Nanocomposite Coatings Based on Polyvinyl Alcohol and Montmorillonite for High-Barrier Food Packaging

Polyvinyl alcohol coating releasing fungal blastospores improves kill effect of attract-and-kill beads

Polyvinyl alcohol (PVA) is a biodegradable, water-soluble polymer with excellent film forming properties, commonly studied or used as tablet coating, food packaging or controlled release fertilizers. Attract-and-kill (AK) beads are sustainable, microbial alternatives to synthetic soil insecticides, whose onset of lethal effect largely depend on how fast the encapsulated entomopathogenic fungus forms virulent conidia. Therefore, the objective of this study was to develop a water-soluble coating accelerating the kill effect of AK beads by immediately releasing virulent Metarhizium brunneum CB15-III blastospores. We assessed three PVA types (PVA 4-88, 8-88, 10-98) which differed in their degree of hydrolysis or molecular weight for their ability to release viable blastospores from thin films after drying at 60-40 °C, and examined how polyethylene glycol and soy-lecithin impact the blastospore survival. Finally, we evaluated the effectiveness of coated AK beads in a bioassay against Tenebrio molitor larvae. The blastospore release rate quadrupled within the first 5 min with decreasing molecular weight and degree of hydrolysis, with PVA 4-88 releasing 79 ± 19% blastospores. Polyethylene glycol and soy-lecithin significantly increased the blastospore survival to 18-28% for all three PVA types. Coated beads exhibited a uniform, 22.4 ± 7.3 µm thin coating layer, with embedded blastospores, as confirmed by scanning electron microscopy. The blastospore coating increased the mortality rate of T. molitor larvae over uncoated AK beads, decreasing the median lethal time from 10 to 6 days. Consequently, the blastospore coating accelerated the kill effect of regular AK beads. These findings pave the way to enhanced pest control efficacy from coated systems such as beads or seeds.

A Comparative Study on the Roll-to-Roll Processing of a Silicate-Polyvinyl Alcohol Composite Barrier Lacquer Using Slot-Die and Reverse Gravure Coating Techniques

The integration of platelet-shaped montmorillonite particles to improve the oxygen barrier of polyvinyl-alcohol-based barrier layers is state-of-the-art, but research on roll-to-roll coatings of such composite barrier lacquers has not been widely published. In this study, two different coating techniques, slot-die and reverse gravure, were used on a roll-to-roll scale to apply barrier lacquers comprising polyvinyl alcohol and montmorillonite. The lacquers were analyzed regarding viscosity at certain shear rates and surface energy and the dried coating layers regarding oxygen barrier, surface morphology, and particle orientation. Low permeability coefficients delivering a high oxygen barrier of 0.14 and 0.12 cm3 (STP) 1 μmm2 d bar were achieved for the coating layers with slot-die and reverse gravure coating, respectively. It turned out that the properties of the barrier lacquer need to be adjusted to the coating technique to achieve high oxygen barrier performance. By tailoring the barrier lacquer formulation, the orientation of the platelet-shaped montmorillonite particles can be achieved using both techniques. A low solid content of down to 3 wt% is preferable for the premetered slot-die coating, because it results in low agglomeration quantity in the coating layer. A high solid content of up to 9 wt% is preferable for the self-metered reverse gravure coating to assure a homogeneously coated layer.

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.

The Neural Circuit Architecture of Social Hierarchy in Rodents and Primates

Social status is recognized as a major determinant of social behavior and health among animals; however, the neural circuits supporting the formation and navigation of social hierarchies remain under extensive research. Available evidence suggests the prefrontal cortex is a keystone in this circuit, but upstream and downstream candidates are progressively emerging. In this review, we compare and integrate findings from rodent and primate studies to create a model of the neural and cellular networks supporting social hierarchies, both from a macro (i.e., circuits) to a micro-scale perspective (microcircuits and synapses). We start by summarizing the literature on the prefrontal cortex and other relevant brain regions to expand the current “prefrontal-centric” view of social hierarchy behaviors. Based on connectivity data we also discuss candidate regions that might inspire further investigation, as well as the caveats and strategies that have been used to further our understanding of the biological substrates underpinning social hierarchy and dominance.