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. Polyethylene terephthalate carbonated soft drink bottles this test method describes a procedure for determining the stress crack resistance of blowmolded polyethylene terephthalate pet carbonated soft drink bottles by measuring the propensity for base cracking upon exposure to an aqueous sodium hydroxide solution. Results of critical strain tests on pet, pctg, and polycarbonate are listed in table. Determination of environmental stress cracking resistance. In this technique, the bottles are filled with a stress cracking solution which fills 10 vol. A study on environmental stress cracking in nanosio2filled polycarbonate. Environmental stress crack resistance escr is a vital property required in plastics for its longevity. This procedure is used to measure properties like the elastic modulus, the stress and the strain properties of a. 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 cracking esc is one of the most common causes of unexpected brittle failure of thermoplastic especially amorphous polymers known at present. Plastic stress test protocols connecticut plastics. Standard test method for environmental stresscracking of. A fractography allows us to locate the initiation site of the crack as well as details. In both methods, the bottle contains a known stresscracking agent.
Test rigs can easily demonstrate the results of chosing the wrong bottlewash detergent see photo showing broken polycarbonate strips. Engineering and manufacturing science and technology, general molding research molding chemical technology polyethylene polyethylene molding strength materials strength of materials. Standard test method for environmental stress crack. 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. 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. It outlines measures that plant personnel can take in both injection and blow molding to prevent this failure. 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. 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 examples from the automotive indsutry jeffrey a. In the 1930s, western electric was an early adopter of ldpe as a replacement for lead sheathing on multipair. The behavior of other, untested liquids can be estimated from hsp correlations based on a limited number of test liquids.
Pdf stresscracking of pet bottle as an unpredictable. This procedure tests the performance of bottles as they are pasteurized. Basic understanding of stress cracking in hdpe products. The thermal expansion of the contents produces about 5 psi in the bottle. Stress cracking is the main reason that high pressure overbraided hoses fail. Environmental stress cracking may account for around 1530% of all plastic component failures in service. For polyethylene, this may range from several months for a milk or juice bottle to.
Conditions of stress and strain that accelerate environmental stress cracking are one of the major goals of the research. Environmental stress cracking esc is one of the most common causes of unexpected brittle failure of thermoplastic especially amorphous polymers known. Determination of environmental stress cracking resistance of. The sidewalls of a container are strong as here the pet is in a highly orientated state. But there are methods for getting to the root of the problem. Environmental stress cracking an overview sciencedirect topics. Pdf environmental stress cracking behavior of bottle and fiber. Tma tests were conducted to determine the level of moldedin stress in the threaded region. Cfc1 is not as aggressive a stress cracker, and rates 0.
Stress cracks or surface crazing near stress concentrators like threads can be a sign of future problems. There is a variety of test methods available for assessing the escr of thermoplastics and they can. 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. This month we want to conclude the discussion with a few more case studies and then discuss tests and material selection techniques that.
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. Environmental stress cracking esc is the premature cracking of a polymer due to the combined action of a stress and a fluid. Stress cracking of csd bottles blow molding advisors at. Control of process and cooling parameters during the moulding process. Environmental stress crack resistance of polyethylene ineos. Test method the strain in the test environmental stress. Stress cracking of csd bottles this course explains the mechanics that underlie stress cracking of pet bottles with petaloid bases. 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. The proposed test methods suggest the exposure to the gaseous product or the. It is associated with the phenomenon of crazing and solvent plasticization of the polymer. 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. 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. Additionally, solvents can be compounded that have no effect on polycarbonate at higher strain levels than these standards up to 1. Replace polycarbonate pieces when you see signs of aging occur to prevent failure during use. A bottle escr test has been developed for assessing the escr of plastic bottles. When force is applied to plastic, it travels along the polymer chains causing molecules to strain to remain in contact.
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. Preform and bottle testing plastic technologies inc. Test method for evaluating the relative stress crack. Environmental stress cracking is involved with some 25% of plastic part failures. The susceptibility of polycarbonate, polymethyl methacrylate, and cellulose acetate butyrate to gasoline. 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. 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. For example, the test method astm f48402 stress crazing of acrylic. High stress levels in plastic are a common cause of component field failures. 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. 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. Environmental stress crack resistance of polyethylene this test method is shown in figure 3. Meanwhile, the astm d2561 test method uses a constant internal pressurization of 5 psig to produce a sustained stress. Plastic failure through environmental stress cracking.
Evaluating environmental stress cracking of medical plastics. The environmental stress cracking esc resistance of commercial virgin bottle and fiber. The presented cases illustrate how the failure analysis process. 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. Environmental stress crack resistance escr testing of. Stress cracking results in failure or breakdown of plastic materials. In both methods, the bottle contains a known stress cracking agent. 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. An automated device for stress crack testing of pet bottles.
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. The intrinsic viscosity of the preform used to blow the bottle. Typically pet environmental stress cracking originates around the base of the bottle. Analysis of polycarbonate stress cracking and cleaning. 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. A variation of this test uses sealed bottles warmed in a 60 degree c oven. Environmental stress cracking the the chemical agent does. Stress cracks or surface crazing near stress concentrators like threads can be a. A single notch cut into the test specimen acts as a crack initiation point. The polymer chains eventually creep toward the pull and deform.
Under the conditions of the test method, high local multiaxial stresses are developed through the introduction of a controlled imperfection 2, 3. The effect of processing variables on the environmental. Stress cracking of plastics by gasoline and gasoline components. Specimens are machined directly from pipe or from a molded plaque. The potential for environmental stress cracking is of paramount concern when. Environmental stress cracking an overview sciencedirect. Polycarbonate pc labware thermo fisher scientific us. Environmental stress crack resistance of polyethylene. Esc is a very important mode of plastic component failure. The surface transitions from a rubber to a glass state and the contraction of the surface due to loss of water yields stress sufficient to cause surface cracking. Environmental stress cracking esc is a common cause of plastic product failure. 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.
An illustration of the simplest tests will help define esc better. 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. Looking inside the casing, i see that where the screws go into the nuts, there are lots of little stress cracks in the plastic. The effect of processing variables on the environmental stress crack resistance of blowmolded polyethylene bottles. Esc may be defined as the acceleration of stress cracking by contact with a liquid or vapor without chemical degradation of the plastic.
The thermal expansion of the contents produces about 0. Stress cracking occurs in the basegate area of a container as here the material is in an amorphous state as well as. It is important to note that solvents can also affect polyethylene, but in an entirely different manner than environmental stress cracking agents. Stress cracking is a frequent problem in plastic applications. 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. Test method the strain in the test environmental stress cracking of plastics h. 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. 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 refers specifically to a phenomenon observed in polyethylene. Prediction of environmental stress cracking in plastics with. Side notches are made to facilitate the cracking in the main notch. How to prevent stress cracking what is stress cracking. Meanwhile, the astm d2561 test method uses a constant internal pressurization of 0.
The mechanisms of environmental stress cracking proposed in the literature. With force and time, crazing or stress cracking occurs. A plastic required enduring the entire life of a product before it fails. Environmental stress cracking escr is the formation of cracks in a part when exposed. This failure for glassy polymers bisphenol a polycarbonate pc. Myth versus science since the introduction of the first 2liter, onepiece pet bottle by continental can co. A variation of this test uses sealed bottles warmed in a 140 f oven. Environmental stress cracking of polypropylene springerlink.
Because of this, environmental stress cracking and creep rupture are parallel failure mechanisms. This procedure measures the permeation rate of co2 through a bottle using a control c iv permatran test instrument. Environmental stress crack resistance escr testing of plastics. To avoid problems, select your material with care and employ the fundamental rules of good design and processing.
6 1299 923 724 870 796 1026 151 1433 1111 349 1202 1076 1385 301 1185 1329 548 985 1215 1223 561 100 18 1589 39 575 408 1249 1479 198 522 118 430 910 1071