Structural analysis of magnetic nanocomposites based on chitosan

Abstract

This work investigates the structure and magnetic properties of chitosan based films with different contents of magnetic nanoparticles (MNPs) of around 10 nm as well as the effects of the addition of glycerol as plasticizer. Synthesized MNPs were dispersed in the chitosan film forming solution by ultrasonication and then composite films were obtained by casting. From the morphological analysis, a bimodal distribution of clusters was detected; the larger ones seem to be present mostly in the plasticized samples. Regarding the mechanical behavior of the samples, for the non-plasticized samples the outstanding increase in modulus and strength with the increasing content of MNP was explained by a strong interfacial adhesion and very good particles dispersion into the chitosan matrix. This fact was also supported by the model applyed to the strength as a function of the volume fraction of MNP. Regarding magnetic properties, all nanocomposite films evidenced systems with particles of strong dipolar interactions that lead to blocking and irreversibility temperatures close to room temperature (RT). Even though the isothermal magnetization results showed that the particles in the nanocomposite films behave as super-paramagnetic at the highest analyzed temperature (RT), Langevin model as well as FESEM and SAXS analysis supported the hypothesis that the formation of aggregates with different features dominates the magnetic response through collective behavior, mainly in the plasticized films.

Chitosan/iron oxide nanocomposite films: Effect of the composition and preparation methods on the adsorption of congo red

“…Accordingly, it is not surprising that the pH of the adsorbent solution changes very little after adsorption onto these neutral in situ films. On the contrary, the pH of the adsorbent solution becomes acidic after adsorption of sonicated samples, which again is in accordance with their preparation procedure (film forming dispersions obtained in aqueous acetic acid solution (1% v/v) by 2 h sonication, then casting and drying (Kloster et al, 2018)). Moreover, it was noticed that after sorption, in situ films remained visually entire, without cracks or fissures that lead us to think that part of the sample mass was lost during the test.…”

“…Finally, the films were dried again under hood at room temperature and then kept in a closed container containing dried silica gel at room temperature (25 ± 1°C) until testing. Conversely, sonicated nanocomposite films were made firstly synthesizing the MNP (Kloster et al, 2018). To obtain the MNP, 4.8 g of FeSO 4 •7H 2 0 and 9.32 g of FeCl 3 •6H 2 O (molar ratio Fe +2 :Fe +3 = 1:2) were dissolved in approximately 40 mL of distilled water.…”

“…10 wt% MNPs were incorporated to the polymer solution to prepare nanocomposite films. Film forming suspensions were obtained by manually mixing MNPs with chitosan (or chitosan/glycerol) solution, followed by ultrasonication for 2 h. Then, the suspensions were poured into Petri dishes (diameter = 14 cm) and dried in a convective oven at 35°C for 24 h, leading to solid films (Kloster et al, 2018). In both systems (in situ and sonicated samples), the MNPs present average diameter sizes around 10 nm Kloster et al, 2018).…”

“…The complete characterization of the films used in this work can be found in previous publications Kloster, Muraca et al, 2015;Kloster et al, 2018).…”

“…These nanoparticles also cause secondary pollution to the environment due to their very minute dimensions (Li et al, 2017). On the other hand, we prepared and characterized thoroughly composite films made from magnetic iron oxides nanoparticles and chitosan by different, but relatively simple and cost-effective obtaining procedures Kloster, Muraca et al, 2015;Kloster et al, 2018). These films can perform as convenient and efficient natural polymer-based adsorbents, without the drawbacks associated to nano-particulate loose systems.…”