Organosilicon surface layer on polyolefins to achieve improved flame retardancy through an oxygen barrier effect

A model system consisting of a polyethylene substrate surface treated by vinyltriethoxysilane and by organoboroxo-siloxane (OBSi), and an OBSi-containing intumescent flame-retarded compound (IFR-OBSi) based on polypropylene, ammonium polyphosphate and pentaerythritol were prepared and investigated. After a radio-frequency plasma treatment of the model system its oxygen permeability decreased by about one order of magnitude. According to XPS studies, enrichment of Si took place on the surface of the untreated IFR-OBSi, while after its ignition in a cone calorimeter surface enrichments of N and P were also detected. According to the evolution of the Si 2p peaks, creation of glass-like surface coatings took place on both the model system upon its RF plasma treatment and on IFR-OBSi upon its flame treatment. A small portion of OBSi remained unreacted in the surface layer of the flame-treated IFR-OBSi, which may ensure the plasticity necessary to prevent it from cracking and to ensure improved flame retardancy. (C) 2001 Elsevier Science Ltd. All rights reserved.