Efficient Flame Retardant Thin Films Synthesized by Atmospheric Pressure PECVD through the High Co-deposition Rate of Hexamethyldisiloxane and Triethylphosphate on Polycarbonate and Polyamide-6 Substrates

An innovative approach to produce high-performance and halogen-free flame-retardant thin films at atmospheric pressure is reported. PDMS-based coatings with embedded dopant-rich polyphosphates are elaborated thanks to a straightforward approach, using an atmospheric pressure dielectric barrier discharge (AP-DBD). Deposition conditions have been tailored to elaborate various thin films that can match the fire performance requirements. Morphology, chemical composition, and structure are investigated, and results show that the coatings performances are increased by taking advantage of the synergistic effect of P and Si flame retardant compounds. More specifically, this study relates the possibility to obtain flame retardant properties on PolyCarbonate and PolyAmide-6 thanks to their covering by a 5 μm thick coating, i.e. very thin films for this field of application, yet quite substantial for plasma processes. Hence, this approach enables deposition of flame retardant coatings onto different polymer substrates, providing a versatile fireproofing solution for different natures of polymer substrates. The presence of an expanded charred layer at the surface acts as a protective barrier limiting heat and mass transfer. This latter retains and consumes a part of the PC or PA-6 degradation byproducts and then minimizes the released flammable gases. It may also insulate the substrate from the flame and limit mass transfers of remaining volatile gases. Moreover, reactions in the condensed phase have also been highlighted despite the relatively thin thickness of the deposited layers. As a result of these phenomena, excellent performances are obtained, illustrated by a decrease of the peak of the heat release rate (pHRR) and an increase of the time to ignition (TTI).