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2004-1186 session 1793

Gel Time and Temperature for Two Thermosetting Resins

Steven D. Gordin, Akbar M. Eslami, Howard L. Price

Department of Technology Elizabeth City State University Elizabeth City NC 27909

Abstract

The results of an investigation of gel time and temperature of two thermosetting resins have been used to design a laboratory experiment for an undergraduate materials science course. The experiment is part of a larger effort to establish an undergraduate program in polymer composites. The experiment enabled each student to bring about the conversion of liquid resin to the solid state and to experience the attendant heat release.

Introduction

Polymer composite materials often are a combination of small fibers (glass, carbon, aramid) and a thermosetting resin such as unsaturated polyester, epoxy, phenolic, polyimide, polyurethane and others being used for specialty composites. All thermosetting resins must undergo a “cure”. Cure is a time-dependent, exothermic, irreversible chemical reaction in which the low molecular weight liquid converts to a high molecular weight, cross linked solid that serves as a matrix for the fibers.

An important change during cure is gelation, when the reaction has proceeded sufficiently so that the resin has achieved a flexible but non-flowing three dimensional molecular structure. Gelation is accompanied by a release of heat resulting in a temperature rise. Gelation marks the end of the “working time” of the resin and fiber. Resin is no longer liquid and attempts to “work” it and the fiber -- shape and smooth them -- are ineffective and may compromise the properties of the composite. Thus, gel time is an important factor in the manufacture of all composites and gel temperature is important for thick or large cross section composites.

As part of an effort to establish an instructional program in polymer composites, an investigation has been made of the gel times and temperature rise of two thermosetting resins. These quantities are especially important in large cross section composites intended to support large external forces. The resins were a vinyl ester and a difunctional epoxy that would be used to make composites as part of the instructional program. The results of the investigation were used to design a laboratory experiment for an undergraduate materials science course. The experiment provided an effective way for each student to experience the conversion of liquid resin to the solid state with the attendant heat release. Both the investigation and the experiment are reported. Proceedings of the 2004 American Society for Engineering Education Annual Conference & Exposition Copyright © 2004, American Society for Engineering Education

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Eslami, A. (2004, June), Gel Time And Temperature For Two Thermosetting Resins Paper presented at 2004 Annual Conference, Salt Lake City, Utah. 10.18260/1-2--12830