| Test | Standard | What It Measures | Key Specification Use |
|---|---|---|---|
| Melt Flow Index (MFI/MFR) | ISO 1133 / ASTM D1238 | Melt viscosity (inverse of MW) at defined T and load | Grade matching, processability, QC incoming |
| Tensile strength & elongation | ISO 527 / ASTM D638 | Stress at yield and break, elongation at break | Structural applications, packaging film |
| Flexural modulus | ISO 178 / ASTM D790 | Stiffness in bending — resistance to deformation | Structural parts, rigid containers |
| Charpy impact (notched) | ISO 179 | Energy to fracture under pendulum impact | Toughness assessment — packaging, automotive |
| Izod impact (notched) | ISO 180 / ASTM D256 | Energy to fracture under cantilever impact | Toughness — US-standard applications |
| Heat Deflection Temp (HDT) | ISO 75 / ASTM D648 | Temp at which standard load causes defined deflection | Heat-resistant applications |
| Vicat Softening Point | ISO 306 / ASTM D1525 | Temp at which needle penetrates surface | Similar to HDT, used for softer materials |
| Shore Hardness (A or D) | ISO 868 / ASTM D2240 | Surface resistance to indentation | Elastomers (A), rigid plastics (D) |
| Density | ISO 1183 / ASTM D792 | Mass per unit volume | Grade identification, blend composition check |
| UL94 Flammability | UL 94 | Flame spread, drip behaviour, self-extinguishing | Electrical, construction, automotive applications |
Melt Flow Index (or Rate) is the test most commonly used in polymer procurement — and most commonly misinterpreted. MFI is always measured at a specific temperature and load: PP at 230°C/2.16 kg; PE at 190°C/2.16 kg; PC at 300°C/1.2 kg; ABS at 220°C/10 kg. Results from different conditions are completely non-comparable. An ABS with MFI 22 at 220°C/10 kg is not comparable to a PP with MFI 22 at 230°C/2.16 kg. Always quote the full test condition when specifying MFI in a procurement document or specification.
MFI is also a single-point measurement at one shear rate — it cannot characterise shear thinning behaviour, molecular weight distribution breadth, or elastic recovery. Two grades with identical MFI but different MWD can process very differently on the same equipment. For applications where processing stability and product quality are critical (film, pipe, precision moulding), request High Load MFI (HLMI) or the Melt Viscosity Ratio (MVR) curve in addition to standard MFI.
Charpy (ISO 179) and Izod (ISO 180) both measure impact energy — but with different specimen geometry, support configuration, and notch placement, giving different absolute values for the same material. They are not interchangeable and should never be compared directly. More importantly: notched vs unnotched impact values can differ by 10–100x for tough polymers. Notched impact is more sensitive to material brittleness and notch sensitivity — a much more discriminating test for detecting the transition between tough and brittle behaviour. Always specify the test standard, notch type (type A, B, or C in ISO 179/180), and test temperature when comparing materials.
Heat Deflection Temperature (ISO 75) is measured at two standardised loads: Method A at 1.80 MPa and Method B at 0.45 MPa. These give dramatically different results for semi-crystalline polymers — unfilled PA66 shows HDT(A) of ~90°C but HDT(B) of ~240°C. Glass-filled grades approach the polymer’s melting point at Method A. Always specify the load when quoting HDT, and always compare materials at the same load. Method A (1.80 MPa) is the more conservative and more discriminating test — use it for structural applications. Method B (0.45 MPa) is relevant where very low loads are applied at temperature.
| UL94 Rating | Burn Time (per 10-second flame) | Dripping Behaviour | Practical Meaning |
|---|---|---|---|
| HB | <76 mm/min burn rate | Drips permitted | Slow burning — minimum classification |
| V-2 | <30 seconds per flame application | Burning drips may ignite cotton | Self-extinguishing — drips can start fires |
| V-1 | <30 seconds per flame application | Non-flaming drips only — cotton not ignited | Self-extinguishing — controlled drips |
| V-0 | <10 seconds per flame application | No drips igniting cotton | Best standard UL94 — fast self-extinguishing |
| 5VA | <60 sec on plaque | No burnthrough of 3.2mm plaque | Highest UL94 — structural fire safety |
A material achieving V-0 at 3.2mm specimen thickness may only achieve V-2 at 1.6mm. Always specify and test at your actual production wall thickness. For FR compound selection for specific applications, see our flame retardant masterbatch guide and our engineering plastics comparison for FR grade details.
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