Hydrolytic Scission

Molecular Breakdown

Water acts as a reactant at the elevated temperatures found in the injection moulding barrel. Each water molecule can break one ester or amide link, effectively cutting the long polymer chains into shorter segments. This process is nearly instantaneous at melt temperatures, making moisture control the most critical variable for these resins.

Physical Outcomes

Parts moulded from hydrolyzed resin show reduced impact strength and lower elongation at break. The melt viscosity also drops significantly, which might cause the material to drool from the nozzle or flash into the tool. These changes are irreversible and cannot be fixed by further drying of the already degraded material.

Economic Impact

Using regrind that has been previously hydrolyzed can contaminate entire batches of virgin resin. The resulting parts might pass visual inspection but fail prematurely in the field under stress. Careful drying verification and limit setting on regrind usage are essential to maintain the integrity of the finished product.