Comprehensive study on synthesis and characterization of nanocellulose reinforced green composites

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PhD; 2022; Centre for product design and manufacturing

Environmental issues caused by the non-biodegradability of synthetic thermoplastics have increased interest in more environmentally friendly alternatives that should be derived from renewable resources. This work focuses on producing green composites and biofilms by synthesizing nanocellulose (NC) from readily available natural and renewable sources like cellulose. The term NC refers to cellulose that has been reduced to the nanoscale. NC is used to describe a variety of cellulose nanostructures, including Micro Crystal Cellulose (MCC), Cellulose Micro Fibrils (CMF), Cellulose nanocrystals (CNC), and Cellulose nanofibers (CNF). Because of its versatility, low toxicity, biodegradability, and carbon neutrality, nanocellulose has attracted considerable attention for generating new materials in several industrial, technological, and biological applications. Nanocellulose has a sizable global market and demand because of these numerous applications. One of the challenges for commercial and industrial production of nanocellulose is finding a source of cellulose that is economically viable, abundant, and sustainable. Bacteria, plants (including trees, shrubs, and herbs), algae, and animals (Tunicates) are the primary sources of nanocellulose. In this study, cellulose nanofibers are synthesized from the bamboo pulp through TEMPO oxidation, high- pressure homogenization, and ultrasonication treatment. Characterization of CNF was done using Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Fourier-Transform Infrared Spectroscopy (FTIR), X-ray powder Diffraction (XRD), and Dynamic Mechanical Analysis (DMA). After characterization, the synthesized NC was evaluated by turning it into films and using it as reinforcement to prepare composites. Bamboo particles are reinforced with CNF suspension to prepare composites using the hot press (HP) and oven-dried (OD) methods. The mechanical properties of these fabricated composites are investigated, such as modulus of elasticity (MOE), modulus of rupture (MOR), and interfacial strength. The properties of the NC and composites are compared for 1st , and 3rd homogenization passes. The mechanical characteristics of the film have been investigated using uniaxial tensile and nanoindentation experiments. The morphological characteristics examined using SEM and TEM showed that the cellulose in the bamboo pulp is reduced to the nanoscale, confirming the formation of CNF. The average diameter of nanofibres of bamboo calculated from TEM images was 8 to 10 nm, respectively. The CNF analyzed using FTIR spectroscopy exhibited the presence of functional groups and their vibrational modes. Further, crystal size (CS)andcrystallinity index (CI) of CNF synthesized from different homogenization passes were calculated usingthe XRD technique. Properties like viscosity, storage modulus, and loss modulus were determined from the rheological characterization, which confirmed the non-Newtonian behavior of pure NC suspension. In addition to morphology analysis, mechanical properties of NC films computed from uniaxial tensile test and nanoindentation showed a 58 MPa tensile strength and a 0.2228 GPa hardness, respectively. Also, dynamic mechanical properties like storage modulus, loss modulus, and tanδ were determined to examine the viscoelastic behavior of the film as a function of temperature. However, from the results, no phase transformation was noticed until 75°C. Furthermore, composites reinforced with 1 % weight consistency of CNF showed an increase in interfacial strength, MOE, and MOR as a function of density. The MOE increased 9 times for HP samples compared to the OD samples. MOR nearly increased by a factor of 4, and the energy-absorbing capacity also increased to 182% in the case of HP samples. From these results, it can be inferred that hot-pressing was an effective manufacturing method than oven drying as it removes maximum moisture content and enhances adhesion between bamboo powder and CNF. Therefore, it can be concluded from the results that nanocellulose derived from bamboo has highly entangled fibers, which can be transformed into a film and used in packaging and biomedical applications. Also, bamboo CNF acts as a binding agent to prepare composites. Hence, the concept of using matrix and reinforcement derived from the same natural sources can be used to make green composites. Consequently, there is a great deal of potential for the TEMPO-oxidized bamboo celluloses to develop into ground-breaking nanotechnology that will connect the domains of biomass and forest refinement with cutting-edge high-tech research.