Heat release rate polymer nanocomposites

The impact of the nanocomposite technology on polymers is huge, reflected in enhanced properties of the resulting PNs, such as enhanced mechanical, barrier, solvent-resistant, and ablation properties.12 The effect of nanocomposite technology on the thermal and fire performance of the polymers is primarily observed in two important parameters of the polymers (1) the onset temperature (7( ,nsct) in the thermogravimetric analysis (TGA) curve—representative of the thermal stability of the polymer, and (2) the peak heat release rate (peak HRR) in cone calorimetric analysis (CCA)—a reflection of the combustion behavior (the flammability) of the polymer. The Tonset will be increased and the peak HRR will be reduced for a variety of polymers when nanoscale dispersion of the nanoadditive is achieved in the polymer matrix. 

The heat release rate curves shown in Fig. 4A are consistent with the characteristic burning patterns of intermediate thick, non-charring samples (II). The PHRR values for PE-ZCHS-5 and PE-ZCHS-10 nanocomposites are reduced by 27 and 25% relative to the pure PE respectively. For smectite clay/polymer nanocomposites, reduction in PHRR has been shown to be correlated with nanodispersion of the additive in the polymer matrix (72). With HDS and related layered metal hydroxide additives, we have also only found PHRR reduction in the case of PVE with CHDS, a system with some... 

Polymer clay nanocomposites exhibit very low flammability. For instance, the heat release rate during the combustion of polyamide 6-clay nanocomposite is reduced by 63% with a clay content of 5wt%. The nanocomposite structure also enhances the property of the char through reinforcement of the... 

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. 

The flame-retardant characteristics of polymer nanocomposites are also found to be enhanced compared to the pristine system. This may be due to a significant reduction in the heat release rate and an increase of nonflammable char residue. The char creates a protective layer which impedes oxygen penetration and creates an insulating layer between the heat and the fuel. 

The flammability behaviour of clay-polymer nanocomposites could be restricted by incorporating the nano-clay as reinforcement in limited volume fraction. The heat release rates also are found to be diminished substantially by nano-clay incorporation. The flammability resistance can be enhanced by the incorporation of nano-clay platelets without compromising other properties [114]. This improvement in flammability resulted in development of Wire Cable jacket material [115]. 

The accumulation of clay at the surface acts thus as a barrier which limits heat transfers and reduces the release of combustible volatiles into the flame. A substantial decrease in the peak heat release rate of the nanocomposite (25 to 50%) can be achieved compared to the neat polymer (Bourbigot et al, 2006). However, this effect is very dependent on the quality of dispersion of the nanoparticles within the host matrix, and a high degree of exfoliation is usually targeted in order to maximize both the mechanical and fire properties (Hackman and Hollaway, 2006). Other types of nanoparticles, such as silica (Si02), titanium dioxide (Ti02), carbon nanotubes or silesquioxane, have also proven to have significant flame-retardant properties (Laoutid et al., 2009). 

The comprehensive flame retardation of polymer-clay nanocomposite materials was reported by Dr. Jeff Gilman and others at NIST [7]. They disclosed that both delaminated and intercalated nanoclays improve the flammability properties of polymer-layered silicate (clay) nanocomposites. In the study of the flame retardant effect of the nanodispersed clays, XRD and TEM analysis identified a nanoreinforced protective silicate/carbon-like high-performance char from the combustion residue that provided a physical mechanism of flammability control. The report also disclosed that The nanocomposite structure of the char appears to enhance the performance of the char layer. This char may act as an insulation and mass transport barrier showing the escape of the volatile products generated as the polymer decomposes. Cone calorimetry was used to study the flame retardation. The HRRs (heat release rates) of thermoplastic and thermoset polymer-layered silicate nanocomposites are reduced by 40% to 60% in delaminated or intercalated nanocomposites containing a silicate mass fraction of only 2% to 6%. On the basis of their expertise and experience in plastic flammability, they concluded that polymer-clay nanocomposites are very promising new flame-retarding polymers. In addition, they predict that the addition... 

The great improvements in flame retardancy caused by the organoclays also opened the possibility of decreasing the level of ATH within the EVA polymer matrix. The content of ATH needed to maintain 200 kW/m as a peak heat release rate could be decreased from 65 to 45 wt% by the presence of only 5 wt% organoclays within the EVA polymer matrix. Reduction in the total amount of these fillers resulted in improved mechanical and rheological properties of the EVA-based nanocomposite. 

In summary, significant reduction in the peak heat release rate for the PA 6/clay nanocomposites was achieved by the formation of protective floccules on the polymer surface, which shielded the PA 6 from external thermal radiation and feedback from the flame. That is, the carbonaceous floccules acted as thermal insulation. 

Combustion of polymeric materials involves a complex process, where both condensed and vapor-phase reactions occur at exposed surfaces that are sources of flame and/or thermal radiation of the most common parameters measuring the flammability of polymeric materials are heat release rate (HRR) and mass loss rate (MLR) from cone calorimetry. Recently, nanocomposites containing nanoparticles have been of great interest in the composite industries. In particular, polymer blends containing clays have not been comprehensively studied for their flammability, in spite of the fact that most plastic products are made out of blends of more than two polymer. Furthermore, because the dispersion of nanoparticles is a key factor in determining the HRR and MLR of nanocomposites [23-26], we investigated correlations between flammability and dispersion in air and under nitrogen, especially for polymer blends. 

Polymer/fullerene [Ceol nanocomposites can be considered environmentally friendly alternatives to some traditional flame retardants. The presence of Ceo can markedly delay thermal oxidative degradation and reduce the flammability of polypropylene at very low loadings. It can decrease the heat release rate of polymeric materials by trapping the free radicals created through thermal degradation and combustion, and subsequently forming three-dimensional gelled networks. This network can increase the melt viscosity and consequently slow down combustion. Furthermore, the incorporation of Qo does not affect the physical properties of the polymer. 

In addition, several studies have reported the use of conventional ATH in combination with other types of nanofillers, particularly organoclays, to improve the FR properties of polymer nanocomposites [12, 13]. Organoclays are not considered as FR despite their ability to decrease peak heat release rates of several polymers under firelike conditions... 

Similar results are also observed in PS nanocomposites [56], which were prepared by free radical polymerization of styrene monomers in the presence of ZnAl and MgAl LDHs intercalated with 4,4 -azobis(4-cyanopentanoate) anions (LDH-ACPA). An intercalated-exfoliated morphology is observed for the composites of ZnAl-ACPA, whereas MgAl-ACPA shows microcomposite formation. The cone calorimetry results show good correlation between the reduction in PHRR and dispersion, in which the reduction in the peak heat release rate for 10% ZnAl-ACPA is 35% relative to the pristine polymer, whereas a 24% reduction is recorded for MgAl-ACPA at a similar loading. 

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