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Polyamide viscosity measurement methods

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Different ways to express the molecular weight of polyamides

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Polyamide viscosity measurement methods

  1. 1. Viscosity of polyamides Ted Brink
  2. 2. Page  2 Effects of molecular weight The molecular weight of a polymer influences: • melt viscosity (flow behaviour) • processing behaviour • mechanical properties • crystallization behaviour • optical properties
  3. 3. Page  3 Methods to measure molecular weight • Melt viscosity as a function of shear rate • MFI (Melt Flow Index) • MVR (Melt Volume Rate) • RSV (Relative Solution Viscosity) • VN (Viscosity Number) • GPC (Gel Permeation Chromatography) • SEC (Size Exclusion Chromatography)
  4. 4. Page  4 MFI and MVR Disadvantages for polyamide characterization: • moisture sensitivity • polymer reactivity Units: • MFI in g/10 min • MVR in cm3/10 min Capillary ( D = 2.0955 mm, L = 8.000 mm ) Barrel ( D = 9.5504 mm ) Piston ( D = 9.4742 mm ) Temperature Control ( ± 0.2oC ) Thermometer or PRT ( ± 0.1oC ) Load (Wt + Piston = ± 0.5% )  Standardized test (ASTM D1238, ISO 1133)  Constant load test  Fixed die diameter  Fixed die L/D ratio  Mass / time measured  MFR  1/Viscosity  May be related to, but is not a strict function of Mw
  5. 5. Page  5 Limitations of MFI measurement 100100010000 0.01 0.1 1 10 100 1000 γ η Two types of materials with the same MFI value but completely different rheological behavior Hygroscopic and chemical character of PA6 influence accuracy of measurement melt index conditions A B
  6. 6. Page  6 RSV and VN according to ISO 307 • solvents used: - 90 % formic acid - 96 % sulphuric acid - 100 % m-cresol - others • concentration 1 g polymer/100 ml • measured at 25 °C • Ubbelohde capillary RSV = Tsolution/Tsolvent VN = (Tsolution/Tsolvent)/c
  7. 7. Page  7 GPC/SEC 0 5 10 15 20 25 15 20 25 30 35 Ve (ml) RawRIsignal(mV) 0 0.2 0.4 0.6 0.8 1 1.2 3 3.5 4 4.5 5 5.5 6 LogM dw/dLogM
  8. 8. Page  8 Methods to express molecular weight η0 at 260 °C MFI at 250 °C Mn Mw VN RSV H2SO4 RSV HCOOH Pa.s g/10 ‘ g/mol g/mol cm3/g 1070 7.7 18000 35000 197 3.3 3.0 1280 7.1 20000 40000 210 3.6 3.2 2600 3.3 22000 47000 245 4.0 3.6
  9. 9. Page  9 Relation MFI and RSV (in formic acid) 0 10 20 30 2 2.5 3 3.5 4 Meltflowindex[g/10min] Relative solution viscosity in formic acid MFI measured at 235 °C and 2.16 kg
  10. 10. Page  10 Contact Ted Brink tel.: +31 (0) 651109899 email: ted.brink@extrusionist.com internet: www.extrusionist.com
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    May. 24, 2014

Different ways to express the molecular weight of polyamides

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