Abstract
This work proposes a novel technique to address the detrimental effect of high loading of halogen-free flame retardants (FRs) on foaming of polymer composites. This is the first time nano-fibrillation is applied to tailor FR composites for foam applications with desired microcellular structure. As highlight of this work, the presence of polytetrafluoroethylene (PTFE) nanofibrils serves multiple roles by compensating for reduced foaming behavior of highly-filled matrix, and contributing to enhancing FR efficiency and stiffness. Inclusion of 1 wt% nanofibrils in polystyrene (PS) filled with 30 wt% expandable graphite (EG), tunned melt rheological properties leading to improving cell density up to two orders of magnitude. The average cell size of the foam also decreased from 103 μm to 10 μm, with respect to PS/EG, improving compressive strength and modulus. The entangled PTFE nanofibrils transformed the fluffy char layer into a dense one, preventing matrix disintegration and dripping to meet UL94-V0. This was confirmed by reduced fire growth rate (FIGRA), peak heat release rate (PHRR) and peak smoke production rate (PSPR) in cone calorimetry. The unique characteristics of this composite make it promising for fabricating FR polymeric foams for various applications including automotive, aerospace, electronics and construction, necessitating high fire safety level.
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