Abstract
Iron particles of sizes between 6 and 20 nm forming aggregates of 57 ± 17 nm were synthesized by chemical reduction of iron precursors on the surface of montmorillonite (MMT). This active MMT-Fe powder was then uniformly distributed in a linear low-density polyethylene (LLDPE) matrix by extrusion at atmospheric conditions, as confirmed by wide-angle X-ray scattering (WAXS), which also detected a partial exfoliation of the nanoclays. Thermogravimetric analysis (TGA) did not detect any significant modification of the degradation temperature between nanocomposites and active nanocomposites. 57Fe Mössbauer spectroscopy evidenced the formation of a majority of iron boride in MMT-Fe as well as in the active film containing it. The LLDPE.Fu15.MMT-Fe3.75 and LLDPE.Fu15.MMT-Fe6.25 films had oxygen-scavenging capacities of 0.031 ± 0.002 and 0.055 ± 0.009 g(O2)/g(Fe), respectively, while the neat powder had an adsorption capacity of 0.122 g(O2)/g(Fe). This result confirms that the fresh film samples were partially oxidized shortly after thermomechanical processing (60% of oxidized species according to Mössbauer spectroscopy). No significant difference in oxygen permeability was observed when MMT-Fe was added. This was related to the relatively small film surface used for measuring the permeability. The reaction–diffusion model proposed here was able to reproduce the observed data of O2 adsorption in an active nanocomposite, which validated the O2 adsorption model previously developed for dried MMT-Fe powder.
Highlights
Much attention is currently being paid to the development of O2 barrier monolayer films that are as performing as the multilayer complex materials currently used for commercial applications and can still maintain the end of life characteristics of a monolayer pure matrix
To obtain monolayer films with good O2 barrier properties, one strategy is to develop materials based on nanocomposites such as, for instance, clay–polymer nanocomposites
Thanks to the dispersion of nanoscale clays in the bulk of the polymer, a significant decrease of O2 permeability can be achieved compared with that of a pure polymer matrix [4,5,6]. This is observed when a highly exfoliated structure is obtained, that is, when the polymer penetrates into the layered structure of the clay platelets, taking them apart and leading to individual clay foils randomly dispersed in the polymer
Summary
Much attention is currently being paid to the development of O2 barrier monolayer films that are as performing as the multilayer complex materials currently used for commercial applications and can still maintain the end of life characteristics of a monolayer pure matrix (recyclability, biodegradability, etc.). Multilayer packaging materials that nowadays offer the required protection against O2 and oxidation are difficult to recycle due to their complex formulations and have very high environmental impact [1,2,3]. Thanks to the dispersion of nanoscale clays in the bulk of the polymer, a significant decrease of O2 permeability can be achieved compared with that of a pure polymer matrix [4,5,6] This is observed when a highly exfoliated structure is obtained, that is, when the polymer penetrates into the layered structure of the clay platelets, taking them apart and leading to individual clay foils randomly dispersed in the polymer. Highly exfoliated structures are difficult to achieve, and the expected decrease in O2 permeability is not always as important as expected, as recently explained by Wolf et al [6]
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