No abstract

Food packaging manufacturers often resort to lamination, typically with materials which are neither non-biodegradable nor biobased polymers, to confer barrier properties to paper and cardboard. The present work considers a greener solution: enhancing paper’s resistance to moisture, grease, and air by aqueous coating suspensions. For hydrophobization, a combined approach between nanocellulose and common esterifying agents was considered, but the water vapor transmission rate (WVTR) remained excessively high for the goal of wrapping moisture-sensitive products (>600 g m−2 d−1). Nonetheless, oil-repellant surfaces were effectively obtained with nanocellulose, illite, sodium alginate, and/or poly(vinyl alcohol) (PVA), reaching Kit ratings up to 11. Regarding air resistance, mineral-rich coatings attained values above 1000 Gurley s. In light of these results, nanocellulose, minerals, PVA, pullulan, alginate, and a non-ionic surfactant were combined for multi-purpose coating formulations. It is hypothesized that these materials decrease porosity while complementing each other’s flaws, e.g., PVA succeeds at decreasing porosity but has low dimensional stability. As an example, a suspension mostly constituted by nanocellulose, sizing agents, minerals and PVA yielded a WVTR of roughly 100 g m−2 d−1, a Kit rating of 12, and an air resistance above 300 s/100 mL. This indicates that multi-purpose coatings can be satisfactorily incorporated into paper structures for food packaging applications, although not as the food contact layer.

The present work aims at glimpsing the rate-determinant process parameters of TEMPO-mediated oxidation of bleached kraft cellulose for developing kinetic models and real-time monitoring tools. This may contribute to the scaling up of this reaction, frequently used as precursor of the production of cellulose nanofibers. For this, the effect of temperature, TEMPO and NaBr contents, and surface area of the fibers was assessed by means of a total experimental batch of 18 combinations, monitoring the carboxyl content (CC) of the samples and the NaOH consumption during oxidation. The obtained data was used to calculate the kinetic constant as a function of the conditions, as well as correlating the CC with the NaOH consumption, obtaining a strong linear correlation between these parameters. It was found that similar correlations could be used regardless process conditions, except for the case of TEMPO, which was found to protect the fibers from depolymerization and, thus, having different behavior at increasing TEMPO contents. Overall, the obtained results in the present study reveal the suitability of upscaling TEMPO-mediated oxidation, as well as having a deeper understanding on how the key parameters involved in the reaction affect the reaction path and, thus, contributing to the industrial deployment of oxidized cellulose and nanofibers.

The use of dithizone (DTZ) for colorimetric heavymetal detection is approximately one century old. However, its pending stability issues and the need for simple indicators justify further research. Using cellulose nanofibers, we attained DTZcontaining emulsions with high stability. These emulsions had water (at least 95 wt %) and acetic acid (1−8 mL/L) conforming the continuous phase, while dispersed droplets of diameter <1 μm contained chloroform-solvated DTZ (3 wt %). The solvation cluster was computed by molecular dynamics simulations, suggesting that chloroform slightly reduces the dihedral angle between the two sides of the thiocarbazone chain. Nanocellulose concentrations over 0.2 wt % sufficed to obtain macroscopically homogeneous mixtures with no phase separation. Furthermore, the rate of degradation of DTZ in the nanocellulose-stabilized emulsion did not differ significantly from a DTZ/chloroform solution, outperforming DTZ/toluene and DTZ/acetonitrile. Not only is the emulsion readily and immediately responsive to mercury(II), but it also decreases interferences from other ions and from natural samples. Unexpectedly, neither lead(II) nor cadmium(II) triggered a visual response at trace concentrations. The limit of detection of these emulsions is 15 μM or 3 mg/L, exceeding WHO limits for mercury(II) in drinking water, but they could be effective at raising alarms.