Fire retardancy nanoparticles

Nanoparticles added to thermoplastic polymers improve the mechanical properties, increase Tg and enhance fire retardancy. Nanoparticles in UPRs bring similar effects [217]. Montmorillonite (MMT) was used to obtain polymer nanocomposites [218]. That general approach was applied to the UPR-layered MMT nanocomposites. The structure of the nanocomposites was investigated by XRD and TEM. Organophilic MMT was applied dodecylammonium-bromide treated MMT was used. A UPR synthesized... 

Some potentially relevant work concerns the attachment of magnesium hydroxide nanoparticles onto multiwall carbon nanotubes (MWCNTs).92 These were prepared from water-in-oil emulsions specifically for conversion into MgO to functionalize and preserve the mechanical and the electrical properties of the CNTs, although not for fire-retardant purposes. However, although more speculative, this work may be of interest as it has been reported that combinations of M WCNT and micron-sized particles of ATH in EVA function as very efficient fire retardants through enhanced char formation and coherency.93... 

This chapter develops at first the more frequent combinations of nanoparticles that concern layered silicates associated with phosphorus compounds, as well as metallic hydroxides and halogen compounds. The association of natural layered silicates with intumescent FR (IFR) systems represents one of the main contributions of the combined use of nanoparticles and FRs. Moreover, combinations of layered silicates with other phosphorus compounds have been studied and have led to significant improvements for fire retardancy. 

The use of nanoparticles in combination with additional materials has been widely studied, with the aim to improve the fire retardancy of nanocomposites. 

Cone calorimeter in standard atmosphere (to assess the effectiveness of nanoparticles and intumescent fire retardants and also measure heat release rates (HRRs) and product yields)... 

It is intended to use these properties for the assessment of alternative flame retardants (FRs) (including nanoparticles, phosphates, and inorganic metal oxides) in comparison with brominated fire retardants by quantitatively assessing ... 

Figure 19.9a-d shows that both the phosphinate FR and the nanoparticles change the structure of char compared with pure PBT. In contrast to the pure polymer, which leaves a char consisting of oligomeric components of PBT, the fire-retarded polymer (by phosphinate or nanoparticles) leaves a char consisting of polycyclic aromatic hydrocarbons (PAHs). The PAH structure of the char is expected to make the char stronger and capable to withstand erosion in full-scale fire tests. This observation is verified from the strength analysis of the char residue in intermediate scale... 

We have shown in this chapter that microscale measurements can provide a good screening method for the design of fire-resistant materials modified by nanoparticles (and fire retardants) and also, they can be used to quantitatively model and predict the behavior in mesoscale experiments even though an additional parameter is needed to predict the reduced MLR in the mesoscale experiments. The major breakthroughs and challenges are the following ... 

New trends involve the use of nanoparticles in synthetic fibers. Polymer-layered silicates, nanotubes, and POSS have been successfully introduced in a number of textile fibers, mainly poly-amide-6, polypropylene, and polyester. Although they reduce the flammability of these fibers, but on their own are not effective enough to confer flame retardancy to a specified level. However, in presence of small amounts of selected conventional FRs (5-10 wt %), synergistic effect can be achieved. With this approach fibers having multifunctional properties can also be obtained, e.g., water repellency or antistatic properties along with fire retardancy. Most of the work in this area at present is on the lab scale and there is a potential to take this forward to a commercial scale. 

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. 

Based on the size, fillers can be broadly classified into two categories, micro and nano sized fillers. Lighter, thinner, stronger and cheaper structures are the goals of material science and engineering applications today. Nanoparticles satisfy these requirements. The use of nanofillers improves mechanical and physical polymer properties. The added cost of the nanofilled matrix can be low due to the small amounts of filler necessary for a significant improvement. Nanofillers can significantly improve or adjust the properties of the materials into which they are incorporated, such as optical, electrical, mechanical, thermal or fire-retardant properties. 

Nowadays a variety of nanoparticles have been used to fabricate fire retardant nanocomposites with improved mechanical and functional properties. The common... 

Montmorillonite (MMT), a smectite clay, is probably the most extensively studied nanomaterial in terms of mechanical, thermal, fire retardant or crystallization behavior of polylactide, especially when these nanoparticles are organically modified allowing the achievement of intercalated and exfoliated nanocomposites.These nanocomposites show enhanced properties as compared to microcomposites and pristine polymer. However, biodegradation and hydrolytic degradation of PLA in the presence of nanoclays has been investigated to a small extent. 

Composites prepared using different types of nanoparticles can show superior properties compared to pure PU and have a wide range of applications in structural and biomedical fields. The surface morphology of nanocomposites is affected by the nature and amount of the nanoparticles embedded in polymer matrix. Different shapes and sizes of the nanoparticles play a significant role in enhancement of the mechanical, rheological, thermal, and fire retardant properties of the PU nanocomposites. Considerable improvements in antibacterial properties have been reported using nanocomposites compared to pure PU. Incorporation of the different kinds of nanoparticles in PU matrix alters the biocompatible nature of the composites, suggesting that PU composites may have use in biomaterial applications. 

Nanocrystals extracted from starch are also used as fillers in polymer matrices. These nanoparticles not only increase the mechanical properties but also the physical properties such as permeability and fire retardancy of these composites. Unlike cellulose or chitin which exhibit needle-like nanocrystals, SNs occur as platelet-like nanoparticles. Thus starch has the versatility of being used both as a matrix and a filler. 

In this chapter, we present a summary of fire retardant nanoclays used in polymer blends based on the authors previous experience and the literature [15-31]. Because the main objective of this work is to study the fire retarding effects of nanoclays on polymer blends, we will focus on the properties affecting the fire performance of polymer blends (a) dispersion of nanoclay, (b) rheology, (c) thermal stability, and (d) flammability (ignition, fire spread, and toxicity), whereas the effects of nanoclays on mechanical properties and compatibilization can be found easily in references listed in Table 8.1 (e.g.. References [16, 17, 19-21] on compatibilization and [16, 18, 21, 25, 26, 29-31] on mechanical properties). A review of the mechanism by which nanoparticles organize in polymer blends is also available in [32]. 

A. Laachachi, E. Leroy, M. Cochez, M. Ferriol, and J. M. Lopez-Cuesta, Use of oxide nanoparticles and organoclays to improve thermal stability and fire retardancy of poly(methyl methacrylate). Polymer Degradation and Stability, 89 (2005), 344-52. 

Kashiwagi, T. Flammability of nanocomposites effects of the shape of nanoparticles, in M. Le Bras, C.A. Wilkie, S. Bourbigot, S. Duquesne, and C. Jama, Eds., Fire Retardancy of Polymers. Royal Society of Chemistry, London, 2005, pp. 81-99. 

The combinations of nanocomposite formation with a variety of conventional fire retardants, including halogen, phosphorus, mineral fillers, and other systems, have been examined and are reported in other places in this book. We feel that this combination approach must continue and will involve other nano-dimensional materials, including other clays, snch as the layered double hydroxides, polyhedral silsesquioxanes (POSSs), carbon nanotnbes and spherical nanoparticles, and other putative flame retardants. 

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