An overview of viscoelastic phase separation in epoxy based blends

The viscoelastic effects during reaction induced phase separation play an important role in toughening epoxy-based blends. The large difference in molecular weight/glass transition temperature between the blend components before the curing reaction results in dynamic asymmetry, causing viscoelastic effects during phase separation accompanying the curing reaction. This review will focus on the key factors responsible for viscoelastic phase separation in epoxy-based blends and hybrid nanocomposites. Time-resolved characterization techniques such as rheometry, small angle laser light scattering, optical microscopy etc., are mainly used for monitoring the viscoelastic effects during phase separation. Incorporation of nanofillers in epoxy thermoplastic blends enhances the viscoelastic phase separation due to the increase in dynamic asymmetry. Different theoretical models are identified for the determination of processing parameters such as temperature, viscosity, phase domain size, and other parameters during the viscoelastic phase separation process. The effect of viscoelastic phase separation has a very strong influence on the domain parameters of the blends and thereby on the ultimate properties and applications.

Effect of Morphology of Calcium Carbonate on Toughness Behavior and Thermal Stability of Epoxy-Based Composites

In this study, the modification of an epoxy matrix with different amounts of cube-like and rod-like CaCO3 nanoparticles was investigated. The effects of variations in the morphology of CaCO3 on the mechanical properties and thermal stability of the CaCO3/epoxy composites were studied. The rod-like CaCO3/epoxy composites (EP-rod) showed a higher degradation temperature (4.5 °C) than neat epoxy. The results showed that the mechanical properties, such as the flexural strength, flexural modulus, and fracture toughness of the epoxy composites with CaCO3 were enhanced by the addition of cube-like and rod-like CaCO3 nanoparticles. Moreover, the mechanical properties of the composites were enhanced by increasing the amount of CaCO3 added but decreased when the filler content reached 2%. The fracture toughness Kic and fracture energy release rate Gic of cube-like and rod-like CaCO3/epoxy composites (0.85/0.74 MPa m1/2 and 318.7/229.5 J m−2, respectively) is higher than the neat epoxy (0.52 MPa m1/2 and 120.48 J m−2).

Thermally flexible epoxy/cellulose blends mediated by an ionic liquid

Blends between the widely used thermoset resin, epoxy, and the most abundant organic material, natural cellulose are demonstrated for the first time.

Advances in cationic photopolymerization

This review discusses cationic UV-curing processes of vinyl ethers, propenyl ethers, and epoxy monomers. Cationic photopolymerization based on photogeneration of acid from onium salts induced by UV light and consecutive polymerization initiated by photogenerated acid was first proposed at the end of the 1970s. The process engendered high interest both in academia and in industry. Cationic photoinduction presents some advantages over comparable radical-mediated processes, particularly the absence of inhibition by oxygen, low shrinkage, and good adhesion, and mechanical properties of the UV-cured materials. Moreover, the monomers employed are generally less toxic and irritant than acrylates and methacrylates, which are widely used in radical photopolymerization. In this overview, particular emphasis is given to our recent contributions to the field of cationic photopolymerization for different classes of monomers.

Molecular weight effects on the mechanical properties of novel epoxy thermoplastics

A series of epoxy thermoplastics (ETPs) with varying molecular weights were synthesized from a difunctional diglycidyl ether of bisphenol-A (DGEBA)-based epoxy resin and an aromatic secondary diamine. The materials possessed glass transition temperatures varying between 73.61 and 85.36°C. The ETP series was characterized for fracture toughness, flexural, and compression properties. In general, fracture properties increased with increasing molecular weight and yet were consistently shown to decrease when higher molecular weight values were the result of increased branching. Flexural ultimate strength and strain-at-break increased with increasing molecular weight while flexural modulus decreased to a plateau. Compression properties were relatively unaffected by changes in molecular weight over the range of materials synthesized.