Fire Retardancy of Polymers: New Strategies and Mechanisms - Hardcover

Hardcover

ISBN 10: 0854041494 ISBN 13: 9780854041497

Publisher: Royal Society of Chemistry, 2008

Synopsis

The latest developments in fire retardancy of polymeric materials, including new systems, formulations and test-methods are detailed in this book.

About this title

About the Author

T Richard Hull is Professor of Chemistry and Fire Science at the University of Central Lancashire. His research focuses on fire retardancy and toxicity and he was involved in the development of the first ISO standard for assessment of fire gas toxicity. He has collaborated extensively with the main fire retardant groups across the globe. A recurrent theme in his work is the use of instrumental methods to understand fire behaviour. Baljinder K Kandola is Professor of Materials Fire Science at the University of Bolton, UK. Her career started with a PhD in chemistry and she has since worked on a range of multidisciplinary research projects involving chemistry, textiles, mechanical engineering and mathematics. Her interests are focused on fire retardancy of natural fibres, thermoplastic fibre-forming polymers and thermoset polymers. Her recent research includes burning and burning induced degradation of mechanical properties of fibre reinforced composites.

From the Back Cover

Globally, fire retardants are needed to satisfy a multibillion dollar market. Fire retardancy of polymeric materials is an important component of fire safety. Fire retardants either reduce the likelihood of ignition and/or reduce the rate of flame spread and hence, escalation of fire. The need to comply with safety legislations forces industry to use fire retardants in materials in order to save lives. With growing consumer demands and new legislations, the development of new systems is an on-going process, which also involves understanding their mechanisms of action. This book covers the latest developments in fire retardant strategies including: -new fire retardant systems (including nanoparticulate fillers, sometimes combined with conventional fire retardants) -intumescent formulations and their recent applications in bulk polymers, fibres and textiles -test-methods for material flammability -material-specific aspects of combustion, smoke and toxicity. Fire retardant strategies covered, include the use of synergistic combinations of alumina with organoclay, organophosphorus compunds, silica and organosilicones, clay-phosphate combinations and a novel tecnhique for investigating fire rerardant behaviour. The section on nanoparticulate fillers includes an investigation on the effect of filler shape, the use of carbon nanofibres and nanotubes, the interpretation of nanocomposite behaviour in the cone calorimeter, and groundbreaking new research on the influence of rheological properties on burning behaviour. The coverage of fibres and textiles includes a discussion on trends in textile fire retardancy and flammability regulations, and some novel halogen-free approaches to fire retardancy of cellulose, acrylic and polypropylene textiles. Finally, the influence of fire retardants on fire toxicity is discussed in detail, followed by an investigation of the toxic products from burning fire retarded polymer nanocomposites. This book will update fire retardant materials' developers with latest in research and design of new fire retardant materials. It will also provide a snapshot of the state-of-the-art for a range of other groups including environmentalists looking for alternatives to brominated flame retardants and engineers needing to use fire safe materials in their projects.

Excerpt. © Reprinted by permission. All rights reserved.

Fire Retardancy of Polymers

New Strategies and Mechanisms

By T Richard Hull, Baljinder K Kandola

The Royal Society of Chemistry

Copyright © 2009 Royal Society of Chemistry
All rights reserved.

ISBN: 978-0-85404-149-7

Contents

Introduction Polymers and Fire T.R. Hull and A.A. Stec, 
Chapter 1 Synergy between Nanometric Alumina and Organoclay in Conventional Fire Retardant Systems for Ethylene–Vinyl Acetate N. Cinausero, J.-M. Lopez-Cuesta, F. Laoutid, A. Piechaczyk and E. Leroy, 
Chapter 2 Strained Organophosphorus Compounds as Reactive Flame Retardants for Polymeric Materials Bob A. Howell, 
Chapter 3 Amorphous Silicon Dioxide as Additive to Improve the Fire Retardancy of Polyamides G. Schmaucks, B. Friede, H. Schreiner and J.O. Roszinski, 
Chapter 4 Use of Organosilicone Composites as Flame Retardant Additives and Coatings for Polypropylene B.B. Marosfoi, A. Szabó, K. Kiss and G. Marosi, 
Chapter 5 Organomodified Ultrafine Kaolin for Mechanical Reinforcement and Improved Flame Retardancy of Recycled Polyethylene Terephthalate B. Swoboda, E. Leroy, J.-M. Lopez Cuesta, C. Artigo, C. Petter and C.H. Sampaio, 
Chapter 6 Complex Micro-analysis Assisted Design of Fire-Retardant Nanocomposites – Contribution to the Nanomechanism A. Szabó, B.B. Marosfoi, P. Anna and Gy. Marosi, 
Chapter 7 Impact of Nanoparticle Shape on the Flammability of Nanocomposites F. Yang, I. Bogdanova and G. L. Nelson, 
Chapter 8 Thermal and Combustion Behaviour of Polymer–Carbon Nanofibre Composites D. Tabuani, S. Pagliari, W. Gianelli and G. Camino, 
Chapter 9 Combination of Carbon Nanotubes with Fire Retardants: Thermal and Fire Properties of Polystyrene Nanocomposites Florentina Tutunea and Charles A. Wilkie, 
Chapter 10 Significant Assessment of Nanocomposites' Combustion Behaviour by the Appropriate Use of the Cone Calorimeter A. Fina, F. Canta A. Castrovinci and G. Camino, 
Chapter 11 Phosphorus-Based Epoxy Resin–Nanoclay Composites Jianwei Hao, Yanbing Xiong and Na Wu, 
Chapter 12 Study of the Relationship Between Flammability and Melt Rheological Properties of Flame-Retarded Poly(Butylene Terephthalate) Containing Nanoclays S. Nazarre, T. R. Hull, B. Biswas, F. Samyn, S. Bourbigot, C. Jama, A. Castrovinci, A. Fina and G. Camino, 
Chapter 13 Thermal and Fire Performance of Flame-Retarded Epoxy Resin: Investigating Interaction Between Resorcinol Bis(Diphenyl Phosphate) and Epoxy Nanocomposites Charalampos Katsoulis, Everson Kandare and Baljinder K. Kandola, 
Chapter 14 Porosity Estimates of Intumescent Chars by Image Analysis J.E.J. Staggs, 
Chapter 15 Efficient Modelling of Temperatures in Steel Plates Protected by Intumescent Coating in Fire J.F. Yuan and Y.C. Wang, 
Chapter 16 Fire Retardancy and Fire Protection of Materials using Intumescent Coatings – A Versatile Solution? S. Duquesne, M. Jimenez and S. Bourbigot, 
Chapter 17 Trends in Textile Flame Retardants – a Market Review R. Hicklin, R. Padda and G. Lenotte, 
Chapter 18 New and Potential Textile Flammability Regulations and Test Methods within the USA P.J. Wakelyn, 
Chapter 19 Flame Retardancy of Cellulosic Fabrics: Interactions between Nitrogen Additives and Phosphorus-Containing Flame Retardants Sabyasachi Gaan, Gang Sun, Katherine Hutches and Mark Engelhard, 
Chapter 20 Synergistic Flame Retardant Copolymeric Polyacrylonitrile Fibres Containing Dispersed Phyllosilicate Clays and Ammonium Polyphosphate A.R. Horrocks, J. Hicks, P.J. Davies, A. Alderson and J. Taylor, 
Chapter 21 Flame Retardance of Polyacrylonitriles Covalently Modified with Phosphorus- and Nitrogen-Containing Groups John R. Ebdon, Barry J. Hunt, Paul Joseph and Tara K. Wilkie, 
Chapter 22 Novel Fire Retardant Backcoatings for Textiles M.A. Hassan, 
Chapter 23 Effect of Yarn, Fabric Construction and Colour in Respect of Red Reflectance and Pigmentation on the Thermal Properties and Limiting Oxygen Index of Flame Retardant Polypropylene Fabrics C. Kindness B.K. Kandola and A.R. Horrocks, 
Chapter 24 Influence of Fire Retardants on Toxic and Environmental Hazards from Fires David Purser, 
Chapter 25 Assessment of Fire Toxicity from Polymer Nanocomposites Anna A. Stec and T. Richard Hull, 
Subject Index, 419, 

CHAPTER 1

Synergy between Nanometric Alumina and Organoclay in Conventional Fire Retardant Systems for Ethylene– Vinyl Acetate

N. CINAUSERO, J.-M. LOPEZ-CUESTA, F. LAOUTID, A. PIECHACZYK AND E. LEROY

1.1 Introduction

Hydrated mineral fillers like aluminium hydroxide (ATH) or magnesium hydroxide (MDH) are used in the cable industry as flame retardants for poly-olefins such as ethylene–vinyl acetate (EVA) copolymers. The very high filler loadings usually required to obtain satisfactory fire properties, mean this results in a decrease in the mechanical performance of the materials. Nevertheless, enhancement of the efficiency of ATH or MDH may be achieved by partially substituting them with synergistic additives, in particular high-aspect ratio inorganic particles such as oMMTs or delaminated talcs. In addition to improvement in the mechanical properties, the presence of such lamellar particles leads to an intumescence phenomenon that occurs before ignition in cone calorimeter tests. A foam-like charred structure is formed as a consequence of heterogeneous bubble nucleation, increased viscosity and the promotion of charring of the host polymer. This structure leads to the formation of a porous protective residue (mainly inorganic), which limits both heat transfer and the diffusion of fuel and oxygen.

In a recent patent we showed that the addition of alumina nanoparticles improved the reactions to fire of flame retardant EVA compositions that contain metal hydroxide and oMMTs. In this chapter we present a detailed study of these complex systems and discuss the influence of the size of alumina particles.

1.2 Experimental

1.2.1 Materials

EVA [Elvax 260, containing 28 weight percent (wt%) of vinyl acetate] was purchased from DuPont. Magnesium hydroxide (MDH; Magnifm H10, d50 = 0.85 urn, specific surface area = 10m2g-1) and oMMT (Nanofil 5: distearyldimethyl-ammonium ion-exchanged bentonite) were supplied by Martinswerk (now Albemarle) and Süd Chemie (now Rockwood Holdings), respectively. Alumina particles of different physical properties were obtained from Degussa (ALU nano, Aeroxide Alu C, d50 = 13 nm, SBET = 86m2g-1) and Alcan (ALU micro, d50 = 0.47 µm, SBET = 6.5m2g-1), respectively.

1.2.2 Processing

Blending of molten EVA copolymer with the different minerals was performed using a Haake internal mixer at 160 °C and 60 revolutions per minute (rpm) for 10 minutes. Thick (4 mm) sheets were then compression moulded at 160 °C at a pressure of 100 bars (1 × 107 Pa) for five minutes. These sheets were cut to the size required for the experiment to be performed. For all the different compositions studied, the total filler content was 10% or 60% w/w. As an example (EVA 40/ MDH 50/ALU nano 5/oMMT 5) means a formulation that contains 40% w/w of EVA, 50% of MDH, 5% of ALU nano and 5% of oMMT.

1.2.3 Testing

Épiradiateur tests (AFNOR NF P 92-505) were carried out on 70 × 70 × 4 mm3 samples to determine the flammability and the self-extinguishability of the different compositions. The heat flux of épiradiateur measured using a flux meter is around 30kW/m2. This test allows the time to ignition (TTI) for the sample placed under the radiator (500 W) to be determined. After first ignition, the radiator is successively removed and replaced as soon as extinction occurs, the procedure being repeated for a period of 5 minutes. The mean inflammation period (MIP) and the number of ignitions (N) are then calculated from results obtained from four experiments for each formulation.

Cone calorimeter tests(ISO 5660) were performed on filled polymer samples (100 × 100 × 3 mm3) placed horizontally, using a FTT cone calorimeter. Irra-diances of 30, 50 and 70kW/m2 were used. Ignition is piloted by a spark generator in contrast to the épiradiateur test, during which ignition is spontaneous. TTI and peak of heat-release rate (PHRR) values are discussed later. The results given correspond to mean values obtained from two experiments for each formulation.

Thermogravimetric analysis (TGA – Perkin Elmer PYRIS 1) was used to study the thermo-oxidative degradation of composites. Samples of typically 15mg were placed in alumina crucibles and subjected to a temperature ramp from 25 °C to 700 °C in air at a heating rate of 5 °C min-1.

1.3 Results and Discussion

To study the interactions between the various components of the formulations above, we performed three series of TGA.

Figure 1.1 shows the effect of the presence of oMMT, ALU micro and ALU nano on the thermo-oxidative degradation of EVA. Pure EVA shows two main mass losses, the first one corresponding to EVA deacylation and the second one to EVA main-chain degradation. In the presence of oMMT, the first mass loss takes place at lower temperatures, while the second one is shifted towards higher temperatures, in agreement with literature results. The main explanation of the acceleration of the acetic acid loss is the catalytic effect of hydroxyl groups on the clay. In contrast, the presence of ALU nano does not affect the temperature of either of the two mass losses, while the presence of ALU micro leads to a slight change in the temperature of the second mass loss.

Figure 1.2 displays the effect of nanofillers on the dehydration of MDH. Pure MDH dehydration takes place between 270 and 390 °C, with a maximum mass loss rate at 370 °C. In comparison, pure oMMT shows a mass loss between 200 and 390 °C, which corresponds to the degradation of its organic part, while ALU nano (and ALU micro) does not show any mass loss in this temperature range. When MDH is mixed with ALU nano (50/50 w/w powder mix), the dehydration of MDH starts at lower temperature, with a maximum mass loss rate at 355 °C. In comparison, when MDH is mixed with oMMT (50/50 w/w powder mix), the opposite occurs, with a maximum mass loss rate at 380 °C. In the meantime, the degradation of the organic part of oMMT does not appear to be influenced by the presence of MDH.

Figure 1.3 shows the TGA and differential thermogravimetric (DTG) curves for the flame retardant formulations. The first mass loss, which corresponds to both the deacylation of EVA and the dehydration of MDH, is slightly influenced by the presence of ALU nano (the maximum mass loss rate is shifted towards lower temperatures). This may confirm its influence on the decrease of the MDH dehydration temperature observed in Figure 1.2. When both ALU nano (or micro) and oMMT are present, a shoulder appears on the low temperature side of the mass loss rate peak. In this case, two phenomena can accelerate the mass loss: ALU nano seems to sharpen the reaction of deacylation of EVA catalyzed by oMMT, as observed in Figure 1.1; in addition, when incorporating both nanofillers, water release may be restricted, which contributes to the acceleration of mass loss at lower temperatures.

Furthermore, the presence of oMMT shifts the first maximum mass loss rate towards a higher temperature, in agreement with the results of Figure 1.2 (dehydration of MDH at higher temperatures). The second mass loss peak is clearly shifted towards higher temperatures in the presence of oMMT, a shift due to EVA charring.

From these TGA results we can make the assumption that the presence of ALU nano (or micro) in flame retardant formulations does not affect the flame retardant action of oMMT, but can modify the dehydration of MDH, which starts at a lower temperature. Besides, oMMT used with alumina particles accentuates the deacylation of EVA in the low temperature range (250–340 °C), which could have a favourable effect on further charring due to double bond formation at lower temperature.

The data obtained from the épiradiateur tests are presented in Figure 1.4. The reference flame retardant formulation (EVA 40/MDH 60w/w%) has the lowest TTI, which means the highest flammability, and the highest MIP, which means a poor auto-extinguishing ability. The introduction of oMMT clearly improves these two characteristics, while in the case of ALU (nano or micro) no significant improvement is observed. When both oMMT and ALU (nano or micro) are present, the TTI increases significantly, compared to formulations that contain only oMMT. The best increase in TTI is obtained for ALU nano. The size of alumina particles is therefore an important parameter.

Figures 1.5 and 1.6 show the cone calorimeter HRR curves obtained at various incident heat fluxes for (EVA 40/MDH 60), and (EVA 40/MDH 50/oMMT 10), formulations, respectively. The behaviour shown in Figure 1.5 is "classical": when the incident heat flux decreases, the TTI increases and the PHRR decreases. In contrast, the presence of oMMT (Figure 1.6) leads to an unusual behaviour at low irradiance (30kW/m2): the TTI becomes extremely long while the PHRR strongly increases. Similar behaviour was observed for the (EVA 40/MDH 55/oMMT 5) formulation, as shown in Table 1.1.

This strong increase of PHRR at low incident-heat flux caused by the presence of oMMT is likely to be a problem for cable applications of the material. Effectively, studies have shown a good correlation between the PHHR in the cone calorimeter at low incident-heat flux (typically below 50 kW/m2) and the passing of the FIPEC cable test, which is a vertical tray test using a 20 kW burner.

As Table 1.1 shows, the introduction of ALU nano allows the negative effect of oMMT on the PHRR at 30 kW/m2 to be decreased. In contrast, when ALU micro is used, the PHRR is increased, showing again that the size of alumina is an important parameter.

As regards ignition, when incorporating nanoclays in flame retardant EVA, an increase of TTI occurs that we have already observed in a previous study. If we now focus on the TTI values obtained in the cone calorimeter test at 30kW/m2, it is striking that they strongly differ from those obtained in épiradiateur tests, although the incident heat flux is nearly the same. Contrary to what is observed for épiradiateur tests (Figure 1.4), the introduction of ALU nano leads to a relative decrease of the TTI in cone calorimeter tests relative to that of the EVA/MDH/oMMT composition. These contradictory evaluations of the TTI are undoubtedly related to different experimental conditions: in the case of épiradiateur tests, the gases emitted from the sample are not aspirated, as in the cone calorimeter tests. To sum up, both the acetic acid and water are produced more efficiently owing to the effect of ALU on the deacylation of EVA catalyzed by oMMT observed in TGA, as well as the regulated water release from the dehydration of MDH. Therefore, we can assume that acetic acid and water may dilute the combustible gases at the surface of the sample during the pre-ignition period of épiradiateur tests. This is likely to delay ignition, which in addition is not promoted by a spark in this test. Then the effectiveness with which ALU nano increases the TTI of a cable in a real fire will depend on the fire scenario. Nevertheless, the "static" conditions of the épiradiateur are more likely than the forced flow of the cone calorimeter.

Let us now come back to the PHRR values at 30 kW/m2. Comparison of the shape of the curves in Figure 1.6 suggests that, for this low external heat flux, a more important flux of combustible gas evolves at the time of ignition, and results in a strong PHRR. Such a "critical phenomenon" observed for (EVA 40/ MDH 50/oMMT 10) could be explained by a stronger migration of clay platelets towards the surface at low irradiance. This forms a protective layer before ignition that becomes "unstable" after ignition because of the additional external heat flux provided by the flame. Such a "critical phenomenon" is not observed for (EVA 40/MDH 60; Figure 1.5) and (EVA 40/MDH 50/ALU nano 10; Table 1.1) formulations, and is significantly reduced when both ALU and oMMT are present (EVA 40/MDH 50/ALU nano 5/oMMT 5; Table 1.1). Eventually, this last formulation is the best compromise concerning TTI and PHRR. In contrast, when ALU micro is used (Table 1.1), the PHRR is increased compared to that of the (EVA 40/MDH 55/oMMT 5) formulation, which confirms the size dependence of alumina particles on flammability properties.

1.4 Conclusion

The effect of alumina particles on the thermo-oxidative degradation and the reaction to fire of conventional flame retardant formulations for EVA that contains MDH and oMMT has been studied. The introduction of alumina particles did not have any direct effect on the thermo-oxidative degradation of the EVA copolymer, but was shown to shift the dehydration of MDH towards lower temperatures. Besides, when mixed with oMMT, alumina particles may accentuate the deacylation of EVA catalyzed by oMMT. It was suggested that the restriction of water release and the acceleration of acetic acid loss could have an effect on the reaction to fire. Effectively, the épiradiateur test showed a strong increase in the TTI in the presence of both alumina particles and oMMT, the best improvement being obtained for nano alumina particles. In addition, the use of alumina nanoparticles allowed the PHRR of EVA/MDH/oMMT formulations to decrease at low external heat flux in cone calorimeter, which showed high values. This phenomenon is particularly relevant since the PHRR at low external heat flux is known to correlate with larger scale cable fire tests.

(Continues...)

Excerpted from Fire Retardancy of Polymers by T Richard Hull, Baljinder K Kandola. Copyright © 2009 Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
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Edition details

• Publisher: Royal Society of Chemistry
• Publication date: 2008
• ISBN 10: 0854041494
• ISBN 13: 9780854041497
• Binding: Hardcover
• Language: English
• Number of pages: 456
• Editor: Terence Richard Hull