Optimization of Laminated Bio-Polymer Fabrication for Food Packaging Application: A Sustainable Plasma-Activated Approach.

The current level of packaging consumption imposes a need to fabricate single-use food packaging with renewable and compostable materials, such as bio-polyesters (e.g., polylactic acid, PLA and polybutylene succinate, PBS) or cellulose, but their use is still problematic. Fabrication of bio-compostable composites can specifically address impeding challenges, and adhesive lamination, achieved with compostable glue, is becoming more and more popular with respect to the less versatile hot lamination. In this context, plasma activation, a chemical-free oxidation technique of a material's surface, is used to increase the affinity of three different biomaterials (cellulose, PLA and PBS) toward a compostable polyurethane adhesive to decrease its amount by gluing bio-polyesters to cellulose. Optical Microscopy reveals activation conditions that do not affect the integrity of the materials, while Water Contact Analyses confirm the activation of the surfaces, with contact angles decreased to roughly 50 deg in all cases. Unexpectedly, ζ-potential analyses and subtractive infrared spectroscopy highlight how the activation performed superficially etches cellulose, while for both PLA and PBS, a general decrease in surface potential and an increase in superficial hydroxyl group populations confirm the achievement of the desired oxidation. Thus, we rationalize continuous activation conditions to treat PLA and PBS and to glue them to neat cellulose. While no beneficial effect is observed with activated PLA, bi-laminate composites fabricated with activated PBS fulfill the benchmark for adhesion strength using less than before, while oxygen permeation analyses exclude plasma-induced etching even at a nanoscale.

Highly Permeable Fluorinated Polymer Nanocomposites for Plasmonic Hydrogen Sensing.

Hydrogen (H2) sensors that can be produced en masse with cost-effective manufacturing tools are critical for enabling safety in the emerging hydrogen economy. The use of melt-processed nanocomposites in this context would allow the combination of the advantages of plasmonic hydrogen detection with polymer technology; an approach which is held back by the slow diffusion of H2 through the polymer matrix. Here, we show that the use of an amorphous fluorinated polymer, compounded with colloidal Pd nanoparticles prepared by highly scalable continuous flow synthesis, results in nanocomposites that display a high H2 diffusion coefficient in the order of 10-5 cm2 s-1. As a result, plasmonic optical hydrogen detection with melt-pressed fluorinated polymer nanocomposites is no longer limited by the diffusion of the H2 analyte to the Pd nanoparticle transducer elements, despite a thickness of up to 100 µm, thereby enabling response times as short as 2.5 s at 100 mbar (≡10 vol. %) H2. Evidently, plasmonic sensors with a fast response time can be fabricated with thick, melt-processed nanocomposites, which paves the way for a new generation of robust H2 sensors.

Two-Step Solvent-Free Synthesis of Poly(hydroxybutyrate)-Based Photocurable Resin with Potential Application in Stereolithography.

A bio-based polymeric ink for stereolithography developed through a two-step solvent-free process is herein proposed. Specifically, low-molecular-weight poly(hydroxybutyrate) (PHB)-diol oligomers are prepared via molten transesterification of bacterial PHB with 1,4-butanediol. Transesterification conditions such as diol concentration, catalyst amount, and reaction time are studied for optimizing the final oligomers' molecular weight and structural features. In the second step, the oligomeric hydroxyl terminals are converted into methacrylate moieties through a solvent-free end-capping reaction and diluted in propylene carbonate in order to obtain a photo-polymerizable ink with suitable viscosity. The ink is UV-cured, and the obtained material properties are investigated by FT-IR and differential scanning calorimetry measurements. The proposed method provides a valuable and environmentally friendly alternative to currently available synthetic routes, overcoming their typical disadvantages related to the used solvents and harsh conditions. Moreover, it opens up a sustainable route for converting polyesters into functionalized oligomeric derivatives, which can potentially find application in 3D printing of customized biomedical devices.

Facile method based on 19F-NMR for the determination of hydroxyl value and molecular weight of hydroxyl terminated polymers.

A new, facile and low-sample consuming technique for the determination of hydroxyl values (OHVs) in poly(hydroxyalkanoate)s (PHAs) is herein presented. After a fast, uncatalyzed and non-destructive trifluoroacetylation of all PHA hydroxyl groups, OHVs are calculated through 19F-NMR measurements, comparing integral values of the only two signals in the spectra: the fluorinated hydroxyl groups and the internal standard (trifluorotoluene) signals. Furthermore, the combined ex situ functionalization with a simple workup of the fluorinated polymer allowed to obtain spectra with an improved signal/noise ratio and short acquisition time if compared to 1H-NMR-based methods. The results obtained by 19F-NMR measurements are then validated by the established standard method based on acid/base titration and the 1H-NMR-based method. The proposed approach shows to be valuable not only for low molecular weight PHAs, but also for high molecular weight samples, which typically cannot be analysed by conventional 1H-NMR-based methods due to the very low concentration of hydroxyl terminal groups. Thanks to the observed high reliability, the method was also successfully applied to evaluate the OHVs of various commercial hydroxyl terminated polymers with different molecular weights in order to further show its wide applicability.