Transparent and Robust All-Cellulose Nanocomposite Packaging Materials Prepared in a Mixture of Trifluoroacetic Acid and Trifluoroacetic Anhydride

Abstract

All-cellulose composites with a potential application as food packaging films were prepared by dissolving microcrystalline cellulose in a mixture of trifluoroacetic acid and trifluoroacetic anhydride, adding cellulose nanofibers, and evaporating the solvents. First, the effect of the solvents on the morphology, structure, and thermal properties of the nanofibers was evaluated by atomic force microscopy (AFM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA), respectively. An important reduction in the crystallinity was observed. Then, the optical, morphological, mechanical, and water barrier properties of the nanocomposites were determined. In general, the final properties of the composites depended on the nanocellulose content. Thus, although the transparency decreased with the amount of cellulose nanofibers due to increased light scattering, normalized transmittance values were higher than 80% in all the cases. On the other hand, the best mechanical properties were achieved for concentrations of nanofibers between 5 and 9 wt.%. At higher concentrations, the cellulose nanofibers aggregated and/or folded, decreasing the mechanical parameters as confirmed analytically by modeling of the composite Young’s modulus. Finally, regarding the water barrier properties, water uptake was not affected by the presence of cellulose nanofibers while water permeability was reduced because of the higher tortuosity induced by the nanocelluloses. In view of such properties, these materials are suggested as food packaging films.

All-Cellulose Composites: A Review of Recent Studies on Structure, Properties and Applications

“…In addition, the obtained ACCs showed high transparency (76% at a wavelength of 800 nm) compared to a microfiber sheet (0.3%) which is about a 250-fold increment. The high transparency of ACCs can be attributed to the thinner reinforcements during the partial dissolving/nanowelding of the microfibers to make ACCs [75] which results in a more effective interface, low void volumes and less surface roughness [75,76] compared to those of cellulose microfiber sheets.…”

“…ACCs are used in a wide range of applications such as structural materials, biomedical engineering (substitution of bone and cartilage materials), photoelectric devices, electro-active paper, sensors, electrical displays, filtration materials, biodegradable food packaging materials and mulching films for agriculture [ 60 , 76 , 79 , 135 , 143 , 146 , 147 , 148 , 149 , 150 , 151 , 152 , 153 , 154 ].…”

Nanocellulose Bio-Based Composites for Food Packaging

“…Both strategies involve the dissolution of cellulose. The most common solvents used for dissolution are LiCL/DMAc, N-methylmorpholine N-oxide (NMMO), NaOH, acetone and ionic liquids (ILs) [ 128 ].…”

“…In the work of Gindl et al [ 129 ], BNC sheets were soaked in a cellulose acetate solution (with acetone as solvent). In the work of Puyol et al [ 128 ] dissolved microcrystalline cellulose (MCC) (with trifluoroacetic acid and trifluoroacetic anhydride) was blended with dispersed NFC in chloroform. Both developed ACCs showed enhanced mechanical properties (tensile strength and Young modulus increased up to 400% and 173%, respectively with BNC) and transparency (higher than 80%) with the incorporation of nanocellulose [ 128 , 129 ].…”

Nanomaterials to Enhance Food Quality, Safety, and Health Impact

“…This method consisted of a two-step process, namely the partial depolymerization of BC under ultrasonic irradiation and the extraction of crystalline regions using microwaves, assisted by manganese (II) chloride (MnCl 2 )-catalyzed hydrolysis, successfully yielding bacterial cellulose nanocrystals (BC-NCs) with similar features to commercially available nanocrystalline cellulose. In another study, Guzman-Puyol et al [2] prepared all-cellulose nanocomposites with potential applications in compostable food packaging by using a simple method consisting of dissolving cellulose in a trifluoroacetic acid/trifluoroacetic anhydride 2:1 (vol/vol) mixture and subsequently adding different cellulose nanofibers (CNFs) dispersed in chloroform. The best performance was achieved for concentrations of nanofibers ranging from 5 to 9 wt%, maintaining excellent transparency, improving the mechanical properties, and reducing the water permeability.…”