Environmental stress crack resistance escr testing of plastics. Environmental stress cracking may account for around 1530% of all plastic component failures in service. Some plastics such as abs, acrylic, polycarbonate, and polystyrene are more susceptible to stress cracking. Standard test method for environmental stress crack.
Reduce environmental stress cracking esc of your plastic parts by better predicting failure occurrence and implementing adequate prevention measures. Environmental stress cracking esc is the occurrence of cracking a polymer by contact with a liquid or vapor environment, combined with stress. It is a physical process driven by the applied stress but accelerated by the presence of. How to prevent stress cracking what is stress cracking. Steps in environmental stress cracking esc is a phenomenon in which a particular plastic resin is cracked through contact with a specific chemical agent while under stress.
The mechanisms of environmental stress cracking proposed in the literature will be discussed in detail along with testing methods commonly employed. Plastics will exhibit environmental stress cracking when exposed to an aggressive chemical environment if and only if a tensile stress is present. Stress cracking results in failure or breakdown of plastic materials. The information obtained with these characterization techniques on the polymer chain structure was correlated to environmental stress cracking resistance. Polycarbonate is among the most widely used plastics that consists. The stress cracking is more severe with detergent, bleach, motor oil and some industrial chemical packaging. In environmental stress cracking, the chemical agent permeates into the molecular structure of the plastic, interfering with the intermolecular forces bonding the polymer chains, allowing accelerated molecular disentanglement. Environmental stress cracking resistance of polyethylene. Esc is a very important mode of plastic component failure. Re your query on environmental stress cracking of plastics, the corrosion resistance data given out by the manufactures sometimes indicate that a given thermoplastic in a given environment at a given temperature may not be suitable. When a glassy polymer is exposed to an organic solvent, it can crack spontaneously or fail more readily under extension. Observation and modeling of environmental stress cracking behaviors of high crystalline polypropylene due to scent oils. Evaluating environmental stress cracking of medical. Investigations on environmental stress cracking resistance of.
Polypropylene has excellent dielectric strength, excellent chemical resistance and outstanding heat resistance. When force is applied to plastic, it travels along the polymer chains causing molecules to strain to remain in contact. The phenomenon is well know by polymer producers and product designers but its mechanisms are not very well understood. Environmental stress cracking the the chemical agent. Environmental stress cracking chemical attacks are sometimes considered esc environmental stress cracking when related to vulnerabilities in the plastic s structure. In other cases, the chemical draws out a plasticizer that was part of the original formulation, causing the plastic to become brittle. Some types of highdensity polyethylene have good resistance against environmental stress crack while some have minor elasticity. Environmental stress cracking resistance escr environmental stress cracking resistance characteristic of samples was measured by ray ran instrument nuneaton, uk according to astm d1693 standard. Unlike polyethylene, polypropylene is not prone to environmental stress cracking. Hmc polymers pp resins are the basic building blocks used by our customers to make countless everyday products that have a positive effect on peoples lives. Environmental stress cracking is a failure mechanism very similar to slow crack growth in terms of shape. The general physical properties of polypropylene are similar to those of highdensity polyethylene, pe, but pp has a harder durometer and is more rigid. These are amorphous plastics, and they bond readily.
Environmental stress crack resistance escr is a vital property required in plastics for its longevity. The tensile stress may be applied externally or may simply be a consequence of residual, or moldedin, stresses. In addition, fluctuations give rise to stresses, because of the variation in surface tension from changes in the surface concentration of. Aug 18, 2017 polypropylene is a lowcost thermoplastic elastomer, which consists of aliphatic hydrocarbon chains and is mainly used in packaging industries owing to its high fatigue resistance, good chemical and environmental stress cracking resistance, low density, and ease of processing. Under the conditions of the test method, high local multiaxial stresses are developed through the introduction of a controlled imperfection 2, 3. 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. Since this is responsible for 15% of all failures of plastics components, environmental stress cracking has long been the subject of intensive research.
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. Similarly, the stress applied is below the level which. Cn103087267b formula for improving escr environmental. Therefore this failure mechanism is of great technical and economical importance. By environmental stress cracking, we understand a failure in which materials in contact with a fluid are subjected to stress. Difference between polypropylene and polycarbonate compare. Hmc pp resins have excellent resistance to environmental stresscracking. Its moisture absorption is practically nil and unsurpassed in flexural strength. The chemical agent does not cause direct chemical attack or molecular degradation. Although esc is often described as a chemical attack, it is a very complex combination of plasticizing, migration, low level stress and mechanical failure initiated by exposure to specific classes of liquids, primarily surfactants soaps. The chemical simply accelerates the stress cracking. Environmental stress cracking of poly3hydroxibutyrate. This fact has been used to accelerate escr as measured. 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.
A controlled notch is cut horizontally across each specimen, which serves as a crack initiation point. This month we want to conclude the discussion with a few more case studies and then discuss tests and material selection techniques that. Environmental stress cracking esc is widely regarded as the leading cause of plastic product failure. 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. This stress relaxation allows testing to run without failure for very long periods 1,500 hours. Other plastics such as polyethylene, polypropylene, and polytetrafluoroethylene teflon are semicrystalline thermoplastics and. The bent strip test is a constant strain test, but polyethylene relaxes when strained. Standard test method for environmental stresscracking of. Significantly, in the absence of the chemical the plastic would undergo stress cracking in air, also known as creep rupture, given sufficient time. Escr problems get more pronounced in the summer, because of several factors related to increased heat and humidity.
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. Conditions of stress and strain that accelerate environmental stress cracking are one of the major goals of the research. Environmental stress cracking of glassy polymers industrial. Environmental stress cracking in plastics rj lee group. Environmental stress crack resistance of polyethylene ten rectangularshaped specimens are cut from a molded plaque prepared with standard methods. Environmental stress cracking examples from the automotive indsutry jeffrey a. Solvent stress cracking, which is often incorrectly referred to as environmental stress cracking, can occur in almost any plastic. Environmental stress cracking of polyvinyl chloride in. Environmental stress cracking resistance increases when the molecular weight and concentration of polymer chains that crystallize in trichlorobenzene between 75 and 85 c increase. Environmental stress cracking failure can occur on polyester based products far below the fracture strength since most composites subjected to external stress are vulnerable to aggressive liquid. 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. Vistamaxx performance polymers discover how vistamaxx performance polymers can be used to create new possibilities in a variety of applications including hygiene products, flexible and rigid packaging, polymer modification, masterbatches, increasing polymer processing efficiencies, roofing, construction and many others.
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. Polypropylene pp is light weight and high in chemical resistance. The chemical materials do not cause any chemical degradation of the polymer but they accelerate the process of macroscopic brittlecrack formation. Environmental stress cracking in polyethylene takes place because of interlamellar failure, which in turn is caused by relaxation of tie molecules. 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 cracking esc is shown to correlate well using a plot of the red number polymersolvent interaction found from hansen solubility parameters hsp versus a molecular size. It is also more resistant to environmental stress cracking than pe. 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. Both cpvc and pvc are subject to environmental stress cracking from a variety of sources, including the chemicals used by the water treatment plant, the acidity or alkalinity of your water, zinc from metal pipes within the system and from contact with certain chemicals, like spray foam. A recent study indicated that approximately 25% of plastic component failures are associated with esc1. Polypropylene is considered to be more resistant to esc than polyethylene and studies in the literature are rare. Another related mechanism is environmental stress cracking esc. Our strategy will be to examine, in some detail, the roles of the three critical components of environmental stress cracking. A materials resistance against this type of failure is called environmental stress cracking resistance escr.
Polypropylene is one of the most versatile materials available today. Simultaneous action of stress and strain on plastics in contact with specific fluids causes the onset of cracking and embrittlement of plastic known as environmental stress cracking. Environmental stress cracking is considered to be the most frequent mode of failure of plastic materials. Environmental stress cracking resistance of plastics. The chemical resistance of polypropylene is outstanding. 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. 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 test is designed to evaluate the effect of chemical media on a plastic material that is under stress or load. Reducing environmental stress cracking in plastic parts. Esc is the occurrence of cracking in a polymer by contact with a liquid or vapour environment and stress. Environmental stress cracking the plastic killer effrey a. Environmental stress cracking esc is one of the most common causes of unexpected brittle failure of thermoplastic especially amorphous polymers known at present. Dec 20, 20 when a glassy polymer is exposed to an organic solvent, it can crack spontaneously or fail more readily under extension. When the solvent diffuses into the polymer, stresses develop because of swelling of the polymer. Because of this, environmental stress cracking and creep rupture are parallel failure mechanisms. Environmental stress cracking the the chemical agent does. Understanding plastics failure and factors that play a key role in environmental stress cracking environmental stress cracking esc is considered a leading cause of plastic part failure.
Approaches to resolve environmental stress failure have limited discussion in the open literature although a significant number of references can be found in the patent literature. Environmental stress cracking an overview sciencedirect. In the escr test, tensile bars are bent to specific strain levels typically 0. This failure is caused when plastic materials, in contact with surface active substances stress cracking agents, start to become brittle at or about room temperature due to concurrent external andor internal stress and strain. Observation and modeling of environmental stress cracking. Environmental stress cracking esc is the formation of cracks in a plastic material caused by low tensile stress and environmental conditions. 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. This month we want to conclude the discussion with a few more case studies and then discuss tests and material selection techniques that can keep us out of trouble with this challenging problem. The presence of internal and external stresses makes plastic parts more vulnerable to chemicalrelated failures. Fittings jaco manufacturing company injection molding. According to astm d883, stress cracking is defined as an external or internal crack in a plastic caused by tensile stresses less than. The addition of a surfaceactive chemical, an environmental effect, accelerates this type of failure, thus this mechanism is termed environmental stress cracking esc.
Environmental stress cracking environmental resistance. It is important resin property caused by tensile stresses. Plastic failure through environmental stress cracking esc, the plastic killer, is a frequent cause of field failures by jeffrey jansen the madison group, madison, wisconsin, usa environmental stress cracking esc is considered a lead ing cause of plastic part failure. Get a handle on stresscracking in hdpe bottles one of the first applications for blow molded hdpe bottles was the replacement of glass for bleach packaging. It is the premature embrittlement and subsequent cracking of a plastic. On predicting environmental stress cracking in polymers. The synergistic effects of the chemical agent and mechanical stresses result in cracking. Environmental stress cracking of polypropylene springerlink. Glassy amorphous thermoplastics are most susceptible, and the most common fluids that cause the problem are lubricants, adhesives, corrosion inhibitors, surfactants, cleaning agents, solvents, and paints. Environmental stress crack resistance of polyethylene today, this test is specified less frequently because it is not as aggressive towards modern resins. However, it usually occurs in amorphous thermoplastics. Environmental stress cracking is involved with some 25% of plastic part failures.
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. Environmental stress cracking akron rubber development. 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. Polypropylene pp is a workhorse in the plastics industry. The goal of this article is to provide a framework for evaluating the suitability of a plastic for medical uses in terms of its stress crack behavior. Environmental stress cracking esc in plastics means the failure at about room temperature. It is important to note that solvents can also affect polyethylene, but in an entirely different manner than environmental stress cracking agents. Polypropylene chemical resistance guide hmc polymers. Plastic materials in chemical environments chemical. In last months article we defined the terms environmental stress cracking and solvent stress cracking, briefly explained the mechanisms involved, and provided a couple of examples of actual case studies. Effect of molecular structure parameters on crystallinity and. 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. Environmental stress cracking esc is the most common failure mechanism, whereby mainly organic fluids accelerate crack initiation and growth under conditions of applied or processedin stress.
Some reduction in tensile strength and an increase in. Polypropylene plastic sheets johnston industrial plastics. Smithers provides an overview of environmental stress cracking for polymer materials, and how test programs can help reduce or even prevent failure. Environmental stress cracking is an example of material degradation by the simultaneous action of two degradants. The specimens are bent and inserted into a c shaped bracket, creating a stress in the specimen. Hmc pp resins have excellent resistance to environmental stress cracking. Basic understanding of stress cracking in hdpe products.
In this mechanism the solvent actually replaces polymer at the surface of the part. Esc is a failure mechanism whereby a plastic resin is effected by a chemical agent while simultaneously under tensile loading. Esc occurs in conjunction with internal and external stresses on a plastic. For specific cases in which the effect of an environment on polyethylene has not been documented, testing is required to identify any possible environmental stress cracking effect. This reduces the energy required for disentanglement to occur. Environmental stress cracking esc is the premature cracking of a polymer due to the combined action of a stress and a fluid. Investigations on environmental stress cracking resistance. Environmental stress cracking esc is a welldocumented phenomenon in plastic polymer components and can occur when a polymer component is exposed to an aggressive chemical agent while under tensile stress, whether residual or applied. Astm d2561 17 standard test method for environmental stress. Environmental stress cracking esc is one of the most common causes of unexpected brittle failure of thermoplastic especially amorphous polymers known. It is the premature embrittlement and subsequent cracking of a plastic due to the. Prediction of environmental stress cracking in plastics. One of the major advantages of polypropylene is its apparently complete resistance to attack by environmental stress cracking. However, for the case of polypropylene pp, little information is available, for example, on how the aging behavior and crack growth resistance in chlorinated.
In environmental stress cracking, the presence of an esc agent accelerates the effect of stress on a polymer material. The behavior of other, untested liquids can be estimated from hsp correlations based on a limited number of test liquids. The polymer chains eventually creep toward the pull and deform. Jansen, stork technimet abstract four case studies are presented to illustrate environmental stress cracking esc within automotive components. The presented cases illustrate how the failure analysis process. It is associated with the phenomenon of crazing and solvent plasticization of the polymer. Plastic failure through environmental stress cracking. Environmental stress cracking an overview sciencedirect topics. Robeson department of materials science and engineering, lehigh university, bethlehem, pennsylvania environmental stress failure of polymers speci. Environmental stress crack resistance of polyethylene. It is one of the most common causes of unexpected brittle failure in thermoplastic. Evaluating environmental stress cracking of medical plastics.
Environmental stress cracking resistance tester escr. Resistance to this mode of failure can be best gauged through constanttensileload testing, while taking into account the differences in. With force and time, crazing or stress cracking occurs. Environmental stress cracking esc is one of the most common failure reasons of plastic parts during their use. 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.
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