Heat protective textiles

Notwithstanding the above, heat and fire protection afforded by any material is environmentally and time dependent and the concept of a perfectly heat protective textile should be dismissed. Levels of protection are therefore relative rather than absolute and so, for example, should be qualified by time of exposure to a heat source having a defined character (e.g. radiant versus flame), intensity, and temperature as well as a measure of access to oxygen as mentioned above. 

Useful for heat protection, the most notable characteristic of asbestos is that it will not bum. It can be spun and woven into textiles. However, asbestos is a known carcint en. It is highly toxic when inhaled as dust particles. The American Conference of Governmental Industrial Hygienists has established a maximum exposure level to chrysotile fibers. A worker may be exposed, without adverse effects, to 2 fibers/cc more than 5 microns long. 

The reported world tonnage in 1990 was 20001 [688]. One of the major limitations to its use in visible applications is that it is available only in black. For protection against intense heat, however, it offers considerably more protection than conventional fire protection textile fibers. A PANOX-based fabric is reported to maintain a barrier against a 900°C flame for more than 5 min. In addition to its low flammability, it has an exceptionally low thermal conductivity [689]. 

Suitable UV and heat protection can be achieved by the textile itself. Heat and UV protection increases with the density of the textile and with the use of bulky microfibres. Cellulose fibres and silk provide lower UV protection when compared to woollen materials or to polyester with aromatic components. Increased UV protection is obtained by the incorporation of pigments like titanium dioxide into the fibres. This absorbs and reflects UV rays and creates a sun protection factor of 50. Finishing agents are alkyl p-aminobenzoates and cinoxates which also absorb UV radiation and convert it into heat. 

This chapter will focus upon flame and heat protection within the technical textile sector only and will consider the reqnirements and properties of the many and varied types of fibre that are currently available. Many other recent reviews of the general flame retardancy of textiles are available s and the reader is recommended to consult these for a fuller understanding of the issues involved. 

Inherently FR polyamide fibres. Nylon or polyamide 6.6 has a higher melting point and superior tensile properties to polyamide 6 and so has the better characteristics to offer technical textiles. However, and in spite of the considerable research over the last 40 years, at the present time only one flame retardant polyamide 6.6 appears to available, which is Nexylon FR, EMS-GRILTECH of unknown composition, announced in September 2012. This fusible fibre is currently being aimed at the protective clothing and workwear markets but such applications will require flame retardancy as their primary property rather than heat protection. 

Table 8.4 Maximum service temperatures for heat resistant fibres in thermally protective textiles ...

In this chapter, issues in personal thermal protection are discussed, focusing on the needs of workers in selected sectors energy (oil and gas), electrical, other industry sectors, and both structural and wildland firefighting. The important protection concerns for workers in each sector are discussed, followed by a discussion of potential trade-offs between thermal protection and thermal comfort. Clothing issues such as fit, comfort, and other ergonomic factors are briefly discussed. Recent developments in protective textile materials are followed by a diseussion of serviceability concerns, including durability and maintenance. A review of international performance standards is followed by a summary of the development of test methods to assess protection from heat, flame, hot liquids, and steam. Issues for future development of technical textiles for personal thermal protection are then discussed briefly. 

Rossi RM, Schmid M, Camenzind MA. Thermal energy transfer through heat protective clothing during a flame engulfment test. Textil Res J 2014 84(13) 1451-60. 

New materials and designs have been developed for heat protective clothing. For example, improved thermal insulation can be provided by non-wovens made with thin hollowed fibres, and can be made thermo-adaptive with two-way shape memory alloys such as nickel-titanium. Better thermoregulation inside the garment is sought with PCM, either encapsulated ° or incorporated in a matrix. Other solutions use external power, e.g., for liquid coolant circulation or with Peltier cells embedded in the textile. ... 

Key words protective textiles, fire resistance, heat resistance, aramid, thermoset, ceramic, intumescent, nanotechnology. 

It is probably evident from the above introductory discussion, and important to realise, that the whole issue of heat and fire protection with respect to textiles is a complex area involving knowledge of elements of fire science, flame retardant treatments, development of heat and fire resistant fibres and derived textile structures and the inter-relationships between regulations, applications and markets. The bibliography lists a number of prime sources of information in these areas, and for an overview of textiles for fire and heat protection the reader should refer in particular to a recent article by this author. In this chapter, the focus will be only on high performance textiles in which fire and heat protection are essential requirements. 

Finally, conductive heat protection is required for textiles that may come into direct contact with a heat source other than a flame. Major threats here include those met by metal industrial workers, who risk contact with hot metal tool handles and molten metal splashes. For this reason, not only must the thermal insulating characteristics of the textile be paramount, but also surfaces which minimise contact, for instance by resisting wetting by molten metals, must be considered. However, in many thermally hazardous environments, a combination of conduction, convection (or flame) and radiation may be operating in concert, and usually the last two are associated with flame sources in particular. 

Zylon or PBO is a more recently developed fibre than PBI and has outstanding tensile properties, as well as thermal and fire properties superior to any of the polymer-based fibres mentioned in this chapter (see Table 4.2). While there are at least two variants of the fibre, Zylon-AS and Zylon-HM, of which the latter has the higher modulus, both have the same thermal and burning parameter values. Principal examples of thermally protective textiles include heat protective clothing and aircraft fragment/heat barriers, where its price, similar to that of PBI, restricts its use to applications where strength, modulus and fire resistance are at a premium. 

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