Flame Retardants for Textile Materials by Asim Kumar Roy Choudhury

Contents

Preface
The words fire and flame have beencurses for millions of people throughout the ages all across the Globe. Those who have lost their homes, belongings, and relatives by fire cannot forget the these events for the rest of their lives. In many cases, fires are silent killers, killing people during sleep. With tremendous efforts by firemen and firefighters, fires may extinguish in time, only leading to realization that many unfortunate individuals have lost their lives, or have been injured, by fire. The most common natural textile materials (namely, cotton, flax, and jute), wood, and many household materials are cellulosic in nature.

All of them burn quickly, spread rapidly, and release toxic gases. People have realized this since ancient times, and the flame retardancy concept has been applied using borax and other flame retardant (FR) materials. With the advent of synthetic fibers and polymers, this problem was intensified due to their poor absorbency, caused by hydrophobicity. They also melt easily, and the dripping of melt drops results in severe injury to the burn victim. The period from 1960 to 1980 saw the development of many of well-established flame retardant materials.

During the last few decades, the knowledge about the toxicity and environmental impact of chemicals has rapidly grown, and people have become more aware of potential dangers associated with FRs. In February 2003, the Restriction of Hazardous Substances Directive (RoHS) was adopted by the European Union. This was followed by banning many FRs, mainly halogen- and halogenated- phosphosphorous FRs by various countries. The researchers put their best efforts to find eco-friendly substitutes and a large number of research works came into light. A good number of books on flame retardancy have been published in the last two decades, but most of them are devoted to specific or limited fields of flame retardancy. I came across a very large number of research publications on various chemicals and substrates. Hence, I decided to write a book covering broader topics. In this book, flame and fire retardancy of textiles and various nontextile materials (e.g., plastics, resins) are discussed which may help researchers to find newer FRs for the textile materials or vice-versa.

This book consists of 10 chapters. Chapter 1 discusses the hazards caused by fire from a historical perspective. From ancient times until the present, many cities in all parts of the world are ruined by fire; fire hazards are very common in cities and thousands of people are burned and die every year. Extinguishing fires is the job of the fireman or firefighter. Most textile materials are flammable and continue burning, even if they are taken away from fire or flame. Moreover, people who are rescued from fire die because of severe burns from burned garments; inhaling toxic gases released by burning; melting and dripping of polymers; and suffocation due to oxygen shortage. Various fire-related aspects, such as combustion, ignition, charring, and flammability are discussed in this chapter.

Chapter 2 discusses thermal and flammability properties and their variations among various natural and manmade textiles. Flammability test methods measure how easily materials ignite, how quickly they burn, and how they react when burned. A large number of flammability tests are in use, and may be classified into five groups: ignition tests (positioning test samples in vertical, horizontal, and inclined position); reaction to fire tests (how easily fire grows and spreads); application-based tests, i.e. performance of firefighters’ clothing; radiant energy tests, i.e., testing on manikins in flash fire scenarios; and scientific assessment of thermal and flammability parameters such as limiting oxygen index (LOI), which measures minimum % oxygen in air required to initiate combustion, and is the most simple, effective and popular measure to express flammability. Various standard methods of flammability tests are discussed very elaborately.

Chapter 3 describes fibers and polymers that are self- or inherent flame retardants (IFR). They do not need any further treatment to protect from fire. Their fire retardancy property is durable and can prevent hazards that are caused during finishing. Wool is naturally flame retardant, while man-made fibers (including synthetics) can be made FR by adding FR chemicals during fiber spinning or by copolymerization. Most important IFR fibers are aramid fibers and polyvinyl chloride polymers.

In Chapter 4, a variety of flame retardants are described. Flame retardant finishes are chemicals which are added to combustible materials to render them resistant to ignition. Various FRs are classified according to characteristics such as chemical structure, and durability. Mineral-, halogen-, phosphorous-, nitrogen-, and silicon-based char-forming intumescent, reactive, and hybrid organic–inorganic FRs are described and their operating principles are explained.

Chapter 5 is devoted to the most economic, most popular, and at the same time most controversial halogen-based FRs. They are widely used in consumer products because of their low impact on other material properties, and the low loading levels required to meet the required flame retardancy. However, halogen-based FRs have raised concerns due to their persistency, their bioaccumulation on living organisms, and their potential toxic effects on human health. As a result, most of them are banned or awaiting substitution by more eco-friendly FRs.

Eco-friendly and versatile, phosphorus-based FRs are described in Chapter 6. Inorganic phosphorous derivatives, mostly nondurable or semidurable, entails primarily phosphoric acid and its ammonium salts. Organophosphorous FRs include aliphatic and aromatic phosphines, phosphine oxides, phosphites, phosphates, phosphinites, phosphinates, phosphonate esters, and phosphonium salts; they promote char formation and act in condensed mode. Nitrogen acts as a synergist in some cases, and some P-N-Si compounds are popular as FRs. These compounds are successfully used, both as additives and as reactive flame retardants for a wide variety of polymer-based systems, namely cotton, rayon, wool, polyester, polyamide, polyacrylic, epoxy resin, polyurethane, and polystyrene. They have also wide applications in nontextile sectors, such as resin, and plastics.

Chapter 7 is devoted to intumescent FRs (IFRs). Researchers showed that the sustainable materials obtained from natural resources can char on burning and form protective layer(s) to make a barrier between substrate and flame/ burning gases. These intumescent FRs (IFRs) are economic, efficient, and easily applicable on various substrates such as textile fibers, resins, and foam. The intumescent behavior resulting from a combination of charring and foaming of the surface of the burning polymers is being widely developed for fire retardance because it is characterized by a low environmental impact. Research work in intumescence is very active. New commercial molecules, as well as new concepts, have appeared.

Chapter 8 examines nanocomposites, The composites are made from two or more constituent materials;at least one of the phases shows dimensions in the nanometer range. These are high-performance materials that exhibit unusual property combinations and unique design possibilities, and are thought of as the materials of the 21st century. Fire retardant, carbon-based nanomaterials are made from graphene, carbon nanotubes (CNTs), and carbon black (CB). Layered aluminosilicates, also popularly described as clays, are one such type of filler; they are responsible for a revolutionary change in polymer composite synthesis, as well as for transforming polymer composites into fire retardant polymer nanocomposites.

Chapter 9 discusses flame retardancy of synthetic fibers. In the absence of functional groups, synthetic fibers are less prone to charring. Furthermore, hydrophobicity and melting are the two disadvantages of making synthetic fibers flame-resistant. To address these problems, back-coating and intumescent FRs are alternative ways to make FR synthetic fibers. The thermallystable FRs can be added in melt or solutions of polymer before spinning, or may be applied as back-coating. Various FRs suitable for synthetic fibers and their methods of application are discussed in this chapter.

Finally, Chapter 10 explores environmental aspects of FRs. While FRs could ensure the production of fire safety products, many of them are not safe to human beings. There are more than 175 different types of FRs in the market, which contain bromine, chlorine, phosphorus, nitrogen, boron, and antimony compounds or their combinations of inorganic and organic origins.

Flame retardant products do not easily obtain eco-labels. The introduction of novel, sustainable, natural-based, intumescent FR systems represents a major scientific and technological challenge. This is expected to make a breakthrough in the production of flame-retarded polymer materials that would follow the principles of eco-designing.

Who will read this book? Students who read portions of this book will gain a basic understanding of principles and issues related to fire retardancy, the knowledge on how FR materials and associated application methods changed with time and how their performances can be tested in different flaming environments.

Researchers in one application field may find how a FR product used in other fields can be developed for their own applications. Developers, including quality assurance professionals, will find a variety of techniques which can fulfill the FR requirements of their products per specific national requirements that are dictated by prevailing national laws. Technical managers will find a coherent approach to prevent loss from burning and improve FR quality of their products. Therefore, a diverse reading audience should benefit from the contents of this book.