Methods to increase the toughness of structural adhesives with micro particles: an overview with focus on cork particles

Abstract

Structural adhesives are used increasingly in new applications replacing conventional joining methods. Epoxy adhesives have the widest range of application of the various classes of adhesives arising principally from their extremely wide set of performance properties. They are known for their high stiffness and strength, as well for their low ductility and toughness. Currently, there is an increasing interest in developing methods of improving toughness. A toughened adhesive in general contains elastic or thermoplastic domains dispersed in discrete form throughout the resin matrix, in order to increase the resistance to crack-growth initiation. This paper provides an overview of the current developments in the use of reinforcement materials and introduces the reader to early findings on the use of micro particles for toughness enhancement of adhesives. The theme of the use of materials of natural origin as reinforcement materials, giving special emphasis to the use of cork particles as toughener material is also presented.

Micro failure analysis of adhesively bonded joints enhanced with natural cork particles: Impact of overlap length and particles volume fraction

“…he volume fraction of particles dispersed in a structural adhesive matrix is usually a significant parameter in controlling the resulting properties of the toughening adhesive. Authors showed that toughness increases with an increasing volume of particles and eventually reaches a maximum value [4]. Fig.…”

“…pplications of adhesives and specially epoxy resins, as an alternative to traditional fasteners, have considerably increased in different industries [1,2]. Although epoxies show good mechanical properties, the structure of these thermoset polymers causes insufficient energy absorption with a low resistance to the propagation of cracks [1,3,4]. For this reason, improving their toughness has been extensively studied in the last decades [5][6][7].…”

Analysis of the effect of size, amount and surface treatment on the tensile strain of a brittle adhesive reinforced with micro cork particles

“…On the other hand, specimens with 0.25% of cork present lower values of maximum strain and higher dispersion. As found in previous research [8,22,25], cork particles do not present a standardized structure as it can vary depending on biological and/or mechanical factors, which are very challenging to control. Therefore, there is an inherent dispersion of results that stems from the conditions of the cork particles.…”

“…Afterwards, the composite was mixed again in the centrifuge mixing machine. This procedure was considered the most simple and effective way to prevent agglomeration of cork particles [8,25]. After, the mixture was cast in a pre-heated steel mould.…”

“…Natural raw materials, such cork, can be used to improve ductility in brittle adhesives and currently different industries are encouraged to include these materials, with the aim to reduce the carbon footprint. Cork is an organic material with unique properties, obtained by a truly sustainable process, since it is renewable and biodegradable [8]. Cork is characterized by being lightweight, flexible, and substantially impermeable to liquids and gases, with excellent thermal, acoustic and vibration insulation, being also an innocuous and rootless material [9][10][11].…”