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Chemical Resistance of Polypropylene
„ BACKGROUND
As a general class of materials, polyethylene (PE) There are many laboratory test procedures available and polypropylene (PP) are recognized for their to evaluate the potential effects of chemical exposure on PP containers of other molded parts including environments. This property has resulted in the ASTM D 542,“Standard Test Method for Resistance of successful utilization of polyolefins in applications Plastics to Chemical Reagents” and ASTM D 5419, such as chemical tanks, industrial piping, “Test Method for ESCR of Threaded Plastic automotive batteries, lab ware, etc. The ability to Closures.” In addition, many molders, fabricators and measure and predict chemical resistance is end-users have developed very specific procedures extremely important. There are two basic types of to determine suitability to exposure. Although chemical “attack”; solvation and chemical reaction. laboratory testing can provide a relative indication of performance between materials or product grades, it Solvation occurs when a chemical either dissolves is of limited value in predicting actual end-use the polymer or is absorbed causing swelling and/or performance unless extensive correlation studies softening of the polymer to occur, often in have been conducted. If testing is conducted using conjunction with a measurable weight change. In laboratory specimens, the variables introduced by this case, no chemical change occurs in the polymer "real" part geometry such as material distribution and may even be reversible in very mild cases where and degree of molded-in stresses and their effects, are not taken into account. Another variable is the composition of the reagents used in the test since in When a chemical reaction takes place, there is a most cases mixtures of various products are used change in the chemical structure of the polymer rather than the pure chemicals used in a laboratory. often causing a change in molecular weight and a It is not uncommon to experience various degrees of synergism in which the mixtures may behave more Another related mechanism is Environmental Stress antagonistically than the individual components. Cracking (ESC). Although ESC is often described as a chemical attack, it is a very complex combination „ SPECIFIC PERFORMANCE OF POLYPROPYLENE of plasticizing, migration, low level stress and It is generally felt any exposure of polypropylene to mechanical failure initiated by exposure to specific environments containing strong oxidizing agents, classes of liquids, primarily surfactants (soaps). halogenated and aromatic hydrocarbons and some ESC is a failure mechanism frequently experienced ketones and ethers should be viewed with concern, with PE. Unlike PE, PP is not susceptible to ESC in Acids, bases, alcohols, detergents, lower ketones, its strictest definition. Exposure to certain fluids, aldehydec and water soluble salts are usually not such as bleach (hypochlorites), causes a failure in regarded as antagonistic. Table 1 is a general guideline to resistance of polypropylene to various PP that resembles ESC and is often described reagents. Performance is relative to the test method accordingly. However, the failure is caused by the used and other variables found in practical strong oxidizing effect of the bleach that causes the applications such as temperature, applied loads, synergism of chemicals and molded-in stresses The temperature of exposure is another key factor which need to be considered when evaluating because of the increased mobility of many chemical product capability. Generally, the choice of a product molecules and the increased rate of reaction at with the highest, practical molecular weight (lowest elevated temperatures. The ability of solvents to Melt Flow Rate) is preferred. Attention to part design diffuse into the polymer also increases with and mold filling/cooling is also important to min imize increased temperatures. In many cases, the level of molded-in stresses and possible stress risers stress applied to a part can accelerate the rate of can accelerate failure. In all cases, it is chemical or solvent attack. Finally, as the recommended that testing be conducted on the concentration or strength of the chemicals actual parts to verify expected performance. increases, the resistance of the polymer generally Chemical Resistance of Polypropylene (Continued)

GENERAL CHEMICAL RESISTANCE GUIDE FOR POLYPROPYLENE *Taken from ASTM D-543-87 Standard Reagents The information on this document is, to our knowledge, true and accurate. However, since the particular uses and the actual conditions of use of our products are beyond our control, establishing satisfactory performance of our products for the intended application is the customer's sole responsibility. All uses of Equistar products and any written or oral information, suggestions or technical advice from Equistar are without warranty, express or implied, and are not an inducement to use any process or product in conflict with any patent. Equistar materials are not designed or manufactured for use in implantation in the human body or in contact with internal body fluids or tissues. Equistar makes no representation, promise, express warranty or implied warranty concerning the suitability of these materials for use in implantation in the human body or in contact with internal body tissues or fluids. More detailed safety and disposal information on our products is contained in the Material Safety Data Sheet (MSDS). All users of our products are urged to retain and use the MSDS. A MSDS is automatically distributed upon purchase/order execution. You may request an advance or replacement copy by calling our MSDS Hotline at (800) 700-0946. Lyondell Chemical Company 1221 McKinney, Suite 700 P.O. Box 2583 Houston, Texas 77252-2583 (800) 615-8999

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