Meaning
The minimum kinetic energy required to initiate molecular flow or chemical degradation in a polymer matrix measures the sensitivity of the material to temperature changes. Thermoplastic resins require a specific amount of heat to overcome the intermolecular forces that restrict chain movement. This value of thermal activation energy determines how rapidly the melt viscosity drops as the processing temperature is increased.
Understanding this material property helps moulders select the optimal barrel temperature settings to ensure efficient flow without causing material degradation.
Flow Sensitivity
High values of the energy barrier mean that the resin viscosity will change dramatically with even minor adjustments to the barrel temperature. When thermal activation energy is high, a small temperature increase can make a stiff polymer flow easily. A moulder must maintain tight control over the heating zones to prevent these flow variations.
Degradation Susceptibility
Excessive heat input can overcome the activation energy for chemical bond scission, causing rapid reduction in molecular weight. When the thermal activation energy for degradation is low, the polymer is highly susceptible to overheating and chain scission during long residence times in the barrel. This degradation reduces the mechanical properties of the finished part, making it brittle and prone to failure under load.
Processor must balance the temperature settings to promote flow while staying well below the threshold for thermal degradation.
Material Specification
Resin datasheets often provide rheological data that allows the calculation of the energy required for molecular flow. Comparing this thermal activation energy between virgin and regrind resins shows how multiple processing steps affect the flow behavior of the material. Regrind resin often exhibits a lower energy barrier due to prior degradation, which requires adjustments to the moulding process parameters.
Tracking this property ensures that the selected material grade is suitable for the thermal conditions of the manufacturing run.
