Fire retardant polymers thermal properties

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. 

Polymer-clay nanocomposites are characterized by improved thermal, mechanical, barrier, fire retardant, and optical properties compared to the matrix of conventional composites, commonly called particulate microcomposites, because of their unique phase morphology deriving from layer intercalation or exfoliation that maximizes interfacial contact between the organic and inorganic phases and enhances bulk properties [8]. 

Thermal analysis experiments have clearly shown that tin-based fire retardants markedly alter both the initial pyrolysis and the oxidative burn off stages that occur during polymer breakdown These changes have been interpreted as being indicative of an extensive condensed phase action for the tin additive, in which the thermal breakdown of the polymer is altered to give increased formation of a thermally stable carbonaceous char at the expense of volatile, flammable products. The consequent reduction in the amount of fuel supplied to the flame largely accounts for the beneficial smoke-suppressant properties associated with zinc stannates and other tin-based fire retardants. 

By reaction of phosphorylated materials with aldehydes, amines or with isocyanates highly thermally stable products have been then produced. TGA studies have indicated their superior properties compared to conventional cardanol/formaldehyde resins of the novolac type. It was also found that a phosphorylated CNSL polymer had improved adhesive properties when compared with conventional CNSUformaldehyde resins (ref.248) and certain compounded products had wear, fade and frictional properties comparable to those of conventional PhOH/formaldehyde/copolymer brake Hnings (ref.249). The phosphorylated product from CNSL and its bromination derivative possessed good fire-retardant characteristics (ref. 250). Phosphorus derivatives of cardanol and of 3-pentadecylphenol have been studied by reaction with phosphorus oxychloride and its thio analogue (ref. 251). 

Nylon, beside its important utility as premium fiber in the textile industry, also serves as an engineering polymer due to its unique properties of rigidity and toughness, low friction coefficient (including self lubrication), high resistance to abrasion and fatigue, supreme chemical resistance (including fire retardancy), as well as excellent thermal and electrical performance. 

In some cases the incorporation of a fire retardant can affect mechanical, electrical and thermal properties of polymers. 

In general, when compared with the conventional polymer composites, polymer nanocomposites exhibit significant improvements in different properties at relatively much lower concentration of filler. The efficiency of various additives in polymer composites can be increased manyfold when dispersed in the nanoscale. This becomes more noteworthy when the additive is used to address any specific property of the final composite such as mechanical properties, conductivity, fire retardancy, thermal stability, etc. In case of polyolefin/LDH nanocomposites, similar improvements are also observed in many occasions. For example, the thermal properties of PE/LDH showed that even a small amount of LDH improves the thermal stability and onset decomposition temperature in comparison with the unfilled PE [22] its mechanical properties revealed increasing LDH concentration brought about steady increase in modulus and also a sharp decrease in the elongation at break [25]. While in this section, fire-retardant properties and electric properties of polyolefin/LDH nanocomposite were described in detail. 

Many workers have used PyMS to study the structures of polymers, both natural and artificial. Understanding the performance of polymers in terms of cohesion and substrate adhesion is of immense commercial significance in the paint and adhesive industries. Similarly, the behavior of polymers under stress and when exposed to external factors such as ultraviolet light has been extensively studied by PyMS and is useful in the development of novel materials that have desirable properties, e.g., fire-retardant coatings and biodegradable fibers. There is much interest in polyhydroxyalkanoates as potentially biodegradable plastics, and PyMS has been a principal method used to study thermal degradation profiles of this material. Similarly, in forensic science, PyMS has been used to analyze fibers and to help match samples of automotive finishes to paint chips found at crime scenes. 

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. 

Fyrolflex BDP from Akzo Nobel Chemicals has been shown to exhibit higher thermal properties and hydrolytic stability than other aryl phosphates, and to provide similar or better fire retardant performance than RDP. It is a bisphenol A bis(diphenyl phosphate) compound that provides good physical properties in formulations based on PC/ABS, HIPS and polyphenylene oxide/HIPS blends. Upon thermal decomposition of the flame-retarded polymers, phosphorus tends to accumulate in the solid residue, a result which indicates that the primary FR action of BDP is most likely to be in the condensed phase. 

It has been observed from the above discussion that mechanical, physico-chemical and fire retardancy properties of UPE matrix increases considerably on reinforcement with surface-modified natural cellulosic fibers. The benzoylated fibers-reinforced composite materials have been found to have the best mechanical and physico-chemical properties, followed by mercerized and raw Grewia optiva fibers-reinforced composites. From the above data it is also clear that polymer composites reinforced with 30% fibers loading showed the best mechanical properties. Further, benzoylated fibers-reinforced composites were also found to have better fire retardancy properties than mercerized and raw fibers-reinforced polymer composites. Fire retardancy behavior of raw and surface-modified Grewia optiva/GPE composites have been found to increase when fire retardants were used in combination with fibers. This increase in fire retardancy behavior of resulted composites was attributed to the higher thermal stability of magnesium hydroxide/zinc borate. 

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