How does moisture change the properties of polyamide (Nylon)?
Moisture can change the properties of polyamide in two ways. The first is that moisture in the raw material (resin) during molding can cause a permanent reduction in the chain length of the material resulting in brittle parts. The second is that moisture can be absorbed into a polyamide part and make it temporarily more flexible until the part dries out again. Moisture reacts with polyamide if it is raised above the melting point of the plastic. The water hydrolyzes the molecular chains in the polyamide and makes the material permanently more brittle. This brittleness can be quite insidious because there may be no visible indication of molding problems. After molding it is no longer possible to test for the moisture because it has reacted with the plastic and then boiled away leaving a completely dry part. It is very important to make sure that polyamide material is completely dry before molding. The moisture content of the resin before molding can be measured by Karl Fischer Titration
