Reactive-type Flame Retardant Research Articles

Reactive flame-retardants prepared by transesterification between erythritol and dimethyl methyl phosphonate for rigid polyurethane foams

The reactive type flame retardants have been applied in rigid polyurethane foams (RPUF) owing to their excellent durability and minimal negative effect on the physical properties, however, their flame retardant efficiency cannot meet the requirements in many practical application scenarios. In this work, two reactive-type flame retardants with several hydroxyl groups were synthesized by a solvent-free transesterification between erythritol and dimethyl methyl phosphonate (DMMP), and they were then introduced into RPUF by reacting with isocyanate respectively. The flammability of the as-prepared RPUF samples was evaluated by limiting oxygen index (LOI) and cone calorimeter tests. With the presence of 10 phr as prepared flame retardant, the LOI value of RPUF was improved from 18.3% to 29.8%, and the peak heat release rate (pHRR) and total heat release (THR) were reduced by 31.4% and 47.8% respectively in contrast to that of control RPUF. Furthermore, the compressive strength and thermal conductivity of RPUF containing reactive flame retardants were similar to those of control RPUF. This study provides an innovative method for the clean production of commercial RPUF with fire safety by using a modified phosphorus ester.

A Phosphorous-Based Bi-Functional Flame Retardant Based on Phosphaphenanthrene and Aluminum Hypophosphite for an Epoxy Thermoset.

A phosphorous-based bi-functional compound HPDAl was used as a reactive-type flame retardant (FR) in an epoxy thermoset (EP) aiming to improve the flame retardant efficiency of phosphorus-based compounds. HPDAl, consisting of two different P-groups of aluminum phosphinate (AHP) and phosphophenanthrene (DOPO) with different phosphorous chemical environments and thus exerting different FR actions, exhibited an intramolecular P-P groups synergy and possessed superior flame-retardant efficiency compared with DOPO or AHP alone or the physical combination of DOPO/AHP in EP. Adding 2 wt.% HPDAl made EP composites acquire a LOI value of 32.3%, pass a UL94 V-0 rating with a blowing-out effect, and exhibit a decrease in the heat/smoke release. The flame retardant modes of action of HPDAl were confirmed by the experiments of the scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and thermogravimetry–Fourier transform infrared spectroscopy–gas chromatograph/mass spectrometer (TG-FTIR-GC/MS). The results indicate that the phosphorous-based FRs show different influences on the flame retardancy of composites, mainly depending on their chemical structures. HPDAl had a flame inhibition effect in the gas phase and a charring effect in the condensed phase, with a well-balanced distribution of P content in the gas/condensed phase. Furthermore, the addition of HPDAl hardly impaired the mechanical properties of the matrix due to the link by chemical bonds between them.

Effect of a Reactive-Type Flame Retardant on Thermal Stability of Thiol-ene Composites

A reactive-type flame retardant, polyvinylphenylsilsesquioxane (PVP), was synthesized and incorporated into thiol-ene (TE) to prepare a flame-retardant TE (FRTE) composite. The thermal stability and thermal degradation kinetics of TE and FRTE in nitrogen were studied by thermogravimetric analysis (TGA). The effect of PVP in dynamic measurements of the kinetic parameters of TE degradation, such as apparent activation energy, was also investigated by the Kissinger and Flynn-Wall-Ozawa methods. The results of TGA showed that the addition of PVP improved the thermal stability of TE in nitrogen. The kinetic results indicated that the apparent activation energy for degradation of the FRTE composites was higher than that of neat TE, suggesting that the flame retardant PVP used in this work could promote the formation of char residue to block the heat flow and delay the thermal degradation of the TE matrix.

Enhancing the Fire Safety and Smoke Safety of Bio-Based Rigid Polyurethane Foam via Inserting a Reactive Flame Retardant Containing P@N and Blending Silica Aerogel Powder.

Rigid polyurethane foams (RPUFs) are widely used in many fields, but they are easy to burn and produce a lot of smoke, which seriously endangers the safety of people’s lives and property. In this study, tetraethyl(1,5–bis(bis(2–hydroxypropyl)amino)pentane–1,5–diyl)bis(phosphonate) (TBPBP), as a phosphorus–nitrogen–containing reactive–type flame retardant, was successfully synthesized and employed to enhance the flame retardancy of RPUFs, and silica aerogel (SA) powder was utilized to reduce harmful fumes. Castor oil–based rigid polyurethane foam containing SA powder and TBPBP was named RPUF–T45@SA20. Compared with neat RPUF, the obtained RPUF–T45@SA20 greatly improved with the compressive strength properties and the LOI value increased by 93.64% and 44.27%, respectively, and reached the V–0 rank of UL–94 testing. The total heat release (THR) and total smoke production (TSP) of RPUF–T45@SA20 were, respectively, reduced by 44.66% and 51.89% compared to those of the neat RPUF. A possible flame–retardant mechanism of RPUF–T45@SA20 was also proposed. This study suggested that RPUF incorporated with TBPBP and SA powder is a prosperous potential composite for fire and smoke safety as a building insulation material.

Synthesis and characterization of flame-retardant rigid polyurethane foams derived from gutter oil biodiesel

In this study, gutter oil biodiesel-based polyols (GOBP) and a reactive-type flame retardant named diethyl bis(2-hydroxyethyl)-aminomethylphosphonate (BHAPE) were both synthesized. Subsequently, gutter oil biodiesel-based flame-retardant rigid polyurethane foams (BPUFs) were prepared with GOBP, BHAPE, aluminum hydroxide (an additive-type flame retardant) and polymeric diphenylmethane diisocyanate. The properties of the BPUFs, including density, thermal conductivity, compressive properties, chemical component, morphology, thermal stability, limiting oxygen index, cone calorimetry testing, char residues stability were characterized. Among them, BPUF-AB owning 6.97 wt% of GOBP, 18.59 wt% of BHAPE and 39.77 wt% of aluminum hydroxide obtained a lower density of 0.097 g/cm3, a lower thermal conduction of 0.048 W/(m * k) and the highest compressive strength of 187 ± 13 kPa. Fire testing revealed a highest limiting oxygen index value of 30.1% and passed the UL-94 standard test. Cone calorimetry testing revealed that the peak heat release rate and peak smoke production release of BPUF-AB were reduced by 51.08% and 57.10%, respectively. Meanwhile, the total heat release rate and total smoke production were respectively decreased by 36.88% and 40.79%. The results indicate that BPUFs derived from gutter oil biodiesel are prosperously potential biomaterials with good thermal stability for fire insulation porous materials in future architecture applications.

Multi-Functional Carbon Fiber Reinforced Composites for Fire Retardant Applications

Development of multifunctional flame retardant (FR) polymer composite was done. Flame retardant polymer composite was prepared by modifying diglycidylether of bisphenol-A (DGEBA) epoxy. Modification involved two types of FR. Reactive type FR used was phosphoric acid and additive type FR used was magnesium hydroxide. Composite was fabricated using resin infusion under flexible tooling (RIFT) process. Different FR epoxy samples were evaluated by compression test, UL 94. The carbon fiber reinforced polymer composite with attributes of flame retardancy were characterized using in-plane shear test, to estimate the structural properties, and UL-94 test, to estimate the fire performance. FR composite exhibited UL-94 rating of V-1 and a shear modulus of 9.7 GPa, which proved it to multifunctional.

An anti-melt dripping, high char yield and flame-retardant polyether rigid polyurethane foam

Endowing rigid polyurethane foam (PUF) with a good fire-retardancy is essential for improving fire safety. Chemical improvement in fire-retardancy by using reactive-type flame retardants is better because of the disadvantages of traditional additive-type flame retardants. A reactive flame retardant tri-glycidyl phosphate (POG), which was synthesized by using phosphorus oxychloride and glycidol, was bound to the cross-linked network structure of PUF. The effects of POG on the physical-mechanical properties, morphology, thermal stability and fire-retardancy of PUF system were systematically investigated. Research results showed that POG resulted in an improvement in the thermal insulation ability and a slight decrease in the compressive strength of PUF. Furthermore, thermogravimetric analysis certified that the thermal stability and the char yield at 700 °C of PUF were significantly enhanced by incorporating POG. The limiting oxygen index increased to 22.3% with rising loading of POG. Moreover, a 30.2% decline in total heat release was achieved, the time to flameout was significantly shortened. Additionally, the vertical burning test illustrated that POG effectively limited the spread of flame and eliminated melt dripping. Further study confirmed that the fire-retardancy of PUF was significantly improved by inhibiting flame in the gas phase and charring in condensed phase.

Synthesis of a novel reactive type flame retardant composed of phenophosphazine ring and maleimide for epoxy resin

It is well known that the high loading of flame retardants is needed to improve the flame-retardant property of epoxy resins accompanied with the serious deterioration of their thermal and mechanical properties. A novel flame retardant with the high flame-retardant effect, namely 1-(4-hydroxyphenyl)-3-(10-oxido-5H-phenophosphazine-10-yl) pyrrolidine-2,5-dione (DPPA-HPM), was synthesized to solve the problem. The nuclear magnetic resonance and high-resolution electrospray ionization mass spectrometry verified the successful synthesis of DPPA-HPM. DPPA-HPM was an efficient flame retardant for epoxy resin. Only 1.5 wt% loading of DPPA-HPM was found to endow the epoxy resin with UL-94 V-0 rating and the high limited oxygen index value of 29.5%. Moreover, the flame-retarded epoxy resin possessed the good comprehensive properties with the maintained glass transition temperature and the improved flexural strength as compared with the control epoxy resin, which exhibits good potential application prospects.

A facile method to flame-retard epoxy resin with maintained mechanical properties through a novel P/N/S-containing flame retardant of tautomerization

A novel phenylphosphonic di-benzothiazolyl amide (PPDAB) and its imine-type tautomer were successfully synthesized via the amidation of phenylphosphonic dichloride (PPDC) with 2-aminobenzothiazole (ABZ), and used to flame-retard epoxy resin (EP). In the help of PPDAB-Amine as an additive-type flame retardant and PPDAB-Imine as a reactive-type flame retardant, PPDAB showed excellent general properties in epoxy resin. EP with 0.69wt% of phosphorus achieved UL-94 V-0 rating, and the LOI value of it was increased to 31.0%. Compared with the EP, its performances in terms of the peak of heat release rate (PHRR), total heat release (THR), and smoke production rate (SPR) obtained from cone calorimeter were obviously improved. Besides, EP-PPDAB in which the amount of PPDAB was lower than 10wt% also exhibited similar glass transition temperature (Tg) to EP, and well-maintained mechanical properties in terms of tensile strength and impact strength.

Intrinsic Flame-Retardant and Thermally Stable Epoxy Endowed by a Highly Efficient, Multifunctional Curing Agent.

It is difficult to realize flame retardancy of epoxy without suffering much detriment in thermal stability. To solve the problem, a super-efficient phosphorus-nitrogen-containing reactive-type flame retardant, 10-(hydroxy(4-hydroxyphenyl)methyl)-5,10-dihydrophenophosphazinine-10-oxide (HB-DPPA) is synthesized and characterized. When it is used as a co-curing agent of 4,4′-methylenedianiline (DDM) for curing diglycidyl ether of bisphenol A (DGEBA), the cured epoxy achieves UL-94 V-0 rating with the limiting oxygen index of 29.3%. In this case, the phosphorus content in the system is exceptionally low (0.18 wt %). To the best of our knowledge, it currently has the highest efficiency among similar epoxy systems. Such excellent flame retardancy originates from the exclusive chemical structure of the phenophosphazine moiety, in which the phosphorus element is stabilized by the two adjacent aromatic rings. The action in the condensed phase is enhanced and followed by pressurization of the pyrolytic gases that induces the blowing-out effect during combustion. The cone calorimeter result reveals the formation of a unique intumescent char structure with five discernible layers. Owing to the super-efficient flame retardancy and the rigid molecular structure of HB-DPPA, the flame-retardant epoxy acquires high thermal stability and its initial decomposition temperature only decreases by 4.6 °C as compared with the unmodified one.

Synthesis of 2, 3-dibromo-succinic anhydride and application on cotton, polyester and polyester/cotton blended fabric

For a poly(ethylene terephthalate) (PET)/cotton blended fabric, a reactive-type flame retardant 2, 3-dibromo-succinic anhydride (DBSA) was used to endow durable flame retardancy via the pad-dry-cure method. DBSA was synthesized via the addition reaction of maleic anhydride and bromine in ethyl acetate solution and extracted by solventing-out crystallization. DBSA was used to finish a cotton fabric firstly with sodium hypophosphite as the catalyst. Thermal behaviors and amount of DBSA that esterified with the cotton was determined. Pyrovatex CP new was applied as a comparison. It was speculated from the thermogravimetric analysis result that esterification of cellulose with DBSA worked similar to phosphate-ester at the initial stage of thermal decomposition. DBSA was also applied to PET and PET/cotton blended fabrics. Flame retardancy, thermal behaviors and durability of the finished fabrics were investigated. Evidence of the condensed phase effect of DBSA was also observed on PET and PET/cotton.

Inherently Flame-Retardant Flexible Polyurethane Foam with Low Content of Phosphorus-Containing Cross-Linking Agent

A halogen-free phosphorus-containing triol named phosphoryltrimethanol (PTMA) was synthesized and used as a cross-linking agent and a reactive-type flame retardant to prepare inherently flame-retardant flexible polyurethane foam (FPUF). Incorporation of a low content (7.8 wt %) of PTMA into the polyurethane chains can increase the flame retardance of FPUF because of good char formation. The residual chars and evolved gases of PTMA-cross-linked FPUFs were analyzed by SEM, FTIR spectroscopy, inductively coupled plasma-atomic emission spectrometry (ICP-AES), energy-dispersive X-ray (EDX) spectroscopy, and thermogravimetric analysis (TGA) coupled with FTIR spectroscopy. The results indicated that more than 60% of the phosphorus in PTMA-cross-linked FPUF was decomposed into polyphosphoric acid or its derivatives and retained in the char residue. This shows that PTMA mainly played a role in the condensed phase of flame-retardant FPUF. Based on the results, a possible thermal degradation mechanism of PTMA-cross-...

Benzoxazine-containing branched polysiloxanes: Highly efficient reactive-type flame retardants and property enhancement agents for polymers

The molecular design concept of silicon-nitrogen synergistic effect for highly-efficient flame retardants has been demonstrated in the preparation of reactive type flame retardants which exhibits high flame retardation efficiency and property enhancement ability for developments of high performance polymers. In the synthetic route, a benzoxazine-containing triethoxysilane compound is obtained and used as a monomer together with diphenylsilanediol to result in branched benzoxazine-containing polysiloxanes (PBz-PSO) through a 3 + 2 condensation polymerization reaction. The chemical structures and properties of Bz-TES and PBz-PSO compounds have been characterized with Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, and differential scanning calorimetry. PBz-PSO samples are reactive polymers as they possess thermally-reactive benzoxazine groups. Thermally-crosslinking the PBz-PSO samples results in silicon-containing polymers which show high thermal stability and high flame retardancy (limited oxygen index > 45). Addition of 5 wt% PBz-PSO to a conventional benzoxazine resin could simultaneously improve its flame retardancy (passing the UL 94-V0 test) and increase its glass transition temperature from 145 °C to 205 °C. PBz-PSO samples are highly-efficient reactive-type flame retardants for preparation of halogen-free and phosphorus-free polymers.

Study on the preparation and properties of novel transparent fire-resistive coatings

A cyclic polyphosphate (CPPA) was synthesized by the reaction of polyphosphoric acid and pentaerythritol. Polyethylene glycol (PEG) was introduced in the structure of CPPA to improve its solubility in water and ethanol and five kinds of reactive type flame retardants (MCPPA) were obtained. 31P NMR, 1H NMR, FTIR, and TGA were used to characterize the composition and structure of CPPA and MCPPAs. The experimental results showed that there were 25% cyclic P–O–C structures in the product and MCPPA had better carbonization ability than CPPA. Five kinds of transparent fire-resistive coatings were prepared by the mixing of amino resin with five kinds of MCPPAs. The results of the fire protection test showed that both the fire-resistive time of coatings and intumescent factor of char layers decreased with the increase of molecular weight of PEG. The results of TGA and EDS showed that the carbonaceous residue of coatings and the antioxidation ability of char layers also decreased regularly with the increase of molecular weight of PEG. The SEM images demonstrated that the coating prepared with low molecular weight of PEG contributed to dense form structure and narrow distribution of cell size. Above all, the transparent fire-resistive coating prepared with PEG 200 had the best fire retardancy and stable thermal behavior.

Novel cyclotriphosphazene-based epoxy compound and its application in halogen-free epoxy thermosetting systems: Synthesis, curing behaviors, and flame retardancy

Abstract A novel cyclotriphosphazene-based epoxy compound (PN-EPC) as a halogen-free reactive-type flame retardant was synthesized via a two-step synthetic route. The chemical structures and compositions of the cyclotriphosphazene precursor and the final product were characterized by 1 H, 13 C, and 31 P NMR spectroscopy, Fourier transform infrared spectroscopy, mass spectroscopy, and elemental analysis. A series of thermosetting systems based on a conventional epoxy resin and PN-EPC were prepared, and their thermal curing behaviors were investigated. These epoxy thermosets achieved a significant improvement in glass transition temperature and also gained the good thermal stability with a high char yield. The incorporation of PN-EPC could impart an excellent nonflammability to the epoxy thermosets due to a synergistic flame retarding effect as a result of the unique combination of phosphorus and nitrogen from the phosphazene rings, and these epoxy thermosets achieved the high limiting oxygen indexes and the UL-94 V-0 rating when 20 wt.% of PN-EPC was added. The study on flame-retardant mechanism indicates that the pyrolysis products of phosphazene rings acted in both the condensed and gaseous phases to promote the formation of intumescent phosphorus-rich char on the surface of the epoxy thermosets. Such a char layer can supply a much better barrier for underlying thermosets to inhibit gaseous products from diffusing to the flame, to shield the surface of the thermosets from heat and air, and to prevent or slow down oxygen diffusion. As a result, the resulting epoxy thermosets obtained an excellent nonflammability.

The effect of chemically reactive type flame retardant additives on flammability of PES toughened epoxy resin and carbon fiber‐reinforced composites

The effect of different concentrations (4 and 8 wt%) of chemically reactive type flame retardant (FR) chemicals on the thermal stability and flammability of an aerospace grade epoxy resin has been studied by thermal analysis, limiting oxygen index, UL‐94, and cone calorimetry. Chemically reactive flame retardant term implies that they interact with the polymer during some part of the pyrolysis and fire chemistries. Flame retardants included (i) phosphorous‐ and nitrogen‐containing, active in condensed phase, (ii) intumescent chemicals, active in condensed phase and also known as char promoters, (iii) organophosphates, active primarily in condensed phase, but in some polymers known to have also shown vapor phase activity, (iv) halogen‐containing, active in vapor phase. During curing process some of the flame retardants settled on the bottom of the resin plaque, affecting the flammability results. All FRs reduced the flammability of the resin, the extent of which depended upon the FR type, concentration of flame retardant elements in the formulation and the type of fire testing performed. With selective FRs, carbon fiber‐reinforced composites have also been fabricated and tested for their fire and mechanical performance. FR chemicals decreased the flammability of composites up to 50% without affecting their mechanical properties. Copyright © 2011 John Wiley & Sons, Ltd.

Photopolymerization behaviors of hyperbranched polyphosphonate acrylate and properties of the UV cured film

A novel hyperbranched polyphosphonate acrylate (HBPPA), used as a reactive-type flame retardant in UV curable systems, was successfully synthesized by the reaction of di(acryloyloxyethyl) benzenephosphonate (DABP) with N-(2-aminoethyl)-piperazine, and characterized by FTIR, 1H NMR and GPC measurements. HBPPA was blended with DABP as a monomer in different ratios to obtain a series of flame retardant resins. Their maximum photopolymerization rates ( R p max ) and final unsaturation conversion ( P f) in the cured films in the presence of a photofragmenting initiator were investigated. The results showed that the P f increased along with HBPPA content and the pure HBPPA has the maximum value of 81.0% in the photo-DSC analysis. Their flame retardancy was monitored by the limiting oxygen index (LOI), and showed that the UV cured films greatly expanded when burning, and the degree of expansion increased along with HBPPA content. However, the LOI values varied from 36.0 to 39.0, which can be ascribed to the condensed phase mechanism. Their thermal degradation behaviors were investigated by thermogravimetric analysis and in situ FTIR spectroscopy, and showed that the phosphonate group of HBPPA first degraded to form poly(phosphoric acid)s at around 300 °C, which had a major contribution to form the compact char to protect the sample from further degradation. The dynamic mechanical thermal properties were studied by dynamic mechanical thermal analysis and showed a good miscibility between HBPPA and DABP. The crosslinking density and T g of the cured films decreased along with the content of HBPPA in the blend.

Preparation and film properties of tri(3,4-epoxycyclohexylmethyl) phosphate based cationically UV curing coatings

A facile synthesis of phosphorus-containing trifunctional cycloaliphatic epoxide resin, tri(3,4-epoxycyclohexylmethyl) phosphate (TECP), used for cationically UV curing coatings as a reactive-type flame retardant, was proposed. The molecular structure was confirmed by FTIR, 1H NMR and 31P NMR spectroscopic analysis. A series of flame retardant formulations by incorporating into a commercial difunctional cycloaliphatic epoxide resin, CYRACURE™ UVR-6110, were prepared, and exposed to a medium pressure lamp to form the cured films under the presence of diaryliodonium hexafluorophosphate salt as a cationic photoinitiator. Their flame retardancy examined by the limiting oxygen index showed the improvement up to 27 for 50 wt% TECP addition compared with 21 for pure UVR-6110. The Ts and Tg decreased from 86°C and 131°C to 55°C and 91°C, respectively, by using dynamic mechanical thermal analysis, whereas the tensile strength showed a slight increase (11%) with 50 wt% TECP addition. The thermogravimetric analysis (TGA) and real-time Fourier transform infrared spectroscopy (RT-FTIR) measurement demonstrated the condensed-phase flame retardant mechanism.

Synthesis and thermal degradation behaviors of hyperbranched polyphosphate

A novel epoxy-terminated hyperbranched polyphosphate (E-HBPP) was synthesized by employing an A 2 + B 3 polycondensation and characterized by FTIR, 1H NMR and GPC. E-HBPP was used as a reactive-type flame retardant for diglycidyl ether of bisphenol-A/ m-phenylene diamine (DGEBA/ mPDA) system. A series of flame retardant resins were prepared and their flame retardancy was monitored by the limiting oxygen index (LOI). The results showed that the LOI value of the cured samples and the degree of expansion of the formed char after burning increased along with the E-HBPP content. Their thermal degradation behaviors were investigated by thermogravimetric analysis and in situ FTIR and showed that the phosphate group of E-HBPP first degraded to form poly(phosphoric acid)s at around 300 °C, which had a major contribution to form the compact char to protect the sample from further degradation. The dynamic mechanical thermal properties were studied by dynamic mechanical thermal analysis (DMTA) and the results showed a good miscibility between E-HBPP and DGEBA. The mechanical properties of the cured films were also investigated. Less than 20% E-HBPP addition improved both the tensile strength and elongation at break.

Flame Resistant Nylon-6,6 Composites with Improved Mechanical Strength by the Combination of Additive- and Reactive-Type Flame Retardants

Characteristics of flame-resistant nylon-6,6 (PA66) composites with improved mechanical strength at high temperatures were studied. The composites prepared by mixing PA66 with organic phosphorus flame retardants of additive-type and reactive-type, the latter of which carrying allyl functionalities turned the resulting composite infusible after the γ-ray irradiation cross-linking. The storage modulus became constant after increased with the exposure period (at [flame retardant] = const.) or the amount of the reactive flame retardant (at exposure period = const.). The cross-linked composites not only showed rubber like elasticity even at temperatures higher than the melting point of uncross-linked PA66, but also provided no drip upon combustion. Although the cross-linked composites with the reactive-type flame retardant gave insufficient flame-resistant grade, the one with both additive- and reactive-type flame retardants realized the UL94/V-0 grade with satisfactory mechanical strength.