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Variation in dielectric properties of an epoxy‐novolac molding compound during dynamic cure
Author(s) -
Hsieh T. H.,
Ho K. S.
Publication year - 1999
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.11521
Subject(s) - materials science , epoxy , differential scanning calorimetry , composite material , dielectric , curing (chemistry) , permittivity , glass transition , conductivity , polarization (electrochemistry) , relaxation (psychology) , polymer , thermodynamics , chemistry , psychology , social psychology , physics , optoelectronics
The variation in dielectric characteristics of an epoxy‐novolac molding compound during dynamic cure was studied by means of dielectrometry (DE). Dielectric parameters such as permittivity (ϵ′), loss factor (ϵ″), and dissipation (tan δ) were observed to depend on various factors including temperature, frequency, the extent of cure (α, measured previously by using differential scanning calorimetry, DSC), as well as contributions from ionic conductivity (σ) and electrode polarization. The characteristic relaxation time (τ) and the relaxed permittivity (ϵ r ), suggested in the literature as possible parameters for cure monitoring purposes, was found difficult to determine because of interfernce from ionic conduction and electrode polarization. In comparison, σ could be measured throughout the entire cure process and was observed to depend only on temperature and α. In combination with our previous DSC results, an empirical function relating α to temperature and α was constructed. Our analysis also indicated that the strong maximum in the ϵ′ and the ϵ″ curves during the course of dynamic cure was a direct result of the α‐and the temperature‐dependence of σ; the strong maximum of ϵ″ is directly related neither to gelation nor to vitrification.