Shahed Ekbatani

Binderless natural fibre composites are attractive for circular manufacturing since the removal of a synthetic matrix improves recyclability and end-of-life processing. However, their applications are often constrained by weak interfacial bonding and limited mechanical performance. This study presents a scalable approach to strengthen binderless luffa fibre composites by combining localised surface reinforcement with cellulose nanocrystals (CNCs) and tailored wet processing conditions. CNCs were introduced by immersing luffa layers in a CNC suspension, enabling diffusion into the porous network and subsequent accumulation at fibre-fibre contact regions during hot pressing, resulting in localised interfacial reinforcement. The process exploits the self-bonding of lignocellulosic fibres under controlled moisture and elevated temperature to mobilise lignin and promote hydrogen bonding. Compared to neat luffa panels, a 280 % increase in peel strength and a 49 % improvement in interlaminar shear strength (from 2.47 to 3.68 MPa) were obtained, alongside substantial improvements in flexural strength and modulus. CNCs further improved interfacial interactions, with FTIR evidences reconfiguration of O–H hydrogen bonding interactions under wet CNC processing, while DSC and TGA confirm reduced chain mobility (higher Tg) and delayed thermal decomposition. The synergistic effects of CNC integration and optimised processing parameters provide a scalable route to high-performance environmentally friendly natural fibre composites without synthetic binders. [Display omitted]

Effective sound absorption materials are essential for mitigating noise pollution in urban and industrial environments, which pose serious health risks to humans. This work develops a hierarchical natural fibre binderless composite based on porous luffa, modified with localised cellulose nanocrystals (CNCs), for application in acoustic panels. The impedance tube approach was employed to systematically evaluate sound absorption performance across a range of frequencies. Adding 3 wt.% and 7 wt.% CNCs to the porous luffa structure improved its sound absorption, especially in mid-to-high frequency areas. The binderless luffa panels with 3% CNC panels exhibited the most balanced performance across various thicknesses, while 7% CNC–luffa panels demonstrated excellent sound absorption averages across all frequency ranges, although increased rigidity and reflective tendencies were observed. The nano-modification successfully maintained the sound absorption coefficient with reduced panel thickness. This study establishes CNC-modified luffa composites as a sustainable and efficient alternative to conventional acoustic materials, leveraging renewable resources and lightweight characteristics. These findings highlight the potential of CNC-luffa composites for noise mitigation, paving the way for environmentally conscious acoustic solutions.

To shed light on the self-stratification mechanism in epoxy–acrylic coatings, 200-, 400-, and 800-micron-thick coatings were applied on glass and aluminum substrates, and their solidification behavior was studied. Some of the applied coats showed self-stratification behavior, with the thermoplastic acrylic copolymer in the top layer. In addition, experiments were performed on epoxy–acrylic solutions without hardeners to evaluate the resulting convective patterns on the solution surface, which exhibited finger-type convection. The final structure of the films had an apparent dependency on the thickness. Thicker films were usually more stratified and had a thicker stratified layer. As these observations could not support diffusion as the primary mechanism of self-stratification, convection experiments were done on epoxy and coatings solutions. The surface patterns on the solutions were studied, and the finger-type convection was observed. Based on these observations, we propose that convection may be the primary movement mechanism rather the diffusion of polymers toward the surface in the self-stratifying coats.

The importance of self-stratifying coatings in attaining two layers by one coat application makes it a point of interest to understand the mechanism of self-separating of resins into two distinct layers. Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (FTIR-ATR) is a good analysis method with the facility of real-time monitoring for tracking the position of components during the film formation. The migration of main components of silicon/epoxy as a self-stratifying coating system during film formation is followed on ZnSe and Ge cells as substrates. By following up the spectra of real-time monitoring during the film formation it was found that the mechanism of epoxy chains movement toward surface in a self-stratifying coating can not be diffusion.

Natural fibre composites have been utilised in many applications such as automotive and buildings, thanks to their high specific properties and environmentally friendly nature. However, the incompatibility between hydrophilic natural fibres and hydrophobic polymer resins remains a longstanding issue in natural fibre composites. Inspired by nature 's hierarchical structures and tailored functionalities, a nano-engineered hierarchical natural fibre composite has been developed in this study, utilising cellulose nanocrystals (CNCs) as localised nanoreinforcements at flax surfaces in a flax/bio-epoxy system. A simple and versatile spray coating technique was used to deposit CNCs on unmodified flax fibres, without using any chemical solvents. With the increased surface roughness and hence improved epoxy wetting on nano-engineered flax surfaces (3 wt% CNC loading), mechanical properties of the hierarchical composites have been significantly improved, with a 60 % increase in interlaminar shear strength, indicating an enhanced interfacial load transfer between flax and epoxy, alongside improved flexural modulus (14 %) and strength (23 %). This green approach without using any chemicals provides a scalable and sustainable way to develop tailored interfaces for natural fibre composites with enhanced resin wetting and mechanical properties.