A novel high-efficient P/N/Si-containing APP-based flame retardant with a silane coupling agent in its molecular structure for epoxy resin

A flame retardant containing multiple antiflaming elements usually exhibits high-efficient flame retardancy. Here, a novel P/N/Si-containing ammonium polyphosphate derivative(APTES-APP) is synthesized from ammonium polyphosphate(APP) and silane coupling agent(3-aminopropyl)triethoxysilane(APTES)via cation exchange, which is quite different in the chemical structure from APTES-modified APP for retaining silicon hydroxyls. APTES-APP is highly efficient for the epoxy resin. 8%(mass) APTES-APP imparts excellent flame retardancy to the epoxy resin, with a V-0 rating at the UL-94 test(1.6 mm)and an LOI value of 26%(vol). The peak heat release rate and total smoke production of the flameretardant epoxy resin are decreased by 68.1% and 31.3%, respectively. The synergy of P/N/Si contributes to the well-expanded char residue with a strong and dense surface layer, which is a very good barrier against heat and mass transfer. Besides, there is no significant deterioration in the mechanical properties of flame-retardant epoxy resin thanks to silicon hydroxyls forming hydrogen bonds with epoxy molecules. Meanwhile, other molecules can be grafted onto APTES-APP via these silicon hydroxyls, if needed.Briefly, this work has developed a new strategy for amino silane as flame retardants. In conjunction with a low-cost and simple preparation method, APTES-APP has a promising prospect in the high-performance flame-retardant epoxy.

Influence of aliphatic epoxy monomer on the blowing-out effect in the flame retardant epoxy resins

An aliphatic epoxy monomer＂polypropyleneglycol-diglycidylether（PPGDGE,YF878）＂is loaded in the epoxy resins（EP）to evaluate the influence of epoxy structure on the blowing-out effect,which is caused by 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide（DOPO）and octaphenyl silsesquioxane（OPS）.The flame retarding properties of these EP composites were tested using the LOI and UL-94 procedures.The pyrolytic gases produced and the thermal stability of the EP composites with different flame retardants were detected by TGA-FTIR in air.The negative effect of YF878 was detected from the TTI,HRR,and p-HRR results after the cone calorimeter test.The char produced by the EP composites after the cone calorimeter test was investigated by FTIR.It is proposed that the aliphatic chain of the YF878 is easy to break down and produce combustible gases,so it does not easily form a crosslinked structure in the condensed phase.These results are very helpful for investigation of the conditions under which the blowing-out effect in epoxy resins can be caused by synergy of phosphorous and silicon.

Phosphorylated Salicylic Acid as Flame Retardant in Epoxy Resins and Composites

A novel,versatile flame retardant substructure based on phosphorylated salicylic acid(SCP)is described and used in the synthesis of new flame retardants for HexFlow
RTM6,a high-performance epoxy resin used in resin transfer molding processes as composite matrix.The starting material salicylic acid can be obtained from natural sources.SCP as reactive phosphorus chloride is converted with a novolak,a novolak containing 9,10-dihydro-9-oxa-10-phospha-phenanthrene-10-oxide(DOPO)substituents or DOPO-hydroquinone to flame retardants with sufficient thermal stability and high char yield.Additionally,these flame retardants are soluble in the resin as well as react into the epoxy network.The determined thermal stability and glass transition temperatures of flame retarded neat resin samples as well as the interlaminar shear strength of corresponding carbon fiber reinforced composite materials showed the applicability of these flame retardants.Neat resin samples and composites were tested for their flammability by UL94 and/or flame-retardant performance by cone calorimetry.All tested flame retardants decrease the peak of heat release rate by up to 54%for neat resin samples.A combination of DOPO and SCP in one flame retardant shows synergistic effects in char formation and the mode of action adapts to neat resin or fiber-reinforced samples,so there is efficient flame retardancy in both cases.Therefore,a tailoring of SCP based flame retardants is possible.Additionally,these flame retardants efficiently reduce fiber degradation during combustion of carbon fiber-reinforced epoxy resins as observed by scanning electron microscopy and energy dispersive X-ray spectroscopy.

Facile Synthesis of a Novel Bio-Based P-N Containing Flame Retardant for Effectively Reducing the Fire Hazards of Epoxy Resin

In this work,a bio-based flame retardant(Cy-HEDP)was synthesized from cytosine and HEDP through a facile salt-forming reaction and embedded into epoxy matrix to improve the flame retardancy and smoke suppression performance.The product Cy-HEDP was well characterized by FTIR,^(1)H and^(31)P NMR and SEM tests.On the basis of the results,by adding 15 wt%Cy-HEDP,the EP15 can pass UL-94 V-0 rating,and the total smoke production(TSP)as well as total heat release(THR)can be decreased by 61.05%(from 22.61 to 8.7 m^(2)/m^(2))and 39.44%(from 103.19 to 62.50 MJ/m^(2))in comparison to the unfilled EP,reflecting the attenuated smoke toxicity and impeded heat generation.According to the analysis results of residual char,it can be concluded that Cy-HEDP possessed the ability to promote the formation of continuous and dense char layers,which would be a physical barrier to insulate oxygen and prevent heat feedback during the combustion of EP.This work provide inspiration towards developing bio-based flame retardant,probably extending the prospects to other polymeric material system.

A Novel Bio-Based Zirconium Phosphonate as a Flame Retardant and Smoke Suppressant for Epoxy Resin

Although epoxy resin has been widely used in various fields,it still suffers from some problems including brittleness and flammability.In this study,a new phosphonic acid,N,N-bis(phosphomethyl)glycine(GDMP),was prepared by Mannich reaction with bio-based glycine and then a novel layered zirconium phosphonate(ZrGDMP)was synthesized using GDMP and zirconyl chloride hydrate as reactants.The chemical structure of ZrGDMP was well characterized by 1 H and 31P NMR,SEM,XRD and XPS.The effect of ZrGDMP on the flame retardancy,smoke suppression,strengthening and toughening performances of the epoxy matrix was investigated and evaluated.TGA results indicated that compared with pure EP,ZrGDMP-EP composites showed higher char yield due to the catalytic charring effect of ZrGDMP.The pure EP exhibited high flammability,while ZrGDMP-EP composites possessed excellent thermal stability and remarkable fire resistance.The PHRR,THR,and TSP values of 3wt%ZrGDMP-EP were obviously declined by 39.6%,40.2%,and 24.9%compared to these of pure EP.Moreover,the tensile and impact tests implied that the addition of ZrGDMP can significantly reinforce the toughness as well as the strength of EP in terms of higher impact strength(24.8 kJ/m^(2))and tensile strength(57.7 MPa),which was mainly contributed to the uniform dispersion of ZrGDMP within the EP matrix.

A Study on a Magnesium-Based Layered Composite Used as a Flame Retardant for Phenolic Epoxy Resins

The effects of a magnesium-based layered composite on the flammability of a phenolic epoxy resin(EP)are studied.In order to produce the required composite material,first,magnesium hydroxide,aluminum salt and deionized water are mixed into a reactor according to a certain proportion to induce a hydrothermal reaction;then,the feed liquid is filtered out using a solid-liquid separation procedure;finally,the material is dried and crushed.In order to evaluate its effects on the flammability of the EP,first,m-phenylenediamine is added to EP and vacuum defoamation is performed;then,EP is poured into a polytetrafluoroethylene mold,cooled to room temperature and demoulded;finally,the magnesium-based layered composite is added to EP,and its flame retardance is characterized by thermogravimetric analysis,limiting oxygen index and cone calorimetry.The X-ray diffraction patterns show that the baseline of magnesium-based layered composite is stable and the front shape is sharp and symmetrical when the molar ratio of magnesium to aluminium is 3.2:1;with the addition of magnesium-based layered composite,the initial pyrolysis temperature of EP of 10%,15%and 30%magnesium-based layered composite decreases to 318.2°C,317.9°C and 357.1°C,respectively.After the reaction,the amount of residual carbon increases to 0.1%,3.45%and 8.3%,and the limiting oxygen index increases by 28.3%,29.1%and 29.6%,respectively.The maximum heat release rate of cone calorimeter decreases gradually.The optimum molar ratio of Mg:Al for green synthesis is 3.2:1,and the NO_(3)-intercalated magnesium-based layered composite has the best flame retardance properties.

Formulating Novel Halogen-Free Synergistic Flame Retardant Epoxy Resins for Vacuum Assisted Resin Infusion Composites

The most common process to manufacture advanced composites is the costly autoclave.One of the out-of-autoclave alternatives is the low-cost vacuum assisted resin infusion(VARI)which produces quality parts with less pollution.Epoxy resin is a widely used composite matrix resin,but its high flammability limits its use as interior composite parts for vehicles.The usual flame retardant for epoxy involves halogen,which is effective but has high smoke toxicity.As a result,halogen-free flame retardant epoxy resin systems become dominant.In this paper,phosphorus flame retardant was combined with benzoxazine(BOZ)to produce synergistic effect and achieve satisfactory flame retardance,as well as mechanical improvement for the epoxy resin.Differential scanning calorimetry(DSC),dynamic mechanical analysis(DMA),thermal gravitational analysis(TGA),the cone calorimeter(CC),and limiting oxygen index(LOI)were used to characterize the resins.The results showed significant improvement on the flame retardance of the synergistically modified resins.Specifically,the carbon residue increased by 113.6%,and the char thickness increased by 6 to 7 times,compared to those of the flammable benchmark resin.The LOI reached 33 and passed the UL94 V-0 vertical burn rating.The modified resins also exhibited adequate stability and viscosity suitable for VARI processes.

Recent advances in constructing new type of epoxy resin flame retardant system using ammonium polyphosphate

In recent years,research has focused heavily on the investigation of functionalized ammonium polyphosphate(APP)flame retardants to improve the fire safety of epoxy resins(EP).The reason for this is the dual nature of APP's performance in fire protection of EP.This article provides a comprehensive overview of the advances in the use of functionalized APP flame retardants to improve the fire resistance of EP materials.It then presents the improvement of the modification of the functionalized APP flame retardants in terms of the hydrophobicity,compatibility and catalytic ability of the flame retardants,as well as the effects on the fire resistance,heat resistance,smoke reduction and mechanical properties of the EP composites.After the summary and comparison of the relevant studies,it is clear that the functionalized APP flame retardants can effectively improve the fire safety of EP composites and offset the adverse effects of APP in EP flame retardant applications.In addition,APP flame retardants can obtain various excellent functions through the use of materials with different properties,and the interaction between APP and materials can also lead to more efficient fire protection.However,the current problem is to find ways to streamline the process and minimise the costs associated with functionalized APP flame retardants,as well as to use them effectively in industrial production.We hope that this review can provide valuable hints and insights for the practical application of functionalized APP in EP and perspectives for future research.

Flame-retardant Mechanism of Magnesium Oxychloride in Epoxy Resin

Flame-retardant mechanism of magnesium oxychloride （M OC） in EP was in-vestigated by limiting oxygen index （LOI）, XRD, SEM, TG-DTG and DSC. The results show that MOC performed well as an inorganic flame-retardant in EP. When the content of MOC is 50%, the LOI of EP reaches 29.6% and mass of residual char reaches 9.6%. The flame retarde mechanism of MOC is due to the synergies of diluting, cooling, catalyzing char forming and obstructing effects.

Synthesis, Characterization and Flame-retardant Properties of Epoxy Resins and AACHH Composites

Flame retardant epoxy resins were prepared by a simple mixed method using ammonium aluminum carbonate hydroxy hydrate （AACHH） as a halogen-free flame retardant. The prepared samples were characterized by X-ray diffraction, thermogravimetric and differential scanning calorimetry, scanning electron microscope and limiting oxygen index（LOI） experiments. Effects of AACHH content on LOI of epoxy resins/AACHH composite and flame retardant mechanism were investigated and discussed. Results show that AACHH exhibites excellent flame-retardant properties in epoxy resin（EP）. When the content of AACHH was 47.4%, the LOI of EP reached 32.2%. Moreover, the initial and terminal decomposition temperature of EP increased by 48 ℃ and 40 ℃, respectively. The flame retarded mechanism of AACHH is due to the synergic flame retardant effects of diluting, cooling, decomposition resisting and obstructing.

A Vanillin-Derived,DOPO-Contained Bisphenol as a Reactive Flame Retardant for High-Performance Epoxy Thermosets

Quest for bio-based halogen-free green flame retardant has attracted many concerns in recent years.Herein a reactive functional flame retardant containing phosphorus VDP is synthesized from vanillin,9,10-dihydro-9-oxa-10-phosphophene-10-oxide(DOPO)and phenol via a facile way.VDP is characterized with^(1)H NMR,^(31)P NMR,FTIR and Time of Flight Mass Spectrometry,and used as a new reactive flame retardant for bisphenol epoxy thermosets.Thermogravimetry analysis shows that when the VDP loading is only 0.5P%(based on phosphorus content),the residue increases from 14.2%to 21.1%at 750℃ in N_(2)compare with neat DGEBA.Correspondingly,the limit oxygen index increased to 29.6%,and flame retardancy reaches UL-94 V0 grade.Micro combustion calorimetry(MCC)and cone calorimetry analyses demonstrate that VDP can significantly lower flammability of the epoxy thermoset.With only 0.5P%of VDP,the heat release rate,total heat release rate and smoke production are reduced markedly.At the same time,the mechanical properties of the modified epoxy thermosets are also improved.The impact strength increases by 34%and the flexural strength increased by 23%,with 1.5P%of VDP.In short,VDP not only improves the flame retardancy,but also improves the mechanical properties of the epoxy thermosets.

Preparation of Poly(phosphoric acid piperazine) and Its Application as an Effective Flame Retardant for Epoxy Resin

A phosphorus-nitrogen containing flame retardant additive of poly（phosphoric acid piperazine）, defined as PPAP, was synthesized by the salt-forming reaction between anhydrous piperazine and phosphoric acid, and the dehydration polymerization under heating in nitrogen atmosphere. Its chemical structure was well characterized by Fourier transform infrared（FTIR） spectroscopy, ^（13）C and ^（31）P solid-state nuclear magnetic resonance measurements. The synthesized PPAP and curing agent m-phenylenediamine were blended into epoxy resin（EP） to prepare flame retardant EP thermosets. The effects of PPAP on the fire retardancy and thermal degradation behavior of cured EP/PPAP composites were investigated by limiting oxygen index（LOI）, vertical burning（UL-94）, thermogravimetric analysis/infrared spectrometry（TG-IR） and cone calorimeter tests. The morphologies and chemical compositions of char residues for cured epoxy resin were investigated by scanning electron microscopy（SEM） and X-ray photoelectron spectroscopy（XPS）, respectively. The results demonstrated that the flame retardant EP thermosets successfully passed UL-94 V-0 flammability rating and the LOI value was as high as 30.8% when incorporating 5 wt% PPAP into the EP thermosets. The TGA results indicated that the synthesized PPAP flame retardant additive possessed high thermal stability and excellent charring capability. Meanwhile, the incorporation of PPAP stimulated the epoxy resin matrix to decompose and charring ahead of time due to its catalytic decomposition effect, which led to a higher char yield at high temperature. The morphological structures and the analysis results of XPS for char residues of EP thermosets revealed that the introduction of PPAP benefited the formation of a sufficient, more compact and homogeneous char layer containing phosphorus-nitrogen flame retardant elements on the material surface during combustion. The formed char layer with high quality effectively prevented the heat transmission and diffusion, limited the production of combustible gases, and inhibited the emission of smoke, leading to the reduction of heat and smoke release.

PROMOTION EFFECT OF MELAMINE ON FLAME RETARDANCY OF EPOXY RESINS CONTAINING CAGED BICYCLIC PHOSPHATE

Caged bicyclic phosphate （CBP） and its dimelamine salt （PDS） were synthesized and added to epoxy resins to obtain the flame retarded epoxy resin composites. The flammability of the composites was characterized by the limiting oxygen index （LOI） and cone calorimeter tests. The LOI values of flame retarded composites increase consistently with the increase of flame retardant amounts, and they are almost the same when the loading of CBP is the same as that of PDS, although the phosphorus content of PDS is much lower than that of CBP. The total heat release increases in the order of CBP30/ER 〈 PDS30/ER 〈 PDS15/ER 〈 CBPI5/ER, whereas that of specific extinction area is CBP15/ER 〉 CBP30/ER 〉 PDS30/ER ≌ PDS15/ER. PDS exhibits more effective inhibition of oxidation of combustible gases. In the tests of thermogravimetric analyses （TG） and Fourier transform infrared spectroscopy （FT-IR）, it is found that the degradation of the composites is influenced greatly by the addition of flame retardants. By scanning electron microscopy （SEM）, a thick and tight char-layer is observed for PDS30/ER, resulting from the interaction of nitrogen species with phosphorus species. Therefore, the combination of CBP with melamine in the flame retarded system can improve the flame retardancy greatly.

Synthesis and Property of Flame Retardant Epoxy Resins Modified with 2-（Diphenylphosphinyl）-l,4-benzenediol

2-（Diphenylphosphinyl）-1,4-benzenediol（DPO-HQ） was synthesized by the reaction of diphenylphos- phine oxide（DPO） with 1,4-benzoquinone（BQ）, and characterized by Fourier transform infrared（FTIR）, and nuclear magnetic resonance（1H NMR, 13C NMR, 31p NMR） spectrometries. The thermal stability of DPO-HQ was investi- gated by thermogravimetric analysis（TGA）. Flame retardant epoxy resin was synthesized based on DPO-HQ. The thermal properties and burning performance of cured epoxy resins were measured by differential scanning calorime- try（DSC）, thermogravimetric analysis（TGA）, limited oxygen index（LOI） and vertical burning test（UL-94V）. The morphologies of cured epoxy resins after combustion were investigated by scanning electron microscopy（SEM） and electron probe microanalysis（EPMA）. Moreover, the thermal stability（both in air and in N2） of DPO-HQ and its cured epoxy resin was compared with that of 10-（2,5-dihydroxyphenyl）-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10- oxide（DOPO-HQ） and its cured epoxy resin. The thermal stability of DPO-HQ is comparable with that of DOPO-HQ, while the thermal stability of cured epoxy resin based on DPO-HQ is better than that based on DOPO-HQ.

New flame retardant epoxy resins based on cyclophosphazene-derived curing agents

To obtain high-efficiency flame retardancy of epoxy resins,a cyclophosphazene derivative tri-(ohenylenediamino)cyclotriphosphazene(3 ACP)was successfully synthesized and used as a curing agent for the thermosetting of an epoxy resin system.The flame retardant properties,thermal stability,and pyrolysis mechanism of the resultant thermosets were investigated in detail.The experiments indicated that the synthesized thermoset achieved a UL-94 V-0 rate under a vertical burning test as well as a limiting oxygen index(LOI)of 29.2%,which was able to reach V-0 even when a small amount of 3 ACP was incorporated.Scanning electronic microscopic observation demonstrated that the char residue of the thermosets was extremely expanded after the vertical flame test.Thermal analysis showed that the samples had a lower initial decomposition temperature when 3 ACP was introduced into the epoxy resin systems.This indicates that the carbonization ability of the thermosets was significantly improved at elevated temperatures.In addition,the incorporation of 3 ACP can effectively suppress the release of combustible gases during the pyrolysis process,and the decomposition of E-44/DDS-3 ACP curing systems also promotes the formation of polyphosphoramides charred layer in the condensed phase.The investigation on the chemical structures of both the gaseous and condensed phase pyrolysis process confirmed the flame-retardant mechanism of the 3 ACP-cured epoxy resins.Therefore,the nonflammable halogen-free epoxy resin developed in this study has potential applications in electric and electronic fields for environment protection and human health.

Improving Thermal and Flame Retardant Properties of Epoxy Resin with Organic NiFe-Layered Double Hydroxide-Carbon Nanotubes Hybrids

To improve the dispersion of carbon nanotubes （CNTs） and flame retardancy of layered double hydroxide （LDH） in epoxy resin （EP）, organic nickel-iron layered double hydroxide （ONiFe-LDH-CNTs） hybrids were assembled through co-precipitation. These hybrids were further used as reinforcing filler in EP. EP/ONiFe-LDH-CNTs nano- composites containing 4 wt% of ONiFe-LDH-CNTs with different ratios of ONiFe-LDH and CNTs were prepared by ultrasonic dispersion and program temperature curing. The structure and morphology of the obtained hybrids were characterized by different techniques. The dispersion of nanofillers in the EP matrix was observed by transmission electron microscopy （TEM）. The results revealed a coexistence of exfoliated and intercalated ONiFe-LDH- CNTs in polymer matrix. Strong combination of the above nanofillers with the EP matrix provided an efficient thermal and flame retardant improvement for the nanocomposites. It showed that EP/ONiFe-LDH-CNTs nanocomposites exhibited superior flame retardant and thermal properties compared with EP. Such improved thermal properties could be attributed to the better homogeneous dispersion, stronger interfacial interaction, excellent charring performance of ONiFe-LDH and synergistic effect between ONiFe-LDH and CNTs.

Synergistic Flame-retardant Effect of Epoxy Resin Combined with Phenethyl-bridged DOPO Derivative and Graphene Nanosheets

Phenethyl-bridged DOPO derivative(DiDOPO)was combined with graphene nanosheets(GNSs)in epoxy resin(EP)to improve its flame retardancy.The results indicated that the introduction of only 1.5 wt%DiDOPO/1.5 wt%GNS in EP increased the limited oxygen index(LOI)from 21.8%to 32.2%,hence meeting UL 94 V-0 rating.The thermogravimetric analyses revealed that char yield rose in presence of GNSs to form thermally stable carbonaceous char.The decomposition and pyrolysis products in gas phase were characterized by thermogravimetry-Fourier transform infrared spectroscopy(TG-FTIR),and the release of large amounts of phosphorus was detected in the gas phase.The evaluation of flame-retardant effect by cone calorimetry demonstrated that GNSs improved the protective-barrier effect of fire residue of EP/DiDOPO/GNS.The latter was further confirmed by digital photography and scanning electron microscopy(SEM).Also,Raman spectroscopy showed that GNSs enhanced graphitization degree of the resin during combustion.Overall,the combination of DiDOPO with GNSs provides an effective way for developing high-performance resins with improved flame retardancy.

Synthesis of Bio-based Epoxy Containing Phosphine Oxide as a Reactive Additive Toward Highly Toughened and Fire-retarded Epoxy Resins

The integration of high mechanical toughness,impact strength as well as excellent flame-retardant properties toward epoxy resins(EPs)have always been a dilemma.The inadequate overall performance of EPs severely restricts their sustainable utilization in engineering aspects over long-term.Herein,a new bio-based agent(diglycidyl ether of magnolol phosphine oxide,referred as DGEMP)derived from magnolol(classified as lignan),extracted from natural plants Magnolia officinalis,was successfully synthesized and further employed as a flameretardant reactive additive to diglycidyl ether of bisphenol A(DGEBA).As demonstration,the composite resin,DGEBA/15DGEMP(15 wt%DGEMP),achieved an Underwriters Laboratories-94 V-0 rating with a high limiting oxygen index(LOI)value(41.5%).In cone calorimeter tests,it showed that heat release and smoke production were effectively inhibited during combustion,wherein the peak heat release rate(PHRR)value of DGEBA/15DGEMP was reduced by 50%compared to neat DGEBA.Additionally,it exhibited a superior tensile strength(82.8 MPa),toughness(5.11MJ/m^(3))and impact strength(36.5 k J/m^(2)),much higher than that of neat DGEBA(49.7 MPa,2.05 MJ/m^(3)and 20.9 k J/m^(2)).Thus,it is highly anticipated that DGEMP imparts significantly improved mechanical and fire-retarded properties to conventional EPs,which holds a great potential to address the pressing challenges in EP thermosets industry.

A bio-based epoxy resin derived from p-hydroxycinnamic acid with high mechanical properties and flame retardancy

Recent advances in epoxy resins have been forward to achieving high mechanical performance,thermal stability,and flame retardancy.However,seeking sustainable bio-based epoxy precursors and avoiding introduction of additional flame-retardant agents are still of increasing demand.Here we report the synthesis of p-hydroxycinnamic acid-derived epoxy monomer(HCA-EP)via a simple one-step reaction,and the HCA-EP can be cured with 4,4′-diaminodiphenylmethane(DDM)to prepare epoxy resins.Compared with the typical petroleum-based epoxy resin,bisphenol A epoxy resin,the HCA-EP-DDM shows a relatively high glass transition temperature(192.9℃)and impressive mechanical properties(tensile strength of 98.3 MPa and flexural strength of 158.9 MPa).Furthermore,the HCA-EP-DDM passes the V-1 flammability rating in UL-94 test and presents the limiting oxygen index of 32.6%.Notably,its char yield is as high as 31.6%under N_(2),and the peak heat rate release is 60%lower than that of bisphenol A epoxy resin.Such findings provide a simple way of using p-hydroxycinnamic acid instead of bisphenol A to construct high-performance bio-based thermosets.

Flame-Retarding Epoxy Resin Films by Curing with Organophosphorus Containing Diamine

An organophosphorus-based diamine has been synthesized and used as a curing and flame retarding bifunctional agent for epoxy resins.This phosphorodiamidate functions not only as a crosslinking materials in the Epon 828 epoxy resin curing process but also as a fire retarding compound to produce thin films or composites upon curing.This phosphorus-containing reactive amine was synthesized via condensation of phenyphosphonic dichloride with ethylenediamine in the presence of sodium methoxide.The product was then purified and later characterized by NMR and FTIR spectroscopy as well as MALDI-TOF mass spectrometry.Kinetics studies of the curing reaction of the phosphorodiamidate were carried out in comparison with the non-phosphorus containing ethylenediamine reference crosslinking agent.Thermal stability of the cured epoxy ware investigated by thermogravimetric analysis(TGA)and differential scanning calorimetry(DSC).Moreover,flame retardant properties of the obtained materials was investigated by limiting oxygen index(LOI)measurements as well as the UL-40 method.The obtained results show that epoxy resin cured with phosphorodiamidate possesses higher thermostability compared to the epoxy cured with the regular ethylenediamine counterpart.This is evident by higher amount of char formed upon burning.More importantly,the LOI value of 27 was observed in the phosphorodiamidate-cured epoxy resin compared with LOI of 20 of the epoxy resin cured with ethylenediamine where no phosphorus was present.The UL-94 highest rating of V-0 materials was obtained with only about 2-3 wt%of the phosphorus element.The chemistry,curing kinetics,and thermal properties of these new epoxy formulations are discussed.