Meaning
Physical transition of entangled polymer coils into a linear or less restrictive state occurs when thermal energy or shear forces overcome intermolecular attractions. During the melting phase of injection moulding, chain disentanglement reduces the viscosity of the melt by allowing long molecules to slide past one another. This state defines the flow characteristics of the resin as it enters the runner system.
It determines the minimum pressure required to fill thin-walled sections of a mould.
Flow Dynamics
Shear rate is the primary driver of molecular alignment in the barrel. Rapid movement through the nozzle forces the polymer into a highly oriented state. This orientation allows for faster cycles but can introduce residual stress in the finished part.
Thermal Interaction
Excessive melt temperatures accelerate the rate at which chains move away from their resting state. If the temperature exceeds the processing window of the specific grade, the polymer may suffer permanent molecular weight loss. This degradation is distinct from the temporary reorganization of physical entanglements.
Molding Outcome
Part shrinkage often results from the chains attempting to return to a coiled state during the cooling phase. Moulders must balance the ease of flow provided by a disentangled melt against the dimensional stability of the cooled component.
