Improvement of environmental stress cracking resistance of. Environmental stress cracking is considered to be the most frequent mode of failure of plastic materials. 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. Ldpe tubing low density polyethylene is economical plastic material with good chemical resistance. A guide to chemical resistance of polycarbonate sheet. Available in natural translucent white, stock and custom colors. Pe is a semicrystalline typically around 50%, whitish, semiopaque commodity thermoplastic that is soft, flexible and tough even at low temperatures with outstanding electrical properties but poor temperature resistance. With force and time, crazing or stress cracking occurs. Scc is highly chemically specific in that certain alloys are likely to undergo scc only when exposed to a small number of chemical environments. Medical device recalls on the rise the nature of the medical device manufacturing market requires companies to manage. The presented cases illustrate how the failure analysis process. A materials resistance against this type of failure is called environmental stress cracking resistance escr. Fatigue crack propagation in polycarbonate materials technology. Polycarbonate is known to experience environmental stress cracking when exposed to solvents.
Environmental stress cracking esc is considered a leading cause of plastic part failure. Environmental stress cracking resistance of polyethylene. Environmental stress cracking resistance of plastics. Plastic failure through environmental stress cracking esc, the plastic killer, is a frequent cause of field failures by jeffrey jansen the madison group, madison, wisconsin, usa environmental stress cracking esc is considered a lead ing cause of plastic part failure. When force is applied to plastic, it travels along the polymer chains causing molecules to strain to remain in contact.
There are factors other than viscosity that can also affect the stress cracking problem. This research studies the stress cracking of polycarbonate plastic by a variety of solvents and solvent blends. Environmental stress crazing 799 ntetradecane hexane isooctane 1400 1600 600 1200 nhexane 7. Environmental stress cracking the the chemical agent does. It has reasonably good temperature resistance, good dimensional stability and low creep but somewhat limited chemical resistance and is prone to environmental stress cracking. According to astm d883, stress cracking is defined as an external or internal crack in a plastic caused. Aggressive exposure of plastics to chemical contaminants to detect instances of environmental stress cracking esc 1, 2. Because the mechanisms of failure for solvent attack and environmental stress cracking are so different, the means of optimizing material parameters are different as well. The third type of attack is often the most difficult to predict since environmental conditions dictate whether or not the plastic will be affected. Failure analysis of steel wire reinforced thermoplastics composite pipe.
The solution to an internal part cracking problem is to change the packing pressure. Lldpe tubing is engineered to resist stress cracking caused by chemicals, soaps, solvents, and oils. How to avoid environmental stress cracking in plastic piping corzan. It is the premature embrittlement and subsequent cracking of a plastic due to the simultaneous and synergistic action of stress and contact with a chemical agent.
Environmental stress cracking is involved with some 25% of plastic part failures. Environmental stress cracking of poly3hydroxibutyrate. Some performance evaluation tests that once took only days to run now take months with todays. The effect of injection moulding processing parameters on the environmental stress cracking resistance of polycarbonate mouldings, materials research. Polysulfone for high temperature applications pbs plastics. It is the premature embrittlement and subsequent cracking of a plastic. Revised stresscracking resistance of polycarbonate in. Behaviour of polycarbonate in different chemical by determination of the timedependence of stress at constant strains. 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. Polycarbonate is an incredibly useful plastic for applications requiring transparency and high impact resistance. Stresses that cause environmental cracking arise from residual cold work, welding, grinding, thermal treatment, or may be externally applied during service and, to be effective, must be tensile as opposed to compressive. Chemical resistance and stress cracking in polyurethanes. Investigations on environmental stress cracking resistance of. At creative mechanisms, we have used polycarbonate in a number of applications across a range of industries.
Polysulfone tubing scandia plastics a pexco company. The test provides analysis for the materials oxidation and alcohol absorption, as well as its resistance to environmental stress cracking. Environmental stress cracking escr is the formation of cracks in a part when. 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. Made from fdaapproved materials, that are ul rated, and provide superior clarity. The chemical simply accelerates the stress cracking. It can lead to unexpected sudden failure of normally ductile metal alloys subjected to a tensile stress, especially at elevated temperature. Polycarbonate is manufactured as a crystal clear and colourless, amorphous engineering thermoplastic notable for its high impact resistance which remains high down to 40c. 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. Environmental stress cracking in plastics rj lee group, inc. Polycarbonate has thousands of applications, from cd manufacture to aircraft cockpit canopies, but the largest user of polycarbonate is the construction sector, where is a replacement for glass.
Environmental stress cracking esc, a brittle failure mode of plastic parts under the. This stress can be caused by a cavity pressure that is either too high or too low. Environmental stress crack resistance of polyethylene. Please contact nordson medical technical support if polycarbonate is planning on being used in a solvent bonding application. Injection molded part defects cracks in molded parts. Environmental stress cracking in polyethylene takes place because of interlamellar failure, which in turn is caused by relaxation of tie molecules. Polymer solutions environmental stress cracking youtube. The applied stress is plotted versus the timetofailure on a double logarith mic scale. By environmental stress cracking, we understand a failure in which materials in. 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. Plasticizer chemical type, level of use, polarity, and severity of environmental conditions all play a role in the development of cracking in stressed polycarbonate. It is a lighter alternative to glass and a natural uv filter, so it is often used in eyewear. 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.
However, along with the decreased mechanical properties, aliphatic polyurethanes are more prone to a physical degradation process termed environmental stress cracking esc than their aromatic counterparts. 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. Chlorinated water induced aging of pipe grade polypropylene random. Give us a call to see what we can do to satisfy your specific plastic tubing needs. Environmental stress cracking is a failure mechanism very similar to slow crack growth in terms of shape. 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. Flexible pvc medical tubing contains plasticizer, the component added to pvc to impart flexibility to the inherently rigid pvc polymer. Ldpe provides high impact strength at low temperatures. 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. Nov, 2012 this stress can be caused by a cavity pressure that is either too high or too low. Esc is a very important mode of plastic component failure. Environmental stress cracking the the chemical agent.
Stress corrosion cracking scc is the growth of crack formation in a corrosive environment. Environmental stress cracking esc is a welldocumented phenomenon in plasticpolymer. Sodium hypochlorite is available as solutions in varying strengths. Another feature of polycarbonate is that it is very pliable. Analysis of polycarbonate stress cracking and cleaning. The addition of a surfaceactive chemical, an environmental effect, accelerates this type of failure, thus this mechanism is termed environmental stress cracking esc. Catastrophic failure occurred in a cpvc pipe through esc associated with contact with an incompatible soundproofing caulk. In general this problem falls into two subcategories.
Polycarbonate tubes provides extraordinary design and fabrication opportunities. It has good chemical resistance, and by adding uv stabilizers, it has good outdoor properties. There are factors other than viscosity that can also affect the stresscracking problem. Although deformation may be simpler with the application of heat, even small angle bends are possible without it. Concentrated solutions for disinfection purposes may contain 10% to 18% available chlorine while domestic and laundry bleaches typically contain 3% to 6% available chlorine. Improvement of environmental stress cracking resistance of polycarbonate by. Either to itself or to other materials, there are glues available for most applications. Scandias success in the custom extrusion of top quality, high performance, low stress polysulfone tubing, for over 40 years, gives us confidence in our ability to meet, and often exceed, even the toughest project requirements. Environmental stress cracking resistance listed as escr.
This month we want to conclude the discussion with a few more case studies and then discuss tests and material selection techniques that. Significantly, in the absence of the chemical the plastic would undergo stress cracking in air, also known as creep rupture, given sufficient time. Esc can occur when a polymer is placed under tensile stress in the presence of an active chemical agent. Because of this, environmental stress cracking and creep rupture are parallel failure mechanisms. Stress cracking of polycarbonate exposed to sunscreen. By environmental stress cracking, we understand a failure in which materials in contact with a fluid are subjected to stress. 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. It is ideal for food processing, pneumatic, water line, drain line, laboratory, and process control plant applications. I am looking for appropriate method for chemical resistance of plastics environmental stress cracking resistance. It is a physical process driven by the applied stress but accelerated by the presence of. Luckily, polycarbonate is a relatively easy plastic to stick. Pbs plastics is pleased to offer custom tubing and profiles made from polysulfone psu, a versatile thermoplastic with characteristics that make it ideal for applications in medical devices, sterilization equipment, beverage processing, industrial separations, and semiconductors polysulfone has one of the highest service temperatures among all meltprocessable thermoplastics. Investigations on environmental stress cracking resistance. Polycarbonate pc bonding tips and adhesive selection.
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. Plasticizerinduced stress cracking of rigid pvc and polycarbonate flexible polyvinyl chloride pvc is the most common material used to manufacture clear flexible tubing for medical applications. 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. 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. Sample at right shows lower stresses from proper annealing. The variation of the stress with the immersion time and threepoint bending method have been used to evaluate the chemical compatibility of polymers and the related environmental stress cracking. Plasticizerinduced stress cracking of rigid pvc and. Polyethylene waterwell tubing a clear, hdpe core shows through if the colored coating is accidentally gouged or cut. Bonding polycarbonate with industrial adhesives surface.
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. Polycarbonate tube polycarbonate tubing order online. For flexible water and air lines where barbed fittings are used, lldpe is preferred because it has better resistance to environmental stress cracking. There are a variety of adhesive choices for bonding polycarbonate. 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. Sodium hypochlorite and its effects on polyethylene. Polycarbonate tubing extruded polycarbonate tubes offer the clarity of glass and the impact resistance of metal. Environmental stress cracking can be avoided by considering and addressing the chemicals and mechanical stresses that will affect the piping. This video captures over 15 hours of video footage a 90 second time lapse. This article discusses polyurethane benefits and challenges, and also provides a test case for a proprietary aliphatic polycarbonate alc polyurethane. Environmental stress cracking of polyvinyl chloride in. The variation of stress with time was recorded, and the surface cracking was observed to evaluate the esc resistance of samples. The problem lies, in part, in the definition of stress cracking.
A family of stress cracks tend to form and propagate into the tube material. How to prevent stress cracking what is stress cracking. It is called environmental stress cracking and basically it means that solvents cause the material to crack due to built in stresses in the polycarbonate. Plastic failure through environmental stress cracking.
This phenomena, although rare and preventable, is known to occur in many types of. It is environment stress cracking of stressed cpvc pipe after being. Environmental stress cracking in polyethylene takes place because of interlamellar failure, which. Jansen, stork technimet abstract four case studies are presented to illustrate environmental stress cracking esc within automotive components. Jun 28, 20 this article discusses polyurethane benefits and challenges, and also provides a test case for a proprietary aliphatic polycarbonate alc polyurethane. Environmental stress cracking examples from the automotive indsutry jeffrey a. Esc is the consequence of a combination of mechanical stress and exposure to an aggressive chemical. Pdf stress cracking of polycarbonate exposed to sunscreen. Environmental stress cracking in plastics rj lee group. 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. The polymer chains eventually creep toward the pull and deform. Stress crazing on acrylic surfaces and its causes stress crazing, which appears as an area of tiny microcracks, occasionally shows up in areas on the surface of most thermoplastic sheets. Combinations of certain environments, coupled with stress andor strain upon the material, cause stress cracking or crazing of the polycarbonate sheet.
497 921 246 925 359 1510 1252 800 626 1247 856 1411 1278 1164 808 1029 1519 563 151 603 243 1332 84 1297 62 340 877 193 452 1418 842 1307 586 1380 505 1255 1311 1065 726 528 68 840 1035 1130 866 164 716