Preparation and flame retardancy of an intumescent flame-retardant epoxy resin system constructed by multiple flame-retardant compositions containing phosphorus and nitrogen heterocycle

doi:10.1016/j.polymdegradstab.2015.05.019

Polymer Degradation and Stability

Volume 119, September 2015, Pages 251-259

https://doi.org/10.1016/j.polymdegradstab.2015.05.019 Get rights and content

Abstract

A phosphorous/nitrogen-containing reactive phenolic derivative (DOPO–HPM) was synthesized via the addition reaction between 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and N-(4-hydroxyphenyl) maleimide (HPM). The structure of DOPO–HPM was characterized by Fourier transform infrared spectroscopy (FTIR), ¹H and ³¹P nuclear magnetic resonance (NMR) and elemental analysis (EA). The studied flame-retardant epoxy resin systems were prepared by copolymerizing diglycidyl ether of bisphenol-A (DGEBA) with DOPO–HPM, triglycidyl isocyanurate (TGIC) and 4,4′-diamino-diphenyl sulfone (DDS). Thermal and flame retardant properties of the cured epoxy resins were investigated by differential scanning calorimeter (DSC), thermogravimeric analysis (TGA), limited oxygen index (LOI) measurement, UL94 test and cone calorimeter. The DSC results indicated that the modified epoxy resins showed little fluctuation in glass transition temperatures (197–205 °C). The results of combustion tests indicated that the modified epoxy resin systems exhibited excellent flame retardant properties. The P-1 and P-1.25 systems acquired LOI values of 37% and 38.5%, respectively, and achieved a UL94 V-0 rating. Compared with the P-0 system, the peak of heat release rate (pk-HRR), average of effective heat of combustion (av-EHC) and total heat release (THR) of P-1.25 system decreased by 61.4%, 23.4% and 34.9%, respectively. In addition, the total smoke production (TSP) of the modified epoxy resin systems decreased with the increasing content of flame retardants, indicating the smoke suppression effect of the flame-retardant systems. Through visual observation, the char residues after cone calorimetry test exhibited intumescent structures with continuous and compact surfaces. The flame retardant mechanism was studied by FTIR, scanning electron microscope (SEM), cone calorimeter and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS).

Introduction

Epoxy resins (EPs) are widely used as advanced matrix resin in the electronic and electrical industries due to their attractive characteristics of high tensile strength and modulus, high adhesion to substrates, good chemical and corrosion resistance, excellent dimensional stability and superior electrical properties [1], [2], [3], [4], [5]. However, conventional epoxy resins are flammable and can not satisfy high flame-resistance requirement of advanced materials [6], [7]. So far, research works on improving the flame retardation of epoxy resins are very attractive for advanced application. Traditionally, halogenated compounds have been widely used to endow epoxy resins with flame resistance. Currently, halogen-containing compounds are not preferred for environmental reasons [8], [9], [10]. Therefore, there is a trend to develop and apply halogen-free flame retardants.

Phosphorus-containing flame retardants modified epoxy resins are considered to be more environmentally friendly and have received outstanding attention [11], [12], [13], [14], [15], [16]. Among the phosphorus-containing flame retardants, DOPO and its derivatives have received considerable attention due to their high reactivity with epoxy monomers, high thermal stability and flame retardant efficiency [17], [18], [19], [20], [21]. However, single flame retardant composition limits the further enhancing of flame retardancy of the modified epoxy resins [22], [23], [24]. Therefore, DOPO-based epoxy resin systems with multiple flame-retardant compositions have been prepared and the synergistic effect of multiple flame-retardant functional groups on flame retardancy of epoxy resins has been observed as reported in a few works [25], [26], [27], [28], [29], [30], [31], [32].

In this work, a phosphorous/nitrogen-containing reactive phenolic derivative (DOPO–HPM) was synthesized via the addition reaction between DOPO and HPM. The structure of DOPO–HPM was characterized by Fourier transform infrared spectroscopy (FTIR), ¹H and ³¹P nuclear magnetic resonance (NMR) and elemental analysis (EA). The investigated flame-retarded epoxy resin systems were prepared by copolymerizing DGEBA with DOPO–HPM, TGIC and DDS. Thermal and flame-retardant properties of the cured epoxy resins were investigated by differential scanning calorimeter (DSC), thermogravimeric analysis (TGA), limited oxygen index (LOI) measurement, UL94 test and cone calorimeter. The flame retardant mechanism was studied by FTIR, SEM, cone calorimeter and Py-GC/MS.

Section snippets

Materials

Diglycidyl ether of bisphenol-A (DGEBA) with an epoxide equivalent weight (EEW) of about 188 g/equiv was provided by Yueyang Baling Huaxing Petrochemical Co., Ltd. N-(4-hydroxyphenyl) maleimide (HPM) was obtained from Puyang Willing Chemicals Co., Ltd. 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was purchased from Huizhou Sunstar Technology Co., Ltd. Triglycidyl isocyanurate (TGIC) was purchased from Jinan Zian Chemicals Co., Ltd. Triphenyl phosphine (TPP), 4,4′-Diamino-diphenyl

Synthesis of DOPO–HPM

As shown by FTIR spectra in Fig. 1, DOPO–HPM showed several characteristic absorption peaks: the peak at 3224 cm⁻¹ was assigned to the stretching vibration of OH; the peaks at 1777 and 1706 cm⁻¹ were assigned to the stretching vibration of C double bond O; the peak at 1393 cm⁻¹ was assigned to the stretching vibration of C–N; the peak at 1189 cm⁻¹ was assigned to the stretching vibration of PO; the peaks at 937 and 758 cm⁻¹ were assigned to the stretching vibration of P–O–Ph. In addition, the stretching

Conclusions

DOPO–HPM was successfully synthesized via the addition reaction between DOPO and HPM. The studied flame-retarded epoxy resin systems were prepared by copolymerizing DGEBA with DOPO–HPM, TGIC and DDS. The DSC results indicated that the modified epoxy resins showed little fluctuation in glass transition temperatures (197–205 °C). The results of combustion tests indicated that the modified EP systems exhibited excellent flame retardant properties. Specifically, the P-0.25 thermoset had a LOI value

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Citation Excerpt :
Moreover, DOPO-HPM containing maleimide was used as a reactant to mix with DGEBA and triglycidyl isocyanurate (TGIC), and the sufficient chemical reaction occurred between hydroxy and epoxide group during the curing process. From Ref. [131], this DGEBA/DDS/DOPO-HPM/TGIC system exhibited V-0 rating in UL-94 at 1 wt% P-loading. Thanks to the covalent linkage between DOPO-HPM and DGEBA, a satisfactory heat resistance was obtained.
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Preparation and flame retardancy of an intumescent flame-retardant epoxy resin system constructed by multiple flame-retardant compositions containing phosphorus and nitrogen heterocycle

Abstract

Introduction

Section snippets

Materials

Synthesis of DOPO–HPM

Conclusions

Polymer (Guildf.)

Polym. Degrad. Stab.

Polym. Degrad. Stab.

J. Anal. Appl. Pyrolysis

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Eur. Polym. J.

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