Polymer Testing 7 (1987) 223-224

Editorial

Continuing from the last issue on the subject of standard reference materials, there is a letter in this issue from D. Ivan James, who is a well known expert on friction. He essentially points out that a very widely used standard reference material, the slider of the TRRL Skid Tester, which is standardised by ASTM and much used for roads, pavements, sports surfaces and floors, is ambiguously specified in the literature and on test certificates.

In searching for the explanation for the change of specification from that given for the original instrument and that used for the supply of rubber sliders today, I initially found further confusion. The present standard material was developed by, and is still supplied by, RAPRA. In a report issued during development in 1974, a third specification appears!

Temperature (°C) 0 10 20 30 40

Resilience (%) 45-50 58-65 64-70 66-74 68-75

I have not found it possible to properly explain the sequence of events which led to the specification changes but it appears that the figures given above applied to the early commercial rubbers. It then transpired that the standard formula for the rubber refused to meet the specification when remixed in 1974, no matter what the technologist tried. Although records cannot be traced, the resulting action was to change the specification for resilience to that used currently and also to make small changes to the rubber formulation.

Although there is no confusion on the part of the suppliers of the material over the last decade, it would appear that no published account of the updating of the reference standard has been given. However, the current specification is published (thanks to Dr West of TRRL for this information) in BS 812 Part 3 1975. This standard is concerned with accelerated polishing of aggregate and not surprisingly was unknown to Mr James or others in the polymer field.

For Mr James and any others who were confused by this change, that is the best answer I can find. However, the message is surely that the

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Polymer Testing (7) (1987)--~ Elsevier Applied Science Publishers Ltd, England, 1987. Printed in Northern Ireland

224 Editorial

suppliers of standard reference materials should make certain that the specification is widely published. In this case it is harsh to lay blame because the suppliers manufacture on behalf of the inventors of the apparatus under contract to the suppliers of the apparatus and responsibility falls between three stools.

A new standard friction rubber for use with the Tortus testing apparatus (which is now at least as popular as the skid tester for floors) has been under development for some time. This rubber is also likely to be used with the Skid Tester. Great care has been taken over selection of a material which gives the best evaluation of slip resistance and care is also being taken over its specification and production. The person entrusted with this development is none other than D. Ivan James who is hence under considerable pressure from the editor to ensure that the specification is properly published!

R. Brown