Stretchable Clay Nanocomposite Barrier Film for Flexible Packaging.

The goal of reconciling all packaging requirements, e.g., mechanical resistance, transparency, flexibility, and gas barrier properties, is immensely challenging for packaging materials. Particularly, the combination of flexibility and good gas barrier properties poses a serious problem, especially when barrier requirements can only be met by lamination with a metal foil, metalization, or vapor-deposited ceramic layers, as all of these tend to be nonstretchable. In this work, we produced a stretchable nanocomposite barrier composed of one-dimensional (1D) crystalline (Bragg stack) barrier films composed of alternating layers of poly(ethylene glycol) (PEG) and synthetic sodium fluorohectorite (Hec) nanosheets. By sandwiching the Bragg stack type film between two plasticized poly(vinyl alcohol) (PVOH) layers, a waterborne laminate was obtained that outperforms commercial polymer materials in terms of water vapor permeability (WVP = 2.8 g mm m-2 day-1 bar-1 at 23 °C and 85% relative humidity), which is remarkable for an entirely water-soluble film. Moreover, no deterioration of barrier performance up to 10% elongation was observed, rendering the transparent self-standing laminate promising for thermoformed blister packaging, shrink wrap, or vacuum packaging. Besides the low WVP, the scalable and green processing method makes this technology auspicious for real-world applications.

New Functional Polymer Materials via Click Chemistry-Based Modification of Cellulose Acetate.

Cellulose acetate (CA) was partially acrylated, and the resulting cellulose acetate acrylate (acryl-substitution degree of 0.2) underwent quantitative thio-Michael click reactions with various thiols. A toolbox of functional CA polymers was obtained in this way, and their properties were studied. The modification with fatty alkyl thiols led to hydrophobic materials with large water drop contact angles. Octadecylthio-, butoxycarbonylpropylthio-, and furanylthio-modifications formed highly transparent materials. The new derivative CAASFur disintegrated completely under industrial composting conditions. Films of modified CA polymers were cast and investigated in terms of barrier properties. The nanocomposite of CAAS18 compounded with a synthetic layered silicate (hectorite) of a large aspect ratio showed permeabilities as low as 0.09 g mm m-2 day-1 for water vapor and 0.16 cm3 mm m-2 day-1 atm-1 for oxygen. This portfolio of functional CA polymers opens the door to new applications.

Disorder-Order Transition-Improving the Moisture Sensitivity of Waterborne Nanocomposite Barriers.

Systematic studies on the influence of crystalline vs disordered nanocomposite structures on barrier properties and water vapor sensitivity are scarce as it is difficult to switch between the two morphologies without changing other critical parameters. By combining water-soluble poly(vinyl alcohol) (PVOH) and ultrahigh aspect ratio synthetic sodium fluorohectorite (Hec) as filler, we were able to fabricate nanocomposites from a single nematic aqueous suspension by slot die coating that, depending on the drying temperature, forms different desired morphologies. Increasing the drying temperature from 20 to 50 °C for the same formulation triggers phase segregation and disordered nanocomposites are obtained, while at room temperature, one-dimensional (1D) crystalline, intercalated hybrid Bragg Stacks form. The onset of swelling of the crystalline morphology is pushed to significantly higher relative humidity (RH). This disorder-order transition renders PVOH/Hec a promising barrier material at RH of up to 65%, which is relevant for food packaging. The oxygen permeability (OP) of the 1D crystalline PVOH/Hec is an order of magnitude lower compared to the OP of the disordered nanocomposite at this elevated RH (OP = 0.007 cm3 µm m-2 day-1 bar-1 cf. OP = 0.047 cm3 µm m-2 day-1 bar-1 at 23 °C and 65% RH).

Alkenyl succinic anhydride modified tree-gum kondagogu: A bio-based material with potential for food packaging.

Tree gums are a class of abundantly available carbohydrate polymers that have not been explored thoroughly in film fabrication for food packaging. Films obtained from pristine tree gums are often brittle, hygroscopic, and lack mechanical strength. This study focuses on the chemical modification of gum kondagogu using long-chain alkenyl groups of dodecenyl succinic anhydride (DDSA), an esterifying agent that introduces a 12-carbon hydrophobic chain to the kondagogu structure. The esterification reaction was confirmed by 1H nuclear magnetic resonance and Fourier-transform infrared spectroscopy. The effect of nano-cellulose as an additive on various film properties was investigated. The developed films were characterized for their mechanical, morphological, optical, barrier, antibacterial, and biodegradable properties. The inclusion of long-chain carbon groups acted as internal plasticizers and resulted in an amorphous structure with better film-forming ability, improved hydrophobicity, and higher elongation at break values. The modified films exhibited antibacterial properties and excellent biodegradability under aerobic conditions.

Lightweight Ultra-High-Barrier Liners for Helium and Hydrogen.

Upcoming efficient air-borne wind energy concepts and communication technologies applying lighter-than-air platforms require high-performance barrier coatings, which concomitantly and nonselectively block permeation not only of helium but also of ozone and water vapor. Similarly, with the emergence of green hydrogen economy, lightweight barrier materials for storage and transport of this highly diffusive gas are very much sought-after, particularly in aviation technology. Here the fabrication of ultraperformance nanocomposite barrier liners by spray coating lamellar liquid crystalline dispersions of high aspect ratio (∼20 000) silicate nanosheets mixed with poly(vinyl alcohol) on a PET substrate foil is presented. Lightweight nanocomposite liners with 50 wt % filler content are obtained showing helium and hydrogen permeabilities as low as 0.8 and 0.6 cm3 µm m-2 day-1 atm-1, respectively. This exhibits an improvement up to a factor of 4 × 103 as compared to high-barrier polymers such as ethylene vinyl alcohol copolymers. Furthermore, ozone resistance, illustrated by oxygen permeability measurements at elevated relative humidity (75% r.h.), and water vapor resistance are demonstrated. Moreover, the technically benign processing by spray coating will render this barrier technology easily transferable to real lighter-than-air technologies or irregular- and concave-shaped hydrogen tanks.