The Dissolution and Fabrication of Hybrid Cellulose- Protein composites in Ionic Liquid of 1- ethyl-3-methyl- imidazolium acetate [Emim][OAc]

Abstract

The increasing demand for sustainable and environmentally friendly materials has accelerated research into renewable bio-based composites as alternatives to conventional petroleum-derived systems. This thesis investigates the dissolution behaviour, structural transformation, and fabrication of all-hybrid cellulose composites based on cellulose–protein systems using hemp–keratin and flax–silk hybrid yarns and woven fabrics. The ionic liquid 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) was employed as a solvent to achieve controlled partial dissolution, enabling the formation of regenerated matrix phases while preserving part of the original fibrous reinforcement structure. The dissolution behaviour of hemp–keratin and flax–silk hybrid yarns was systematically studied as a function of temperature and time using optical microscopy (OM), wide-angle X-ray diffraction (XRD), gravimetric analysis, and mechanical testing. The results demonstrated that dissolution strongly depends on both processing temperature and dissolution time, with cellulose dissolving more rapidly than protein components. In hemp–keratin systems, cellulose dissolution occurred at lower temperatures, while keratin required significantly higher energy due to the presence of disulfide bonds. Activation energies determined using time–temperature superposition (TTS) analysis and Arrhenius modelling were 55 ± 5 kJ/mol for hemp cellulose and 111 ± 9 kJ/mol for wool keratin. For flax–silk hybrid yarns, optical microscopy revealed distinct dissolution mechanisms for each component. Cellulose dissolved progressively from the outer surface inward, forming a coagulated matrix layer that gradually restricted further ionic liquid penetration. In contrast, silk dissolved individually from the outer surfaces of each filament, initially filling internal gaps before merging with the cellulose matrix at later stages of dissolution. XRD analysis confirmed the transformation of cellulose I into cellulose II and amorphous cellulose during dissolution and regeneration. The raw flax–silk yarn contained approximately 57 % cellulose I, which decreased to 8 % after treatment at 50 °C for 2 hours, while cellulose II increased to 23 %. Evidence of overlapping diffraction peaks indicated intermolecular interactions and partial phase mixing between cellulose and silk. TTS analysis demonstrated Arrhenius-type behaviour for both components, yielding activation energies of 95 ± 5 kJ/mol for flax cellulose and 76 ± 9 kJ/mol for silk. Mechanical analysis yielded activation energies of 73–82 kJ/mol, consistent with structural observations. Following the yarn-scale studies, all-hybrid woven composites were fabricated from hemp–keratin and flax–silk fabrics using two processing routes: an excess ionic liquid bath process and a batch process. Mechanical testing showed that Young’s modulus and tensile strength initially increased with dissolution temperature due to improved interfacial bonding and matrix formation, before decreasing at higher temperatures because of excessive dissolution of the reinforcing fibrous network. This behaviour confirmed the existence of a preformed stage during composite consolidation. The incorporation of an interlayer cellulose film significantly improved peel strength and interfacial adhesion by promoting the formation of a continuous regenerated matrix at the interface, although increased matrix content reduced stiffness under some conditions. Cellulose–keratin composites consistently exhibited higher stiffness than cellulose–silk composites, while differences between warp and weft directions highlighted the influence of fabric architecture, yarn alignment, and crimp on composite performance. TTS analysis of woven composites further confirmed Arrhenius-type dissolution behaviour at the fabric scale and produced an activation energy of 16 ± 3 kJ/mol, providing quantitative insight into the dissolution kinetics at the fabric scale. The relatively low activation energy compared to individual hybrid yarn systems suggests that the woven architecture and partial dissolution–consolidation mechanism facilitate solvent transport and matrix formation during composite processing. Overall, this thesis demonstrates that [Emim][OAc] is an effective solvent for producing sustainable all-hybrid cellulose composites through controlled partial dissolution of cellulose–protein fibre systems. The work provides new insight into dissolution kinetics, structural evolution, interfacial interactions, and structure–property relationships in hybrid biopolymer composites, contributing to the development of high-performance renewable materials for sustainable engineering applications.