Development of a Novel Electrically Conductive Flame Retardant Bio-based Thermoplastic Polyurethane

The central topic of this thesis was the design and development of a bi-functional thermoplastic polyurethane (TPU) composite, which is halogen-free bio-based flame retardant (UL94-V0) with an electrical resistivity ≤ 1000 Ω.cm and a filler load that does not exceed 25 wt.%. In order to reach this goal, the experimental activities were divided into the following tasks: (a) materials pre-selection, (b) design of experiment (DOE), (c) materials compounding, (d) specimens preparation (injection moulding), and (e) materials characterization (electrical resistivity tests, flammability tests, and microstructure analysis). In other words, the main tasks were identifying the ingredients (in a first stage) and defining the optimal proportions of additives (in a second stage) capable of simultaneously conferring to the polymer of interest the most desirable values of flame retardancy (as high as possible) and electrical resistivity (as low as possible); followed by the material preparation (third stage) and the material characterization (forth stage). The materials (flame retardants and electrically conductive additives) used in the development of this novel formulation were pre-selected mainly based on bibliographical studies. Then, the experimental activities and the analysis of the test results allowed to identify positive and negative effects among the components of the formulation such as synergistic effects among flame retardants on the improvement of the fire resistant performance. The obtained final formulation accomplished the desired target values of flame retardancy (V0 compliant) and electrical resistivity (≤1000 Ω.cm). It was compared to commercial products from the companies RTP, BASF and LUBRIZOL, which are used in the same field of application. The material developed during this work showed a lower electrical resistivity than these commercially available products while being bio-based and V0 (UL-94 test) at the same time. In addition, an innovative online acquisition apparatus for monitoring the surface growth of flame retardant protective layers was designed and developed during this thesis, which provided a deep insight of the dynamic behaviour of a phosphorous-based flame retarded material. The measurement of the surface protective layer growth rate provided a better understanding of the behaviour of the flame retardant systems, correlating the speed of the chemical reaction with the performances of the material.