Abstract
In the present study, poly(ethylene-co-vinyl alcohol) with 44 mol % ethylene content (EVOH44) was managed to be processed, for the first time, by electrospinning assisted by the coaxial technology of solvent jacket. In addition to this, different suspensions of cellulose nanocrystals (CNCs), with contents ranging from 0.1 to 1.0 wt %, were also electrospun to obtain hybrid bio-/non-bio nanocomposites. The resultant fiber mats were thereafter optimally annealed to promote interfiber coalescence at 145 °C, below the EVOH44 melting point, leading to continuous transparent fiber-based films. The morphological analysis revealed the successful distribution of CNCs into EVOH44 up to contents of 0.5 wt %. The incorporation of CNCs into the ethylene-vinyl alcohol copolymer caused a decrease in the crystallization and melting temperatures (TC and Tm) of about 12 and 7 °C, respectively, and also crystallinity. However, the incorporation of CNCs led to enhanced thermal stability of the copolymer matrix for a nanofiller content of 1.0 wt %. Furthermore, the incorporation of 0.1 and 0.5 wt % CNCs produced increases in the tensile modulus (E) of ca. 38% and 28%, respectively, but also yielded a reduction in the elongation at break and toughness. The oxygen barrier of the hybrid nanocomposite fiber-based films decreased with increasing the CNCs content, but they were seen to remain high barrier, especially in the low relative humidity (RH) regime, i.e., at 20% RH, showing permeability values lower than 0.6 × 10−20 m3·m·m−2·Pa−1·s−1. In general terms, an optimal balance in physical properties was found for the hybrid copolymer composite with a CNC loading of 0.1 wt %. On the overall, the present study demonstrates the potential of annealed electrospun fiber-based high-barrier polymers, with or without CNCs, to develop novel barrier interlayers to be used as food packaging constituents.
Highlights
Polymers have been replacing the materials traditionally used in packaging, such as metal, glass, or cardboard, because they are more flexible, lighter, and habitually more cost-effective [1]
The pure EVOH44 solution presented a viscosity of 71.9 cP, a surface tension of 23.8 mN/m, and a conductivity of 11.63 μS/cm
The present study demonstrated the potential of the electrospinning process to obtain a new high-gas-barrier transparent fiber-based EVOH44 film
Summary
Polymers have been replacing the materials traditionally used in packaging, such as metal, glass, or cardboard, because they are more flexible, lighter, and habitually more cost-effective [1]. Polymer-based materials present certain disadvantages, such as higher permeability and sorption to gases like oxygen or carbon dioxide, moisture, and organic vapors. Polymer films must present transparency, high mechanical and chemical resistance as well as be food contact approved [2]. In this sense, the thermoplastic poly(ethylene-co-vinyl alcohol) (EVOH), habitually termed ethylene vinyl alcohol copolymers, are one of the most used polymer materials in highbarrier packaging films. The EVOH copolymers, including that with 44 mol % ethylene content (EVOH44), with high vinyl-alcohol contents, have been proven to be able to degrade under certain environmental conditions and biological media [9,10,11,12]
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