ASTM D5422-00
(Test Method)Standard Test Method for Measurement of Properties of Thermoplastic Materials by Screw-Extrusion Capillary Rheometer
Standard Test Method for Measurement of Properties of Thermoplastic Materials by Screw-Extrusion Capillary Rheometer
SCOPE
1.1 This test method covers the use of a screw-extrusion-type capillary rheometer for the measurement of flow properties of thermoplastics and thermoplastic compounds. The measured flow properties, which are obtained through laboratory investigation, may help to describe the material behavior that occurs in factory processing.
1.2 Since a screw-type capillary rheometer imparts shear energy to the material during testing, the measurements will usually differ from those obtained with a piston-type capillary rheometer (see Test Method D3835).
1.3 Capillary rheometer measurements for thermoplastics and thermoplastic compounds are described in Test Method D3835.
1.4 The values stated in SI units are to be regarded as standard.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
Note 1--There is currently no equivalent ISO standard.
General Information
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Standards Content (Sample)
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Designation: D 5422 – 00
Standard Test Method for
Measurement of Properties of Thermoplastic Materials by
Screw-Extrusion Capillary Rheometer
This standard is issued under the fixed designation D 5422; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
This test method uses capillary rheometry to measure the rheological properties of thermoplastics
and thermoplastic compounds. This test method utilizes a screw-extrusion-type capillary rheometer.
1. Scope * Polymeric Materials by Means of a Capillary Rheometer
1.1 This test method covers the use of a screw-extrusion-
3. Terminology
type capillary rheometer for the measurement of flow proper-
3.1 Definitions (See Terminology D 883) :
ties of thermoplastics and thermoplastic compounds. The
3.1.1 apparent shear rate (g˙ )—shear strain rate (or veloc-
a
measured flow properties, which are obtained through labora-
ity gradient) of the thermoplastic or thermoplastic compound
tory investigation, may help to describe the material behavior
extrudate as it passes through the capillary die.
that occurs in factory processing.
3.1.1.1 Discussion—This velocity gradient is not uniform
1.2 Since a screw-type capillary rheometer imparts shear
through the cross-section of the capillary die. The shear rate is
energy to the material during testing, the measurements will
calculated for the region of highest shear, which is at the wall
usually differ from those obtained with a piston-type capillary
of the capillary. By selecting a die diameter and controlling the
rheometer (see Test Method D 3835).
volume flow per unit time through the die, a specific level of
1.3 Capillary rheometer measurements for thermoplastics
apparent shear rate may be achieved. Alternately, the shear
and thermoplastic compounds are described in Test Method
stress (entrance pressure) may be controlled, and the apparent
D 3835.
shear rate measured.
1.4 The values stated in SI units are to be regarded as
3.1.1.2 Discussion—Mathematically, the apparent shear
standard.
rate at the wall of the capillary for a Newtonian fluid at the
1.5 This standard does not purport to address all of the
capillary wall is given by the following:
safety concerns, if any, associated with its use. It is the
32 · Q
responsibility of the user of this standard to establish appro-
g˙ 5 (1)
a 3
priate safety and health practices and determine the applica-
p · D
bility of regulatory limitations prior to use.
where:
−1
NOTE 1—There is currently no equivalent ISO standard.
g˙ = apparent shear rate, s ,
a
Q = quantity of fluid extruded per time, mm /s,
2. Referenced Documents
p = 3.142, and
2.1 ASTM Standards:
D = diameter of the measuring capillary, mm.
D 618 Practice for Conditioning Plastics for Testing
3.1.2 apparent shear stress (t )—the measured resistance to
a
D 883 Terminology Relating to Plastics
the flow through a capillary die. It may be determined by
D 1238 Test Method for Flow Rates of Thermoplastics by
measuring the die entrance pressure for a specific die, then
Extrusion Plastometer
applying appropriate geometric factors.
D 3835 Test Method for Determination of Properties of
3.1.2.1 Discussion—Mathematically, apparent shear stress
is given by the following:
P
t 5 (2)
a
4· L/D
~ !
This test method is under the jurisdiction of ASTM Committee D20 on Plastics
and is the direct responsibility of Subcommittee D20.30 on Thermal Properties.
Current edition approved Nov. 10, 2000. Published February 2001. Originally
published as D 5422 – 93. Last previous edition D 5422 – 93.
2 3
Annual Book of ASTM Standards, Vol 08.01. Annual Book of ASTM Standards, Vol 08.02.
*A Summary of Changes section appears at the end of this standard.
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NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 5422
using two or more dies of different length, but of the same
where:
diameter (and thus the same apparent shear rate, as calculated
t = apparent shear stress, Pa,
a
P = pressure at the entrance of the measuring capillary, in 3.1.4.2). If the data from these additional dies are compared,
either graphically or mathematically, a linear relationship of
Pa,
L = length of the measuring capillary, mm, and extrusion pressure with die geometry is usually obtained in the
D = diameter of the measuring capillary, mm.
following form:
3.1.3 apparent viscosity (h )—ratio of apparent shear stress
a
L
P 5 c · 1 E (4)
F G
to apparent shear rate, Pa·s.
D
3.1.3.1 Discussion—For an extrusion capillary rheometer,
the ratio is usually calculated at a given shear rate. At constant
where:
temperature, the apparent viscosity of most polymers is not
E = the Bagley Correction Factor. (This term is often
constant, but varies with shear rate. The viscosity is generally
called “end effect.” It is expressed as the equivalent
annotated with the shear rate at which the measurement was
length of capillary necessary to extrapolate the
made.
pressure-line value on the P versus L/D plot to zero,
3.1.4 capillary rheometer—an instrument in which thermo-
mm.)
plastics or thermoplastic compounds can be forced from a
c = slope of the line.
reservoir through a capillary die. The temperature, pressure
entering the die, and flow rate through the die can be controlled
The Bagley Correction Factor (E) and the slope (c) are
and accurately measured.
functions of the thermoplastic compound and the shear rate.
3.1.5 corrected shear rate (g˙ )—the actual shear rate at the
w
Corrected shear stress is therefore as follows:
wall of the capillary die determined by applying the Rabinow-
−1
P
itsch correction for non-Newtonian materials, s .
t 5 (5)
w
4· @~L/D! 1 E#
3.1.5.1 Discussion—The Rabinowitsch correction math-
ematically adjusts the shear-rate values to compensate for 3.1.6.4 Discussion—Each value of corrected shear stress
non-Newtonian behavior of the polymer. To obtain corrected must be annotated with the shear rate with which it is
shear rate, at least two measurements of apparent shear stress measured.
and apparent shear rate are made. This is generally accom- 3.1.7 corrected viscosity (h)—the ratio of corrected shear
plished by increasing the rate of extrusion (Q) while using the stress to corrected shear rate, Pa·s.
same measuring capillary. 3.1.7.1 Discussion—Since both the material properties and
3.1.5.2 Discussion—As a first step, the Bagley correction the correction equations are functions of shear rate, it is very
(as stated in 3.1.6) is made to the shear-stress values. Then, important to state the particular value of shear rate at which
either by algebraic means (if only two measurements are each measurement is made.
made), or by a regression method (for a greater number of 3.1.7.2 Discussion—Other corrections to measured values
points), the equation in 3.1.11 is solved for n, using the are often made in rheological research studies to compensate
corrected shear stress (t ). for the effects of pressure, viscous heating, compressibility,
w
3.1.5.3 Discussion—The corrected shear rate (g˙ ) is deter- time effects, etc. The terms “true shear stress,” “true shear
w
mined by the following: rate,” and “true viscosity” are often used for the results of such
exhaustive calculations. This test method addresses only the
3 1 1
n
g˙ 5 · g˙ (3)
F G
w a two most important corrections, Bagley and Rabinowitsch.
n
3.1.8 die entrance pressure (P)—the pressure in the reser-
For most thermoplastics and thermoplastic compounds, the magni-
voir at the die entrance.
tude of shear sensitivity (n) will vary, depending on material compo-
3.1.9 newtonian fluid—a material for which the measure-
sition.
ment of viscosity is not changed by changing the shear rate.
3.1.6 corrected shear stress (t )—the actual shear stress at
W
Simple liquids, such as water, are considered Newtonian
the wall of the capillary die, Pa. The corrected shear stress is
whereas most polymeric materials are not.
obtained by applying the Bagley Correction Factor (E)tothe
3.1.10 power-law fluid—a material for which the viscosity
apparent shear stress (see 3.1.7.1 and 3.1.7.2). The Bagley
varies with the shear rate in accordance with the following
correction compensates for energy losses at the entrance and
known relationship:
exit of the die.
n
t 5 K· ~g˙ ! (6)
a a
3.1.6.1 Discussion—This correction is often applied as
though it were an additional length of capillary. The correction
where:
is often termed “end effect.” Capillary entrance angle and
t = apparent shear stress, Pa,
a
−1
geometry have great influence on the magnitude of this
g˙ = apparent shear rate, s ,
a
correction.
K = a material constant, often called “consistency index,”
3.1.6.2 Discussion—The Bagley correction will also re- and
move the influence of any static pressure in the system that n = shear sensitivity, dimensionless.
does not vary with die length. Most non-Newtonian fluids follow this relationship for at
3.1.6.3 Discussion—Since the magnitude of correction is a least short ranges of the shear rate variable. The power-law
function of shear rate, data for this correction are obtained by equation is generally used in its logarithmic form as follows:
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 5422
log ~t ! 5 log ~K! 1 n ~log ~g˙ !! (7)
raw-polymer molecular properties, but will also be affected by
a a
the type and amount of filler, additive, plasticizer, or stabilizer,
3.1.11 shear sensitivity (n)—a dimensionless material pa-
by the type of copolymer blend, and by the addition of other
rameter, also called the “power-law index,” that represents the
compounding materials. This test method can serve as a
magnitude of the shear sensitivity of a polymer. It is equal to
quality-control tool for either incoming materials or for in-
1.00 for Newtonian fluids, and generally less than 0.8 for
house quality-assurance checks on production mixing. This test
non-Newtonian fluids.
method is useful to the research and development of new
3.1.11.1 Discussion—Mathematically, the shear sensitivity
products in that the rheological behavior of a yet uncharacter-
is given by the following:
ized thermoplastic or thermoplastic compound can be mea-
d log~t !
w
sured and considered for comparative analysis.
n 5 (8)
d log ~g˙ !
a
6. Interferences and Precautions
where:
6.1 Since the flow properties of non-Newtonian materials
d log (t ) = the change in log corrected shear stress over
w
are not linear, capillary rheometers should be operated at
varying extrusion rates, and
conditions of flow (temperature, pressure, and rate) similar to
d log (g˙ ) = the change in log apparent shear rate over
a
those of selected commercial processes. These processes in-
varying extrusion rates.
clude mixing, calendering, molding, and extrusion of thermo-
4. Summary of Test Method
plastics and thermoplastic compounds.
4.1 The thermoplastic material is fed into a laboratory 6.2 Screw-extrusion-type rheometers impart significant
extruder, the barrel of which is equipped with a temperature amounts of energy to the thermoplastic or thermoplastic
control. The output end of the extruder is equipped with a compound before the measurement is made. Interpretation of
capillary die containing an insert of specified dimensions. the data for factory operations such as production extrusion,
Temperatures of the extruder barrel and capillary die are calendering, or injection molding is therefore more straightfor-
normally kept constant. (It may be necessary to alter the die-set ward than for compression-molding operations, where factory-
temperature only to compensate for shear heating of the work input is quite small.
material at different extrusion rates.) 6.3 Increasing the rate of extrusion will induce shear heat-
4.2 A suitable pressure transducer and temperature- ing, and therefore may alter the temperature of the material
measuring device, such as a thermocouple, are positioned in flowing through the capillary die. It is essential to maintain a
constant melt temperature in the die in order to perform
the die just before the entrance to the insert.
4.3 The rate of material extrusion, or mass throughput (Q)is accurate viscosity measurements. It may be necessary to
compensate for shear heating by manually adjusting the
determined by collecting extrudate over a timed interval and
then weighing it. Extrusion rate may be controlled by adjusting die-heater set temperature.
6.4 Extruder residence time and shearing actions at a
the drive speed.
4.4 In order to calculate the flow properties of the material, particular melt temperature may often affect a material’s
viscosity. It is recommended that consideration be given to the
extrusion is performed at a minimum of two different drive
speeds through an insert of specified dimensions (Die A). Then, temperature and shear-stability characteristics of each thermo-
plastic or thermoplastic compound before using this test
extrusion is performed again, at the same drive speeds, through
at least one additional die insert of different specified dimen- method.
sions (Die B or Die C).
7. Apparatus
4.5 This procedure allows for the determination of apparent
7.1 A schematic diagram of a screw-extrusion capillary
shear rate, apparent shear stress, apparent viscosity, corrected
rheometer is shown in Fig. 1. Only those parts essential to the
shear stress, corrected shear rate, corrected viscosity, shear
measurement are depicted. Suitable supports, drive compo-
sensitivity, and entrance/exit effects.
nents, and fixtures, such as devices for securing the die to the
5. Significance and Use
barrel are essential, but are not shown.
5.1 This test method is useful for the characterization of 7.2 The screw-extrusion system controls both the rate of
thermoplastics and thermoplastic compounds, in terms of extrusion and the temperature of the stock at the die entrance.
viscosity, or resistance to flow. 7.2.1 A single-screw-type laboratory extruder having a bar-
5.2 The data produced by this test method has been found rel diameter of not greater than 31.7 mm nor less than 19 mm
useful in both quality-control testing and compound develop- is recommended. The length to diameter (L/D) ratio of the
ment. However, direct correlation with factory condi
...
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