EFFECTS OF THE ENVIRONMENT ON PLASTICS

  Environmental factors, such as ambient moisture, chemicals (liquid or vapor), exposure to sunlight, high temperatures, hot water and/or steam, bacterial/fungi (underground conditions), and irradiation all tend to attack plastic materials. Materials may not only change appearance, but have a significant decrease in properties, such as impact and tensile strength. Again check the supplier's literature carefully.

  Plastic materials do not rust or corrode and many plastics perform significantly better than metals in corrosive environments. Also understand that the MORE CHEMICALLY RESISTANT a plastic is, the MORE DIFFICULT it is to bond to since bonding generally requires some chemical attack.

  Chemical resistance is also a critical factor if the part is to be PAINTED. The solvents in the paint must be compatible with the material to be painted. It is best to use paints recommended by the material supplier.

  Gaskets, "0" rings, or other dissimilar materials that will be in intimate contact with a plastic over a long period of time MUST not contain chemicals,solvents, or plasticizers that will leach out and attack the base material. Flexible vinyl is an example of a material softened by a chemical additive. This vinyl is also a good example of plasticizer migration (outgassing) from pieces inside a car and it ends up fogging the windows.

  The outgassing of volatiles is accelerated when the material is exposed to high temperatures and/or vacuum. In critical applications requiring no outgassing, a material must be selected that does not contain any plasticizers or other additives that can outgas. Often, pre-baking the material at a temperature slightly above the application temperature will drive out most of the volatiles. Check with the material suppliers. Materials such as polycarbonate, acetals, nylons, and acrylics have been used in these applications.