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105 Flame Retardant Natural Rubber Formulations

Wednesday, October 14, 2009: 4:15 PM
329 (David L. Lawrence Convention Center )
Marina S. D. Fernando , Tun Abdul Razak Research Centre, Hertford SG 13 8NL, United Kingdom
Colin D. Hull , Tun Abdul Razak Research Centre, Hertford SG 13 8NL, United Kingdom
Jonathan L Clark , Tun Abdul Razak Research Centre, Hertford SG 13 8NL, United Kingdom
To ensure structural integrity and human safety, specialist fire resistant and smokeless rubber formulations are needed in industry. Legislation concerning materials of construction exists in many countries to safeguard the public. In the rubber industry, it is customary to use halogenated elastomers or halogenated addtives in non halogenated elastomers to achieve the required level of fire resistance. However, halogenated rubber compounds produce smoke and toxic fumes and therefore the current trend is to develop 'halogen free' fire retardant elastomer compounds.

In this work, a methodology is developed to assess the fire resistance of isoprene based halogenated compounds as a precursor to a study on 'non halogenated' systems . It is generally known that the addittion of large amounts of inorganic fillers to achieve an acceptable level of fire retardancy has a detrimental effect on the strength properties of a rubber vulcanizate. During some preliminary investigations, it became apparent that epoxidised natural rubber;ENR (Ekoprena) had better fire resistance than other isoprene rubbers, such as SMR CV, deproteinised natural rubber(DPNR) and synthetic polyisoprene(SKI3 and Nipol 2200). Thus a base formulation consisting of epoxidised natural rubber was used to investigate the effect of four key ingredients on fire retardancy. A four factorial experimental design was used to measure the time to initiate a flame. The  tensile strength of the vulcanizates were also measured. The measured properties were optimised using desirability functions. The optimised formulation was used as a basis for a comparative investigation on other NR variants. The decomposition kinetcs were also measured using thermogravimetric analyses(TGA) and a modified TGA-FTIR approach. The TGA measurements confirmed the superior fire resistance of ENR. The processability of the optimised formulations were also measured.

The work has demonstrated the usefulness of a designed experiment approach to assessing fire retardancy and the extent to which inert fillers can be reduced to achieve sufficient flame resistance. The flame resistant behaviour of ENR has been demonstrated and has provided a basis for the extension of this work into ENR based halogen free systems. During this investigation no attempt has been made to characterise the smoke density, heat release rate and smoke toxicity. Nevertheless, the work highlights the interaction of commercial fire retardant additives in providing safe rubber compounds for use in industrial applications.