Abstract
As the important matrix material, epoxy resin has been widely used in the composites for various fields. On account of the poor toughness of epoxy resin limiting their suitability for advanced applications, considerable interests have been conducted to modify the epoxy resin to meet the engineering requirements. In this study, the bio-based polyurethane (PU) modified resin was adopted to modify the pure bisphenol-A epoxy by blending method with various proportions. Aiming to illuminate the curing behavior, mechanical and thermal properties, the blended epoxy systems were characterized by viscosity-time analysis, dynamic mechanical analysis (DMA) at different frequencies and temperatures, mechanical tensile test, thermogravimetric analysis (TGA) and Fourier transform infrared (FT-IR) spectroscopy. The results indicated that the introduction of PU modified epoxy was found to significantly inhibit the viscosity growth rates especially when the content of PU modified epoxy resin is higher than 60%. Notwithstanding the dynamic modulus and Tg reduced with the increment of PU modified epoxy, remarkable increment on the elongation at break was found and the flexibility was greatly promoted with the introduction of PU modified epoxy. The proportion of PU modified epoxy in the blends should be put balance considerations to obtain optimal mechanical properties. TGA results and FTIR spectrum demonstrated that the addition of PU modified epoxy did not change the thermal decomposition mechanism and chemical reaction mechanism, but the addition of PU modified epoxy inhibits the curing reaction of epoxy resin by measured and calculated the damping temperature domain ΔT from 35.7°C to 48.9°C.
Highlights
The epoxy resin composite materials can realize the integration of design, structure and manufacture so as to reduce the whole life cycle cost
When the contents of PU modified epoxy resin are higher than 60%, the blended epoxy systems present significantly lower viscosity growth rate than the systems with dominant bisphenol-A epoxy resin, which shows the similar conclusion with reference [28,29]
The advantage of all the above mentioned characteristics can be sensitively reflected in the dynamic mechanical properties, so considerable interests have been put on the dynamic mechanical analysis (DMA) by researchers in the field of polymer material science and engineering
Summary
Composite materials are prepared by physical, chemical or other blending methods composing of at least two materials with different specialties [1,2]. The epoxy resin composite materials can realize the integration of design, structure and manufacture so as to reduce the whole life cycle cost. Specific materials with elastic chain, such as the rubber elastomer and thermoplastic resin, are added into the epoxy resin during curing process [14,18]. Dispersed phases such as rigid particles, liquid crystal polymers, coreshell polymers and inorganic nanomaterials are added to the epoxy resin matrix to increase toughness [19–21]. Some thermosetting resins are penetrated into the epoxy resin network to form interpenetrating and semipenetrating network structure [23] These interesting works have proved the advantages of toughness improvement for epoxy. The heat resistance and toughness of epoxy resin are difficult to be improved by general methods due to mutual restriction. Comparisons of the characteristic absorption peak before and after modification were studied by Fourier transform infrared (FT-IR) spectroscopy to analyze the reaction mechanism
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