Nanosized Fire Retardants

With the need to improve both performance and toxicity of fire retardants, there is an emerging focus onnanomaterials. The chemical mechanisms offire retardance using nanomaterials are a subject with a great potential for exploration in the coming years. 

One of the difficulties in using nanomaterials is that they generally do not incorporate easily into polymers with a high degree of dispersion and/or exfoliation 

There have been recent commercial developments at some major FR producers where nanoclays have been combined with metal hydroxide fire retardants acting synergistically. As nanodays are added at relatively small amounts, typically 1-5 wt%, and metal hydroxides traditionally at much higher loadings, these synergies may be exploited to allow lower overall loading levels of nanoday and metal hydroxide. 

Recent research on alternative nanomaterials indudes douhle-layered hydroxides, and polyhedral oligomeric silsesquioxanes (see Chapters 20 and 23). The potential of nanodays as intumescent fire retardants to protect materials such as wood that are easily combustible in contact with air is also exploited. It is expected that the pace of this type of research will increase in the coming years [74—77]. 

---

Many variations of these processes exist with the aim of controlling particle surface area, shape, and purity these characteristics define the fire retarding performance of magnesium hydroxide fillers, especially in more demanding applications where processability and good mechanical properties are also important considerations. In more recent developments, nanosize magnesium hydroxide variants have also been produced. 

Nanocomposites refer to the combination of nanosized fillers (10 m diameter) with polymers, rather than the combination of polymer matrix (filled with nanoparticles) and fiber reinforcement The most popular fillers used as fire retardants are layered silicates. Loading of 10% or less (by weight) of such fillers significantly reduces peak heat release rates and facilitates greater char production [7]. The char layer provides a shielding effect for the composites below and the creation of char also reduces the toxicity of the combustion products, as less carbon is available to form the CO and CO2. 

Fillers are typically used to enhance specific properties of polymers, and the polymer/ nanocomposites based on nanoclays have gained attention because of their ability to improve the mechanical, thermal, barrier, and fire-retardant properties of polymers [3]. Nanosized fillers have been introduced in a wide spectrum of applications ranging from providing photocatalyst activation and conductivity to improve melting... 

Chang et al. [20] used a nanosized hydroxyl aluminum oxalate (nano-HAO) with a dioctahedral 1 1 layered clay mineral (nanokaolin) to investigate their fire retardancy effects on a LDPE/ EPDM blend. In Table 8.5, the TTls and HRRs of the composites containing 48 wt% nano-HAO and 12 wt% nanokaolin are compared with that of the composites containing 60 wt% nano-HAO alone. Whereas nano-HAO or nanokaolin has essentially no effect on the TTI, the peak and average HRRs are dramatically reduced with the addition... 

---