MELT FLOW TESTING

ISO 1133, ASTM D1238

Both Melt Flow and Rheology Tests can be very helpful

tools for QC monitoring and development of polymers.

This presentation is designed to be an informative

introduction and guide to Melt Flow test, and to assist

with troubleshooting inconsistencies in results.

MELT FLOW

Melt Mass-Flow Rate(MFR) The mass of material flowing through a die at a specified

temperature (g/10 min)

Melt Volume Rate(MVR) The volume of material flowing through a die at a

specified temperature (cm3/10 min)

MVR = MFR/density of material at melted state

“Measure of the ease of flow of melted polymer”

MELT FLOW: Typical

Index for QC of

thermoplastics

WHY MELT FLOW?

• Melt Flow is a Typical Index for polymer materials

• Verify incoming/entrance material

• Check regular quality control of material

• Compare new materials in a product development setting

• Predict how a polymer will behave in a number of processing

techniques

Raw Material Producers

Compounders

Manufacturers/Convertors

A TRUE STORY

As an example of an actual case of how Melt Flow information can be

used:

An injection molded polycarbonate part was found to crack when dropped. The virgin

resin had an MFR of 28.5 g/10min. A sample from a known “good” lot of parts was

ground up and tested in a melt flow tester. It had an MFR of 27 g/10min, well within

established tolerances (±30%). But a “problem” part showed an MFR of 90

g/10min. From this evidence, it was discovered that the “bad” lot contained a large

amount of regrind that had been thermally degraded in processing.

Manufacturers/Convertors

THE EQUIPMENT

MASS

KNOWN/SET

TEMPERATURE

(variable per

material)

KNOWN DIE SIZE

(per standard –

ASTM D1238,

ISO 1133)

KNOWN/SET

MASS

(variable per

material)

MFR: Amount of material

extruded in 10 minutes

Melted Polymer

General standards:

• ISO 1133-1,-2 (Method A, B)

• ASTM D1238 (Methods A, B, C, D)

Material specific standards, such as:

• ASTM D3364 (for PVC)

• ISO 1872-1 (for PE)

MELT FLOW STANDARDS

ISO 1133 : 2 methods (A & B)

A : Manual test, measure of mass flow (MFR)

B : Encoder-assisted tests, measure of volume flow

(MVR)

(*) ISO 1133-2 introduced new stricter tolerances for temperature

profile inside the barrel, and is dedicated for materials that are

sensitive to time-temperature history and/or moisture

ASTM D1238 : 4 procedures (A, B, C & D)

A : Manual test, measure of mass flow (MFR)

B : Encoder-assisted tests, measure of volume flow

(MVR)

C : For high-flow materials (special procedure, die with

D= 1.048, L= 4 mm and a Die Plug Device)

D : For multiple-weight tests

INTERNATIONAL STANDARDS FOR MFT

Easy test procedure: • Preheat barrel, die, and piston at working

temperature

• Choose the test mass

• Insert the right amount of sample

• Apply the test mass to compact the

sample

• Measure the amount of sample flowing

through the die during a fix time or for a

specific piston displacement

• Clean carefully piston, die, and barrel

MELT FLOW: THE TEST

Polymer

Melt

Extrudate

Constant Test

Temperature

KEY FACTORS THAT INFLUENCE RESULTS

Temperature Accuracy

Preparation of Sample

(moisture)

Sample Compacting

Method Parameters

Melt Density Value

Manual Operations within Test

Maintenance of Die and Piston

Cleaning Procedures

Temperature Stability

Choice of Procedure

Encoder Accuracy

Extrudate Cutting

Precision

= most common

• Is the barrel clean? Or is the die clean?

• Increased friction between the barrel & piston will reduce melt flow rates

• Is the test being run at the correct temperature?

• Is system temperature control accurate and consistent throughout length of barrel?

• Especially critical for materials that are sensitive to time-temperature history

• Has the material been pre-conditioned according to procedure?

• Hygroscopic materials give unreliable test results if they are not dried in consistent

manner

• Moisture tends to generate bubbles and trigger degradation of sample

• Is the melt density being used in the MFR calculations correct?

• Was the material compacted properly (or were there air bubbles)?

KEY FACTORS THAT INFLUENCE RESULTS

MANUAL v. AUTOMATIC TEST OPERATIONS

• Controlled Compacting

• Better reproducibility and less

scattering of results

• No physical effort required by

operator (reduces risk of injury)

• Post-test automatic purging

• Reduces total test time

• Operator is ready to run next

test more quickly

• Cleaning

• Thorough cleaning extends life

of equipment & helps maintain

consistent results

THANK YOU FOR YOUR TIME!

Please contact your local

Instron® Sales Representative

with any questions.