Enhancement of Water Vapor Barrier Properties of Biodegradable Poly(butylene adipate-co-terephthalate) Films with Highly Oriented Organomontmorillonite

Abstract

Low water vapor permeability is highly demanded for biodegradable packaging and agricultural film applications. However, biodegradable poly(butylene adipate-co-terephthalate) (PBAT) films demonstrate poor water vapor barrier properties. A series of nanocomposite (NC) films composed of organically modified montmorillonite (OMMT) dispersed at levels ranging from 0 to 13 wt % in PBAT were thus generated using both film blowing and biaxial orientation. Films were characterized with wide-angle X-ray diffraction, transmission electron microscopy, thermal analysis and mechanical testing (static and dynamic), and their water vapor permeation (WVP) values were determined. The WVP of PBAT-OMMT NC films relative to that of the pure PBAT dropped and began leveling at the maximum OMMT concentrations tested. NCs for which OMMT layers better aligned with film surfaces, in this case those generated via biaxial orientation, provided for faster and more substantial decreases in WVP values relative to those produced with film blowing. The WVPs can be predicted using the Bharadwaj model, which accounts for OMMT aspect ratio, concentration, as well as orientation. The experimental results are in good agreement with the prediction values of the model. The addition of 13 wt % OMMT more than doubled the Young's modulus, but resulting in a decrease of film tensile strength. The elongation at break was found to initially climb up to OMMT levels of about 6 wt % but declines sharply with higher concentrations. Results demonstrate the viability of reducing WVP levels of PBAT using orientated OMMT addition and provide insights on key structural parameters.

Ionic Liquids as Delaminating Agents of Layered Double Hydroxide during In-Situ Synthesis of Poly (Butylene Adipate-co-Terephthalate) Nanocomposites

“…It seems that the relatively high polarity of the PBAT backbone caused by the presence of ester groups promotes strong interactions between PBAT and polar molecules such as CO 2 and H 2 O [2]. As a result, the determined solubility coefficients of CO 2 and H 2 O are much higher than those of O 2 , which further results in significantly faster permeation of these polar molecules through PBAT materials as compared to O 2 .…”

“…Contrary to CO 2 and O 2 transport properties, the neat PBAT exhibited high water vapor permeabilities (WVP, Table 2), which limits its use for food packaging [2,3]. The addition of pristine LDH resulted in a very slight WVP decrease (6.5%) due to poor filler dispersion in the PBAT matrix (Figure 4a).…”

“…Other lamellar fillers (e.g., the most frequently used organically modified montmorillonite—OMMT, [2,3,46]) have been shown to provide similar WVP decrease of the PBAT nanocomposites at much higher OMMT loadings (e.g., 5 wt % [2], Figure 6). However, when non-polar phosphonium IL-modified montmorillonite is introduced, the relative permeability values of the PBAT/OMMT nanocomposites can be decreased even further (down to 0.2, Figure 6) [47].…”

“…However, its low crystallization degree results in insufficient stiffness and modulus. Together with low water vapor barrier properties, these are the main drawbacks limiting the PBAT usage for food packaging [2,3]. A possibility to overcome the PBAT shortcomings is to incorporate lamellar inorganic particles, such as cationic clays (talc and montmorillonites [2,4,5,6,7]), anionic clays such as layered double hydroxides (LDH) [8], and carbon compounds such as graphite or graphene-based nanoplatelets [9,10] in the PBAT matrix.…”

“…The melt blending involves dispersing of LDH in PBAT in the molten state using a strong shear force [16,17]. This straightforward technique does not require any solvent and is most commonly used for the dispersion of cationic clays (smectitic clay minerals, e.g., montmorillonites, MMT) in PBAT [2], while its application for exfoliation of bulky anionic clays (LDH) was found more difficult due to their high charge density [18]. This method, however, does not permit full exfoliation of all LDH particles, and often a mixture of mono- and multi-lamellar sheets is received [8].…”