Environmental stress cracking chemicals

Resistance to Chemical Environments and Solubility. As a rule, amorphous plastics are susceptible, to various degrees, to cracking by certain chemical environments when the plastic material is placed under stress. The phenomenon is referred to as environmental stress cracking (ESC) and the resistance of the polymer to failure by this mode is known as environmental stress cracking resistance (ESCR). The tendency of a polymer to undergo ESC depends on several factors, the most important of which are appHed stress, temperature, and the concentration of the aggressive species. 

Many engineering thermoplastics (e.g., polysulfone, polycarbonate, etc.) have limited utility in applications that require exposure to chemical environments. Environmental stress cracking [13] occurs when a stressed polymer is exposed to solvents. Poly(aryl ether phenylquin-oxalines) [27] and poly(aryl ether benzoxazoles) [60] show poor resistance to environmental stress cracking in the presence of acetone, chloroform, etc. This is expected because these structures are amorphous, and there is no crystallinity or liquid crystalline type structure to give solvent resistance. Thus, these materials may have limited utility in processes or applications that require multiple solvent coatings or exposures, whereas acetylene terminated polyaryl ethers [13] exhibit excellent processability, high adhesive properties, and good resistance to hydraulic fluid. 

Polypropylene It has similar chemical properties to polyethylene but is less susceptible to environmental stress cracking. It may also be used at somewhat higher temperatures. 

Environmental stress cracking is the cracking of certain plastic products that becomes exposed to a chemical agent while it is under stress. This effect may be caused by exposure to such agents as cleaners or solvents. The susceptibility of affected plastics to stress cracking by a particular chemical agent varies considerably among plastics, particularly the TPs. 

Published by the Plastics Design Library, PDLCOM is an exhaustive reference source of how exposure environments influence the physical characteristics of plastics. Data include resistance to thousands of chemicals, weathering and UV exposure (i.e. color change after accelerated weathering or outdoor exposure) sterilization (radiation, ethylene oxide, steam, etc.) thermal air and water aging environmental stress cracking and much more. 

One of the principal weaknesses of pure polystyrene is its low impact resistance. To counteract this problem, we toughen it with various types of rubber. This is most effective when a portion of the rubber is chemically grafted to the polystyrene. The rubber forms small inclusions within a matrix of polystyrene. The presence of rubber also improves polystyrene s extensibility, ductility, and resistance to environmental stress cracking. 

Synergy of Load and Chemical Attack Environmental Stress Cracking... 

For trials involving exposure to heat, liquid chemical, environmental stress cracking and artificial weathering, attention is drawn to ISO 11403 [3], Acquisition and presentation of comparable multipoint data - Environmental influences on properties. 

A range of chemicals are given in an appendix to ISO 175 [16] which includes reference to the standard oils (but not the fuels) given in ISO 1817 [15]. A further list is given in ISO 11403 [3] of liquids for which chemical resistance and environmental stress cracking data is commonly needed, again including reference to ISO 1817 [15] for oils and a fuel. 

Rapra have published their own chemical resistance data sheets [9, 10], based on results of tests at Rapra performed by a small team of operators. They are thus comparable one with another and their sources are known. Rapra s Plascams materials selection database provides durability properties on a ranking basis and their Plastics Design Guide includes Plascams and other useful programmes. In 2002 Rapra and Faraday Plastics have launched a new website of environmental stress cracking data (www.esc-plastics.com). 

When a plastic exposed to air is subjected to a stress or a strain below its yield point, cracking can occur after a very long duration. The simultaneous exposure to a chemical environment under the same stress or strain can lead to a spectacular reduction of the failure time. The accelerated cracking in this way corresponds to environmental stress cracking (ESC). 

ISO 6252 1992 Plastics - Determination of environmental stress cracking (ESC) -Constant-tensile-stress method ISO/TR 7620 1986 Rubber materials - Chemical resistance... 

PMMA is handicapped by a low impact resistance, limited heat behaviour (except for the acrylic imides), inherent flammability, sensitivity to environmental stress cracking in the presence of certain chemicals, chemical attack by certain current solvents. For some grades, processing can be more difficult than for some other current thermoplastics. 

Polycarbonates are handicapped by their sensitivities to light and hydrolysis, requiring efficient protection for outdoor exposure fire behaviour, except for FR grades sensitivity to environmental stress cracking and attacks by chemicals such as bases, oils, chlorinated solvents, ketones. The cost, which is justified by the performances, is higher than that of PMMA and, of course, the commodities. 

Polysulfones are handicapped by their light and UV sensitivity, requiring efficient protection for outdoor exposure sensitivity to environmental stress cracking and attack by chemicals such as aromatic hydrocarbons, chlorinated solvents and ketones the cost, justified by the performances a sometimes insufficient fire resistance, but special grades are marketed. Trade name examples Acudel, Mindel... 

Liner types available are suitable for a wide variety of chemical services, including acids, alkalies, and various solvents. All liners are permeable to some degree, and manufacturers use various methods to vent gas out of the interspace between the liner and casing. All plastics are subject to environmental stress cracking (ESC). ESC can occur even when the liner is chemically resistant to the service. Lined pipe manufacturers should always be consulted regarding liner selections and service apph-cations. Also consult manufacturers regarding vacuum service limits. 

PDLCOM William Andrew, Inc., Plastics Design Library test data on the chemical compatibility and the environmental stress crack resistance of plastics... 

Environmental stress-cracking is the failure of plastic materials in the presence of certain chemicals types. This failure is not a result of chemical attack, but rather the simultaneous presence of three factors tensile stress, a stress-cracking agent, and inherent susceptibility of the plastic to stresscracking. 

Environmental stress cracking or corrosion (ESC) is the phenomenon that materials fail, in the presence of relatively inert chemical agents (liquids or gasses) and /or radiation, at much lower stresses, than in their absence, under the formation of many little cracks. We distinguish real chemical corrosion and stress corrosion, each with its own characteristics. 

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