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Polyesters with DOPO substituents can be successfully synthesized with 10-[2,5-Bis(2-hydroxyethoxy)phenyl]-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide(DOPO-HQ-glycolether) and DOPO-substituted dimethyl succinate (PIta). These polyester materials show an effective flame retardancy which can be fine-tuned by the chemical structure of the polyester backbone.
A rigid aromatic phosphorus-containing hyperbranched flame retardant structure is synthesized from 10-(2,5 dihydroxyphenyl)-10H-9-oxa-
10-phosphaphenanthrene-10-oxide (DOPO-HQ), tris(4-hydroxyphenyl)phosphine oxide (THPPO), and 1,4-terephthaloyl chloride (TPC). The resulting poly-(DOPO-HQ/THPPO-terephthalate) (PDTT) is implemented as a flame retardant into an epoxy resin (EP) at a 10 wt% loading. The effects on EP are compared with those of the monomer DOPO-HQ and triphenylphosphine oxide (OPPh3) as low molar mass flame retardants. The glass transition temperature, thermal decomposition, flammability (reaction to small flame), and burning behavior of the thermosets are investigated using differential scanning calorimetry, thermogravimetric analysis, pyrolysis combustion flow calorimetry, UL 94-burning chamber testing, and cone calorimeter measurements.
Although P-contents are low at only 0.6 wt%, the study aims not at attaining V-0, but at presenting a proof of principle: Epoxy resinswith PDTT show promising fire performance, exhibiting a 25% reduction in total heat evolved (THE), a 30% reduction in peak heat release rate (PHRR) due to flame inhibition (21% reduction in effective heat of combustion (EHC)), and an increase in Tg at the same time. This study indicates that rigid aromatic hyperbranched polymeric structures offer a promising route toward multifunctional flame retardancy.
Polyesters with 9,10-dihydro-9-oxy-10-phosphaphenanthrene-10-oxide-containing comonomers are synthesized aiming to improve the flame retardancy of aliphatic polyesters such as poly(butylene succinate) and poly(butylene sebacate). The influence of the chemical structure on the thermal decomposition and pyrolysis is examined using a combination of thermogravimetric analysis (TGA), TGA-Fourier transform infrared (FTIR) spectroscopy, pyrolysis-gas chromatography/mass spectrometry, and microscale combustion flow calorimetry. Thermal decomposition pathways are derived and used to select suitable candidates as flame retardants for PBS. The fire behavior of the selected polymers is evaluated by forced-flaming combustion in a cone calorimeter. The materials show two modes of action for flame retardancy: strong flame inhibition due to the release of a variety of molecules combined with charring in the solid state.
A siloxane compound (MVC) and a bi-group phosphaphenanthrene/triazine compound (TGD) were employed in epoxy thermosets to explore high-efficiency flame retardant systems. With only 1wt% MVC and 3wt% TGD, an epoxy thermoset passed UL 94 V-0 rating test and achieved a limiting oxygen index value of 34.0%, exhibiting an excellent flame retardant effect. The MVC/TGD system not only decreased the peak value of heat release rate and effective heat of combustion but also imparted an improved charring ability to thermosets, thereby outstandingly reducing the flammability of 1%MVC/3%TGD/EP. Compared with the fire performance of 4%TGD/EP and 4%MVC/EP, the MVC/TGD system showed an obvious flame retardant synergistic effect, mainly depending on the general improvement of flame inhibition, charring and barrier effects of the thermoset during combustion. Evolved gas analysis combinedwith condensed-phase pyrolysis product Analysis jointly revealed the details of the changed pyrolysis mode.
Increasing waste of the natural environment with plastic waste with extremely long lifetime requires more and more the application of plastic materials with a certain degradability, but comparable property profile. One of the possible alternatives for the standard polyesters PET and PBT is offered by poly(butylene succinate) (PBS), an aliphatic and therefore degradable polyester with comparable mechanical properties but lower heat deflection temperature which has already been introduced into the market. However, aliphatic polyesters are easily combustible with high heat release capacities and require flame retardant additives.
Phosphorus-containing polyesters with DOPO (6H Dibenz[c,e][1,2]oxaphosphorin 6-oxide)containing comonomers with stepwise varied structure consisting of (at least partially) biobased monomers were synthesized and their properties evaluated with respect to their suitability as flame retardant in PBS. Efforts to increase the phosphorus content yielded a polyester with two DOPO substituents per repeating unit. P(P-ItaP) showed an enhanced gas phase activity and released a number of DOPO-compounds into the gas phase as found by TGA-FTIR and pyrolysis GC/MS measurements. The char formation is only moderate.
Two DOPO-polyesters (P(P-ItaP) with increased gas phase activity, and PET-P-DOPO known from former work to show a combination of solid phase and gas phase activity with intumescence were employed as FR additive in PBS. The blends of PBS with the DOPO-polyesters were prepared by melt compounding in a twin screw extruder and analyzed with different methods. The thermodynamic immiscibility caused demixed morphologies with a reduction in impact strength and a high tendency of dripping upon burning. Forced flame investigations in the cone calorimeter showed, however, the potential as flame retardant in particular for the itaconyl-based polyester.
A phosphaphenanthrene and triazinetrione group containing flame retardant (TAD) is combined with organically modified montmorillonite (OMMT) in epoxy resin thermosets (EP) to improve the performance of the flame-retardant system. When only 1 wt% OMMT/4 wt% TAD is introduced into the EP, the limited oxygen index (LOI) rises from 26% to 36.9% and a V-0 rating is achieved in a UL 94 test. The decomposition and pyrolysis products in the gas phase and condensed phase were characterized using thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR). The influence on the decomposition of EP, such as the increase in char yield, is limited with the incorporation of OMMT; a large amount of the phosphorus is released into the gas phase. The flame-retardant effect evaluation based on cone calorimeter data testified that OMMT improves the protective-barrier effect of the fire residue of OMMT/TAD/EP on the macroscopic scale, while TAD mainly causes flame inhibition. The fire residues showed a corresponding macroscopic appearance (digital photo) and microstructure (scanning electron microscope [SEM] results). The protective barrier effect of OMMT and the flame-inhibition effect of TAD combined to exert a superior flame-retardant effect, resulting in sufficient flame-retardant performance of OMMT/TAD/EP
PET-P-DOPO is a phosphorus-containing polyester prepared from the glycol ether of the hydroquinone derivative of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and dimethyl terephthalate. PET-P-DOPO and a blend of PBT with PET-PDOPO were investigated with respect to pyrolysis and fire behavior. PET-P-DOPO achieves a V-0 rating in the UL 94 test and exhibits a high LOI of 39.3%. The outstanding flame-retardant properties of PET-P-DOPO are the result of three different mechanisms (flame inhibition, charring and a protection effect of the intumescent char) that are active in PET-P-DOPO. The fire load and the peak of heat release rate (pHRR) are reduced to 34% and 17%, respectively. The char exhibits an intumescent multicellular structure enabling it to act as an efficient protection layer. As PET-P-DOPO is immiscible with PBT, the blend shows a lower breaking elongation than pure PBT. Compared to pure PET-P-DOPO, the flame retardancy of the blend is decreased according to the fraction of PET-P-DOPO used. Nevertheless, the flame-retardancy of PET-P-DOPO in the blend was good enough to compete with PBT flame-retarded by AlPi-Et (aluminum diethylphosphinate) that was used as a Benchmark.
Novel DOPO-based flame retardants in high-performance carbon fibre epoxy composites for aviation
(2011)
Two novel, halogen-free, phosphorus-based oligomeric flame retardants are investigated in the commercial epoxy resin RTM6 and ~70 wt.% carbon fibre RTM6 composites (RTM6-CF) with respect to pyrolysis and fire behaviour. The flame retardants are based on 9,10-dihydro-9-oxy-10-phosphaphenanthrene-10-oxide (DOPO) units linked to the star-shaped aliphatic ground body tetra-[(acryloyloxy)ethyl] pentarythrit (DOPP), or heterocyclic tris-[(acryloyloxy)ethyl] isocyanurate (DOPI), respectively. The glass transition temperature is reduced by adding DOPP and DOPI, but the mechanical properties of the composites (e.g. interlaminar shear strength (ILSS) and Gc in mode I and II) remain unchanged. Decomposition models are proposed based on mass loss, evolved gas analysis (TGFTIR) and condensed product analysis (hot stage cell within FTIR). The fire behaviour is investigated comprehensively (UL 94, limiting oxygen index (LOI) and cone calorimeter). Both flame retardants act in the gas phase through flame inhibition and in the condensed phase through charring. The UL 94 of RTM6 is improved from HB to V-1 and V-0; the LOI from 25% to 3438%. Peak heat release rate (PHRR) and total heat evolved (THE) are lowered by 31-49% and 4044%, respectively. Adding CF increases the residue, reduces the THE, but suppresses the charring due to RTM6 and flame retardants. Thus the THE of RTM6-CF is reduced by about 25% when DOPI and DOPP are added. However, UL 94: V-0 and LOI of 45% and 48% are achieved with ~0.6 wt.% phosphorus.