In recent years, the demand for environmental sustainability has caused a great interest in finding novel polymer materials from natural resources that are both biodegradable and eco-friendly. Natural biodegradable polymers can displace the usage of petroleum-based synthetic polymers due to their renewability, low toxicity, low costs, biocompatibility, and biodegradability. The development of novel starch-based bionanocomposites with improved properties has drawn specific attention recently in many applications, including food, agriculture, packaging, environmental remediation, textile, cosmetic, pharmaceutical, and biomedical fields. This paper discusses starch-based nanocomposites, mainly with nanocellulose, chitin nanoparticles, nanoclay, and carbon-based materials, and their applications in the agriculture, packaging, biomedical, and environment fields. This paper also focused on the lifecycle analysis and degradation of various starch-based nanocomposites.

The current trend of using plastic material in the manufacturing of packaging products raises serious environmental concerns due to waste disposal on land and in oceans and other environmental pollution. Natural polymers such as cellulose, starch, chitosan, and protein extracted from renewable resources are extensively explored as alternatives to plastics due to their biodegradability, biocompatibility, nontoxic properties, and abundant availability. The tensile and water vapor barrier properties and the environmental impacts of natural polymers played key roles in determining the eligibility of these materials for packaging applications. The brittle behavior and hydrophilic nature of natural polymers reduced the tensile and water vapor barrier properties. However, the addition of plasticizer, crosslinker, and reinforcement agents substantially improved the mechanical and water vapor resistance properties. The dispersion abilities and strong interfacial adhesion of nanocellulose with natural polymers improved the tensile strength and water vapor barrier properties of natural polymer-based packaging films. The maximum tensile stress of these composite films was about 38 to 200% more than that of films without reinforcement. The water vapor barrier properties of composite films also reduced up to 60% with nanocellulose reinforcement. The strong hydrogen bonding between natural polymer and nanocellulose reduced the polymer chain movement and decreased the percent elongation at break up to 100%. This review aims to present an overview of the mechanical and water vapor barrier properties of natural polymers and their composites along with the life cycle environmental impacts to elucidate their potential for packaging applications.

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The inferior water vapor permeability and water resistance properties are the major challenges that hindered the development of chitosan-CNF composites for packaging applications. In this study, the chitosan-CNF composite films were prepared with in situ crosslinking of citric acid (CA) to reduce the percent water uptake (WU) and water vapor permeability (WVP). The composite films were produced by the solvent casting method with 10%, 15%, and 20% CNF as a reinforcement, 20%, 25%, and 30% CA as a crosslinker, and 20% glycerol as a plasticizer. The Fourier transform infrared (FTIR) spectra of composite films with a peak at 1710 cm À1 confirmed the effective crosslinking of citric acid on the chitosan-CNF matrix. The crosslinked composite films exhibited the lowest WU of 39% and WVP of 9.99 Â 10 À7 g/Pa s m 2 with reduced light transmittance due to CNF reinforcement. The scanning electron microscopy (SEM) study showed the smooth surface morphology of composite films. The CA crosslinking slightly decreased the tensile strength of composite films.However, the composite film with optimal CNF and CA concentration (25% and 20%, respectively) exhibited comparable tensile strength with other synthetic and biopolymer composites and can be used as a potential biopolymer composite for packaging applications.

The cellulose reinforced polylactic acid (PLA) composites are one of the most widely explored biopolymer composites in packaging applications. In this study, the cellulose microfibers (CMF) isolated from cotton noil were reinforced with 1%, 3%, 5%, 10%, and 20% in PLA matrix by solvent casting method. The strong interfacial adhesion and enhanced dispersion of CMF in PLA polymer matrix increased the tensile, water vapor, ultraviolet (UV) light barrier properties of the composites. The ultimate tensile stress and Young's modulus of 1% CMF reinforced composites were increased by 46% and 30% respectively than that of control films. A further increase in percent CMF reinforcement of up to 20% slightly reduced the tensile strength of composites but was comparable to that of low‐density polyethylene polymer. The water vapor permeability was decreased while increasing the CMF reinforcement due to the increased diffusion path by the dispersed CMF. The UV light absorbance of the composite was improved by up to 90% with the increase in CMF reinforcement by up to 20% due to the increased chromophore groups of cellulose. Hence, the PLA‐CMF composites could be used for packaging and storing light and moisture‐sensitive products.