Meaning
Chemical degradation pathways break the backbone of condensation polymers through a reaction with water molecules. Ester hydrolytic scission is the process by which moisture cleaves the ester bonds in materials such as polyethylene terephthalate or polybutylene terephthalate. This reaction occurs at elevated temperatures typical of injection moulding or extrusion, converting the long polymer chains into shorter fragments.
The result is a reduction in molecular weight, which negatively impacts the mechanical properties of the finished part.
Mechanical Consequence
Physical strength decreases as the average length of the molecular chains shortens. Because ester hydrolytic scission destroys the structural integrity of the resin, parts may exhibit brittleness or premature failure under load. Impact resistance often drops long before any visual defect appears on the surface.
A moulder might notice that parts snap during ejection or fail in the field despite looking perfect.
Process Variable
Temperature and moisture concentration determine the speed at which the chemical bonds fail. While ester hydrolytic scission is a chemical event, its presence is dictated by the efficiency of the material drying process. Excess water in the melt provides the primary reactant.
High melt temperatures accelerate the cleavage, making precise thermal control as important as moisture control.
Economic Loss
Scrap rates increase when degraded material cannot meet the performance specifications of the end application. Avoiding ester hydrolytic scission requires a large investment in high performance desiccant dryers and airtight conveying systems. The cost of this equipment is offset by the reduction in rejected batches and the ability to maintain higher proportions of regrind.
Excessive degradation limits the number of times a material can be reprocessed without losing its functional utility.
