NIST SPECIAL PUBLICATION 260-148

U. S. DEPARTMENT OF COMMERCE/Technology Administration 

National Institute of Standards and Technology 

Standard Reference Materials®

Certification of 

Standard Reference Material 1474a, 

A Polyethylene Resin 

 

J. R. Maurey, K. M. Flynn, and C. M. Guttman 
NIST Special Publication 260-148 

Standard Reference Materials®

Certification of Standard Reference Material 1474a, 

A Polyethylene Resin

J. R. Maurey, K. M. Flynn, and C. M. Guttman 

Polymers Division 

Materials Science and Engineering Laboratory

National Institute of Standards and Technology

Gaithersburg, MD 20899-8540 

U.S. DEPARTMENT OF COMMERCE, Donald L. Evans, Secretary

TECHNOLOGY ADMINISTRATION, Phillip J. Bond, Under Secretary of Commerce for Technology

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, Arden L. Bement, Jr., Director 

Issued November 2003 
Certain commercial equipment, instruments, or materials are identified in this paper in 

order to specify the experimental procedure adequately. Such identification is not intended 

to imply recommendation or endorsement by the National Institute of Standards and 

Technology, nor is it intended to imply that the materials or equipment identified are 

necessarily the best available for the purpose. 

National Institute of Standards and Technology Special Publication 260-148 

Natl. Inst. Stand. Technol. Spec. Publ. 260-148, 18 pages (November 2003) 

CODEN: NSPUE2

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WASHINGTON: 2003 

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iii 

Table of Contents 

Abstract ............................................................................................................................iv

1.0 Introduction................................................................................................................1

2.0 Experimental Procedure............................................................................................1

2.1 Sampling and Randomization of Charge Sequence of SRM 1474a .......................1

2.2 Instrument Calibrations and Alignment...................................................................1

2.2.1 Temperature Indication..........................................................................................1 

2.2.2 Metering of Plastometer Components ...................................................................2 

2.2.3 Alignment of Plastometer ......................................................................................2 

3.0 Melt Flow Rate of SRM 1474a....................................................................................3

4.0 Data Analysis on SRM 1474a ....................................................................................4

5.0 Uncertainty Estimates of Melt Flow Rate Data ........................................................4

5.1 Repeatability and Sampling Uncertainties...............................................................4

5.2 Charge-to-Charge Variability Within a Bottle ..........................................................5

5.3 Bottle-to-Bottle Variability.........................................................................................5

5.4 Day-to-Day Variability................................................................................................5

5.5 Operator-to-Operator Variability...............................................................................5

5.6 Systematic Uncertainties ..........................................................................................5

5.6.1 Instrument Variability.............................................................................................6 

5.6.2 Measurement Uncertainties...................................................................................6 

5.7 Combined Standard Uncertainty ..............................................................................9

5.8 Expanded Uncertainty ...............................................................................................9

6.0 Conclusions of Melt Flow Rate Study ......................................................................9

Acknowledgment ..............................................................................................................9

References.......................................................................................................................10

Tables ..............................................................................................................................11

Table 1 Estimates of Uncertainties in Melt Flow Rate of SRM 1474a Polyethylene 

Under Condition 190/2.16...............................................................................................11

Table 2 Variation of Temperature with Height in Undisturbed Melt in Cylinder Bore

..........................................................................................................................................12

Appendix: Certificate of Analysis, SRM 1474a.............................................................13 
iv

Abstract 

The melt flow rate of Standard Reference Material (SRM®) 1474a, a linear polyethylene 

(narrow MWD ethylene-hexene copolymer) resin, was determined to be 5.10 g/10 min at 

190 oC under a load of 2.16 kg using the ASTM Method D 1238-00. The average results 

from 45 determinations on samples with a standard deviation of 0.056 g/10 min. The 

overall expanded uncertainty, including type A and type B uncertainties, is estimated as 

0.42 g/10 min. 
1 

1.0 Introduction 

Melt flow rate is widely used in polymer technology as a product specification since this 

value, which includes a statement of the load and temperature under which it is obtained, 

gives an indication of the processing properties of the polymer(1-4). The value of melt 

flow rate is expressed as the mass of polymer melt pushed from the heated cylinder of the 

extrusion plastometer through its precision bore orifice by its piston in a period of time, the 

standard units of the value being grams per ten minutes (g/10 min). 

This is a report on the melt flow rate certification of Standard Reference Material (SRM®) 

1474a, a polyethylene resin. SRM 1474a is the designated successor to SRM 1474 the 

characterization of which was described in an earlier report (5). SRM 1474a is from a 

different material from a different supplier, but with a closely matched melt flow rate. 

2.0 Experimental Procedure 

2.1 Sampling and Randomization of Charge Sequence of SRM 1474a 

Material for SRM 1474a came as pellets of polyethylene. The supplier of this resin 

identifies the resin as narrow molecular mass distribution linear ethylene-hexene 

copolymer with an estimated density of 0.948 g/cm3

. The NIST Standard Reference 

Materials Group (SRMG) blended the resin and divided the pellets into 404 units of 60 g 

each. Fifteen of these units were chosen by stratified random selection for homogeneity 

and certification studies. Three charges were taken for extrusion from each of the 

randomly chosen bottled samples of SRM 1474a during the course of the melt flow rate 

experiments. In preparation for the melt flow rate determinations, the charges to be 

extruded were identified by ordinal numbers. Three such charge numbers were assigned 

to each identified sample. The sequence of numbered charges taken from the bottled 

samples for extrusion was randomized according to a procedure described by Natrella (6). 

2.2 Instrument Calibrations and Alignment 

2.2.1 Temperature Indication 

The temperature of the extrusion plastometer cylinder was measured by a mercury 

column thermometer of the form described in paragraph 5.7 of the ASTM method (7). 

Calibration of the thermometer is traceable to the Thermometry Group of the NIST 

Process Measurements Division. An iron-constantan thermocouple was calibrated by 

correlating its voltage with the scale readings of an ASTM 68 o

C thermometer at 10 points 

from 185 o

C to 194 oC, in a constant temperature oil bath. The ASTM 68 oC thermometer 

had been calibrated at the ice point and at 190 OC in the Thermometry Group of the NIST 

Process Measurements Division by means of a platinum resistance thermometer. The 

temperature indication by the scale of the cylinder thermometer in the extrusion 

plastometer was calibrated by correlating the thermometer scale readings with the 
2

temperature measured by the emf from the calibrated thermocouple with its hot junction 

stationed in a column of polyethylene melt in the bore, as described in paragraph 5.5.2 of 

the ASTM method. Thermal conductivity between cylinder and thermometer was 

enhanced by adding Wood’s metal to the thermometer well in the cylinder. The standard 

uncertainty in the final temperature indication may be regarded as equal to the nominal 

limit of resolution on the scales of the ASTM 68 o

C thermometer, and of the thermometer 

in the extrusion plastometer, 0.1 o

C. The effect of a 0.1 oC standard uncertainty in 

temperature on the melt flow rate of SRM 1474a is described in the subsequent section 

on uncertainty analysis. 

2.2.2 Metering of Plastometer Components 

Many dies and piston feet were obtained from Tinius Olsen Testing Machine Co.* so that 

during any given day, a different die and piston foot was used for each melt flow 

determination made on that day. Methods of cleaning the dies and piston feet were 

designed to avoid dimensional changes (see section 3.0). The geometric dimensions of 

the plastometer cylinder, piston feet, and dies were all measured and found to comply with 

the specifications described in the ASTM method. 

The diameter of the cylinder bore was determined by a Brown and Sharpe model 599-281 

Intrimik inner diameter (ID) micrometer. The ID of the bore was measured from the top to 

the bottom at one centimeter intervals. The top diameter measurement was made at a 

depth of 2 cm into the bore; the bottom diameter measurement was made with the 

micrometer head resting on a die at the bottom of the bore. The resulting measurements 

varied from (0.9548 to 0.9554) cm, in compliance with the tolerance of this specification 

described in paragraph 5.2 of the ASTM method. The apparent mass of the nominal 2060 

g load was determined in the Mass Group of the NIST Automated Production Technology 

Division, and found to be 2059.8 g. New detachable piston feet were used to conduct the 

extrusions; a different foot was used on the piston for each extrusion. The assembled 

piston varied in apparent mass from 100.027 g with the lightest foot attached, to 100.071 

g with the heaviest foot attached. Thus the calculated combined apparent mass of piston 

and load varied from 2159.83 g with the lightest foot attached to the piston, to 2159.87 g 

with the heaviest foot attached to the piston, both limits well within the 0.5 % tolerance 

described in paragraph 5.4.3 of the ASTM method (7). 

* Certain commercial materials and equipment are identified in this paper in order to specify adequately the 

experimental procedure. In no case does such identification imply recommendation or endorsement by the 

National Institute of Standards and Technology, nor does it imply necessarily the best available for the 

purpose. 

2.2.3 Alignment of Plastometer 

The cylindrical axis of the bore was aligned with the gravity vector by the following plumbline procedure. First, a die was selected as the "target" die and stationed on the structural 

base plate of the extrusion plastometer directly below the cylinder. Its position on the 

plane of the base plate was adjusted to have the axis of its bore coincide with the 
3

projection from the axis of the cylinder bore onto that plane. This was accomplished by 

viewing the target die through the bores of two "sighting" dies, one stationed at its 

operational position in the bottom end of the cylinder bore and the other stationed at the 

top end of the cylinder bore. The position of the target die on the plane of the base plate 

was adjusted until it appeared centered in the view from above the cylinder through the 

sighting dies in the cylinder bore. 

Next a plumb-bob was suspended by a plumb-line from the axis of a die supported in the 

top end of the cylinder bore, with the pointer of the suspended bob extending down to a 

level where the pointer was almost touching the top surface of the target die. The leveling 

screws were adjusted until the pointer of the plumb-bob appeared to be centered over the 

bore of the target die. 

The deviation of the plumb bob pointer was observed to be less than 1 mm from the point, 

which would indicate ideally vertical orientation of the cylinder bore, at the end of a 

pendulum length of 41 cm. Consequently, this procedure is considered to obtain 

alignment of the cylindrical axis of the cylinder bore with the gravity vector, with a 

calculated uncertainty of (1 mm/41 cm). Thus, the maximum uncertainty in terms of 

possible angle of displacement of the bore axis from the gravity vector is estimated as 

sin-1(1 mm/41 cm) = 0.14o

. It is estimated that such a maximum displacement in angle 

from the gravity vector would diminish the force of the loaded piston to a level of its total 

mass multiplied by cos (0.14o), or (2.16 kg)(0.999997) in the present case. This factor 

would thus diminish the effective mass of the loaded piston by a decrement of 3x10-4 %, 

incomparably less than the (+/-)0.5 % tolerance in combined mass of piston and load 

described in paragraph 5.4.3 of the ASTM method. Standard uncertainties cited in this 

report are considered equivalent to those corresponding to a 95 % level of confidence, as 

explained in the subsequent section on uncertainty estimates in the melt flow rate data. 

The initial bore alignment was conducted at ambient temperature in preparation for the 

characterization. The alignment was also occasionally tested, during the course of the 

characterization extrusions while the cylinder was hot, with a circular level which can be 

mounted atop the piston rod mounted in the bore, as described in the bore alignment 

section, Section 5.8 and Appendix X1 of ASTM method (7). 

3.0 Melt Flow Rate of SRM 1474a 

The melt flow rates of SRM 1474a samples were determined by procedure A described in 

Section 9 of ASTM Method D1238-00 (7). Standard test condition 190/2.16 was used. 

Thus the flow rate was determined at (190.0 ± 0.1) oC using a load of 2.16 kg. The flow 

rate of the melt was measured by a manually operated extrusion plastometer 

manufactured by the Tinius-Olsen Testing Machine Co. 

A 6.2 g charge of pellets was used for each extrusion. The end of the 7.0 min preheat 

period was marked as the beginning of timed test extrusion by making the initial extrudate 

cut at 7.0 min and discarding the preheat segment. (The reader should note that in 

previous certifications of melt flow rate a 6.0 min preheat was used. The 6.0 min preheat 

was allowed in ASTM D-1238 methods with a date before 1990. In the current methods a 

7.0 min preheat is prescribed with a range of (+/-) 0.5 min allowed.) It was also observed 
4

that the 4 mm start section of the piston had always entered the top of the guide collar 

part way at the moment of the initial cut to begin collecting timed test extrudate. Three 

timed test extrudate segments were cut at 1.0 min intervals thereafter. After the third 

timed test extrudate segment had been cut, the remaining melt in the cylinder was purged 

and discarded. Following ASTM D1238-00 only the first timed extrudate was used in the 

final data analysis for certification of SRM 1474a. The piston and bore were cleaned free 

of the polymer at the end of each extrusion. Many dies and piston feet were obtained 

from Tinius-Olsen Testing Machine Co. During a given day a different die and piston foot 

was used for each separate charge. The dies and piston feet were then cleaned in 

preparation for the next day’s run. Tools of brass and copper, considerably less hard than 

steel, were applied in the cleaning process. The use of steel tools was avoided in order to 

prevent changing dimensions of instrument components due to cleaning wear. Cotton 

gun cleaning patches and 38 caliber gun bore brushes with bronze bristles were used to 

clean the cylinder bore. The dies and piston feet were exposed to a vapor of boiling 

xylene for the final cleaning. 

Two operators were used in the operation of the equipment. Each operator made 

measurements on six extrusions (charges) on randomly chosen days. 

4.0 Data Analysis on SRM 1474a 

Data from 45 charges were analyzed for the 2.16 kg load following the ASTM Method 

D1238-00. The average melt flow rate of SRM 1474a was found to be 5.10 g/10 min with 

a standard deviation of 0.056 g/10 min with 44 degrees of freedom. This standard 

deviation includes bottle- to-bottle, charge-to-charge, operator-to-operator and day-to-day 

variability. The standard deviation of the mean was calculated to be 0.0083 g/10 min. 

Our estimates of systematic uncertainties in the measurement will be discussed in the 

following sections. 

5.0 Uncertainty Estimates of Melt Flow Rate Data 

The measurement uncertainties encountered in the process of determining the melt flow 

rate were determined or estimated in compliance with the NIST policy governing the 

reporting of uncertainties in measurement (8). The uncertainty due to instrument 

variability among the results from a large population of laboratories was derived from 

expected precision limits tabulated in the ASTM method description (7). 

5.1 Repeatability and Sampling Uncertainties 

In this section, the uncertainty will be discussed in terms of variations of the measured 

melt flow rate arising from sampling and bottling differences. 

For SRM 1474a, the standard deviation was 0.056 g/10 min for 45 melt flow rate 

determinations in a range from 4.95 g/10 min to 5.21 g/10 min. The standard uncertainty 

arising from the overall experimental extrusion repeatability is taken as the standard 

deviation of the mean of all the melt flow rate determinations, u = 0.0083 g/10 min. 
5

5.2 Charge-to-Charge Variability Within a Bottle 

As described in Section 2.1,15 bottles were selected for measurement from the original 

bottling. Three charges from each bottle were measured so a study of charge-to-charge 

variation within an individual bottle was easily performed. The mean charge-to-charge 

standard deviation of the melt flow rate value from charges removed from an individual 

bottle was 0.055 g/10 min, with a range from (0.0091 to 0.11) g/10 min. These data are 

not reported separately in Table 1, since this uncertainty is included in the relative 

standard uncertainty reported in line 1 of Table 1. 

5.3 Bottle-to-Bottle Variability 

The bottle-to-bottle variability was estimated from the population of all charges taken from 

all 15 bottles. The mean value of the melt flow rate for any bottle was found to lie within 

two standard deviations of the mean melt flow rate for all the charges. The mean of any 

bottle was not found to be significantly different at the 95 % confidence level from any 

other mean in the group. The bottle-to-bottle variability is not reported separately in Table 

1 since this uncertainty is included in the overall standard uncertainty reported in line 1 of 

Table 1. 

5.4 Day-to-Day Variability 

Six melt flow rate experiments could be conducted in a single day. The day-to-day 

variability was small compared to the charge-to-charge variability. The day-to-day 

variability is not reported separately in Table 1, since this uncertainty is included in the 

overall standard uncertainty reported in line 1 of Table 1. 

5.5 Operator-to-Operator Variability 

Six melt flow rate determinations could be conducted in a single day. On any one day a 

single operator used the instrument. The operator for any given day was chosen at 

random. A two-way ANOVA run comparing the two operators concluded the two 

operators were not different. This uncertainty is not reported separately in Table 1 since it 

is included in the overall standard uncertainty reported in line 1 of Table 1. 

5.6 Systematic Uncertainties 

Obtaining a systematic uncertainty analysis of the melt flow rate is a difficult matter since 

the melt flow rate is not a fundamental property of the material and there is no simple 

relationship describing its estimation. Nonetheless an effort shall be made in this section 

to estimate the uncertainties from their possible contributing sources, and their 

contribution to the combined uncertainty to be computed. 
6

5.6.1 Instrument Variability 

As noted before, the estimates of the measurements repeatability are in line 1 of Table 1. 

These data reflect the repeatability of the experiments and do not reflect any instrumentto-instrument variation since only one instrument was used. 

However, the results in Table 4 in ASTM D1238-00 (7) provide a means of estimating the 

uncertainty among the results from a large population of instruments and operators 

applying procedure A. For the purposes of this estimation for SRM 1474a with a melt flow 

rate of 5.10 g/10 min, the uncertainty data for the polyethylene using the same melt flow 

conditions with a melt flow rate of 2.04 g/10 min was used. The table of precision limits 

lists the within laboratory standard deviation of the average, Sr, and the between 

laboratory standard deviation of the average, SR, in addition to other related statistical 

parameters, all defined in ASTM Standard E 691-99, "Standard Practice for Conducting 

an Interlaboratory Study to Determine the Precision of a Test Method" (9). The standard 

deviation of the mean of an array of average melt flow rate results from a large population 

of laboratories can be derived from the SR given in the precision tables of ASTM D 1238-

00 by applying their relationship with the more fundamental standard deviation of the 

mean described in ASTM E 691-99. Thus a standard deviation of the mean of 

0.079 g/10 min was obtained for the average melt flow rate 2.04 g/10 min from its 

corresponding SR listed in Table 4 of ASTM D 1238-00. Assuming the measurement has 

the same percent standard deviation of the mean arising from this instrument variability, 

the uncertainty due to instrument variability in the results from a large population of 

laboratories is estimated as 0.20 g/10 min. This standard uncertainty due to instrument 

variability is also listed in Table 1 of this report. Predicated on statistical analysis of 

measurements from nine laboratories in a study coordinated by ASTM Committee D-20, 

this is a Type A uncertainty in the nomenclature described in NIST Technical Note 

1297(8). 

5.6.2 Measurement Uncertainties 

An effort was made to estimate the intrinsic uncertainty in the measurement. This was 

done by considering the uncertainties in the measured quantities (mass and time) as well 

as the uncertainties in the controlled quantities (temperature). The melt flow rate, F, is 

given by 

 F = Mass/Time 

Thus the relative standard uncertainty in the melt flow rate, δF/F, is then obtained as the 

root-sum-of-squares of the uncertainties in the systematic physical factors upon which the 

melt flow rate depends (8). 

 (δF/F)2

 = (δm/m)2 + (δt/t)2 + (cT δT/F)2. 

where the relative standard uncertainty in mass of extrudate is δm/m, δt/t is the relative 

standard uncertainty in timing of the extrudate cut and δT/T term arises from the 

uncertainty in the temperature control and in the calibration of temperature indication. The 

factor cT is the sensitivity coefficient, cT=(dF/dT). The causes of these uncertainties are 
7

discussed in the next few paragraphs. These uncertainties together with the other 

uncertainties are given in Table 1. An estimate of the combined standard uncertainty 

resulting from all sources is also given in Table 1. 

5.6.2.1 Weighing Uncertainty 

The extrudate segments were weighed on a balance with 0.1 mg resolution and an 

estimated uncertainty of 0.1 mg. Replicate weighings of the segments always agreed to 

within 0.1 mg. Paragraph 9.12 of ASTM Method D 1238-00 instructs the experimenter to 

"weigh the extrudate to the nearest 1 mg when cool." 

The extrudate segments were routinely weighed within one hour after having been cut, in 

compliance with the instruction in paragraph 9.12 of the ASTM method. Considering the 

hydrophobic character of polyethylene it would not be anticipated that the extrudate would 

accumulate moisture beyond the initial cooling stage prior to being weighed. On a few 

occasions during the characterization of another polyolefin, extrudate segments, which 

had been weighed at the end of a day, were weighed again on the following day without 

detecting any statistically valid change of mass within the groups. All individual changes, 

either positive or negative, did not exceed 0.1 mg. 

The extrudate mass was about 500 mg. With an estimated overall weighing uncertainty of 

 0.1 mg from the above sources, the relative standard uncertainty 

δm/m = 0.02 %. 

Since this weighing uncertainty appears negligible in comparison with larger uncertainties 

from other sources, the weighing uncertainty was taken to be zero. 

5.6.2.2 Timing Uncertainty 

The 1 min interval (t = 60 s) between extrudate cuts for SRM 1474a was measured with a 

battery powered stopwatch having a 0.01 s resolution in time indication and an uncertainty 

of less than 0.05 s. Thus the extrudate cut was assumed to be timed to better than 0.1 s. 

Consequently, 0.1 s is taken as a practical estimate of the timing uncertainty. Hence, the 

relative standard uncertainty in time interval may be expressed 

δt/t = 0.1 s/60 s = 0.17 % 

The timing uncertainty is taken as zero, since it appears negligible in comparison with 

larger uncertainties from other sources. 

5.6.2.3 Temperature Uncertainty 

As described in Section 2.2.1, the extrusion cylinder temperature was measured by a 

mercury column thermometer of the form described in paragraph 5.7 of the ASTM method 

D1238-00. The uncertainty of the thermometer is certified to be within the tolerances of 
8

the ASTM method, by comparison to standards traceable to NIST. The standard 

uncertainty in the temperature indication calibration is less than 0.1 oC. 

Paragraph 5.7 in the ASTM method acknowledges that the temperature in the 

thermometer well may not necessarily be the temperature of the polymer melt at the 

calibration point in the bore. This is due to the steady state heat transfer gradients in the 

plastometer cylinder. Thus, the thermal profile of an undisturbed column of polyethylene 

melt was scanned along the cylindrical axis of the cylinder bore while the temperature was 

maintained at 190.0 oC at the calibration point in the melt column. This experiment was 

conducted in another extrusion plastometer during an earlier determination of the melt 

flow rate of SRM 1475. The column of melt was held stationary by plugging the flow. The 

temperature in the stationary melt column was measured with a thermocouple hot junction 

stationed at different heights above the top surface of the die, along the cylindrical axis of 

the bore. Throughout the experiment the reading of the mercury column thermometer 

remained at (190.0 ± 0.1) oC. The results are listed in Table 2. 

Inspection of the tabulated results indicates that the departure of melt temperature from 

the measured cylinder temperature is within 0.1 oC at any location in the melt column from 

12 mm above the die upward. There is a 0.7 oC drop in temperature between the 12 mm 

and 1 mm levels above the die. This temperature drop is probably at least partially erased 

by the downward flow of melt during an extrusion. Thus only part of that total drop is 

taken as the uncertainty in the temperature. The 0.4 oC temperature drop determined at 

the bottom end of the melt column adjacent to the die, observed in Table 2, was taken as 

an estimate of the temperature uncertainty due to possible thermal gradients in the melt 

column. This uncertainty is combined with the nominal standard uncertainty in 

temperature indication, 0.1 oC, by root-sum-of-squares, and the result rounded up to 

0.5 oC, as an estimate of maximum expected standard uncertainty in temperature, δT, due 

to temperature indication and to possible gradients in the thermal profile of the melt 

column. 

The effect of small variations in temperature on the apparent melt flow rate was 

determined during the characterization of SRM 1473a reported earlier (10). In that study, 

the effect of temperature variation on melt flow rate was determined by conducting a set of 

five extrusions at 188.4 oC, and another set of five extrusions at 191.5 oC. The two sets of 

extrusions at the different temperatures were conducted with charges of polyethylene 

resin all taken from the same bottle of SRM 1473a. 

From the resulting average melt flow rates from the first timed extrudate segments of 

those extrusions, and from that at 190 oC it was estimated for SRM 1473a 

 (dF/dT) = 0.040 g/10 min / oC 

For the purpose of estimating uncertainty, this value of (dF/dT) was taken as the 

quantitative expression for the temperature dependence and the sensitivity coefficient, cT, 

of the melt flow rate of SRM 1474a at temperatures near 190 o

C. 

Considering the standard uncertainty in temperature, δT = 0.5 o

C, this result yields an 

estimate of 0.020 g/10 min for the uncertainty in melt flow rate of SRM 1474a due to 

uncertainty in temperature. 
9

5.7 Combined Standard Uncertainty 

The combined standard uncertainty (10) for the melt flow rate, uc, is obtained as the rootsum-of-squares of component uncertainties from all sources. The combined standard 

uncertainty computed thus from the sources discussed in the preceding paragraphs is 

uc = 0.21 g/10 min. 

5.8 Expanded Uncertainty 

With the object of presenting an uncertainty consistent with the reproducibility’s tabulated 

in the ASTM method, the combined standard uncertainty from Table 1 of this report is 

expanded to the form of a 95 % confidence interval estimate. This is accomplished by 

applying a coverage factor of 2 to the combined standard uncertainty to obtain an 

expanded uncertainty. The resulting expanded uncertainty is 0.42 g/min for the melt flow 

rate of SRM 1474a. 

6.0 Conclusions of Melt Flow Rate Study 

The melt flow rate of SRM 1474a was found to be 5.10 g/10 min, with a standard deviation 

of an average single measurement of 0.056 g/10 min, and a standard deviation of the 

mean of 0.0083 g/10 min. The combined standard uncertainty is 0.21 g/10 min, and the 

expanded uncertainty is 0.42 g/10 min. 

Acknowledgment 

The authors gratefully acknowledge Bruno Fanconi of the NIST Polymers Division for the 

technical counsel and direction and Stefan Leigh of NIST Statistical Engineering Division 

for guidance in the statistical analysis. 
10

References 

1. H. P. Frank: "Polypropylene," p.75, Gordon and Breach Science Publishers, N.Y. 

(l968). 

2. S. Matsuoka and T. K. Kwei, in "Macromolecules, an Introduction to Polymer Science," 

p.346, ed. by F. A. Bovey and F. H. Winslow, Academic Press. N.Y. (l979). 

3. N. G. McCrum, C. P. Buckley, and C. B. Bucknall: "Principles of Polymer Engineering," 

p.p. 279-280, Oxford University Press, N.Y. (l988). 

4. J. L. Throne: "Plastics Process Engineering," p.p. 239-247, 288, Marcel Dekker, Inc., 

N.Y. (l979). 

5. J. R. Maurey, and C. M. Guttman: "Studies on the Melt Flow Rate of the SRM 1474, A 

Polyethylene Resin," NISTIR 90-4239, March 1990 

6. M. G. Natrella: "Experimental Statistics," NBS Handbook 91, Section 1-4, p. 1-6. 

7. 2001 Annual Book of ASTM Standards, Vol. 08.01, D1238-00. 

8. B. N. Taylor and C. E. Kuyatt: "Guidelines for Evaluating and Expressing the 

Uncertainty of NIST Measurement Results," NIST Tech. Note 1297, January 1993. 

9. 1992 Annual Book of ASTM Standards, Vol. 14.02, E691-99. 

10. J. R. Maurey, W.R. Blair and C. M. Guttman: "Certification of the Standarad Reference 

Material 1473a, A Low Density Polyethylene Resin," NISTIR 5639, October 1995. 
11

Tables 

Table 1 Estimates of Uncertainties in Melt Flow Rate of SRM 1474a Polyethylene 

Under Condition 190/2.16

Sources of standard uncertainty 

 ui g/10 min Type c

1. Due to experimental repeatability 0.056 A 

2. Due to instrument variability as estimated 

from precision tables in ASTM D 1238-00 0.20 A 

3. Due to weighing <0.001 B 

4. Due to timing a <0.001 B 

5. Due to temperature 0.020 B 

Combined standard uncertaintyb

, uc 0.21 

Expanded uncertainty, U = 2uc 0.42 

a. Sensitivity coefficient, cT = dF/dT, for variation of flow rate in response to small 

changes in melt temperature. 

b. The combined standard uncertainty is computed by root-sum-of-squares of the 

component uncertainties (8). 

c. Type of uncertainty(8) 

 Type A uncertainties are evaluated by statistical methods. 

 Type B uncertainties are evaluated by other means. 
12

Table 2 Variation of Temperature with Height in Undisturbed Melt in Cylinder Bore 

 Height Above Die Melt Temp. 

 (mm) (oC) 

 48 190.09 

 36 189.93 

 24 189.97 

 12 189.94 

 1 189.23 
National Institute of Standards & Technology 

Certificate of Analysis 

Standard Reference Material 1474a 

Polyethylene Resin 

This Standard Reference Material (SRM) is intended for use in calibration and performance evaluation of

instruments used in polymer technology and science for the determination of the Melt Flow Rate using ASTM 

Method D1238-00. A unit of SRM 1474a consists of approximately 60 g of white polyethylene pellets in an amber

glass bottle. 

Certified Values and Uncertainties: This material is certified for Melt Flow Rate using ASTM Method D1238-00, 

Test Method for Flow Rates of Thermoplastics by Extrusion Plastometer [1] Standard Test Condition 190/2.16. The

flow rate of the melt was determined at 190.0 oC ± 0.1 oC and a load of 2.16 kg by procedure A of the ASTM

method. A manually operated extrusion plastometer was used. Under these conditions [2], the certified melt flow 

rate for this material is as follows: 

Melt Flow Rate (FR) = 5.10 g/10 min ± 0.42 g/10 min 

The uncertainty is an expanded uncertainty U = 2kuc with U determined from a combined standard uncertainty, uc

and coverage factor k = 2 with a level of confidence of approximately 95 %. Type A and Type B contributions to 

the expanded uncertainty include the standard deviation of the melt flow measurements, instrument-to-instrument

variation as discussed in ASTM D 1238-00, operator dependence of the measurement, and temperature gradients in

the apparatus [2]. The standard deviation for single measurement is 0.056 g/10 min, with 44 degrees of freedom [2].

Expiration of Certification: The certification of SRM 1474a is valid until 01 January 2008, within the 

measurement uncertainties specified, provided that the SRM is handled in accordance with the storage instructions 

given in this certificate. This certification is nullified if the SRM is modified or contaminated. 

Maintenance of SRM Certification: NIST will monitor this SRM over the period of its certification. If 

substantive technical changes occur that affect the certification before expiration of this certificate, NIST will notify 

the purchaser. Return of the attached registration card will facilitate notification.

Storage: The SRM should be stored in the original bottle with the lid tightly closed and under normal laboratory

conditions. 

Homogeneity: The homogeneity of SRM 1474a was tested by melt flow rate measurements using ASTM

D1238-00. The characterization of this polymer is described in Reference 2. 

The technical coordination leading to certification of this SRM was provided by B.M. Fanconi of the NIST

Polymers Division. 

The technical measurement and data interpretation were provided by K.M. Flynn, C.M. Guttman, J.R. Maurey, of

the NIST Polymers Division. 

Guidance in the statistical analysis was provided by S.D. Leigh of the NIST Statistical Engineering Division. 

The support aspects involved in the preparation, certification, and issuance of this SRM were coordinated through

the Standard Reference Materials Program by J.W.L. Thomas and B.S. MacDonald. 

Eric J. Amis, Chief 

Polymers Division 

Gaithersburg, MD 20899 John Rumble, Jr. Chief

Certificate Issue Date: 18 March 2003 Measurement Services Division 

SRM 1474a Page 1 of 2
SRM 1474a Page 2 of 2 

REFERENCES 

[1] ASTM D 1238-00; Test Method for Melt Flow Rates of Thermoplastics by Extrusion Plastometer; ASTM 

Standards, Vol. 08.01, American Society for Testing and Materials, West Conshohocken, PA (2001). 

[2] Maurey, J.R.; Flynn, K.M.; Guttman, C.M.; Certification of Standard Reference Material 1474a, A 

Polyethylene Resin; NIST Special Publication Number SP 260-148. 

[3] Guide to the Expression of Uncertainty in Measurement; ISBN 92-67-10188-9, 1st Ed., ISO, Geneva, 

Switzerland, (1993); see also Taylor, B.N.; Kuyatt, C.E.; Guidelines for Evaluating and Expressing the 

Uncertainty of NIST Measurement Results; NIST Technical Note 1297, U.S. Government Printing Office; 

Washington, DC (1994); available at http://physics.nist.gov/Pubs/. 

Users of this SRM should ensure that the certificate in their possession is current. This can be accomplished by 

contacting the SRM Program at: telephone (301) 975-6776; fax (301) 926-4751; e-mail srminfo@nist.gov; or via 

the Internet http://www.nist.gov/srm.