Effect of Different Types of Block Copolymers on Morphology, Mechanical Properties, and Fracture Mechanisms of Bisphenol-F Based Epoxy System

Bajpai Bajpai,Wetzel Wetzel

doi:10.3390/jcs3030068

Abstract

The effect of adding different types of soft block copolymer on the tensile properties, fracture mechanic properties, and thermo-mechanical properties of bisphenol F based epoxy resin were studied. Two different self-assembling block copolymers, (a) constituting of a center block of poly (butyl acrylate) and two side blocks of poly (methyl) methacrylate-co-polar co-monomer (BCP 1) and (b) poly(ethylene oxide)-b-poly(butylene oxide) (PEO-PBO) diblock copolymer (BCP 2), were used with an epoxy-hardener system. The maximum fracture toughness and fracture energy were measured as KIc = 2.75 MPa·m1/2 and GIc = 2.37 kJ/m2 for the 10 wt % of BCP 1 modified system, which were 366% and 2270% higher in comparison to reference epoxy system, and a 63% reduction in tensile strength was also observed. Similarly, for BCP2 modified systems, the maximum value of KIc = 1.65 MPa·m1/2 and GIc = 1.10 kJ/m2 was obtained for epoxy modified with 12 wt % of BCP2 and a reduction of 32% in tensile strength. The fracture toughness and fracture energy were co-related to the plastic zone size for all the modified systems. Finally, the analysis of the fracture surfaces revealed the toughening micro-mechanisms of the nanocomposites.

Highlights

Epoxies are highly cross-linked thermoset polymers which exhibit high modulus, high strength and low creep and are used in wide range of applications e.g., automotive, aerospace, electronics, adhesives, etc
The maximum fracture toughness and fracture energy were measured as KIc = 2.75 MPa·m1/2 and GIc = 2.37 kJ/m2 for the 10 wt % of BCP 1 modified system, which were 366% and 2270% higher in comparison to reference epoxy system, and a 63% reduction in tensile strength was observed
The BCP1 phase separated into dispersed micron-size particles till 6 wt % of BCP1 and into a co-continuous microstructure for 8 wt % and 10 wt %, and complete phase inversion was observed at 12 wt % of BCP1

Summary

Introduction

Epoxies are highly cross-linked thermoset polymers which exhibit high modulus, high strength and low creep and are used in wide range of applications e.g., automotive, aerospace, electronics, adhesives, etc. To enhance the toughness of brittle epoxy polymers, the most common method is to add the multiphase structure with a distinct rubbery (softer) phase in the epoxy matrix. Liu et al [5] from their work reported that, with an incorporation of 5 wt % of the BCP material into bisphenol A-based epoxy resin, there was an improvement in the fracture toughness of 100% over the neat epoxy resin. This is because in general, at lower BCP wt % in epoxy resin, they may self-assemble into micro/nanostructures following different morphologies: Vesicles, spherical micelles and wormlike micelles. The structure formed with such interactions mainly depends on parameters like block length, molecular weight, composition, and matrix-block interaction

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Results

Conclusion