Abstract
In the present paper, a novel epichlorohydrin/cardanol adhesive was reinforced by multi-walled carbon nanotubes (MWCNTs) and characterized experimentally. The adhesive was reinforced by MWCNTs in weight ratios (wt %) of 0.5%, 1.0% and 2.0%. The bulk properties of the reinforced adhesive were characterized through dynamic mechanical analysis tests, tension tests, and fracture toughness tests, while its shear behavior was characterized through single-lap shear tests on aluminum and composite bonded specimens. The morphology of the reinforced adhesive was characterized using scanning electron microscopy tests. Due to the high viscosity of the bio-based adhesive, special efforts were placed on the dispersion of the MWCNTs into the adhesive, which was achieved through mechanical mixing. The results from the tests show that the presence of the MWCNTs increases the glass transition temperature, the Young’s modulus and the fracture toughness of the reinforced bio-based adhesive, while it decreases its tensile strength. This contradictory finding is attributed to the formation of MWCNT agglomerates into the adhesive. For the content of 2.0 wt %, the shear strength of the reinforced adhesive is increased by 57% for the aluminum joints and by 10.4% for the composite joints. The findings of the study reveal that the reinforcement of the bio-based adhesive by MWCNTs is feasible from a manufacturing viewpoint and may increase the efficiency of the adhesive in structural applications.
Highlights
In the last decades, the epoxy-adhesive applications are expanding very fast to interior and secondary structural applications in the aerospace [1,2], the automotive industries [3] and used in the construction industry in a semi-cured state [4]
It was found that the epichlorohydrin/cardanol adhesive is prone to hygrothermal ageing since its bulk properties are considerably decreased
The examination of the scanning electron microscopy (SEM) images has revealed the presence of multiwalled carbon nanotubes (MWCNTs) agglomerations despite the special effort spent in the production process to optimize the MWCNTs dispersion
Summary
The epoxy-adhesive applications are expanding very fast to interior (cosmetic) and secondary structural applications in the aerospace [1,2], the automotive industries [3] and used in the construction industry in a semi-cured state [4]. A method to enhance the mechanical properties of bio-based polymers is to reinforce them by nanoparticles In this direction, many works have been reported in the literature for conventional epoxy resins and adhesives, e.g., [7,8,9]. Given that the bio-based polymers are prone to environmental conditions, in [15], the effects of hygrothermal ageing on the mechanical properties of the epichlorohydrin/cardanol adhesive have been characterized experimentally by subjecting bulk specimens and bonded joints to the conditions of 70 ◦C/RH85% until saturation and testing them mechanically. It was found that the epichlorohydrin/cardanol adhesive is prone to hygrothermal ageing since its bulk properties are considerably decreased This is not the case for the shear strength measured from single-lap shear tests on aged bonded specimens. The morphology of the MWCNT-filled adhesive was characterized by scanning electron microscopy (SEM) tests
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