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Abstract The 3D printing technique has recently become more prevalent among researchers for the fabrication of nanocomposites. The low crystallinity of polylactic acid (PLA) leads to the poor mechanical and thermal properties of its 3D-printed products, which restrict their applications in many fields. To overcome the limitations of PLA, the present work aims to develop PLA-based bionanocomposite filaments with varying percentages (1, 3, and 5 wt%) of crystalline nanocellulose (CNC) through a single screw extruder. The filaments will be further utilized for the development of bionanocomposite samples to evaluate their properties. The effect of CNC reinforcement on the chemical structure of the filaments was analyzed by FTIR analysis. XRD analysis revealed that the crystallinity of the filaments was significantly improved due to the nucleating effect of CNC. The maximum crystallinity was observed in the filament containing 1 wt% CNC, which was 26% higher than the pure PLA filament. The thermal and mechanical performance of the filaments was also considerably improved after CNC reinforcement, which was confirmed by DSC-TGA and tensile test analysis. The maximum tensile strength and tensile modulus were observed to be 48.9 MPa and 1700 MPa, respectively, in the filament reinforced with 1 wt% CNC, which was 35.5% and 21.89%, respectively, higher than those of the pure PLA filament. Rheological analysis showed that the complex viscosity, storage modulus, and loss modulus of the filaments were significantly affected by the reinforcement of CNC.

In recent decades, demand for sustainable materials in place of low cost and high strength materials has been trigged globally, which has motivated researchers towards biocomposites/green composites. The PLA has been the most promising matrix material for suistanable biocomposites owing to its biodegradability, good availability, eco-friendliness, antibacterial property, and good mechanical and thermal properties. The PLA-based biocomposites are economical, full/partial biodegradable depends upon types of reinforcement, light in weight, and also offer good thermal and mechanical properties. A number of research works have been performed on PLA and its biocomposites to explore their potential for sustainable products. However, no comprehensive review with up-to-date research data on PLA and its biocomposites are reported so far. This fact motivated to summerize the reported studies on PLA and its biocomposites. The aim of present review is to highlight the current and past trends in the research of PLA and its biocomposites. This review article covers current and past efforts reported by researchers on the synthesis and sustainability of PLA, processing, characterization, applications and future scope of its biocomposites. This study observed that PLA-based composites are the most emerging materials that can replace existing non-biodegradable and non-renewable synthetic materials. The PLA-based biocomposites could be considered as the best source of sustainable products. PLA's mechanical and thermal properties can be enhanced by reinforcing the nano and micro sizes of natural fibers and cellulose.

In the present decades, nanocellulose has been very popular in the field of nanotechnology and is receiving much attention from researchers because of its advantageous physicochemical properties, high aspect ratio, and high specific strength and modulus. The available non-eco-friendly conventional methods for the extraction of nano-crystalline cellulose (NCC) use highly concentrated chemicals and are time-consuming as well. The present adopted cost-effective method for the extraction of nano-crystalline cellulose involves minimum usage of chemicals and is environmentally friendly and relatively fast compared to other conventional methods. The nano-crystalline cellulose from sisal (NCC–S) fibers were extracted by steam explosion-assisted mild concentrated chemical treatments followed by mechanical grinding. The Dynamic light scattering (DLS) and Transmission electron microscopy (TEM) characterization confirmed the size of extracted NCC-S. A high aspect ratio was observed as 19.23, which signifies it could be a promising reinforcing material in developing nanocomposites for advanced applications. An increase in crystallinity and the removal of amorphous materials for NCC-S were confirmed by X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) analysis, respectively. Antibacterial study shows that NCC-S did not show any antibacterial properties against E. coli and S. aureus. The calculated yield of extracted nanocellulose was about 50 %. The aerogel with a porosity of 95.1 % and a density of 0.075 g/cm3 was prepared by vacuum freeze-drying method using extracted nanocellulose and chitosan. The cross-linking network structure and thermal stability of the aerogel were also confirmed by FTIR and TGA analysis respectively.