Enhanced Interface Adhesion by Novel Eco-Epoxy Adhesives Based on the Modified Tannic Acid on Al and CFRP Adherends

Nataša Z Tomić,Marija Vuksanović,Sofia Teixeira De Freitas,Andreja Živković,Johannes A Poulis,Aleksandar Marinković,Mohamed Nasr Saleh

doi:10.3390/polym12071541

Nataša Z Tomić, Marija Vuksanović + Show 5 more

Open Access

https://doi.org/10.3390/polym12071541

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Journal: Polymers	Publication Date: Jul 12, 2020
Citations: 11	License type: CC BY 4.0

Affiliation: University of Belgrade, Delft University of Technology

Abstract

This paper presents a new process for obtaining eco-epoxide adhesives synthesized from bio-renewable raw material (tannic acid—TA) and used for bonding lightweight materials (aluminum (Al) and carbon fiber reinforced polymer (CFRP)). Two synthesized bio-epoxy components based on TA, (A) glycidyl ether and (B) glycidyl phosphate ester of TA, were used as a replacement for the toxic epoxy component based on Bisphenol A. The effect of eco-epoxy components on the interface adhesion was measured by the determination of adhesion parameter b, which was compared to the reference epoxy (REF). The increase of adhesion parameter b was 77.5% for A and 151.5% for B. The adhesion of both eco-adhesives was tested using the bell peel test (BPT) with the Al and CFRP adherends. When compared to REF, the average peel load for B was 17.6% (39.3%) and 58.3% (176.9%) higher for the Al and CFRP adherends, respectively. Complete adhesion failure of REF reflected the weak adhesion to both Al and CFRP, which was improved by the addition of eco-epoxy components A and B showing the presence of cohesive failure. The microhardness testing method of interface adhesion was proven to be a fast and reliable testing method, providing a qualitative indication in adhesive selection.

Highlights

Nowadays, thermosetting polymers have a significant share in plastic production (20%) due to their outstanding properties [1]
The aim of this study is to investigate the interface adhesion of novel eco-epoxy adhesives by the addition of two types of modified tannic acid: (A) glycidyl ether and (B) glycidyl phosphate ester of TA, which are used as a bio-based replacement of the Bisphenol A (BPA)-based epoxy component
The characteristic structural changes of TA by the epoxidation process is reflected by the existence of C–H vibrations at 2932 and 2877 cm−1 for both A and B when compared to TA

Summary

Introduction

Nowadays, thermosetting polymers have a significant share in plastic production (20%) due to their outstanding properties [1]. Epoxy materials are characterized with high a cross-linking density, their ease of use, and high applicability in the industry. They are essential for structural lightweight materials for aerospace, maritime, and automotive industries, as well as used as adhesives, coating, paints, etc. Cured epoxy polymer networks possess numerous hydroxyl and benzoyl functional groups that contribute to their high thermal stability, great mechanical properties, and their adhesion ability to different adherends [3]. Bisphenol A (BPA) is a petroleum based chemical that represents a building block of most epoxy materials (>90%). The aromatic core of such compounds contributes to the stability, as well as high thermal and mechanical properties of epoxy materials.

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