Development of high performance W7 thermal protective clothing
In clothing development, a primary focus is the selection of the proper type of textile fibers, as they are the basic raw material to manufacture clothing [169,170]. The selection of fibers is dependent upon the end-use of the clothing . For instance, one of the major considerations for fibers used in firefighters’ protective clothing is high performance in fire-retardancy/resistancy [4,172]. By using fibers that meet this criterion, fire-retardant/resistant fabrics can be developed. The following sections thoroughly discuss the development of high-performance fibers, fabrics, and clothing, specifically for heat and flame.
Development of fire-retardant/resistant fibers
One of the common characteristics of all fibers (harvested/natural and man-made/ synthetic) is that they burn in the presence of oxygen and high temperatures [173,174]. Natural fibers start to pyrolyse at elevated temperatures in the presence of oxygen. If the supply of oxygen continues and/or temperatures continue to rise, the natural fibers ignite after some time, resulting in their combustion. During their combustion, gaseous substances, water vapor, and radiant heat/flame generate. The behavior of natural fibers at high temperatures in the presence of oxygen is demonstrated in Fig. 4.1 [175-177].
Fig. 4.1 Behavior of natural fibers in the presence of oxygen and high temperature.
Thermal Protective Clothing for Firefighters. http://dx.doi.org/10.1016/B978-0-08-101285-7.00004-6
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Synthetic fibers are commonly manufactured through melt spinning or solution spinning techniques. In the case of melt spinning, a polymer is melted and passed through a spinneret; after passing through the spinneret, the extruded filament is solidified through cooling. The resultant solidified filament is conditioned through moisture, and finishing is applied to the final product. For solution spinning, a polymer is dissolved in a solvent or chemically treated to make a fluid polymer; this fluid polymer is forced through a spinneret in a spinning bath, where the polymer cools down to a rubbery state and then finally solidifies. These melt-spun and solution-spun synthetic fibers are mainly thermoplastic in nature and become soft at high temperatures. This condition is called the glass transition period, and the temperature at which synthetic fibers soften is called the glass transition temperature. Subsequently, these fibers melt at their melting temperatures and, later, they pyrolyse/degrade at their pyrolysing temperatures. Finally, these synthetic fibers ignite and their combustion occurs at the combustion temperature (Fig. 4.2) [178,179].
Fig. 4.2 Behavior of synthetic fibers in the presence of oxygen and high temperature.
For natural and synthetic fibers, the amount of oxygen required for combustion varies from fiber to fiber [180-182]. The combustibility (or fire-retardant/resistant property) of a fiber is expressed in terms of the minimum amount (%) of oxygen required for its combustion, the limiting oxygen index (LOI). If the LOI value of any natural or synthetic fiber is >21%, such fiber can be called a fire-retardant/resistant fiber. Generally, the frequently used first-generation natural (wool, cotton, and viscose) or second-generation synthetic (polyester, nylon, and acrylic) fibers can easily pyrolyse or soften, respectively. Consequently, the combustibility of these fibers is high, and the LOI values of these fibers are low (<21%). Through chemical modifications, the pyrolysing temperature (for natural fibers) or glass transition temperature (for synthetic fibers) could be increased; therefore, the LOI values of these fibers could improve (at least >21%). These types of fibers are referred to as chemically modified fire-retardant fibers [4,16,17,183].