Abstract
In this work, we present the development of bionanocomposite coatings on poly(ethylene terephthalate) (PET) with outstanding oxygen barrier properties. Pullulan and graphene oxide (GO) were used as main polymer phase and nanobuilding block (NBB), respectively. The oxygen barrier performance was investigated at different filler volume fractions (ϕ) and as a function of different relative humidity (RH) values. Noticeably, the impermeable nature of GO was reflected under dry conditions, in which an oxygen transmission rate (OTR, mL·m−2·24 h−1) value below the detection limit of the instrument (0.01 mL·m−2·24 h−1) was recorded, even for ϕ as low as 0.0004. A dramatic increase of the OTR values occurred in humid conditions, such that the barrier performance was totally lost at 90% RH (the OTR of coated PET films was equal to the OTR of bare PET films). Modelling of the experimental OTR data by Cussler’s model suggested that the spatial ordering of GO sheets within the main pullulan phase was perturbed because of RH fluctuations. In spite of the presence of the filler, all the formulations allowed the obtainment of final materials with haze values below 3%, the only exception being the formulation with the highest loading of GO (ϕ ≈ 0.03). The mechanisms underlying the experimental observations are discussed.
Highlights
In materials science, the advent of nanotechnology has represented a revolutionary step forward to unprecedented possibilities in the fabrication of materials and structures with outstanding functional properties
The advantages of nanocomposites mainly arise from the nano-length-scale entities that are used within the main polymer matrix, providing it with new performance capabilities
These nanoparticles—often named nanobuilding blocks (NBBs)—can be different in shape and origin [1,2]
Summary
The advent of nanotechnology has represented a revolutionary step forward to unprecedented possibilities in the fabrication of materials and structures with outstanding functional properties. The advantages of nanocomposites mainly arise from the nano-length-scale entities that are used within the main polymer matrix, providing it with new performance capabilities These nanoparticles—often named nanobuilding blocks (NBBs)—can be different in shape (round/spherical, platy, or rods/whiskers) and origin (organic or inorganic) [1,2]. Multifunctionality is a highly sought-after feature, especially when the high unit cost of the nanocomposite material represents a hurdle to market applications In these circumstances, this high cost is somehow counterbalanced by the multiple functional properties offered by the material, which make any commercial exploitation more affordable. BBootthh tthhee tthhiicckknneessss ((ll)) ooff bbaarree aanndd ccooaatteedd ppoollyy((eetthhyylleennee tteerreepphhtthhaallaattee)) ((PPEETT)) fifillmmss aanndd ooxxyyggeenn ttrraannssmmiissssiioonn rraattee ((OOTTRR)) ddaattaa aarriissiinngg ffrroomm tthhee ppeerrmmeeaabbiilliittyy tteessttss aarreesshhoowwnniinnTTaabbllee. For all the formulations, the benefits arising from the coating deposition disappeared at 90% RH, the OTR value of the bare PET being restored (~100 mL·m−2·24 h−1)
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