Introduction plastic components are used in various kinds of equipment and machinery, but depending on the environmental factors involved, various kinds of degradations may arise. A new method to characterize environmental stress cracking resistance escr of polyethylene pipes ben jar, patrick ward, chester jar and yi zhang, university of alberta, edmonton, alberta, canada wajdy ateerah, polytyubes, edmonton, alberta, canada abstract a new test method has been developed to evaluate environmental stress cracking. Environmental stress crack resistance of polyethylene this test method is shown in figure 3. Environmental stress crack resistance escr testing of plastics environmental stress crack resistance escr is a vital property required in plastics for its longevity. Environmental stress cracking resistance tester is a unique test cabinet designed to detect the change in the physical characteristics of the plastic material and to ascertain the actual working life of test samples at environmental stress. Environmental stress cracking of polyethylene hittmair, p ullman, robert 19620101 00. Environmental stress cracking resistance of polyethylene. Investigations on environmental stress cracking resistance. Environmental stress cracking, often referred to as esc, causes a stressed plastics part to become brittle and crack when in contact with a wide range of fluids that act as stress cracking agents. Environmental stress cracking resistance of plastics 2001. It is associated with the phenomenon of crazing and solvent plasticization of the polymer. Determination of environmental stress cracking esc of polyethylene.
A study was conducted to develop a new approach for characterizing environmental stress cracking resistance escr of polyethylene pe. Among these is environmental stress cracking, which. Environmental stress cracking escr is the formation of cracks in a part. Environmental stress cracking resistance improves with increasing hbpe content, and, for a constant hbpe concentration, it increases with increasing octene content of the hbpe. Environmental stress crack resistance of polyethylene stress crack reagent concentration 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. 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. 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. Different polymers exhibit varying degrees of escr. Environmental stress cracking esc is where polyethylene and other plastics, when exposed to nonsolvents and stress, break down unexpectedly. Environmental stress cracking of polyethylene environmental stress cracking of polyethylene hittmair, p ullman, robert 19620101 00. The test is carried out on notched test specimens cut from compressionmoulded sheet or finished products, as applicable. Environmental stress crack resistance escr testing of plastics. 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.
Basic understanding of stress cracking in hdpe products. In this research, the esc behaviour of hdpe pipes was studied in asp floods under conditions that simulated the eor reality. Most studies on the environmental stress cracking of polyethylene focus on the effect of tiemolecules, but physical chain entanglements are another source of interlamellar linkages that contribute to esc of polyethylene. 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.
Mdpe exhibited excellent scg and stress crack resistance, and dominated pe pipe manufacture for 30 years until the development of bimodal hdpe pe100. A tensile strain hardening test indicator of environmental. It is important resin property caused by tensile stresses. A new method to characterize environmental stress cracking. Standard test method for environmental stresscrack. This thesis studies the resistance of hdpe pipeline materials to environmental stress corrosion cracking due to the exposure to asp chemicals. It was a polyethylene bottle with dilute soap in it and it had been stressed by the fall to the cement a situation just begging for environmental stress cracking and that was what i got. The test is carried out on notched test specimens machined from moulded sheetsspecimens or from finished products. A materials resistance against this type of failure is called environmental stress cracking resistance escr.
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. Environmental stress cracking resistance tester escr. Disclosed is a polyethylene composition having faster crystallization rate and improved environmental stress cracking resistance. If a tensile load is applied normal to the face of the lamellae.
The phenomenon is well know by polymer producers and product designers but its mechanisms are not very well understood. It is the premature embrittlement and subsequent cracking of a plastic due to the simultaneous and synergistic action of stress and contact with a chemical agent. Environmental stress cracking esc is the occurrence of cracking a polymer by contact with a liquid or vapor environment, combined with stress. Environmental stress crack resistance of polyethylene. 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. Pdf in this work the environmental stress cracking resistance of two high density polyethylene grades, employed for the manufacturing of. Environmental stress cracking resistance of plastics. Environmental stress cracking resistance of blends of high. Escr problems get more pronounced in the summer, because of several factors related to increased heat and humidity.
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 the laboratory. Because of this, environmental stress cracking and creep rupture are parallel failure mechanisms. Fibrillation was found to occur in the aggressive environment, and this effect increased with temperature. Environmental stress crack resistance lyondellbasell. Different types of polyethylene plastics as defined in specification d1248 are generally tested under different levels of strain and stress. Recent results from environmental stress cracking of pe pipe and exposed polyamide pa66 to detergent will be presented and correlated to mechanical properties degradation. Throughout a semicrystalline polymer, there may be small packets of crystals contained within the amorphous matrix, with some polymer chains being so long that they can be in two different crystals at the same time. Environmental stress cracking environmental resistance. The main objective is to reduce time for the testing, to be shorter than that required for the current standard escr tests. This was traced to soap application 1, 2 and resistance to surfactant. Pdf degradation and failure of some polymers polyethylene.
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 commonly used test for determining escr of hdpe can be time consuming and rather imprecise. I need information on any laboratoryorganisation conducting these type of testings. Temperature effect environmental stress cracking of polyethylene. Environmental stress corrosion cracking resistance of high. The effects of melt cooling rate on the morphology and environmental stress cracking resistance escr of a commercialgrade highdensity polyethylene hdpe were investigated by dsc, waxs, raman. The ability of a polymer to resist slow crack growth or environmental stress cracking is known as escr. Many of the variables were investigated, such as the. Environmental stress cracking has been found to occur most readily under such conditions. 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.
A polyethylene resin is considered crack re molded containers continued on page 2. Investigations on environmental stress cracking resistance of. The number of tie molecules and the strength of the crystals that anchor them are considered the controlling factors in determining the polymer resistance to esc. Furthermore, the system contains carbon black as filler. Environmental stress cracking is involved with some 25% of plastic part failures. Environmental stress crack resistance escr testing of. Environmental stress cracking of polypropylene springerlink. Environmental stress cracking of poly3hydroxibutyrate. The stress cracking is more severe with detergent, bleach, motor oil and some industrial chemical packaging. It is the combination of stress and fluid contact that causes failure to occur much earlier than either component could achieve in isolation, if at all. Environmental stress crack resistance escr is a vital property required in plastics for its longevity. Effect of temperature on environmental stress cracking. Polyethylene of narrow molecular weight distribution, characteristic of certain types, have slightly less tendency to crack under environmental stress.
Environmental stress cracking wikimili, the best wikipedia. Environmental stress cracking is a physical phenomenon that is initiated as a slow. Environmental stress cracking of polyethylene, journal of. Environmental stresscracking has been found to occur most readily under such. This document specifies a method for determining the environmental stress cracking esc resistance of polyethylene pe materials in a defined test environment. Environmental stress cracking esc is one of the most common causes of unexpected brittle failure of thermoplastic especially amorphous polymers known at present. Polyethylene resins with higher short chain branch content have higher esc crack activation energy. These are caused by the combined presence of stresses and environmental effects. 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. Environmental stress crack resistance of polyethylene today, this test is specified less frequently because it is not as aggressive towards modern resins. Environmental stress cracking the the chemical agent. Polymethylmethacrylate, environmental stress cracking, chemiluminescence, radical 1.
In environmental stress cracking, the presence of an esc agent accelerates the effect of stress on a polymer material. I am looking for appropriate method for chemical resistance of plastics environmental stress cracking resistance. Environmental stress cracking, according to howard, is the failure in surfaceinitiated brittle fraction of a polyethylene specimen or part under polyaxial stress in contact with a medium in the absence of which fracture does not occur under the same conditions of stress. Standard test method for environmental stresscracking of. To accelerate the effect of in the crystalline areas of the polyethylene molecules forming the surface of the each inspection, the number of failures is recorded. The bent strip test is a constant strain test, but polyethylene relaxes when strained. The polymers resistance to such failures is called environmental stress crack resistance escr. Environmental stress cracking refers specifically to a phenomenon observed in polyethylene.
The nature of polyethylene pipe failure plasticstoday. According to astm d883, stress cracking is defined as an external or internal crack in a plastic caused by tensile stresses less than. Environmental stress cracking esc is the premature cracking of a polymer due to the combined action of a stress and a fluid. 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 cracking resistance escr is an important indicator of performance for high density polyethylene hdpe in structural and polymer pipe applications. 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. In general, the mechanism of environmental stress cracking in polyethylene involves the disentanglement of the tie molecules from the crystals. Timetemperature equivalence in environmental stress cracking of. It usually occurs at high levels of applied stress. Under the conditions of the test method, high local multiaxial stresses are developed through the introduction of a controlled imperfection 2, 3. This stress relaxation allows testing to run without failure for very long periods 1,500 hours. By understanding the basic structure of polyethylene, it is easy to see how this can affect environmental stress cracking.
Environmental stresscracking has been found to occur most readily under such conditions. It is one of the most common causes of unexpected brittle failure in thermoplastic. Environmental stress cracking esc is considered a leading cause of plastic part failure. Enhancing the environmental stress crack resistance of hdpe. Specimens are machined directly from pipe or from a molded plaque. All joking aside, the potential for environmental stress cracking escr of hdpe bottles has always existed because of the materials inherent semicrystalline characteristics. Environmental stress cracking may account for around 1530% of all plastic component failures in service. Environmental stress cracking the the chemical agent does. Standard test method for environmental stress crack resistance escr of plastic tighthead drums not exceeding 60 gal 227 l in rated capacity. It is the tendency for polyethylene parts to fail prematurely in the presence of detergents, oils, and other active environments. Environmental stress cracking an overview sciencedirect. Jun 19, 2008 environmental stress cracking resistance escr is an important indicator of performance for high density polyethylene hdpe in structural and polymer pipe applications. Stress cracking agents, such as the liquids mentioned above, migrate into minute cracks in the crystalline areas of the polyethylene molecules forming the surface.
Jansen stork technimet new berlin, wisconsin e nvironmental stress cracking esc is a phenomenon in which a plastic resin is degraded by a chemical agent while under stress, and it is the leading cause of plastic component failure. Environmental stress cracking esc is one of the most important causes of polymer premature failure, occurring when a combination of mechanical load and an aggressive fluid is applied. Understanding environmental stress cracking in polyethylene a graphic model for failure. The multimodal polyethylene comprises from 25 to 50 wt % of a low molecular weight ethylene homopolymer component, from 25 to 50 wt % of a medium molecular weight ethylene. In order to understand environmental stress cracking on. It is associated with the phenomenon of crazing and solvent plasticization of. The most common victims are hdpe containers for liquid detergents, motor oil, and industrial chemicals. The polyethylene composition comprises a multimodal polyethylene and a nucleating agent. Geomembranes made from high density polyethylene hope have a high percent crystallinity and are therefore of concern with regard to stress cracking. An assessment of polymer resistance to potential esc agents is undertaken during the design stage of development, where an appropriate test program can measure the impact of these primary environments on the material. Astm d2561 17 standard test method for environmental stress.
Studies of environmental stress cracking of high density. Degradation and failure of some polymers polyethylene and. Polyethylene of narrow molecular weight distribution, characteristic of certain types, has slightly less tendency to crack under environmental stress. 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 cracking is a failure of the polymer material due to surface initiated micro cracks or fractures.
Environmental stress crack resistance of polyethylene figure 2 astm f1473 the polyethylene notch tensile pent test this method is used in the united states to test pe pipe grade materials that exhibit high escr values, as this test generally provides more timely results. A single notch cut into the test specimen acts as a crack initiation point. Environmental stress crack resistance of polyethylene ineos. 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. 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. This research taken an industrial focus, as a result, test methods were selected. Effect of temperature on environmental stress cracking resistance and crystal structure of polyethylene. Semicrystalline polymers such as polyethylene show brittle fracture under stress if exposed to stress cracking.
723 880 773 386 366 1123 405 46 1105 1003 1006 940 1124 677 1293 1 147 1445 304 1599 1526 1155 1268 1544 442 959 1160 1481 753 820 184 581 1444 107 1380 18 868 308 681 238 1392 272 584 685 440 355