Novel spirocyclic phosphazene-based epoxy resin for halogen-free fire resistance: synthesis, curing behaviors, and flammability characteristics

Study on flame retardancy of TGDDM epoxy resin blended with inherent flame-retardant epoxy ether

In this article, inherent flame-retardant epoxy ether, 9,10-dihydro-9-oxa-10-[1,1-bis(4-glycidyloxyphenyl)ethyl]-10-phosphaphenanthrene 10-oxide (DPBAEP), with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide moieties was synthesized via an economical method and was used to improve the flame retardancy of 4,4′-tetradiglycidyl diaminodiphenyl methane (TGDDM). A series of epoxy resins were prepared and cured with 4,4′-diaminodiphenyl sulfone. The glass transition temperatures ( Tg) of resin composites were above 243°C and decreased only slightly after DPBAEP was added. The thermal stabilities under the nitrogen (N2) and air atmosphere were also measured using thermogravimetric analysis. The results indicated that DPBAEP had a high decomposition temperature and affected the thermal degradation and promoted the charring of resins. When only over 5 wt% of DPBAEP was introduced, the thermosets obtained a high limiting oxygen index value of around 33.0%, achieved vertical burning V-0 rating and presented fast-swelling char barriers. In order to better understand the flame-retardant mechanisms, the residual char was investigated by scanning electron microscopy observation and Fourier transform infrared spectra. We inferred that the phosphorus (P) moieties reacted with the resin matrix, which played a significant role in promoting the formation of char with special structure, as well as making it rich and tough enough. This kind of char barrier could protect the underlying resin matrix against oxygen and heat transfer and inhibited volatile combustible from diffusing to the flame. Hence, thanks to the synergistic effect of P–N and the excellent compatibility, DPBAEP could impart excellent flame retardancy to TGDDM epoxy resin.

Highly transparent and flame-retardant epoxy composites based on a hybrid multi-element containing POSS derivative

Epoxy resin modified with ODMAS comprising a POSS core and sixteen DOPO groups possess high transparency, excellent flame retardant property and enhanced mechanical strength.

A novel DOPO-containing flame retardant for epoxy resin

A novel halogen-free flame retardant (6,6′-(((methylenebis(4,1-phenylene))bis(azanediyl))bis((4-hydroxy-3-methoxyphenyl)methylene))bis(6H-dibenzo[c,e][1,2]oxaphosphinine 6-oxide)(DP-DDM))) was synthesized via a one-pot procedure based on the Pudovik reaction between 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide and imine directly resulting from 3-methoxy-4-hydroxybenzaldehyde with 4,4′-methylenedianiline (DDM). The thermal curing behaviors of epoxy resins with different contents of DP-DDM were investigated by differential scanning calorimetry under a nonisothermal condition, aimed to suggest an optimized curing procedure in accordance with the property of DP-DDM. These DP-DDM-modified epoxy thermosets under optimized curing procedure showed high glass transition temperature and thermal degradation activation energy. Moreover, their high flame-retarding performance has been found: the epoxy thermosets with a relatively low addition amount of DP-DDM (on account of the phosphorus content of 0.75 wt%) can reach UL 94 V-0 (Instrumental analysis and measurements) rating with limiting oxygen index value of 34.5.

Flame–retarded epoxy resin with high glass transition temperature cured by DOPO-containing H-benzimidazole

A halogen-free flame retardant of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide-containing H-benzimidazole (DHBI) was synthesized and subsequently used as co-curing agent of 4,4′-diamino-diphenylmethane for diglycidyl ether of bisphenol-A. The structure of DHBI was characterized by Fourier transform infrared (FTIR) spectroscopy, proton, carbon 13 and phosphorus-31 nuclear magnetic resonance, and mass spectroscopy. A series of cured epoxy resins (EPs) were prepared and their flame retardancy, thermal stability, flexibility, and dielectric properties were investigated. The resulting cured EP (EP-10) with 7.45 wt% of DHBI successfully achieved UL 94 V-0 rate with limited oxygen index of 35.6% and without dropping phenomenon. Compared with the cured pristine EP (EP-00), the glass transition temperature of EP-10 was increased by 6.9°C, accompanied with an enhancement of flexible strength by 13.1 MPa and a decrement of dielectric constant by 0.3 at the testing frequency of 1 MHz.

Loading an organophosphorous flame retardant into halloysite nanotubes for modifying UV-curable epoxy resin

Novel flame-resistant UV-curable epoxy (EP) composites were prepared using the organophosphorous flame retardant dimethyl methylphosphonate (DMMP) which was loaded into halloysite nanotubes (HNTs).

Impact of halogen-free flame retardant with varied phosphorus chemical surrounding on the properties of diglycidyl ether of bisphenol-A type epoxy resin: synthesis, fire behaviour, flame-retardant mechanism and mechanical properties

This work aimed to investigate the effect of two types ofphosphorus-containing flame retardants (P-FRs) with different chemical surroundings on flame-retardant efficiency for diglycidyl ester of bisphenol-A type epoxy (EP).

Novel Multifunctional Organic-Inorganic Hybrid Curing Agent with High Flame-Retardant Efficiency for Epoxy Resin

A novel multifunctional organic-inorganic hybrid was designed and prepared based on ammonium polyphosphate (APP) by cation exchange with diethylenetriamine (DETA), abbreviated as DETA-APP. Then DETA-APP was used as flame-retardant curing agent for epoxy resin (EP). Curing behavior, including the curing kinetic parameters, was investigated by differential scanning calorimetry (DSC) and X-ray photoelectron spectroscopy (XPS). The flame retardance and burning behavior of DETA-APP cured EP were also evaluated. The limiting oxygen index (LOI) value of DETA-APP/EP was enhanced to 30.5% with only 15 wt % of DETA-APP incorporated; and the UL-94 V-0 rating could be easily passed through with only 10 wt % of the hybrid. Compared with DETA/EP, the peak-heat release rate (PHRR), total heat release (THR), total smoke production (TSP), and peak-smoke production release (SPR) of DETA-APP/EP (15 wt % addition), obtained from cone calorimetry, were dropped by 68.3, 79.3, 79.0, and 30.0%, respectively, suggesting excellent flame-retardant and smoke suppression efficiency. The flame-retardant mechanism of DETA-APP/EP has been investigated comprehensively. The results of all the aforementioned studies distinctly confirmed that DETA-APP was an effective flame-retardant curing agent for EP.

Permanent flame retardant finishing of textiles by allyl-functionalized polyphosphazenes

Despite their excellent flame retardant properties, polyphosphazenes are currently not used as flame retardant agents for textile finishing, because a permanent fixation on the substrate surface has failed so far. Here, we present the successful synthesis and characterization of a noncombustible and foam-forming polyphosphazene derivative, that can be immobilized durably on cotton and different cotton/polyester blended fabrics using photoinduced grafting reactions. The flame retardant properties are improved, a higher limiting oxygen index is found, and the modified textiles pass several standardized flammability tests. As flame retardant mechanism a synergistic effect between the immobilized polyphosphazene and the textile substrate was observed. The polyphosphazene finishing induces an earlier decomposition of the material with a reduced mass loss in thermogravimetric analysis. The decomposition of cotton and polyester leads to the formation of phosphorus oxynitride, which forms a protecting barrier layer on the fiber surface. In addition, the permanence of the flame retardant finishing was proven by laundry and abrasion tests.

Synthesis and Characterisation of Phosphazene Derivatives Containing Dioxybiphenyl and 4-Sulfanylquinazoline Groups

2,2-Dichloro-4,4,6,6-bis[spiro(2′,2″-dioxy-1′,1″-biphenylyl)]cyclotriphosphazene was synthesised from the reaction of hexachlorocyclotriphosphazene with biphenyl-2,2′-diol. 2,2-Bis(4-formylphenoxy)-4,4,6,6-bis[spiro(2′,2″-dioxy-1′,1″-biphenylyl)]cyclotriphosphazene was obtained from the reaction of 2,2-dichloro-4,4,6,6-bis[spiro(2′,2″-dioxy-1′,1″-biphenylyl)] cyclotriphosphazene with 4-hydroxybenzaldehyde. 2,2-Bis[4-(4-quinazolinone)phenoxy]-4,4,6,6-bis[spiro(2′,2″-dioxy-1′,1″-biphenylyl)]cyclotriphosphazene was synthesised from the reaction of 2,2-bis(4-formylphenoxy)-4,4,6,6-bis[spiro(2′,2″-dioxy-1′,1″-biphenylyl)]cyclotriphosphazene with anthranilamide in N,N-dimethylformamide. The novel cyclophosphazene derivatives were synthesised under mild conditions from the reaction of 2,2-bis[4-(4-quinazolinone)phenoxy]-4,4,6,6-bis[spiro(2′,2″-dioxy-1′,1″-biphenylyl)]cyclotriphosphazene with 4-chlorobenzenemethanethiol, p-thiocresol, 4-aminothiophenol, and 4-chlorothiophenol in the presence of p-toluenesulfonyl chloride via C-OH bond activation under mild conditions. All products were generally obtained in high yields. Their structures were characterised by HRMS, IR and 1H, 13C spectroscopy.

Interfacial carbonation for efficient flame retardance of glass fiber-reinforced polyamide 6

The interfacial carbonation mode is introduced to solve the high flammability of GF-reinforced polymer composites through interfacial char produced.

Intumescent flame retardancy of a DGEBA epoxy resin based on 5,10-dihydro-phenophosphazine-10-oxide

Only 2.5 wt% DPPA makes the epoxy resin achieve a V-0 rating in the UL-94 test due to the combination of intumescent charring and the blowing-out effect.

Multifunctional cyclotriphosphazene/hexagonal boron nitride hybrids and their flame retarding bismaleimide resins with high thermal conductivity and thermal stability

A novel hybridized multifunctional filler (CPBN), cyclotriphosphazene/hexagonal boron nitride (hBN) hybrid, was synthesized by chemically coating hBN with hexachlorocyclotriphosphazene and p-phenylenediamine, its structure was systemically characterized. Besides, CPBN was used to develop new flame retarding bismaleimide/o,o'-diallylbisphenol A (BD) resins with simultaneously high thermal conductivity and thermal stability. The nature of CPBN has a strong influence on the flame behavior of the composites. With the addition of only 5 wt % CPBN to BD resin, the thermal conductivity increases 2 times; meanwhile the flame retardancy of BD resin is remarkably increased, reflected by the increased limited oxygen index, much longer time to ignition, significantly reduced heat release rate. The thermogravimetric kinetics, structures of chars and pyrolysis gases, and cone calorimeter tests were investigated to reveal the unique flame retarding mechanism of CPBN/BD composites. CPBN provides multieffects on improving the flame retardancy, especially in forming a protective char layer, which means a more thermally stable and condensed barrier for heat and mass transfer, and thus protecting the resin from further combustion.

Effect of hexaphenoxycyclotriphosphazene combined with octapropylglycidylether polyhedral oligomeric silsesquioxane on thermal stability and flame retardancy of epoxy resin

A novel phosphazene-based compound called hexaphenoxycyclotriphosphazene (HPCTP) was synthesized and characterized by Fourier transform infrared spectroscopy as well as proton and phosphorus nuclear magnetic resonance spectroscopies. Epoxy (EP) resin composites containing HPCTP and octapropylglycidylether polyhedral oligomeric silsesquioxane (OGPOSS) were prepared using 4,4′-diamino diphenylmethane as curing agent. Differential scanning calorimetry, thermogravimetric analysis, UL 94 vertical burning test, and cone calorimetry test were used to assess thermal stability and flame retardancy of the composites. Evaluation of thermal properties demonstrated that the resulting composites achieved less thermal stability compared with control EP resin but possessed high char yields at high temperatures. It indicated that both HPCTP and OGPOSS could induce the formation of intumescent char layer that retarded the degradation and combustion process of EP resin. The peak heat release rate of EP resin composite containing 15 wt% HPCTP was 61% less than that of control EP resin. Meanwhile, other flame-retardant parameters were also improved. Results of scanning electron microscopy and energy-dispersive x-ray spectroscopy of residual chars confirmed that both HPCTP and OGPOSS can enhance thermal stability and flame retardancy of EP resin.

Preparation and properties of epoxy resin composites containing hexaphenoxycyclotriphosphazene

Hexaphenoxycyclotriphosphazene (HPCTP) was synthesized by a nucleophilic substitution reaction between hexachlorocyclotriphosphazene and phenol. The chemical structure of HPCTP was then characterized by Fourier transform infrared spectroscopy as well as 1H and 31P nuclear magnetic resonance spectroscopy. The synthesized HPCTP was incorporated into the diglycidyl ether of bisphenol A to prepare epoxy resin (EP) composites using 4,4′-diamino diphenylmethane as curing agent. The thermal and flame-retardant properties of cured samples were investigated by differential scanning calorimetry, thermogravimetric analysis, UL-94 vertical burning test, and cone calorimetry. Evaluation of thermal properties demonstrated that the resulting composites achieved high thermal stability with high char yields. The UL-94 V-0 rating was easily achieved with the addition of HPCTP, and the heat release intensity simultaneously decreased. Results of scanning electron microscopy and energy-dispersive x-ray spectroscopy confirmed that HPCTP can enhance the thermal stability and flame retardancy of epoxy resin.