Structure‐property relationships in rubber‐toughened epoxies

Abstract

Epoxies toughened with two reactive liquid rubbers, an epoxy‐terminated butadiene acrylonitrile rubber (ETBN) and an amino‐terminated butadiene acrylonitrile rubber (ATBN), were prepared and studied in terms of their structure property relationships. A two‐phase structure was formed, consisting of spherical rubber particles dispersed in an epoxy matrix. A broad distribution of rubber particles was observed in all the materials with most of the particles ranging in size from 1 to 4 μm, but some particles exceeding 20 μm were also found. Impact strength, plane strain fracture toughness (KIC), and fracture energy (GIC) were increased, while Young's modulus and yield strength decreased slightly with increasing rubber content and volume fraction of the dispersed phase. Both GIC and KIC were found to increase with increasing apparent molecular weight between crosslinks and decreasing yield strength. The increased size of the plastic zone at the crack tip associated with decreasing yield strength could be the cause of the increased toughness. An ATBN‐toughened system containing the greatest amount of epoxy sub‐inclusion in the rubbery phase demonstrated the best fracture toughness in this series. In the present systems, rubber‐enhanced shear deformation of the matrix is considered to be the major toughening mechanism. Curing conditions and the miscibility between the liquid rubber and the epoxy resin determine the phase morphology of the resulting two‐phase systems. Kerner's equation successfully describes the modulus dependence on volume fraction for the two‐phase epoxy materials.

Rubber toughened epoxy

“…The effect of acrylonitrile content is also demonstrated. 26,27 Generally, CTBN having higher acrylonitrile content has higher miscibility with the epoxy resin in terms of solubility parameter and undergoes phase separation at a later stage of curing and gives lower amount of phase separated rubber. CTBN with acrylonitrile content more than 30% results single-phase morphology.…”

The Mechanical Properties of Epoxy Composites Filled with Rubbery Copolymer Grafted SiO2

“…However, many epoxies are brittle and have poor fracture toughness, weak impact strength and low resistance to fatigue crack propagation [1]. Epoxies can be toughened by adding rubbery fillers, such as liquid rubbers [2][3][4] and preformed core/shell rubber particles [5][6][7][8]. Rubber cavitation happens under local hydrostatic stress.…”

Toughening of epoxy resin by reacting with functional terminated‐polyurethanes

“…Figure 1 Typical droplet shape of pullout test (X400). Temperature dependence of tan 6 for the PUOnce cured, the microdroplet dimension and the fiber diameter were measured by an optical microscope.…”