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.
Similar content being viewed by others
References
Anand H R and Singh Anand Pal 1993J. Polym. Mater. 10 161
Bidstrup W W, Sheppard N F and Senturia S D 1986Polym. Engg. & Sci. 26 358
Gotro J and Yandrasite M 1989Polym. Engg. & Sci. 29 278
Kranbuehl D E 1980Developments in reinforced plastics-5 (ed.) G Pritchard (London: Elsevier) p 181
Kranbuehl D E, Delos S E, Hoff M S, Whitham M E and Weller L M 1986Proc. of the second conference on advanced composites (America: ASM International Publishers) p 61
Sanford W M and McCullough R L 1987Proc. of the American society for composites second technical conference (USA) p 21
Sanjana Z N 1986Polym. Engg. & Sci. 26 373
Senturia S D and Sheppard N F 1986Adv. Polym. Sci. 80 1
Songzhen Wu, Gedeon S and Fouracre R A 1988IEEE Trans. Elect. Insul. 23 409
Zee R H, Huang Y H, Chen J J and Jang B Z 1989Polym. Comp. 10 205
Author information
Authors and Affiliations
Additional information
Paper presented at the poster session of MRSI AGM VI, Kharagpur, 1995
Rights and permissions
About this article
Cite this article
Singh, A.P., Anand, H.R. Frequency dependence of gel time in thermosetting resins. Bull. Mater. Sci. 19, 165–176 (1996). https://doi.org/10.1007/BF02744800
Issue Date:
DOI: https://doi.org/10.1007/BF02744800