Heat protective textiles applications

RCF is sold in a variety of forms, such as loose fiber, blanket, boards, modules, doth, cements, putties, paper, coatings, felt, vacuum-formed shapes, rope, braid, tape, and textiles. The products are principally used for industrial applications as insulation in furnaces, heaters, kiln linings, furnace doors, metal launders, tank car insulation, and other uses up to 1400°C. RCF-consuming industries indude ferrous and nonferrous metals, petrochemical, ceramic, glass, chemical, fertilizer, transportation, construction, and power generation/incineration. Some newer uses include commercial fire protection and applications in aerospace, eg, heat shields and automotive, eg, catalytic converters, metal reinforcement, heat shields, brake pads, and airbags. 

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]. 

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. 

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. 

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. 

Shape-memory alloys (e.g. Cu-Zn-Al, Fe-Ni-Al, Ti-Ni alloys) are already in use in biomedical applications such as cardiovascular stents, guidewires and orthodontic wires. The shape-memory effect of these materials is based on a martensitic phase transformation. Shape memory alloys, such as nickel-titanium, are used to provide increased protection against sources of (extreme) heat. A shape-memory alloy possesses different properties below and above the temperature at which it is activated. Below this temperature, the shape of the alloy is easily deformed due to its flexible structure. At the activation temperature, the alloy can be changed by applying a force, but the structure resists this deformation and returns back to its initial shape. The activation temperature is a function of the ratio of nickel to titanium in the alloy. In contrast with Ni-Ti, copper-zinc alloys are capable of a two-way activation, and therefore a reversible variation of the shape is possible, which is a necessary condition for protection purposes in textiles used to resist changeable weather conditions. 

The requirements for a material to be effective as a UV protection finish include efficient absorption of UV radiation at 300-320 mn, quick transformation of the high UV energy into the vibration energy in the absorber molecules and then into heat energy in the surroundings without photodegradation. Further requirements are convenient application to textile fibres and lack of added colour for the neated fibre. Some typical chemical snuctures useful for UV protection are shown in Fig. 

Heat resistant fibres, however, are those having chemical structures that are little changed physically or chemically by temperatures above the 200°C, and even the 300°C, levels and, in the case of ceramic fibres, above 1000°C. For textiles used in high temperature industrial processes, such as gas and liquid filtration, long term exposure to temperatures of about 100°C is often required, but not all these fibres are used in thermally protective applications. However, in long term exposure thermally protective applications, we need to be able to define maximum service fife temperatures, and these are listed in Table 4.2 for selected heat resistant fibres. 

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