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).

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The aim of this study is to evaluate the efficiency of different intumescent formulations to flame retard polylactic acid (PLA). First, the ammonium polyphosphate (APP)/pentaerythritol (PER) system is chosen because it previously demonstrated a good behavior for polyethylenic matrices. The PER is then substituted by bioresources such as lignin and starch. The flame retardant properties of the various formulations are evaluated by limiting oxygen index (LOI), UL‐94, and cone calorimetry. Compared to the PLA/APP/PER composite, the materials containing lignin and starch show lower LOI values but still commercially acceptable (superior to 32%). In contrast, the UL ratings obtained for these formulations are superior to that containing PER (V0 against V2 rating). The cone calorimeter analysis confirms the formation of an intumescent structure for the “green” composites, with a final residue corresponding to 50% of the initial sample mass and also a decrease in the peak of heat release of 50%. Finally, the composition of the formulation is optimized following a mixture design methodology to maximize the quantity of bioresources. A 32% LOI value is obtained for a composite containing 60% PLA, 12% APP, and 28% starch. Copyright © 2008 John Wiley & Sons, Ltd.