WHAT DATA SHEETS TELL YOU – AND WHAT THEY DON’T
INTRODUCTION
By Dr Nick Henwood, Rotomotive Limited
When we are considering which grade of polyethylene (PE) to use for a new application, or we are considering switching to another grade for an existing application, the Material Data Sheet is usually our first port of call.
A Data Sheet can give you useful data to help you make your choice, as long as you know what to look for and have a clear idea of what the various parameters stated actually mean.
Over the next few issues of the ARMO magazine, I will explain the various parameters that are stated on a typical Data Sheet for a rotomoulding grade of PE.
Years ago, when I first got involved in rotomoulding, Data Sheets from different suppliers often contained a bewildering array of strange-sounding properties, many of which had little bearing on what a rotomoulder really needed to know. The Polyolefins Committee at the Association of Rotational Molders (ARM) International should be given full credit for their sustained efforts, over a considerable period of time, to rationalise the information contained on Data Sheets for roto grades. ARM still publish a useful document called the “Resin Properties Booklet”, where materials suppliers are invited to submit data in a totally standardised form. This makes direct comparisons easier and assists moulders in making rational choices between different product offerings.
The table shows the data required for a supplier to be included in the Resin Properties Booklet.
For some parameters, ISO (ie European-based) standards can be substituted for ASTM (ie American-based) standards, although most suppliers use ASTM standards throughout. The measurement of Continuous Tensile Load Environmental Stress Crack Resistance (CTL ESCR) and Low Temperature Impact Strength is to proprietary Test Methods developed by ARM International. Copies can be obtained from ARM International.
No-one is claiming that the test methods chosen are necessarily absolutely the best way of measuring material properties and at the ARM Materials Committee we regularly review and discuss alternatives. However, sticking to common procedures, that yield results that we can all understand and compare, is obviously very beneficial. Supplying data in conformance with the table should not be an onerous task for any material supplier who is serious about serving the roto industry.
Data Sheets certainly don’t tell you everything you need to know about roto grades and I will explain what else you need to know in later articles in this series.
| Parameter | Units | Test Procedure | Notes |
| Density | g/cm3 | ASTM D-1505/D-4883/D-792 or ISO 1183, Method D |
1 |
| Melt Index | g/10 min | ASTM D-1238 at 2.16kg load, 190°C or ISO 1133 |
– |
| ESCR Condition A, F50 |
hr | ASTM D-1693 100% Igepal and 10% Igepal |
1,3 |
| CTL ESCR | hr | ARM International Test Method | 1,3 |
| Flexural Modulus | psi or MPa |
ASTM D-790 at 1% Strain or ISO 178 at 2% Strain |
2 |
| Tensile Strength at Yield | psi or MPa |
ASTM D-638, Type IV specimen, 2 in/min (50.8 mm/min) at 0.125 in (3.1mm) thickness or ISO 75-2, Type 1B |
2 |
| Heat Distortion Temperature | °C | ASTM D-648 at 66 psi (4.64 kg/cm2) and 264 psi (18.56 kg/cm2) or ISO75-2 at 4.5 kg/cm2 and 18.00 kg/cm2 |
2 |
| Low Temperature Impact Strength | ft lbs or J |
ARM International Test Method 1/8 in (3.17mm) specimen and 1/4 in (3.17mm) specimen |
2 |
Notes:
- Measurements of samples cut from compression-moulded sheets are preferred.
- Measurements from samples of rotomoulded pieces are mandated
- Data from either ESCR test can be submitted, or both.