The cycles of cold (and very dry) and medium cold and very wet could form very fine micro- cracks in the material. Those micro-cracks could help the process of hydrolysis of the material and the cut of its chains (bonds). So, use SEM, XRD and mass analysis techniques. (Dr. Lucien Veleva)

Polyetheretherketone (PEEK) is inherently a hydrophobic polymer in nature that posses some of the most outstanding mechanical and physical characteristic make it a suitable choice as an engineering polymer. Because of its nature, the presence of humid in short or long term will not change the characteristics of the polymer dramatically. However, if you are trying to investigate the effect of moisture on its behavior, some tests may help you. You have to undergo TGA,DSC, FTIR, and SEM as the most rampant characterization tests available in many universities as well as industrial R&D units. On TGA: after a long period of time the adsorbed moisture, if any, will show its presence as a very shallow decrease in the TGA plot that will be interpreted to the amount of adsorbed moist. DSC will help you to find out the effect of water on the crystalinity of the specimen since it has been denoted that water has a plasticizing ability. FTIR will show, of course ATR-FTIR is more elaborated, the possible hydrogen bond between water and PEEK. And SEM will hardly show changes of the morphology, I mean development of micro cracks. Finally you can measure the effect of moisture on the mechanical behavior of your molded or casted part following a mechanical stretching test. Impact-Izod test will also help you find out if the nature of the specimen has tended towards rubbery state. In short, and as a conclusion I advice you to perform physical/mechanical test as follows: TGA, DSC, mechanical stretching, Impact-Izod.