Filtern
Dokumenttyp
Sprache
- Englisch (5)
Referierte Publikation
- ja (5)
Schlagworte
- Organoclay (5) (entfernen)
Low amounts (<7.5 wt%) of organically modified layered silicate (LS) as well as large amounts (>10 wt%) of spherical amorphous SiO2 (sSiO2) has been used successfully as adjuvants in commercial polymeric materials flame retarded with metal hydroxide. The combination of LS and SiO2 is investigated in different thermoplastics with respect to their fire behavior, particular to overcome the restrictions in maximum and minimum filler contents know for the single additives. The aim was to check the potential of combinations of the inert fillers in absence of a real fire retardant. The combination of LS and sSiO2 harbors the potential for flame retardancy effects close to superposition or even synergy, due to an improved structure of the fire residue. LS-sSiO2 combinations are proposed to work as adjuvants superior to LS and sSiO2 in flame retarded polymeric materials.
The pyrolysis and flammability of phosphonium-modified layered silicate epoxy resin nanocomposites (EP/LS) were evaluated when LS was combined with two flame retardants, melamine borate (MB) and ammonium polyphosphate (APP), that also act via a surface protection layer. Thermogravimetry (TG), TG coupled with Fourier Transform Spectroscopy (TG-FTIR), oxygen index (LOI), UL 94 burning chamber (UL 94) and cone calorimeter were used. The glassy coating because of 10 wt % MB during combustion showed effects in the cone calorimeter test similar to nanodispersed LS, and somewhat better flame retardancy in flammability tests, such as LOI and UL 94. Adding APP to EP resulted in intumescent systems. The fire retardancy was particularly convincing when 15 wt % APP was used, especially for low external heat flux, and thus, also in flammability tests like LOI and UL 94. V0 classification is achieved when 15 wt % APP is used in EP. The flame retardancy efficiency of the protection layers formed does not increase linearly with the MB and APP concentrations used. The combination of LS with MB or APP shows antagonism; thus the performance of the combination of LS with MB or APP, respectively, was disappointing. No optimization of the carbonaceous-inorganic surface layer occurred for LS-MB. Combining LS with APP inhibited the intumescence, most probably through an increase in viscosity clearly above the value needed for intumescent behavior.
Barrier formation and increasing the melt viscosity are addressed as the two main general fire retardancy mechanisms of polymer nanocomposites. They result in specific impacts on fire properties that consequentially cause varying flame retardancy efficiency in different fire tests. The barrier formation retards mainly flame spread (peak of heat release rate) in developing fires, but does not reduce fire load (total heat evolved), ignitability or flammability (limiting oxygen index, UL 94). Furthermore, this flame retardancy effect increases with increasing irradiation and vanishes with decreasing irradiation. The increased melt viscosity prevents dripping, which is beneficial or disadvantageous depending on the fire test used. In some test, it become the dominant influence, transforming self-extinguishing samples into flammable materials or causing wicking. Advantages and the limits are sketched comprehensively for exploiting the main general fire retardancy mechanisms of polymer nanocomposites. It is concluded that barrier formation and changing the melt viscosity in nanocomposites are not sufficient for most applications, but must be accompanied by additional mechanisms in special systems or in combination with other flame retardants.
Phosphonium-modified layered silicate epoxy resin nanocomposites were evaluated by testing the thermal/thermo-mechanical properties [differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), torsional pendulum, Sharpy toughness], flammability (limiting oxygen index LOI) and fire behavior (cone calorimeter with different irradiations). The morphology of the composites was determined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The drying conditions of phosphonium-modified layered silicate were varied in order to improve the nanocomposite formation and properties. The results were compared with using a commercial ammonium-modified montmorillonite. Enhanced nanocomposite formation was found for the commercial systems due to the amount of excess surfactant, but this effect was overcompensated through the advanced morphology of the phosphonium-modified systems. Several fire retardancy mechanisms and their specific influence on the different fire properties, such as ignitability, flammability, flame spread, total heat release (fire load), and the production of CO and smoke were discussed comprehensively. The main mechanism of layered silicate is a barrier formation influencing the flame spread in developing fires. Several minor mechanisms are significant, but important fire properties such as flammability or fire load are hardly influenced. Hence combinations with aluminum hydroxide and organo-phosphorus flame retardants were evaluated. The combination with aluminum hydroxide was a promising approach since it shows superposition in properties such as the fire load and only in some properties very little antagonism. The combination with an organo-phosphorus flame retardant disillusions, since it was characterized mainly by antagonism.
Polymeric nanocomposites are discussed as one of the most promising advanced materials whose nanoscale effects can be exploited for industry. Layered silicate polypropylene-graft-maleic anhydride nanocomposites are investigated as a model to clarify the potential of such materials in terms of fire retardancy. The nanostructure is characterized using transmission electron microscopy (TEM) and shear viscosity. The fire behavior is characterized using different external heat fluxes in cone calorimeter, limiting oxygen index and UL 94 classification. A comprehensive fire behavior characterization is presented which enables an assessment of the materials’ potential with respect to different fire scenarios and fire tests. The influence of morphology and the active mechanisms are discussed, such as barrier formation and changed melt viscosity. To our knowledge, it is the first attempt to illuminate the concept’s strengths, such as the reduction of flame spread, and weaknesses, such as the lack of influence on ignitability, in a clear, comprehensive and detailed manner.