Claudia Fasel

In this study, the flame retardant effect of the Zn salt of 10-hydroxy-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (Zn-DOPOx), melamine polyphosphate (MPP) and their mixture was investigated towards the mode of action in glass fiber-reinforced polyamide 66 (PA 66 GF). The flammability was evaluated using UL 94 V and cone calorimetry. Influence on char formation was analyzed by SEM. Thermal decomposition of Zn-DOPOx and MPP was studied by TGA and ATR-FTIR. The release of gaseous PA 66 decomposition products was investigated using TGA-DTA-FTIR. Combining Zn-DOPOx and MPP leads to an improvement in flame retardancy, most pronounced for equal parts of weight. Mode of action changes significantly for Zn-DOPOx:MPP (1:1) compared to the sole components and a strong interaction between Zn-DOPOx and MPP is revealed, resulting in a more open char structure. Fuel dilution as well as less exothermic decomposition are essential for the mode of action of the combination. Through low HRR values and high CO/CO₂ ratio during cone calorimetry measurements, a significant increase in gas phase activity was proven. Therefore, it is concluded that Zn-DOPOx:MPP (1:1) leads to a significant increase in flame retardancy through a combination of mode of actions in the gas and condensed phase resulting from the change in thermal stability.

Of the three crystallographic allotropes of nanocrystalline titania (rutile, anatase and brookite), anatase exhibits the greatest potential for a variety of applications, especially in the area of catalysis and sensors. However, with rutile being thermodynamically the most stable phase, anatase tends to transform into rutile on heating to temperatures in the range of 500 °C to 700 °C. Efforts made to stabilize the anatase phase at higher temperatures by doping with metal oxides suffer from the problems of having a large amorphous content on synthesis as well as the formation of secondary impurity phases on doping. Recent studies have suggested that the as-synthesised phase composition, crystallite size, initial surface area and processing conditions greatly influence the anatase to rutile transformation temperature. In this study nanocrystalline titania was synthesised in the anatase form by a chemical vapour synthesis (CVS) method using titanium tetra iso-propoxide (TTIP) as a precursor under varying flow rates of oxygen and helium. The anatase to rutile transformation was studied using high temperature X-ray diffraction (HTXRD) and simultaneous thermogravimetric analysis (STA), followed by transmission electron microscopy (TEM). It was demonstrated that the anatase–rutile transformation temperatures were dependent on the oxygen to helium flow rate ratio during CVS and the results are presented and discussed.