Recent Advances for Intumescent Polymers

Abstract

Summary: This paper reviews recent approaches for making intumescent systems. The mechanisms of action involving intumescence are described and commented on. Synergistic aspects using zeolites and organoclays are also considered and discussed. New strategies are examined on the basis of the mechanism of intumescence. The approach of using char forming polymers as additives (blend technology) is also fully discussed. This consists of substituting classical polyols (char forming agents) with char forming polymers (polyamides and thermoplastic polyurethane). It will be shown that the advantages of this concept are to obtain flame‐retarded (FR) polymer blends with improved mechanical properties in comparison with polymers loaded with classical formulations, and the avoidance of problems due to the water solubility of the polyols and their migration. The “nanocomposite approach” enhances the performance of intumescent systems by using a nanostructured char forming polymer. It will be shown that this combination of intumescence via the blending approach and nanocomposites enhances both flame retardancy and mechanical properties, and allows many specifications to be produced (for example, the design of EVA‐based materials for flame retarded low voltage cables and wire). This appears to be one of the most promising ways for designing new efficient intumescent materials.Intumescent residue after LOI test of an intumescent poly(propylene).magnified imageIntumescent residue after LOI test of an intumescent poly(propylene).

Introduction to Flame Retardancy and Polymer Flammability

“…This mechanism of action is mostly physical because the polymer itself is not necessarily involved in the charring process, but its volatilization is retarded significantly. Intumescent systems for various polymers have been reviewed by Bourbigot et al 43,44 The chemistry of formation of the intumescent chars was described thoroughly by Camino et al 45,46 Phosphorus flame retardants can remain in the solid phase and promote charring or volatilize into the gas phase, where they act as potent scavengers of H ž or OH ž radicals. Volatile phosphorus compounds are among the most effective inhibitors of combustion.…”

Study on intumescent flame retarded polystyrene composites with improved flame retardancy

“…The IFR system is commonly composed of a precursor of a carbonization catalyst, such as ammonium polyphosphate (APP), a carbonization agent, such as a polyol, and a blowing agent. By the sequence of esterification, carbonization, expansion and solidification, the intumescent char generated from the IFR will cover the underlying material to protect it from the heat or flame and slow the mass transfer [1] and [2]. Over the past decade, inorganic nanofillers (montmorillonite clay [3] and [4], carbon nanotubes, [5] zirconium phosphate [6]), metallic oxides [7], [8], [9] and [10] (MoO3, Fe2O3, TiO2, La2O3) and catalysts [11] have been added to the IFR to improve its flame retardant efficiency and thermal stability.…”

Mechanism of enhancement of intumescent fire retardancy by metal acetates in polypropylene

“…The fire protection of flammable polymers using an intumescent additive system is a complicated chemical processes [1] . These additive systems usually contain three main ingredients: an acid source, a carbon source, and a gas source, which decomposes, above the polymer processing temperature, to form a foamed cellular char layer, through release of gas, dehydration and crosslinking, to protect the underlying material from the action of heat or flame [2][3][4] .…”