Products such as acetone and xylene may cause stress cracking even at very low stress levels and should therefore be. Stress concentration can cause polycarbonate parts. I am worried about flame polishing inducing stress in the component. For this reason, use caution when using solvents to clean the surface of polycarbonate. Feeding makrolon polycarbonate sheet at excessive rates can cause vibration and cracking. According to chemical resistance of plexiglass acrylic alcohol is not as aggressive as you mention with plexiglass acrylic. Environmental stress cracking esc is one of the most common causes of unexpected brittle failure of thermoplastic especially amorphous polymers known at present. Polycarbonate technical properties data sheet engineering. Test fixtures should, of course, be thoroughly cleaned after each test series.
Complementary tests were done by size exclusion chromatography, uvvisible. The bent strip method described in astm d1693 will be described below as the environmental stress cracking test method for the molded plate. Lexan f6000 sheet product datasheet description typical. Constantstress test can be another contributor to stresscracking.
This whitepaper explains the cause and impact of plasticizerinduced stress cracking, as well as the relative stress crackresistance of specialtyformulated rigid pvc versus polycarbonate et al when exposed to pvc plasticizers commonly used in pvc medical tubing applications. Painting lexan 9600 sheet is ideally suited for use with a wide variety of modern decoration techniques. Although deformation may be simpler with the application of heat, even small angle bends are possible without it. The number of specimens that crack over a given time is. Its made of polycarbonate and the adhesive in the stickers will ruin the impact resistance of the helmet. Polycarbonate technical properties data sheet engineering grade author. This is known as the longterm hydrostatic strength lths.
Measuring residual stress in transparent plastics mddi online. Astm d 1693 describes a test for evaluating the stresscrack resistance of ethylene plastics in environments such as soaps, wetting agents, oils, or detergents. Combinations of certain environments, coupled with stress andor strain upon the material, cause stress cracking or crazing of the polycarbonate sheet. 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.
Makrolon polycarbonate sheet can be cut using industrial. Possibilities of why a polycarbonate pc part is cracking. Plastic failure through environmental stress cracking. Another variable to be considered in polycarbonate stress crack testing is solvent application method. Crazing can be induced at moderate to high stress levels by low molecular weight hydrocarbons. Revised stresscracking resistance of polycarbonate in. The mathematical relationship between outer fiber strain, radius of curvature r and thickness t is. Under the conditions of the test method, high local multiaxial stresses are developed through the introduction of a controlled imperfection 2, 3. 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.
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. The variation of stress with time was recorded, and the surface cracking was observed. The chemicals listed have been evaluated for lexan according a very stringent getest method. 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. They had been having this issue on a specific part from one of their current suppliers. This research studies the stress cracking of polycarbonate plastic by a variety of solvents and solvent blends. The amount of crystalline content in the container depends on the rate of cooling. A single notch cut into the test specimen acts as a crack initiation point. Pdf stress cracking of polycarbonate exposed to sunscreen. Such myths are either wholly wrong or correct just part of the time. Aug 01, 2007 since the introduction of the first 2liter, onepiece pet bottle by continental can co. The stress intensity factor k for a single edge notched specimen is determined by.
The mixed solvent test for polycarbonate is well developed. Strips of a plastic, each containing a controlled defect, are placed in a bending rig and exposed to a stresscracking agent. Strips of a plastic, each containing a controlled defect, are placed in a bending rig and exposed to a stress cracking agent. Since some of these materials can cause environmental stress cracking, please consult sabic innovative plastics for advice on specific applications. A number of myths have arisen as to the causes and remedies for stresscracking. This makes it an excellent plastic for prototyping applications where transparent or electrically nonconductive parts are needed, which cannot otherwise be made from sheet metal. And finally, as is the case with so many properties, molecular weight is critical. Improvement of environmental stress cracking resistance of. Standard test method for environmental stresscracking of. First, key set points like the dryer settings were not included in the process sheets. It can typically be formed at room temperature without cracking or breaking, similar to aluminum sheet metal. The results of this research can be used to develop targeted replacements for 1,1,1trichloroethane and cfc1, replacements that have equivalent or better compatibility with polycarbonate plastics. The most important factor to consider when drilling lexan sheet products is the heat generated during the actual process.
Investigations on environmental stress cracking resistance. Environmental stress cracking esc is widely regarded as the leading cause of plastic product failure. Basic understanding of stress cracking in hdpe products. In a set of experiments, certain cleaning solvents were. The applied stress is plotted versus the timetofailure on a double logarithmic scale. Astm d 1693 describes a test for evaluating the stress crack resistance of ethylene plastics in environments such as soaps, wetting agents, oils, or detergents. Stress cracking of polycarbonate exposed to sunscreen.
The presence or absence of residual stresses is a major concern in the production of plastics for applications such as medical devices and packaging, instrument manufacturing, optical components, and others. Analysis of polycarbonate stress cracking and cleaning solvent. The results confirmed the high deterioration of pmma by both gamma radiation and the active fluid. Environmental stress cracking esc is the premature cracking of a polymer due to the combined action of a stress and a fluid. While crystallinity provides strength, it also can lead to cracking. Stress crack will only develop, however, if tensile production andor are applied from the outside. Reference 2 uses the following to describe the chemical resistance of polycarbonate to a solvent. Learn about a wide range of highperformance polycarbonate resins and polycarbonate blends with outstanding properties along with dedicated cae support to help you simulate and achieve numerous different surface effects, textures and colors. For example, the test method astm f48402 stress crazing of acrylic plastics in contact with liquid or semiliquid compounds uses flexural stress levels of 3,000, 3,500, and 4,500. Environmental stress cracking the the chemical agent does. The exposed bars were then put in contact with ethanol, a stress cracking agent of pmma. Its the reason you cant put stickers on your motorbike helmet. Side notches are made to facilitate the cracking in the main notch.
Astm d2561 17 standard test method for environmental stress. Because standard test methods for measuring escr on plastics take such a long. If a plasticized pvc tube is mounted on a stressfree polycarbonate pipe, for instance, the. The chemicals listed have been evaluated for lexan according a very stringent ge test method. Plastic stress test protocols connecticut plastics.
Stress cracking and photodegradation behavior of polycarbonate. We recently had been asked by a potential customer why a polycarbonate would crack postmolding. Plasticizerinduced stress cracking of rigid pvc vs. Products such as acetone and xylene may cause stress cracking even at very low stress levels and should therefore be avoided. Carbonate stress corrosion cracking acscc is a common problem in the oil and gas production, petroleum refining, and petrochemicalchemical processing industries. Environmental stress cracking is considered to be the most frequent mode of failure of plastic materials. Diagnose it before it ruins your parts residual stress is an inherent result of plastics manufacturing processes and occurs when molten polymer is cooled and shaped. 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. Provides technical data and properties for engineering grade polycarbonate rod and sheet keywords.
Stress cracking sc and environmental stress cracking esc are two main mechanisms for cracked polycarbonate parts 1 2 345678. Chemical exposure can result in discoloration, softening, swelling, crazing, cracking or loss of properties of the thermoplastic. Environmental stress cracking the the chemical agent. Cleaning polycarbonate sheet before vinyl application. Other anecdotal data from experienced plastic part designers tends to echo. Test method the strain in the test environmental stress. Painting lexan f6000 sheet is ideally suited for use with a wide variety of modern decoration techniques. One example is the contact between polycarbonate and plasticized pvc. Since the introduction of the first 2liter, onepiece pet bottle by continental can co. It involves varying concentrations of npropyl alcohol as the inert ingredient and toluene as the stress crack agent. A laminate comprising a sheet of polycarbonate laminated to another sheet comprising, on a weight basis, a 30 to 90% polyvinyl butyral and b 70 to 10% thermoplastic polyurethane, containing a plasticizing amount of one or more c 2 c 5 alkanediols or diethylene glycol. Lexan cracking plastics engineering general discussion. The stress cracking effects were evaluated by solvent absorption, stress relaxation and mechanical testing during solvent exposure. Hdpe is a semicrystalline material, with no crystals in the melted state.
Environmental stress crack resistance of polyethylene. Sometimes stress is not visible until the component is subject to loading or exposure to chemicals by the end user. But, we have to signal that acrylics is a big family of polymers thermoplastics or thermosets derived from acrylic acid. Acscc is a form of alkaline stress corrosion cracking that often occurs more aggressively at higher ph and high concentrations of carbonate solutions.
Esc is a failure mechanism whereby a plastic resin is effected by a chemical agent while simultaneously under tensile loading. A recent study indicated that approximately 25% of plastic component failures are associated with esc1. Carbonate stress corrosion cracking acscc inspectioneering. Improvement of environmental stress cracking resistance of polycarbonate by. Evaluation of residual stress in molded resin jfe techno.
It is important to feed the sheet against the rotation of the router bit and to provide a fence for sizing when making straight cuts. Testing residual stresses and molecular orientation throughout a product provide important information about how that product will perform. 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. Plasticizers within pvc, such as phthalates can trigger stress cracking and result in damage to the polycarbonate. Test method the strain in the test environmental stress cracking of plastics h. Evaluating environmental stress cracking of medical plastics. The applied stress is plotted versus the timetofailure on a. Another feature of polycarbonate is that it is very pliable. In this test, strips of a plastic are positioned in a fixed flexural strain and exposed to a stresscracking agent for a predetermined period. Since variance of any of these factors can change the environmental stresscrack resistance of the container, the test results are representative only of a given test performed under defined conditions in the laboratory. Environmental stress crack resistance of polyethylene this test method is shown in figure 3. The tensile bars suggested for use in this test are injection molded and measure 8. 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. The use of polycarbonate in automotive applications is limited to low stress applications.
Adhesive types uv curable adhesives, cyanoacrylates, structural acrylics and. Fatigue crack propagation in polycarbonate materials technology. 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. Aside from being difficult to predict or test for, stress cracking is. Lexan 9600 sheet product datasheet description typical. The recommended procedure for cleaning polycarbonate is to wash it with warm water and a little nonabrasive detergent, such as 409 cleaner or either. Aluminum test fixtures used to induce stress cracking of the polycarbonate specimens had varying radii of curvature, providing a range of strain values from 0. A list of approved paint systems and suppliers is available on request. Exposure to some solvents can ultimately cause stress cracking or cloud the surface of the exposed plastic. Polycarbonate cracking polymer engineering engtips. Specimens are machined directly from pipe or from a molded plaque. Environmental stress crack resistance of polyethylene under.
A guide to chemical resistance of polycarbonate sheet. Investigations on environmental stress cracking resistance of. Stress from fasteners, plastic welding and molding render polycarbonate susceptible to stress corrosion cracking when it comes in contact with certain accelerants such as salt water and plastisol. Stress cracks or surface crazing near stress concentrators like threads can be a sign of future problems. As little as 10 percent glass fiber can reduce problems with stress cracking in materials like polycarbonate and polysulfone. Environmental stress cracking of polypropylene springerlink. Unlike most other plastics, polycarbonate is capable of undergoing large hot moulding deformations without cracking or breaking. Rapra in the united kingdom states that in nearly onethird of all failed plastic applications the problem is stress cracking. Escr testing can also be performed using tensile bars that are cut from sheet stock or. Polycarbonate technical properties data sheet engineering grade.
If the molded part is completely stress free or is subject solely to compressive stress, then no stress cracking will occur. The fatigue crack propagation tests are carried out with a force controlled sinusoidal. Environmental stress cracking is involved with some 25% of plastic part failures. The effect of injection moulding processing parameters on the. 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. Stress cracking is one of the most common problems associated with field failures in plastic products. Your polycarbonate is probably just fine initially but has been exposed to some unsuitable liquid.
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