Novel organophosphorus flame retardants and their synergistic application in novolac epoxy resin. (December 2018)

• Record Type: Journal Article
• Authors: Schmidt, Christian; Ciesielski, Michael; Greiner, Lara; Döring, Manfred
• Is Part Of: Polymer degradation and stability. Volume 158(2018)
• Page Start: 190
• Page End: 201
• Publication Date: 2018-12
• Subjects: Flame retardant -- Epoxy resin -- 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) -- Glass transition temperature; Polymers -- Deterioration -- Periodicals; Stabilizing agents -- Periodicals; Polymères -- Dégradation -- Périodiques; Stabilisants -- Périodiques; 668.9
• DOI: 10.1016/j.polymdegradstab.2018.09.001
• Languages: English
• ISSNs: 0141-3910

Abstract

Abstract: The novel oligomeric organophosphorus compounds oligo[DOPAc-2-TAEI] (oDOPI), oligo[DOPAc-1-DMPAc-1-TAEI] (oDOMPI) and oligo[DMPAc-2-TAEI) (oDMPI) were prepared in a one-pot process. At first, a Phospha-Michael-addition of 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and/or dimethylphosphite (DMP) to tris(acryloyloxy)ethyl isocyanurate (TAEI) was carried out using a ratio that approximately one third of the acrylate groups remained, which were subsequently polymerized. The novel FR's as well as two commercially available flame retardants (FR's), a phosphazene (PZ) and a phosphorus-containing oligomeric compound with aromatic OH-groups, were incorporated into the epoxy novolac resin system DEN438/DICY/Fenuron, with and without the synergists melamine polyphosphate (MPP) and boehmite (AlO(OH)). The influence on glass transition temperature (Tg ) was determined by differential scanning calorimetry (DSC) and the minimum phosphorus contents needed to pass the vertical burning test UL-94 with a V-0 classification was identified. The synergistic approach, especially the addition of MPP, led to a highly increased performance with the amount of needed organophosphorus FR being reduced significantly without any drop of Tg . Most promising systems were investigated by TGA and cone calorimetry and the residue after the cone measurements was observed by scanning electron microscopy (SEM). These investigations indicate that the superior flame-retardant properties are evoked by formation of dense char combined with gas-phase action of the organophosphorus compounds. Highlights: Novel oligomeric phosphorus- and nitrogen-containing flame retardants were successfully synthesized and tested in a novolac-based epoxy resin. One of the novel compounds achieved UL94 V0 rating already at a phosphorus content of 1 wt% in the epoxy resin. Synergistic combinations of the novel compounds with melamine polyphosphate (MPP) showed superior flame retardant efficiency (V0 rating with 2.8 wt% organophosphorus compound and 15 wt% MPP). The synergistic flame retardant systems did not cause any deterioration of the glass transition temperature of the epoxy resin. The superior flame retardant properties are evoked by the formation of dense char combined with gas-phase action.