177,99 €
Mehr erfahren.
- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
A one-stop, practical handbook containing all of the current commercial non-halogenated flame retardant technologies as well as experimental systems near commercialization In response to the emphasis on replacing halogenated flame retardants with alternate technologies, this handbook focuses on existing non-halogenated flame retardants and the experimental close-to-production systems that are available today. The Non-Halogenated Flame Retardant Handbook starts with an overview of the regulations and customer perceptions driving non-halogenated flame retardant selections over older halogenated technologies. It then moves on to cover the known major classes of non-halogenated flame retardants, before concluding with the current niche-performing technologies and untried commercial contenders of the future. The Non-Halogenated Flame Retardant Handbook: * Takes a practical approach to addressing the narrow subject of non-halogenated flame retardancy--placing more emphasis on flame retardant selection for specific plastics, practical considerations in flame retardant material design, and the various technologies' strengths and limits * Focuses on the proper use of non-halogenated flame retardants, rather than the mechanics of how they work * Discusses important future trends in flame retardancy * Features sections written by industrial and chemical experts who know how to apply the technology to polymers for fire safety needs
Sie lesen das E-Book in den Legimi-Apps auf:
Seitenzahl: 652
Veröffentlichungsjahr: 2014
Ähnliche
Contents
Cover
Half Title page
Title page
Copyright page
Preface
List of Contributors
Chapter 1: The History and Future Trends of Non-halogenated Flame Retarded Polymers
1.1 Introduction
1.2 Key Flame Retardancy Safety Requirements
1.3 Geographical Trends
1.4 Applications for Non-halogenated FRP’s
References
Chapter 2: Phosphorus-based FRs
2.1 Introduction
2.2 Main Classes of Phosphorus-based FRs
2.3 Polyolefins
2.4 Polycarbonate and Its Blends
2.5 Polyphenylene Ether Blends
2.6 Polyesters and Polyamides
2.7 Thermoplastic Elastomers (TPE) and Thermoplastic Polyurethanes (TPU)
2.8 Epoxy Resins
2.9 Unsaturated Polyesters
2.10 PU Foams
2.11 Textiles
2.12 Conclusions and Further Trends
References
Chapter 3: Mineral Filler Flame Retardants
3.1 Introduction
3.2 Industrial Importance of Mineral Flame Retardants
3.3 Overview of Mineral Filler FRs
3.4 Working Principle of Hydrated Mineral Flame Retardants
3.5 Thermoplastic and Elastomeric Applications
3.6 Reactive Resins/Thermoset Applications
3.7 Summary, Trends and Challenges
References
Chapter 4: Nitrogen-based Flame Retardants
4.1 Introduction
4.2 Main Types of Nitrogen-based Flame Retardants
4.3 Ammonia-based Flame Retardants
4.4 Melamine-based Flame Retardants
4.5 Nitrogen-based Radical Generators
4.6 Phosphazenes, Phospham and Phosphoroxynitride
4.7 Cyanuric Acid-based Flame Retardants
4.8 Summary and Conclusion
References
Chapter 5: Silicon Based Flame Retardants
5.1 Introduction
5.2 Basics of Silicon Chemistry
5.3 Industrial Applications of Silicones
5.4 Silicones as Flame Retardant Materials
5.5 Mode of Actions of Silicone-based Flame Retardants
5.6 Toxicology and Environmental Effects of Silicones
5.7 Future Trends in Silicon-based Flame Retardants
5.8 Summary
References
Chapter 6: Boron-based Flame Retardants in Non-Halogen-based Polymers
6.1 Introduction
6.2 Major Functions of Borates in Flame Retardancy
6.3 Major Commercial Boron-based Flame Retardants and Their Applications
6.4 Mode of Actions of Boron-based Flame Retardants
6.5 Conclusions
References
Chapter 7: Polymer Nanocomposites: A nearly Universal FR Synergist
7.1 Introduction
7.2 Inorganic Materials as Candidate for Nanocomposite Formation
7.3 Nanocomposites as Non-Halogenated Flame Retardation Solutions
7.4 Combinations of Nanocomposite with Traditional Flame Retardants
7.5 Contribution of Nanocomposites to Achieve New FR Cable Standard (EU CPR)
7.6 New Developments and Outlook
References
Chapter 8: Intumescent Systems
8.1 Introduction
8.2 The basics of Intumescence
8.3 Intumescent Products and Formulations Used in Thermoplastic and Thermoset Materials
8.4 Intumescent Systems in Fire Protection
8.5 Trends and Challenges in Intumescent Systems
8.6 Conclusions
References
Chapter 9: Other Non-Halogenated Flame Retardant Chemistries and Future Flame Retardant Solutions
9.1 The Periodic Table of Flame Retardants
9.2 Transition Metal Flame Retardants
9.3 Sulfur-based Flame Retardants
9.4 Carbon-based Flame Retardants
9.5 Tin-based Flame Retardants
9.6 Engineering Non-Hal FR Solutions
9.7 Future Directions
Acknowledgements
References
Index
Non-Halogenated Flame Retardant Handbook
Scrivener Publishing
100 Cummings Center, Suite 541JBeverly, MA 01915-6106
Publishers at Scrivener
Martin Scrivener([email protected])
Phillip Carmical ([email protected])
Copyright © 2014 by Scrivener Publishing LLC. All rights reserved.
Co-published by John Wiley & Sons, Inc. Hoboken, New Jersey, and Scrivener Publishing LLC, Salem, Massachusetts.
Published simultaneously in Canada.
No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 750-4470, or on the web at www.copyright.com. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) 748-6011, fax (201) 748-6008, or online at http://www.wiley.com/go/permission.
Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The advice and strategies contained herein may not be suitable for your situation. You should consult with a professional where appropriate. Neither the publisher nor author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages.
For general information on our other products and services or for technical support, please contact our Customer Care Department within the United States at (800) 762-2974, outside the United States at (317) 572-3993 or fax (317) 572-4002.
Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic formats. For more information about Wiley products, visit our web site at www.wiley.com.
For more information about Scrivener products please visit www.scrivenerpublishing.com.
Cover design by Russell Richardson
Library of Congress Cataloging-in-Publication Data:
ISBN 978-1-118-68624-9
Preface
Over the past 20-30 years, there has been a major change in flame retardant material science as certain chemical additives have been under intense scrutiny for persistence, bioaccumulation, and toxicity (PBT) issues. The class of flame retardants that has taken the brunt of the scrutiny is the oldest and most commonly used modern flame retardants, those based upon halogen (chlorine or bromine). As such, brominated and chlorinated flame retardants have either been banned from use or voluntarily de-selected by end-users as the market and regulations have pushed them out of use. The fire threat has not gone away however as those halogen based flame retardants were deselected, and so flame retardants without halogen content, or broadly named non-halogenated flame retardants, have surged into use and demand. Unlike halogenated flame retardants, which can be widely used in several applications and polymers (but not universally) due to their vapor phase flame retardant mechanism, non-halogenated flame retardants tend to be more restricted to specific polymers and specific fire risk scenarios. Therefore, among material scientists, there has been a clear need for non-halogenated flame retardant understanding in how to use them and in which polymers those flame retardants would be useful. This handbook, one of the first to focus solely on non-halogenated retardants, is a reflection of that market and scientific community need.
The book you are holding is broken down into an introduction on why non-halogenated solutions are needed, several chapters on the specific classes of non-halogenated flame retardants available, and then a conclusion on the unmet needs and future of non-halogenated flame retardants. Industrial experts on the practical use of non-halogenated flame retardants were solicited to write chapters and have done so, along with inputs from key scientific researchers in some chapters. The book is called “handbook” for a reason; it is meant to be a practical distillation of knowledge to capture the scientific literature and comfortable enough to get started on the use of non-halogenated flame retardants, and serve as a quick reference point for when more complex solutions or research, development, testing, and evaluation (RDT&E) are required. Based upon our many combined decades of flame retardant science and knowledge, we believe this handbook will help the reader understand and utilize non-halogenated flame retardants, and educate them on what is known and still unknown about this wide range of materials. We hope that you will find the book to be of great utility now and in the future.
As with all prefaces, we would like to thank those who helped make this book possible, especially the authors of the individual chapters who have taken time out of their busy lives to write the chapters. We also wish to thank Scrivener for their publishing support. Finally, we would like to thank our wives, Julie Ann Morgan and Nancy Wilkie for their continued support.
Alexander B. MorganJanuary 27, 2014. Dayton, Ohio USA
Charles A. WilkieJanuary 27, 2014. Milwaukee, WI USA
List of Contributors
Dr. Günter Beyer pioneered the use of nanoclays as flame retardant synergist in halogen free wire and cable compounds and is one of the most well-known flame retardant experts in the world.
Dr. Paul Cusack is currently Technology Manager (Polymers and Fire Testing) at ITRI Ltd, UK – his main research interests being fire-retardant technology, fire testing and chemical / polymer product development.
Professor Sophie Duquesne of the University of Lille researches in the development of new FR formulations for polymeric materials (process and characterization), in particular intumescent systems and nanocomposites and the recycling of polymeric wastes.
Dr. Thomas Futterer has many years’ experience in the development and marketing of flame retardants in polymer and coatings applications. His current position is at Chemische Fabrik Budenheim as Head of Business Development.
Dr. Mert Kilinc is a Materials & Finishing Engineer with Philips Consumer Lifestyle, Drachten, the Netherlands.
Dr. Martin Klatt is a leading the flame retardancy research at BASF SE with a special focus on new flame retardant molecules and development of flame retardant polymeric compositions.
Dr. Tie Lan is an expert in bentonite clay chemistry and technology, particularly in the use of refined bentonite clay in the formation of polymer nanocomposites, and their commercial applications including flame retardation, packaging barrier and mechanical reinforcement.
Dr. Sergei Levchik is R&D Director with ICL-IP America doing research and new product development in phosphorus based flame retardants.
Dr James W. Mitchell is the Electrical Equipment Global Market Director, Solvay Engineering Plastics, Lyon, France.
Dr. Alexander B. Morgan is at the University of Dayton Research Institute (UDRI) where he is currently the group leader for the Applied Combustion and Energy group.
Dr. Reiner Sauerwein is the Senior Manager Development & Application Technology, Division Functional Fillers with Nabaltec AG, Schwandorf, Germany.
Dr. Kelvin K. Shen is a consultant of flame retardant polymers for Rio Tinto Minerals/U.S. Borax, NASA, and other plastics/rubber companies.
Charles A. Wilkie is currently Professor Emeritus at Marquette University after having served as the Pflettchinger-Habberman Chair of Chemistry.
Chapter 1
The History and Future Trends of Non-halogenated Flame Retarded Polymers
James W. Mitchell
Solvay Engineering Plastics
*Corresponding author: [email protected]
Abstract
Non-halogenated flame retardants have emerged as the dominant additive system used in engineering plastics. This is mainly due to new environmental regulations but also due to their ability to meet the end customer requirements without compromising safety. Key fire tests like the UL94 and the glow wire can be passed to the highest safety levels using these additives. Further, unlike traditional halogenated systems they provide a low fume toxicity and density allowing their use in railway and other public transportation systems where ease of escape is a key requirement.
High growth potential is expected in various Asian countries with special attention on China and India. In Europe, applications are moving east into countries like Poland and Bulgaria, while Russia appears to offer future opportunities. North America has re-emerged as a power in engineering plastics due to the revolution in cheap energy coming from shale gas fracking. This new possibility of cheap energy could change the face of the industry over the coming years and will depend highly on political decisions coming from individual states.
While standard electrical protection applications will continue to provide growth it is with new applications that the major growth is expected. LED lighting, photovoltaic parts and both electrical and structural parts in the automotive industry are of particular interest.
Non-halogenated flame retardant use shows little sign of slowing down and will continue as the additive of choice for the considerable future.
Keywords: Non-halogenated flame retardants, engineering plastics, ENFIRO, melamine cyanurate, organo phosphorus, glow wire, UL94, shale gas, photovoltaic, LED
1.1 Introduction
1.1.1 Why Non-Halogenated Flame Retardants?
During the last 10–15 years there has been a constant trend in Engineering Plastics to move from traditional halogenated “Flame Retarded Polymers” (FRP’s) towards non-halogenated alternatives. Some of the reasons for this are linked to the toxicology, or assumed toxic effects and environmental concerns of the halogenated additives and/or of their synergists (such as antimony trioxide (ATO) and zinc substances) [1–7]. Another reason is that by declaring a “blanket ban” on all halogenated substances, regardless of their chemical nature or supposed link to toxic or environmental problems, the part producers have a much simpler way to manage their purchasing policy. This, of course, can also have a negative effect on both the physicochemical properly performance and the robust safety of the end product [8–10]. However, in most cases equivalent performance is achievable by using FRP’s containing non-halogenated substitutes. The Electric and Electronical market (E & E), a major user of FRP’s, by understanding correctly the safety requirements of the end part, has been able to tailor simpler and lower costing formulations than the traditional halogenated based products. One example of these types of products is polyamide flame retarded with melamine cyanurate which dominates production of high volume items like connectors and mini circuit breakers. Even though relatively low cost, in comparison to traditional halogenated systems, these melamine cyanurate FRP’s fully comply with the required safety norms and regulations [11].
The drive to change from halogenated FRP’s, due to toxicology and environmental concerns, came about in the middle of the last decade driven by the introduction of three new regulations, RoHS (Restriction of Hazardous substances) [12], REACH (Regulation on Registration, Evaluation, Authorization and Restriction of Chemicals), specifically SVHC (substances of very high concern) and the WEEE (Waste Electric and Electronical Equipment). These regulations basically pushed the additive suppliers, the compounders and the E & E industry to act, innovate and control the type of additive systems used in their formulations. Today these regulations, or very similar regulations, have circumnavigated the globe, mainly due to the globalisation of major companies and the need to import into Europe, so that in essence all consolidated manufacturing countries now follow to a greater or lesser extent these or like regulations [13]. One of the major benefits of these regulations is the push they have given to the industry to innovate and find new and often better solutions. A huge amount of investment at manufacturers and universities has occurred and now for any application requiring FRP’s a suitable non-halogenated solution is more than often available. That is not to say that all properties will be equivalent to the halogenated FRP’s. Some properties will be enhanced while other properties will decrease [14–15]. Halogenated additives provide an undeniable highly robust flame retardant behaviour over a myriad of different polymers, tests and applications that a single chemical type of non-halogenated flame retardant cannot. Therefore, it is necessary to carefully match the non-halogenated flame retardant to the type of polymer formulation and the required end part properties. For the E & E and the Automotive and Consumer Goods markets different flame retardant additives are used, each displaying either a combination or a single type of four principle mechanisms to retard the flame [16, 17, 23, 10, 11, 23, 29, 31, 32]. For further needs a number of very good training resources, which covers this issue in detail, exist and can be found online by simply searching for “Flame Retardant Mechanisms” [18].
Water in the gas phase helps to keep oxygen away and to extinguish the flame. Furthermore the heavy oxides create a non-burning layer (char) which insulate the specimen from the heat source.
Magnesium and Aluminium Hydroxides are the additives which use the dilution action.
Melamine polyphosphate is a good example of an additive displaying intumescence.
These modes of actions help the fire scientist/formulation engineer to select the correct additive system for the given application of the end product. Four such examples of commonly used flame retardants are shown below,
Melamine Cyanurate or other melamine salts
Organophosphorus compounds
Red phosphorus
Aluminium and Magnesium oxides
All of these additives have peculiarities in how they provide flame retardancy and they all have positive and negative points related to their usage [19]. Therefore, picking the correct type of flame retardant additive to use in FRP’s is both difficult and requires a broad range of experience and knowledge. It is in the author’s opinion that the development of a new type of FRP’s is only successful when there is clarification and full cooperation from the part producer, the compounder/manufacturer and the additive supplier. These three parties each have a very important and essential role to play in order that the new FRP meets the need of the end consumer in terms of safety and performance. In the past, the type of additives and the FRP’s themselves were considered more a black art than actual chemical/material engineering. However, there has emerged a much greater transparency and cooperation between these three parties over the last few years which is helping improve FRP’s performance allowing a wider flexible in terms of part design and cost.
Some concerned parties think that a complete ban on flame retardants is the way to actually proceed [20–21]. However, FRP’s are both expensive and can negatively affect the physicomechanical properties of part in which they are used. This is in a sense a self-regulation and will, with the onset of tighter toxicological studies and environmental concerns and knowledge, self-govern their use to a “just-as-necessary” scenario in the future [22].
The very latest information regarding the adverse effect of FRP’s and the way in which to minimise such effects over a product life time has been published in the outcome of the ENFIRO project [23]. This research project was sponsored by the European Union and involved concerned parties from every part of the industry even including representatives from the NGO (Non-Government Organisation) Green Peace. Although the emphasis of the LCA (Life Cycle Analysis) results is on many different aspects than just hazardous flame retardant chemicals, they do also confirm that substitution of brominated FRPs by non-halogenated FRP’s leads to a reduction of (eco) toxicological impacts. In research projects focusing on the substitution of hazardous chemicals, LCA analyses produce valuable complementary information which allows a more complete evaluation of the viability and sustainability of alternatives. One of the most important findings of the ENFIRO project was that improper disposal of FRP’s lead to the worse LCA results. If disposed of correctly or recycled the negative effect of FRP’s is very much minimized [23].
1.2 Key Flame Retardancy Safety Requirements
There has been many papers published over the last twenty or so years by many fire scientists regarding the use of the cone calorimeter as the tool to use to measure the performance of FRP’s. To a great extent the cone and different measurements of heat release has helped us to understand better the overall science of fires [24–29]. However, for everyday use of testing and development of FRP’s, the tried and tested methods, for better or worse, still dominate the industry. The UL94 test is perhaps the best known of these and whilst the idea of the UL94 flame measurement is quite simple, in practice it is highly complicated test requiring a great deal of skill and investment to do correctly. The glow wire flammability index is a test much used in the E & E industries and one that can be tested by all parties on the end product. This test is one of the most prevalent in the low voltage electrical protection applications that are governed mainly by the IEC regulations. With an important update to the standard UL1077 the switch to halogen free engineering plastics in the USA and South America should now be a real possibility and should enable a change from traditional thermoset based products to more flexible and multifunctional thermoplastic parts [30]. The appliance industry introduced the IEC 60335-2 regulation in 2003 with the main outcome being that everybody, additive supplier, compounder, part manufacturer had to become expert in glow wire testing. The main determining factor for these parts is the ability to pass a glow wire “no flame” test on the end part at a temperature above 750°C. This test however, is very sensitive to variations between operators, test apparatus and the method used and so results have been found to vary by up to 150°C on the same product. This uncertainty led to materials being certified as meeting the IEC 60335-2 at major electrical test certification houses like the VDE (the Association for Electrical, Electronic & Information Technologies) and Underwriters Laboratory (UL). Below is a list of the most common types of measurements used to measure the flammability performance of FRP’s [31–32].
UL 94
– Rating of the ability to self-extinguish after ignition by a naked flame.
Glow wire flammability Index
(GWFI IEC
60995-2-12)
– Measures the materials ability to self-extinguish after the application of a hot (glow) wire.
Glow wire ignition temperature
(GWIT IEC
60995-2-13)
– Measures the material’s ability to resist ignition from a hot (glow) wire.
Hot wire ignition
(HWI
UL746A
) – Measure material ability to resist to ignition by a hot wire wrapped around a sample.
Limiting oxygen index
(LOI
ISO 4589
) – Measures the material’s ability to self-extinguish as function of the percentage of O
2
required.
Cone Calorimeter
– a bench scale apparatus that can simulate real fire scenarios and measures the material response such as rate of heat release, time to ignition or smoke release rate
One of the latest regulations to be introduced is the EN 45545-2 for railways. This regulation harmonises various country regulations into an application and hazard rated testing of products. The current widely used European standards, such as the French NF F 16–101, the German DIN 5510 and British BS 6853, have had a massive impact on the railway sector for many years through quantifying the impact of a fire regarding fumes emission (toxicity, opacity) and ease of ignition. The new European standard EN 45545-2 that has been published in April 2013 will supersede the national standards by March 2016. Even though national and European standards will coexist for 3 years, it is key to prepare the phase-out [33].
This new European standard keeps the same objective of minimizing the probability of a fire starting and to control its development, but also highlights the importance of allowing the evacuation of passengers and staff in satisfying conditions. Therefore, like several national standards, EN 45545-2 covers two aspects of the fire risk
the material behaviour during and after ignition
the opacity and the toxicity of the fumes
However, the structure of this standard is unique. Hazard levels (HL1, HL2; HL3) have been created depending on the vehicle type (e.g. sleeping wagon, double deck trains,), but also its operating environment (tunnels). Depending on the usage of the part, technical requirements (R1 to R26) are defined and must be evaluated according to a list of testing methods (T1 to T17). The combination provides the classification of the material.
A wide majority of small E & E components will need to satisfy R22 (interior) and R23 (exterior) requirements. The tests are the same, only the required performance level varies. In comparison with NF F 16–101, R22/R23 applications require LOI but not glow wire measurements. As far as fume testing is concerned, the smoke density is tested on horizontal plates instead of vertical plates, and toxicity must be evaluated using the widely used NFX 70–100 standard with the quantification of NOx in addition to the gases which were already tested such as monoxide (CO), carbon dioxide (CO2), hydrogen chloride (HCl) and hydrogen bromide (HBr). This new regulation shows that flame testing can be both specific and intelligent to the needs of the part and its risk in use [34–35]. It is the opinion of the author that such regulations could and should be built to improve both safety and pragmatism in other forms of transportation, such as coaches and automobiles, which show much higher death rates as a result of fires, as reported in the NFPA 556 [36].
1.3 Geographical Trends
The world of flame retarded plastics and plastics in general is rapidly changing and adjusting to suit different market perspectives. Geographically the market attention has switched, from western mature nations, to the so called BRIC regions of Brazil, Russia, India and China. However, even some of these so called emerging nations are rapidly becoming mature as wages soar and trade barriers are put in place to try and protect their position. Russia, although laden with risk, and perhaps more importantly India, even though major problems exist with infrastructure, look to be the new growth regions driving the market forward into the next decade. Further major trend changes are likely and already the seeds have been sown in the US with their rapid gain in fuel costs and their near loss of dependency on Middle Eastern energy due to the quantum leap’ of technological advances in shale gas and oil extraction. North America is set to become the largest producer of gas and oil in the near future, with just one site estimated to hold over 3 trillion barrel alone [37–38]! Nations like China, Poland, Russia and the UK are trying hard to put in place similar programmes to ensure their energy needs in the future lie in their own hands. Mainland European nations, like France and Germany, shackled with the inability to come to a consensus decision, look set to miss the boat on energy, which, moving forward, could spell the end of their elite position in plastics and thus the highly attractive flame retardant sector. Politics and material and energy resource policy is quick to change and so these comments must be judged on the current geopolitical situation of each country mentioned.
The flame retardant plastics landscape and battlefield is equally undergoing rapid change in terms of applications and materials offered. Automotive is emerging as a key development area for FR plastics as manufacturers rush to put in place materials for new high electrical resistance applications, such as battery housings, connectors and fuel cell separators. Other structural parts are also being targeted with FR products with large volumes and radical new applications seemingly coming on a daily basis.
India offers a relatively new and exciting playground for flame retardant plastics, in particular for ABS and commonly used engineering plastics like polycarbonate and polyamide. Many companies in both the E & E and transportation industries see the low costs and lessening of taxes, coupled with a young and well educated English speaking population as the ideal mix to drive the industry forward away from the shackles of a difficult European situation. The vision for these mature nations, stuck in a quagmire of indecision and inability to kick start the member states monetary problems, is foggy at best. In India major OEMs are emerging such as Tata, Havells and C & S, while major FR polymer users, such as Schneider Electric, Legrand, Hager, TE connectivity and ABB to name just a few, have carefully established their presence mainly by tactical investments and sound investment in these growth regions. The market in India can be divided roughly into 3 categories;
Given recent disasters in this region caused by fires [39] and the increased need to improve safety in automobile electronics [40] the middle range of just good enough but quality products look to increase rapidly and dominate for the coming years. The major investment into R & D in India also means that it seems likely that they will emerge as a powerhouse in terms of regulations and innovation rather than being just a low cost production zone.
Moving onto China, it is clear that they have undertaken massive strides not only to improve the quality and safety of the parts produced but also by massive investments in innovation. However, China still remains principally a manufacturing zone for the world, meaning it is highly influenced by the on-going crisis in Europe and other zones. Couple this to a rapidly ageing population, a shortage of skilled workers, high inflation and rapidly increasing wages in its major cities and the outlook for China is not so certain. However, the Chinese government has for many years had the ability and means to shape their own destiny and so it remains highly unlikely that anything other than growth will remain for the region with a more sustainable internal, less export oriented, outlook model being followed. With rapidly inflating wages and higher demanding consumers China should move the way of previous low cost countries, such as like Korea and Italy, and move to high quality, highly regulated electrical and electronical parts and end products. A vision of the market for the different types of flame retardant products and how their usage has changed can be found in Table 1.1 and Table 1.2.
Table 1.1 Type and volume of FR additives sold 2007–2015 (KT).
Table 1.2 Quantity of FR additives sold to major countries (KT).
1.4 Applications for Non-halogenated FRP’s
Non-halogenated FRP’s are used in an increasingly diverse and rich number of applications, from the traditional LVSG (Low Voltage Switch Gear) usage in the construction industry, to their start up in structural and electrical parts for the automotive industry. In fact FRPs are so numerous it would be easier to state the applications that they are not used to those where they are the norm.
Certainly, they are used extensively in markets such as electrics and electronics, construction, public transportation, wire and cable, appliances and lighting and many publications exist highlighting their usage, examples of standard applications can be seen in Figure 1.1. However, for this introduction just a few of the new types of applications will be highlighted.
Figure 1.1 Standard usage applications of Flame Retardant Polymers.
The photovoltaic industry has emerged as a driving force for a new phase of sustainable energy generation. The types of materials being used to manufacture photovoltaic panels and electrical components have themselves changed as they are now much more regulated (such as by UL and TÜV Rheinland [41]). These applications have the same cost and performance pressures as any other electrical components found in construction, as they have moved from a speciality to a mainstream market. One key application area for FRP’s use is the junction box and its components, Figure 1.2. This is the box where the wires coming from the solar panel connect with the wires taking the power to an electrical converter. This electrical box therefore, is required to withstand high electrical exposure over an extended outdoor usage. Materials used in this type of application have to pass both the UL 5VA and ULF1 rating making the choice of materials extremely difficult.
Figure 1.2 Photovoltaic Junction Box.
Another equally and perhaps, volume wise, a significantly more interesting application is the automotive industry. Due to the unsatisfactory situation that exists today, where there is basically no FR requirements for cars, a new guide to Fire and Hazard in cars has been issued by the National Fire Protection Association (NFPA) called the NFPA 556. The purpose of the NFPA document is to provide guidance and tools for persons investigating methods to decrease the fire hazard, or fire risk, in passenger road vehicles. The overall aim is to make road vehicles safer by providing additional time for occupants of the passenger road vehicle to be able to exit or be rescued in case of the occurrence of a fire involving the passenger road vehicle. This is at the moment a guidance document but it is already starting to influence both government and industry and will place responsibility on the car manufacture to improve their use of fire resistant materials in key areas. The use of plastics is continuing to expand at ever faster growth levels due to weight saving linked to environmental concerns while the testing of the plastics has remained more or less in the Stone Age. One key point that is being pushed by this document is to move away from the old FMVSS 302 and rather assess materials based on their HRR (Heat Release Rate), which is what we see being used today for trains specifically in the new EN 45545-2. An updated version of the NFPA 556 is scheduled for release in 2016.
A key need for FRP’s is in the application of LED lighting. This is principally driven by a metal replacement need to both reduce weight and cost of the end part. This application is doubly difficult as it not only demands the use of non-halogenated flame retarded resins but also requires the key properties of heat conduction and electrical insulation in a white coloured system. Success in switching the LED lighting to FRP’s over metals like aluminium will secure a sound growth moving forward, Figure 1.3.
Figure 1.3 LED Heat conductive cover.
FRP’s need to continue to adapt to the geopolitical and the safety and toxicology needs of the world. New innovations more focused environmental and toxicity regulations and increasing end applications means that their use will continue to grow helping to enhance the safety of consumers for the considerable future.
References
1. Soderstrome, G; Marklund, S, 2002: PBCDD and PBCDF from incineration of waste-containing Brominated flame retardants. ES & T, Vol. 36.
2. Law, R; Allchin, C, 2006: Levels and trends of Brominated Flame Retardants in the European Environment. Chemosphere Vol. 64.
3. Muriel Rakotomalala, Sebastian Wagner and Manfred Döring Recent Developments in Halogen Free Flame Retardants for Epoxy Resins for Electrical and Electronic Applications. Materials 2010, 3, 4300–4327
4. greensciencepolicy.org/sites/default/files/Leonards.pdf
5. Adams (2006), Smart ecoDesign - Eco-design Checklist, For manufacturers of Printed Wiring Boards, Asia Eco-Design Electronics (AEDE), Graham Adams, October 2006.
6. Andrae, A. (2005), Significance of intermediate production processes in life cycle assessment of electronic products assessed using a generic compact model, A. Andrae, D. Andersson and J. Liu, Journal of Cleaner Production 13 (2005) 1269–1279.
7. NHXMH and NHMH cable.” SP Swedish National Testing and Research Institute. SP Report 2005:45.Bergendahl (2005), Environmental and economic implications of a shift to halogen-free printed wiring boards, Carl Gunnar Bergendahl, Kerstin Lichtenvort, Glenn Johansson, Mats Zackrisson, Jonna Nyyssönen, Circuit World, 2005.
8. Andersson, P.; Simonson, M.; Tullin, C.; Stripple, H.; Sundqvist, J.O.; Paloposki, T. (2004) Fire-LCA guidelines. SP report 2004:43. Sweden, ISBN 91-85303-21-6.
9. Brooke, D.N.; Crookes M.J.; Quarterman, P.; Burns, J.: “Environmental risk evaluation report: Tetraphenyl resorcinol diphosphate (CAS no. 57583-54-7)” UK Environment Agency, Product Code, SCHO0809BQUL-E-P, 2009.
10. Alaee, M. (2003), An overview of commercially used brominated flame retardants, their application, their use patterns in different countries/regions and possible release, M. Alaee, P. Arias, A. Sjodin, A. Bergman, Elsevier, Environment International 29 (2003), 683–689.
11. Injection world, March 2013; New Ideas in Flame Retardant PA
12. RoHS, 2002/95/EC
13. Http://commerce.nic.in/trade/Elec%20Machinery/EU/docs%20to%20link/3Additional%20INformation/Comparison_of_RoHS_legislations_around_the_world.pdf
14. Albemarle: “Stable Brominated Polystyrene.” US Patent no. PCT/US2000/003473, 2000.Albemarle: “Bromination Process.” US Patent no. 6974887, 2005.
15. ChemSec – the International Chemical Secretariat: “Brominated Flame Retardants and PVC – a Market Overview”, 2010.
16. http://www.specialchem4polymers.com/tc/flame-retardants/?id=9303
17. http://www.epa.gov/dfe/pubs/flameret/altrep-vl/altrep-vla-sec2.pdf
18. http://www.flameretardants-online.com/web/en/106/84575cb4764b9030e1338c8cfd52c9a2.htm
19. Bernhard Schartel, Phosphorus-based Flame Retardancy Mechanisms—Old Hat or a Starting Point for Future Development? Materials 2010, 3(10), 4710–474
20. Brigden, K.; Webster, J.; Labunska I.; Santillo, D.: “Toxic Chemicals in Computers Reloaded.”, Greenpeace Research Laboratories, Technical note 06/07, 2007.
21. Cobbing, M.: “Toxic Tech – not in our backyard. Uncovering the hidden flows of e-waste”, Greenpeace report, 2008.
22. Blomqvist, P.: “Emissions from fires. Consequences for Human Safety and the Environment” doctoral thesis, Lund University, 2005.
23. Niels Jonkers, FP7-ENV-2008-1, project nr. 226563 ENFIRO-Life Cycle Assessment of Environment-Compatible Flame Retardants (Prototypical Case Study)
24. Lyon, R.E., Heat Release Kinetics, Fire and Materials, 24(4), 179–186 (2000).
25. Conshohocken, W., Standard Test Method for Heat and Visible Smoke Release Rates for Materials and Products Using an Oxygen Consumption Calorimeter, ASTM E 1354, American Society for Testing and Materials, PA, 2004
26. Benson, S.W., Thermochemical Kinetics: Methods for the Estimation of Thermochemical Data and Rate Parameters, John Wiley & Sons, New York, NY 1968.
27. Cullis, C.F. and M.M. Hirschler, The Combustion of Organic Polymers, Oxford University Press, New York, NY, 1981.
28. Lyon, R.E., R.N. Walters and S.I. Stoliarov, Thermal Analysis of Flammability, Journal of Thermal Analysis and Calorimetry, 89(2), 441–448 (2007).
29. Pouche, F., Fire Resistance in Plastics 2009, Fire and its consequences on material -What material for which applications?
30. SpecialChem - Aug 16, 2013; Recent Amendment In UL Standard Paves Way For Enhanced Use of Dsm’s Engineering Plastics In E &E
31. Horold, S., Nass, B., Flame Retardants 2004. A new generation of Flame retarded Polyamides based on Phosphinates.
32. Mitchell, J. W., FR products 21st Century Flame Retardants 08, Cologne, October 2008
33. EN 45545-2:2013
34. Schutz, F., New European railways fire safety standard: Solvay on the tracks to a successful transition. Railway technology 2013.
35. Pinfa, Innovative and Sustainable Flame Retardants in Transportation brochure, 2010.
36. NFPA 556: Guide on Methods for Evaluating Fire Hazard to Occupants of Passenger Road Vehicles Current Edition: 2011
37. http://www.shalegas.cn/en/research/201204057448.html
38. Alexander, T., Shale Gas Revolution, Oilfield review, 04/2011
39. Sujata Satapathy., Disaster Management & Response, Volume 5, Issue 4, October-December 2007, Pages 111–118
40. http://www.rushlane.com/tata-nano-catches-fire-in-chennai-videos-1220198.html
41. http://www.tuv.com/en/usa/home.jsp
Chapter 2
Phosphorus-based FRs
Sergei Levchik
ICL-IP America, 430 Saw Mill River Rd., Ardsley, NY 10502
*Corresponding author: [email protected]
Abstract
Phosphorus-based flame retardants are on the fast growing track mostly due to environmental considerations, although sometimes efficiency, lower density and good light stability are significant factors. Discontinuation of use of decabromo-diphenyl oxide in polyolefins stimulated development of new intumescent flame retardants and systems. Patents dealing with the flame retardancy of polycarbonate and its blends are especially numerous. Well established resorcinol-based and bisphenol A-based oligomeric aryl phosphates are included in many formulations but there are also new developments directed to more thermally stable phosphates and phosphonates. There are a substantial number of patents and academic publications dealing with dialkylphosphinic acid salts, and, more recently, with hypophosphite salts which are useful in thermoplastic polyesters and polyamides. Largely driven by the waste disposal regulations and “green” marketing strategies by OEMs, interest has increased in non-halogen flame retardant systems for printer wiring boards. Many patents and publications have appeared on epoxy systems in which 9, 10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide is reacted into epoxy polymer or used as a curing agent. Fast changing regulations in furniture fire safety stimulated development of new phosphorus-based reactive and oligomeric flame retardants for flexible polyurethane foams.
Keywords: Phosphorus flame retardant, intumescent, char, plastic, textile, epoxy resin, polyurethane foams
2.1 Introduction
It is generally accepted that phosphorus flame retardants are more effective in the oxygen- or nitrogen-containing polymers, which could be either heterochain polymers or polymers with oxygen or nitrogen in the pendant groups. Phosphorus flame retardants are more specific to the polymer chemistry than halogen-based flame retardants. This relates to the condensed phase mechanism of action where phosphorus flame retardants react with the polymer and involve it in the charring. The char impedes the heat flux to the polymer surface and retards diffusion of the volatile pyrolysis products to the flame.
However, if conditions are right, the phosphorus-based moieties can volatilize and be oxidized producing active radicals in the flame. Volatile phosphorus compounds are among the most effective inhibitors of combustion. However, it has been challenging to design phosphorus-based flame retardants, which will volatilize into the flame at relatively low temperatures and at the same time will not be lost during polymer processing. Therefore, there are not many commercial phosphorus-based flame retardants which provide mostly gas phase action.
In the past the author of this chapter co-authored two reviews on phosphorus-based flame retardants [1–2]. This current chapter is an update and extension of the previous reviews. This chapter does not cover the large class of chloroalkyl phosphates since they are not halogen-free, but these products were reviewed previously. Although there is large body of academic publications and patent literature on new phosphorus flame retardants, this chapter focuses only on commercial FRs and products which, to the best of author’s knowledge, are in advanced commercial development. Broader non-selective reviews were published elsewhere [3–4]. The effect of phosphorus flame retardants on human health and environment was recently reviewed by Van der Veen and De Boer [5]
2.2 Main Classes of Phosphorus-based FRs
The ammonium phosphate treatment of cellulosic materials (canvas, wood, textiles etc.) has been known for almost three centuries. However, only with commercialization of synthetic polymeric materials in the twentieth century, organophosphorus compounds have become an important class of flame retardants.
All phosphorus-based flame retardants can be separated into three large classes
Inorganic represented by red phosphorus, ammonium phosphates and metal hypophosphates.
Semi-organic represented by amine and melamine salts of phosphoric acids, metal salts of organophosphinic acids and phosphonium salts.
Phosphate and phosphonate esters.
Phosphate esters is the most diverse class of phosphorus flame retardants which can be further separated into
Aliphatic phosphates
Aliphatic chloro-phosphates
Aromatic phosphates
Phosphonates
Phosphinates
Phosphine oxides (not in commercial use)
Phosphazenes
Water-soluble phosphorus flame retardants mostly used for topical treatment of wood, textile and other cellulosic products. Some water soluble FRs can be further reacted with cross-linkers (cured) which provides durable water resistant treatment. Water-insoluble phosphorus FRs find a very broad range of applications in thermoplastics, thermosetting resins, synthetic foams, coatings etc.
Phosphorus flame retardants have certain advantages over other flame retardants (mostly halogen based) but also have some disadvantages which are both listed below:
Advantages:
Low specific gravity which results in light plastic parts
Achieving flame retardant efficiency at lower phosphorus content compared to the halogen content needed for the same rating
No need for antimony trioxide synergist
Effective in promoting char barrier/formation in charrable polymers
Better UV stability than most halogen-based FRs
Less tendency to intensify smoke obscuration
High comparative tracking index (CTI) test performance
Less acidic smoke compare to halogen FRs
Most phosphorus FRs are biodegradable and therefore not persistent
No halodioxin/furan formation (provided no halogen in phosphorus FR structure) even in poor incineration of the plastics
Disadvantages:
Very low efficiency in polyolefins, styrenics and elastomers unless charring agent is added.
Absence of good general synergist.
Many phosphorus FRs are hydrophilic and possibly cause moisture uptake limiting use in some applications.
May hydrolyze to give acids which decrease molecular weight of acid-sensitive polymers (polycarbonates, polyesters, polyamides etc.)
Apart from red phosphorus, inorganic phosphates have low thermal stability and therefore their use is limited to low processing temperature polymers
Recycling of acid sensitive polymers is problematic due to hydrolytic instability of organophosphates.
Some phosphates are toxic to aquatic organisms.
Apart from a few selected cases, the cost/efficiency of phosphorus FRs is higher than halogen based FRs.
2.3 Polyolefins
Upon thermal decomposition, polyolefins produce significant amounts of aliphatic hydrocarbons which are highly flammable. Furthermore, polyolefins melt, flow and drip during combustion because of the relatively low melting point of these polymers. They burn relatively cleanly with very little, if any, char left behind. All of this creates serious challenges in flame retardancy of polyethylene, polypropylene and their copolymers. Although polyethylene and polypropylene produce similar aliphatic hydrocarbons, polypropylene is relatively easier to flame retard because it decomposes at lower temperature and there is better match with the temperature range of decomposition of common flame retardants.
The successful flame retardants for polyolefins have usually been halogen types, most often synergized by antimony oxide, or endothermic types used at high loadings, like ATH or magnesium hydroxide. It is also generally accepted that phosphorus based flame retardants are inefficient in polyolefins unless they provide significant gas phase efficiency or are combined with an intumescent system. In order to adapt most common phosphorus FRs for the latter, they should be utilized along with a charring agent. In the past, a significant effort was made by industry and academic laboratories in development of intumescent flame retardant systems for polyolefins. The intumescent flame retardant systems require three essential components: (1) a charring agent, typically pentaerythritol, (2) a strong acid which promotes charring, usually originated from decomposition of ammonium phosphates and (3) a foaming agent which is typically melamine or a melamine salt. The intumescent systems concept was originally developed for flame retardant coatings [6] and later adapted for low temperature processed polymers, like polyolefins.
Numerous academic publications on intumescent flame retardant systems for polyolefins are out of the scope of this chapter. The broad subject of intumescent flame retardants was discussed in a book edited by Le Bras et al. [7] and also in a more recent review [8] and book chapter [9].
Although intumescent systems based on ammonium phosphates are very efficient in polyolefins the main factors limiting their broad application are thermal stability and water solubility. Both thermal stability and water solubility can be improved by increasing the chain length (molecular weight) of the polyphosphate. Two crystalline phases of ammonium polyphosphate (APP, forms I, and II) are commercially sold as flame retardants.
It is believed that form I has a linear chain structure and relatively low molecular weight (from 30 to about 150 repeating units). Form I has relatively low thermal stability (onset of weight loss at about 230°C) and relatively high water solubility. This form is available from ICL-PP as Phos-Chek® P30. It is mostly used in coatings.
The form II is available from Clariant as Exolit® 462 and related products, from Budenheim in their FR CROS product group, from ICL-PP as Phos-Chek® P40 and from numerous Asian producers. It is believed that form II has a cross-linked structure [10] and its molecular weight is much higher (700-1000 repeating units) than form I. Form II is more thermally stable (beginning of thermal decomposition at about 270°C) than form I and less water soluble. Many varieties of APP form II with various coatings/encapsulations which further decrease water solubility are commercially available. For example, Budenheim offers a range of surface coated APP as FR CROS 486- a silane surface-reacted, FR CROS 487 – melamine formaldehyde resin coated, FR CROS C30/C40 – melamine surface reacted and FR CROS C60/C70, FR CROS 489 – melamine-formaldehyde surface reacted [11]. ICL-PP offers the coated grade of APP as Phos-Chek® P42. These surface treatments allow decreasing water solubility of form II APP from 0.5 to 0.01–0.1 g/liter. These coatings can also provide a synergistic effect to APP because they can work as charring agents to further enhance the activity of APP.
Recently G. Liu et al. [10, 12] reported commercially viable processes of synthesis of APP, Form V. This form has similar thermal stability and water solubility as Form II. It is believed that Form V is also high molecular weight cross-linked polyphosphate, but the branching units instead of ultraphosphate as in Form II, consist of triazine structures. To the author’s best knowledge there is no commercial production of the Form V at the time of writing of this chapter.
Over many years, APP producers and compounders tried to develop flame retardant compositions (formulated packages) which included along with APP the charring and foaming agents. Nitrogen-containing low molecular weight or polymeric products behave the best because they combined both charring and foaming functions. For example patents suggest that an early Exolit® IFR by Hoechst contained tris(hydroxyethyl)isocyanurate [13, 14]. Another combination of charring agent with APP was developed at Himont (now Basel) as Spinflam® MF80 and MF82, [15] where an oligomer consisting of triazine rings linked by diamine was used in those products [16]. Often urea-formaldehyde or melamine-formaldehyde resins are used in two functions as encapsulating and charring agents. Active research on APP coatings continues in China, where for example this recent publication [17] shows use of poly (p-ethylene terephthalamide) as a charring agent.
A Swiss company MCA technologies recently introduced the condensation product of melamine, morpholine and piperazine (PPM Triazine HF) as a charring agent and synergist with APP [18, 19]. Reportedly, APP combined with PPM Triazine HF provides a V-0 rating in PP at only 20 wt.% loading [20]. Interestingly, aliphatic polyamides which are considered as not very charrable can be also used along with APP as a charring agents. For example, the group of French researchers [21] developed a formulated system of APP/polyamide 6/EVA, where EVA is used as a compatibilizer for polyethylenic polymers.
It has been long recognized [22] that addition of a small amount (typically 2–3 wt.%) of multivalent metal salts or oxides provides synergistic effect in APP based intumescent systems. Some natural products like talcs, zeolites [23] and clays show similar behavior. The synergistic effect is observed in a very narrow concentration range and it is believed to be due to formation of cross-links in polyphosphoric acid involving multivalent metals [24]. Increasing the concentration of the synergist results in formation of stochiometric crystalline phosphates which negatively affect intumescence and the effect switches from synergistic to antagonistic. In the recent academic literature there are numerous publications on addition of organically modified clays to the intumescent systems. Synergistic effects are often, perhaps erroneously, attributed to the physical effect of the clay reinforcing char, whereas it could be the same effect of chemical interaction with polyphosphoric acid and cross-linking.
More advanced formulated systems are on the market nowadays. For example Clariant offers two series of Exolit® AP 75x and AP 76x. Exolit® AP 750 is a standard grade of the formulated system suitable for polypropylene and polyethylene, AP 751 (TP) is a special grade for reinforced polypropylene and AP 752 is for PP copolymers. All these grades require about 30 wt.% loading to achieve a V-0 rating, which is a lower loading than needed for mineral flame retardants (ATH and MDH) and some halogen-based systems. A proprietary improvement, Exolit AP 760, has been introduced and this product appears especially suited for cable ducts and trays. AP 765 grade provides further improvement in the glow wire ignition test (GWIT) which achieves 800°C [25]. Budenheim sells APP based systems containing a charrable component under the trade names BUDIT 3077 and BUDIT 3076 DCD [11]. The main advantages of these APP-based systems over halogenated flame retardants are lower smoke and excellent UV stability. However, relatively high hydrophilicity still limits their application in electrical and electronic products and some outdoor products. Although cable manufacturers are trying to adopt APP or APP formulated systems in the cables jacketing [26] it seems to still have a very limited application due to the water absorption issues.
The mechanism of char formation in the pentaerythritol-APP systems was very extensively studied and described in great detail by Camino and Delobel [27]. Since some of the principal intermediates in the char formation are bicyclic or spirocyclic pentaerythritol phosphates, significant effort has been channeled into development of pentaerythritol phosphate-based intumescent flame retardants.
For example, in the past, Great Lakes marketed bis(melamine) salt of pentaerythritol bis(acid phosphate) (Formula 2.1) for use in polypropylene. Originally this product was developed in the Borg-Warner laboratories, [28] later it was studied at Alcan Chemicals [29] in the UK and apparently it still continues to be of interest in China, as shown by recent studies [30, 31]. A decade ago, Budenheim introduced to the market phosphate esters of aliphatic alcohols (probably pentaerythritol) having acid groups neutralized with melamine under trade names BUDIT 3118 and 3118F [11, 32]. The structure of these products can be similar to that shown in Formula 1. These products can be used as intumescent additives in coatings and polypropylene sheets and fibers. They allow smoother surfaces in those sheets and fibers probably because they melt or partially melt during processing.
(2.1)
Another product of high interest for the intumescent flame retardants is pentaerythritol bicyclic phosphate (PEPA) (Formula 2.2). This phosphorus-containing alcohol was available from Great Lakes, but probably discontinued now. It is available in China. PEPA can be further reacted with phosphorus oxychloride to form phosphate with four phosphorus atoms. Reportedly, this phosphate is commercial in China [33]. The salt of di-PEPA acid phosphate and melamine (Formula 2.3) was also in advanced development [28, 29].
(2.2)
(2.3)
The blends of PEPA and melamine phosphate were more successful as suggested in patents of Great Lakes’ researchers [34, 35]. It is believed these mixtures were the basis for Great Lakes Reogard® 1000 and 2000 products, recommended for extruded profiles and electrical parts to meet a V-0 rating with good impact strength and heat distortion temperature. For example, at 19% of the PEPA-melamine phosphate mixture with 0.8% (amount critical) of the montmorillonite, a V-0 rating was obtained in polypropylene [34, 35].
Melamine phosphate also has been originally developed for intumescent coatings but found some use in polyolefins. Later additions to this family of the more thermally stable melamine pyrophosphate and melamine polyphosphate ensured safe processing in most polyolefins. Non-coating applications of the melamine phosphates (including the pyrophosphate) were reviewed by Weil et al. [36]. Melamine phosphate and pyrophosphate are available in the USA from Cytec Industries and Broadview Technologies. Melamine polyphosphate is sold in the USA and Europe by BASF as Melapur® 200. In an intumescent formulation in a polyolefin, the melamine phosphates such as Melapur® 200 have been shown to have an advantage over ammonium polyphosphate by causing less mold deposition and having better water resistance [37]. However melamine phosphates are also less efficient than APP, because they are more thermally stable and have lower phosphorus content.
There are also intumescent flame retardants which are based on different amine salts other than melamine salts. It is advantageous to use at least a diamine which allows higher thermal stability and lower water solubility compare to monoamines. An example of such successful product is ethylenediamine phosphate (EDAP) firstly introduced by Albright & Wilson as Amgard® EDAP in the late 80s. [38]. In contrast to APP and melamine salts EDAP shows self-intumescent behavior because it melts at about 250°C, right around where its thermal decomposition starts and because it contains aliphatic carbons which undergo charring. So it quickly melts and activates as an intumescent once it reaches this temperature. EDAP is more soluble in water compared to the form II of APP and less thermally stable which limits its applications in polyolefins. In the USA EDAP is available from Broadview Technologies, Unitex Corp and JJI Technologies.
In order to improve thermal stability and decrease water solubility EDAP has often been sold as a mixture with melamine or melamine phosphates. Some of these mixtures are also synergistic because the temperature of thermal decomposition of EDAP and melamine phosphates is different and the extended temperature interval better matches the thermal decomposition of the host polymer. Some further synergists, such as phase transfer catalysts (quaternary ammonium salts) or spirobisamines may further enhance the action of EDAP and melamine pyrophosphate or APP combinations as claimed in Broadview [39] and JJI [40] patents. Recently Thor GmbH introduced a new intumescent flame retardant Aflammit® PPN903 which reportedly does not contain APP but has high thermal stability (>270°C), low solubility and better acid resistance [41]. Various inorganic synergists, like talc or zinc borate, were reported [42] for phosphorus-based intumescent systems.
Another interesting development was use of ammonium salt of amide aminomethyl phosphonic acid (Formula 2.4) as a self-intumescent FR [43]. At 25 wt.% it showed LOI=29 and UL-94 V-0 rating in polypropylene. This product was developed in Russia and briefly marketed by Isle Firestop (UK) under a trade name of Bizon. Because of water solubility it was sold as a coated/encapsulated form.
(2.4)
Intumescent systems based on the mixed salts of melamine and piperazine phosphates were first developed in Italy by Montel [44] (Basel now) and marketed as Spinflam® MF-83 for wire and cable applications [45]. Recently, Asahi Denka [46] developed improved method of synthesis of piperazine pyrophosphate, which allows obtaining a product with superior thermal stability. Another patent [47] shows milling of piperazine pyrophosphate together with melamine pyrophosphate and addition of some polymethylsiloxane oil probably for decreasing dusting and improving processability. This is probably the basis for the new Asahi Denka ADK STAB FP-2200 product [48]. This intumescent flame retardant is said to be effective in polypropylene at about 20%, and in LDPE, HDPE or EVA at about 30%. It is stable enough to permit extrusion and molding at 220–240°C. It appears to be better than the previous intumescent system ADK STAB FP-2100 in regard to water resistance, processability, shear stability, heat and mechanical properties.
In spite of the fact that red phosphorus is effective in both condensed and gas phase [49] it achieves V-0 rating only in charrable polymers, mostly engineering thermoplastics. In polyolefins, red phosphorus was found useful for a V-2 rating and high LOI especially in polyethylene [50]. It is believed there is better match between the temperature of the thermal decomposition of polyethylene and the volatilization of red phosphorus compare to polypropylene [51]. It was shown that a V-2 rating at 1.6 mm could be obtained at as low as 2.5% finely-divided red phosphorus (5 um) [52]. To obviate the risk of handling finely-divided red phosphorus, masterbatches of encapsulated red phosphorus are available from Italmatch in various polyolefins [53] and from Clariant in low melting wax and novolacs [54]. The masterbatches in polyamide 6.6 and other charrable polymers are also useful as additives in polyolefins [53] because they provide charring to enhance the flame retardant effect of the phosphorus [55].
Some time ago Italmatch introduced to the market aluminum hypophosphite (Phoslite® IP-A) and calcium hypophosphite (Phoslite® IP-C) [56]. A surface treated version of the aluminum salt, Phoslite®
