Water Repellence and Oxygen and Water Vapor Barrier of PVOH-Coated Substrates before and after Surface Esterification

Approaches in Sustainable, Biobased Multilayer Packaging Solutions

The depletion of fossil resources and the growing demand for plastic waste reduction has put industries and academic researchers under pressure to develop increasingly sustainable packaging solutions that are both functional and circularly designed. In this review, we provide an overview of the fundamentals and recent advances in biobased packaging materials, including new materials and techniques for their modification as well as their end-of-life scenarios. We also discuss the composition and modification of biobased films and multilayer structures, with particular attention to readily available drop-in solutions, as well as coating techniques. Moreover, we discuss end-of-life factors, including sorting systems, detection methods, composting options, and recycling and upcycling possibilities. Finally, regulatory aspects are pointed out for each application scenario and end-of-life option. Moreover, we discuss the human factor in terms of consumer perception and acceptance of upcycling.

Core-shell encapsulation formulations to stabilize desiccated Bradyrhizobium against high environmental temperature and humidity

Engineered materials to improve the shelf-life of desiccated microbial strains are needed for cost-effective bioaugmentation strategies. High temperatures and humidity of legume-growing regions challenge long-term cell stabilization at the desiccated state. A thermostable xeroprotectant core and hydrophobic water vapour barrier shell encapsulation technique was developed to protect desiccated cells from the environment. A trehalose core matrix increased the stability of desiccated Bradyrhizobium by three orders of magnitude over 20 days at 32°C and 50% relative humidity (RH) compared to buffer alone; however, the improvement was not deemed sufficient for a shelf-stable bioproduct. We tested common additives (skim milk, albumin, gelatin and dextran) to increase the glass transition temperature of the desiccated product to provide further stabilization. Albumin increased the glass transition temperature of the trehalose-based core by 40°C and stabilized desiccated Bradyrhizobium for 4 months during storage at high temperature (32°C) and moderate humidity (50% RH) with only 1 log loss of viability. Although the albumin-trehalose core provided exceptional protection against high temperature, it was ineffective at higher humidity conditions (75%). We therefore incorporated a paraffin shell, which protected desiccated cells against 75% RH providing proof of concept that core and shell encapsulation is an effective strategy to stabilize desiccated cells.

Effect of PVOH/PLA + Wax Coatings on Physical and Functional Properties of Biodegradable Food Packaging Films

Biodegradable polymers suffer from inherent performance limitations that severely limit their practical application. Their functionalization by coating technology is a promising strategy to significantly improve their physical properties for food packaging. In this study, we investigated the double coating technique to produce multifunctional, high barrier and heat-sealable biodegradable films. The systems consisted of a web layer, made of poly(lactide) (PLA) and poly(butylene-adipate-co-terephthalate) (PBAT), which was first coated with a poly(vinyl) alcohol based layer, providing high barrier, and then with a second layer of PLA + ethylene-bis-stereamide (EBS) wax (from 0 to 20%), to provide sealability and improve moisture resistance. The films were fully characterized in terms of chemical, thermal, morphological, surface and functional properties. The deposition of the PVOH coating alone, with a thickness of 5 μm, led to a decrease in the oxygen transmission rate from 2200 cm³/m² d bar, for the neat substrate (thickness of 22 μm), to 8.14 cm³/m² d bar (thickness of 27 μm). The deposition of the second PLA layer did not affect the barrier properties but provided heat sealability, with a maximum bonding strength equal to 6.53 N/25 mm. The EBS wax incorporation into the PLA slightly increased the surface hydrophobicity, since the water contact angle passed from 65.4°, for the neat polylactide layer, to 71° for the 20% wax concentration. With respect to the substrate, the double-coated films exhibited increased stiffness, with an elastic modulus ca. three times higher, and a reduced elongation at break, which, however still remained above 75%. Overall, the developed double-coated films exhibited performances comparable to those of the most common synthetic polymer films used in the packaging industry, underlining their suitability for the packaging of sensitive foods with high O₂-barrier requirements.

The Preparations and Water Vapor Barrier Properties of Polyimide Films Containing Amide Moieties

Flexible displays are a systematic revolution in the field of display, in which high-performance and high-barrier polymer substrates are considered to be one of the most important key materials. In this work, high water vapor barrier polyimides containing amide moieties were synthesized via the ternary polymerization of 4,4'-diaminobenzailide (DABA), 4,4'-diaminodipheny ether (ODA), and 3,3',4,4'-biphenyl-tetracarboxylic acid dianhydride (BPDA) followed by thermal imidization. The relationship between the content of amide moieties and the water vapor barrier property of the prepared polyimides was studied by means of density test, water absorbing test, water contact angle test, water vapor permeation test, fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), thermogravimetry coupled with fourier transform infrared spectrometry (TG-FTIR), wide-angle X-ray diffraction analysis (WXRD), mechanical performance test, etc. The results show that the introduction of amide groups into polyimide (PI) main chains can improve the water vapor barrier properties of the polyimides effectively. The water vapor transmission rate (WVTR) of the polyimide films can be improved from 8.2365 g·(m²·24 h)-1 to 0.8670 g·(m²·24 h)-1 with the increasing content of amide moieties.

Effect of Chemical Grafting Parameters on the Manufacture of Functionalized PVOH Films Having Controlled Water Solubility

This study investigated the chemical grafting of a single-layer poly(vinyl alcohol) (PVOH) film. The effect of the grafting parameters (grafting time, grafting temperature, and concentration of fatty acid chloride) on the hydrophobicity of the film surface and the film solubility were evaluated. The PVOH substrate film (cold-water soluble at 20°C) was manufactured by flat extrusion and had a thickness of 50 μm (±5 μm). The chemical grafting was performed using the transfer method with palmitoyl chloride (C₁₆). The solubility, surface energy, and water vapor transmission rate of the grafted films were measured. The process parameters which produced the most hydrophobic PVOH film were found to be a fatty acid concentration of 3%, a grafting time of 14 min, and a grafting temperature of 130°C. These studies involved systematic adjustment of the hydrophobicity of one side of PVOH films. The results open up opportunities for packing fluids in water soluble packaging.

Review on the Processing and Properties of Polymer Nanocomposites and Nanocoatings and Their Applications in the Packaging, Automotive and Solar Energy Fields

For the last decades, nanocomposites materials have been widely studied in the scientific literature as they provide substantial properties enhancements, even at low nanoparticles content. Their performance depends on a number of parameters but the nanoparticles dispersion and distribution state remains the key challenge in order to obtain the full nanocomposites' potential in terms of, e.g., flame retardance, mechanical, barrier and thermal properties, etc., that would allow extending their use in the industry. While the amount of existing research and indeed review papers regarding the formulation of nanocomposites is already significant, after listing the most common applications, this review focuses more in-depth on the properties and materials of relevance in three target sectors: packaging, solar energy and automotive. In terms of advances in the processing of nanocomposites, this review discusses various enhancement technologies such as the use of ultrasounds for in-process nanoparticles dispersion. In the case of nanocoatings, it describes the different conventionally used processes as well as nanoparticles deposition by electro-hydrodynamic processing. All in all, this review gives the basics both in terms of composition and of processing aspects to reach optimal properties for using nanocomposites in the selected applications. As an outlook, up-to-date nanosafety issues are discussed.

Recent Prospects in the Inline Monitoring of Nanocomposites and Nanocoatings by Optical Technologies

Nanostructured materials have emerged as a key research field in order to confer materials with unique or enhanced properties. The performance of nanocomposites depends on a number of parameters, but the suitable dispersion of nanoparticles remains the key in order to obtain the full nanocomposites' potential in terms of, e.g., flame retardance, mechanical, barrier, thermal properties, etc. Likewise, the performance of nanocoatings to obtain, for example, tailored surface affinity with selected liquids (e.g., for self-cleaning ability or anti-fog properties), protective effects against flame propagation, ultra violet (UV) radiation or gas permeation, is highly dependent on the nanocoating's thickness and homogeneity. In terms of recent advances in the monitoring of nanocomposites and nanocoatings, this review discusses commonly-used offline characterization approaches, as well as promising inline systems. All in all, having good control over both the dispersion and thickness of these materials would help with reaching optimal and consistent properties to allow nanocomposites to extend their use.

Synthesis, Characterization, Thermal Stability and Sensitivity Properties of New Energetic Polymers-PVTNP-g-GAPs Crosslinked Polymers

A series of energetic polymers, poly(vinyl 2,4,6-trinitrophenylacetal)-g-polyglycidylazides (PVTNP-g-GAPs), were synthesized via cross-linking reactions of PVTNP with three different molecular weight GAPs using toluene diisocyanate as the cross-linking agent. The structures of these energetic polymers were characterized by ultraviolet visible spectra (UV–Vis), attenuated total reflectance-Fourier transform-infrared spectroscopy (ATR-FTIR), and nuclear magnetic resonance spectrometry (NMR). The glass-transition temperatures of these energetic polymers were measured with differential scanning calorimetry (DSC) method, and the results showed that all the measured energetic polymers have two distinct glass-transition temperatures. The thermal decomposition behaviors of these energetic polymers were evaluated by differential thermal analysis (DTA), thermogravimetric analysis (TGA) and thermogravimetric analysis tandem infrared spectrum (TGA-IR). The results indicated that all the measured energetic polymers have excellent resistance to thermal decomposition up to 200 °C, and the initial thermal decomposition was attributed to the breakdown of azide group. Moreover, the sensitivity properties of these energetic polymers were measured with the national military standard methods and their compatibilities with the main energetic components of 2,4,6-trinitrotoluene (TNT)-based melt-cast explosive were evaluated by using the DTA method. The results indicate that these energetic polymers have feasible mechanical sensitivities and can be safely used with TNT, cyclotetramethylene tetranitramine (HMX), 1,1-diamino-2,2-dinitroethene (FOX-7), 3-nitro-1,2,4-triazol-5-one (NTO) and 1,3,5-triamino-2,4,6-trinitrobenzene (TATB).