Enhancement of mechanical and barrier properties of chitosan-based bionanocomposites films reinforced with eggshell-derived hydroxyapatite nanoparticles

P. Upadhyay, A. Ullah, Enhancement of mechanical and barrier properties of chitosan-based bionanocomposites films reinforced with eggshell-derived hydroxyapatite nanoparticles, International Journal of Biological Macromolecules, Volume 261, Part 2, 2024.

About

Globally, approximately over 350 million metric tons of plastic are produced annually, with projections indicating a potential doubling in the next two decades. The predominant use of plastic-based packaging materials is observed in food packaging. The prevalence of plastics in food packaging is due to its low cost, easy formation, high strength modulus, and excellent physiochemical properties. However, the non-biodegradability of synthetic plastics and their accumulation in the environment create a significant issue and a serious problem for the environment. Consequently, the food packaging industry is shifting toward the adoption of environmentally friendly, biobased, and biodegradable materials, referred to as bioplastics. Bioplastics are plastics derived from renewable resources synthesized either chemically or biologically. In this context, the utilization of eggshell waste for the production of valuable biomaterials not only contributes to sustainable development by addressing environmental concerns associated with eggshells disposal but also helps reduce carbon dioxide emissions. Therefore, the primary objective of our work was to develop chitosan-based bionanocomposites reinforced with varying amounts of eggshell-derived hydroxyapatite nanoparticles (HANPs) for food packaging applications.

Approach

Chicken eggshells were washed with water and then boiled at 100 °C for 3 h to remove any impurities. The eggshells were dried in the oven at 80 °C overnight. Subsequently, they were ground to a fine powder. HANPs were prepared from eggshells as described in our previous work. In brief, the calcium precursor was obtained by slowly adding concentrated HNO3 into the eggshell powder (ES) with vigorous stirring using a magnetic stirrer. The chitosan-hydroxyapatite (CS-HA) film was prepared using a physical evaporation/solvent casting method. Different amounts of HANPs (0, 1, 3, 5, and 10%) (w/v) were added. The films were labeled as CS-HA 0% (control-chitosan film only), CS-HA 1% (chitosan with 1% hydroxyapatite nanoparticles), CS-HA 3% (chitosan with 3% hydroxyapatite nanoparticles), CS-HA 5% (chitosan with 5% hydroxyapatite nanoparticles), and CS-HA 10% (chitosan with 10% hydroxyapatite nanoparticles). Thickness, width, mechanical properties of the bionanocomposites films were measured. X-ray diffraction and Fourier transform infrared specttroscopu (FTIR) were done to evaluate the structural characterization of the films.

Analysis of Results

The reinforcement of chitosan with HANPs greatly influenced the tensile properties of the bionanocomposite films. All the bionanocomposites reinforced with HANPs (1, 3, 5, and 10%) exhibited a significant improvement in tensile strength compared to chitosan film without HANPs. Water vapor permeability (WVP) determines the transmission rate, speed, and amount of water passing through the packaging material. A low WVP is desired to improve the food shelf life and protect it from direct contact with moisture. The WVP of the neat chitosan film (CS-HA 0%) was 8.85 × 102 gmm/m2 d k Pa and it greatly decreased after the addition of HANPs. The addition of HANPs affected both the moisture content (MC) and water solubility (WS) of the films. Moisture content in bionanocomposite films decreased with an increase in HANPs content, likely due to the hydrophilic properties of hydroxyapatite nanoparticles in the films. The WS of bionanocomposites film decreased from 21.03% in the pure chitosan film (CS-HA 0%) to 14.51% in CS-HA film with 1% inclusion of HANPs. Considering diffusion phenomena, HANPs may act as a barrier, impeding water penetration into the film structure through strong hydrogen bond interactions with chitosan. The bionanocomposite with nanoparticles showed much higher intensity than the neat chitosan film without nanoparticles, which may be because of intramolecular hydrogen bonding. Moreover, the other peaks representing amide I, II and III also exhibited a sharp increase in peak intensities compared to the neat chitosan film. Hence, FTIR results indicate that the addition of nanoparticles increased the interaction between the chitosan matrix and nanofiller. The pure chitosan film (CS-HA 0%) exhibited a consistently even microstructure with a smooth surface. In contrast, all the bionanocomposite films with nanoparticles display noticeable surface roughness characterized by numerous bumps and clustered distributions. This roughness becomes more pronounced as the content of hydroxyapatite nanoparticles (HANPs) increases.

Application

In this work, chitosan-based bionanocomposites reinforced with HANPs were prepared by a solvent casting approach without any cross-linking agent (glycerol was used as a plasticizer). The results clearly indicated that the addition of HANPs showed exceptional mechanical and barrier properties of bionanocomposites film. Overall, the incorporation of HANPs at lower concentrations (1% and 3%) not only enhanced the thermo-mechanical properties but also showed great enhancement in barrier properties. However, achieving a consistent dispersion of hydroxyapatite nanoparticles within the chitosan matrix can be a challenging endeavor, especially when dealing with higher concentrations. Any irregularities in dispersion may lead to noticeable discrepancies in both the mechanical and barrier properties of the composite material. Furthermore, it is imperative to conduct assessments of the antimicrobial and antioxidant properties of these prepared bionanocomposites to substantiate their effectiveness as active materials in food packaging applications.

Abstract

In this study, Hydroxyapatite nanoparticles (HANPs), derived from eggshell waste, were employed to reinforce chitosan biopolymer-based films through the solvent-casting method. The impact of varying HANPs content (1%, 3%, 5%, and 10 wt %) in bionanocomposites was investigated. The influence of HANPs addition on the final film properties was comprehensively analyzed using Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA), mechanical (tensile) testing, and Water Vapor Permeability (WVP). The morphological aspects of bionanocomposites and the dispersion of nanoparticles within the matrix were studied using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and X-ray Diffraction (XRD). The structural changes in the films were probed using Fourier-Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) techniques. Results indicated that the addition of 1% and 3% of HANPs exhibited a higher glass transition temperature and improved thermal stability in bionanocomposites. Films with 3% HANPs content exhibited a notable increase in tensile strength, showing a 61.54% increase, while films with 1% HANPs content displayed a 52% reduction in WVP compared to pristine chitosan films. These findings underscore the significant potential of chitosan-hydroxyapatite bionanocomposite films for applications in food packaging applications.

KEYWORDS: Synthesis, Bionanocomposite film, Chitosan, Hydroxyapatite nanoparticles, Mechanical properties