MATERIAL SOLUTIONS
garments are fit for service as regards absorption prevention. There are recognised methods for this, ranging from simple droplet test up to a laboratory measurement of hydrostatic head resistance using the universally trusted ISO method. The droplet test can be carried out daily, in-house, on each batch of treated garments. It involves placing one droplet of water on one or more treated garments from the batch and measuring the time taken for the droplet to become absorbed. A useful refinement for this test is to use the hazardous liquid at the customer’s premises, provided the safety conditions for this can be accommodated at the rental laundry and a specific acceptable absorption time agreed. The laboratory test method can then be applied at less frequent intervals as a double check that the systems are working satisfactorily.
High-vis garments
Many hi-vis garments achieve their superb reflectance using tiny aluminium discs embedded in a flexible plastic carrier layer. Even when new, the plastic layer is not totally impervious, so it is essential that the wash process does not involve anything which can attack aluminium. This rules out the use of any alkali (such as sodium hydroxide, sodium metasilicate or calcium carbonate) and explains why most standard commercial wash processes cause such rapid degradation of hi-vis fabrics. The solution is to formulate detergents for hi- vis using neutral ingredients, which works fine for dust and light grime. Removal of skin oils, from neck and wrist, requires a suitable emulsifier designed to work at low temperature with the correct HLB (hydrophilic lipophilic balance) value, or avoid reflective materials made from aluminium. Of far greater importance for hi-vis garments carrying mineral oil or grease contamination is to include emulsifiers able to solubilise these, if wearers have been working on rail and train maintenance for example. The effectiveness of a hi-vis fabric after repeated wearing and cleansing can be measured using a specialist reflectometer. The meter is placed on the fabric and a light (made up of a standard mix of wavelengths) is shone from an angle. The percentage of the light reflected from the fabric surface is then measured using a photocell and this reading is recorded as the effective reflectance of
28 LCNi | May 2024
the material. It is thus possible for the rental customer to specify the minimum reflectance acceptable, below which the garment must be rejected (and usually scrapped). The rental operator might be asked to monitor sample reflectance from each batch using an in-house meter. Or the rental supplier might agree with the customer the maximum number of wears which a garment can be allowed before it is scrapped. This would then be monitored using a bar code or similar system, with scanning during sorting.
Garments with low surface resistivity
Unwanted electric discharge across the surface of an operator’s garment can play havoc in the micro-electronic, paint spraying and even pharmaceutical sectors. A wide range of fabrics can accumulate a static charge and pose different risks to product quality, so it is necessary to select the fibre mix for the garment carefully and implement the appropriate control to ensure neutral electrical activity across the surface.
Assembling a roll of wool fabric after finishing and drying often builds a static charge running into thousands of volts, despite the high moisture regain of wool fibres. One cannot rely on the increasing pick-up of moisture from the environment to discharge this satisfactorily. In contrast, the inclusion of the cotton in a polycotton
blend effectively reduces the risk of explosion in plants processing hydrogen, because the cotton does regain moisture and the risk of a spark occurring is very low. The dissipation of a static charge on workwear can be achieved by creating a conductive finish on the cloth surface. This might be capable of withstanding multiple wear and cleansing (in which case monitoring the number of previous washes in sorting by scanning a bar code might be appropriate). Alternatively, the finish might need to be re-applied after every cleansing, making for less expensive garments, but higher processing costs. Most success has been achieved by incorporating a grid of conducting metallic or carbon fibres in the weave of the fabric, which is a very robust way of ensuring total and uniform coverage of the protection. The grid in the weave is often very visible, aiding quality assurance.
‘Cleanroom’ garments with low fibre and particle counts Again, it is the pharmaceutical and microelectronics and paint spraying sectors who led the way with demands for fabrics and garments which could be reliably delivered to users in a condition which was free from particles and fibres, even down to 10μ (ten micron) in size. Some sectors relied on disposable fabrics initially, but as cloth suppliers developed continuous filament yarns and fabrics
ADVANCED ASSURANCE:Modern cleanrooms for microelectronics and pharmaceuticals demand specialist garments with advanced quality assurance. Editorial credit: StockphotoVideo /
Shutterstock.com
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