Thermal properties of amine cured diglycidyl ether of bisphenol A epoxy blended with poly(ether imide)

doi:10.1016/S0040-6031(99)00336-6

Thermochimica Acta

Volume 344, Issues 1–2, 28 January 2000, Pages 137-143

https://doi.org/10.1016/S0040-6031(99)00336-6 Get rights and content

Abstract

Thermal properties of an epoxy system containing diglycidyl ether of bisphenol A (DGEBA) and 1,3-bisaminomethylcyclohexane (1,3-BAC) as curing agent modified with poly(ether imide) (PEI) were studied using both dynamic mechanical (DMA) and thermogravimetric (TG) analysis. The effect of thermal degradation in air and in vacuum on the dynamic mechanical and thermogravimetric properties for the DGEBA/1,3-BAC/PEI system was investigated. The results showed that this system can be considered miscible for PEI contents up to 10 phr (phr: number of parts of PEI per hundred parts of the DGEBA epoxy resin), and also that even very small contents of PEI in the blends reduced the thermal stability of the material. Thermal degradation during a short period of time of this material both, in air or in vacuum yields a decrease of thermal stability and an increase of the glass transition temperature with respect to the material without degradation.

Introduction

Thermosetting epoxies possess properties such as high tensile strength and modulus, dimensional and thermal stability and excellent chemical and solvent resistance. So, epoxy resins have been used extensively as matrices in fibre-reinforced composites. However, these materials are generally brittle due to high crosslink densities.

Polymeric thermoplastics can enhance fracture toughness without sacrificing the glass transition temperature, strength, stiffness or other desirable properties of thermosetting resins. Rubber modification of epoxies [1], firstly realised, became ineffective because toughness improvements in most rubber-modified thermosetting systems usually result in a significant decrease in the glass transition temperature of the cured resins.

Polymeric materials are subjected to various types of degradation, ranging from thermal degradation to biodegradation. Degradation of polymers is an undesirable process involving a deterioration of their properties. This view, however, is a limited one since it is possible to utilise degradation process for the creation of new materials with useful properties [2].

In this work the thermal properties of an epoxy system containing diglycidyl ether of bisphenol A (DGEBA) and 1,3-bisaminomethylcyclohexane (1,3-BAC) as curing agent modified with a high performance thermoplastic poly(ether imide) (PEI) were investigated using both dynamic mechanical (DMA) and thermogravimetric (TG) analysis. The PEI has been used specially in the modification of tetrafunctional epoxy resins [3], [4] but it was less used with DGEBA, where the success in the improvement of the mechanical properties is not guaranteed initially [5].

The cure kinetics of the DGEBA/1,3-BAC system [6], and some of their thermal and mechanical properties [7], [8], [9] have been previously reported. This work is part of a larger study on the modification of DGEBA/1,3-BAC system with different thermoplastics. The objective of this part was to study the influence of PEI contents on thermal stability, glass transition temperature, and modulus of the DGEBA/1,3-BAC/PEI system via DMA and TG analysis. Also, the influence of thermal degradation on the DMA and TG properties was investigated for the DGEBA/1,3-BAC/PEI system when carried out in air or in vacuum during a relatively short time.

Section snippets

Materials

The three components used for the blends were the resin diglycidyl ether of bisphenol A (DGEBA), Shell Epikote 828, with weight per epoxy equivalent of 192.2 g eq⁻¹ which was determined by hydrochlorination [10], the curing agent 1,3-BAC, Mitsubishi Gas Chem., with molecular weight of 142.18 and manufacturer purity value of >99% according to the supplier, and the thermoplastic poly(ether imide) (PEI), General Electric Ultem 1000. The structures of these components are as follows

All components

DMA and TG properties of the DGEBA/1,3-BAC/PEI system

Fig. 1 displays the dynamic storage modulus, E′, and the loss factor, tan δ, curves for two of the dynamic mechanical tests. It is appreciable that the glass transition region is less broad for: (a) the neat system than for (b) the modified one. No second peak in tan δ was detected in the glass transition region of PEI, around 220°C [11], for any of the studied blends, i.e., there was no sign of the existence of two phases in the blends.

In Table 1 are shown the glass transition temperatures, T_g,

Conclusions

From all the results obtained it can be concluded that even small contents of PEI in the blends reduce the thermal stability of the material, having a less effect on T_g.

Only one peak was observed in tan δ curves for all the blends so, the DGEBA/1,3-BAC/PEI system can be considered miscible for PEI contents up to 10 phr, i.e., there is a single-phase structure for these materials.

Thermal degradation of the material in air or in vacuum at a temperature above the glass transition temperature during

Acknowledgements

Financial support for this work has been provided by Xunta de Galicia, through grant XUGA-17201B97.

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Thermal properties of amine cured diglycidyl ether of bisphenol A epoxy blended with poly(ether imide)

Abstract

Introduction

Section snippets

Materials

DMA and TG properties of the DGEBA/1,3-BAC/PEI system

Conclusions

Acknowledgements

Polymer

Eur. Polym. J.

Thermochim. Acta

Polym. Internat.