Tensile testing of condom rings

Interlaboratory consistency in the tensile testing of condoms is well known to be very poor. In many cases this is not an important matter as the inherently high tensile strength of natural rubber ensures that almost all products can pass the minimum tensile strength requirements easily, however it can occasionally represent a serious problem. There is no doubt that some of the problem is due to intrinsic product variability, however the work reported here clearly shows that other factors, such as sample preparation and thickness measurement, also have significant influence. In this extensive study, involving up to eighteen laboratories in seven different countries, variability due to the product itself and to sample preparation factors were minimized by using products from a single production line and by having the samples prepared in one laboratory. A major, and surprising, conclusion form this study is that reliable measurement of the thickness of thin latex rubber is very difficult. Despite the examination of a number of possible factors no clear explanation for the difficulty was found. However, this study has also shown that the weight of the ring test-piece may be used instead of thickness measurement and that this approach gives similar mean values of tensile strength but with much reduced variability. In the future, requirements for condom tensile strength measurements are likely to be much reduced due to the current preference for force at break values, but for as long as condom tensile strengths are required it is recommended that weight measurements should be substituted for the intrinsically variable thickness measurements. The difficulty of thickness measurement of thin soft rubber films, shown very clearly by this work, is important in other areas, for example where minimum thickness values are specified for examination or surgical gloves. Again, consideration should be given to substitution of a weight measurement. A further conclusion from this work is that the measurement of force at break is also not very reproducible, although the difficulty may not be the measurement of force itself but due to cutters producing rings of differing widths. Whatever the cause this factor needs to be considered in any specification for this property.