Clay Nanolayer Reinforcement of a Glassy Epoxy Polymer

Abstract

Glassy epoxy-clay nanocomposites (Tg ≈ 82 °C) have been prepared by the reaction of diglycidyl ether of bisphenol A and a polyoxyalkylene amine curing agent in the presence of organo cation exchanged smectite (montmorillonite) clays. Commercially available AMS and CWC montmorillonites purified on the industrial scale (Nanocor, Inc.) afforded nanocomposites with performance properties comparable to those obtained from montmorillonite purified by laboratory methods. We provide the first evidence for clay nanolayer reinforcement of a glassy epoxy matrix under compressive strain. Compression stress - strain experiments revealed substantial improvements in the modulus and yield strength when the clay nanolayers were exfoliated in the glassy matrix. However, no improvement in the modulus or yield strength was observed when the clay component was merely intercalated by the epoxy matrix, signifying that nanolayer exfoliation is an essential feature of reinforcement. Furthermore, the mechanical properties of epoxy-clay nanocomposites prepared with the C18H37NH3+ - exchanged forms of the AMS and CWC clays have been tested by dynamic mechanical analysis and thermal mechanical analysis. The nanocomposites exhibit improved dynamic storage modulus above and below the glass transition temperature, as well as lower coefficients of thermal expansivity compared to the pure polymer. In addition, the solvent resistant properties of the nanocomposites are substantially improved compared to the pristine polymer.

Nanoindentation and Morphological Studies of Epoxy Nanocomposites

“…The internal stress in the cured composite due to different cure speeds in bulk epoxy and at the silicate interfaces was found to cause a substantial loss of mechanical properties and even formation of powdery materials. [16][17][18][19][20] It was also reported that, the improved stiffness and toughness was frequently accompanied by drastic and unacceptable losses of tensile strength. [21] However, Carsten Zilg et al [22] have discovered that the incorporation of compatibilizer, e.g., long chain alkyl or alkylene groups, respectively, into epoxy resins and curing agents afforded substantially higher tensile strengths without sacrificing modulus and toughness.…”

Effect of temperature, duration and speed of pre-mixing on the dispersion of clay/epoxy nanocomposites

“…The intercalated or exfoliated forms of nanolayer silicates in many polymer systems have improved stiffness, strength, fracture toughness, fire resistance, barrier properties, and dimensional stability of the material [1][2][3][4][5][6]. The reinforcing ability of nanoclay is due to its high modulus, high strength and high aspect ratio.…”

The influence of silicate modification and compatibilizers on mechanical properties and morphology of anhydride-cured epoxy nanocomposites

“…Different cure speed in bulk epoxy and at the silicate interfaces can account for internal stresses and substantial loss of mechanical properties and even formation of powdery materials. [13][14][15][16][17][18] A recent detailed study on the influence of various alkylammonium cations with variable functionalities on the toughness/stiffness/ strength balance of anhydride-cured epoxy resins revealed that improved stiffness and toughness was frequently accompanied by drastic and unacceptable losses of tensile strength. [19] Objectives of this research were to improve simultaneously toughness, stiffness and strength of hexahydrophthalic anhydride-cured bisphenol-A diglycidyl ether-based epoxy resin containing organoclay and to examine the role of compatibilizer addition.…”