FOOTWEAR TECHNOLOGY
Standing up to the test of time
what the industry might look forward to. An understanding of how materials and constructions are likely to
D
perform during prolonged use is essential in order to produce a quality product. It is also particularly valuable in helping sourcing companies and retailers to manage customer expectation and, ultimately, brand perception. The testing of new materials and newly-made constructions gives a good
indication of how a product will perform fresh off the production line. It will not, however, lead to an understanding of how properties can change with wear or exposure to time and the elements. It should not be overlooked that the ageing process for footwear begins as soon as the finished product leaves the factory. During transportation and storage, the product may be exposed to a range of different environments which can have an adverse effect on the materials used in the footwear’s construction, even before it reaches the consumer’s feet. Where consumers expect a certain level of performance and longevity in
a product (which is likely to be the case with most footwear items) there is an argument for including contrived ageing in any pre-sales testing programme when incorporating new materials or design concepts into the footwear. A reduction in scuff resistance, the appearance of discolouration and badly cracked surfaces or a quickly-diminishing resistance to rain or snow are all likely to be unacceptable to the modern consumer. Dissatisfied customers may return the product and, potentially, lose loyalty to the footwear brand. SATRA uses a range of assessments to simulate aspects of the ageing
process. These are intended to replicate what is likely to occur to the materials and construction during and after prolonged time and use. Care is taken, however, not to induce faults that are solely due to the method of ageing. For example, heat is normally expected to accelerate the ageing process, but excess heat may damage materials in ways that would not occur during normal exposure, such as the softening of certain polymers.
Testing for wear SATRA’s PEDATRON test equipment has been designed to assess the
abrasion of soling materials in a manner which mimics the human walking action. This not only determines the amount of material shed from the sole, but also identifies the pattern of wear, which may have an impact on slip resistance and gait stability. PEDATRON testing can be followed by other separate whole shoe and/or solings tests, including the slip resistance test, to obtain a comprehensive picture of change in performance with wear. The way in which soles wear will be determined by a number of factors: • The chemical composition of the material including the presence of any fillers;
• The design of the sole unit, particularly with respect to the amount of contact between the cleats and ground;
• The style of the shoe. As with all guidelines and tests, there must be a consideration of fitness
for purpose. A slipper sole will not be expected to encounter such severe wear as a sole used on an outdoor shoe or safety boot would, and the test surfaces and duration are altered to take account of this.
Restricted substances An important issue is the possibility of potentially harmful substances being produced during the lifetime of the product. The azo dye legislation
42 • FOOTWEAR TODAY • JUNE/JULY 2010
etermining long-term durability of footwear by means of laboratory testing involves using techniques designed to accelerate the ageing process and replicate product wear in hours rather than months or years. SATRA’s John Hubbard reviews current options and suggests
SATRA’s John Hubbard reviews current options
arose out of concern that certain dyestuffs in the azo class may breakdown in situ when exposed to heat, sweat and/or washing, and form aromatic amines that are recognised as potential carcinogens. Suppliers of chrome-tanned leather into Germany are currently being
asked to provide an assessment of their material’s potential to form toxic hexavalent chromium (chrome VI) from the normal trivalent chromium (chrome III) in the tanned leather. The assessment is in the form of a contrived ageing test that heats the leather to 80ºC before determining the chrome VI content. While this test procedure does not reflect real conditions of wear or storage, it is being used to predict those leathers that exhibit the greatest potential to release this irritant chemical. SATRA is currently investigating this ageing process and looking at alternative procedures that may better predict the chrome VI development that may occur in real situations.
Discolouration Up to the point of sale, many items of footwear will not have been outside
their protective packaging for any significant length of time. As soon as the product is worn, it will be exposed to a whole series of environmental agents that may induce changes in appearance in some of the materials used in construction. Such agents will include moisture, which can be linked to corrosion of
trims and the staining of uppers and hydrolysis of polyurethane materials, and gaseous pollutants such as hydrogen sulphide and oxides of nitrogen, which arise from the burning of fossil fuels in industry and transport and may cause yellowing of certain materials. Sunlight can have a detrimental effect on some materials by fading deep colours, inducing yellowing in susceptible white and light-coloured materials, and even causing the physical breakdown of some polymers. In order to assess the potential for discolouration, a variety of tests are
available which expose materials to discolouring agents. Compatibility tests can be carried out to ensure adjacent materials do not induce discolouration in each other.
Manufacturers and retailers can enquire about determining the long-
term durability of footwear by contacting the SATRA footwear team on +44(0) 1536 410000 or
footwear@satra.co.uk or visit
www.satra.co.uk/durable_footwear
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