Ionic liquids platform for biomass dissolution leading to advanced biocomposite materials
The focus on biomass as a renewable resource has been triggered by the increasing demand for non-renewable supplies and the distress of imminent depletion of petroleum reserves. The term "biorefinery" has been defined in analogy to fuel and petrochemical refineries, and has the purpose to process raw biomass for fuel production, but also a variety of platform chemicals and materials that would complement the current chemical refineries. The ability of ionic liquids (ILs) to serve as non-derivative solvents for biomass facilitates the preparation of chemicals and materials from biorenewable feedstocks. This window of opportunity allows the research community to explore and develop the next generation of materials, products and processes. This dissertation focuses on the development of novel functional materials using ILs technology initiated in 2002. A tunable approach was developed which allows the preparation of composite materials with added functionality for specific applications. Throughout the studies, we were able to understand the interactions among polymers, additives, and ILs, and also evaluate the properties of biocomposite materials processed from ILs/biopolymers solutions embedded with various functional additives. By adjusting one or more of the ILs process variables (ILs' basicity, concentration of the biopolymer, the additive's load in the biopolymer matrix, additive's particle size, regeneration solvent, etc.), we were able to influence the fundamental and specific properties of the composites. It was determined that the ILs' capability for biopolymer dissolution increases with anion's basicity and decrease of the cation's side chain. The molecular weight and concentrations of the biopolymer are factors that influence the morphology and strength of the fibers. Using high molecular weight cellulose the strength of the fibers was increased, but the surface texture of the fibers became wrinkled compared to smooth cellulose fibers obtained from small molecular weight polymers. The addition of micron size inorganic particles such as TiO2 and magnetite to the IL/cellulose solutions can bring functionality to the prepared composite cellulosic material, but can also generate stress failure of the fibers. However, after changing the additive's particle size from micron to nano size and using ultrasonic dispersion for homogeneity enhancement of the IL/additive mixture, the functionality of the particles was retained in the composite and the mechanical properties were significantly improved. ILs also facilitate the preparation of composite materials with swelling capacity and flame-retardant properties through combination of alginic acid and structural polymers like cellulose. These materials can be successfully used as reinforced wound care dressings in the medical field. Chitin nanobeads (~ 25 nm) have been prepared directly from shrimp shells powder and IL solution through the electrospinning process. The nanosize of the chitinous materials provides a large surface area for potential applications such as selective metal extraction media or support for drug delivery systems. In conclusion, the ILs process overall facilitates the preparation of biocomposite materials in various shapes that can retain both biopolymer and additive particular properties (such as flexibility, biocompatibility, and magnetic or antimicrobial properties) after regeneration from IL/biopolymer/additive blends and can be easily used for specific applications.