When the material is under certain conditions of stress, these reagents can accelerate the cracking process which is one of the most. 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 cracking of polycarbonate catheter. It is one of the most common causes of unexpected brittle failure in thermoplastic. Esc is a very important mode of plastic component failure. To explore the possibility of using surface coating to reduce environmental stress cracking esc of transparent polycarbonate pc parts, silicone coated and sio 2 coated pc were tested in a selfmade threepoint bending apparatus in the presence of ethanol. Environmental stress cracking examples from the automotive indsutry jeffrey a. The stresscracking of stressed polycarbonate and other sensitive plastics is the result of a liquid diffusing into the substrate of the polymers matrix. Stress cracking is the main reason that high pressure overbraided hoses fail. Polycarbonate tube online catalogue source supplier of.
Behaviour of polycarbonate in different chemicals by determination of the timedependence of stress at constant strains. The environmental crazing from a central hole in extruded polycarbonate sheets, using ethanol as a crazing liquid, was studied. Polycarbonate cracking polymer engineering engtips. Evaluating environmental stress cracking of medical plastics. The third type of attack is often the most difficult to predict since environmental conditions dictate whether or not the plastic will be affected. Medical device recalls on the rise the nature of the medical device manufacturing market requires companies to manage.
The problem lies, in part, in the definition of stress cracking. A stress analysis was made to analyse the criteria for craze initiation and growth. Because of this, environmental stress cracking and creep rupture are parallel failure mechanisms. This problem is well known and is called environmental stress cracking. It has reasonably good temperature resistance, good dimensional stability and low creep but somewhat limited chemical resistance and is prone to environmental stress cracking. The stresses can arise from multiple sources, many of which are difficult to identify and to control. Environmental stress cracking is involved with some 25% of plastic part failures. Polysulfone psu plastic has excellent electrical and chemical resistant properties, which enables it to satisfy many highheat, highperformance demands. Standard test method for environmental stresscracking of. Of the two types of polymer, polycarbonate has been used in a wide range of products, since its introduction in the 1960s, and the problem of.
Polymer solutions environmental stress cracking youtube. Investigations on environmental stress cracking resistance. Using the thumb and forefinger to grasp the towel with firm pressure, the cable. Adhesive types and methods to reduce stress cracking. The test provides analysis for the materials oxidation and alcohol absorption, as well as its resistance to environmental stress cracking. 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 escr is the formation of cracks in a part when exposed to chemicals, if the parts have residual stress in them after molding. How to prevent stress cracking what is stress cracking. 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. Properties of lldpe are different from those of conventional ldpe and hdpe. Environmental stresscracking resistance escr is the number of hours that 50% of the specimens tested exhibit stress cracks. Environmental stress crack resistance escr testing of. Environmental stress cracking of polypropylene springerlink.
Environmental stress cracking is considered to be the most frequent mode of failure of plastic materials. Polysulfone tubing scandia plastics a pexco company. A family of stress cracks tend to form and propagate into the tube material. Testing based on astm d1693, standard test method for environmental stresscracking of ethylene plastics. 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. Environmental stresscracking has been found to occur most readily under. This article discusses polyurethane benefits and challenges, and also provides a test case for a proprietary aliphatic polycarbonate alc polyurethane. Plastics will exhibit environmental stress cracking when exposed to an aggressive chemical environment if and only if a tensile stress is present. A guide to chemical resistance of polycarbonate sheet.
Inspect polycarbonate regularly and before each use for signs of aging including permanent discoloration yellow, brown, orange, or pink, crazing spider web cracks, stress cracking vertical cracks, or permanent clouding or pitting. The polymer chains eventually creep toward the pull and deform. 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. It is environment stress cracking of stressed cpvc pipe after being exposed to pht. This stress relaxation allows testing to run without failure for very long periods 1,500 hours. Its the reason you cant put stickers on your motorbike helmet. According to astm d883, stress cracking is defined as an external or internal crack in a plastic caused. Evaluating environmental stress cracking of medical. One of the fastest growing plastics today is linear lowdensity polyethylene lldpe, used mainly in film applications but also suitable for injection, rotational and blow molding. Often we tend to group all the problems into the environmental category, but in reality most of the field problems we see have to do with solvent stress cracking. Engineering and manufacturing science and technology, general cracking materials research failure mode and effects analysis methods strains and stresses stress relaxation materials stress relieving materials stresses materials thermoplastics.
Some performance evaluation tests that once took only days to run now take months with todays. Plastic failure through environmental stress cracking. Environmental stress cracking esc is the premature cracking of a polymer due to the combined action of a stress and a fluid. I am looking for appropriate method for chemical resistance of plastics environmental stress cracking resistance. Pdf stress cracking of polycarbonate exposed to sunscreen.
The chemical simply accelerates the stress cracking. Environmental stress crazing 799 ntetradecane hexane isooctane 1400 1600 600 1200 nhexane 7. 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. 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. The rayran environmental stress cracking apparatus determines the susceptibility of ethylene plastics to stresscracking when exposed to different environments such as soaps, wetting agents, oils and detergents. Presto testing instruments manufacturers of environmental stress cracking resistance etc. It is associated with the phenomenon of crazing and solvent plasticization of the polymer. With force and time, crazing or stress cracking occurs. Stress cracking of polycarbonate exposed to sunscreen. Environmental stress cracking is the formation of cracks in a material caused by relatively low tensile stress and environmental conditions. This video captures over 15 hours of video footage a 90 second time lapse. 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 cracking esc is a welldocumented phenomenon in plasticpolymer components and can occur when a polymer component is exposed to an aggressive chemical agent while under tensile stress, whether residual or applied.
Bonding amorphous plastics again, examples include abs, acrylic, polycarbonate, and. Behaviour of polycarbonate in different chemical by determination of the timedependence of stress at constant strains. 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. Environmental stress cracking the the chemical agent. While both polymers have high tensile moduli and crack resistance, they can be sensitive to environmental stress cracking when exposed to the very wide range of liquids encountered in modern hospitals. It is environment stress cracking of stressed cpvc pipe after being. An extruded tube or sheet, for example, may show decreased performance in the unstretched direction.
The tensile stress may be applied externally or may simply be a consequence of residual, or moldedin, stresses. Chemical resistance and stress cracking in polyurethanes. Jansen, stork technimet abstract four case studies are presented to illustrate environmental stress cracking esc within automotive components. Polycarbonate pc labware thermo fisher scientific us.
Environmental stress cracking of poly3hydroxibutyrate. Environmental stress cracks, once formed, are known to propagate rapidly if the tube remains exposed to the active chemical environment. In the case of premature babies, such a line provides nutrition in the form of a synthetic milk tpn and antibiotics to prevent infection. Environmental stress cracking in plastics rj lee group, inc. The bent strip test is a constant strain test, but polyethylene relaxes when strained. Improvement of environmental stress cracking resistance of. The craze length was found to change linearly with the square root of time and the rate of crazing was found to vary exponentially with the applied stress above a. As is evident from the photos, even a small amount of cracking can result in loss of material. Environmental stress cracking may account for around 1530% of all plastic component failures in service. The connectors are made from several alternative polymers, but polycarbonate is used widely.
Environmental stress crack resistance of polyethylene. Environmental stress cracking esc is widely regarded as. Prediction of environmental stress cracking in plastics. Under the conditions of the test method, high local multiaxial stresses are developed through the introduction of a controlled imperfection 2, 3. Environmental stress crack resistance escr is a vital property required in plastics for its longevity.
Its made of polycarbonate and the adhesive in the stickers will ruin the impact resistance of the helmet. 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 can occur when a polymer is placed under tensile stress in the presence of an active chemical agent. Polycarbonate is manufactured as a crystal clear and colourless, amorphous engineering thermoplastic notable for its high impact resistance which remains high down to 40c. The variation of stress with time was recorded, and the surface cracking was observed to evaluate the esc resistance of. If the plastic is under stress, it may also experience environmental stress cracking, which can be defined as the crazing and cracking that may occur when a. Environmental stress cracking resistance of plastics. Combinations of certain environments, coupled with stress andor strain upon the material, cause stress cracking or crazing of the polycarbonate sheet. Standard test method for environmental stresscracking of ethylene plastics 1. Environmental stress cracking in plastics rj lee group. Your polycarbonate is probably just fine initially but has been exposed to some unsuitable liquid. Impact, tear, and heatseal strengths and environmental stresscrack resistance of lldpe. The behavior of other, untested liquids can be estimated from hsp correlations based on a limited number of test liquids.
Significantly, in the absence of the chemical the plastic would undergo stress cracking in air, also known as creep rupture, given sufficient time. However, it is also extremely sensitive to liquids that come in contact with it and will become weakened and crack. The presented cases illustrate how the failure analysis process. 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. However, the material is susceptible to environmental stress cracking esc from a variety of fluids. Aliphatic polycarbonate polyrethanes with broad chemical. In general this problem falls into two subcategories. Deny kyriacos, in brydsons plastics materials eighth edition, 2017.
A tube which meets requirements of the simplified tests is highly likely to meet. Replace polycarbonate pieces when you see signs of aging occur to prevent failure during use. Environmental stress cracking esc is a welldocumented phenomenon in plasticpolymer. When force is applied to plastic, it travels along the polymer chains causing molecules to strain to remain in contact. High levels of stress also lower a products impact strength and can contribute to environmental stress cracking and diminished performance at high or cycling temperatures. 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.
1312 584 394 183 1161 27 1071 438 659 1493 1111 1391 750 875 486 168 1601 1356 1434 1394 138 1461 1478 622 987 102 1111 501 608 395 981