Cyclic Olefin Copolymer Interleaves for Thermally Mendable Carbon/Epoxy Laminates.

Riccardo Costan Zovi,Andrea Dorigato,Alessandro Pegoretti,Giulia Fredi,Haroon Mahmood

doi:10.3390/molecules25225347

Abstract

Thin cyclic olefin copolymer (COC) foils were used as intrinsic thermoplastic healing agents in carbon fiber (CF)-reinforced epoxy laminates. COC films were produced by hot pressing and were interleaved in the interlaminar regions between each EP/CF lamina, during the hand layup fabrication of the laminates. Three samples were produced, i.e., the neat EP/CF laminate without COC, and two laminates containing COC layers with a thickness of 44 μm and 77 μm, respectively. It was observed that the fiber volume fraction decreased, and the porosity increased with the introduction of COC layers, and this effect was more evident when thick films were used. These two effects, combined with the sub-optimal adhesion between COC and EP, caused a decrease in the mechanical properties (i.e., the elastic modulus, flexural strength, interlaminar shear strength and interlaminar fracture toughness) of the laminates. Specimens subjected to mode I interlaminar fracture toughness test were then thermally mended under pressure by resistive heating, through the Joule effect of conductive CFs. A temperature of approximately 190 °C was reached during the healing treatment. The healing efficiency was evaluated as the ratio of critical strain energy release rate (GIC) of the healed and virgin specimens. Healed specimens containing COC layers of 44 μm and 77 μm exhibited a healing efficiency of 164% and 100%, respectively. As expected, the healing treatment was not beneficial for the neat EP/CF laminate without COC, which experienced a healing efficiency of only 2%. This result proved the efficacy of COC layers as a healing agent for EP/CF laminates, and the effectiveness of resistive heating as a way to activate the intrinsic healing mechanism.

Highlights

Carbon fiber reinforced polymers (CFRPs) are in use since the 1950s in the aerospace industry, to fill the need for materials with better specific properties, compared to those of metals [1,2]
On the basis of these considerations, the present study investigates the healing potential of thin cyclic olefin copolymer (COC) foils in epoxy/carbon fiber (EP/CF) laminates
This work reported the use of thin films of an amorphous cyclic olefin copolymer (COC) as a healing agent for epoxy/carbon (EP/CF) laminates

Summary

Introduction

Carbon fiber reinforced polymers (CFRPs) are in use since the 1950s in the aerospace industry, to fill the need for materials with better specific properties, compared to those of metals [1,2]. Structural polymer composites are of interest especially in the transportation field, as they lead to the production of lightweight components with great structural performance, which allow saving fuel and decreasing CO2 emissions [3]. These materials are attractive for the possibility of pairing the mechanical function with additional functionalities, such as strain monitoring, self-healing and energy storage capabilities [4,5,6,7,8]. Typical failure mechanism of thermosetting fiber-reinforced polymer composites (FRPCs) include interfacial delamination and matrix cracking [9,10,11].

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