New Developments of Intumescent Phosphorous Based flame reta

New Developments of Intumescent Phosphorous Based flame retardants

New Developments of Intumescent Phosphorous Based

Flame Retardants

ABSTRACT

The performance of a novel intumescent flame retardant based on a special coating technology, which is compared with current technology, is discussed.

INTRODUCTION:

Polymers that contain flame retardant (FR) additives are currently used in many sectors. Important applications can be found in the public transport, automotive industry, buildings, electronics industry etc. In the case of fire or heat, flame retarded polymers help to reduce or even neutralise the risk of fire spreading. However new standards and harder regulations for combustible materials make it necessary to improve flame retardants for polymeric materials1. At the same time polymers are also used in many new applications and regarding to fire safety the right solutions for flame retardants must be given.

Currently used FR’s in polymers are:

Halogenated additives and antimony trioxide

Aluminium trihydroxide and other inorganic fillers Melamine derivatives Phosphate-based materials

Halogenated additives in resins show a remarkable efficiency as flame retardants and do not seriously impact the mechanical, thermal, ultraviolet thermo stability or electrical properties of the polymers. The mechanism of fire retarding takes place in the gaseous phase by the interception of highly reactive free radicals by halogenated organic compounds. Antimony trioxide is often used as a synergist together with the halogen containing FR’s. However, there are increasing concerns over environmental and toxicological impacts of the decomposition products formed when the blended polymer is disposed off or burned. Also they generate a great quantity of smoke and toxic fumes, which are unacceptable for many applications in public areas2.

Aluminium tri hydroxide (ATH), which is also widely used in polymers is an alternative to halogenated formulations. The effect of the flame retardant is based on the endothermic release of water at higher temperatures. However, very high loadings of ATH (50 - 60 %) are required for effective levels of fire retarding. At the same time mechanical and optical properties of the polymeric material decrease substantially and the field of applications of these materials is only limited.

Melamine Derivatives, especially phosphate salts of melamine (see also under phosphate derivatives), are new products, which have a good performance as flame retardants, because of their balanced P/N-ratio. Another important flame retardant is melamine cyanurate T. Futterer, H-D. Naegerl, Chemische Fabrik Budenheim, Rheinstr. 27, 55257 Budenheim, Germany V. Mans, E. Tortosa, Budenheim Iberica, Extramuros S/N, 50784 La Zaida (Zaragoza), Spain

New Developments of Intumescent Phosphorous Based flame retardants

(Budit 315). This additive is very attractive for the polymer industry: It is used in large quantities for fire resistant polyamide. Very low addition levels of 8-12 % can give a V-0 classification.

Phosphate derivatives are well known as flame retardants for a long time and already used for wood, paper and cotton fibres. In the fire protection of plastics nowadays phosphates and their derivatives are getting more and more important. Representatives are phosphate esters (Budit 380, 3092, 3096), melamine phosphates (Budit 310, 312), and melamine pyrophosphate (Budit 311). Latter is a very effective and cheap flame retardant with a low water solubility and a high thermal stability. It is used in glass filled polyamide systems, varnishes, paints and for textile treatment.

One of the most established products, because of its versatility, is ammonium polyphosphate3 (APP, FR CROS 484). By using the unique technology of intumescency4it can be used as a very effective flame retardant for polyolefins, polyesters, etc. This well established technique builds up an insulation layer in the case of fire. The combustible material gets separated from the heat source by a heat isolating foam. In contrast to halogenated flame retardants the mechanism of stopping the fire takes place in the solid state. The ammonium polyphosphate is fully decomposed at temperatures of 275 °C by an endothermic reaction. Polyphosphoric acid and ammonia are set free and act as a dehydrating agent respectively blowing agent. In the case of polymers like polyolefins, which do not contain any oxygen or OH-functional groups, a dehydration is not possible. Therefore the presence of a polyol additive is necessary. APP based intumescent systems do contain a polyol. They are specially designed for the use in polyolefins. Due to the presence of the polyol the dehydration by polyphosphoric acid can take place. Char is formed and simultaneously blown up by the evolving ammonia to a carbonaceous insulation, which acts as a very efficient barrier to heat.

Looking on the development of the plastics market (Chart 1), it is getting obvious that polyolefins (70 % of total production of polymers), particularly Polypropylene, is a significant growing market. It is mainly used in automotive, building, electrical, and electronics industry, where it is subsidising PVC, PS and also metals. New developed intumescent systems based on ammonium polyphosphate are versatile flame retardants and can provide the right solutions for fire safe polypropylene5.

New Developments of Intumescent Phosphorous Based flame retardants

EXPERIMENTAL

Materials

The polypropylene (Table I) that was used in the present work is commercially available as Isplen D50 from Repsol Quimica.

TABLE I. Isplen D50 Polypropylene Molecular Weight

Mw Mn Mw / Mn (g / 10 m) (°C) Hc / Tc Hm / Tm (g / 10 cm3)

334400 59500 5.62 5.8 58.5 -51.8 / 123 56.4 / 164

0.9

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