Adhesives

Short fibre-reinforced adhesives (SFRAs) are increasingly used in wind turbine blades to enhance stiffness and fatigue resistance, yet their heterogeneous microstructure poses significant challenges for predictive modelling. This study presents a fully automated digital workflow that integrates micro-computed tomography (µCT), image processing, and finite element modelling (FEM) to investigate the mechanical response of SFRAs. Our aim is also to establish a computational foundation for data-driven modelling and future AI surrogates of adhesive joints in wind turbine blades. High-resolution µCT scans were denoised and segmented using a hybrid non-local means and Gaussian filtering pipeline combined with Otsu thresholding and convex hull separation, enabling robust fibre identification and orientation analysis. Two complementary modelling strategies were employed: (i) 2D slice-based FEM models to rapidly assess microstructural effects on stress localisation and (ii) 3D voxel-based FEM models to capture the full anisotropic fibre network. Linear elastic simulations were conducted under inhomogeneous uniaxial extension and torsional loading, revealing interfacial stress hotspots at fibre tips and narrow ligaments. Fibre clustering and alignment strongly influenced stress partitioning between fibres and the matrix, while isotropic regions exhibited diffuse, matrix-dominated load transfer. The results demonstrate that image-based FEM provides a powerful route for structure–property modelling of SFRAs and establish a scalable foundation for digital twin development, reliability assessment, and integration with physics-informed surrogate modelling frameworks.

Bio-based phenolic resins were developed with phenol substitution levels of 20% and 40% with crude extracts obtained from spent coffee grounds. The experimental resins were characterized in terms of their physical, chemical and bonding properties and exhibited the typical property levels of Phenol-Formaldehyde-type resins. Plywood panels were produced bonded with the novel experimental resins, exhibiting satisfactory performance, comparable to the reference panels in terms of both shear strength and wood failure, based on the requirements of the European standards. The results demonstrate the potential of using biomass-derived compounds as substitutes for petrochemical phenol in the production of wood adhesives, thereby increasing the bio-based content of the wood panel composites produced with them and improving their sustainability.

Chañar brea gum exhibits properties that make it a promising material for paper adhesion. As the concentration of chañar brea gum (CBG) in solution increases, the following key changes are observed in its properties, which are relevant to its use as an adhesive. The surface tension (σ) decreases with increasing gum concentration. Viscosity (η) increases dramatically with increasing chañar brea gum concentration. While higher viscosity is often desirable for many adhesives, excessive viscosity, as may be observed at very high concentrations, can hamper application. However, adequate viscosity is crucial to ensure initial bond strength, as it allows for the formation of a uniform layer and prevents excessive penetration into porous substrates. A concentration of 10% wt. by weight offers this balance. Surface adsorption (Γ₂₍₁₎) increases linearly with gum concentration, indicating that higher interfacial adsorption is crucial for the formation of an effective adhesive layer. The contact angle (θ) increases slightly with concentration; although a lower contact angle typically indicates better wetting, the increase is marginal (from 88° ± 4 for water to 99° ± 4 for 30% wt.), so wetting is still acceptable. Chañar brea gum exhibits good surface adsorption capacity and reduced surface tension, which favors interaction with the paper surface. The adhesive strength of chañar brea gum (CBG) clearly depends on its concentration, increasing from 6.36 ± 0.22 MPa (at 5% wt.) to a significant maximum of 50.24 ± 1.19 MPa at a concentration of 10% wt. The decrease in adhesive strength at concentrations above 10% wt. by weight is an important aspect to consider in order to optimize its performance as a paper adhesive. Therefore, intermediate concentrations, such as 10% wt., offer the most favorable balance of properties for achieving good adhesive performance.