Lignocellulosic building blocks for aerogel and nanocomposite applications

Each new dawn is marking our success in the field of science and technology, fortifying our knowledge, but at the same time risks associated with the plethora of environmental challenges in the form of climate change, air and ocean pollution and use of fossil fuels are rapidly growing as well. In these circumstances, a paradigm shift from a fossil-based society to a greener, bio-based one is highly encouraging. The growing concerns associated with the end of life of plastics and new legislation from governments have generated a demand for lignocellulosic materials. Lignocellulosic biomass, consisting of the natural polymers, cellulose and lignin, have been recognized as possible raw material for innovative bio-based products with added value. In this work, two major components of lignocellulosic biomass, cellulose at its nanoscale morphology, termed as "cellulose nanofibrils" (CNF), obtained via fibrillation and "colloidal lignin nanoparticles" (CLPs), transformed through the self-assembly process of crude lignin, have been utilized as building block materials for diverse practical applications. Among different enticing features of CNF, its low thermal conductivity was emphasized by preparing flame-retardant CNF aerogels. The readily available sodium bicarbonate proved itself as an effective eco-friendly flame-retardant. Mixing CNF with sodium bicarbonate enabled the production of low-density aerogels with self-extinguishing behavior upon the removal of the flame source and decreased combustion velocity while retaining the good insulating properties of the aerogels. Due to the challenges posed by the hydrophilic nature of CNF, the second nano component of lignocellulosic biomass, "CLPs" were examined for their interfacial properties using surface-sensitive methods. The gained fundamental understanding was put forth to develop strong nanocomposites from CNF and CLPs. Both CLPs and CNF demonstrated excellent suitability for water-based systems and the prepared nanocomposite films showed a significant increase in toughness at an optimum ratio between CLPs and CNF. In response to the hydrophilic surface character of CNF and CLPs, the following work utilized a water-based PU system in combination with CNF to selectively hydrophobized one side of the nanocomposite film, retaining the hydrophilicity of the other side. The further exploration of CLPs as low-cost enzyme carriers for aqueous ester synthesis exhibited 95% of the synthetic activity under a high aqueous reaction medium. Enzyme immobilized c-CLPs demonstrated excellent stability under esterification conditions, reusability, and high molar yield of esterification reaction yield.

In conclusion, we demonstrated that nano-morphologies of CNF and CLPs provide a new toolbox for designing products of biological-origin with the possibility to functionalize and modify the interface between different building components.

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