Melt Flow Index (MFI)
Calculate the melt flow index (MFI), MFI = (mass × 600) ÷ time, from the mass of polymer extruded (g) and the extrusion time (s), normalizing to the mass that flows in 10 minutes. The result, in g/10min, measures how easily the molten polymer flows under standardized load and temperature (plastometer test). High MFI indicates a low-viscosity, low-molar-mass polymer, easy to inject; low MFI indicates high viscosity, high molar mass, better for extrusion and blow molding. It is the most used quality control parameter in the plastics industry. Enter the extruded mass and the time.
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Melt flow index (MFI)
The melt flow index (MFI, also reported as MFR) is the simplest, quickest and most widespread test for characterizing a thermoplastic in industry. The principle: the polymer is heated until it melts inside a standardized barrel (the plastometer), a defined weight is applied to a piston, and the mass of molten plastic extruded through a calibrated die over a set time is measured. The result is normalized to the mass that would flow in 10 minutes: MFI = (mass × 600) ÷ time (the 600 converts seconds into tenths of an hour), giving the index in g/10min. MFI is, in essence, an inverse measure of melt viscosity — and therefore of the molar mass of the polymer. A high MFI means a thin melt that flows easily: it points to a low molar mass polymer, ideal for injection molding (it fills complex molds readily) and fiber spinning. A low MFI means a viscous melt of high molar mass: better for profile extrusion, bottle blowing and film (where the melt needs enough strength to survive being stretched without tearing). Every commercial polymer grade comes with its MFI specified, and the process engineer picks the grade to suit the conversion technique. MFI also serves in quality control: index drift between batches betrays changes in molar mass or degradation of the material. Worth noting: MFI is a single-point measurement at one (low) shear rate, so it does not capture the full rheological behavior — but its simplicity made it the universal yardstick for comparing thermoplastics. Enter the extruded mass and the extrusion time.
Related Tools
Intrinsic Viscosity (Mark-Houwink)
Calculate a polymer's intrinsic viscosity by the Mark-Houwink-Sakurada equation, [η] = K·Mᵃ, from the constants K and a (specific to the polymer-solvent-temperature system) and the viscosity-average molar mass M. The result, in dL/g, relates the viscosity of a dilute polymer solution to its molar mass — the basis of molar mass determination by viscometry, a simple and cheap technique. The exponent a (between 0.5 and 0.8) reflects the chain conformation in the solvent: 0.5 for a theta solvent (coiled chain) and up to 1.0 for an extended chain in good solvent. Enter the constants K, a and the molar mass.
Viscosity Index (VI)
Calculate the viscosity index (VI) of a lubricating oil, VI = (L − U) ÷ (L − H) × 100, from the reference kinematic viscosities L and H (of VI-0 and VI-100 standard oils with the same viscosity at 100 °C) and the oil's viscosity U at 40 °C. The dimensionless result measures how much the oil's viscosity changes with temperature: a high VI means little change (good lubrication both cold and hot), desirable in multigrade automotive and hydraulic oils. A low VI means an oil that thins greatly when heated. Enter the viscosities L, U and H.
Polydispersity Index (PDI)
Calculate a polymer's polydispersity index (PDI), PDI = M_w ÷ M_n, dividing the weight-average molar mass (M_w) by the number-average molar mass (M_n). The dimensionless result (always ≥ 1) measures the breadth of the molar mass distribution: PDI = 1 means a monodisperse polymer (all chains the same size, rare, typical of living polymers); larger values mean a wide range of sizes. Commercial polymers have PDI of 2 to 20, depending on the polymerization process. PDI affects processability, strength and flow properties. Enter M_w and M_n.
Ideal Diameter of Hardenability (ASTM A255)
Computes the Grossmann ideal diameter D_I using the calculated hardenability method of ASTM A255: it starts from the carbon base diameter, D_I = 0.54·√(%C) inches for ASTM grain size No. 7, and multiplies it by the alloy factors (1 + 3.3333·Mn)·(1 + 0.7·Si)·(1 + 2.16·Cr)·(1 + 0.363·Ni)·(1 + 3.0·Mo). The result, already converted to millimetres, is the bar diameter that would still quench to 50 % martensite at its centre in an ideal cooling medium — that is, the index ranking steels by hardening DEPTH, not by peak hardness, which depends almost only on carbon. Because the factors are multiplicative rather than additive, 1 % manganese alone multiplies hardenability by 4.33 while the same 1 % nickel raises it by just 36 % — the order of potency is manganese, molybdenum, chromium, silicon and nickel, and it is why nickel earns its place in engineering steels through toughness rather than hardenability. One reading caveat: D_I is the diameter that would through-harden in an ideal quench of infinite severity — in oil the real critical diameter lands between a third and a half of it. The manganese factor holds up to 1.2 %, beyond which the standard switches expression, and the page rejects it from there on. Enter the carbon, manganese, silicon, chromium, nickel and molybdenum contents.
CBR — California Bearing Ratio
Calculates a soil's CBR by comparing the pressure measured in the penetration test against the standard crushed stone: 6.9 MPa at 2.54 mm and 10.3 MPa at 5.08 mm. By the standard the HIGHER of the two governs, not just the 2.54 mm one — the trap that shows up most often in subgrade reports. Enter both measured pressures.
Paper Tear Index
Compute the paper tear index, index = tear force (mN) / grammage (g/m²), in mN·m²/g, normalizing the tear resistance by the grammage. Tearing depends greatly on fiber length (long fibers resist more) — which is why packaging papers use long softwood fibers. It is a property that often competes with tensile (more refining raises tensile but lowers tear). Enter the tear force and the grammage.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.