Dr Ningtao Mao looks at the minutiae of fabric construction and the lengths researchers go to in order to achieve worker safety. Here he reviews the properties of materials used – including traditional fibres and high performance fibres – in existing specialist workwear, and compares those properties against the requirements for the fabric materials set in the CE marking standards.
Regular readers of H&SI will know that it’s unusual for us to serialise articles. We’ve made an exception in this instance, however, since the sheer depth and breadth of an article submitted by Dr Ningtao Mao, Senior Lecturer in Performance Textiles at the University of Leeds, commanded it. In July’s edition, Dr Mao gave readers an overview of how different kinds of workwear serve different purposes, explored the global market and focused on the many regulations pertaining to specialist workwear. You can read part one of the article here: http://www.bay-publishing.com/article.php?article_id=696 In this edition, Dr Mao explores the essential elements necessary for achieving worker protection, and gives a thorough review of the major requirements set in EU CE marking standards. Central to his research is a table outlining the minimum requirements of some specialist workwear. The table on page 60-63 will serve as a vital reference for readers.
Both conventional and high performance fibres are employed to produce fabrics for specialist workwear. Fabrics made from traditional synthetic fibres such as polyethylene, polypropylene, polyester, polyamide and polyurethane fibres are still widely used in the specialist workwear for the purpose of balanced performance and cost effectiveness. For example, polyamide fibres, e.g. Nylon, are still used as a durable layer of much protective workwear. Some high performance fibres have poor abrasion resistance; in this case, they are usually blended with conventional fibres having superior abrasion resistance properties, e.g. polyamide fibres, combined with polyurethane coating, or layered with polyamide fabrics. Microfibres, bicomponent fibres, hollow fibres, fibres/filaments having non-circular cross-sections made from those conventional synthetic polymers are also frequently used in protective clothing, clothing comfort and durability purposes. Natural fibres and fibres regenerated from natural polymers such as cotton, wool, down (see Figure 1(a)) and viscose rayon (including their special variants, e.g. FR modified) are also frequently employed to achieve protection such as thermal and cold protection, and clothing comfort properties. Fabrics made from those conventional fibres are usually in a mixture form and additionally blended with other special performance fibres for antistatic, fire resistant and chemical resistant functions. Those fabrics usually require special treatment and finishing such as multiple coating, lamination and other special finishing. These treatments could achieve water/oil repellent, moisture permeable, softness, antibacterial, or insecticide properties for multiple protection functions. High performance textile materials having exceptional mechanical properties, fire resistant properties and chemical resistant properties are available in the form of fibre, film, membrane and liquid, and are frequently used in specialist workwear. These fibres are made from a wide source including organic polymers and inorganic materials such as ceramic fibres, carbon fibre, and stainless steel and aluminium fibres. They feature Aramid (including p-aramid (poly-para-phenylene terephthalamide) and m-aramid (poly(meta-phenyleneisophthalamide)), PI (Polyimide), PBI (Polybenzimidazole), PEN (polyethylene-2,6-naphtalat), PBO (p-phenylene-2,6-benzobisoxazole), UHMWPE (Ultra-high Molecule Weight Polyethylene), LCP (Polyarylate), PPS (Polyphenylene sulphide), PEEK (Polyetheretherketone), Novoloid (cured phenol-aldehyde), Melamine, PTFE, and fire resistant natural (zirpro-wool) and regenerated (FR viscose) fibres. Those fibres are usually mixed or interwoven in the fabrics, or used as layered fabric structures to have a combination of multiple protection functions in specialist workwear. Most high performance fibres – except those converted from natural fibre sources – do not have moisture management properties, however, and have high stiffness. The fabrics made from them are frequently used together with natural fibres to achieve required clothing comfort properties.
Yarn and fabric structure is also crucial in the design of specialist workwear. For example, composite cord threads using metal filaments as core and other high performance fibres as sheath are used in special fabrics to provide flexibility as well as cut protection, ballistic-proof and stab-proof, protections from gunshots, shrapnel and knife stabs are reported. The super-strong, high performance fibres (such as UHMWPE fibres) absorb the impact energy to stop the damaged knife and minimise trauma, while the metal wire blunts the sharp edge of knives and shrapnel. Strong polyester filament sheath-core composite yarns are also created to realise both strength and comfort properties. Fabric weaves are also important. For example, basket weaves and rip-stop structures are well known for their superior mechanical strength. It was found in the research that the specific energy absorption increases with the increase of the fabric tightness and fabric areal density for fabrics made from p-Aramide, PBO and UHMWPE fibres. New fabric structures and their uses in specialist workwear might also be worth exploring, such as fabrics made from metal wire-high performance fibre composite yarns, spacer fabric, 3D fabric, multidirectional weave fabrics, honeycomb composite, Autex structure, and biomimetic inspired materials. Woven and nonwoven fabrics made from synthetic filaments (e.g. polyester, polyamide, polyethylene and polypropylene) are frequently used in making reusable and disposable workwear. These fabrics not only protect people from many hazards such as biological and chemical substances, steam, temperature extremes, sharp-edged tools, harsh cleaning solutions, they also prevent contaminants both carried by workers and existing in workwear itself from entering the controlled environment and making contact with equipment or product. The materials used in those products are required to be both lint-free and able to stand the degradation during harsh sterilisation (either chemical or radiation) and laundering (for reusable clothing) processes.
Specialist workwear has long remained functionality driven and products are equipped with hybrid materials, smart technology and nanotechnology. Technological innovations include: • High performance materials used for protection; for example, a new concept energy absorption material (e.g. shear-thickening fluid, magnetic shear-thickening materials, air inflatable structures) to make flexible and lightweight fabric without compromising protection and comfort properties • Intelligent materials – intelligent polymer membrane (see Figure 1(c)), shape memory polymers, electro-active polymers, piezoelectric, pyroelectric, thermoelectric or photovoltaic materials • New materials and structures used for thermal comfort; for example, nanopartcile-fabric composites (see Figure 1(b)), Phase Change Materials (PCM), moisture/temperature responsive materials, electric conductive yarns, carbon nanotubes These materials are able to sense the wearers’ physiological condition, their posture and activity and outside environment, as well as responsive action.
Published: 01st Sep 2012 in Health and Safety International