According to astm d883, stress cracking is defined as an external or internal crack in a plastic caused by tensile stresses less than its shortterm mechanical. Aug 01, 2008 moldedin stress can be another contributor to stress cracking. Apr 16, 2015 presto testing instruments manufacturers of environmental stress cracking resistance etc. Engineering and manufacturing science and technology, general cracking chemical environmental aspects cracking process molecular dynamics research polyethylene stress analysis engineering analysis. Since variance of any of these factors can change the environmental stress crack resistance of the container, the test results are representative only of a given test performed under defined conditions in the laboratory. Resistance to this mode of failure can be best gauged through constanttensileload testing, while taking into account the differences in. Environmental stress cracking esc is not the result of the continual battle that the plastics industry has in convincing environmentalists and politicians that plastics can be the solution to environmental problems and not the cause. Due to its high density, hdpe is a crystalline material and when a high tensile stress is applied, the material will stretch and yield before ductile failure but at low tensile stress, the material will fail suddenly with a smooth break typical of brittle failure.
Cn103087267a formula for improving escr environmental. Enhancing the environmental stress crack resistance of hdpe. Studies of environmental stress cracking of high density. Effect of molecular structure parameters on crystallinity and. Esc is the occurrence of cracking in a polymer by contact with a liquid or vapour environment and stress. Enhancing the environmental stress crack resistance of hdpe vistamaxx performance polymers can be used to improve the environmental stress crack resistance escr of high density polyethylene hdpe.
An examination of environmental stress cracking failure in various forms of. The behavior of other, untested liquids can be estimated from hsp correlations based on a limited number of test liquids. Some polymers, such as polypropylene, are not affected by slow crack growth. Jul 29, 2010 a recent report on a study of the expected lifetime of highdensity polyethylene hdpe pipes containing chlorinated potable waters adds a new, and perhaps primary, parameter to the conventional parameters of stress cracking resistance scr, oxidative induction time oit, and carbonyl index ci for the determination of remaining lifetime of hdpe piping. Environmental stress cracking is one of the most common causes of unexpected brittle failure of thermoplastic polymers known at present. Environmental stress crack resistance service temperatures up to 60c 140f is highly resistant to a wide variety of rather reactive cracking of escr is carried out on molded specimens 18 in. The use of high density polyethylene hdpe pipes has increased significantly in last fifty years in different sectors of civil and environmental engineering. Investigations of environmental stress cracking resistance of hdpeeva and ldpeeva blends article in journal of applied polymer science 14 february 2014 with 73 reads how we measure reads. Introduction to environmental stress cracking and escr. Environmental stress crack resistance of hdpe abg geosynthetics. Because parts made with vistamaxx enhanced hdpe are tougher than those made with pure hdpe, they are less likely to fail through environmental stress cracking. Environmental stress cracking in polyethylene takes place because of interlamellar failure, which in turn is caused by relaxation of tie molecules. Experimental study of stress cracking in high density polyethylene pipes a thesis submitted to the faculty of drexel university by jingyu zhang.
Stress cracking sc is recognized as one of the major concerns for high density polyethylene hdpe pipes. According to astm d883, stress cracking is defined as an external or internal crack in a plastic caused by tensile stresses less than its shortterm mechanical strength. Standard test method for environmental stresscrack. There are any number of reasons for stress cracking in hdpe including detergents and fatty acids. Sc is a brittle failure that occurs at a stress level lower than the shortterm. Chen the state key lab of polymer materials engineeringpolymer research institute of sichuan university, chengdu. Investigations on environmental stress cracking resistance of. Pdf according to linear elastic fracture mechanics the stress intensity factor and the energy release rate are two fracture parameters linked by the. Because of this, environmental stress cracking and creep rupture are parallel failure mechanisms. Experimental study of stress cracking in high density. Environmental stress cracking resistance of blends of high.
Escr is used for determining the susceptibility of ethylene plastics, to environmental stress cracking when subject to certain conditions. Plastic failure through environmental stress cracking. Investigations of environmental stress cracking resistance of hdpeeva and ldpeeva blends. A tensile strain hardening test indicator of environmental. This thesis studies the resistance of hdpe pipeline materials to environmental stress corrosion cracking due to the exposure to asp chemicals. Environmental stress cracking resistance improves with increasing hbpe content, and, for a constant hbpe concentration, it increases with increasing octene content of the hbpe. It is one of the most common causes of unexpected brittle failure in thermoplastic. Environmental stress cracking may account for around 1530% of all plastic component failures in service. This is because stress from different sources increases during the summertime. Environmental stress cracking an overview sciencedirect. Environmental stress crack resistance of polyethylene stress crack reagent concentration. Highdensity polyethylene hdpe resins are well suited for a range of extrusion film applications such as grocery, garbage and deepfreezer bags 10 to 25 microns and injection, blown and rotational molding processes.
Jan 18, 2011 hence, an important design factor for pe pipes became commonly known as environmental stress cracking resistance escr, which led to the development of mdpe. Environmental stress corrosion cracking resistance of high. Environmental stress cracking resistance of polyethylene. Environmental stress cracking is a physical phenomenon that is initiated as a slow. Grace hsuan, jy zhang and wk wong department of civil, architectural and environmental engineering, drexel university, philadelphia, usa abstract the 100year stress crack resistance scr of corrugated hdpe pipes was evaluated using a 600 mm diameter pipe. Environmental stress cracking esc is one of the most common causes of unexpected brittle failure of thermoplastic especially amorphous polymers known at present. Environmental stress crack resistance of polyethylene ineos. Paxon hdpe product grades provides outstanding quality in blow molding and rotational molding applications. Conditions of stress and strain that accelerate environmental stress cracking are one of the major goals of the research. Environmental stress crack resistance escr is a vital property required in plastics for its longevity. This research taken an industrial focus, as a result, test methods were selected. Environmental stress cracking is considered to be the most frequent mode of failure of plastic materials. Pdf in this work the environmental stress cracking resistance of two high density polyethylene grades, employed for the manufacturing of.
During the summer months, stresscracking of hdpe containers reaches its peak. Environmental stress cracking of interior polymers of a. Environmental stress cracking escr is the formation of cracks in a part when exposed to chemicals, if the parts have residual stress in them after molding. The ability of a polymer to resist slow crack growth or environmental stress cracking is known as escr. Each phase of the application development process shown in figure 2 can influence environmental stress cracking. Environmental stress cracking of interior polymers of a car pcabs and abs ashish kumar bhalla master of science thesis interior polymers group. High density polyethylene hdpe, on the other hand, can crystallize up to 80% 2.
Environmental stress cracking resistance escr can be defined as the susceptibility of a thermoplastic article under the influence of certain chemicals and stresses. In the case of the most commonly used stress crack reagent, igepal co630, as the concentration of water in the stress cracking media increases, the faster the esc onset. The escr of polyethylene, one of the most widely used plastic materials, is of particular concern in the plastics industry and is the subject of this investigation. Studies on the environmental stress cracking resistance of polyethylene blends have, so far, only been described for blends of lldpe and ldpe for polyethylene water tubes, and for hdpeldpe blends in the context of the testing of a new method to determine stress cracking resistance and to optimize polymer properties 15, 16. The nature of polyethylene pipe failure plasticstoday. Investigations of environmental stress cracking resistance. Hdpe geomembrane may result in environmental stress cracking esc where the chemical accelerates the fundamental stress cracking phenomenon.
Cn103087267b formula for improving escr environmental. Resistance to this mode of failure can be best gauged through constanttensileload testing, while taking into account the differences in yield point among various polyethylenes. Mdpe exhibited excellent scg and stress crack resistance, and dominated pe pipe manufacture for 30 years until the development of bimodal hdpe pe100. Geomembranes made from high density polyethylene hope have a high percent crystallinity and are therefore of concern with regard to stress cracking.
Hdpegeomembranes used in four projects after exposure in different climatic zones were tested for the amount of stabilization and for changes of their properties. Experimental study of stress cracking in high density polyethylene. Smithers provides an overview of environmental stress cracking for polymer materials, and how test programs can help reduce or even prevent failure. Prediction of environmental stress cracking in plastics with.
Environmental stress crack resistance escr is a commonly used test to characterize cracking failure of high density polyethylene in applications such as wires, cables, blow molded containers, and other rigid packaging applications. Exhibits excellent processing properties, good rigidity, high environment stress cracking resistance escr and medium impact strength. At a high enough stress a polymer will crack even with a poorlycompatible solvent. Environmental stress cracking esc is the premature cracking of a polymer due to the combined action of a stress and a fluid. A materials resistance against this type of failure is called environmental stress cracking resistance escr. In this work the slow crack growth and the environmental stress cracking resistance of two high density polyethylene grades were investigated, differing for their molecular weight distribution and fracture resistance. Wire and cable polymer compounds thermal stress cracking. While crystallinity provides strength, it also can lead to cracking. Environmental stress cracking esc is one of the most common causes of unexpected brittle.
The invention provides a formula for improving escr environmental stress cracking resistance performance of highdensity polyethylene and a preparation method of the formula, and belongs to the technical field of high polymer materials. The amount of crystalline content in the container depends on the rate of cooling. Investigations of environmental stress cracking resistance of ldpeuhmwpe and ldpeeva blends z. Effect of molecular structure parameters on crystallinity. Environmental stress cracking of polypropylene springerlink. Adding hbpe also improves the environmental stress cracking resistance. Astm d2561 17 standard test method for environmental stress. Environmental stress cracking escr is the formation of cracks in a part. Investigations on environmental stress cracking resistance. Hdpe, like steel, is a semicrystalline material, with no crystals in the melted state.
In this work the environmental stress cracking resistance of two highdensity polyethylene grades, employed for the manufacturing of bleach bottles, was investigated by using a fracture mechanics. Environmental stress cracking resistance of blends of highdensity polyethylene with other polyethylenes. New thoughts on hdpe pipe durability in chlorinecontaining. Determination of environmental stress cracking resistance of. Both cause the plastic to crystalize which increases the risk for environmental stress cracking. Environmental stress cracking esc is not the result of the continual battle that the plastics industry has in convincing environmentalists and politicians that plastics can be the solution to environmental problems and not the cause esc is the consequence of a combination of mechanical stress and exposure to an aggressive chemical. The stress cracking is more severe with detergent, bleach, motor oil and some industrial chemical packaging. Environmental stress cracking can take place through continuous crack growth or via a stepwise progressive mechanism of cracking and arrest, depending on the molecular structure of the plastic, the composition of the chemical agent, the level of stress, and other environmental conditions.
Sep 17, 2019 in this work the slow crack growth and the environmental stress cracking resistance of two highdensity polyethylene grades were investigated, differing for their molecular weight distribution and fracture resistance. Over the past decade, highdensity polyethylene hdpe materials have improved significantly and. A products thermal stress cracking resistance tscr depends on the polymer compound formulation and the processing conditions under which the wire or cable was extruded, in addition to the temperature of the environment. Myth versus science since the introduction of the first 2liter, onepiece pet bottle by continental can co. Prediction of environmental stress cracking in plastics. Environmental stress crack resistance of polyethylene. Since variance of any of these factors can change the environmental stresscrack resistance of the container, the test results are representative only of a given test performed under defined conditions in.
With constant stress tests the higher crystallinity hdpe has better escr as the strain is much lower at equal stress due to the higher modulus. Designing for escr application development material physical properties. Ageing resistance of hdpegeomembranes evaluation of longterm. Environment stress cracking of hdpe products is quite common due to its semi crystalline nature which gets attacked due to chemicals present in the environment. Environmental stress crack resistance of polyethylene introduction to environmental stress cracking and escr over the past decade, highdensity polyethylene hdpe materials have improved significantly and now meet more stringent performance standards. Premature cracking can be caused by topload stress, internal pressure, moldedin stress, and tail swing. Environmental stress cracking resistance escr is an important indicator of performance for high density polyethylene hdpe in structural and polymer pipe applications. The formula is obtained by mixing 100 parts of high density polyethylene by weight, 0. Heng the state key lab of polymer materials engineeringpolymer research institute of sichuan university, chengdu 610065, china, y.
Because parts made with vistamaxx enhanced hdpe are tougher than those made with pure hdpe, they are less likely to fail through environmental. Hdpe, with fewer branches than mdpe or ldpe, has a greater proportion of crystals, which results in greater density and greater strength see. Wyzgoski, prediction of environmental stress cracking of polycarbonate from solubility considerations, journal of applied polymer science, 23, 11531166, 1979. Esc is the consequence of a combination of mechanical stress and exposure to an aggressive chemical. The commonly used test for determining escr of hdpe can be time consuming and rather imprecise. A recent report on a study of the expected lifetime of high density polyethylene hdpe pipes containing chlorinated potable waters adds a new, and perhaps primary, parameter to the conventional parameters of stress cracking resistance scr, oxidative induction time oit, and carbonyl index ci for the determination of remaining lifetime of hdpe piping. The invention provides a formula for improving escr environmental stress cracking resistance performance of high density polyethylene and a preparation method of the formula, and belongs to the technical field of high polymer materials. All joking aside, the potential for environmental stress cracking escr of hdpe bottles has always existed because of the materials inherent.
Designing for escr application development material physical properties shrinkage chemical compatibility flame resistance design wall section sharp corners knit lines ribs wall transition tooling. Polymerization takes place under lowpressure conditions with the support of catalysts. In this research, the esc behaviour of hdpe pipes was studied in asp floods under conditions that simulated the eor reality. Available in the latin american and north american markets. Different polymers exhibit varying degrees of escr. Some grades of hdpe have very good resistance against esc, while some have marginal resilience. Modeling of the fracture mechanism of hdpe subjected to. Esc is taken advantage of in laboratory tests that are performed in a surface active detergent at elevated temperature. 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.
Thermal stress cracking can be minimized or eliminated by carefully choosing the polymer compound formulation and. This type of cracking typically involves brittle cracking, with little or no ductile drawing of the material from its adjacent failure surfaces. High density polyethylene hdpe resins from lyondellbasell are thermoplastics made from the polymerization of ethylene in gas phase, slurry or solution reactors. Environmental stress cracking is a type of failure that occurs through surface interactions of polyolefins such as high density polyethylene with surfactants or detergents. Timetemperature equivalence in environmental stress cracking of. Basic understanding of stress cracking in hdpe products.
With the increasing use of high density polyethylene hdpe pipes in eor process, environmental stress cracking esc poses a threat to the integrity of the pipe in asp floods. Definition of environmental stress cracking esc environmental stress cracking esc in plastics means the failure at about room temperature due to continuously acting external andor internal stresses in the presence of surface active substances known as stress cracking agents such as alcohols, soaps, dyes, agents containing moisture. Another issue can be caused by too much heat and dwell time during the forming of the bottle. Exxonmobil hdpe product grades combines toughness and stiffness with resistance to environmental stress cracking at elevated temperatures and warping. Environmental stress cracking occurs because of a process of local plasticization due to the diffusion of an active degradant, craze formation, and its growth under stress. Ageing resistance of hdpegeomembranes evaluation of. Environmental stress crack resistance escr testing of plastics. The addition of a surfaceactive chemical, an environmental effect, accelerates this type of failure, thus this mechanism is termed environmental stress cracking esc. The results reported here confirm that environmental stress cracking phenomena in plastics depend on the size and shape of the test liquids molecules as well as their hansen solubility parameters hsp relative to those of the polymer. Environmental stress crack resistance escr testing of. It is associated with the phenomenon of crazing and solvent plasticization of the polymer.