Comparison of reaction mechanisms of epoxy resins undergoing thermal and microwave cure from in situ measurements of microwave dielectric properties and infrared spectroscopy

Abstract

New methods have been developed which enable one to monitor in situ the changes in the dielectric and spectroscopic properties of epoxy materials as they undergo cure by microwave as well as by thermal energy. In situ measurements at 2.45 GHz of the complex dielectric constant and of the infrared spectra of a DGEBA/DDS system undergoing isothermal cure at a number of temperatures have been conducted. Results have shown that although microwave radiation accelerates the curing reaction during early stages of the process, the induced rapid cross-linking creates a molecular network which is rigid enough to trap unreacted functional groups, thus actually causing a lower degree of cure. The cross-linking in samples cured by microwave radiation is caused by an accelerated reaction of the secondary amine group whose reactivity becomes similar to that of the primary amine.

Comparison of the mechanical and physical properties of a carbon fibre epoxy composite manufactured by resin transfer moulding using conventional and microwave heating

“…It is, thus, more appropriate to consider microwave heating as conversion of electromagnetic energy to thermal energy rather than heat transfer [5]. A considerable amount of research has been devoted on microwave curing of different polymer [2,[6][7][8][9][10][11][12][13] and composite systems [14][15][16][17][18][19][20][21][22][23]. The implementation of microwave heating into common manufacturing methods for polymer composites, such as resin transfer moulding [24], however, has not yet been fully exploited.…”

Microwave Effect on Curing of Waterborne Polyurethane

“…Some significant improvement in properties of the cured polyurethanes(PU denotes after this) with microwave has been reported. [4][5][6] PU is one of the important organic materials with ever increasing applications due to their excellent adhesion to most materials, excellent scratch resistance, excellent chemical stability etc. In the connection with environmental concern, the waterborne polyurethanes are more and more popular compared to the solvent-borne polyurethanes.…”

Microwave curing of carbon–epoxy composites: Penetration depth and material characterisation

“…Many papers have been published in the field of MW heating of materials, such as cement [6], rubber [7], polymers [8][9][10][11][12] and polymer composites [13][14][15][16][17][18][19][20][21][22][23]. The current summary will only focus on MW heating of carbon fibre reinforced polymer (CFRP) composites, more specifically carbon-epoxy composites, as these present some specific challenges (e.g.…”