Meaning
Chemical degradation process involving the loss of a carboxyl group and the release of carbon dioxide from a molecule. In polymer science, decarboxylation typically occurs during the thermal processing of polyesters and polyamides at elevated temperatures. Molecular weight and mechanical strength drop significantly when these chains break down.
Processing Impact
Heat and moisture act as catalysts for this reaction during the injection moulding or extrusion process. When CO2 is released inside the barrel, it can form gas bubbles that appear as splay or silver streaks on the surface of the part. This defect is a clear sign that the melt temperature is too high or the residence time is too long.
Material Degradation
Loss of carboxyl groups changes the chemical structure of the resin, often making it more brittle. This transformation is particularly problematic for recycled materials that have already undergone multiple heat cycles. The reduction in viscosity caused by chain scission makes the melt flow more easily but compromises the impact resistance of the finished component.
Analytical Detection
Titration methods for moisture analysis can be compromised by the presence of CO2 because it reacts with certain reagents. If decarboxylation happens inside a headspace oven, the released gas might be mistaken for moisture. Modern Karl Fischer systems use specific buffers to prevent this interference and ensure the reading reflects only the water content of the resin.
