Applications of FTIR on Epoxy Resins –

Identification, Monitoring the Curing

Process, Phase Separation and Water Uptake

María González González, Juan Carlos Cabanelas and Juan Baselga

University Carlos III of Madrid

Spain

1. Introduction

Epoxy resins are a family of thermosetting materials widely used as adhesives, coatings and

matrices in polymer composites because of the low viscosity of the formulations, good

insulating properties of the final material even at high temperatures and good chemical and

thermal resistance (May, 1988). Epoxy thermosets can be described as 3D polymer networks

formed by the chemical reaction between monomers (“curing”). This 3D covalent network

structure determines the properties of thermosetting polymers: unlike thermoplastics, this

kind of polymers does not melt, and once the network has been formed the material cannot

be reprocessed. Maybe one of the main advantages of epoxy thermosets is that the starting

monomers have low viscosity so that complex geometries can be easily shaped and fixed

after curing the monomers. Thus the formation of the network via chemical reaction is a key

aspect in this kind of materials.

Epoxy formulations usually include more than one component, although there are different

crosslinking mechanisms involving either chemical reaction between one single type of

monomer (homopolymerization) or two kinds of monomers with different functional

groups. In both cases, a common constituent is always found: the epoxy monomer. The

main feature of the epoxy monomer is the oxirane functional group, which is a three

member ring formed between two carbon atoms and an oxygen, as shown in Figure 1. This

atomic arrangement shows enhanced reactivity when compared with common ethers

because of its high strain. Due to the different electronegativity of carbon and oxygen, the

carbon atoms of the ring are electrophilic. Thus epoxies can undergo ring opening reactions

towards nucleophiles. The polarity of the oxirane ring makes possible detection by IR

spectroscopy.

There are mainly two families of epoxies: the glycidyl epoxies and non-glycidyl epoxies

(also called aliphatic or cycloaliphatic epoxy resins). The absence of aromatic rings in

aliphatic epoxies makes them UV resistant and suitable for outdoor applications and also

reduces viscosity. The most common epoxy monomers of each family are diglycidylether of

bisphenol A (known as DGEBA) and 3,4-Epoxycyclohexyl-3’4’-epoxycyclohexane

carboxylate (ECC) respectively and their structures are given in Figure 2 (a, b).

Cycloaliphatic resins are usually found in the form of pure chemicals with a definite

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Fig. 1. Oxirane ring

Fig. 2. Chemical structures of common epoxy resins: a) 2,2-Bis[4-(glycidy

Dear researcher

It will be appreciated if you have a specific figure of epoxy / polysufide reinforced with Sic.

Thanks in advance