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The effects of exposing to ultrasound compounded melts of polypropylene (PP) and polyamide 6 (PA6) formulations comprising nanoclays both alone and in the presence of other flame retardants are explored in terms of their improved dispersion, their consequent ability to be extruded into filaments and their burning behaviour. Clays used were Nanomer 1.3T in PP and this and Cloisite 25A in PA6. Flame retardants selected were ammonium polyphosphate (in PP) and aluminium phosphinate (in PA6) present at the low concentration of 5 wt%.
50 and 100 W 30 kHz ultrasonic probes were fitted to the end of the compounder barrel and compounded formulations were collected as strands which were pelletised and then separately extruded into filaments. Compounded extrudates, filaments and fabrics were assessed morphologically by optical microscopy, SEM-EDS and TEM. Thermal stability and flammability were undertaken by thermal analysis and limiting oxygen index and for fabrics, vertical strip testing.
Clear evidence of improved dispersion after ultrasound treatment has been shown using image processing software of SEM-EDS data for PP samples and increased intercalation in PP and exfoliation of clays in both PP and PA6 demonstrated by TEM. Increased ease of extrusion into filaments was also noted. For PP formulations, ultrasonification reduced fabric burning rates and drip formation. In PA6, the only positive effects were seen for the PA6/Cloisite 25A/aluminium phosphinate formulation which showed some evidence of synergy and ultrasound increased the LOI of polymer strands from 21.1 to 23.3 vol%. Fabric burning behaviour was more mixed with no clear cut advantages of ultrasound being apparent for PA6.
DOI: https://www.sciencedirect.com/science/article/pii/S0141391012002625?via%3Dihub |
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