Synthesis of a novel phosphorus-containing epoxy curing agent and the thermal, mechanical and flame-retardant properties of the cured products

Preparation and characterization of novel flame-retardant paint of substituted cyclodiphosph(V)azane sulfonomide and their Cu(II), Cd(II) metal complexes as new additives for exterior wood coating protection

The development of flame-retardant materials has become an important research direction. For the past dozen years, researchers have been exploring flame retardants with high flame-retardant efficiency, low toxicity, less smoke, or other excellent performance flame retardants. Therefore, this work aimed to synthesize new cyclodiphosph(V)azane derivatives and their Cu(II) and Cd(II) metal complexes and investigated their potential applications as high flame-retardant efficiency. Various techniques were used to characterize the prepared ligand H2L and its metal complexes, including elemental analyses, mass spectra, conductivity measurements, electronic spectral data UV-vis, FT-IR, 1H,13C-NMR, TGA, XRD, and molecular docking experiments studies were M. tuberculosis receptors (PDB ID: 5UHF) and the crystal structure of human topoisomerase II alpha (PDB ID: 4FM9). Wood-based paint was physically mixed with the ligand H2L and its metal complexes. The obtained results of mechanical characteristics of the dried paint layers were noticed to improve, such as gloss value, which ranged from 85 to 95, hardness 1.5-2.5 kg, adhesion 4B to 5B, and impact resistance, which improved from 1.3 to 2.5 J. Moreover, the obtained results of flame-retardant properties showed a significant retardant impact compared to the blank sample, such as ignitability, which includes the heat flux which increased from 10 to 25 kW/m2, and ignition time, ranging from 550 to 1200 s, respectively, and limiting oxygen index (LOI) (%) which has been increased from 21 to 130 compared with the plywood sample and sample blank. The ordering activity of the observed results was noticed that coated sample based on Cd(II) metal complexes > coated sample based on Cu(II) metal complexes of Cyclophosphazene ligand > coated sample based on phosphazene ligand H2L > coated sample without additives > uncoated sample. This efficiency may be attributed to (1) the H2L is an organophosphorus compound, which contains P, N, Cl, and aromatic six- and five-member ring, (2) Cu(II) and Cd(II) metal complexes characterized by high thermal stability, good stability, excellent performance flame retardants, and wide application.

Composites Filled with Metal Organic Frameworks and Their Derivatives: Recent Developments in Flame Retardants

Polymer matrix is vulnerable to fire hazards and needs to add flame retardants to enhance its performance and make its application scenarios more extensive. At this stage, it is more necessary to add multiple flame-retardant elements and build a multi-component synergistic system. Metal organic frameworks (MOFs) have been studied for nearly three decades since their introduction. MOFs are known for their structural advantages but have only been applied to flame-retardant polymers for a relatively short period of time. In this paper, we review the development of MOFs utilized as flame retardants and analyze the flame-retardant mechanisms in the gas phase and condensed phase from the original MOF materials, modified MOF composites, and MOF-derived composites as flame retardants, respectively. The effects of carbon-based materials, phosphorus-based materials, nitrogen-based materials, and biomass on the flame-retardant properties of polymers are discussed in the context of MOFs. The construction of MOF multi-structured flame retardants is also introduced, and a variety of MOF-based flame retardants with different morphologies are shown to broaden the ideas for subsequent research.

A phosphorus-containing imidazole derivative towards the liquid oxygen compatibility and toughness of epoxy resin

In order to develop a liquid oxygen-compatible (LOX-compatible) matrix resins for polymer-based fiber-reinforced composites, a novel phosphorus-containing imidazole derivative called VAD containing multifunctional groups was synthesized and used as a co-curing agent for epoxy resin (EP) with simultaneous LOX-compatibility and mechanical improvement. A phosphorus group was introduced into the EP to capture the free radicals generated during the pyrolysis of the polymer to improve LOX compatibility, and the trimethylene group was introduced as a flexible spacer to enhance the toughness of the cured material. In comparison to pure EP, the modified EP with only 2.5 wt% VAD showed excellent mechanical properties with 23.0% and 75.6% increase in tensile and impact strength, respectively. Furthermore, as the content of VAD increased, a thermoset compatible with LOX (according to the liquid oxygen impact test) was obtained, and the flame retardancy was improved (according to the limiting oxygen index test). However, there was no significant sacrifice of transparency or thermal stability. In addition, the LOX compatibility mechanism was analyzed using X-ray photoelectron spectroscopy. As an efficient multi-functional modifier, VAD has a bright future in the modification realm of EP materials.

An Effective Method for Preparation of Liquid Phosphoric Anhydride and Its Application in Flame Retardant Epoxy Resin

A novel liquid phosphorous-containing flame retardant anhydride (LPFA) with low viscosity was synthesized from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and methyl tetrahydrophthalic anhydride (MeTHPA) and further cured with bisphenol-A epoxy resin E-51 for the preparation of the flame retardant epoxy resins. Both Fourier transform infrared spectroscopy (FT-IR), mass spectrometry (MS) and nuclear magnetic resonance (NMR) measurements revealed the successful incorporation of DOPO on the molecular chains of MeTHPA through chemical reaction. The oxygen index analysis showed that the LPFA-cured epoxy resin exhibited excellent flame retardant performance, and the corresponding limiting oxygen index (LOI) value could reach 31.2%. The UL-94V-0 rating was achieved for the flame retardant epoxy resin with the phosphorus content of 2.7%. With the addition of LPFA, the impact strength of the cured epoxy resins remained almost unchanged, but the flexural strength gradually increased. Meanwhile, all the epoxy resins showed good thermal stability. The glass transition temperature (T_g) and thermal decomposition temperature (T_d) of epoxy resin cured by LPFA decreased slightly compared with that of MeTHPA-cured epoxy resin. Based on such excellent flame retardancy, low viscosity at room temperature and ease of use, LPFA showed potential as an appropriate curing agent in the field of electrical insulation materials.

Novel phosphorus/nitrogen/boron-containing carboxylic acid as co-curing agent for fire safety of epoxy resin with enhanced mechanical properties

It is a great challenge to develop a high-efficiency reactive flame retardant, applied to anhydride-cured epoxy resin (EP) system, simultaneously possessing good compatibility with matrix and mechanical reinforcement. In this respect, we successfully synthesized a novel phosphorus/nitrogen/boron-containing carboxylic acid (TMDB) through the facile esterification and addition reaction among 1,3,5-tris(2-hydroxyethyl)isocyanurate (THEIC), maleic anhydride (MAH), 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and boric acid (BA). TMDB was utilized as a co-curing agent for EP/methyltetrahydrophthalic anhydride (MeTHPA) system and finally cured EP behaved great transparency, suggesting excellent compatibility of TMDB with EP. Compared with pure EP, modified EP exhibited comparable thermal stability and heat resistance but higher flame retardance. With only 15.1 wt% TMDB loading, the LOI value of anhydride-cured EP increased to 29.6% from 20.1% of pure EP, and UL-94 V-0 rating was achieved. The peak heat release rate (PHRR), total heat release (THR) and total smoke production (TSP) remarkably decreased by 58.5%, 41.7% and 47.2% compared with that of pure EP, respectively. Besides, different measurements revealed TMDB simultaneously functioned in the condensed and gaseous phase during combustion. Furthermore, after incorporation of TMDB, mechanical properties of cured EP were improved and the maximum increments of flexural and tensile strength can reach 11.8% and 61.4%, respectively.

Flame Retardant Epoxy Composites on the Road of Innovation: An Analysis with Flame Retardancy Index for Future Development

Nowadays, epoxy composites are elements of engineering materials and systems. Although they are known as versatile materials, epoxy resins suffer from high flammability. In this sense, flame retardancy analysis has been recognized as an undeniable requirement for developing future generations of epoxy-based systems. A considerable proportion of the literature on epoxy composites has been devoted to the use of phosphorus-based additives. Nevertheless, innovative flame retardants have coincidentally been under investigation to meet market requirements. This review paper attempts to give an overview of the research on flame retardant epoxy composites by classification of literature in terms of phosphorus (P), non-phosphorus (NP), and combinations of P/NP additives. A comprehensive set of data on cone calorimetry measurements applied on P-, NP-, and P/NP-incorporated epoxy systems was collected and treated. The performance of epoxy composites was qualitatively discussed as Poor, Good, and Excellent cases identified and distinguished by the use of the universal Flame Retardancy Index (FRI). Moreover, evaluations were rechecked by considering the UL-94 test data in four groups as V0, V1, V2, and nonrated (NR). The dimensionless FRI allowed for comparison between flame retardancy performances of epoxy composites. The results of this survey can pave the way for future innovations in developing flame-retardant additives for epoxy.

Improved thermal properties of epoxy resin modified with polymethyl methacrylate-microencapsulated phosphorus-nitrogen-containing flame retardant

Epoxy resin (EP) composites with improved thermal resistance were fabricated. To solve the problem of low thermal resistance derived from phosphazene flame-retardant additives, we designed a system based on flame-retardant microcapsules P(H), with hexaphenoxycyclotriphosphazene as the core and polymethyl methacrylate as the shell. The core–shell structure was characterized and confirmed. The thermal resistance of the cured EP composites containing 1 wt% P(H) microcapsules was improved because of the increased glass transition temperatures. The P(2.75H)/EP composites can reach a limited oxygen index of 30.5% and V-1 rating in UL-94 tests. Heat and gas release rates were reduced during combustion tests. Residual images implied that the P(H) microcapsules may promote the formation of a flame-retardant char layer. Pyrolysis analysis demonstrated that the P(H) microcapsules can decompose in two procedures to produce flame-retardant gas components. Therefore, the flame-retardant mechanism involved the flame inhibition effect in the gas phase, and the charring effect in the condensed phase.

Epoxy resin composites with improved thermal resistance and flame retardancy were fabricated based on P(H) microcapsules.

Flame retardancy and toughening properties of epoxy composites containing ammonium polyphosphate microcapsules and expanded graphite

Ammonium polyphosphate microcapsules (BM (polybenzoxazine modified) APP) were prepared through the in situ ring-opening polymerization of allyl group containing benzoxazine monomers on the surfaces of ammonium polyphosphate (APP), and they were significantly hydrophobic than the APP. A flame retardant system of epoxy (EP) resin was prepared with BMAPP and expanded graphite (EG). Flame retardancy, the thermal degradation behavior, a mechanical property of EP and EP/BMAPP/EG composites was investigated through limited oxygen index, vertical burning test, cone calorimetry (CONE), and the thermogravimetric analysis (TGA). The flame retardancy tests indicated that the EG could improve the thermal performance, promote the charring, and enhance the char quality of EP/BMAPP. Scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR) were employed to analyze the morphology and composition of the char residue formed during CONE testing, and to understand the mechanism of char formation. The results of TG-FTIR confirmed the possible mechanism of flame retardancy of EP/BMAPP/EG in the gas phase during combustion. The EG content effects on Young’s modulus, the tensile strength, and the fracture toughness ( KIC) of the EP/BMAPP composites were also investigated. The KIC of the composites containing 1% of EG and 10% of BMAPP increased by approximately 76% and 153%, respectively, compared to the neat matrix and EP/BMAPP-10%. The SEM images of the fractured surface indicated that the enhanced toughness of EP/BMAPP/EG composites mainly attributed to the debonding of the BMAPP and the subsequent plastic void growth of the matrix, as well as the crack deflection effect of the BMAPP/EG.

Novel flame retardancy effect of phenethyl-bridged DOPO derivative on epoxy resin

A series of flame-retardant epoxy resins (EPs) containing either phenethyl-bridged 9 or 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide derivative (bisDOPO) were prepared. The flame-retardant properties of bisDOPO on EP composites were characterized by the limiting oxygen index (LOI), the UL-94 vertical burning, and the cone calorimeter test (CCT).The LOI of the EP/bisDOPO composites increased from 21.8% to 38.0%, and the hybrids with the 10 wt% bisDOPO obtained a V-0 rating in the UL94 vertical burning test. The char residue following the CCT showed intumescent structures with continuous and compact surfaces that can effectively suppress the spread of the flame and extinguish the fire. This was confirmed through both visual observation and scanning electron microscopy (SEM) measurements. The flame-retardant mechanism was studied by Fourier transform infrared spectroscope (FTIR), thermogravimetric analysis/infrared spectrometry, SEM/energy-dispersive X-ray, and pyrolysis-gas chromatography/mass spectrometry. Overall, bisDOPO was an effective flame retardant with potential applications within EP.

Flame-retardant effect of a phenethyl-bridged DOPO derivative and layered double hydroxides for epoxy resin

Flame-retardant epoxy resin (EP) composites were prepared by the incorporation of a phenethyl-bridged DOPO derivative (DiDOPO) and modified layered double hydroxide (OLDH).