Meaning
The reduction in the average chain length of polymer molecules caused by thermal or mechanical stress during processing alters the mechanical properties of the finished product. In resin supply and component manufacturing contracts, molecular weight degradation represents a critical quality risk that must be monitored to ensure the long-term durability of plastic parts. This phenomenon occurs when excessive melt temperatures or high shear rates break the covalent bonds of the polymer backbone.
Processing Safeguard
Maintaining low moisture levels in the raw resin before extrusion or molding is essential to prevent hydrolytic degradation. Dryers are used to remove moisture to within strict parts-per-million limits specified by the resin manufacturer. Processors must document these drying times and temperatures to prove compliance with processing guidelines.
Mechanical Impact
A decrease in the polymer chain length directly reduces the impact strength and tensile properties of the molded component. When molecular weight degradation occurs, the product becomes brittle and susceptible to premature failure under stress. This degradation can be detected through melt flow rate testing or gel permeation chromatography.
Liability Allocation
Supply contracts for polymer components specify the maximum allowable change in melt flow index between the raw resin and the finished part to control for processing damage. If a batch of components fails due to brittleness, testing of the polymer chain length determines whether the failure resulted from poor resin quality or improper processing by the molder. When the molder exceeds the recommended melt temperature, they must bear the cost of the replacement parts and any associated recall expenses.
This clear division of responsibility protects both the resin supplier and the OEM from bearing the financial consequences of the other’s processing errors.
