|The need to transition to more sustainable and renewable technology has resulted in a focus on the two bio-renewable polymers, cellulose and lignin. Cellulose nanocrystals (CNCs) and lignin can be the materials of the future, with the potential of replacing currently used synthetic materials. CNCs are naturally hydrophilic due to the abundance of hydroxyl (-OH) groups on their surface, making them an excellent recipient for functional composite materials. However, their hydrophilicity is a deterrent to many industries, subsequently limiting their application scope. In either light, the increased rate of progress using CNCs in advanced material applications is well underway and is becoming applicable on an industrial scale. Lignin, a biopolymer found in biosphere, is a by-product of pulp industries. Due to its chemical structure, it can be used as a UV- stabilizer, antioxidant, antiradical, and antimicrobial biopolymer in material applications. However, because of its complexity in structure and inconsistencies in properties associated with differences in the source and extraction process, the use of lignin in specialty materials is limited. Nanoparticles of renewable polymers have gained an interest in academia due to the advantageous properties they offer. Thus, the synthesis of lignin nanoparticles can be of relevance.
Epoxy is an extensively used polymer in several applications such as coatings, adhesives, structural composites, etc. However, it is a poor ultraviolet (UV) absorber and suffers from UV- degradation, which usually leads to discolouration and loss of structural integrity. In this study, cellulose nanocrystals (CNCs) conjugated with UV absorber molecules were investigated as a functional nanomaterial to enhance the UV absorption of epoxy polymers. The grafting of a UV absorbing molecule, para-aminobenzoic acid (PABA), on the surface of CNC was confirmed using FTIR, proton NMR, and via elemental analysis. The modified CNC was then incorporated into an epoxy polymer and its efficacy in mitigating the photo-degradation of epoxy was evaluated. The incorporation of native CNC displayed some UV absorption and reduction in the UV mediated discolouration of the epoxy, but the most pronounced effect was obtained in PABA decorated CNC based epoxy nano-composites. The use of such tailored CNCs has great potential to mitigate the UV induced degradation of a range of polymers that are used especially in outdoor applications where direct exposure to UV is significant.
Lignin, an aromatic, renewable, and biodegradable material offers many unique properties. The potential of lignin can be valorized with the synthesis of nanoparticles. In this study, lignin (Dealkaline lignin) was used to produce lignin nanoparticles (LNP) through top-down and bottom- up processes. LNPs produced through a top-down process used ultrasonication as the source of energy to break down the larger molecule. A shift in pH was used inthe bottom-up approach, where LNPs were synthesized in three different solvents: water, glycerol, and ethylene glycol. LNPs produced were characterized, analyzed and compared through different methods. LNPs synthesized through different approaches maintained a similar structure. LNPs with functional attributes such as UV-absorbing and antioxidant properties can be used for functional material applications.