Novel phosphorus-modified polysulfone as a combined flame retardant and toughness modifier for epoxy resins |
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Authors: | RM Perez V Altstädt T Hoffmann M Ciesielski U Braun B Schartel |
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Affiliation: | a Polymer Engineering, University of Bayreuth, Universitätsstraße 30, D-95447 Bayreuth, Germany b Faculty of Macromolecular Chemistry, Department of Polymer Structures, Leibniz Institute of Polymer Research Dresden, Hohe Straße 6, D-01069 Dresden, Germany c Institute of Technical Chemistry, Research Center Karlsruhe GmbH, D-76021 Karlsruhe, Germany d Federal Institute for Material Research and Testing, Unter den Eichen 87, D-12205 Berlin, Germany |
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Abstract: | A novel phosphorus-modified polysulfone (P-PSu) was employed as a combined toughness modifier and a source of flame retardancy for a DGEBA/DDS thermosetting system. In comparison to the results of a commercially available polysulfone (PSu), commonly used as a toughness modifier, the chemorheological changes during curing measured by means of temperature-modulated DSC revealed an earlier occurrence of mobility restrictions in the P-PSu-modified epoxy. A higher viscosity and secondary epoxy-modifier reactions induced a sooner vitrification of the reacting mixture; effects that effectively prevented any phase separation and morphology development in the resulting material during cure. Thus, only about a 20% increase in fracture toughness was observed in the epoxy modified with 20 wt.% of P-PSu, cured under standard conditions at 180 °C for 2 h. Blends of the phosphorus-modified and the standard polysulfone (PSu) were also prepared in various mixing ratios and were used to modify the same thermosetting system. Again, no evidence for phase separation of the P-PSu was found in the epoxy modified with the P-PSu/PSu blends cured under the selected experimental conditions. The particular microstructures formed upon curing these novel materials are attributed to a separation of PSu from a miscible P-PSu-epoxy mixture. Nevertheless, the blends of P-PSu/PSu were found to be effective toughness/flame retardancy enhancers owing to the simultaneous microstructure development and polymer interpenetration. |
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Keywords: | Flame retardants Phosphorus-modified polysulfone Fracture toughness |
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