Development of environmentally friendly epoxy and composite adhesives and applications in single and mixed-modulus joints

Abstract

Epoxy adhesives are common and useful materials in several fields, especially in making joints for the aerospace industry. Lately, there is a growing demand for this kind of adhesives to become more environmentally friendly. In this work, an environmentally friendly epoxy adhesive is developed using commercially available materials, exhibiting a 12% increase in green carbon content and 22% increase in shear strength. The commercial eco-friendly epoxy system is then reinforced with dry olive pit powder in order to produce an eco-friendly composite adhesive, giving a 20% shear modulus increase, for the 2.5% filler content, compared to the pure matrix. The behavior of these two materials is investigated, when these are used as adhesives in lap joints, and their main shear properties are determined. In order to manufacture adhesively bonded joints using a thick layer of liquid resin without any pre-curing step, therefore achieving improved properties, two casting-like designs of the overlap area are made and tested, one in a single-modulus configuration and a second one in a mixed-modulus mode. When an eco-friendly epoxy adhesive is applied on each edge of the mixed modulus mode instead of a fossil-based epoxy adhesive, a 30% increase in shear strength is observed. Finally, the Property Predictive Model, a modification and extension of the Modulus Predictive Model, is proposed, allowing the accurate prediction of several properties of virtually any series of particulate composite materials. When the model is applied to the aforementioned composites, it proves to be capable of accurately predicting their main shear properties.