The Use of the ATD Technique to Measure the Gelation Time of Epoxy Resins.

Jakub Smoleń,Mateusz Chudy,Mateusz Kozioł,Piotr Olesik,Paweł Gradoń,Bogusław Mendala

doi:10.3390/ma14206022

Abstract

In this paper, we investigated the thermodynamics of the resin curing process, when it was a part of composition with graphite powder and cut carbon fibers, to precisely determine the time and temperature of gelation. The material for the research is a set of commercial epoxy resins with a gelation time not exceeding 100 min. The curing process was characterized for the neat resins and for resins with 10% by weight of flake graphite and cut carbon fibers. The results recorded in the analysis of temperature derivative (ATD) method unequivocally showed that the largest first derivative registered during the test is the gel point of the resin. The innovative approach to measuring the gelation time of resins facilitates the measurements while ensuring the stability of the curing process compared to the normative tests that introduce mechanical interaction. In addition, it was found during the research that the introduction of 10% by weight of carbon particles in the form of graphite and cut carbon fibers rather shortens the gelation time and lowers the temperature peak due to the effective absorption and storage of heat from the cross-linking system. The inhibiting (or accelerating) action of fillers is probably dependent on chemical activity of the cross-linking system.

Highlights

The use of epoxy resins in polymer matrix composites (PMC) is dictated by gaining good properties, especially in terms of mechanical strength, electrical insulating properties, and resistance to environmental and chemical corrosion [1]
The PMCs are commonly used in many industries due to relatively easy processing methods
It is generally accepted that thermoplastic polymers are more difficult to incorporate powder fillers than thermosetting polymers due to the significantly higher viscosity in the processing state [9,10]

Summary

Introduction

The use of epoxy resins in polymer matrix composites (PMC) is dictated by gaining good properties, especially in terms of mechanical strength, electrical insulating properties, and resistance to environmental and chemical corrosion [1]. Introducing the reinforcement material to the volume of the resin leads to the improvement of certain properties [2,3,4,5] but may cause difficulties, e.g., sedimentation of powder fillers leading to inhomogeneity of the material. Depending on the morphology of filler, there may be different interactions between the matrix phase and the reinforcement phase [6,7,8]. Spherical filler interacts with the resin matrix in a different way than fibers, for which the interaction depends on the length of the fibers and their orientation/arrangement. The introduction of fillers into polymer composites is a complex issue that closely depends on the type of liquid matrix. It is generally accepted that thermoplastic polymers are more difficult to incorporate powder fillers than thermosetting polymers due to the significantly higher viscosity in the processing state [9,10]

Methods

Results

Conclusion