tearing test results and failure mode of trapezoidal specimens with a slit were investigated, and the effect of the slit on the strength and deformation characteristics of the specimen were discussed by introducing the “damage ratio of tearing force (RTF)” and “damage ratio of tearing displacement (RTD)”. In addition, the mechanical tearing behavior of HDPE and PET trapezoidal specimens was also compared. The test results indicated that the failure mode of HDPE and PET specimens subjected to tearing force was ductile and brittle failure. The strength and deformation characteristics of post-damage HDPE and PET trapezoidal specimens decreased. The slit had a significant impact on the tearing displacement of HDPE and PET specimens, especially the post-peak tearing displacement. The post-peak tearing displacement of HDPE was 10.99 times that of PET. The peak tearing force of the HDPE specimen without the slit was about 1.61 times that of specimen with the slit. Before local tearing, the peak tearing force of the PET specimen without the slit was about 3.27 times that of the specimen with the slit. The strength damage to the HDPE and PET geocell strips caused by the slit was 38.0%, and 69.46%. The impact of the slit on the tearing force of the PET specimen was greater than that of the HDPE, and was 1.82 times for the HDPE. This study can enhance our understanding of the mechanical tearing behavior of the geocell strip after damage and develop effective mitigation measures.

Thermal analysis under static and fatigue conditions on HDPE

High Density Polyethylene (HDPE) represents one of the best choices for water and gas distribution pipeline thanks to its light weight and good mechanical performance. One of the strengths of this plastic material is the possibility to join it via welding adopting a procedure according to the standard. However, the welding procedure can severally alter the mechanical performance of the material under service loads. In the present work comparison between virgin and welded HDPE specimens is carried out adopting rapid approaches, such as the Risitano’s Thermographic Method and the Static Thermographic Method, monitoring the evolution of the specimen’s superficial temperature under static tensile and fatigue tests. Mechanical performance has been compared, as well as the fatigue limit obtained with traditional fatigue tests, showing good agreement. Reliable fatigue data have been obtained in a very short amount of time and with few specimens by adopting Energy Methods.

Assessing the weathering-induced degradation on the structural integrity of high-density polyethylene

Marine plastic pollution is a growing environmental concern, with plastic debris in the ocean having negative impacts on marine life and human health. One of the major challenges in addressing this problem is the slow degradation rate of plastics in the marine environment. In this study, the degradation of high-density polyethylene (HDPE), being extremely common in marine debris, is investigated when exposed to either (a) marine or (b) atmospheric environmental exposure. The weathering effects for this type of plastic were examined through ultraviolet spectrophotometer and tensile investigations. A chain-breaking activity in the microstructure of the weathered HDPE specimens was revealed. During the investigated eight (8) months of atmospheric and sea weathering, an approximate 10 % and 6 % decrease in ultimate tensile strength σUTS was noticed for the two different environments, respectively. Higher decrease was noticed for the respective elastic modulus E (Young’s modulus) that was approximate 23 % and 21 %, respectively. Based on the available experimental test results, a linear decrease rate equation of all the investigated mechanical properties was proposed, to give valuable information regarding the residual tensile mechanical properties of HDPE after weathering exposure.

Effects of Ultraviolet Radiation on Recycled and Virgin HDPE Corrugated Pipes Used in Road Drainage Systems

High-density polyethylene (HDPE) pipe is one of the materials of interest for use in road drainage systems. The combination of ultraviolet (UV) light, temperature, and moisture can produce weak spots and lead to pipe degradation during the storage, installation, and repair process. The objective of this study was to evaluate changes in the chemical, morphological structure, and thermomechanical properties of recycled and virgin pipes under UV exposure. Laboratory accelerated aging tests were conducted by exposing pipes to UV for 3600 h with an irradiance of 0.89 W/(m2 nm) at a wavelength of 340 nm. A cycle of 12 h—comprised of 8 h of UV radiation at 60 °C and 4 h of no UV radiation at 50 °C corresponding to no water condensation—was performed to condition the specimens. HDPE specimens were taken out after 3600 h and analyzed with FTIR (Fourier-transform infrared spectroscopy), SEM (scanning electron microscopy), DSC (differential scanning calorimetry), oxidative-induction time (OIT) measurements, and tensile tests. The results show that the recycled pipes maintained good properties and were not significantly affected by UV radiation, similarly to the virgin pipes. Statistical analysis using one-way analysis of variance (ANOVA) shows that there was no significant difference between tensile strength, elastic modulus, and hardness measurements before and after UV exposure. There were only a few small changes in the surface of the pipes. The addition of carbon black, antioxidants, and UV stabilizers prevented further aging of the pipes during UV exposure.

A Novel Accelerated Aging Test for Floats in a Floating Photovoltaic System

Countries around the globe have recently been actively developing a new type of solar power system known as the floating photovoltaic (FPV) system. The FPV system is advantageous in terms of efficiency and is economic; however, the environmental conditions on the surface of water are harsher than on the ground, and regulations or standards of the long-term durability of the float are insufficient. As a result, this study aims to investigate the durability of the float through three types of accelerated aging tests, including the damp heat test, the ozone-aging test, and the ultraviolet (UV) aging test. After the 7-day damp heat test (80 °C/95% RH), the results revealed that four groups of high-density polyethylene (HDPE) extrusion specimens neither produced more oxygen-containing functional groups, according to Fourier-transform infrared (FTIR) spectrum analysis, nor became more easily broken by the tensile test. Furthermore, more oxygen-containing functional groups were produced after the 7-day ozone-aging test (80 °C/95% RH/500 ppm) than the 17-day UV-aging test (60 °C/0% RH/60 kW·h·m−2). On the contrary, UV aging would make HDPE specimens harder and more brittle than ozone aging. To conclude, both ozone- and UV-aging tests can evaluate the durability of the float quickly and efficiently.

Effect of Processing Techniques on the Microstructure and Mechanical Performance of High-Density Polyethylene.

The versatility of high-density polyethylene (HDPE) makes it one of the most used polymers for vast applications ranging from food packaging to human implants. However, there still is confusion regarding the proper selection of processing techniques to produce HDPE specimens for high-end applications. Herein, we compare the processing of HDPE by two relevant techniques: compression and injection molding. The fabricated samples were studied using uniaxial tensile testing to determine their mechanical performance. Furthermore, the microstructure of samples was analyzed using different characterization techniques. Compression-molded specimens recorded a higher degree of crystallinity (DC) using two different characterization techniques such as differential scanning calorimetry (DSC) and X-ray diffraction (XRD). With this information, critical processing factors were determined, and a general structure–property relationship was established. It was demonstrated that having a higher DC resulted in higher yield strength and Young’s modulus. Furthermore, premature failure was observed in the injection-molded specimens, resulting in lower mechanical performance. This premature failure was caused due to flow marks observed using scanning electron microscopy (SEM). Therefore, it is concluded that compression molding produces superior samples compared to injection molding.

Effect of impact angle and impact velocity on the slurry erosion behavior of high density polyethylene (HDPE)

High density polyethylene is widely used in many applications which deal with slurry because of its high erosion resistance characteristics. Slurry erosion is a type of erosive wear which takes place when a stream of liquid hits a solid body and results erosion in this body surface. Slurry erosion is affected by some parameters as material hardness, impact velocity, impact angle, slurry content, ambient temperature, particle hardness, particle size and particle shape. The changing of these parameters individually will result in useful analysis for the changing in slurry erosion rate with respect to the changed parameter. This experimental work aims to investigate the slurry erosion behavior of high density polyethylene under the effect of different impact velocities. A slurry impingement test rig will be used to make the wear test and wear rate of HDPE is investigated as a function of impact velocity and impact angle. Results showed that the maximum wear rate is at the lowest impact angle and maximum impact velocity. Weight loss is the indication of wear rate of the HDPE specimens after experiment and wear rate is defined as weight loss during the test time in [mg/h] unit

Polyethylene swelling in organic solvents and its influence on mechanical properties

The results of kinetic investigations of the orthodichlorbenzene and orthoxylene sorption by the high density polyethylene specimens of different thickness for 35 days are presented. It is shown that the sorption of solvents results in swelling of the polymer and its plasticization, which is expressed in changes in its mechanical characteristics such as ultimate strength, deformation to failure, and Young's modulus.

Chemo-mechanical modeling of static fatigue of high density polyethylene in bleach solution

High density polyethylene (HDPE) is increasingly used in infrastructure applications with a design service lifetime of several decades. In many cases, the HDPE member is exposed to a corrosive environment, such as in pipes carrying potable water, where the dissolved bleach selectively attacks the loosely packed amorphous phase of the polymer. The failure mechanism of HDPE transitions from a ductile to a brittle mode as the corrosion level increases. This leads to subcritical crack propagation, which deteriorates the load capacity of the structure. In this study, we develop a coupled chemo-mechanical model to simulate stress corrosion cracking (SCC) in HDPE members exposed to a bleach solution. The mechanical response of the polymer is described by a constitutive model that separately considers the individual deformation and damage behaviors of the amorphous and the crystalline phases. The model accounts for the intermolecular deformation and homogeneous void growth in the crystalline and amorphous phases, along with the resistance of the entangled network and craze damage in the amorphous phase. The embrittlement due to corrosion is captured by relating the constitutive parameters of amorphous phase to the molecular weight of the polymer. The diffusion and chemical reaction of bleach are described by a reduced order kinetics model that links the extent of polymer oxidation to the reduction of the molecular weight. The material constitutive model and diffusion–reaction model are combined in a single finite element (FE) code to investigate the SCC behavior of double edge notched HDPE specimens. The simulation yields the stress-life curves and fracture kinetics under different environments. The predicted stress-life curve qualitatively matches the measured stress-life data of polymer pipes. It is shown that the stress-life curve exhibits different regimes corresponding to distinct failure mechanisms, as indicated by the stress and strain distributions in the specimen.

Fourier transform fatigue analysis of the stress in tension/tension of HDPE and PA6

AbstractMechanical fatigue under strain controlled tension/tension (T/T) of rectangular un‐notched and notched specimens of high density polyethylene and polyamide 6 was performed. Under large amplitude oscillatory elongation, the stress response is nonlinear asymmetric due to a different stress response during loading and unloading and was analyzed via discrete Fourier transform. Dynamic strain (ε0) sweep tests revealed odd (I3/1 α ε02) and even (I2/1 α ε01) harmonics in the stress, well described by the Neo‐Hooke's law. Before crack onset for the Nc specimens, the storage and loss moduli and I2/1 are constant, but I3/1 increases with fatigue. The first derivative of I3/1 (dI3/1/dN) and the cumulative nonlinearity Qf parameter (integral of I3/1/ε02) were found to be strong criteria predicting fatigue. To break the unnotched specimens in the low and high cycle fatigue regime, large strain amplitudes were applied, resulting for both materials in initial plastic deformation followed by buckling when a critical compression force is exceeded. This results in a different time evolution of the linear and nonlinear parameters, especially as a minimum in the I2/1 curve. Finally, a model is proposed to describe the nonlinear viscoelastic specimen response under T/T and the effect of buckling.

Nonlinear ultrasonic evaluation of high-density polyethylene natural gas pipe thermal butt fusion joint aging behavior

High-density polyethylene (HDPE) pipes are widely used in urban natural gas pipelines. Thermal butt fusion (BF) welds are the weakest components of pipelines. Welding joint aging causes degradation of the PE thermal BF joint material properties. Using the nonlinear ultrasonic technique as a nondestructive testing (NDT) method was proposed for evaluating aging damage. Nonlinear ultrasonic measurements were conducted for HDPE thermal BF joint samples exposed to compression creep. Ultrasonic harmonics are generated due to aging damage. The acoustic nonlinearity parameter β based on the fundamental and second harmonics is calculated. The results indicate that β is sensitive to the variation in HDPE specimens under different aging conditions. This NDT method is useful in tracking microstructural changes in BF joints due to aging during the service process.

Assessment of Mechanical Properties of Recycled HDPE and LDPE Plastic Wastes

Most plastic materials can be recycled, and turning them into some useful products can be one of the options in reducing environmental pollutions. In this project, High Density Polyethylene (HDPE) and Low Density Polyethylene (LDPE) were used, shredded into smaller pieces and were hot-pressed to become flat plates. Both materials were then mixed with industrial waste sawdust with an aim to investigate their material properties and their suitability to be used in domestic applications such as bricks, pavement and roof tiles. Three destructive and one non-destructive methods have been conducted: tensile, impact, water absorption and ultrasonic testing. It was found that the tensile properties and impact resistance of the recycled HDPE are better than the recycled LDPE, but 10% lower than their virgin polymers. Higher stiffness and lower impact resistance were observed from specimens with additional sawdust filler in comparison to their original polymers. From the ultrasonic measurement, higher wave velocity and lower attenuation in HDPE specimens were observed, compared to the LDPE specimens, attributed by a higher modulus and density of the HDPE specimens. The ultrasonic velocity, which reflects the elastic modulus, and the attenuation that reflect the microstructure inhomogeneity are respectively decreased and increased when more fillers were added to the original specimens. This study reveals that the mechanical properties of the recycled HDPE and LDPE are closer to their virgin materials, and they have huge potential for plastic recycling.

Flexural Creep Behavior of High-Density Polyethylene Lumber and Wood Plastic Composite Lumber Made from Thermally Modified Wood.

The use of wood plastic composite lumber as a structural member material in marine applications is challenging due to the tendency of wood plastic composites (WPCs) to creep and absorb water. A novel patent-pending WPC formulation that combines a thermally modified wood flour (as a cellulosic material) and a high strength styrenic copolymer (high impact polystyrene and styrene maleic anhydride) have been developed with advantageous viscoelastic properties (low initial creep compliance and creep rate) compared with the conventional WPCs. In this study, the creep behavior of the WPC and high-density polyethylene (HDPE) lumber in flexure was characterized and compared. Three sample groupings of WPC and HDPE lumber were subjected to three levels of creep stress; 7.5, 15, and 30% of the ultimate flexural strength (Fb) for a duration of 180 days. Because of the relatively low initial creep compliance of the WPC specimens (five times less) compared with the initial creep compliance of HDPE specimens, the creep deformation of HDPE specimens was six times higher than the creep deformation of WPC specimens at the 30% creep stress level. A Power Law model predicted that the strain (3%) to failure in the HDPE lumber would occur in 1.5 years at 30% Fb flexural stress while the predicted strain (1%) failure for the WPC lumber would occur in 150 years. The findings of this study suggest using the WPC lumber in structural application to replace the HDPE lumber in flexure attributable to the low time-dependent deformation when the applied stress value is withing the linear region of the stress-strain relationship.

Critical lifetime of HDPE pipes through damage and reliability models

Damage models are not directly applicable on high-density polyethylene (HDPE) pipes. In this paper, static and strain-unified theory damage models are adapted to fit the HDPE case by substituting the dynamic tests’ endurance limits by preloading simulation through notch and stiffness evaluation. Then, tensile and burst tests are following up to evaluate the specimens’ residual life. Compared to virgin specimens, the rupture limit of old HDPE pipes’ specimens had dropped significantly and their elongation decreased from 275 mm to about 26 mm. The degradation of the seven categories of specimens are different. Indeed, the degradation is too noticeable, disappearance of the plastic phase, for the categories 6 and 7, which are in the bottom of the pipe. Then, a reduced plastic phase on the lateral categories 4 and 5 showing an important impact of degradations. Finally, a larger plastic phase for the categories 1 and 2 taken from the top of the pipe, showing a medium impact of degradation. Thus, the use of the stiffness factor, reflecting the variability of degradation of the different categories of specimens, and the thickness reduction as life fractions for both aged and neat HDPE specimens was possible. The developed strains damage model compared to static burst pressures’ one confirmed the damage stages and the critical life fraction of HDPE pipes. By comparing these models, the drastic change of HDPE pipes’ behavior, from a ductile to a brittle one, have been proved. These findings allowed us to find out the critical life fraction of neat and old HDPE pipes, which has been confirmed by comparing the burst pressure curves of a notched and an old pipe. The presented approach is cost effective allowing a deep analysis of HDPE pipes failure and damage quantification through simply made models based on static tensile and burst test instead of tedious and very costly dynamic ones.

Shear strength and temperature distribution model of friction spot lap joint of high density polyethylene with aluminum alloy 7075

PurposeThe purpose of this paper is to join a sheet of the AA7075 with the high-density polyethylene (HDPE) by a lap joint using friction spot processing and investigate the temperature distribution of joint during this process using the finite element method (FEM).Design/methodology/approachA semi-conical hole was manufactured in the AA7075 specimen and a lap joint configuration was prepared with the HDPE specimen. A rotating tool was used to generate the required heat to melt the polymer by the friction with the AA7075 specimen. The applied tool force moved the molten polymer through the hole. Four parameters were used: lower diameter of hole, rotating speed, plunging depth and time. The results of shear test were analyzed using the Taguchi method. A FEM was presented to estimate the temperature distribution of joint during the process.FindingsAll specimens failed by shearing the polymer at the lap joint region without dislocation. The specimens of the smallest diameter exhibited the highest shear strength at the lap joint. The maximum ranges of temperature were recorded at the contact region between the rotating tool and the AA7075 specimen. The tool plunging depth recorded the highest effect on the generated heat compared with the rotating speed and plunging time.Originality/valueFor the first time, the AA7075 sheet was joined with the HDPE sheet by friction spot processing. The temperature distribution of this joint was simulated using the FEM.

До задачі розрахунку релаксації напружень у тонкостінних трубчастих елементах із лінійно- в’язкопружних матеріалів

The relaxation of isotropic homogeneous and non-aging linear-viscoelastic materials under conditions of complex stress state is considered. Thin-walled tubular specimens of High Density Polyethylene (HDPE) for creep under a single-axial stretching, with a pure twist and combined load tension and torsion are considered as base experiments, tests. The solution is obtained by generalizing the initial one-dimensional viscoelasticity model to a complex stressed state, constructed using the hypothesis of the proportionality of deviators. The heredity kernels are given by the Rabotnov’s fractional-exponential function. The dependence between the kernels of intensity and volumetric creep is established, which determine the scalar properties of linear viscoelastic materials in the conditions of a complex stressed state in the defining equations of the type of equations of small elastic-plastic deformations, and the kernels of longitudinal and transverse creep defining the hereditary properties of linear-viscoelastic materials under the conditions of the uniaxial tension. The problems of stress relaxation calculation of thin walled tubes under combined tension with torsion have been solved and experimentally approved.

Prediction and analysis of surface roughness in selective inhibition sintered high-density polyethylene parts: A parametric approach using response surface methodology–grey relational analysis

Selective inhibition sintering (SIS) process intends to produce near-net-shape components through sintering of specific region of powder particles. The prediction of surface quality in SIS parts is a challenging task due to its complex part building mechanism and influence of abundant process parameters. Therefore, this study investigates the key contributing parameters such as layer thickness, heater energy, heater feedrate and printer feedrate on the surface quality characteristics ( Ra, Rzand Rq) of high-density polyethylene specimens fabricated through selective inhibition sintering process. The SIS system is custom built and experiments are conducted based on four-factor, three-level Box–Behnken design. The empirical models have been developed for predicting the influence of selected parameters on surface quality. The optimal process parameters such as the layer thickness of 0.1 mm, heater energy of 28.48 J/mm2, heater feedrate of 3.25 mm/s and printer feedrate of 110 mm/min are attained using grey relational multi-criteria decision-making approach. Furthermore, response surface analysis revealed that surface quality of sintered components is influenced significantly with heater energy and heater feedrate, followed by layer thickness. The confirmation experiments based on optimal process variables validate the developed grey relational analysis strategy.

Use of Digital Image Correlation to study the effect of temperature on the development of plastic instabilities in a semi-crystalline polymer

The plastic deformation processes that occur in a tensily deformed High Density Polyethylene specimen were studied from full-field strain and strain rate measurements obtained by 3D DIC (Digital Image Correlation). The tensile tests were performed every 10°C from room temperature to 120°C. For temperatures below 60°C, it is shown that the strain localization effect becomes less pronounced when the temperature increases. For temperatures higher than 60°C, the material is found to exhibit double yielding behavior. By analyzing the DIC data in Lagrangian representation, it was possible to quantitatively highlight the strain localization effect that is specifically associated with the second yield. The second yield strain (εY2) was measured and appeared to be nearly independent of temperature. For temperatures smaller than 60°C, it was found that the threshold strain corresponding to εY2 also marks the onset of the deformation process phase during which the volume strain strongly increases. On the basis of previous WAXS (Wide Angle X-ray Scattering) studies of our research team and on literature we concluded that the critical strain εY2 corresponds to the onset of the lamellar morphology destruction. At high strain levels, the neck stabilization phase was shown to proceed according to a strain driven scheme characterized by threshold strains that are temperature-independent. The experimental values of the threshold strain marking the onset of the stabilization phase are found to be in good agreement with those found using the Haward-Thackray model.