Thermal properties fire retardants

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. 

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. 

It should also be noted that the presence of surface modifiers can also influence other properties. This includes properties such as bulk density, powder flow and dustiness. They can also have unexpected effects on properties such as thermal stability, fire retardancy and ageing. These effects may be positive or negative. 

Film or sheet generally function as supports for other materials, as barriers or covers such as packaging, as insulation, or as materials of constmction. The uses depend on the unique combination of properties of the specific resins or plastic materials chosen. When multilayer films or sheets are made, the product properties can be varied to meet almost any need. Further modification of properties can be achieved by use of such additives or modifiers as plasticizers (qv), antistatic agents (qv), fire retardants, sHp agents, uv and thermal stabilizers, dyes (qv) or pigments (qv), and biodegradable activators. 

The compounds so formed have excellent thermal stability and are self-extinguishing and even completely fire-retardant. Their properties are given in Table 13.14. A few common types of insulators and supports are shown in Figure 13.31. 

Aluminium hydroxide is essentially non-toxic, but does require high addition levels to be effective. As a result, the physical properties of the compound usually suffer. Its fire retardancy action results from the endothermic reaction which releases water under fire conditions and produces a protective char . The endothermic reaction draws heat from the rubber/filler mass and thus reduces the thermal decomposition rate. The water release dilutes the available fuel supply, cooling the rubber surface and mass. 

FIRE RETARDANT FILLERS. The next major fire retardant development resulted from the need for an acceptable fire retardant system for such new thermoplastics as polyethylene, polypropylene and nylon. The plasticizer approach of CP or the use of a reactive monomer were not applicable to these polymers because the crystallinity upon which their desirable properties were dependent were reduced or destroyed in the process of adding the fire retardant. Additionally, most halogen additives, such as CP, were thermally unstable at the high molding temperatures required. The introduction of inert fire retardant fillers in 1965 defined two novel approaches to fire retardant polymers. 

In 2000, NEC developed an epoxy resin with what it describes as a fire-retardant structure that avoids the need for either TBBA or phosphorus-based flame retardants in circuit boards. The new resin contains a metal hydroxide retardant. The company claims the new board is almost totally free of pollutants, and is easy to process and thermally recycle. By also integrating flame retardant properties within the board, use of the metal hydroxide is minimised, while offering good electrical properties, higher heat resistance and improved processing characteristics. ... 

An extensive study was conducted on the effect of chemical and structural aspects of zeolites on the fire performance of the intumescent system, ammonium polyphosphate-pentaerythritol (APP-PER), where a marked improvement of the fire-retardant properties within different polymeric matrices has been observed.56 58 The synergistic mechanism of zeolite 4A with the intumescent materials was investigated using solid-state NMR. Chemical analysis combined with cross-polarization dipolar-decoupled magic-angle spinning NMR revealed that the materials resulting from the thermal treatment of the APP-PER and APP-PER/4A systems were formed by carbonaceous and phosphocarbonaceous species, and that the zeolite enhances the stability of the phosphocarbonaceous species. 

Perez RM, Sandler JKW, Altstadt V, Hoffmann T, Pospiech D, Ciesielski M, Doling M. Effect of DOP-based compounds on fire retardancy, thermal stability, and mechanical properties of DGEBA cured with 4,4 -DDS. J. Mater. Sci. 2006 41 341-353. 

Kandola, B.K. and Horrocks, A.R. 2000. Complex char formation in flame-retarded fibre intumescent combinations—IV. Mass loss calorimetric and thermal barrier properties. Fire Mater., 24 265-275. 

In contrast to stabilizers, fire retardants must be added in much higher concentrations, which affect thermal and mechanical properties as well as cost. Sherr and co-workers report that novel derivatives of phosphine oxides, phosphonic acids, phosphinic acid, and phosphonium halides may be used generally in concentrations as low as 2.5-5 p.p.h. to be effective fire retardants in polyethylene and poly (methyl methacrylate). 

Related problems must be considered in individual products. Bromine, chlorine, and antimony add to the smoke of a fire, while phosphorus and water do not, and some metal oxides can actually reduce it. Toxicity of combustion gases is a major concern but the main problem is that oxidation of carbon compounds in an enclosed space—indoors— produces carbon monoxide, no matter whether the carbon compounds are wood or plastics. Other problems include the cost of flame-retardants, difficulties in processing, and loss of mechanical or thermal properties. 

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