Meaning
Material properties define the degree to which a polymer absorbs water from the surrounding environment and how that water affects its structure. Moisture sensitivity is a critical factor for resins like polyamide and polycarbonate which can undergo chemical degradation if processed while wet. This characteristic dictates the type of drying equipment and the storage conditions required to maintain the integrity of the resin.
Absorption Rate
Environmental factors like humidity and temperature determine how quickly a polymer reaches its equilibrium moisture content. Higher moisture sensitivity in a resin means it will pick up water faster than a non-polar material like polyethylene. This rate can be measured by weighing samples at regular intervals or by using sensors that track the diffusion of water into the pellet.
Hydrolytic Risk
Chemical reactions between water molecules and the polymer backbone lead to a permanent loss of molecular weight. For materials with high moisture sensitivity, this hydrolysis happens at the high temperatures found inside a moulding barrel. The resulting parts will have poor impact strength and may show surface defects like splay marks and bubbles.
Processing Environment
Controlled conditions in the warehouse and the production hall are necessary to manage the risks associated with water uptake. Dealing with moisture sensitivity requires the use of desiccant dryers that can reach a dew point of minus 40 degrees Celsius. These systems must be regularly maintained to ensure they are removing enough water to keep the resin below the maximum allowable moisture level for the specific moulding application.
Failure to control this variable is the most common cause of brittle failures in engineering grade plastics.
