Dynamic mechanical methods were used to study the effect of absorbed moisture on the properties of an epoxy resin matrix CFRP. The glass transition temperature (Tg)of the matrix resin, determined as the onset of the characteristic fall in dynamic modulus with increasing temperature, was found to decrease with increasing moisture content. Maximum shifts in Tg of 80 to 90°C, relative to the dry material, were observed for a resin moisture content of 5.2% by weight. The effects of sample geometry, fibre orientation, and frequency of oscillation, on the dynamic mechanical properties are discussed. Results are given of an analysis of the observed dependence of Tg on water content using two theoretical models.
Continuation of work on the curing characteristics of an epoxy resin which is widely used as a composite matrix is reported. Results are given of study of the cure of the resin with dicyandiamide as hardener and diuron as accelerator, using differential scanning calorimetry to monitor the cure. The effect of diuron on the cure of the resin with an aromatic amine curing agent is also described. Distinctive effects of composition are found and values of the apparent activation energy of the curing reaction are derived.
The cross-linking reactions of 4,4'-diaminodiphenyl sulphone (DDS) with stoichiometric quantities of glycidyl ether- or tetraglycidyl amine-based epoxy resins were monitored using chemiluminescence (CL) and rheometry. It was found that, when a sample was cured isothermally in air, the CL profile increased to a maximum, then decreased again. The maximum was found to correspond well with the gel time (tgel), as measured by rheometry. This observation is discussed in relation to the chemical reactions occurring within the material and the physical state of the matrix. The effect of impurities in DDS on the gel time of these epoxy resins is reported.
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