Melt Flow Figures Quoted without Their Load and Temperature
An unconditioned melt flow value lacks physical meaning without its test load, temperature, and standard protocol specified.
Activation Energy of Flow
Meaning
Rheological parameter quantifying the thermodynamic energy barrier that polymer chains must overcome to flow under shear at elevated temperatures. High values for activation energy of flow indicate that melt viscosity shifts sharply with small changes in barrel temperature, whereas low values describe polymers whose flow behavior remains stable across a wide temperature window. This property governs process window selection during injection moulding and profile extrusion.
The measurement stops applying when thermal degradation breaks the polymer chain or when shear rates induce severe non-Newtonian shear thinning that masks temperature effects.
Viscous Sensitivity
Polymer chains with rigid backbones require substantial thermal energy to slide past one another in a melt stream. Polycarbonate and branched polymers exhibit high activation energy of flow, meaning slight thermal drops during runner transit cause sudden viscosity spikes that cause short shots. Polyolefins possess lower values, keeping melt viscosity relatively consistent even during minor temperature drifts.
Melt Temperature
Processing window boundaries depend heavily on how melt viscosity responds to barrel heat inputs. Adjusting barrel zones changes polymer flow significantly when activation energy of flow is high, enabling precise fill control without increasing injection pressure. Moulders processing temperature-sensitive resins utilize higher injection speeds rather than increased heat to avoid thermal degradation while maintaining low melt viscosity.
Rheological Margin
Datasheets list viscosity values at specific temperatures, but processing conditions inside a production tool fluctuate continuously. High activation energy of flow narrows the acceptable processing window, increasing part variance whenever nozzle temperatures drift by even a few degrees. Tool designs must incorporate uniform cooling and balanced runner channels to prevent localized flow hesitation.