The non-halogen flame retardant epoxy resin based on a novel compound with phosphaphenanthrene and cyclotriphosphazene double functional groups

doi:10.1016/j.polymdegradstab.2011.03.001

Polymer Degradation and Stability

Volume 96, Issue 6, June 2011, Pages 1118-1124

https://doi.org/10.1016/j.polymdegradstab.2011.03.001 Get rights and content

Abstract

A novel flame retardant additive hexa-(phosphaphenanthrene -hydroxyl-methyl-phenoxyl)-cyclotriphosphazene (HAP–DOPO) with phosphazene and phosphaphenanthrene double functional groups has been synthesized from hexa-chloro-cyclotriphosphazene, 4-hydroxy-benzaldehyde and 9,10-dihydro-9-oxa-10- phosphaphenanthrene 10-oxide(DOPO). The structure of HAP–DOPO was characterized by Fourier transformed infrared (FT-IR) spectroscopy and ¹H nuclear magnetic resonance (¹H NMR) and ³¹P nuclear magnetic resonance (³¹P NMR). The additive HAP–DOPO was blended into diglycidyl ether of bisphenol-A (DGEBA) to prepare flame retardant epoxy resins. The flame retardant properties and thermal properties of the epoxy resins cured by 4, 4′-Diamino-diphenyl sulfone (DDS) were investigated from the differential scanning calorimeter (DSC), the thermogravimetric analysis (TGA), UL94 test, the limiting oxygen index (LOI) test and Cone calorimeter. Compared to traditional DOPO–DGEBA and ODOPB–DGEBA thermosets, the HAP–DOPO/DGEBA thermosets have higher T_gs at the same UL94 V-0 flammability rating for their higher crosslinking density and have higher char yield and lower pk-HRR at same 1.2 wt.% phosphorus content which confirm that HAP–DOPO has higher flame retardant efficiency on thermosets. The scanning electron microscopy (SEM) results shows that HAP–DOPO in DGEBA/DDS system obviously accelerate formation of the sealing, stronger and phosphorus-rich char layer to improve flame retardant properties of matrix during combustion.

Introduction

The non-halogen flame retardant epoxy resins containing 9,10-dihydro-9-oxa-10- phosphaphenanthrene-10-oxide (DOPO) have been widely researched and a few have been applied in semiconductor encapsulants, fiber reinforced composites and printed circuit boards for its excellent flame retardancy [1], [2], [3], [4], [5]. Most of them is based on diglycidyl ether of bisphenol-A (DGEBA) owing to its remarkable adhering, low shrinkage on cure, good electrical and mechanical properties, and especially ease of handling and processability [6], [7], [8], [9], [10], [11]. Usually, the epoxy resins containing DOPO group are prepared by the methods that P–H bond of DOPO react with epoxide group of epoxy resins by addition reaction or that DOPO derivatives react with epoxide group [11], [12], [13], [14].

But the functionality of the flame retardant epoxy resins prepared by above methods is obviously decreased for the addition reaction of DOPO and its derivatives with epoxide groups. Consequently, it directly leads to a less crosslinking density in the cured epoxy resins and the low T_gs of thermosets [15]. Further, the flame retardant epoxy resins based on DOPO reach UL94 V-0 flammability rating still need a higher adding ratio of DOPO or its derivatives for their phosphorus content below 14.4 wt.% [16], [17]. For more convenient application, more excellent flame retardant performance and more outstanding physical–mechanical properties, it is necessary to explore an unreactive way of utilizing DOPO which can preserve the functionality of resins for more excellent physical–mechanical properties. The cyclotriphosphazene compounds, which have been attention for its excellent thermal and charring properties, can provide improved flame retardant properties to polymers and their composites [18], [19], [20], [21], [22]. We tend to integrate phosphaphenanthrene and cyclotrphosphazene groups into one molecule as flame retardant additive instead of reactive DOPO and its derivatives in epoxy resin thermosets.

In this work, we synthesized a novel-structure additive hexa-(phosphaphenanthrene- hydroxyl-methyl-phenoxyl)–cyclotriphosphazene (HAP–DOPO) derived from DOPO, 4-hydroxy-benzaldehyde and hexa-chloro-cyclotriphosphazene. The additive is also mixed into DGEBA to prepare non-halogen flame retardant epoxy resins and then the flame retardant properties and mechanism of cured epoxy resins are characterized and disclosed. We also explore the difference of flame retardant behaviors between HAP–DOPO resins and DOPO–DGEBA resins and ODOPB–DGEBA resins.

Section snippets

Materials

Hexa-chloro-cyclotriphosphazene (HCP) was purchased from Zibo Lanyin Chemical Co. Ltd., China. 4-Hydroxy-benzaldehyde was purchased from Kunshan Keyida Chemical Co. Ltd., China. The epoxy resin (DGEBA) with an epoxide equivalent weight (EEW) of 184–194 g/equiv was kindly supplied by Wuxi Bluestar Co. Ltd., China. 4,4′-Diamino-diphenyl sulfone (DDS) was supplied by Shanghai SSS Reagent Co. Ltd., China. DOPO and 2-(6-oxide-6H-dibenz<c,e><1,2>oxaphos-phorin-6-yl)-dihydroxyphenylene (ODOPB) were

Synthesis of HAP–DOPO

As an intermediate of HAP–DOPO, HAP firstly was prepared by elimination reaction between HAP and 4-Hydroxy-benzaldehyde. Then the flame retardant additive HAP–DOPO was synthesized through the addition reaction of HAP and DOPO. The chemical structure of HAP–DOPO is confirmed by FT-IR in S1 in Supplementary data, ¹H NMR in Fig. 1 and ³¹P NMR in Fig. 2. The absorption peak at 3383 cm⁻¹ of HAP–DOPO indicates the formation of –OH, and correspondingly the disappeared >C double bond O absorption peak at 1700 cm⁻¹

Conclusion

A novel flame retardant additive HAP–DOPO with phosphazene and phosphaphenanthrene double functional groups has been successfully synthesized from hexa-chloro-cyclotriphosphazene, 4-hydroxybenzaldehyde and DOPO. The HAP–DOPO/DGEBA/DDS thermosets with just 1.2 wt.% phosphorus content in thermosets has the LOI value 31% and reach UL94 V-0 flammability rating. Comparing with traditional DOPO–DGEBA and ODOPB–DGEBA epoxy resin, HAP–DOPO/DGEBA thermosets has higher T_g at the same UL94 V-0

Acknowledgements

Financial support provided by National High Technology Research and Development program of China (No. 2010AA065103) and the Research Foundation for Youth Scholars of Beijing Technology and Business University (09-08).

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The non-halogen flame retardant epoxy resin based on a novel compound with phosphaphenanthrene and cyclotriphosphazene double functional groups

Abstract

Introduction

Section snippets

Materials

Synthesis of HAP–DOPO

Conclusion

Acknowledgements

Polymer

Polymer

Polymer

Polym Degrad Stab

Polym Degrad Stab

Polymer

Polym Degrad Stab

Polym Degrad Stab

React Funct Polym

Polymer

Polymer

Eur Polym J

Polym Degrad Stab

Eur Polym J