Intumescence-based development

Fire-retardant paints for wood have been developed using urea-formaldehyde resins and ammonium phosphate. Heat causes this compound to intumesce and develop an insulating layer for the surface upon which it is applied. Oil-based fire-retardant paints usually contain organic materials such as resins, paraffins, or chlorinated rubbers combined with inorganic vehicles, or they may be compounded of inorganics such as ammonium compounds. 

More recently there have been developed water- resistant phosphorus-based intumescence catalyst. This commercially available product, as an example Phos-Chek P/30 tradename from Monsanto, can be incorporated (with other water insoluble reagents) into water-resistant intumescent coatings of either the alkyd or latex-emulsion type. These intumescent coatings, formulated ac-... 

A series of compounded flame retardants, based on finally divided insoluble ammonium phosphate together with char-forming nitrogenous resins, has been developed for thermoplastics.23 These compounds are particularly useful as intumescent flame-retardant additives for polyolefins, ethylene-vinyl acetate, and urethane elastomers. The char-forming resin can be, for example, an ethyle-neurea-formaldehyde condensation polymer, a hydroxyethyl isocyanurate, or a piperazine-triazine resin. Commercial leach-resistant flame-retardant treatments for wood have also been developed based on a reaction product of phosphoric acid with urea-formaldehyde and dicyandiamide resins. 

In this part, we will distinguish between natural and synthetic fibers because different methods are usually involved to provide flame retardancy by intumescence for the two classes. A few papers report recent development and performance of intumescent textiles. Very often the authors describe the mechanism of action of their materials as mechanism via charring enhancement or something similar. Nevertheless based on the chemical nature of the flame retardant used and by the described... 

X-ray diffraction (XRD) has been poorly used to characterize the carbon phase of intumescent structure. Indeed, as shown previously, the carbon structure resulting from the development of the intumescent system is mainly disordered whereas XRD characterizes ordered structure. However, this technique may be of interest to study the carbonization process in the case of flame-retardant systems containing layered additives, such as expandable graphite,28,42 or even more in the case of lamellar nanocomposites, such as MMT-based nanocomposites. 

The materials included in this chapter for illustration are nanocomposite polymers combined with intumescent commercial phosphorous fire retardants. In this chapter, different base polymers (e.g., PA6, PBT, PP, and EVA) are mentioned for illustrating the methodology but the focus will be on PA6. For the present purpose, the composition of a PA6 nanocomposite is described next to make the development of the present methodology more clear. 

The sueeess of graphite in this applications shows that filler with plate like struetures should be considered when intumescent materials are being formulated. Reeent developments in intumescent paints show that performanee ean be improved if a layer of organic material is inserted between the layers of the plate like filler. The degradation of this material in the enclosed space increases the expansion rate and the retention of gas inside the degrading material. Based on this prinei-ple any plate like filler has the potential to be useful in an intumescent applieation. The eomposition of filler is also important. When clay was used as a filler in fire retardant applieations, it was found that some of its components interfere with the action of carbonization catalysts and detract from the overall performance of the system in terms of limiting oxygen index. ... 

A new US company based in Hudson, Massachusetts has developed intumescent coatings and additives that enhanee the fire properties of plastic and composite structures. Avtec Industries now offer Thermashield mastic coatings that can withstand temperatures in excess of 1200 °C for sustained periods. The coatings material is non-toxic and does not flake, peel or chip. It is resistant to water and chemieal attack and is claimed to withstand multiple high-impact shocks. 

A new type of intumescent additive is expandable graphite. This material has already found uses as a special effect pigment due to its metallic sheen and grey-black colour. Nord-Min has been developed by suppliers Nordmann Rassmann with flame retarding of plastics in mind. It is a halogen-free fire barrier additive from Chinese sources, based on natural graphite flakes with... 

As part of the research, the investigation of the coatings based on perchlorovinyl resin and containing the developed intumescent additive PEDA on fire protective properties was conducted. The results are presented in Table 18.1. 

The intumescent approach has been used for about 50 years in coatings for the protection of metal and wood structures [1,2]. The introduction of intumescent systems in the bulk of polymeric materials is relatively recent [3-5]. The early developments in intumescent additives for polymers were based on experience acquired in coating applications. Indeed, the empirical approach had led to a recognition of the need for compounds capable of supplying the charred residue (a carbonific ) and of blowing it to a foamed cellular structure ( spumific ) as components of formulations showing intumescent behaviour in coatings. 

The char formers commonly used in intumescent formulations for thermoplastics are polyols such as pentaerythritol, mannitol, and sorbitol. However, exudation and water solubility are problems associated with these additives. Moreover, these additives are often not compatible with the polymeric matrix, and the mechanical properties of the formulations are then very poor. We have developed intumescent polyolefin-based formulations using charring polymers [thermoplastic polyurethane (TPU) and polyamide-6 (PA6)] as carbonization agents. " These formulated blends have improved mechanical properties compared with polymers loaded with classical flame retardants, and they avoid the problems... 

Curves of heat release rate (HRR) versus time for intumescent EVA-based formulations (Figure 6.11) exhibit two peaks assigned to the development of intumescence. The first corresponds to formation of a protective layer, and the second corresponds to its destruction or failure. It clearly appears that when a nanocomposite is included in the formulation (in the matrix, in the carbonization agent, or in both), the first peak heat release rate (PHRR) is reduced (from about 340 kW/m to 200 kW/m ). However, the second peak decreases only when EVAnano is used, suggesting the formation of a stronger char. Work is in progress to explain these phenomena. 

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