It is important to have an understanding of the amount of stress used in any given test to better evaluate liquids or cleaners that may cause crazing. Environmental stress crack resistance of polyethylene ineos. Jansen, stork technimet abstract four case studies are presented to illustrate environmental stress cracking esc within automotive components. Solvent blends can be compounded that meet existing telephone standards for stress cracking of polycarbonate. The proposed test methods suggest the exposure to the gaseous product or the. Stress cracking of plastics by gasoline and gasoline components. A plastic required enduring the entire life of a product before it fails. We can compute the amount of stress both ways, so that the reader can use the type of stress with which he is more familiar. The behavior of other, untested liquids can be estimated from hsp correlations based on a limited number of test liquids.
This month we want to conclude the discussion with a few more case studies and then discuss tests and material selection techniques that. In this technique, the bottles are filled with a stress cracking solution which fills 10 vol. Standard test method for environmental stresscracking of. 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. Cfc1 is not as aggressive a stress cracker, and rates 0. Stress cracking occurs in the basegate area of a container as here the material is in an amorphous state as well as. Environmental stress cracking refers specifically to a phenomenon observed in polyethylene. 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 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 effect of processing variables on the environmental stress crack resistance of blowmolded polyethylene bottles. Stress cracking is the main reason that high pressure overbraided hoses fail. For polyethylene, this can range from a few months for a juice bottle to several decades for natural gas pipelines and an automobile fuel tank. Evaluating environmental stress cracking of medical plastics. Environmental stress cracking examples from the automotive indsutry jeffrey a. It is important to note that solvents can also affect polyethylene, but in an entirely different manner than environmental stress cracking agents. Stress cracks or surface crazing near stress concentrators like threads can be a. In the 1930s, western electric was an early adopter of ldpe as a replacement for lead sheathing on multipair. Determination of environmental stress cracking resistance. Test method the strain in the test environmental stress cracking of plastics h.
Environmental stress cracking is involved with some 25% of plastic part failures. When force is applied to plastic, it travels along the polymer chains causing molecules to strain to remain in contact. Conditions of stress and strain that accelerate environmental stress cracking are one of the major goals of the research. Under the conditions of the test method, high local multiaxial stresses are developed through the introduction of a controlled imperfection 2, 3. Preform and bottle testing plastic technologies inc. Looking inside the casing, i see that where the screws go into the nuts, there are lots of little stress cracks in the plastic. Esc is a very important mode of plastic component failure. This failure for glassy polymers bisphenol a polycarbonate pc. It is associated with the phenomenon of crazing and solvent plasticization of the polymer. Environmental stress cracking an overview sciencedirect. Plastic stress test protocols connecticut plastics. In both methods, the bottle contains a known stresscracking agent. It outlines measures that plant personnel can take in both injection and blow molding to prevent this failure. This procedure is used to measure properties like the elastic modulus, the stress and the strain properties of a.
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. The susceptibility of polycarbonate, polymethyl methacrylate, and cellulose acetate butyrate to gasoline. Test rigs can easily demonstrate the results of chosing the wrong bottlewash detergent see photo showing broken polycarbonate strips. An illustration of the simplest tests will help define esc better. A fractography allows us to locate the initiation site of the crack as well as details. Stress cracking of pet bottle as an unpredictable factor limiting the commercial life of carbonated soft drinks article pdf available in italian journal of food science 244. High stress levels in plastic are a common cause of component field failures. Analysis of polycarbonate stress cracking and cleaning. The sidewalls of a container are strong as here the pet is in a highly orientated state. Stress cracking results in failure or breakdown of plastic materials.
Typically pet environmental stress cracking originates around the base of the bottle. Esc may be defined as the acceleration of stress cracking by contact with a liquid or vapor without chemical degradation of the plastic. Stress cracking of pet bottles is caused by a combination of the reduced tensile strength of the base from chemical attack from the fillingline lubricant, internal stress from the carbonation pressure, and moldedin stresses in the base. The thermal expansion of the contents produces about 0. Environmental stress cracking esc is the premature cracking of a polymer due to the combined action of a stress and a fluid. The presented cases illustrate how the failure analysis process. An automated device for stress crack testing of pet bottles. The potential for environmental stress cracking is of paramount concern when. Control of process and cooling parameters during the moulding process. Despite the product conformity concerning thermal stability, burst test and stress cracking test performed in alkaline conditions, pet bottles quality and performances may become altered if the iv. The thermal expansion of the contents produces about 5 psi in the bottle. This procedure measures the permeation rate of co2 through a bottle using a control c iv permatran test instrument.
The polymer chains eventually creep toward the pull and deform. Environmental stress cracking of polypropylene springerlink. Pdf stresscracking of pet bottle as an unpredictable. How to prevent stress cracking what is stress cracking. Environmental stress cracking esc is one of the most common causes of unexpected brittle failure of thermoplastic especially amorphous polymers known. The intrinsic viscosity of the preform used to blow the bottle. Meanwhile, the astm d2561 test method uses a constant internal pressurization of 5 psig to produce a sustained stress.
Specimens are machined directly from pipe or from a molded plaque. Environmental stress cracking the the chemical agent does. Stress cracks or surface crazing near stress concentrators like threads can be a sign of future problems. Plastic failure through environmental stress cracking. Engineering and manufacturing science and technology, general molding research molding chemical technology polyethylene polyethylene molding strength materials strength of materials. With force and time, crazing or stress cracking occurs. The effect of processing variables on the environmental. But there are methods for getting to the root of the problem. A bottle escr test has been developed for assessing the escr of plastic bottles. Environmental stress cracking an overview sciencedirect topics. 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. Aug 01, 2008 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.
The two fixing screws go into nuts which are embedded in hard clear plastic possibly acetate or thin perspex on the far side of the case. Determination of environmental stress cracking resistance of. Stress cracking of csd bottles blow molding advisors at. 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.
Environmental stress crack resistance of polyethylene this test method is shown in figure 3. Standard test method for environmental stress crack. Replace polycarbonate pieces when you see signs of aging occur to prevent failure during use. Meanwhile, the astm d2561 test method uses a constant internal pressurization of 0. 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. Myth versus science since the introduction of the first 2liter, onepiece pet bottle by continental can co. Environmental stress crack resistance escr testing of. Nov 22, 2000 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. A single notch cut into the test specimen acts as a crack initiation point. To avoid problems, select your material with care and employ the fundamental rules of good design and processing. There is a variety of test methods available for assessing the escr of thermoplastics and they can. Mar 01, 2012 stress cracking with the wrong kind of detergent can can occur rapidly and reduce the number of viable wash cycles of the bottle while encouraging algal growth green bottles. Environmental stress cracking may account for around 1530% of all plastic component failures in service.
It is one of the most common causes of unexpected brittle failure in thermoplastic. 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. Test methods for evaluation of escr of plastics a common laboratory request for escprone polymers is to check escr performance for quality control, competitive product evaluations, and research and development work. Environmental stress crack resistance of polyethylene.
The mechanisms of environmental stress cracking proposed in the literature. Results of critical strain tests on pet, pctg, and polycarbonate are listed in table. Test method for evaluating the relative stress crack. 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 escr is a vital property required in plastics for its longevity.
A variation of this test uses sealed bottles warmed in a 140 f oven. Additionally, solvents can be compounded that have no effect on polycarbonate at higher strain levels than these standards up to 1. The environmental stress cracking esc resistance of commercial virgin bottle and fiber. Stress cracking is the crazing or cracking that occurs when a pet container is under tensile stress and in its weakest state.
Environmental stress cracking escr is the formation of cracks in a part when exposed. This procedure tests the performance of bottles as they are pasteurized. Environmental stress crack resistance escr testing of plastics. For example, the test method astm f48402 stress crazing of acrylic. Stress cracking is a frequent problem in plastic applications. 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. For polyethylene, this may range from several months for a milk or juice bottle to. Pdf environmental stress cracking behavior of bottle and fiber. Environmental stress cracking esc is a common cause of plastic product failure. Side notches are made to facilitate the cracking in the main notch. Tma tests were conducted to determine the level of moldedin stress in the threaded region. This eliminates one of the two ingredients necessary for failure and guarantees that some materials that would fail a true stress crack test will pass the standard chemical resistance tests.
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