Int. J. Adv. Sci. Eng. Vol. 2 No.3 155-158 (2016) 155 ISSN 2349 5359 Usha Sayed et. al International Journal of Advanced Science and Engineering www.mahendrapublications.com ABSTRACT: Flame retardant materials are materials that inhibit combustion thereby preventing the spread of fire. They are extensively used in fire fighting equipment, apparels worn by armed forces,security personnel and in places where there is a huge risk of explosions. Limiting oxygen index (LOI) of a material is the measure of its flame retardancy. Oxidised PAN fibre with a LOI between 45 and 55 acts as an excellent flame retardant material. The manufacturing process, properties and applications of oxidised PAN fibre are reviewed in this paper. Keywords: Flame Retardant Materials, Limiting Oxygen Index, Oxidised PAN Fibre. © 2016 mahendrapublications.com, All rights reserved *Corresponding Author: ushatxt@gmail.com Received: 20.12.2015 Accepted: 02.02.2016 Published on: 25.02.2016 Oxidised polyacrylonitrile fibre as a flame retardant material Usha Sayed*, Harshit Jain, Sairohit Raghupathy Department of Fibres and Textile Processing Technology, Institute of Chemical Technology, Nathalal Parekh Marg, Matunga, Mumbai-400019, India INTRODUCTION PAN fibre is oxidised by regulated low temperature heating in the range of 200 0 -300 0 C in air to convert it to a form that can withstand high temperatures without melting or fusion of fibres. In order to accomplish this aim, a slow and gradual heating rate must be used to avoid run-away exotherms which occur during the oxidation process. Moreover PAN fibre is a poor conductor of heat which makes a regulated heating rate all the more vital. There are three methods for oxidising PAN fibre. In the first method, oxidation of PAN fibre can be achieved isothermally by heating at a constant temperature. The second method involves a stepwise increase in temperature. This is a more practical method and is widely followed in the industry. The third method involves oxidation in a single step where temperature increases along a tubular furnace. Figure 1:- Change in Enthalpy v/s Oxidation Time In the oxidation stage, the PAN fibre density increases from 1.18 g/cc to 1.36-1.38 g/cc. The actual density will depend on whether it is used as an oxidised PAN fibre or is required for further processing to carbon fibre. The final density of the product will depend upon the specification of the oxidised PAN fibre. After heating the PAN fibre in air at 230 degree celsius for 3 hours, about 35% of the exothermic heat remains in the oxidised PAN fibre. Tension was measured when PAN fibre was heated in air at constant length and a temperature of 230 0 C was maintained. It was observed that the fibre developed a rapid initial tension. It was attributed to the entropic recovery of the drawn and quenched fibre. This tension reached the peak as the temperature approached Tg (140 0 -150 0 C). This was followed by relaxation of the stress down to about the initial stress, followed by a slow increment of stress. This underscores the importance of tension control during the heating process in the oxidation ovens. This tension control helps to prevent adjacent passes touching each other as the fibre expands or avoid breakage of fibres if the tension is applied in excess. Figure 2:- Shrinkage Force v/s Temperature More the density of the oxidized PAN fibre , more will be itǯs limiting oxygen index. More the limiting oxygen index more will be the flame retardancy of the material. Advanced oxidation methods could produce oxidised PAN fibres with higher density than the conventional oxidation methods, thus enhancing their flame retarding potential. One such method is based on non-thermal, atmospheric pressure plasma processing of PAN fibres. In this method PAN fibres are subjected to an oxidation process in which reactive oxidizing species are maintained in close enough proximity to the PAN fibres during the oxidation process such that core of the PAN fibre is converted to a crosslinked thermoset morphology before an oxidized shell of the PAN fibre becomes thick enough to substantially inhibit penetration of the reactive oxidizing