Flame Retardant Siloxane Polymers Produced by Eco-Friendly Synthetic Methods

There is a tremendous interest in the area of flame-retardant (FR) materials due to their numerous applications in clothing, construction, aviation and telecommunications.  Current flame retardant (FR) materials on the market are based on halogenated polymers and additives that are either classified as harmful/toxic or give off such products upon combustion.  While these materials have offered cost-effective solutions for FR applications, there is now an increased global emphasis on discontinuing the use of these materials and replacing them with environmentally and human safe alternatives.  Thus, there exists the need to develop a new generation of environmentally-safe, economical polymeric FR materials with efficient FR performance.  Our work centers on the creation of novel polysiloxane copolymers (PS) by incorporating additives (e.g. boron, organoclays and fillers) through a facile, environmentally benign, solvent-free synthetic approach.  It is well-known in the literature that boron is inherently thermally stable, environmentally safe and has extreme durability to air oxidation.  Furthermore, boroxo silanol derivatives, used as ceramic precursors, exhibit efficient FR properties.¹     We have synthesized boron containing polysiloxane copolymers (polyborosiloxanes - PBS) without the use of solvents.  Several different terpolymers, consisting of a boronic acid (PBA) and an aromatic dianhydride (Oxy or DAH) at various PBA/dianhydride molar feed ratios, have also been synthesized.  PBS terpolymers have exhibited efficient flame and thermal properties with a decomposition temperature (T_d) of 400-430ºC and a heat release capacity (HRC) of 170-250 J/g-K.  Concurrently, PS-organoclay nanocomposites have been synthesized.  When polymers are combined with small amounts of organoclays, they can exhibit improved thermal, mechanical and FR properties.²  Here, polysiloxane copolymers containing Oxy or DAH have been blended with three different organoclays and two different fillers.  PS-organoclay nanocomposites exhibit a T_d of 400ºC and an HRC of 160-200 J/g-K.  A synergistic approach is being employed to determine if further enhancement of the FR properties can be achieved by creating PBS terpolymer organoclay nanocomposites.  PS-filler blends created to determine the influence of fillers such as cellulose and chitosan on thermal and flame retardant properties will also be discussed.  The eco-friendly synthesis of PS-based nanocomposites and blends and resulting flame retardant and thermal properties represent an opportunity for a new generation of environmentally and human safe FR polymers for military and civilian applications.

 [1] (a) Armitage, P.; Ebdon, P.R.; Hunt, B.J.; Jones M.S.; Thorpet, F.G. Polymer Degradation and Stability, 1996, 54, 387. (b) Martín, C.; Ronda, J.C.; Cádiz, V. PolymerDegradation and Stability, 2006, 91, 747.

[2] A.B. Morgan and C.A.Wilkie, (Eds.) Flame Retardant Polymer Nanocomposites, Wiley-Interscience, New York, 2007.