FLAME RETARDED POLYMERS AND COATINGS: EXPERIMENTAL DEVELOPMENT AND THEORETICAL MODELLING

It is well known that both polypropylene (PP) and wood, which is generally coated to protect it from environmental factors (moisture, UV radiation, etc) are extensively used in many applications. Both materials are flammable but a performing fire reaction is needed to safely use them in practical application; thus, the main aim of this work is to improve the flame retardancy of both PP and wood coatings. In particular a transparent and high-performing FR-coating as well as a sustainable FR-PP have to be developed. For both systems, the use of halogen flame retardants (FRs) have been avoided, while for PP also the use of phosphorus-based FRs, which are obtained from phosphate rocks, that are critical raw materials within Europe, has been disregarded. To achieve both these goals, the experimental development has been assisted by statistical methods (Design of Experiment, DoE), to show that this approach can always be helpful in avoiding time-consuming experiments. In particular, the models developed for coatings consider not only fire reaction but also coating transparency. The models proposed for PP are able to predict both “non-dripping” as well as “non-flaming dripping” behaviour during the UL94 test; the latter behaviour, never modelled in the literature before, has been predicted thanks to a new parameter proposed in this work, i.e. the “V0 probability”. The models proposed for PP allow the optimisation of the formulations in terms of fire reaction, lowest phosphorus and total filler content. The optimised formulations identified by the use of the predictive models for both coating and PP have been produced and experimentally tested to validate the reliability of the models proposed. Furthermore, through the use of the models, several interactions, in particular synergies, among the different FRs used have been suggested. These synergies have been experimentally proved by several techniques (TGA, TGA-FTIR, FTIR, SEM, dripping behaviour, rheology), thus assessing that these models are useful also to give insight into the interactions between flame retardants, before studying the FRs system in details. It has been also shown that it is thanks to these synergies that very good fire reaction can be achieved for both PP and coating formulations, since a single FR alone, whatever it was, was not enough to reach this very good fire reaction. Finally, it is also noteworthy to mention that, although the models developed in this work are suitable for the particular systems considered, this research has shown, in general, the usefulness of this statistical methodology to shorten the development time of new formulations.