Meaning
Water formed as a result of a chemical reaction during the processing or testing of a polymer. Condensation reactions and certain types of thermal degradation frequently produce these unwanted molecules. Side-product water is distinct from absorbed moisture because it is generated in situ rather than being taken up from the environment.
Chemical Origin
Polyamides and polyesters can release water if the polymerization reaction continues during the melt phase. This typically happens when the material is held at high temperatures for an extended period, such as in a stalled extrusion line. The presence of this water then accelerates further hydrolytic scission of the polymer chains.
Analytical Confusion
Karl Fischer titration measures this generated water alongside the actual moisture content of the resin. If the titration temperature in an oven evaporator is set too high, the polymer may begin to degrade and produce water during the test. This results in a false high reading that does not reflect the state of the resin before it entered the lab.
Process Management
Stabilizers and chain extenders are added to some resins to suppress the reactions that produce side-product water. Controlling the residence time in the barrel also limits the extent of these secondary chemical pathways. Moulders must distinguish between surface moisture and reaction water to properly diagnose the cause of bubbles or splay in their parts.
