Fire Retardancy and Morphology of Nylon 6-clay Nanocomposite Compositions
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Fire Retardancy and Morphology of Nylon 6-clay Nanocomposite Compositions. Kadhiravan Shanmuganathan 1, Sandeep Razdan2, Nick Dembsey3 Qinguo Fan1, Yong K Kim1, Paul D Calvert1, Steven B Warner1 and Prabir K Patra1. 1. Department of Materials and Textiles, University of Massachusetts - Dartmouth, North Dartmouth, MA-02747. 2. Department of Material Science and Engineering, Rensselaer Polytechnic Institute, Troy, NY. 3. Dept of Fire Protection Engineering, Worcester Polytechnic Institute, MA-01609 ABSTRACT We investigated the effect of organically modified clay on the thermal and flammability behavior of nylon 6 nanocomposites. We also used zinc borate along with layered silicate with an aim of achieving synergistic effect in flame retardancy. It is found that addition of 10 wt% clay reduced the onset decomposition (5% wt loss) temperature of nylon 6 by 20ºC, while addition of 5 wt% zinc borate and 5 wt% clay in combination reduced it by around 10ºC. Differential thermogravimetric analysis indicated that the peak decomposition temperature was not affected by the addition of clay, but the rate of weight loss decreased with increasing clay concentration. The horizontal burning behavior of the nanocomposite films of approximately 0.5mm thickness changed with additive concentration. The nanocomposites with 2.5 wt% and 5 wt% clay burned for almost the same duration as neat nylon 6 but dripping was reduced. The 10 wt% clay nanocomposite sample burned without any dripping and the flame spread rate was reduced by 25-30%. The burn rate of 5 wt % zinc borate/5 wt% clay nanocomposite sample was about 20% higher than that of 10 wt% clay nanocomposite sample, which could be attributed to varying char morphology. Scanning electron microscopy images of the 10wt% clay nanocomposite char surface and cross- section revealed an integrated layer of clay platelets with increasing density gradient from the center to the surface, while the 5 wt% zinc borate/5 wt% clay nanocomposite char appeared foamy and porous. The 5 wt% zinc borate and 5 wt% clay sample developed into a very good intumescent system in cone calorimeter test, swelling about 10-13mm height prior to ignition forming a cellular char structure. This was as effective as the 10wt% clay nanocomposite sample in reducing the heat release and mass loss rate of nylon 6 by around 65%. Fourier transform infrared spectroscopy of the 10 wt% clay nanocomposite char showed the presence of amides, indicating possible residual polymer within the shielded char. INTRODUCTION Nanocomposites are a distinct class of composite materials showing impressive performance for multifunctional applications at a very low filler level of 2-5 wt%. They are defined by the particle size of the dispersed phase having at least one dimension less than 100 nm [1]. Polymerlayered silicate nanocomposites (PLSN) have been in the realm of research since 1961 [2] owing to their enhanced mechanical [3], thermal [4] and barrier properties [5] over conventional composites with micron size fillers. The enh
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