Preparation and characterization of cyanate/epoxy foam

Abstract

A new type of cyanate (CE)/epoxy (EP) foam with bisphenol-A dicyanate ester prepolymer and diglycidyl ether of bisphenol-A (BADCy/DGEBA) has been successfully prepared through a two-step process. The structure and properties of CE/EP foam were studied. The results reveal that the CE/EP foams, with relatively uniform cell structure, were composed of closed cells as confirmed by scanning electron microscopy. The compressive strength increased from 0.507 MPa to 3.021 MPa, and the compressive modulus (E) increased from 15 MPa to 123 MPa as the density increased from 0.103 g cm À3 to 0.305 g cm À3. Dynamic mechanical analysis revealed that the CE/EP foams possessed a high glass transition temperature (T g ) (203 C) and that density had only a little impact on T g . Moreover, the excellent thermal stability presented with the onset of weight loss taken at 5% value was above 320 C, and the residual weight of the foam was more than 21.6% at 800 C. With increase in the density of CE/EP foams, the dielectric constants (") gradually decreased. For the foam with density of ¼ 0.162 g cm À3 , the value of " was as low as 2.28 at the frequency of 10 kHz.

Preparation and mechanical properties of thermosetting epoxy foams based on epoxy/ 2-ethyl-4-methylimidazol system with different curing agent contents

“…4 The light weight of foams can save materials and energy in the practical application, 5 and the cellular structure of foams would be helpful to heat or sound insulation and electric insulation. 6,7 This would make epoxy foams widely utilized in the areas of aircraft, spacecraft, and automobiles.…”

Preparation of Microcellular Epoxy Foams through a Limited‐Foaming Process: A Contradiction with the Time–Temperature–Transformation Cure Diagram

“…The FTIR spectra show that there is no difference between Fre‐foams and Lim‐foams, both in soluble and gel components of the foams (Figure b). The peak related to epoxy group vibration at 915 cm −1 disappeared, indicating the complete reaction of the epoxy group . A strong peak at 3500 cm −1 can be attributed to the OH or hydrogen bond stretching vibration.…”

“…Lim‐foams show stable compressive properties irrespective of the postcuring temperature and time, whereas the specific compressive strength and modulus of Fre‐foams decrease with increasing postcuring temperature. This decreasing trend is attributed to the decreasing density of Fre‐foams . The decrease in density, in turn, can be due to the decomposition reaction of the composite at high temperature.…”

“…During the foaming process, gas released by the decomposition or reaction of the blowing agent favors to phase separation from the resins and then forms nucleated and grown cells, leading to an increment of the interfacial area and interfacial free energy due to the thermodynamic instability. The majority of the blowing agents only acts as a gas source to foam the polymer without affecting its chemical structure; thus, the thermal stability of foams and their corresponding bulk epoxy thermosets do not exhibit significant difference, and the T g of the fully cured foams remains unchanged with foam density . These relationships indicate that the foaming process has negligible influence on the curing degree of the epoxy composite.…”

Preparation of hybrid cyanate ester resin in the presence of polysilazane and its properties

“…To improve the controllability of the prepolymerization process, catalysts may be used to reduce the reaction temperature and shorten the polymerization time by controlling the formation of the dimer and triazine ring. 14 –18 Compounds containing active hydrogen and transition metal catalysts are often used to catalyze the curing reaction of cyanate esters. 2,19 –21 For active hydrogen-containing compounds, these small molecular catalysts remain in the prepolymer system, which will induce internal stress and defects in the cured resin.…”