A novel nitrogen,phosphorus, and boron ionic pair compound toward fire safety and mechanical enhancement effect for epoxy resin

In this work, a novel nitrogen, phosphorus and boron ionic pair compound (DTPA[AZB]), composed of a protonated flame retardant (DTPA) 6,6'‐(1,4‐phenylenebis((pyrazin‐2‐ylamino)methylene))bis(dibenzo[c,e][1,2]oxaphosphinine 6‐oxide) and a counter anion alizarin borate (AZB), has been prepared and fully characterized, AZB was synthesized by the reaction of alizarin with boric acid. DTPA was produced in two steps. First, terephthalaldehyde was condensed with aminopyrazine to form the corresponding imine. This was treated with 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) to generate DTPA. Blending with DTPA greatly reduced the flammability of epoxy resin. When the amount of DTPA added was 4%, a modified epoxy resin passed the V‐0 rating and the limiting oxygen index (LOI) reached 32.5%. With the introduction of 3% AZB into the EP/DTPA material, the LOI reached 33.5%. Simultaneously, compared with that of neat EP, the peak heat release rate and smoke production rate for EP/DTPA‐4 was decreased by 24.1% and 40.7%, respectively, and the peak heat release rate and smoke production rate for EP/DTPA[AZB]‐3 was decreased by 32.9% and 43.4%, respectively. The results indicate that AZB and DTPA show good cooperative flame retardant effects. The flame retardancy of the modified epoxy is improved with greater heat release suppression combustion of the resin. A mode of flame retardant action has been proposed based on analysis results from Py‐GC/MS for DTPA, and SEM, IR and Raman for the residual carbon from cone calorimeter and UL‐94 tests, respectively. Importantly, the tensile strength, fexural strength, and fexural modulus of the EP/DTPA[AZB] increased compared with the same properties of neat EP.     

Effect of ethyl‐bridged diphenylphosphine oxide on flame retardancy and thermal properties of epoxy resin

Three commercialized flame retardants, 1,2‐bis(diphenylphosphinoyl)ethane (EDPO), 6,6‐(1,2‐phenethyl)bis‐6H‐dibenz[c,e][1,2]oxaphosphorin‐6,6‐dioxide (HTP‐6123), and hexa‐phenoxy‐cyclotriphosphazene (HPCTP), were used to prepare the flame retardant diglycidyl ether of bisphenol A (DGEBA) epoxy resin (EP) under the same experimental conditions. The effects of T_g, thermal stability, and water absorption properties of EP caused by the three flame retardants were investigated and compared, together with their flame retardant efficiency. Results showed that the introduction of the three flame retardants improved the flame retardant performance of EP but led to decreases in T_g and decomposition temperature. EDPO showed higher flame retardant efficiency than the other two flame retardants. EP/EDPO showed higher thermal stability, better flame retardant performance, higher T_g value, and lower water absorption than EP/HTP‐6123 and EP/HPCTP. The study discovered that EDPO and HTP‐6123 primarily act through the gas phase flame retardant mechanism, while HPCTP is primarily driven by the condensed phase mechanism.     

A flame‐retardant phosphate and cyclotriphosphazene‐containing epoxy resin: Synthesis and properties

A novel flame‐retardant epoxy resin, (4‐diethoxyphosphoryloxyphenoxy)(4‐glycidoxyphenoxy)cyclotriphosphazene (PPCTP), was prepared by the reaction of epichlorohydrin with (4‐diethoxyphosphoryloxyphenoxy)(4‐hydroxyphenoxy)cyclotriphosphazene and was characterized by Fourier transform infrared, ³¹P NMR, and ¹H NMR analyses. The epoxy resin was further cured with diamine curing agents, 4,4′‐diaminodiphenylmethane (DDM), 4,4′‐diaminodiphenylsulfone (DDS), dicyanodiamide (DICY), and 3,4′‐oxydianiline (ODA), to obtain the corresponding epoxy polymers. The curing reactions of the PPCTP resin with the diamines were studied by differential scanning calorimetry. The reactivities of the four curing agents toward PPCTP were in the following order: DDM > ODA > DICY > DDS. In addition, the thermal properties of the cured epoxy polymers were studied by thermogravimetric analysis, and the flame retardancies were estimated by measurement of the limiting oxygen index (LOI). Compared to a corresponding Epon 828‐based epoxy polymer, the PPCTP‐based epoxy polymers showed lower weight‐loss temperatures, higher char yields, and higher LOI values, indicating that the epoxy resin prepared could be useful as a flame retardant. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 972–981, 2000     

Synthesis of a novel DPPA‐containing benzoxazine to flame‐retard epoxy resin with maintained thermal properties

The flame‐retarded epoxy resin with improved thermal properties based on environmentally friendly flame retardants is vital for industrial application. Hereby, a novel reactive‐type halogen‐free flame retardant, 10‐(3‐(4‐hydroxy phenyl)‐3,4‐dihydro‐2H‐benzo[e] [1,3] oxazin‐4‐yl)‐5H‐phenophosphazinine 10‐oxide (DHA‐B) was synthesized via a two‐step reaction route. Its structure was characterized using ¹H, ¹³C, and ³¹P NMR and HRMS spectra. For 4,4′‐diaminodipheny ethane (DDM) and diglycidyl ether of bisphenol A (DGEBA)‐cured systems, the epoxy resin with only 2 wt% loading of DHA‐B passed V‐0 rating of UL‐94 test. Significantly, its glass transition temperature (T_g) and initial decomposition temperature (T_5%) were as high as 169.6°C and 359.6°C, respectively, which were even higher than those of the corresponding original epoxy resin. Besides, DHA‐B decreased the combustion intensity during combustion. The analysis of residues after combustion suggested that DHA‐B played an important role in the condensed phase.     

Low flammability and smoke epoxy resins with a novel DOPO‐based imidazolone derivative

In this work, a DOPO‐based imidazolone derivative named DHI was synthesized using DOPO, 5‐amino‐2‐benzimidazolinone and 4‐hydroxybenzaldehyde as raw materials. The chemical structure of DHI was characterized by ¹H‐NMR, ³¹P‐NMR and Fourier transform infrared spectra (FTIR). Then, a series of different flame‐retardant epoxy resin (EP) thermosets were prepared by mixing flame retardant DHI. The thermal properties of the cured EPs was investigated by thermogravimetry analysis (TGA) and differential scanning calorimeter (DSC), and the results showed the thermal stability and glass transition temperature (T_g) of the cured EP modified with DHI declined slightly compared with that of neat EP. The limited oxygen index (LOI) and UL94 test results exhibited DHI imparted good flame retardancy to EP. The EP‐4 (phosphorus content of 1.25%) possessed a LOI value of 36.5% and achieved a V‐0 rating. Furthermore, the peak of heat release rate (PHRR) and total heat release rate (THR) of EP‐4 decreased by 38.7% and 24.5%, respectively. Excitedly, the total smoke production (TSP) of EP‐4 sample declined by 62.5%, which meant DHI also made EP obtain excellent smoke suppression property. Moreover, the flame‐retardant mechanism was studied by scanning electron microscopy (SEM) and pyrolysis‐gas chromatography/mass spectrometry (Py‐GC/MS). It was reasonable inferred that DHI could not only promote EP to form dense char layer in condensed phase, but also restrain combustion in gaseous phase through catching the free radicals sourced from the degradation of EP.     

Thermal properties and flame retardancy of novel epoxy based on phosphorus‐modified Schiff‐base

Through addition reaction of Schiff‐base terephthalylidene‐bis‐(p‐aminophenol) ( DP‐1 ) and diethyl phosphite (DEP), a novel phosphorus‐modified epoxy, 4,4'‐diglycidyl‐(terephthalylidene‐bis‐(p‐aminophenol))diphosphonate ether ( EP‐2 ), was obtained. An modification reaction between EP‐2 and DP‐1 resulted in an epoxy compound, EP‐3 , possessing both phosphonate groups and C?N imine groups. The structure of EP‐2 was characterized by Fourier transform infrared (FTIR), elemental analysis (EA), ¹H, ¹³C, and ³¹P NMR analyses. The thermal properties of phosphorus‐modified epoxies cured with 4,4'‐diaminodiphenylmethane (MDA) and 4,4'‐diaminodiphenyl ether (DDE) were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The activation energies of dynamic thermal degradation (E_d) were calculated using Kissinger and Ozawa's methods. The thermal degradation mechanism was characterized using thermogravimetric analysis/infrared spectrometry (TG‐IR). In addition, the flame retardancy of phosphorus‐modified epoxy thermosets was evaluated using limiting oxygen index (LOI) and UL‐94 vertical test methods. Via an ingenious design, phosphonate groups were successfully introduced into the backbone of the epoxies; the flame retardancy of phosphorus‐modified epoxy thermosets was distinctly improved. Due to incorporation of C?N imine group, the phosphorus‐modified epoxy thermosets exhibited high thermal stabilities; the values of glass‐transition temperatures (T_gs) were about 201–210°C, the values of E_d were about 220–490 kJ/mol and char yields at 700°C were 49–53% in nitrogen and 45–50% in air. These results showed an improvement in the thermal properties of phosphorus‐modified epoxy by the incorporation of C?N imine groups. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of a triazine ring‐containing charring agent on fire retardancy and thermal degradation of intumescent flame retardant epoxy resins

A triazine ring‐containing charring agent (PEPATA) was synthesized via the reaction between 2,6,7‐trioxa‐l‐phosphabicyclo‐[2.2.2]octane‐4‐methanol (PEPA) and cyanuric chloride. It was applied into intumescent flame retardant epoxy resins (IFR‐EP) as a charring agent. The effect of PEPATA on fire retardancy and thermal degradation behavior of IFR‐EP system was investigated by limited oxygen index (LOI), UL‐94 test, microscale combustion calorimetry (MCC), thermogravimetric analysis (TGA) and thermogravimetric analysis/infrared spectrometry (TG‐IR). The glass transition temperatures (T_g) of IFR‐EP systems were studied by dynamic mechanical analysis (DMA). The LOI values increased from 21.5 for neat epoxy resins (EPs) to 34.0 for IFR‐EP, demonstrating improved flame retardancy. The TGA curves showed that the amount of residue of IFR‐EP system was largely increased compared to that of neat EP at 700 °C. The new IFR‐EP system could apparently reduce the amount of decomposing products at higher temperatures and promotes the formation of carbonaceous charred layers that slowed down the degradation. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis of a caged bicyclic phosphates derived anhydride and its performance as a flame‐retardant curing agent for epoxy resins

A novel curing and flame‐retardant agent (PEPA‐TMAC) was successfully synthesized. The chemical structure was characterized by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR). Use of PEPA‐TMAC as part of the curing agent in combination with another anhydride for a commercial epoxy resin (EP) was studied. Results of differential scanning calorimetry (DSC) indicated that PEPA‐TMAC was an effective curing agent for EP. The dynamic mechanical analysis (DMA) results showed that the glass transition temperature (T_g) and cross‐linking density (V_e) of EP composites exhibited an increase trend with the addition of PEPA‐TMAC. The limiting oxygen index (LOI) value of EP composites reached 26.9%, and the cone calorimeter results indicated that peak heat release rate (PHRR), total heat release (THR), smoke produce rate (SPR), and total smoke produce (TSP) remarkably decreased with increasing PEPA‐TMAC content. TGA data showed that the addition of PEPA‐TMAC greatly increased the amount of residual char during combustion. The morphology of the residual char was studied by SEM and showed that the addition of PEPA‐TMAC greatly increased the stability of EP composites. The thermogravimetric analysis (TGA), energy‐dispersive X‐ray spectroscopy (EDS), and FTIR results revealed the flame‐retardant mechanism that PEPA‐TMAC can promote the formation of charred layers with the phospho‐carbonaceous complexes in the condensed phase during burning of EP composites.     

Synergistic flame‐retardant effect and mechanisms of boron/phosphorus compounds on epoxy resins

To explore the component synergistic effect of boron/phosphorus compounds in epoxy resin (EP), 3 typical boron compounds, zinc borate (ZB), boron phosphate (BPO₄), and boron oxide (B₂O₃), blended with phosphaphenanthrene compound TAD were incorporated into EP, respectively. All 3 boron/phosphorus compound systems inhibited heat release and increased residue yields and exerted smoke suppression effect. Among 3 boron/phosphorus compound systems, B₂O₃/TAD system brought best flame‐retardant effect to epoxy thermosets in improving the UL94 classification of EP composites and also reducing heat release most efficiently during combustion. B₂O₃ can interact with epoxy matrix and enhance the charring quantity and quality, resulting in obvious condensed‐phase flame‐retardant effect. The combination of condensed‐phase flame‐retardant effect from B₂O₃ and the gaseous‐phase flame‐retardant effect from TAD effectively optimized the action distribution between gaseous and condensed phases. Therefore, B₂O₃/TAD system generated component synergistic flame‐retardant effect in epoxy thermosets.     

Nanostructures and thermal‐mechanical properties of cyanate ester/epoxy thermosets modified with poly(ethylene oxide)‐poly(propylene oxide)‐poly(ethylene oxide) triblock copolymer

Phase structures and mechanical properties of epoxy/acryl triblock copolymer alloys using several curing agents were studied. The nanostructured thermosets were obtained at the compositions investigated for every blends studied. The dependence of the morphological structures on block copolymer content and dicyanate ester, 2,2′‐bis(4‐cyanatophenyl) isopropylidene (BCE)/epoxy (EP) ratio for thermosetting blends was interpreted on the basis of the difference in hydrogen bonding interactions and reaction resulting from the cross‐linked network structures of matrixes. Moreover, the effect of F68 (poly(ethylene oxide)‐co‐poly(propylene oxide)‐co‐poly(ethylene oxide) block copolymer) on the curing characteristics and performance of BCE/EP resin was discussed. Results show that the incorporation of F68 cannot only effectively promote the curing reaction of BCE/EP but can also significantly improve the toughness of the cured BCE/EP resin. In addition, the toughening effect of F68/EP is greater than single EP resin. For example, the notched impact strength of systems with BE‐80/20 (B and E being the overall contents of BCE and EP, respectively) modified with 10 wt% F68 showed 55% increase compared with neat BCE/EP resin and even is more than three times of that value for pure BCE resin, 5.9 kJ/cm². Copyright © 2015 John Wiley & Sons, Ltd.     

A vanillin-derived flame retardant based on 2-aminopyrimidine for enhanced flame retardancy and mechanical properties of epoxy resin

In order to give epoxy resin good flame retardance, a novel bio-based flame retardant based on 2-aminopyrimidine (referred to as VAD) was synthesized from renewable vanillin as one of the starting materials. Its structure was confirmed by NMR and mass spectra. The epoxy resins containing VAD were prepared by utilizing 4,4-diaminodiphenylmethane (DDM) as a co-curing agent, and their flame-retardant, mechanical and thermal properties and corresponding mechanisms were studied. VAD accelerated the cross-linking reaction of DDM and E51 (diglycidyl ether of bisphenol A). 12.5 wt% VAD made the epoxy resin achieve UL-94 V-0 rating and its limited oxygen index (LOI) value increase from 22.4% to 32.3%. The cone calorimetric testing results revealed the decline in the values of total heat release (THR) and peak of heat release rate (pk-HRR) and the obvious enhancement of residue yield. A certain amount of VAD enhanced the flame inhibition, charring and barrier effects, resulting in good flame retardance of the epoxy resin. Furthermore, the tensile strength, flexural strength and flexural modulus of the epoxy resin with 12.5 wt% loading of VAD were 6.5%, 14.9%, 15.2% higher than those of EP, indicating the strengthening effect of VAD. This work guarantees VAD to be a promising flame retardant for enhancing the fire retardancy of epoxy resin without compromising its mechanical properties.     

Development of novel phosphorus‐containing epoxy resins from renewable resources

Novel biobased epoxy resins were prepared from two fatty acid derivatives; epoxidized 10‐undecenoyl triglyceride and epoxidized methyl 3,4,5‐tris(10‐undecenoyloxy)benzoate, with 4,4′‐diaminodiphenylmethane as a crosslinking agent. The flame retardancy of these epoxy resins was improved by the addition of 10‐[2′, 5′‐bis(9‐oxiranyl‐nonayloxy)phenyl]‐9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide and by crosslinking with a phosphorus‐containing curing agent, bis(m‐aminophenyl)methylphosphine oxide. The thermal, thermomechanical, and flame‐retardant properties of the cured materials were measured with differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analysis, and the limiting oxygen index. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6717–6727, 2006     

Flame‐retardant epoxy resins with high glass‐transition temperatures. II. Using a novel hexafunctional curing agent: 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene 10‐yl‐tris(4‐aminophenyl) methane

We synthesized a novel phosphorus‐containing triamine [9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene 10‐yl‐tris(4‐aminophenyl) methane (dopo‐ta)] from the nucleophilic addition of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene 10‐oxide and pararosaniline chloride, using triethylamine as an acid receiver. We confirmed the structure of dopo‐ta by IR, mass, and NMR spectra and elemental analysis. dopo‐ta served as a curing agent for diglycidyl ether of bisphenol A (DGEBA) and dicyclopentadiene epoxy (hp7200). Properties such as the glass‐transition temperature (T_g), thermal decomposition temperature, flame retardancy, moisture absorption, and dielectric properties of the cured epoxy resins were evaluated. The T_g's of cured DGEBA/dopo‐ta and hp7200/dopo‐ta were 171 and 190 °C, respectively. This high T_g phenomenon is rarely seen in the literature after the introduction of a flame‐retardant element. The flame retardancy increased with the phosphorus content, and a UL‐94 V‐0 grade was achieved with a phosphorus content of 1.80 wt % for DGEBA/dopo‐ta/diamino diphenylmethane (DDM) systems and 1.46 wt % for hp7200/dopo‐ta/DDM systems. The dielectric constants for DGEBA/dopo‐ta and hp7200/dopo‐ta were 2.91 and 2.82, respectively, implying that the dopo‐ta curing systems exhibited low dielectric properties. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5971–5986, 2005     

Synthesis of DOPO‐based pyrazine derivative and its effect on flame retardancy and thermal stability of epoxy resin

A novel DOPO‐based pyrazine derivative 6‐((2‐hydroxyphenyl)(pyrazin‐2‐ylamino)methyl)dibenzo[c,e][1,2]oxaphosphinine 6‐oxide (DHBAP) was triumphantly synthesized by a two‐step addition reaction using 2‐aminopyrazine, 2‐hydroxybenzaldehyde and 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) as reactants, and characterized by Fourier‐transform infrared (FTIR), ³¹P nuclear magnetic resonance (NMR) and ¹H NMR. Afterwards, the addition type flame retardant (DHBAP) was utilized to modify epoxy resin (EP) by blending method. When the content of DHBAP in neat EP was 8 wt%, it reached to the V‐0 rating and the limited oxygen index (LOI) value up to 34.0%. Furthermore, according to the cone calorimeter (CC) test results, the heat release rate (HRR), total heat release (THR), smoke produce rate (SPR) and total smoke production (TSP) of EP/8% DHBAP decreased by 26.3%, 21.3%, 37.0% and 60.9% when compared with neat EP, respectively, indicating that DHBAP had good inhibition on heat and smoke releases. Eventually, the flame‐retardant mechanism of DHBAP was further explored by X‐ray photoelectron spectroscopy (XPS), Raman spectroscopy, and pyrolysis‐gas chromatography/mass spectrometry (Py‐GC/MS). The results showed that DHBAP had good flame‐retardant activity in the gasous‐condensed two phases.     

Flame retardant epoxy resins based on diglycidyloxymethylphenylsilane

Silicon‐containing epoxy resins were prepared from diglycidyloxymethylphenyl silane (DGMPS) and diglycidylether of bisphenol A (DGEBA) by crosslinking with 4,4′‐diaminodiphenylmethane (DDM). Several DGMPS/DGEBA molar ratios were used to obtain materials with different silicon contents. Their thermal, dynamomechanical, and flame‐retardant properties were evaluated and related to the silicon content. The weight loss rate of the silicon‐containing resins is lower than that of the silicon free resin. Char yields under nitrogen and air atmospheres increase with the silicon content. The LOI (limited oxygen index) values increased from 24 for a standard commercial resin to 36 for silicon‐containing resins, demonstrating improved flame retardancy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5580–5587, 2006     

New poly(amide–imide)s syntheses. XXIII. Synthesis and properties of poly(amide–imide)s derived from 4,4′‐[1,4‐phenylenebis(isopropylidene‐1,4‐phenyleneoxy)]dianiline and various bis(trimellitimide)s

A series of poly(amide–imide)s III_a–m containing flexible isopropylidene and ether groups in the backbone were synthesized by the direct polycondensation of 4,4′‐[1,4‐phenylenebis(isopropylidene‐1,4‐phenyleneoxy)]dianiline (PIDA) with various bis(trimellitimide)s II_a–m in N‐methyl‐2‐pyrrolidone (NMP) using triphenyl phosphite and pyridine as condensing agents. The resulting poly(amide–imide)s had inherent viscosities in the range of 0.80–1.36 dL/g. Except for those from the bis(trimellitimide)s of p‐phenylenediamine and benzidine, all the polymers could be cast from DMAc into transparent and tough films. They exhibited excellent solubility in polar solvents. The 10% weight loss temperatures of the polymers in air and in nitrogen were all above 495°C, and their T_g values were in the range of 201–252°C. Some properties of poly(amide–imide)s III were compared with those of the corresponding poly(amide–imide)s V prepared from the bis(trimellitimide) of diamine PIDA and various aromatic diamines. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 69–76, 1999     

Synthesis and application of a dual functional P/N/S‐containing microsphere with enhanced flame retardancy and mechanical strength on EP resin

A phosphazene derivative flame retardant with a highly cross‐linked microsphere structure, named poly(cyclotriphosphazene‐c‐sulfonyldiphenol) (PCPS) microspheres, were synthesized by 1‐pot reaction and then applied on flame retarded epoxy (EP) resin. The microstructure and chemical composition of PCPS microspheres were characterized using scanning electron microscopy, transmission electron microscopy, and element mapping. The thermal stability of PCPS microspheres and PCPS/EP composites was explored through thermogravimetric analysis. Thermogravimetric data showed that the PCPS microspheres have excellent thermal stability, and the char yield is about 43% at the end of 800°C. The incorporation of PCPS microspheres significantly increased the char yield of PCPS/EP composites. The flammability was investigated by limited oxygen index tests and cone calorimeter. The limited oxygen index value of PCPS/EP composite was increased to 29.8 from 26.6 when 3 wt% of PCPS microspheres was added. Compared with neat EP, the flame retardancy was greatly improved. The peak heat release rate and smoke production rate of PCPS/EP composites were reduced by 45.0% and 43.6%, respectively. The mechanical properties including tensile strength and modulus were both improved due to the enhancement of PCPS microspheres. The PCPS microspheres act as a dual function for improving both the flame resistance and mechanical strength of PCPS/EP system.     

Syntheses,structure, reactivity,and thermal properties of new cyclic phosphine oxide epoxy resins cured by diamines

A new type of epoxy resin which contained cyclic phosphine oxide group in the main chain was synthesized. The structure of the new type of epoxy resin was confirmed by elemental analyses (EA), infrared spectroscopy (IR), and ¹H-NMR and ¹³C-NMR spectroscopies. In addition, compositions of the new synthesized cyclic phosphine oxide epoxy resin (EPCAO) with three curing agents, e.g., bis(3-aminophenyl)methylphosphine oxide (BAMP), 4,4′-diamino-diphenylmethane (DDM), and 4,4′-diaminodiphenylsulfone (DDS), were used for making a comparison of its curing reactivity, heat, and flame retardancy with that of Epon828 and DEN438. The reactivities were measured by differential scanning calorimetry (DSC). Through the evaluation of thermal gravimetric analysis (TGA), those polymers which were obtained through the curing reactions between the new epoxy resin and three curing agents (BAMP, DDM, DDS) also demonstrated excellent thermal properties as well as a high char yield. © 1996 John Wiley & Sons, Inc.     

Preparation and characterization of microencapsulated LDHs with melamine‐formaldehyde resin and its flame retardant application in epoxy resin

Layered double hydroxides (LDHs) are emerging as a new and green high‐efficient flame retardant. But LDHs aggregate seriously because of their hydrophilicity, which affect deeply the mechanical and flame retardant properties of their composites. For the first time in this paper, microencapsulated LDHs (MCLDHs) with melamine‐formaldehyde (MF) resin were prepared by microencapsulation technology to enhance their compatibility and dispersion within epoxy resin (EP). The mechanical and flame retardant performances of EP/MCLDH composite were studied by comparing with EP/LDH composite. Results showed that the water contact angle of MCLDHs increased from 8.9° to 122.1°, which indicated good compatibility. The particle size of MCLDHs decreased sharply, and more than one‐third were up to submicron scale, which can be conducive to dispersion. Moreover, the tensile strength and elongation at break of EP/MCLDHs with different flame retardant contents were higher than those of EP/LDHs. And the addition of MCLDHs increased the glass transition temperature (Tg) of EP/MCLDHs, which meant a strong interfacial interaction. Besides, compared with EP/LDHs, the limiting oxygen index values of EP/MCLDHs were higher, and its peak of heat release rate and total heat release decreased by 16.3% and 5.5% respectively. EP/MCLDHs achieved from V‐1 to V‐0 rate with the increasing content of MCLDHs from 20% to 30%, while LDHs/EP never passed tests. In the process of heating, H₂O, CO₂, and NH₃ released from MCLDHs formed gaseous phase, and the remaining dense char layers and oxides produced condensed phase, which played an important role in inhibiting combustion.     

Synthesis of CeO2‐loaded titania nanotubes and its effect on the flame retardant property of epoxy resin

A series of CeO₂‐loaded titania nanotubes (CeO₂‐TNTs) hybrid materials with different CeO₂ loadings were synthesized by co‐precipitation method and then incorporated into epoxy resin (EP) to prepare CeO₂‐TNTs flame‐retardant epoxy nanocomposites. Structure and morphology characterization indicated the successful synthesis of CeO₂‐TNTs. The effect of CeO₂‐TNTs with different CeO₂ loading capacity on the flame retardance of EP was compared and analyzed by the thermogravimetric analysis, Cone and Raman. The results showed that CeO₂ loading could increase the carbon residue of nanocomposites, reduce the peak heat release rate (PHRR) and total heat release (THR), and improve the fire safety of EP. The residual carbon content of EP/0.1CeO₂‐TNTs sample at 700°C reached 19.8% with the lowest degradation rate, and the PHRR and THR were reduced to 680 kW/m² and 32.9 MJ/m², respectively. Such a significant improvement in flame‐retardant properties for EP could be attributed to the protective effect of CeO₂‐TNTs.