Material Selection Requirements
Consider and evaluate the effect of the chemical environment the part may be exposed to during its entire life. Chemical resistance of plastics is much more complex than that of metals. Also, different families of plastics vary greatly in their ability to resist different chemicals. Plastics interact with chemical environments by different mechanisms like chemical reaction, solvation, absorption, plastication etc. Chemical reactions include hydrolysis by water, acids and alkaline compounds, and oxidation by oxygen. Exposure to chemicals in the presence of tensile stress speeds up the reaction. Chemical reaction is also faster at higher temperatures. The reaction is more rapid if both conditions are present concurrently. Chemical reaction causes degradation of plastics which increases with the time of exposure. Hydrolysis can occur in hydrolyzable polymers with neutral water. The rate of hydrolysis is enhanced by the presence of acidic or alkaline condition. As with chemical reactions in general, high temperature accelerates hydrolysis. Some chemicals attack plastics by dissolving them. Amorphous plastics are more susceptible to such attack than crystalline plastics. Fats, oils and organic solvents may interact with plastics causing swelling, softening and ultimately dissolution. Pay special attention to the possibility of unintentional or unexpected exposure to chemicals which may be considered "Reasonable Misuse," such as insect sprays, lubricants, cleaning agents etc. Consult Bayer literature for chemical resistance data of Bayer materials. |