Terrence roop introduction chemical compatibility of plastic structural materials is a significant recurring concern central to the material sciences. Environmental stress cracking esc is widely regarded as the leading cause of plastic product failure. Environmental stress cracking due to unreacted monomer or leachable from abs plunger. Failure analysis in medical applications of polymeric materials stephen spiegelberg october 1415, 20 houston, tx. In general this problem falls into two subcategories. Environmental stress cracking resistance, nanocomposites. Improvement of environmental stress cracking resistance of. The incorporation of nanoparticles into pc leads to an improvement in esc. 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. A stress analysis was made to analyse the criteria for craze initiation and growth. The environmental effects on the susceptibility and crack growth of nearneutral ph stress corrosion cracking scc were characterized using mechanical testing, hydrogen permeation and potential drop measurements. Pc can be filled with glass fiber to increase further the rigidity. Environmental stress crazing 799 ntetradecane hexane isooctane 1400 1600 600 1200 nhexane 7. Failure analysis in medical applications of polymeric.
However, the material is susceptible to environmental stress cracking esc from a variety of fluids. The most critical effect of chemical attack is stress cracking or crazing, which. Plastic failure through environmental stress cracking. Stress corrosion cracking wikimili, the best wikipedia. The connectors are made from several alternative polymers, but polycarbonate is used widely. Failure occurs as a result of the accelerated fracture of polymeric materials due to the combined action of environmental exposure and stress. Reduce environmental stress cracking esc of your plastic parts by better predicting failure occurrence and implementing adequate prevention measures.
Stress cracking of commercial plastics by chemical environmental effects colin ayres mentored by dr. 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. In the case of premature babies, such a line provides nutrition in the form of a synthetic milk tpn and antibiotics to prevent infection. In many cases, you will also see that the part is hanging up on the core during ejection. Behaviour of polycarbonate in different chemical by determination of the timedependence of stress at constant strains. In this study, the environmental stress cracking esc resistance of nanosio 2 particlefilled polycarbonate pc was investigated at room temperature by using a fracture mechanical test method. This may result in stress cracks that affect the formed or fabricated parts appearance or mechanical properties. Statements concerning possible or suggested uses of the products described herein. Inhibition of environmental stress cracking in polycarbonate possible approaches. There are provided aqueous cleaning or rinsing composition for, respectively, cleaning or rinsing a surface, preferably wherein the surface comprises at least partially a polycarbonate surface. The stress at which esc cracking occurs is often well below the nominal. The combination of these factors may result in eventual stress crack failure. Because of this, environmental stress cracking and creep rupture are parallel failure mechanisms. 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.
Astm d5571 16 standard test method for environmental. As telephone construction and maintenance operations eliminate ozonedepleting solvents, questions on the compatibility of replacements with various telephone components arise. Stress cracking even in small quantities, a small number of chemicals can penetrate the surface of tuffak. Polycarbonate resistance to various chemicals and products. The mechanism of environmental stress cracking esc of amorphous polycarbonate in isopropyl alcohol, ethylene glycol monomethyl ether and methanol were studied. Furthermore, there are provided concentrate compositions for the preparing of said cleaning and rinsing compositions. Analysis of polycarbonate stress cracking cleaning solvent compatibility with telephone components. Influencing the environmental stress cracking resistance of. Environmental stress cracking the the chemical agent. To prepare the sample a small piece of a plastic material which is to be tested is cut as per the standards and notched on the centre. Environmental stress cracking esc is the development of cracks and eventual catastrophic failure due to a combination of mechanical stress from external loading or from moulding strain and exposure to an aggressive chemical a near solvent for the thermoplastic material.
Evaluating environmental stress cracking of medical plastics. Esc is a failure mechanism whereby a plastic resin is effected by a chemical agent while simultaneously under tensile loading. Environmental stress cracking esc is one of the most common causes of unexpected brittle failure of thermoplastic especially amorphous polymers known. Stress corrosion cracking scc is the growth of crack formation in a corrosive environment. 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. Polycarbonate is prone to environmentalstress cracking esc in the. Analysis of polycarbonate stress cracking and cleaning. Blog analyse environmental stress cracking of plastics. Two pcbased nanocomposites with nanosio 2 content of 1 and 4 vol% were compounded using a twinscrew extruder.
The stress at which esc cracking occurs is often well below the nominal fracture stress of the. 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. Environmental stress cracking of poly3hydroxibutyrate under. The solution from the plastics point of view is to reduce shrinkage by increasing cavity pressure pack. 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 certain stress level. This stress relaxation allows testing to run without failure for very long periods 1,500 hours. Chemical resistance of palram polycarbonate products at room temperature the mechanism of chemical attack on thermoplastic sheets differs significantly from the mechanism of corrosion of metals. Other additives can be heat boosters or additives improving escr environmental stress cracking. Failure analysis in medical applications of polymeric materials 20pdf version.
The potential for environmental stress cracking is of paramount concern when plastics are used in medical device components such as luers and stopcocks. Environmental stress cracking in polyethylene takes place because of interlamellar failure, which in turn is caused by relaxation of tie molecules. A recent study indicated that approximately 25% of plastic component failures are associated with esc1. Standard test method for environmental stresscracking of ethylene plastics 1. On predicting environmental stress cracking in polymers. Environmental stress cracking is involved with some 25% of plastic part failures. The strain in the test environmental stress cracking of plastics h. Environmental stress cracking refers specifically to a phenomenon. Environmental stress cracking of polycarbonate catheter. Thus polycarbonate is sensitive to attack by alkalis, but not by acids.
Cracks in corners when cracks appear in the corners of plastic parts, the cause is too much plastic shrinkage onto the mold core in that corner. Test method the strain in the test environmental stress. Whereas some cracking results from excessive loads, or from thermal or uv degradation, a large percentage of plastic part failure results from a phenomenon termed environmental stress cracking esc, which is the result of an external chemical acting on a plastic part that contains internal stresses. It can lead to unexpected sudden failure of normally ductile metal alloys subjected to a tensile stress, especially at elevated temperature. With transparent grades of tuffak, stress cracks are generally easy to detect. Environmental stresscracking has been found to occur most readily under such. Reducing environmental stress cracking in plastic parts. The problem lies, in part, in the definition of stress cracking. The variation of stress with time was recorded, and the surface cracking was observed to evaluate the esc resistance of samples. Environmental stress cracking and other solvent effects. It is also know by the term bent strip bs escr test. Environmental stress cracking esc is one of the most common causes of unexpected brittle failure of thermoplastic especially amorphous polymers known at present.
Prediction of environmental stress cracking of polycarbonate from. This can range from minor fading, color change, whitening to stress cracking or crazing which can be serious conditions leading up to possible catastrophic mechanical and or electrical failures. Influencing the environmental stress cracking resistance of amorphous thermoplastic parts by the example of polycarbonate and water. Investigations on environmental stress cracking resistance. Environmental stress cracking of poly3hydroxibutyrate. Resistance to this mode of failure can be best gauged through constanttensileload testing, while taking into account the differences in. To measure the amount of stress cracking which may develop in the material, one of the most widely used method is the bell telephone test method. Li b a department of macromolecular science and the key laboratory of molecular engineering of polymers, fudan university, shanghai, 200433, china b shanghai koito automotive lamp co.
Pdf stress cracking of polycarbonate exposed to sunscreen. Plastic materials exhibit high quality of stress or tensile properties. Windows made from polycarbonate often show evidence of crazing. Standard test method for environmental stresscracking of. Scc is highly chemically specific in that certain alloys are likely to undergo scc only when exposed to a small number of chemical environments. Environmental stress crack resistance of polyethylene today, this test is specified less frequently because it is not as aggressive towards modern resins. The bent strip test is a constant strain test, but polyethylene relaxes when strained. A study on environmental stress cracking in nanosio2. 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 of polyethylene. Corrosion of metals results in a gradual loss of surface material as a result of electrolytic action by the relevant chemicals. Chemical resistance of palram polycarbonate products. Polycarbonate has superior uv stability and this can be even further improved by adding uv stabilizers.
However, extended exposure of plastic surface to rain, moisture, heating, incr. 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 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 one of the most important causes of. Pdf environmental stress cracking resistance of halloysite. Blog testing stress crack resistance of plastic material. 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. 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.
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