Toughening mechanism of rubber reinforced epoxy composites by thermal and microwave curing

Abstract

The carboxyl terminated polybutadiene (CTBN) is utilized to improve the toughness of diglycidylether of bisphenol A epoxy cured by heat and microwave. The change of viscosity, chemical groups, and the glass transition temperature (T g ) of system are analyzed. The impact performance is characterized to evaluate the fracture toughness, and tensile properties also are investigated. The fracture morphologies are observed by the scanning electron microscopy for exploring toughening mechanism. The viscosity results indicate that viscosity of system increases with increasing of CTBN, demonstrating the formation of precrosslinking and interpenetrating network structure of two phases. The Fourier transform infrared spectrometer results show that effective chemical bonds are formed between CTBN and epoxy resins. The T g decreases with introducing CTBN, indicating the decline of crosslinking density, which further suggests inherent three-dimensional structure have been changed. The impact strength and energy increase with increasing of CTBN, and reach a maximum value of 5.92 kJ/m 2 and 0.13 kJ at 15% for thermal curing, respectively, increased by 36.8% and 23.1% relative to microwave curing system, while tensile strength and modulus reach the optimum at 5%. Scanning electron microscopy observation finds that "plastic tensile" and "microvoid" deriving from "sea-island" structure exist, presenting the ductile fracture features.

High‐toughness, environment‐friendly solid epoxy resins: Preparation, mechanical performance, curing behavior, and thermal properties

“…In particular, the reactive liquid rubbers have been extensively used for enhancing the fracture toughness of epoxy resins, such as the carboxyl‐terminated butadiene acrylonitrile copolymer, amine‐terminated copolymer of butadiene and acrylonitrile, and hydroxyl terminated polybutadiene (HTPB) . Also, there are several studies on the toughening mechanism of liquid rubber toughened epoxy resins.…”

“…When the liquid rubber particles spread evenly among the epoxy resin, they can effectively absorb stress and play a role in dispersing energy to relieve stress concentration through rubber holes and shear deformation . Moreover, the other toughening mechanisms such as plastic void growth rubber particle bridging, crack deflection, crack bifurcation, and crack pinning are also widely accepted .…”

A renewable tung oil-derived nitrile rubber and its potential use in epoxy-toughening modifiers

“…The chemical reaction between carboxyl and epoxy groups is able to improve the compatibility between CTBN and epoxy resin, and the long exible chains may toughen epoxy matrices by developing stress concentrations under stress. [10][11][12] Laura et al have studied CTBN-modied epoxy resin by laser confocal microscopy characterization and found that the fracture toughness increases, whereas the glass transition temperature and the tensile modulus decrease as the size and phase volume of CTBN increase; 13 Huang et al have prepared a exible and transparent epoxy resin with tunable mechanical properties by the reaction between hydrazine hydrate and the epoxy functional group diglycidyl ether of bisphenol A (DGEBA). The curing systems incorporated with the modied resin demonstrated excellent exibility; however, no phase separation was observed.…”

Mechanical, thermal, and morphological properties of PLA biocomposites toughened with silylated bamboo cellulose nanowhiskers

“…The tensile modulus of the untreated composite was 427.71 MPa while it decreased to 207.80, 139.32, and 132.84 MPa after 8 wt% A‐151, A‐174, and A‐189 treatments, respectively. This phenomenon is much common in polymer toughening systems and can be explained by the fact that the tensile modulus is related to tensile stress and tensile strain once the tensile strain increases sharply, usually accompanied by a decrease in tensile modulus . Moreover, the tensile strength and tensile modulus of A‐1100‐treated composites were slightly increased with the increasing concentrations.…”