Fire Retardant Materials

A. Richard Horrocks, D. Price

• Publisher: Woodhead Publishing
• Year: 2001
• Print ISBN: 9781855734197
• eBook ISBN: 9781855737464
• Topic: Tecnologia e ingegneria
• Subtopic: Scienza dei materiali

This is a comprehensive source of information on all aspects of fire retardancy. Particluar emphasis is placed on the burning behaviour and flame retarding properties of polymeric materials and textiles. It covers combustion, flame retardants, smoke and toxic products generally and then goes on to concentrate on some more material-specific aspects of combustion in relation to textiles, composites and bulk polymers. Developments in all areas of fire retardant materials are covered including research in new areas such as nanocomposition.Fire retardant materials is an essential reference source for all those working with, researching into, or designing new fire retardant materials.- Detailed analysis of the burning behaviour and flame retarding properties of ploymers, composites and textiles- Covers smoke and toxic gas generation- Analysis of material performance in fire

1

Introduction: polymer combustion, condensed phase pyrolysis and smoke formation

Dennis Price Fire Chemistry Research Group, School of Sciences, University of Salford, Salford, UK

Geoffrey Anthony Great Lakes Chemical Corporation, Trafford Park, Manchester, UK

Peter Carty School of Applied Molecular Sciences, University of Northumbria, Newcastle upon Tyne, UK

Plastics and textiles find many uses and add greatly to the quality of modern-day life. However, a major problem arises because most of the polymers on which these materials are based are organic and thus flammable. In the UK alone some 800–900 deaths and roughly 15 000 injuries result from fire each year.¹ Most of the deaths are caused by inhalation of smoke and toxic combustion gases, carbon monoxide being the most common cause, whilst the injuries result from exposure to the heat evolved from fires. In addition, the annual cost of damage to buildings and loss of goods varies between £0.5 billion and £1.0 billion. Thus, there are great economic, sociological and legislative pressures on the polymer industries to produce materials with greatly reduced fire risk. To facilitate such developments this book aims to be an authoritative reference source for the highly diverse field of flame retardant materials. This introductory chapter gives an overview of the various interacting stages of the complex phenomenon of polymer combustion and flame retardance together with a more detailed consideration of condensed-phase processes and smoke. Thus it provides the background for understanding the many and varied aspects of flame retarded materials which are considered in much greater detail in the following chapters.

1.1 Polymers

1.1.1 Classification of polymers

Polymers can be classified in a variety of ways, several of which are worth considering.² Firstly, they have often simply been classified as natural or synthetic (and sometimes as synthetic modifications of natural polymers). However, a classification based on their physical/mechanical properties can also be used, in particular their elasticity and degree of elongation. Under these criteria, polymers can be classified into elastomers, plastics and fibres. Elastomers (rubbers) are characterised by having a high extensibility and recovery; plastics have intermediate properties, while fibres can have very high tensile strength but low extensibility. Plastics are often further subdivided into thermoplastics (whose deformation at elevated temperature is reversible) and thermosets (which undergo irreversible changes when heated).

1.1.2 Chemical classes of polymers

Polymers can also be classified in terms of their chemical structure, and this gives an important indication of their reactivity, including their fire performance and their tendency to produce smoke when they burn.

The main carbon-containing polymers with no heteroatoms present are the polyalkenes (polyolefins) and the aromatic hydrocarbon polymers. The main polyolefins are thermoplastics: polyethylene (repeating unit: –(CH₂–CH₂)–) and polypropylene (repeating unit: –(CH(CH₃)–CH₂–), which are the most widely used synthetic polymers. The most important aromatic hydrocarbon polymers are based essentially on polystyrene (repeating unit: –(CH(Phenyl)–CH₂)–). Polystyrene is extensively used as a foam and as a plastic for injection-moulded articles. A number of styrenic copolymers including acrylonitrile-butadiene-styrene terpolymers (ABS), styrene-acrylonitrile polymers (SAN) and methyl methacrylate butadiene styrene terpolymers (MBS) are also important.

The most important and widely used oxygen-containing polymers are cellulosics, polyacrylics and polyesters. Polyacrylics (not to be confused with polymers based on acrylonitrile) are the only major oxygen-containing polymers which contain carbon-carbon chains. The most important cellulosics are used in the timber industry and in the manufacture of paper and textiles. The main polyacrylic is poly(methyl methacrylate) (repeating unit: –(CH₂–C(CH₃)–CO–OCH₃)–; PMMA), widely used as a substitute for glass. The most important polyesters are manufactured from glycols (such as polyethylene terephthalate (PET), or polybutylene terephthalate (PBT)), or from bisphenol A (polycarbonate). They are used as engineering thermoplastics, in applications such as soft drink bottles (PET), as fibres (PET), for injection-moulded articles and as unbreakable replacements for glass (polycarbonate). Other oxygenated polymers include phenolic resins, polyethers, such as polyphenylene oxide (PPO), a very thermally stable engineering polymer and polyacetals (such as polyformaldehyde), used for their intense hardness and resistance to solvents.

Nitrogen-containing materials include nylons (polyamides), polyurethanes and polyacrylonitrile. Nylons, having repeating units containing the characteristic group –CO–NH–, are made into fibres and also into a number of injection-moulded articles, as well as for specialist uses in the wire and cable industry. Nylons are synthetic aliphatic polyamides, but there also exist natural polyamides (wool, silk, leather) and synthetic aromatic polyamides (of exceptionally high thermal stability) which are used as fibres in protective clothing. Polyurethanes (with repeating units containing the characteristic group –NH–COO–),are normally manufactured from the condensation of polyisocyanates and polyols. Their principal area of application is as foams (flexible, for use in furniture or as filling materials and rigid, for use in packaging or as thermal insulation). Both these types of polymers have carbonnitrogen chains, but nitrogen can also be contained in materials with carbon-carbon chains, the main example being polyacrylonitrile (repeating unit –(CH₂–CH–CN–)). It is used mostly to make into fibres and as a constituent of the engineering copolymers SAN and ABS.

The most important chlorine-containing polymer is poly(vinyl chloride) (PVC, repeating unit: –(CH₂–CHCl)–). (Together with polyethylene and polypropylene, it is the most widely used synthetic polymer.) PVC is unique in the sense that it is used both as a rigid material (unplasticised, as pipes, sheets, rods, bottles, siding, injection-moulded appliance housings, etc.) and as flexible material (plasticised, as wire and cable coatings, wall coverings, furniture fabrics, foams, inflatable toys, protective clothing, etc.). Flexibility is achieved by adding plasticisers. Semi-flexible materials can also be made; they are manufactured into pipes and wire and cable materials. The further chlorination of PVC leads to another member of the family of chlorinated materials: chlorinated poly(vinyl chloride) (CPVC), which has very different physical and fire properties from PVC. An additional chlorinated material of commercial interest is poly(vinylidene chloride) (PVDC, with a repeating unit: –(CH₂–CCl₂)–) used for making films and fibres.

Fluorine-containing polymers are c...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright page
• Preface
• List of contributors
• 1: Introduction: polymer combustion, condensed phase pyrolysis and smoke formation
• 2: Mechanisms and modes of action in flame retardancy of polymers
• 3: Toxicity of fire retardants in relation to life safety and environmental hazards
• 4: Textiles
• 5: Composites
• 6: Nanocomposites
• 7: Recent developments in flame-retarding thermoplastics and thermosets
• 8: Applications of halogen flame retardants
• 9: Natural polymers, wood and lignocellulosic materials
• 10: Intumescent materials
• 11: Graft copolymerisation as a tool for flame retardancy
• 12: Performance-based test methods for material flammability
• 13: Fire safety design requirements of flame-retarded materials
• 14: Mathematical modelling
• Index