Wednesday, 26 August 2015

Flame Retardancy and Protection against Biodeterioration of Natural Fibers: State-of-Art and Future Prospects

2014, Pages 801–836

Since natural fibers have several advantages in comparison with man-made ones, they are widely used in the apparel sector and in interior furnishing. Lignocellulosic and protein fibers comprise the two most important groups of natural fibers. The third group includes mineral and carbon fibers, which contrary to lignocellulosic and protein fibers, are more stable in fire conditions. Lignocellulosic natural fibers have very low fire resistance. The most widely used representatives of this group are fibers made from cotton, flax, hemp, jute, sisal, ramie, abaca, and cabuya. On the other hand, protein fibers (wool, alpaca, silk, and hair), containing nitrogen and sulfur, present better performance, mainly during the ignition stage. For protecting natural fibers against fire flame retardants are used, whose role is to delay ignition time, decrease heat release and surface spread of flame, and also to reduce mass loss rate and fire propagation. For cellulosic fibers, nondurable, semidurable and durable finishes are used. Organophosphorus and trimethylomelamine, and “Zirpro” flame retardant treatment based on complexes of titanium/zirconium with fluorides citrates or others is applied for wool and silk. Recently, flexible intumescent coatings emerged as a promising approach for protecting the backside of decorative fabrics. Moreover, the development of fire retardants with reduced leachability, low bioavailability, and generally with reduced environmental impact has drawn a great deal of interest. Chemical, biochemical, and genetic modification of natural fibers is within the scope of research as well.
On the other hand, natural lignocellulosic and protein fibers are susceptible to biodeterioration, caused by microorganisms, such as bacteria and saprophytic fungi (i.e. mildew). This is one of the important limiting factors of the use of natural fibers. The process of decomposition can occur in anaerobic and aerobic conditions. For this reason, employing systems and applying methods (involving physicochemical treatment and genetic modification) to protect fibers and textiles against microorganisms is of great importance. Recently, the application of natural biocides has grown in popularity; this group includes natural alkaloids, flavonoids, terpenes, tannins, essential oils, chitosan with antimicrobial activity, and active peptides such as cytopine, protegrine, temporine, amiganane, and periganane. However, there are some concerns regarding the bioavailability of different biocides and their mutagenic activity.
In this chapter, the flammability properties of various natural fibers in comparison with man-made ones are presented. Focus is placed also on the flame retardancy of leather, because of its wide use especially in interior upholstery. Furthermore, considering the significance of the “microbiological decay” effect, methods for developing and incorporating antimicrobial agents natural fibers, textiles, and leather are described, providing information on research trends.