Meaning
Published standard protocols govern the single-point rheological characterization of thermoplastic materials under standardized thermal and loading conditions. Specified under international testing guidelines, iso 1133 melt flow quantifies the extrusion rate of molten polymer through a standardized die under a specified weight and temperature. The test produces two core values, namely melt mass-flow rate measured in grams per ten minutes and melt volume-flow rate measured in cubic centimetres per ten minutes.
Higher values indicate lower molecular weight and lower melt viscosity.
Viscosity Rheology
Extrusion rate under static load reflects average polymer chain length and melt fluidity. Standard testing for iso 1133 melt flow applies a low shear rate that correlates with capillary rheology only at low shear levels. Polymer shear thinning behavior during high-velocity injection moulding causes actual cavity viscosity to drop far below predictions based on melt index.
Thermal degradation during processing breaks polymer chains and artificially elevates output rates.
Extrusion Drift
Resin consistency during processing depends on steady flow properties across incoming material lots. Unstable iso 1133 melt flow in virgin or regrind feedstock produces flash in high-pressure mould cavities or short shots when viscosity spikes. Regrind containing thermal degradants increases flow variability across a production shift.
Moulding technicians adjust holding pressure and barrel temperature profiles when melt index values drift.
Standard Boundary
Single-point testing provides quality control metrics but fails to describe complete non-Newtonian flow curves. An iso 1133 melt flow measurement does not record elastic recovery, die swell or high shear rate behavior encountered inside runner systems.
