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Different ways to express the molecular weight of polyamides
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Viscosity of polyamides
Ted Brink
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
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)
Page 4
MFI and MVRDisadvantages for polyamidecharacterization:• 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 )
Thermometeror 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
Page 5
Limitations of MFI measurement
0.01 0.1 1 10 100 100010
01
00
01
00
00
γ
η
Two types of materials with the same MFI valuebut completely different rheological behaviorHygroscopic and chemical character of PA6 influence accuracy of measurement
melt indexconditions
A
B
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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/TsolventVN = (Tsolution/Tsolvent)/c
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GPC/SEC
0
5
10
15
20
25
15 20 25 30 35
Ve (ml)
Raw
RI s
ign
al (
mV
)
0
0.2
0.4
0.6
0.8
1
1.2
3 3.5 4 4.5 5 5.5 6
LogMd
w/d
Lo
gM
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Methods to express molecular weight
η0 at
260
°C
MFI at
250
°C
Mn Mw VNRSV
H2SO4
RSV
HCOO
H
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
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Relation MFI and RSV (in formic acid)
2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 40
10
20
30
Relative solution viscosity in formic acid
Melt
flow
in
dex [
g/1
0
min
]MFI measured at 235 °C and 2.16 kg
Page 10
Contact
Ted Brink
tel.: +31 (0) 651109899
email: [email protected]
internet: www.extrusionist.com
