Comparison studies on covalently and non-covalently modified MWNTs using chitosan and their starch nanocomposites

Nanotechnology in food packaging materials: role and application of nanoparticles

Global concerns about food security, driven by rising demand, have prompted the exploration of nanotechnology as a solution to enhance food supply. This shift comes in response to the limitations of conventional technologies in meeting the ever-increasing demand for food products. Consequently, nanoparticles play a crucial role in enhancing food production, preservation, and extending shelf life by imparting exceptional properties to materials. Nanoparticles and nanostructures with attributes like expansive surface area and antimicrobial efficacy, are versatile in both traditional packaging and integration into biopolymer matrices. These distinctive qualities contribute to their extensive use in various food sector applications. Hence, this review explores the physicochemical properties, functions, and biological aspects of nanoparticles in the context of food packaging. Furthermore, the synergistic effect of nanoparticles with different biopolymers, alongside its different potential applications such as food shelf-life extenders, antimicrobial agents and as nanomaterials for developing smart packaging systems were summarily explored. While the ongoing exploration of this research area is evident, our review highlights the substantial potential of nanomaterials to emerge as a viable choice for food packaging if the challenges regarding toxicity are carefully and effectively modulated.

Effective dispersion of oxidized multi-walled carbon nanotubes using a water-soluble N,O-carboxymethyl chitosan via non-covalent interaction

Dispersible multi-walled carbon nanotubes (MWCNTs) in water have been widely applied in the nanotechnology field. This study reports a water-soluble N,O-carboxymethyl chitosan(N,O-CMCS) assisted individual dispersion of oxidized multi-walled carbon nanotubes (oMWCNTs) as a dispersant. First, the dispersing agent N,O-CMCS was successfully synthesized using the nucleophilic substitution of deacetylated chitosan with chloroacetic acid in an alkaline solution. It was further confirmed using Fourier transform infrared spectroscopy (FTIR). Second, after the treatment with the concentrated hydrochloric acid, the prepared oMWCNTs were dispersed in an aqueous solution of N,O-CMCS under ultrasonic vibrations. Finally, the dispersed aqueous solution was subjected to centrifugation to collect the supernatant of individually dispersed N,O-CMCS/oMWCNTs. In addition, transmission electron microscopy (TEM) further confirmed that the purity of oMWCNTs was improved after the acidification progress. Besides, the stability of the dispersion solution was evidenced by digital photos of oMWCNTs dispersed by N,O-CMCS before and after. Moreover, the UV-vis spectrum (the characteristic peak of dispersed oMWCNTs downshifted 13 nm) showed that the supernatant was enriched by the individual oMWCNTs. In particular, the analytical results of FTIR (the –NH₂ band of N,O-CMCS downshifted 7 cm⁻¹), resonance Raman spectroscopy (the I_D/I_G ratio of dispersed oMWCNTs only increased 0.14), and XRD identified the formation of a non-convalent interaction between N,O-CMCS and oMWCNTs. These findings reveal the dispersing nature of N,O-CMCS towards oMWCNTs in water media.

The stability of a dispersion solution was evidenced by images of oMWCNTs-dispersed by N,O-CMCS before (b) and after (a). UV-vis further showed that individual oMWCNTs were enriched via the non-covalent interaction between oMWCNTs and N,O-CMCS.

Functionalized multiwalled carbon nanotubes by loading phosphorylated chitosan

Novel flame-retardant phosphorylated chitosan-multiwalled carbon nanotubes (PCS-MWCNTs) were obtained by the loading of PCS on the surface of MWCNTs by a chemical deposition cross-linking method. A series of polyethylene terephthalate (PET) composites were prepared by melt compounding with MWCNTs or PCS-MWCNTs to investigate the flame-retardant properties. Field-emission scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared (FTIR) spectrometry were employed to characterize the morphology, chemical structure, and functionalization effect of MWCNTs. The coating degree and thermal stability of PCS-MWCNTs were investigated by thermogravimetric analysis (TGA). Thermal decomposition products after TGA and flame-retardant properties of PET composites were characterized by FTIR and CONE measurements, respectively. The results indicated that PCS is loaded on the MWCNT surface. Modified PCS-MWCNTs exhibited better dispersion and efficient flame retardancy. TGA data indicated that PCS-MWCNTs can enhance the onset temperature of PET and increase the amount of the char residues. The char residue with 1 wt% PCS-MWCNTs/PET increased from 12.62% (pure PET) to 15.46%. The analysis of the decomposition products and morphology of the char residue indicated that PCS-MWCNTs not only retain the effect of alternating couplet carbon (C) and physical barrier by MWCNTs, but also form P–C compounds, improving the flame retardancy of PET. CONE tests demonstrated that the PCS-MWCNTs lead to the efficient decrease in the flammability parameters, such as the heat release rate (HRR), total release heat rate (THR), total smoke production (TSP), mean mass loss rate (MMLR), and the total combustion time. The peak HRR value decreased from 513.22 kW m−2 to 341 kW m−2. The THR, TSP, and MMLR values decreased by 20.38 MJ m−2, 1.1 m2, and 1.32 g s−1, respectively. The total combustion time decreased by 98 s, from 388 s to 290 s, indicating that PCS-MWCNTs extinguish fire.