Currently, the production of fibre-reinforced composites with natural fibres based on thermoplastic and thermoset matrices is a very active area of research. However, obtaining a strong interface between natural fibre and a petrochemical derived polymer matrix may be problematic. Issues of fibre-matrix compatibility may be solved through the concept of monocomponent (or single-polymer) composites that utilise a single type of polymer for both the reinforcement and matrix phases. The concept of a single-polymer composite also simplifies the recycling of composites. Recently a new type of single polymer composites based on cellulose has been developed, where cellulose is used for both reinforcement and matrix phases. All-cellulose composites (aka ACCs) are able to avoid the main problem of many fibre reinforced composite materials that is poor interaction between the reinforcement and matrix phases.

Cellulose does not melt due to the large number of intra- and inter-chain hydrogen bonding. However, cellulose can be dissolved in suitable solvents, and then regenerated by removing the solvent so as to form the matrix of the composite. ACCs can be produced via two different routes: (a) partially dissolution of cellulose fibres with solvent and following matrix formation in situ; and (b) infusion of cellulose fibres with predissolved portion of cellulose in solution. Subsequent regeneration of the dissolved component of cellulose occurs in the presence of different coagulants, such as water, ethanol, or acetone.

In the present work, the potential for a facile aqueous-based solvent processing route for the synthesis of ACCs is explored using aqueous solutions containing tertabutylphosphonium hydroxide (TBPH). Specifically, ACC laminates are prepared via the partial dissolution of a woven textile of cellulose II using aqueous TBPH solutions. The dissolved cellulose was then regenerated to reform a cellulose II matrix phase in situ that acts to bond the original undissolved fibres. The hygroscopic behaviour and dissolution rate of the solvent system were studied to investigate the breadth of processing conditions suited to the production of ACC laminates via TBPH. The effect of processing conditions on the microstructure, crystallinity index and tensile properties of ACCs is reported. The use of TBPH enables reductions in the processing cycle time and improved control over the properties of ACCs, indicative of a promising solvent system for the upscaled production of ACCs and their laminates.

The possibility of eliminating the need for pre-drying the cellulose precursor, thereby reducing energy consumption, cost and time of ACC production, is one of the main advantages of TBPH. The relatively low viscosity of TBPH compared to most ionic liquids promotes faster and more uniform impregnation of cellulose. ACC laminates washed in water experienced significant warpage due to variable shrinkage. ACCs made using TBPH and EmimAc had comparable properties and microstructure. The TBPH concentration is observed to affect the matrix volume fraction in the final composite. The choice of coagulant is also shown to significantly influence the final microstructure and properties of ACCs. Complex 3D-shaped ACCs have been successfully produced using a combination of solvent infusion processing and rigid moulding. Both, EmimAc and TBPH are found to be suited to such a production route. Thermomechanical analysis was used to study the effect of solvent and coagulant on shrinkage. Dimensionally-stable ACC laminates were produced using ethanol as a coagulant. The processing factors that were determined to be the origin of defects in the ACC laminate structure were also identified.