Fatigue testing of condoms

Fatigue testing of condoms

Polymer Testing 28 (2009) 567–571 Contents lists available at ScienceDirect Polymer Testing journal homepage: www.elsevier.com/locate/polytest Test...

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Polymer Testing 28 (2009) 567–571

Contents lists available at ScienceDirect

Polymer Testing journal homepage: www.elsevier.com/locate/polytest

Test Method

Fatigue testing of condoms John Paul Gerofi*, Pak Man Wong Enersol Pty Ltd, 235 Nelson St, Annandale, NSW 2038, Australia

a r t i c l e i n f o

a b s t r a c t

Article history: Received 29 January 2009 Accepted 9 March 2009

Tests currently used for condoms are surrogates for the challenges they face in use. The tests involve looking for holes and slow stretching to break. This article describes a test that adds cyclic strain to a level well below breakage, and examines the differences among brands and types of condom. It is shown that there are very significant differences in resistance to cyclic straining. Such a test could be developed into a standard test for condom acceptability. Ó 2009 Elsevier Ltd. All rights reserved.

Keywords: Condoms Natural rubber Fatigue Testing

1. Introduction Sweden was the first country to regulate the quality of condoms and began testing them in 1950 [1]. The first British standard on condoms was published in 1964 [2], and went through a number of revisions, until it was harmonized with the European standard in 1996 [3]. The first US standard was published in 1976 [4]. ISO began work on an international standard for condoms in 1975, but the standard was only published in 1990. It was subsequently revised in 1996 and 2002. The first European standard was published in 1996, and is now identical to the ISO standard [5]. Gradually, other countries are adopting the ISO standard. WHO uses most of the ISO standard in its model specification for condoms [6] so that, effectively, even condoms bought by aid agencies for countries without effective regulation of medical devices must comply with ISO requirements. The US ASTM standard is very similar to the ISO standard.

test. There are other tests of dimensions and lubricant quantity. There are two alternative methods for the freedom from holes test. The first involves putting 300 mL of water into the condom, examining it visually, and then rolling it on absorbent paper to look for smaller holes. The second method is a conductivity test that measures the current that flows between the inside and the outside of the condom when it is filled with water and then immersed in a water bath. The inflation test measures the burst pressure and volume of the condom when it is inflated with air at a rate of approximately 0.5 L/s. From time to time, new test methods are proposed. One, which was examined by ISO and rejected, is the RQTS [7] (Rheological Quality Test System) method. The proponent described the test as applying a shock wave to the condom (using a large quantity of water) and testing for holes by measuring the conductivity afterwards.

2. Existing tests

3. Limitations of current tests

The principal tests required in the ISO standard are a test for holes, the inflation test and a package seal

Although they appear to stress the condom beyond the normal challenges of use, both the test for holes and the inflation tests are quasi-static. The condom is not subject to rapid distortions or challenges. The mechanical behaviour of condoms in use has not been widely studied, and

* Corresponding author. Tel.: þ61 2 9552 1707; fax: þ61 2 9552 1709. E-mail address: jgerofi@enersol.com.au (J.P. Gerofi). 0142-9418/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymertesting.2009.03.010


J.P. Gerofi, P.M. Wong / Polymer Testing 28 (2009) 567–571

probably will not be, because of the attendant technical and social difficulties. It is nonetheless clear that they can be subject to some fatiguing due to repeating stretching and flexure, and possibly to a shearing effect if they are insufficiently lubricated. The movements involved in actual use will vary from couple to couple, but it is clear that some can be relatively rapid compared to those in the existing tests. It is inevitable that many of the stresses will be largely cyclic because of the nature of sexual intercourse. A recent study [8] focussing mainly on breakage of polyurethane condoms, suggests that breakage may occur through repeated local stretching, especially where the material does not return to its original unstrained shape between stretches. The local strain may be quite high compared with the average strain over the whole condom. 4. Relationship between existing tests and failure in use The effect of holes on condom efficacy appears selfevident. It is widely believed that any hole in a condom poses a major risk of failure, and that every effort should be made to reduce the number and size of holes to the minimum possible. Currently, the ISO standard places an upper limit of 0.25% holes, without specifying the size. In fact, the best manufacturers are operating at better than 0.08% holes, and the holes that are found are usually very small. They are generally visualised only by rolling the condom (filled with water) on absorbent paper and looking for damp spots. When the first British Standard for condoms was published in 1964, the AQL set was 1.0%. This was subsequently reduced to 0.4%, and currently the international consensus is at 0.25%. The relative importance of holes in condoms was investigated by the USFDA [9,10], and it was concluded that for exposure to larger volumes of fluid the risk from leakage was not significant compared to that from breakage. Exposure to smaller volumes through condom leakage is more likely and the risk of exposure to approximately 10 nL of seminal fluid is similar to the risk of condom breakage. The inflation test is the surrogate for a breakage test, and stretches the condom until it breaks. This test was pioneered in Sweden, and initially constrained the mean and standard deviation of the burst volume. The minimum mean was initially 10 L. By the time the first international standard was published in 1990, the limit was at 15 L and was on the lower 1% of the distribution, rather than the mean. Hence, the ISO limit was considerably more stringent than that in the early Swedish standards. A similar limit was imposed on the burst pressure in the ISO standard. For political reasons, these limits were relaxed slightly when the ISO and European standards were harmonised. A correlation between breakage in use and performance in the inflation test was demonstrated by Free et al. [11,12], and also by a Family Health International study [13]. Clinical trials conducted in developed countries in recent years have shown breakage in use of approximately 1% [14]. With the exception of one trial conducted in the UK in the 1980s [15], earlier clinical trials [16] showed much higher breakage rates, suggesting that the improvement in condom quality has been a factor in reducing breakage in use.

5. Fatigue testing The tests in the current standards are surrogates for what happens in use. Although there is some evidence that implementation of the inflation test has decreased condom failure, the test is still clearly a long way from mimicking what happens in use. In order to move one step closer to reality, a fatigue test has been developed in order to simulate an additional failure mode that can occur in use. The first concept used only air, and stretched the area near the closed end to about 3 times its natural diameter. This test involved a relatively low level of stretching compared with the inflation test, but still one that was likely to exceed the expected stretching in use. On the other hand, the stretching was applied repeatedly. The end-point of the test was considered to be breakage or leakage of the condom. Initially, the test was done manually, and condom failure was detected by visual inspection. In general, failure was seen as shattering, or failure to inflate to the expected volume. Major differences were detected among brands, as shown in Table 1. Later, automation was attempted, using a camera and pattern recognition software. It became clear that the automation method adopted would not work on all brands because some shattered while others developed small holes, which were extremely difficult to detect automatically. It was concluded that a different approach was needed, and, accordingly, the fatigue test was redesigned to be a modification of the conductivity test for holes. The condoms had 500 mL of water in them, and were immersed in a conductive bath. They were then inflated with air to approximately the same dimensions as in the first test design, and then deflated with vacuum. The test runs continuously and the end-point of the test is when the condom fails the conductivity criterion laid down in Annex L of ISO 4074 (resistance between the inside and outside of the condom of less than 1.96 MU). The cycle of this fatigue testing is 2 s of inflation and 1 s of deflation. The apparatus of the redesigned fatigue testing device comprises mainly the test heads, pneumatic components and a microcontroller. The test head is used to hold the condoms in place for the inflating and deflating motions. It also tightens up around the condoms so that there is no water leak between the condom and the water bath. The pneumatic circuit was designed to use compressed air to inflate the condom and a vacuum to deflate the condom. The pneumatic circuit also includes the parts to control the air pressure and the volume flow. The microcontroller is the centre of the device. It is programmed so that it generates the waveform to produce the inflation and deflation cycle for the condom, detects leakage through conductivity and communicates with the PC to transfer test data. Table 1 Typical results from prototype fatigue tester (air only). Product

Mean cycles to burst

SD of cycles to burst

1 (Synthetic polyisoprene) 2 (Natural latex)

5664 870

891 60

J.P. Gerofi, P.M. Wong / Polymer Testing 28 (2009) 567–571

Figs. 1 and 2 are the schematic diagram and a photograph of the redesigned fatigue machine. The schematic shows how the water level inside the test head is pushed down and pulled up by the compressed air and vacuum to inflate and deflate the condom. When this stretching and relaxing motion is applied to the condoms continuously, the condom will eventually break. Once the condom breaks or starts to leak after a certain number of cycles, the voltage across the condom film will drop from almost 10 V to a lower value. The voltage across the series resistor is monitored using a microprocessor with an A–D converter. Once the voltage across the resistor increases to over 50 mV (voltage across the condom less than 9.95 V), the condom is deemed to have failed, as in the conductivity test in ISO 4074. 6. Results Tests were conducted on ten different types of condoms (A–J), from different manufacturers and countries. Eight of these types of condoms (A–H) were natural rubber products and had been tested according to the inflation test and the freedom of holes test. They all passed these tests. 20 samples were tested from each product for fatigue. The


number of cycles completed before the condom broke or leaked was recorded. Products I and J were only tested by the condom fatigue testing device, and, because of a lack of samples, the number tested was 9 and 6 respectively. Although the condoms tested were under different levels of stress, depending on the latex properties and thickness of the condoms, they all broke by developing microscopic holes rather then tearing or bursting. This suggests that condoms are likely to fail with microscopic holes at the first moment of breakage, which are not likely to be spotted visually. This was not obvious in the earlier version of the test, where failure was detected visually. The results from the fatigue device and the inflation machine are shown in Table 2. Different brands of condoms have different degrees of endurance under the fatigue test. The mean number of cycles to break ranges from 422 to 5973, a factor of more than 13. Products I and J have the highest mean breaking cycles, about 30% higher than the best latex condoms. I and J are synthetic polyisoprene condoms. The minimum number of cycles to break for I is recorded as 0. The reason for that is that one condom in the sample had an existing hole before testing. This product was

Fig. 1. Schematic diagram of fatigue tester.


J.P. Gerofi, P.M. Wong / Polymer Testing 28 (2009) 567–571

A has a mean of 2190 and product G has a mean of 1584, and the t-test gives a P value of more than 0.05, so the difference of their mean values is considered to be not statistically significant. The fact that the difference between some other pairs is not statistically significant means that there is insufficient evidence based on the sample size used to conclude that the difference in results is meaningful. A larger sample size would be needed to get a more definite outcome for these pairs, namely: A and G, B and C, D and E, D and I, D and J, E and I, E and J, F and H, I and J. 7. Conclusions

Fig. 2. Photograph of fatigue tester.

unfoiled and was several months old, so the risk of deterioration prior to testing was enhanced. The relative standard deviations ranged from 11% to 60%, so the t-test was conducted for each pair of brands, to establish to what extent the results were statistically different. Table 3 shows a matrix with the results of the t-test. For the results which have a P value less than 0.05, the entries are in bold type. For those cells with bold entries, the pair of products has a P value of less than 0.05, and hence the difference in mean values of that pair is considered to be statistically significant. Thus, it can be concluded that the difference in mean values for those pairs is not due to chance. For example, product A has a mean of 2190 and product B has a mean of 422, and the t-test gives a P value of less than 0.05, so the difference of their mean values is considered to be statistically significant. Similarly, product

All the natural rubber products above (A–H) had also been tested by the conventional inflation test and had passed. However, they all have a different number of cycles to failure with the fatigue test. For the sample sizes used in this study, some pairs of products are statistically equivalent in fatigue behaviour, while others are quite different. Products I and J are marketed products made of synthetic polyisoprene, and they had the highest mean number of cycles to breakage. There is not a clear correlation between the breaking cycle and the bursting pressure or volume. There are major differences among brands. Of the 45 possible pairs of products in this trial, 36 were significantly different according to the t-test with a 95% confidence limit. The number of mean cycles to breakage ranges from 422 to 4358 for the natural latex condoms. The polyisoprene condoms last longer, with means of 5805 and 5973. The results from the prototype testing system using air and visual detection at break were similar to those obtained using the conductivity system. Clearly, the results from the latter are more accurate. The test described indicates that different products respond very differently to cyclic extension. Cyclic extension is a probable mechanism of damage to condoms in use. The optimum extent of extension appropriate for this test has yet to be determined, and the value chosen for this article was selected on the basis of stretching the rubber more than one would subjectively expect in use, but considerably less than the elongation at burst. The test inherently takes a considerable time to perform. The better the condom in terms of this parameter, the longer the test takes (4000 cycles take 200 min). This

Table 2 Fatigue and inflation test results by product. Product











Fatigue test result Number of condoms tested Mean (cycles) Maximum (cycles) Minimum (cycles) Standard deviation

20 2190 4481 535 1234

20 422 987 169 181

20 474 660 189 116

20 4202 9725 282 2547

20 4358 10,963 306 2218

20 1019 2228 357 492

20 1584 2868 654 607

20 1001 1845 297 337

9 5805 9181 0 3990

6 5973 18,634 1325 647

Inflation test result Mean pressure (kPa) Mean volume (L)

2.343 35.82

1.742 37.85

2.314 32.29

2.223 27.67

2.256 36.19

2.109 36.67

1.379 41.49

1.83 40.72

– –

– –

J.P. Gerofi, P.M. Wong / Polymer Testing 28 (2009) 567–571


Table 3 Paired t-test results for the fatigue test. Product












1.0000 0.0000 0.0000 0.0029 0.0005 0.0003 0.0560 0.0002 0.0008 0.0163

1.0000 0.2644 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0005

1.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0005

1.0000 0.8377 0.0000 0.0001 0.0000 0.1906 0.3164

1.0000 0.0000 0.0000 0.0000 0.2093 0.3377

1.0000 0.0025 0.8909 0.0000 0.0015

1.0000 0.0006 0.0001 0.0044

1.0000 0.0000 0.0014

1.0000 0.9492


test is readily applicable to type testing, but can be applied to lot by lot testing using small sample sizes (similar to those used for dimensions). Refinements to improve the speed of testing are possible. The significant difference in fatigue behaviour among brands and the likelihood that cyclic stretching is involved in breakage both call for further research on a possible fatigue test for condoms, and by analogy, for medical gloves. Acknowledgements The authors thank Dr Maria Cristina Bo for her comments and assistance in finalising the manuscript. References [1] S. Linde, Inspection and control of contraceptives at Apotekens Centrallaboratorium, Sartryck ur Svensk Farmaceutisk Tidskrift 77 (1973) 588–594. [2] BS 3704, British Standard Specification for Rubber Condoms, British Standards Institute, 1964. [3] EN 600 – Natural Rubber Latex Male Condoms, Comite´ Europe´en de Normalisation, 1996. [4] ASTM D-3492-03, Standard Specification for Rubber Contraceptives (Male Condoms), ASTM, 2003.

[5] ISO 4074:2002, Natural Latex Rubber Condoms, International Organisation for Standardisation, 2002. [6] The Male Latex Condom, WHO, 2004. [7] J. Torres, H. Anabitarte, R. Usieto, E. Noguera, RQTS, quality standard of condoms based on a rheological model, in: , International Conference on AIDS, 5, 1989, p. 1042. [8] N.D. White, D.M. Hill, S. Bodemeier, Male condoms that break in use do so mainly by a blunt puncture mechanism, Contraception 77 (2008) 360–365. [9] C.D. Lytle, L.B. Routson, Lack of latex porosity: a review of virus barrier tests, J. Rubb. Res. 2 (1) (1999) 29–39. [10] C.D. Lytle, et al., An in-vitro evaluation of condoms as barriers to a small virus, Sex. Transm. Dis. 24 (3) (Mar 1997) 161–164. [11] M.J. Free, J. Hutchings, F. Lubis, R. Natakusumah, An assessment of burst strength distribution data for monitoring quality of condom stocks in developing countries, Contraception 33 (3) (1986) 285. [12] M.J. Free, E.W. Skiens, M.M. Morrow, Relationship between condom strength and failure during use, Contraception 22 (1) (1992) 279. [13] M. Steiner, R. Foldesy, D. Cole, E. Carter, Study to determine correlation between condom breakage in human use and laboratory test results, Contraception 46 (3) (1992) 279. [14] T.L. Walsh, et al., Effectiveness of the male latex condom: combined results for three popular condom brands used as controls in randomised clinical trials, Contraception 70 (2004) 407–413. [15] J. Peel, A male-oriented fertility control experiment, Practitioner 202 (1969) 677–681. [16] Latex Condom Breakage Study, Barbados and St Lucia Condom Lot Site, Family Health International, Sept 1990.