Abstract. The combustion behavior of a blend made of high impact polystyrene (HIPS) with sodium montmorillonite (MMT-Na + ) and triphenyl phosphite (TPP), as a halogen-free flame retardant, is analyzed in detail in this work. The blend is processed through various extrusion methods aimed to improve clay dispersion. The UL94 method in vertical position, oxygen index and cone calorimetric measurements assess HIPS blend behavior in combustion. TGA, FTIR, SEM and X-ray measurements, together with mechanical and rheological tests evaluate the thermal degradation, morphology, intercalation and degree of dispersion of particles. The use of a static-mixing die placed at the extreme of a single screw extruder improves clay platelets distribution and reduces the peak heat release rate better than employing a twin screw extrusion process. In addition, mechanical and rheological properties are affected substantially by changing the extrusion process. A correlation between clay dispersion and HIPS fire retardant properties is found, as the peak heat release rate decreases with good clay dispersion in cone calorimetric tests.
Natural keratin fibres derived from Mexican tannery waste and coconut fibres from coconut processing waste were used as fillers in commercially available, biodegradable thermoplastic starch-polyester blend to obtain sustainable biocomposites. The morphology, rheological and mechanical properties as well as pyrolysis, flammability and forced flaming combustion behaviour of those biocomposites were investigated. In order to open up new application areas for these kinds of biocomposites, ammonium polyphosphate (APP) was added as a flame retardant. Extensive flammability and cone calorimeter studies revealed a good flame retardance effect with natural fibres alone and improved effectiveness with the addition of APP. In fact, it was shown that replacing 20 of 30 wt. % of APP with keratin fibres achieved the same effectiveness. In the case of coconut fibres, a synergistic effect led to an even lower heat release rate and total heat evolved due to reinforced char residue. This was confirmed via scanning electron microscopy of the char structure. All in all, these results constitute a good approach towards sustainable and biodegradable fibre reinforced biocomposites with improved flame retardant properties.
A set of emulsions containing sodium polyacrylate as emulsifier was prepared. The effect of pH, temperature, and polymer concentration on sample stability was studied. Stability of the sample was evaluated through rheology and the morphology techniques. The sample containing 2% (w/w) sodium polyacrylate exhibited more evident changes in storage G′ and loss G″ moduli with respect to 1% and 1.5% (w/w) samples, evidencing a more structured elastic material, even at high temperatures at which a more stable sample is assumed. For most of the systems studied, the storage modulus (G′) was always higher than the loss modulus (G″) which is attributed to the formation of a strong network arising from the polymer interacting with the oil and aqueous phases; the complexity of this network is related to the action of pH and temperature. These results reveal the conditions at which the polyacrylate offers the best advantages in industrial cosmetic applications, that is, pH levels near 6.5, with a 2% (w/w) polymer concentration and a temperature of 25°C.
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