Laboratory Testing for Colour Fastness in Flexible Polyurethane Foams

R. L. Daher, M.Sc.


This study was supported by a National Health Grant #606-7-258, Department of Health and Welfare, Canada.

Products of flexible polyurethane foam are being used routinely in artificial limbs and other appliances in many clinics. The SACH foot was probably one of. the first polyurethane products to have a clinical application. Because the flexible foams are quite soft yet tough, and are easily moldable, they have been used most recently in the manufacture of cosmetic covers. However, one disadvantage of polyurethane foam is its tendency to discolour from exposure to the ultraviolet rays of sunlight. Each type of available foam is affected to a varying degree. For controlled evaluation of the effects of ultraviolet light, a simple test was devised by the Prosthetics/Orthotics Research and Development Unit, Health Sciences Centre.

Equipment Used

The equipment shown in Fig. 1 consists of an enclosure lined with aluminum foil, having a rotisserie arrangement, and illuminated by a Sylvania F15T8/BL fluorescent black-light blue lamp. This lamp was selected because of its low heat emission and an ultraviolet radiation intensity which comes close to that of normal sunlight on earth at high noon1. The lamp's peak intensity of 1 watt/10 millimicrons occurs at a wavelength of 375 millimicrons. The range of greatest emission is between 300 and 400 millimicrons. Fig. 2 indicates the general range with respect to the Electromagnetic Spectrum2. Consequently, all test specimens are exposed to the equivalent of ultraviolet radiation from sunlight on a clear day at noon.

The rotisserie arrangement was installed to insure that all samples are subjected to equal radiation intensity. In addition to testing for effects of ultraviolet light, the enclosure has been designed to include a humidifier which could be used to study the effects of high humidity on the various samples.

The present test program on commercially available SACH feet is being conducted in two phases. In phase one, the effect of ultraviolet light on the durometer of the feet will be studied. This study will be followed by a test to determine the effects of high humidity. Phase two of the program will subject the feet to ultraviolet radiation and high humidity simultaneously, followed by cycle testing. The results of these tests, compared to those of feet cycled without prior exposure to humidity and ultraviolet radiation, should indicate any deterioration in durability as a result of these factors. Upon completion of the test program, publication of all results is planned.

Health Sciences Centre, Rehabilitation Centre Winnipeg, Manitoba, Canada

References:
1. Threlkeld, J. L., Thermal environmental engineering. Prentice-Hall Inc., 1962.
2. Sylvania Electric (Canada) Limited, Commercial Engineering Dept., Engineering Bull. 0-306C, (no publication date available). Code No. 667.