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Bulletin of Materials Science

, Volume 19, Issue 1, pp 165–176 | Cite as

Frequency dependence of gel time in thermosetting resins

  • Anand Pal Singh
  • H R Anand
Proceedings Of The Workshop On ‘Hydrogen In Materials’, New Delhi, 1994

Abstract

The increasing use of thermosetting resins in fibre reinforced composites for structural and insulating applications has necessitated the need to understand the process of crosslinking and systematics of curing time of resins with and without the reinforcing fine fibre filaments. We have employed dynamical measurements of loss tangent and dielectric constant over the frequency range 1 kHz–100kHz for investigating cure characteristics of composites. After adding crosslinking agents to resinous matrices (epoxy and polyester styrenated alkyd resins) the time variation of dielectric parameters was recorded until the completion of curing. The resin flow, the onset of gelation and completion of curing were unambiguously mapped by variations in dielectric parameters. Onset of gelation coincided with precipitous fall of dielectric constant and resonant maximum of dielectric loss. Asymptotic stabilization of dielectric parameters signalled completion of curing. The gel time and curing time were found to be substantially larger for fibre reinforced resins as compared to pure resins. The variation of electrically determined gel and cure time with frequency of ac signal employed and on the libre fraction in the composite are discussed in the paper. The present study shows that if dielectric measurements are to be employed to infer the completion of curing, low frequency measurements would be needed to correctly infer onset of gelation and time for curing.

Keywords

Thermosets composite materials dynamic dielectric analyses gel time curing time 

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Copyright information

© The Indian Academy of Sciences 1996

Authors and Affiliations

  • Anand Pal Singh
    • 1
    • 2
  • H R Anand
    • 1
  1. 1.School of Basic and Applied ScienceThapar Institute of Engineering and TechnologyPatialaIndia
  2. 2.Post Graduate Department of ChemistryKhalsa CollegeAmritsarIndia

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