Polymer Green Flame Retardants (eBook)

Pantelis Kiliaris, Constantine D. Papaspyrides (Herausgeber)

eBook Download: EPUB

2014 | 1. Auflage
942 Seiten
Elsevier Science (Verlag)
978-0-444-53809-3 (ISBN)

Infos

Polymer Green Flame Retardants covers key issues regarding the response of polymers during fire, the mechanisms of their flame retardation, the regulations imposed on their use, and the health hazards arising from their combustion. Presenting the latest research developments, the book focuses in particular on nanocomposites, believed to be the most promising approach for producing physically superior materials with low flammability and ecological impact. The fire properties of nanocomposites of various matrixes and fillers are discussed, the toxicological characteristics of these materials are analyzed, addressing also their environmental sustainability. Edited by distinguished scientists, including an array of international industry and academia experts, this book will appeal to chemical, mechanical, environmental, material and process engineers, upper-level undergraduate and graduate students in these disciplines, and generally to researchers developing commercially attractive and environmentally friendly fire-proof products. - Provides recent findings on the manufacture of environmentally sustainable flame retardant polymeric materials - Covers legislation and regulations concerning flame retarded polymeric material use - Includes tables containing the fire properties of the most common polymeric materials

Textauszug

Chapter 1

Polymers on Fire

P. Kiliaris,  and C.D. Papaspyrides     National Technical University of Athens, Athens, Greece

Abstract

This introductory chapter discusses the fundamentals of polymer combustion, presents the typical pattern of fire growth and evolution of fire hazards, describes the main tests applied to estimate the performance of polymeric materials against fire, summarizes the modes of flame retardation, and briefly analyzes the action of the commonly used flame retardants along with the positive synergistic effects that their combination can exert on polymer flammability. The objective is to lay the foundations for understanding the many and various aspects of polymer flame retardancy, which are thoroughly analyzed in the following chapters.

Keywords

Combustion; Fire retardant; Fire tests; Flame retardancy; Polymer

Chapter Outline

1. Introduction?1

2. Polymer combustion?3

3. The stages of fire evolution and the corresponding hazards?5

4. Fire testing?8

5. Strategies of flame retardancy?12

5.1 Halogen-based flame retardants?15

5.2 Phosphorous-based flame retardants?18

5.3 Nitrogen-based flame retardants?21

5.4 Intumescent systems?24

5.5 Mineral flame retardants?27

5.6 Silicon-based flame retardants?30

5.7 Nanoparticles?32

6. Conclusions?35

References?36

1. Introduction

Owing to their outstanding combination of properties—low weight and ease of processing—polymeric materials, being used in countless application areas and under the most demanding conditions, have added greatly to the quality of modern life and the progress of human civilization. However, one of the most important problems arising by their use is associated to the fact that the majority of the polymers, on which these materials are based, are organic and thus flammable. Unwanted fires account for considerable losses of life and property; therefore, fire hazards related to the use of polymeric materials are of particular concern among government regulatory bodies, consumers, and manufacturers, and there are great economic, sociological, and legislative pressures on plastics industries to produce materials with greatly reduced fire risk. The approach, typically followed for enhancing the performance of polymers against fire, involves the addition of the so-called flame retardants. The role of the flame retardant is to render the polymer formulation less flammable by interfering with the chemistry and/or the physics of the combustion process. In most cases, the use of flame retardants to reduce polymer combustibility (along with smoke or toxic fume production) comprises a critical part of the plastics materials production. Among the major markets, in which flame retardants are required, are the industries dealing with construction, transportation, and electrical and electronics components [1–3].

The interest in reducing the flammability of polymeric materials goes back to the nineteenth century when highly flammable cellulose nitrate and celluloid were discovered. Until quite recently, however, the enhancement of polymer flame retardancy has been as much an art as it has been a science. The strategies commonly adopted involve incorporating nonflammable fillers, compounds that decompose endothermically, substances that provoke char formation, and/or materials that during fire liberate gases acting as radical traps in the gas phase. Typical of the last mentioned group of fire retardants are halogenated compounds (such as chlorinated and brominated aliphatics and aromatics), which evolve hydrogen halides when heated. Traditionally, the incorporation of halogen-based compounds comprised the most widely applied method for enhancing the flame retardancy of polymers, since, besides its low cost, it led to materials exhibiting mechanical performance similar to that of their Flame retardant-free (FR-free) analogs. However, despite these benefits, concerns were recently raised which were caused by findings of brominated flame retardants in the environment, biota, and humans, and evidence of formation of toxic dioxins and furans during the combustion of halogens. These concerns have led to restrictions to the marketing and use of certain flame retardants, e.g. the ban on penta- and octa-brominated diphenyl ethers. Moreover, some Scandinavian countries like Norway and Sweden have been considering national banning of some additional brominated compounds, even restricting some which had a positive European Union (EU) risk assessment. As a consequence, the market trend has been pushed to halogen-free flame retardants. Nevertheless, nonhalogen compounds are also confronted with disadvantages associated with their inefficiency at low concentrations, which may lead to additional costs and inferior polymer mechanical properties. Therefore, the development of environmentally friendly and highly effective flame retardants is a hot topic in the plastics industry that has prompted extensive research into deeply understanding the action of existing flame retardants (so as to improve their performance and extend their application field), as well as into novel technologies [4–6].

This chapter provides a concise introduction to the flame retardancy of polymers; more specifically, the fundamentals of polymer combustion are discussed presenting the typical pattern of fire growth and evolution of fire hazards, the main tests applied to estimate the fire performance of polymeric materials are described, and the modes of flame retardation along with the mechanisms of (synergistic) action of the major classes of flame retardants are briefly reviewed. The main objective of this chapter is to make this book and, thus, the field of “(green) flame retardants for polymers” more accessible to the community of materials science and engineering. However, though designed with a “back to basics” orientation in order to comprise a useful tool for people new to these topics, scientists who expertise in this field may also find new interesting information.

2. Polymer combustion

Polymers are chemical compounds or mixtures of compounds consisting of a relatively large number of repeating structural units (of low relative molecular mass). The binding of these smaller molecules is achieved through the process of polymerization. The term derives from the ancient Greek words “?o??” (“poly,” meaning “many”) and “???o?” (“meros,” meaning “part”), and refers to a process through which molecules of high molecular weight (exceeding 1500 g mol?1) are formed exhibiting properties not shared by low-molecular-weight materials. Polymers are thus composed of “chains” of atoms linked to one another; the simplest (carbon–carbon) chain is that of polyethylene, in which the repeating unit is ethylene (–CH2–). Polymers are neither purely crystalline nor purely amorphous, and thus they are not, strictly speaking, solid materials (even though they are normally solids in the sense that they are bounded by plane surfaces). When all the structural units correspond to the same monomer, the material is called a homopolymer; on the contrary, copolymers are compounds in the molecules of which different structural units exist [7,8].

Polymers can be natural or synthetic and they were initially classified, according to their response to temperature, into thermoplastics (whose deformation at elevated temperature is reversible) and thermosets (which when heated undergo irreversible changes). A categorization based on their physical/mechanical properties (in particular their elasticity and degree of elongation) is also used, classifying polymers into elastomers, plastics, and fibers. Elastomers (rubbers) are characterized by high extensibility and recovery, plastics exhibit intermediate properties, whereas fibers possess very high tensile strength but low extensibility. Polymers are also classified according to the type of the polymerization reaction through which they are formed: condensation and addition. However, the most useful classification method is the one based on their chemical composition since it gives indication of their reactivity, including thermal decomposition and response against fire. According to this method, polymers are basically categorized into carbon-containing (e.g. polyolefins), oxygen-containing (e.g. polyesters), nitrogen-containing (e.g. polyamides), chlorine-containing (e.g. poly(vinyl chloride)), and fluorine-containing polymers (e.g. polytetrafluoroethylene) [9,10].

Due to their chemical structure, polymers are generally highly combustible. When exposed to sufficient heat, they decompose (pyrolyze) generating combustible gases which mix with the oxygen of the ambient air to form an ignitable blend. Ignition occurs either impulsively if the temperature is adequate for autoignition (defined as the temperature at which the activation energy of the combustion reaction is achieved) or at a lower temperature (called the flash point) due to the presence of an external source (flame or spark). Upon combustion, heat is released, a part of which is transferred to the substrate promoting further decomposition. If the heat evolved is enough to keep the decomposition rate of the polymer above that required to maintain the concentration of the volatiles within the flammability limits, then a self-sustaining...

Produkt-Details

• Erscheint lt. Verlag: 14.8.2014
• Sprache: englisch
• Themenwelt: Medizin / Pharmazie ► Pflege
• Themenwelt: Medizin / Pharmazie ► Physiotherapie / Ergotherapie ► Orthopädie
• Themenwelt: Naturwissenschaften ► Chemie ► Technische Chemie
• Themenwelt: Technik ► Bauwesen
• Themenwelt: Technik ► Maschinenbau
• Themenwelt: Technik ► Medizintechnik
• Themenwelt: Technik ► Umwelttechnik / Biotechnologie
• ISBN-10: 0-444-53809-7 / 0444538097
• ISBN-13: 978-0-444-53809-3 / 9780444538093