Rubber-modified epoxies. II. Morphology and mechanical properties

Chemical Recycling of Fully Recyclable Bio-Epoxy Matrices and Reuse Strategies: A Cradle-to-Cradle Approach

Currently, the epoxy resin market is expressing concerns about epoxy resins' non-recyclability, which can hinder their widespread use. Moreover, epoxy monomers are synthesized via petroleum-based raw materials, which also limits their use. So, it is crucial to find more environmentally friendly alternative solution for their formulation. Within this context, the aim of this paper is to exploit a Cradle-to-Cradle approach, which consists of remodeling and reshaping the productive cycle of consumer products to make sure that they can be infinitely reused rather than just being recycled with a downgrading of their properties or uses, according to the principle of the complete circular economy. Indeed, after starting with a fully-recyclable bio-based epoxy formulation and assessing its recyclability as having a process yield of 99%, we obtained a recycled polymer that could be reused, mixing with the same bio-based epoxy formulation with percentages varying from 15 wt% to 27 wt%. The formulation obtained was thoroughly characterized by a dynamic-mechanical analysis, differential scanning calorimetry, and flexural tests. This approach had two advantages: (1) it represented a sustainable disposal route for the epoxy resin, with nearly all the epoxy resin recovered, and (2) the obtained recycled polymer could be used as a green component of the primary bio-based epoxy matrix. In the end, by using replicated general factorial designs (as statistical tools) combined with a proper optimization process, after carrying out a complete thermo-mechanical characterization of the developed epoxy formulations, the right percentage of recycled polymer content was selected with the aim of identifying the most performing epoxy matrix formulation in terms of its thermo-mechanical properties.

Effects of Relative Positions of Defect to Inclusion on Nanocomposite Strength

It is generally accepted that material inhomogeneity causes stress concentrations at the interface and thus reduces the overall strength of a composite. To overcome this reduction in strength, some groups experimented on coating the nanoinclusions with a layer of rubbery material, aiming for higher energy absorption. However, representative volume element (RVE) nanocomposite models, established with randomly distributed core–shell nanoparticles and single nanoparticle cells, show that the enhancement in strength observed in some experiments remains elusive computationally. By including a pre-existing crack in the matrix of the RVE, the stress concentration at the crack tip is reduced for cases where the nanoparticle and precrack are aligned away from the loading direction. This suggests that stress concentrations around inherent defects in materials can sometimes be reduced by adding nanoparticles to improve material strength. The effect is reversed if the crack and nanoparticle are aligned towards the loading direction. Parametric studies were also carried out in terms of the relative stiffness of the nanoparticle to the matrix and crack length. Validation tests were performed on 3D RVEs with an elliptical crack as the initial defect, and the results match with the 2D findings.

A liquid elastomer for epoxy resin toughening

A liquid elastomer was synthesized using butyl acrylate, acrylic acid and acrylonitrile. The elastomer was characterized and used as a toughener for a high-functionality novolac epoxy resin to improve the impact strength of the resin castings. A chemical reaction between the epoxy resin used and the liquid elastomer synthesized was confirmed by infrared and dynamic mechanical analysis. Preliminary results indicated a 66% increase in impact strength of the castings with addition of 10% by weight of the elastomer. Scanning electron micrographs of the fractured surfaces showed the phase separation of the elastomer.