Polymer nanocomposites flame properties

Koo and co-workers [78] attempted to develop polyamides 11 and 12 with enhanced flame retardancy and thermal and mechanical properties by the incorporation of montmorillonite clays, silica and carbon fibre-polymer nanocomposites. Flammability properties of the nanocomposites were compared with those of the virgin polyamides, using cone calorimetry with an external heat flux of 50 kW/m. Cone calorimetry was also used in an evaluation of polyamide 6 - anion modified Mg/Al interlayer formulation [79]. The data from the cone calorimeter shows that the heat production rate (HPR) and mass loss weight of the sample with 5 wt% MgAl(H-DS) decrease considerably to 664 kW/mVs and 0.161 g/mVs from 1064 kW/mVs and 0.252 g/mVs... 

Zhang, J., Jiang, D. D., and Wilkie, C. A. Thermal and flame properties of polyethylene and polypropylene nanocomposites based on an oligomerically-modified clay, Polym. Degrad. Stab. (2006), 91, 298-304. 

Most of the previous studies on flame retardation of polymer nanocomposites are focused on the relationship between macroscopic morphologies of chars and the flammability properties. Fang et al. studied the relationship between evolution of the microstructure, viscoelasticity and graphitization degree of chars and the flammability of polymers during combustion (68). The flame retar-dancy of ABS/clay /MWNTs nanocomposites was strongly affected by the formation of a network structure. Flammability properties... 

Carbon nanotubes (CNTs) and carbon nanofibers (CNFs), due to their unique structure and properties, appear to offer quite promising potential for industrial application [236]. As prices decrease, they become increasingly affordable for use in polymer nanocomposites as structural materials in many large scale applications. In fact, three applications of multiwall CNT have been discussed recently first, antistatic or conductive materials [237] second, mechanically reinforced materials [238,239] and third, flame retarded materials [240,241]. The success of CNTs in the field of antistatic or conductive materials is based on the extraordinary electrical properties of CNTs and their special geometry, which enables percolation at very low concentrations of nanotubes in the polymer matrix [242]. 

In overall, the use of polymer-coated CNTs produced by in situ polymerisation, whether by covalent or non-covalent methods leads to the production of polymer nanocomposites displaying much better thermomechanical, flame retardant and electrical conductive properties, even at very low nanotube loadings. As mentioned above, the covalent approach allows the formation of a strong interface between the nanotube and polymer matrix due to strong chemical bonding of polymer molecules to the CNT surface. The in situ polymerisation technique also enables the preparation of composites with very high nanotube loadings. 

The desirable properties of polymer nanocomposites which are obtained by the incorporation of small amounts of nanomaterials make them of signihcant value to the scientihc community. Properties such as tensile strength, tensile modulus, thermal and barrier properties, flame retardancy and chemical resistance of vegetable oil-based polymer matrices are improved signihcantly without affecting the light weight characteristics and flexibility of the pristine polymer system. 

In the past decade, clay-based polymer nanocomposites have attracted considerable attention from the research field and in various applications. This is due to the capacity of clay to improve nanocomposite properties and the strong synergistic effects between the polymer and the silicate platelets on both a molecular and nanometric scale [2,3], Polymer-clay nanocomposites have several advantages (a) they are lighter in weight than the same polymers filled with other types of fillers (b) they have enhanced flame retardance and thermal stability and (c) they exhibit enhanced barrier properties. This chapter focuses on the polymer clay-based nanocomposites, their background, specific characteristics, synthesis, applications and advantages over the other composites. 

Depending on the distribution of micro/nanofiller in the polymer matrix, the composites may be classified as microcomposites or nanocomposites. These two types of composites differ significantly with respect to their properties. The nanocomposites show improved properties compared to pure polymer or that of microcomposites. It started only back in 1990, when Toyota research group showed that the use of montmorillonite can improve the mechanical, thermal, and flame retardant properties of polymeric materials without hampering the optical translucency behaviour of the matrix. Since then, the majority of research has been focused in improving the physicochemical properties, e.g. mechanical, thermal, electrical, barrier etc. properties of polymer nanocomposites using cost effective and environmental friendly nanofillers with the aim of extending the applications of these materials in automotive, aerospace, construction, electronic, etc. as well as their day to day life use. The improvements in the majority of their properties have invariably been attributed... 

Over the past decade, polymer nanocomposites have attracted considerable interests in both academia and industry this is because of the outstanding mechanical properties like elastic stiffness and strength which can be achieved with only a small amount of the nanoadditives. This is caused by the large surface area to voliune ratio of nanoadditives when compared to the micro- and macro-additives. Other superior properties of polymer nanocomposites include barrier resistance, flame retardancy, scratch/wear resistance, as well as optical, magnetic and electrical properties. 

In spite of the encouraging results obtained in polymer/LDH flame retardant nanocomposites, the use of LDHs alone is insufficient for ensuring adequate fire resistance to meet the required standards, such as LOI values and UL-94 test ratings, especially at low LDH concentrations. The combination of LDH with conventional flame retardants is an effective way to avoid this limitation. By this means, it is possible to reach the flame retardancy required by the market with a halogen-free, nontoxic flame retardant system and improved mechanical properties. There are also many issues concerning the synergy between LDH and conventional flame retardants. 

Organic/inorganic nanocomposites prepared by in situ polymerization methods have received extensive attention in recent years. Unlike microscale fillers, nanoscale fillers can offer excellent properties to a polymer matrix. Nanosized filler, with a few weight percent in the reinforced polymer nanocomposites, strongly influences the macroscopic properties of the polymer. The resultant polymer nanocomposites can significantly improve some of their properties, such as higher heat distortion temperatures, enhanced flame resistance, increased modulus, better barrier properties, reduced thermal expansion coefficient, and altered electronic and optical properties. 

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