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Degradation of HDPE, LLDPE, and blended polyethylene geomembranes in extremely low and high pH mining solutions at 85 °C
Abstract
The durability of five 1.5-mm thick geomembranes (GMBs) is investigated in pH 0.5 and 13.5 synthetic mining solutions using immersion tests. Two high density polyethylene (HDPE), two linear low density polyethylene (LLDPE), and one blended polyethylene (BPO) GMBs are investigated at 85 • C for incubation durations of 4.5-6.5 years. It is shown that the degradation of all five GMBs in the high pH solution is faster than in the low pH solution. In the pH 0.5 solution, one of the HDPEs and the BPO GMBs exhibited polymer degradation before or at the time of the depletion of their antioxidants. In pH 13.5, four out of the five GMBs exhibited degradation and followed the conceptual three-stage degradation model until nominal failure. However, there is no correlation between the long-term performance of these GMBs and their resin type or their initial properties since one of the examined LLDPEs outperformed all the higher density/crystallinity GMBs with higher initial properties while the other LLDPE did not perform well. Thus, when selecting a GMB for a desired application, the relative performance of different candidate GMBs can be only assessed using immersion tests using the solutions expected in the field.
... [4] advocated for PVC-HX and thermoplastic polyolefin (TPO) geomembranes, particularly those exceeding 1.0mm in thickness, after a detailed mechanical analysis of commonly used geomembranes in membrane-faced rockfill dams. While the international research community has delved deep into the durability of high-density polyethylene (HDPE)/PE geomembranes [5,6], there has been a notable gap in developing aging models for PVC-P geomembranes, crucial for predicting their service life in dam engineering. ...
... (1) yielded the thermal air aging models for each PVC-P geomembrane type, as defined in Eqs. (4)- (6). The aging rate of PVC-HX geomembrane was found to be higher than the other two types, attributed to its lower plasticizer content, suggesting less resistance to aging. ...
... The lifespan of PVC-P geomembranes in anti-seepage structures was estimated by incorporating the annual average environmental temperature (expressed as thermodynamic temperature in K) and a value of ε equating to half of the original elongation (ε = 0.5ε 0 ) into Eqs. (4)- (6). For instance, considering the PVC-HX geomembrane at an operational temperature of 5℃, this data was input into Eq. ...
... High-density polyethylene (HDPE) geomembranes (GMBs) play an essential role in various geoenvironmental barrier systems, as they serve to contain liquids and gases with a design life that spans from decades to millennia (Giroud and Bonaparte 1989;Rowe et al. 1998Rowe et al. , 2004Rowe et al. , 2020Rowe and Sangam 2002;Sangam and Rowe 2002;Rowe 2005;Abdelaal et al. 2014bAbdelaal et al. , 2023aAbdelaal et al. , 2023bRowe 2017, 2020a;Clinton and Rowe 2023;Rowe and Somuah 2023;Zafari et al. 2023aZafari et al. , 2023bZafari et al. , 2024. HDPE GMBs are prone to various degradation mechanisms when exposed to long-term field exposure conditions Hsuan et al. 2008;Scheirs 2009), resulting in a reduction in both their mechanical and physical properties (Rowe 2005(Rowe , 2020Abdelaal et al. 2014a). ...
... Textured GMB rolls commonly have a smoothedge portion to facilitate welding in the field. Several studies have examined the longevity of black smooth HDPE GMBs under various exposure conditions (Mueller and Jakob 2003;Rowe et al. 2009;Rowe 2014, 2017;Rowe and Ewais 2014;Rowe and Shoaib 2017;Tian et al. 2017;Ewais et al. 2018;Abdelaal et al. 2019Abdelaal et al. , 2023aMorsy et al. 2021). However, only a few studies have explored the effect of texturing on aging of HDPE GMBs in recent research (Morsy and Rowe 2020a). ...
The effect of blown-film co-extrusion texturing (using entrained nitrogen gas) on the long-term performance of high-density polyethylene geomembranes (GMBs) immersed in synthetic municipal solid waste leachate is examined over an approximately 8-year period. Antioxidant depletion of the textured part is shown to be much faster than that of the smooth edge. Likewise, the degradation in the tensile break properties at 85 °C is faster for the textured part than for the smooth-edge portion and smooth equivalent. The updated estimates for antioxidant depletion time based on data at four different temperatures (40, 55, 75, and 85 °C) over 98 months of data collection are compared with predictions based on 34 months of data, and the implications are discussed. Nominal failure was reached at 75 °C, and this combined with data at 85 °C allows prediction of the time between depletion of standard oxidative induction time and nominal failure at lower temperatures. The effect of salt concentration in incubation fluid on the time to degradation is examined. Finally, the paper comments on the uses of textured versus smooth GMB.
... Most existing studies on marine sand grain size concentrate on a range from 1 mm to 2 mm [66][67][68][69]. Accordingly, the particle sizes of marine sand selected in this paper are between 1 mm and 2 mm to reduce the particle size effect [70][71][72]. ...
The utilization of geomembrane reinforcement technology is pervasive in marine sand foundation reinforcement projects. However, the elevated temperatures and intricate stress conditions prevalent in marine environments exert a notable influence on the mechanical characteristics of geomembrane interfaces comprising marine sand, which impedes the efficacy of geomembrane reinforcement in marine sand foundations. Nevertheless, there is a lack of research investigating the temperature-dependent interfacial mechanical performance of geomembranes and marine sand under diverse stress states. In this study, a series of monotonic shear tests were carried out on the interface between geomembranes and marine sand within a temperature range of 5 °C to 80 °C. These experiments were carried out using a self-developed large-scale temperature-controlled interfacial dynamic and static shear device. The experimental results demonstrate that temperature has a pronounced effect on the monotonic mechanical characteristics of the geomembrane–marine sand interface, which displays clear temperature dependence. The findings of this study may help in the design and optimization of offshore projects where a marine sand–polymer layer interface exists.
... None of the samples showed loss of flow reduction capacity that would interfere in the function for which they were designed. Abdelaal et al. [7] studied the durability of five different types of geomembranes in synthetic mining solutions with different pH of 0.5 and 13.5. The authors concluded that in alkaline environments the degradation of geomembranes occurred more intensely. ...
The durability study of a high-density polyethylene (HDPE) geomembrane that has been acting as a fluid barrier for 10 years in a gold mining dam/reservoir in Brazil was evaluated. The system stores waste considered hazardous, according to Brazilian legislation, with an average pH of 8 and presence of a cyanide solution. Samples exhumed after 10 years of service were exposed to the following three conditions: 1- only the weather; 2- contact with waste and exposure to the weather; 3- with field seams in contact with the tailings and exposure to the weather. Tensile strength, deformation under traction, tear resistance, puncture resistance and stresscracking tests were carried out. With the use of statistical tools, the results obtained were compared with the GM13 standard. Through the results analysed, it was not possible to observe significant losses in the geomembrane's resistances or a significant increase in its tensile deformation. It was observed the geomembrane did not present significant alteration in 10 years of service, with stress crack exception. The geomembrane may be able to continue to perform the function for which it was designed. It is necessary to carry out additional tests and monitor the system to understand whether or not its low performance in stress crack test is affecting the flow barrier function.
... In engineering, the application of statistical tools to data analysis and the prediction of the behavior of systems during their service lives is a common practice aimed at enhancing reliability [47][48][49][50][51][52][53]. Various studies indicate variability in the test results in assessing the aging and degradation of geomembranes, such as the high-pressure oxidative induction time (HP-OIT) and SCR [30,31,[33][34][35]46,54]. These variations are evident even when considering the same batch of geomembranes, as the data are random variables. ...
The tailings from gold beneficiation can cause various negative impacts, necessitating measures to prevent their transport and environmental contamination. Geomembranes serve as hydraulic barriers in mining tailings reservoirs, thereby supporting the Sustainable Development Goals (SDGs). To ensure that the geomembrane effectively mitigates environmental impact, it is essential to study its durability when applied in the field. This article examines the long-term performance of an HDPE geomembrane exposed for 7 and 11 years at a gold mining tailing site in Brazil. Samples were exhumed from different locations at the dam, and their properties were evaluated. Non-parametric statistics were employed using the Kernel Density Estimator (KDE). For the 11-year-old geomembranes, the probability of the geomembrane reaching nominal failure in terms of tensile strength was 0.4%. The peel separation values exceeded the maximum allowable by the GRI GM13 standard. Although the geomembranes showed significant antioxidant depletion, suggesting they were close to or had already reached their residual stages, they approached nominal failure based on their stress crack resistance but did not rupture. The environmental analysis indicated no significant contamination in the area, corroborating that the geomembrane is fulfilling its function. The non-parametric methodology proved promising for durability analysis and could be applied to other engineering projects with geosynthetics, thereby adding reliability to decision-making in alignment with sustainable development.
... There is no single geomembrane that is good for all chemistries. Studies on the effect of geomembrane-chemistry interaction, with particular emphasis on pH, have been reported by [67][68][69][70][71]. Temperature also significantly impacts the service life, with the service life decreasing significantly as the temperature increases. ...
This paper is a summary of many of the key findings on the application of geosynthetics in tailings storage facilities. Topics include the compressibility and permeability of tailings, the equations predicting leakage through circular and non-circular geomembrane holes, the effect of the subgrade permeability, and the effect of a lateral drainage system within tailings on leakage predictions. Two commonly encountered engineering problems relating to the piping through circular geomembrane holes and the opening width of non-circular defective geomembrane seams are given to demonstrate the potential application of leakage prediction equations. Meanwhile, issues related to the subgrade imperfection and the long-term performance of both high-density polyethylene (HDPE) and bituminous geomembranes in tailings storage applications are addressed. The research highlights that an appropriate HDPE geomembrane liner can be expected to perform very well for an extremely long time, limiting leakage and contaminant migration from the facility into the surrounding environment if the liner is well constructed on a suitable subgrade.
... Thermal-oxidative ageing of the geogrids was conducted by placing geogrid samples in a forced air oven (600 l capacity) at a temperature of 90 ± 1°C to accelerate the ageing of the geogrid specimens. Previous studies carried out the accelerated ageing of geosynthetic products (geogrids, pipes, and geomembranes) made of PET and HDPE at a temperature range of 80-110°C to investigate their mechanical degradation (Zimmerman and Kim 1980;Viebke and Gedde 1997;Elias et al. 1999;Dear and Mason 2001;Le Clerc et al. 2006;Kasozi et al. 2014;Klosowski et al. 2019;Rowe et al. 2020;Abdelaal et al. 2023). Thus, the ageing temperature used in the current study conforms to the range used in the literature. ...
The effect of thermal-oxidative ageing on the in-isolation and in-soil stiffness is investigated for two high-density polyethylene (HDPE) and two polyester (PET) geogrids when incubated in an oven at 90 o C. It is shown that the in-isolation and in-soil stiffness of three out of the four geogrids decreased during the 4-month ageing time with a faster degradation of the two PET geogrids. In contrast, one of the HDPE geogrids examined with thicker rib shows slower degradation compared to the PET counterparts. It is also shown that a geogrid might have a higher unaged stiffness, but less aged stiffness compared to another geogrid made of the same polymer type. It is suggested that the ageing approach used in this study could be adopted for selection of geogrids based on their long-term stiffness for structures such as reinforced embankments or mechanically stabilized earth walls that require a long service life. Moreover, results indicate that the stiffness improvement factor for the PET geogrids decreases with ageing time. On the contrary, the stiffness improvement factor of the HDPE geogrid increases with time and hypothetically might keep increasing followed by a sudden drop to zero at full degradation of the geogrid.
The degradation of a HDPE geomembrane in heap leaching environments is evaluated using immersion tests at five temperatures. The incubation solutions had a pH of 9.5, 11.5, and 13.5, relevant to gold and silver pregnant liquor solutions. After 9.3 years, the geomembrane's mechanical properties had reached nominal failure at 95, 85, and 75 • C in all three solutions. It is shown that the pH 13.5 solution had the greatest effect on the anti-oxidant depletion (Stage I) and polymer degradation (Stage III), but was the least aggressive to initiate the degradation (Stage II) compared to the pH 11.5 and 9.5 solutions. Overall, the time to nominal failure (time to 50% of the initial or specified property value) in pH 13.5 was slightly shorter than the pH 9.5 and 11.5 solutions. Based purely on immsersion tests, the time to nominal failure of this specific geeomembrane at 30 o C is predicted to be 150 years in the pH 9.5 and 11.5 solutions, and 140 years in the pH 13.5 solution. Assuming a good liner design that limits the tensile strains in the GMB, nominal failure in a composite liner configuration is predicted to exceed 260 years at 30 • C and the expected value could exceed 1000 years at 10 • C.
What liner configuration should you use for a tailings facility? Do you need a geosynthetic liner? Should you include overdrains above your liner? This paper presents an approach to answer these questions for a case study tailings facility in a semi-arid environment. The case study project includes a performance criterion that the seepage flux be limited below the impoundment. Four liner configurations were shortlisted, and the efficacy of each arrangement compared with numerical modelling. The configurations are: (1) tailings directly over a liner, (2) tailings on an overdrain system over a liner, (3) tailings on an overdrain system over a blinding layer over a liner, and (4) sealing the foundation with tailings slimes (i.e., no geosynthetic membrane). This paper also presents estimates of the longevity of an HDPE liner system, as this is vital in assessing performance over very long time periods. Seepage and consolidation modelling results indicate that overdrains do not improve the potential to meet the performance criterion and overdrains have a limited post-closure consolidation benefit. All configurations with geosynthetics indicated the liner system would function adequately during the period prior to geosynthetic membrane degradation. The slimes sealing case was shown to not provide an adequate impedance to flow.
Per- and polyfluoroalkyl substances (PFAS) are synthetic chemicals formed by carbon chains where fluorine atoms replace one or more hydrogen atoms. These bonds are extremely stable and PFAS components are known to be persistent environmental contaminants. The impact of these contaminants on two geomembranes is studied. Specifically, the short-term behaviour of a linear-low density LLDPE and a high-density HDPE polyethylene geomembrane immersed in a PFAS solution at an evaluated temperature is examined after 6.5 months of ageing. Results are presented for a PFAS solution with each priority component at 20 ppm or 1 ppm, a control solution (deionized water with CaCO3 28 ppm), and an MSW leachate solution at two representative temperatures of landfills (65°C and 85°C). Results show significant depletion of oxidative induction time (OIT) due to the consumption of antioxidants present in these materials. The values obtained suggest the need to consider the potential impacts of PFAS on the performance of geomembranes used in barrier systems.
The durability study of a high-density polyethylene (HDPE) geomembrane that has been acting as a fluid barrier for 10 years in a gold mining dam/reservoir in Brazil was evaluated. The system stores waste considered hazardous, according to Brazilian legislation, with an average pH of 8 and presence of a cyanide solution. Samples exhumed after 10 years of service were exposed to the following three conditions: 1-only the weather; 2-contact with waste and exposure to the weather; 3-with field seams in contact with the tailings and exposure to the weather. Tensile strength, deformation under traction, tear resistance, puncture resistance and stress-cracking tests were carried out. With the use of statistical tools, the results obtained were compared with the GM13 standard.
The long-term performance of geomembranes with 12 different resin–antioxidant master-batch combinations, including eight high-density polyethylene (HDPE), three linear low-density polyethylene (LLDPE), and one blended polyolefin (BPO) base resins, is investigated. Results are reported for immersion tests in chlorinated water (0.5 ppm) for 35 months at 85 °C. The degradation trends show that the choice of resin type played a key role in the longevity of the geomembranes but also that some hindered amine light stabilizer (HALS) packages contributed to better resistance to degradation in chlorinated water. The results show that the specific antioxidant package is more important than the initial oxidative induction time (OIT) in terms of long-term performance. Finally, it is shown that while increased thickness may be beneficial, a more resistant resin or antioxidant–stabilizer package can be more effective than increasing thickness in improving geomembrane performance in chlorinated water. The conclusion regarding the beneficial role of HALS is specific to chlorinated water and generally is not true in other cases of submerged or buried geomembranes.
An approach for selecting a high-density polyethylene (HDPE) geomembrane (GMB) for a long design life is described and illustrated for five 2 mm thick textured GMBs when immersed in a simulated municipal solid waste leachate (L3) and two simulated leachates representative of low-level radioactive waste leachates (L7 and L9) for 9–16 months at a range of temperatures. Although made from the same nominal resin, substantial differences are reported in both the initial properties and the rate of antioxidant depletion for the five GMBs. At an expected operating liner temperature of 10 °C and immersed in L3, the projected time to antioxidant depletion for the five GMBs ranges from 125 to over 2000 years. The antioxidant depletion in leachates L7 and L9 were similar or slower than in leachate L3. There was no evidence of traditional thermal-oxidative degradation reported over the 9–16 months of monitoring; however, there was a significant reduction in stress crack resistance due to physical ageing ranging between 30% and 70% of the initial value. Two GMBs are considered highly likely to have service life well in excess of the required design life of 550 years. It is suggested that the proposed approach could be adopted for selecting GMBs for other projects that require a long design life.
The effect of texturing (co-extrusion using blowing agent) on the longevity of a geomembrane (GMB) when immersed in synthetic municipal solid waste leachate is investigated over a ∼3 year period. Based on data at four temperatures (40, 55, 75, and 85 °C), the time to antioxidant depletion of the textured portion of a 1.5 mm core thickness high-density polyethylene (HDPE) GMB is 40% (standard oxidative induction time) and 9% (high-pressure oxidative induction time) faster compared to the 1.5 mm smooth edge of the GMB. However, despite this, stress crack resistance results show that texturing may have no significant effect on the time to nominal failure for this GMB. It is also shown that HDPE GMBs made from nominally the same resin but from different production lots have different rates of stress crack resistance degradation and hence time to nominal failure; this should be considered both in landfill design and landfill construction quality assurance.
Antioxidant depletion from a high-density polyethylene (HDPE) geomembrane with hindered amine light stabilizers (HALS) immersed in seven different low pH solutions is examined over a 3 year period. The examined solutions had the range of pH (0.5, 1.25, and 2.0) likely to encompass the pH of the leach solutions found in copper, nickel, and uranium heap leach pads. The metal concentration for these solutions is adopted from copper raffinate solutions. Additional solutions are investigated to examine the effects of field practices such as using surfactants in the leach solutions and pre-curing of the ores used to improve the metallurgical response of the ore. For the antioxidants detected by standard oxidative induction time (Std-OIT), there was a depletion to residual value of about 20% of the initial Std-OIT that varied depending on the incubation temperature and pH of the solution whereas decreasing the pH from 2 to 0.5 did not significantly affect the depletion rates of Std-OIT. The antioxidants detected by high-pressure oxidative induction time (HP-OIT) exhibited the fastest depletion in pH = 1.25 with the highest residual values followed by pH 2.0 and the slowest HP-OIT depletion was in pH = 0.5, but with the lowest residual values. Arrhenius modelling is used to predict the length of the antioxidant depletion stage for each solution based on both Std-OIT and HP-OIT.
Heap leaching is one of several leaching methods (in-situ leaching, dump leaching, pressure leaching and tank leaching) whereby metal and other ores are leached with various chemical solutions to extract valuable minerals. Commonly HDPE is used in the pad under the ore to protect the environment and to preserve the leached solution containing the desired mineral. The most extensive application of heap leach pads is for copper ore processing. In this application, weak sulphuric acid is usually used to dissolve copper from the mineral ore. Typically copper pregnant leach solution has a pH less than 2.0 with a concentration of copper that varies from 1 to 5g/l and iron concentration up to 5g/l. A program for examining the effect on the aging of HDPE geomembranes of these and other solutions relevant to heap leach pads at both very low and high pH and to low level radioactive waste facilities where the leachate has a high pH is described. Tests are being conducted at temperatures of 40, 65, 75, 85, and 95 o C. The geomembrane properties and solution chemistry being used are also presented. Preliminarily antioxidant depletion rates for geomembrane incubated in a solution with a pH=0.5 are presented and a preliminary extrapolation to field temperature is provided.
This paper discusses the need to adopt a systems engineering approach to the design and operation of municipal solid waste landfills. It discusses how the interaction between the different components affects the performance of the entire system and how, due to this interaction, the performance of the system as a whole is much greater than the individual contributions of each of the parts. Issues discussed in this context include: landfill covers and the role that they play, the effect of landfill operations such as the waste placement and leachate recirculation on liner temperature and leachate characteristics, leachate collection and the control of head on the liner, diffusion of contaminants through composite liners, the effect of geomembrane-clay liner interaction on leakage, the significance of wrinkles in a geomembrane, the effect of liner temperature on leakage, possible means of controlling liner temperature, geomembrane protection, the long-term performance of geomembranes and geosynthetic clay liners, and finally the contaminant transport implications of these issues. It is concluded that by taking a systems approach to design, construction and operations we can provide safer containment of waste and long term-environmental protection.
To properly understand and assess the long-term behaviour of geosynthetic materials it is necessary to investigate the various types of possible degradation mechanims. This includes both chemical and mechanical behaviour, and sometimes even their interactions with one another. Clearly, chemical degradation of geosynthetics depends on the polymer type. For example, polyolefins are vulnerable to oxidation; polyesters are susceptible to hydrolysis; and plasticizers can leach from polyvinyl chloride. This paper describes the concept of these three types of degradation, but focuses on the oxidation of polyolefins since the majority of the geosynthetics is made from this type of polymer. The methods used to predict the lifetime of antioxidants and service life of the geosynthetic material will be illustrated. Furthermore, the influence of temperature, pressure, and ultraviolet light on the service life are also demonstrated. Finally, the current specifications targeting the longevity of different geosynthetics are presented. Regarding mechanical degradation, the paper mainly focuses upon the creep deformation of geogrids and stress crack resistance (SCR) of polyethylene geomembranes and geopipe. The method to assess stress crack resistance is described, and the microscopic mechanisms that lead to such failure are explained. For creep evaluation, different acceleration tests are presented and their applicability with respect to the different types of polymers is illustrated. In addition, the long-term shear behaviour of geocomposites and geosynthetic clay liners is presented.
A geomembrane-compacted clay composite liner system used to contain municipal solid waste (MSW) landfill leachate for 14 years is evaluated. Field observations of the geomembrane revealed many defects, including holes, patches, and cracks. Physical, chemical, and mechanical tests conducted on samples collected from five different locations of the liner suggest that samples continuously exposed to sunlight and high temperatures experienced more degradation compared to samples that were covered by leachate or soil. Sorption and diffusion tests revealed that the permeation coefficients of volatile organic compounds were in the range of 4x10(-12) to 6x10(-11) m(2)/s and that, with respect to these parameters, there was no significant difference between samples with different exposure levels. However, the permeation coefficients were between four and five times lower than values obtained for unaged HDPE geomembranes typical of present day production. Contaminant modelling of the entire lagoon liner suggests that the geomembrane liner most likely stopped being effective as a contaminant barrier to ionic species sometime between 0 and 4 years after the installation.
Accelerated aging tests to evaluate the depletion of antioxidants from a high density polyethylene geomembrane are described. The effects of temperature, high pressure, and continuous leachate circulation on the aging of geomembranes in composite liner systems are examined. The antioxidant depletion rates 0.05, 0.19, and 0.41 month −1 at 55, 70, and 85° C, respectively obtained for the simulated landfill liner at 250 kPa vertical pressure are consistently lower than that obtained from traditional leachate immersion tests on the same geomembrane 0.12, 0.39, and 1.1 month −1 at 55, 70, and 85° C. This difference leads to a substantial increase in antioxidant depletion times at a typical landfill liner temperature 35° C with 40 years predicted based on the data from the landfill liner simulators tests, compared to 15 years predicted for the same geomembrane based on leachate immersion tests. In these tests, the crystallinity and tensile yield strain of the geomembrane increased in the early stages of aging and then remained relatively constant over the testing period. There was no significant change in other geomembrane properties within the testing period.
The crystallization behavior of high density polyethylene/isotactic polypropylene blends (HDPE/PP) was investigated. The overall kinetics of crystallization of HDPE may be strongly influenced by the addition of a small fraction of PP. At 398 K the half crystallization time of the blend containing 10% by weight of PP is around three times larger than for pure polyethylene. This effect may be accounted for by an increase in the melt viscosity of liquid HDPE caused by PP molecules. For crystallization temperatures high enough to prevent HDPE crystallization (Tc > 400 K), the presence in the melted blends of liquid HDPE influences the crystallization of PP. In fact, the half time of crystallization of PP increases with increasing the fraction of HDPE in the blend. The kinetics show a minimum at a well defined composition (around 60% in PP) before phase inversion. The same trend is observed when the surface free energy of folding and the lamellar thickness of crystals are reported as function of composition.
Reliable lifetime prediction of underground polyethylene (PE) pipes must be based on a more in-depth understanding of failure mechanisms and a more reliable extrapolation procedure of relatively short test data into long-term service environment. However, there still remain many limitations in the current lifetime prediction methods of PE pipes, such as the deviation of accelerated tests from operating conditions and the empiricism in prediction models. This paper summarizes the failure mechanisms of PE pipes and reviews the researches on lifetime prediction method from two aspects “mechanical” and “chemical” lifetime. A detailed presentation of limitations in current lifetime prediction methods are provided, including failure to consider the material aging and defects or imperfections, crack initiation time, crack tip plasticity and aging, diffusion-limited oxidation and nonlinear Arrhenius behavior. Potential trends of lifetime prediction of PE pipes are further discussed. The chemo-mechanically coupled model and crack layer (CL) model is proposed for the lifetime prediction to reduce the empiricism due to the diffusion-limited oxidation (DLO) or the transition from a continuous SCG to discontinuous.
A high density polyethylene geomembrane (GMB) stabilized with hindered amine (light) stabilizers (HALS or HAS) is immersed in four chlorinated water solutions with a simulated free chlorine concentration range of 0.5-5 ppm at five different temperatures (25, 40, 65, 75, and 85 °C) for 70 months. Standard and high pressure oxidative induction time (OIT) tests are performed to monitor antioxidants depletion while melt flow index, tensile, and stress crack resistance (SCR) tests are conducted to monitor degradation in physical and mechanical properties. Degradation in the GMB properties occurred shortly after immersion in chlorinated water at all temperatures except at 25 °C. Increasing the free chlorine concentration resulted in faster degradation of the tensile properties and SCR. The predicted time to nominal failure based on SCR ranges between 25 years at 40 °C and 5 years at 85 °C in chlorinated water (with 0.5 ppm free chlorine). A comparison between the degradation in SCR of this GMB and a GMB with a different resin and without HALS shows significant difference in their performance in chlorinated water but not in other incubation media.
The decrease in stress crack resistance (SCR) of geomembranes (GMBs) due to physical ageing is examined. It is shown that the SCR of a 1.5 mm high density polyethylene (HDPE) GMB immersed in municipal solid waste (MSW) leachate, deionized (DI) water, and air experienced a decrease to an equilibrium value, denoted herein as SCRm, in a few months and then did not change for the remainder of a 116-month test. The same GMB was also immersed in basic mining pregnant leach solution (PLS) and brine and a similar decrease in SCR to SCRm was observed in the first three months. For this GMB, SCRm was about 50% of the initial SCR value (i.e., SCRm ∼ 0.5·SCRo) for all incubation fluids examined. It is then shown that this behaviour is not unique. Seven other high density polyethylene (HDPE) and one blended polyolefin (BPO) GMBs are shown to experience a decrease in SCR to 0.17·SCRo ≤ SCRm ≤ 0.56·SCRo without any evidence of oxidative degradation. The magnitude of SCRm is shown to be product specific. In contrast, the one linear low density polyethylene (LLDPE) examined exhibited no such physical ageing. The implications for designing with GMBs are discussed.
A 17-year investigation of a geomembrane (GMB) aged at 55, 70 and 85°C in air, water and leachate is reported. At test termination, the mechanical properties had only reached nominal failure in leachate and water at 70 and 85°C. Consistent with a previous study, there is a significant reduction in stress crack resistance (SCR) before there is clear evidence of oxidative degradation; this is attributed to the morphological changes due to disentanglement of entangled polymer chains. The effect of this apparent morphological change on SCR appeared to be greatest for the GMB when immersed in water and leachate at 70°C, although it is evident for all fluids at all three test temperatures. Using the most conservative estimates, the time to nominal failure (tNF, time to 50% of the initial or specified property value) in leachate, water and air (no UV exposure) ranged from >13, 18 and 170 years at 60°C to 660, 1500, and 1700 years, respectively, at 20°C. Assuming minimal tensile strains in the GMB, the time to nominal failure of this GMB in a composite liner is likely estimated to vary from >50 years at 60°C to >550 years at 35°C and > 1100 years at 20°C.
Blended polyolefin (BPE) is a proprietary blend of polyolefin. There is little independent data on the potential long-term performance of this polymer resin to compare with that of high-density polyethylene and linear low density polyethylene under the same exposure conditions. This paper examines the performance of a BPE geomembrane immersed in incubation solutions relevant to its potential use in heap leach pads, Bayer process, municipal solid waste landfills, water lagoons, and potable water reservoirs. Results presented provide preliminary insight regarding antioxidant depletion as measured by Std-OIT in the immersion fluids and hence with respect to the first stage of the service life of BPE GMBs in these different applications.
Two types of linear low density polyethylenes (LLDPE) with different comonomer sequence distributions were blended with high density polyethylene, and the effect of the distribution on the miscibility behavior in the melt state was studied. Phase diagrams were constructed based on thermal behavior of the blends quenched from the melt. LLDPE prepared with Ziegler-Natta catalyst, which had more uneven comonomer distribution, was found to be more miscible with lower upper critical solution temperature compared to LLDPE prepared with metallocene catalyst. Rheological behavior and morphology of the blends were also examined, and the results showed good agreement with the phase behavior determined by thermal analysis.
Linear low density polyethylenes (LLDPE) prepared by Ziegler-Natta catalyst (ZNLLD) and LLDPE by metallocene catalyst (MLLD) were respectively blended with high density polyethylene (HDPE), and the effect of the comonomer distribution on the crystallization behavior and morphology was studied. ZNLLD cocrystallized with HDPE in a wider range of blend compositions and with a smaller amount of separate-crystallized LLDPE than MLLD did. The result was considered to be due to the fact that MLLD had more even comonomer distribution than ZNLLD had. The etched-surface morphology exhibited that banded spherulites were more uniformly formed when cocrystallization only occurred. The non-uniform morphology appeared to be due to the mixed stacking of cocrystals and separate-crystals.
Antioxidant depletion from a high-density polyethylene (HDPE) geomembrane with hindered amine light stabilizers (HALS) immersed in three different high pHs solutions is examined over a 3-year period. The three solutions had the same concentration of inorganic salts but a range of pH (9.5, 11.5, and 13.5) likely to encompass those found in low-level radioactive waste leachate and other geoenvironmental applications. Increasing the pH from 9.5 to 13.5 increased the antioxidant depletion rates detected by both standard and high-pressure oxidative induction time tests (Std-OIT and HP-OIT) and also increased the residual HP-OIT values. Arrhenius modeling is used to predict the length antioxidant depletion stage for each solution.
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The effect of geomembrane thickness (1.5, 2.0, and 2.5 mm) on aging when immersed in a synthetic leachate is investigated over a period of approximately 7 years. Based on data at five different temperatures (55, 65, 70, 75, and 85°C), the predicted time required for a reduction in stress crack resistance to 150 h (half the typically specified value) at 35°C is 62% longer for the 2.5 mm than for the 1.5-mm geomembrane tested and 12% longer for the 2.0-mm than for the 1.5-mm geomembrane. Thus, other things being equal, the results suggest a longer time to nominal failure with increasing geomembrane thickness. It is also shown that the data from a proposed stage-parallel testing procedure collected over 2.5 years fit well with data from traditional incubation of virgin samples over almost 7 years and hence provides a viable means of obtaining good data in a reasonable period of time.
The changes in the stress crack resistance, SCR (measured by the single point notched constant tensile load; ASTM D5397 – appendix) for a 1.0 mm high-density polyethylene (HDPE) geomembrane aged in synthetic leachate at six temperatures (25, 40, 55, 70, 85 and 95 °C) and in air and water at 55 °C were investigated for almost five years. There are observed changes in the SCR before the geomembrane chemically degraded (as manifest by melt index and tensile properties) and even before the antioxidants depletion at temperatures below 70 °C (as manifest by the standard and high pressure oxidative induction times). This change is attributed to morphological changes during aging that affected the inter-lamellar connections due to: (a) annealing that increased the strength of the inter-lamellar connections (over the temperature ranges examined), and (b) the proposed chain disentanglement mechanism. The annealing and chain disentanglement mechanisms have a counteracting effect on the inter-lamellar connections and hence on the SCR. Chain disentanglement dominated over the annealing effect at 25, 40, 55 and 70 °C, resulting, respectively, in a decrease in SCR to an equilibrium SCRm of 0.83, 0.65, 0.26 and 0.43 of the initial stress crack resistance of the geomembrane (SCRo). The maximum decrease in SCR is observed when the geomembrane is aged in leachate at 55 °C with the SCR decreasing to 0.26 SCRo. The SCR of the geomembrane aged in air and water at 55 °C decreased to about 0.5 SCRo, implying that the surfactant used in leachate may have enhanced the rate and the extent of chain disentanglement (i.e., decreasing the time to reach a lower SCRm) due to plasticization of the amorphous zone.
HDPE/poly(ethylene-co-vinylacetate) (EVA) and low-density polyethylene (LDPE)/EVA blends were tested and compared with respect to their environmental stress cracking resistance (ESCR) using the Bell-telephone test. The time to failure in the ESCR test improves with increasing EVA content, and considerable improvements were produced for LDPE/EVA blends while small improvements were observed for HDPE/EVA blends. Thermal, rheological, mechanical, and morphological studies were conducted which established a quantitative relationship between morphological features and composition. Furthermore, the failed specimens were further characterized by scanning electron microscopy and fractographic methodology to investigate the failure mechanism for ESCR samples. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39880.
Aging of the same geomembrane immersed in the same four synthetic municipal solid waste leachates tested by Rowe et al. (2008) for 2.65 years is continued for an additional 6.5 years (i.e., providing data over more than 9 years of aging). The additional data is used to (a) update the initial estimates for antioxidant depletion stage, and (b) investigate the effect of leachate constituents on the timing and magnitude of the changes in the physical properties of the geomembrane. While all the examined leachates had surfactant and trace metals in common, reduced Leachate 1 (full leachate) had salts and volatile fatty acids (VFAs), Leachate 2 was not reduced and had neither salts nor VFAs, reduced Leachate 3 had salts, reduced Leachate 4 had VFAs, and Leachate 5 was similar to Leachate 2 except that it was reduced. Incubation in all leachates gave very similar predictions of the antioxidant depletion stage, however, the salts in Leachates 1 and 3 are shown to have the largest effect on the geomembrane mechanical properties, especially stress-crack resistance, resulting in a shorter time to nominal failure than for leachates without salts. Furthermore, reduced Leachates 1 and 3 showed faster degradation in stress-crack resistance than Leachate 2 which was not reduced and without salts. Arrhenius modeling is used to extrapolate the time to nominal failure (i.e., a reduction in stress-crack resistance to 150 h) at a range of temperatures.
The effect of elevated temperatures, typically 95–115 °C, on antioxidant depletion from a high-density polyethylene (HDPE) geomembrane (GMB) incubated in air, water and synthetic leachate is examined. It is shown that the antioxidant depletion in synthetic leachate at 95–115 °C is consistent with what would be expected from Arrhenius modeling based on data from lower temperatures (25–85 °C). A similar finding is reached for incubation in air. However, when incubated in water the antioxidant depletion is more complicated. At temperatures above 100 °C a four-parameter exponential model was needed to fit oxidative induction time data that exhibited quite different early-time and later-time depletion rates. The early-time depletion rate decreases with an increase of the temperature while the later-time depletion rates follow the more typical pattern of increasing with increasing temperature. Three additional HDPE GMBs with different antioxidant packages are examined at elevated temperatures in air. The GMB with the lowest initial standard (Std) oxidative induction time (OIT) and without hindered amine light stabilizer (HALS) has the longest antioxidant depletion stage based on Std-OIT at these elevated temperatures. GMBs stabilized with HALS showed only a slight change in their high pressure OIT during the current study. It is shown also that degradation in physical properties can start at Std-OIT values above the residual OIT values.
The degradation of three high density polyethylene geomembranes (GMBs) (denoted xA, xB and xC) when immersed in simulated landfill leachate at 85 °C is examined. All three GMBs met the requirements of the generic industry specification GRI-GM13 with respect to their performance properties. The large high-pressure oxidative induction time (HP-OIT) (i.e., 790 min for xB and 960 min for xC) combined with the relatively high level of trace nitrogen detected, suggest the presence of hindered amine light stabilizers (HALS) as part of the antioxidant package in these GMBs, whereas, the relatively low initial HP-OITs (i.e., 260 min) and the low level of trace nitrogen for xA, suggest the absence of HALS in xA. Although xA had the lowest initial standard Std-OIT (Std-OIT was 115, 158 and 175 min for xA, xB and xC, respectively) it exhibited the longest time to antioxidant depletion based on Std-OIT. For the three GMBs, the HP-OIT depleted following exponential decay model until reaching a residual value. xB had the slowest HP-OIT depletion (0.016 month−1) and was still depleting without reaching a residual value at the end of this study (after 46 months). xA experienced the fastest HP-OIT depletion (∼62 times faster than of xB) and reached a residual value of 78 min. For xC, HP-OIT depleted 40 times faster than for xB reaching a residual value (∼610 min) that was still higher than the HP-OIT of 400 min specified by GRI-GM13 for a new GMB. xB had the longest time to nominal failure despite having the lowest initial SCR value (330 h for xB compared to 910 and 800 h for xA and xC, respectively) and not having the highest OITs values. Although xC had a residual HP-OIT of 610 min, the SCR, melt index (MI) and tensile properties for xC had decreased to the point that xC was at nominal failure, indicating that the degradation can take place without the total depletion of antioxidants/stabilizers captured by the HP-OIT.
A review of 92 heap leach projects from 15 countries provides a starting point for a series of experiments, at 22 °C and a vertical pressure of 2000 kPa, to examine short-term puncturing and the development of geomembrane strains that could affect longer-term performance. Underliners of gravel with some sand or those of gravel and sand caused significant puncturing and excessive strains in the geomembrane for the conditions examined. The shape of the underliner grading curve had a much greater effect on the potential for puncturing and the magnitude of the strains in the geomembrane than just the maximum particle size. Of the six granular underliners examined, the best performance was for the well graded gravelly sand with some silt which offered sufficient support to minimize the strains in the geomembrane due to the overliner while not inducing significant strains directly from the underliner. Nevertheless even in this case the maximum strain of 11% is almost double the maximum recommended in the literature for ensuring good long-term performance of the geomembrane. Consideration of composite liners with GCLs and compacted clay liners shows that the more deformable the foundation, the larger are the indentations and strains induced in the geomembrane by a given overliner. For the specific conditions examined, it is shown that there was no apparent improvement in performance for an LLDPE geomembrane versus the HDPE geomembrane tested. A 540 g/m2 geotextile protection layer above the geomembrane was also found to be insufficient to prevent significant strains in the geomembrane due to the overliner examined.
Degradation of linear high density polyethylene (HDPE) and butyl branched linear low density polyethylene (LLDPE) was studied during moulding in a closed mixing chamber. At the beginning of the process the rate of oxidative degradation was found faster for LLDPE than for HDPE but later this relation reversed. The degradation mechanism was the same for both types of polyethylenes but the rate of elementary steps depended on the chemical structure of the polymer chain. The differences were attributed to the structural differences in the original materials and the products formed during degradation.
A major issue in the use of geomembranes for waste containment is an estimate of the material`s durability (i.e., its lifetime) to various aging phenomena. For high density polyethylene geomembranes, which are the focus of this study, there are three stages in assessing lifetime: depletion of antioxidants, induction time, and time to reach half-life of a relevant engineering property. This paper addresses the first stage of these three sequential processes. Twenty laboratory incubation devices were made to simulate landfill conditions. Four sets of five columns were maintained at elevated temperatures of 85, 75, 65 and 55 C. Samples were retrieved at various intervals over a 24-month incubation period. Various physical, mechanical, and chemical properties were evaluated. The depletion of antioxidants in the incubated samples was monitored using both standard and high pressure oxidative induction time tests. Arrhenius modeling was used on the data to extrapolate the antioxidant lifetime to a typical landfill site temperature of 20 C. The resulting predicted time was 200 to 215 years. Also, it should be emphasized that within this period of time the physical and mechanical properties of the incubated samples remained unchanged.
Data are reported from oven aging in air for more than 13 years (!) and from water immersion tests for 6 years at 80 °C on various high-density polyethylene geomembranes (GM) used in landfill lining. The mechanical properties and oxidative induction times (OIT) of the samples were monitored during the long-term testing. Aging behavior in hot air is different from that in hot water. During oven aging a slow, exponential decrease of OIT is observed. Even after 13.6 years there is no indication of an oxidative degradation of the mechanical properties. During immersion in water a strong reduction in OIT occurs within the first year, after which time the curve levels off. Oxidation starts when very low OIT-values are reached after about 5 years at which time the mechanical strength rapidly falls to values below the yield point. We conclude from these data that the service life of HDPE GM's is essentially determined by the slow loss of stabilizers due to migration. The oxidation starts only after the depletion of antioxidants and then quickly leads to brittleness of the sample. However, no complete oxidative deterioration has been observed to date. We estimate by the van't Hoff rule that under normal ambient conditions many centuries will have to pass before the functional mechanical properties of state-of-the-art stabilized HDPE bulk material will be reduced below acceptable limits by oxidative degradation.
The molecular interactions of phenolic anti-oxidants, aromatic amines and HALS stabilizers are successfully studied by heating the stabilizers under oxidative conditions in polar and non-polar solvents. The polar solvent bis(2-methoxyethyl)ether is used to mimick polar engineering plastics like e.g. TPE-U's, whereas the non-polar solvent squalane or 2,6,10,15,19,23-hexamethyltetracosane is used to mimick polypropylene. The oxidation rate is followed by the analysis of samples taken in time using various analytical techniques as e.g. IR, HPLC–PDA, GC–FID, GC–MS and LC–MS. A general occuring interaction between sterically hindered phenols and aromatic amines, i.e. regeneration of the aromatic amine by the sterically hindered phenol, is demonstrated by varying the molecular structure of the phenol as well as the polarity of the system. Studies using mixtures of a HALS with structurally different sterically hindered phenols visualized a general antagonistic effect between the phenols and the HALS, in which the HALS consumes the phenol. In all stabilizer combinations using the sterically hindered phenols studied here, a stabilization of the resulting quinone form is observed which can, dependent on the molecular structure of this quinone, lead to solubility issues in polymers.
The role of analysis in the evaluation and design of barriers is discussed. Factors considered include (i) the mechanisms controlling contaminant migration through barriers; (ii) the determination of diffusion and distribution coefficients; (iii) leachate mounding and the effect of clogging of leachate collection systems upon contaminant migration through barriers; (iv) the importance of considering the finite mass of contaminant available for transport into the soil and a method of modelling the effect of finite mass of contaminant; and (v) examples of how analysis may improve the geotechnical engineer's feel for the effectiveness of potential contaminant attenuation mechanisms in both glacial till deposits and fractured rock.
The effect of high-density polyethylene (HDPE)/polypropylene (PP) blending on the crystallinity as a function of the HDPE melt index was studied. The melting temperature and total amount of crystallinity in the HDPE/PP blends were lower than those of the pure polymers, regardless of the blend composition and melt index. The effects of the melt index, blending, and foaming conditions (foaming temperature and foaming time) on the void fractions of HDPEs of various melt indices and HDPE/PP blends were also investigated. The void fraction was strongly dependent on the foaming time, foaming temperature, and blend composition as well as the melt index of HDPE. The void fraction of the foamed 30:70 HDPE/PP blend was always higher than that of the foamed 50:50 HDPE/PP blend, regardless of the melt index. The microcellular structure could be greatly improved with a suitable ratio of HDPE to PP and with foaming above the melting temperature for long enough; however, using high-melt-index HDPE in the HDPE/PP blends had a deleterious effect on both the void fraction and cell morphology of the blends. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 364–371, 2004
A major stream of post-consumer plastics is a commingled blend of polyethylenes and polypropylenes, which usually exhibits lower performance compared with that of the homopolymers due to the incompatible nature of polyethylenes and polypropylenes. Various studies have been carried out to characterize the structure, morphology, mechanical, thermal, and rheological behavior of this blend. The effect of processing, modification, and compatibilization have also been studied by various workers. This article is a review of the work done on polyethylene–polypropylene blends to help in the understanding of this important blend. © 1994 John Wiley & Sons, Inc.
A special modified tensile creep test was used to investigate the stress cracking behavior of various high-density polyethylenes (HDPE). Blends of HDPE with other HDPEs, with linear low-density polyethylene (LLDPE), and specifically with various slightly long-chain branched linear low-density polyethylenes (HBPE) were tested for their failure times. Whereas HDPE blends, including higher-molecular-weight HDPE components, yield only a minor improvement in stress cracking resistance, a considerable improvement was produced when an LLDPE weight fraction of 0.3 or more was used. Adding HBPE also improves the environmental stress cracking resistance. Environmental stress cracking resistance improves with increasing HBPE content, and, for a constant HBPE concentration, it increases with increasing octene content of the HBPE. Adding HBPE with a low octene content, however, results in reduced failure times of the blend compared with HDPE blends that exhibit relatively good environmental stress cracking behavior. The results are explained in terms of the tie-molecule density.
Important experimental parameters for FTIR spectra acquisition were studied: apodization, beam aperture, number of scans and spectral resolution, using polyethylene samples. The optimum conditions for the analyses were established and permitted unequivocally to identify the three most important commercially available grades: low density, high density and linear low density products (LDPE, HDPE and LLDPE respectively).
The kinetics of slow crack growth were measured in a polyethylene copolymer in a notched tensile specimen under constant load. The microscopic changes in the crack morphology were linked to the crack opening displacement and to the crack advance. The jump distance during the discontinuous crack growth decreased as the applied stress decreased. The jump distance decreased as the temperature decreased because the yield point was increasing. These observations are explainable by the Dugdale theory. The initiation time for fracture depends on the rate of disentanglement of the fibrils in the craze and occurs in the fibrils adjacent to a tough skin at the base of the craze. The crack grows until it meets fibrils whose strength matches the value of the stress intensity at which point the crack is arrested. Re-initiation of fracture occurs when the fibrils at the root of the crack have been sufficiently weakened by the process of disentanglement. Thus, the overall kinetics depend on (1) the rate of disentanglement of the fibrils, (2) the gradient in the fibrilla strength between the base and the tip of the craze, (3) the value of the stress intensity, and (4) the yield point of the matrix.
Heap leach pads are used in the mining industry as an integral component for metal extraction and processing. The design of modern heap leach pads utilize an engineered liner system that often is a blend of natural and geosynthetic materials in order to achieve a desired performance, such as ore heap stability, solution drainage, and efficient recovery. An important issue that is often overlooked in the design of heap leach pad liner systems is the compatibility between geosynthetic materials (e.g. geomembrane, geopipe, geotextile, etc), native materials, ore, and operational conditions/restrictions. This issue becomes more pronounced as heap leach pads are constructed in steep terrain, harsh climates (wet, cold, etc), and subjected to high ore loads (exceeding 4 MPa). This paper discusses design approaches for heap leach pad liner systems, with a focus on compatibility with geosynthetic materials.
The authors present a summary of the state of the practice of containment design in copper and gold heap leaching, focusing on recent advancements and how these applications differ from the more conventional landfill design practices. Advancements both within the Americas and worldwide are presented, including consideration of increasing heap depths, which are now approaching 150 m (with ore densities generally in the range of 1500–1800 kg/m3). Liner system performance under these pressures will be reviewed, including the latest developments in drainage pipe performance testing. The authors will also explore the recently emerging technology of using concentrated sulfuric acid pre-curing for copper ores and the related compatibility issues with conventional geomembrane materials.
The latest findings regarding the long-term performance and service life of HDPE geomembrane (GM) samples exposed to air, water and leachate are presented based on data from samples that have been ageing for 8–10 years. Some of the GM samples are in Stage II, some in Stage III and some have completed all three stages of the service life. The paper provides: (1) improved data on antioxidant depletion rates for GMs immersed in air, water and leachate; (2) estimates of antioxidant depletion time (Stage I) at typical liner temperatures in air, water and leachate and, based on this data, an estimate for a composite liner at typical liner temperatures; (3) data regarding the changes in the physical and mechanical properties of the GM samples with time; (4) a surface analysis of virgin and aged GMs; (5) an initial estimate of the induction time (Stage II) and polymer degradation time (Stage III) and service lives of GM in laboratory immersion tests; and (6) predictions of the service life of leachate immersed GM at typical landfill temperatures. Based on these predictions, it appears likely that the service life of the specific GM tested immersed in leachate is likely to exceed 700 years and will probably be of the order of 1000 years (or longer) at 20 °C, more than 150 years and likely 225–375 years at 35 °C and more than 40 years and likely 50–90 years at 50 °C. The service life in a liner configuration may be expected to be longer than predicted here for immersion in leachate.
HDPE is widely used in outdoor applications in which dielectric, mechanical and thermal behaviors combined with high environmental resistance are a major concern. Unfortunately, the required processing conditions of the material often result in residual stresses that in connection with environmental exposure are responsible for premature failure. In an attempt to combine good durability with more facile processing conditions for HDPE based components, blends of this polymer with LDPE and LLDPE were studied, as a function of the blend composition ratio. Measurements of crystallinity and dynamical mechanical studies were conducted which established a quantitative relationship between morphological features and composition. The optimal results of performance were obtained with HDPE/LLDPE blends which are discussed here in terms of their morphology and mobility of the amorphous phase.
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