Polyaniline-Grafted Chitin Nanocrystals as Conductive Reinforcing Nanofillers for Waterborne Polymer Dispersions.

Due to its intrinsic electrical conductivity, polyaniline (PANI) is one of the most promising conducting polymers for high-performance applications in a wide range of technological fields. However, its poor dispersibility in water and organic solvents markedly imparts its processability and electrical conductivity. Herein, we report a green and one-step approach to preparing stable colloidal dispersions of highly dispersible hybrid nanoparticles by polymerizing PANI onto chitin nanocrystals (ChNCs) as biotemplates, via initiation through the surface amino groups of ChNCs. Evidence of the grafting of PANI onto ChNCs was supported by transmission electron microscopy (TEM), as well as Raman and Fourier transform infrared (FTIR) spectroscopies. Nanocomposite films were prepared by mixing the PANI-g-ChNCs with a waterborne poly(vinyl acetate) latex dispersion followed by casting and film formation at room temperature. The mechanical properties were tested as a function of the PANI-g-ChNC content. In addition, it was shown that at a proper content of PANI in ChNCs, and over a critical loading in the PANI-g-ChNCs, a conductive film was obtained, without sacrificing the reinforcing effect of the rodlike nanofiller. As a potential application, conductive waterborne adhesives for wood were prepared and the performance of the adhesives was tested. This research provides a facile route to fabricating a new class of hybrid nanofiller from a biobased origin, stable in water and easy to mix with waterborne dispersions, combining the merits of the ChNC nanofiller with the conductivity of PANI.

Processing Polymer Blends of Mater-Bi® and Poly-L-(Lactic Acid) for Blown Film Application with Enhanced Mechanical Strength.

Mater-Bi® is one of the most commercialized starch-based blends used in biodegradable flexible packaging. However, the high ductility and low stiffness of Mater-Bi® might limit its application and developing a solution to tailor the stiffness and mechanical strength is highly desirable. In the present work, blends based on Mater-Bi® and poly-L-(lactic acid) (PLLA) at a different ratio from 70/30 to 50/50 wt% were prepared via melt-extrusion and the effect of the PLLA content and Joncryl ADR® as a reactive compatibilizing agent, on the mechanical properties, melts rheology, morphology and disintegration aptitude were investigated. The inclusion of PLLA in Mater-Bi® has a marked beneficial effect on the tensile strength and stiffness of the blend while maintaining acceptable ductility. The addition of the reactive compatibilizing agent contributed to improving the strength and elongation at the break of the blend. The melt rheology of the blend was also affected by the ratio of the two components, mostly when the Joncryl ADR® was present. The disintegration by biodegradation of the blend was preserved in the presence of PLLA, and it takes less than 30 days for the films to completely decompose and disintegrate under controlled composting conditions. Interestingly, a thin film from Mater-Bi®/PLLA 60/40 was successfully prepared by blown film extrusion, demonstrating a good balance between stretchability (elongation at break exceeding 100%) and stiffness (1.8 GPa). This work opened to broadening the use of starch-based biodegradable plastic toward more demanding applications such as mulching films.

Hybrid levan-Ag/AgCl nanoparticles produced by UV-irradiation: properties, antibacterial efficiency and application in bioactive poly(vinyl alcohol) films.

Foodborne diseases caused by resistance of microorganisms to multiple antimicrobial agents have emerged as a major public health concern around the world. The search for potential antimicrobials has resulted in the emergence of metal nanoparticles for protection against these infections. In this study an eco-friendly and green approach was used to biosynthesize hybrid Ag/AgCl nanoparticles (NPs), using levan from Bacillus mojavensis as a stabilizing/reducing agent, with a high efficiency against a broad spectrum of foodborne bacteria as well as biofilm formations. The morphology and physicochemical characteristics of levan-Ag/AgCl NPs were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-vis spectroscopy (UV), dynamic light scattering (DLS) and thermogravimetric analysis (TGA). The hybrid levan-Ag/AgCl was evaluated for antibacterial activity against foodborne pathogenic bacteria (Escherichia coli, Klebsiella pneumoniae, Salmonella enterica, Pseudomonas aeruginosa, Staphylococcus aureus, Micrococcus luteus, Listeria monocytogenes, Enterococcus faecalis, Bacillus subtilis and Bacillus thuringiensis). The study demonstrated the strong efficiency of hybrid levan-Ag/AgCl NPs as a potent inhibitor against all tested strains, with much higher activity against Gram-negative than Gram-positive bacteria. Furthermore, bacterial strains were found to be highly sensitive to hybrid levan-Ag/AgCl NPs in comparison to the tested antibiotics. As a possible application of levan-Ag/AgCl NPs as an additive in packaging, PVA films with different amounts of hybrid levan-Ag/AgCl NPs were prepared by casting and their antibacterial, mechanical, and optical properties and ability to expand the shelf life of beef meat were explored. Interestingly, the amount of Ag leached out from films was below the permissible limit. This work demonstrates the strong antibacterial action of hybrid levan-Ag/AgCl NPs and their potential use in bioactive packaging material.

Vinyltriethoxysilane-functionalized starch nanocrystals as Pickering stabilizer in emulsion polymerization of acrylic monomers. Application in nanocomposites and pressure-sensitive adhesives.

Emulsion polymerization provides a sustainable way to produce latex polymers for coatings and adhesives thanks to the use of water as a dispersion medium. This synthesis approach can be even more attractive if synthetic surfactant can be replaced by biobased solid particles as a stabilizer, through what is known as a "Pickering effect". Herein, latex dispersions with solid content up to 35 wt% were successfully produced by emulsion polymerization using starch nanocrystals (SNCs) as a sole stabilizer and H2O2/citric acid as a redox-initiator. The effect of the SNC modification with vinyltriethoxysilane (VTES) on the colloidal properties of the polymer dispersion and performance of the resulting nanocomposite film were investigated. As an application of this approach, pressure-sensitive adhesive (PSA) dispersions have been prepared via Pickering emulsion polymerization in the presence of 8 wt% SNCs. The use of VTES-SNCs has a beneficial impact on the performance of PSAs with improved peel strength and wettability. The possibility to use SNCs as a stabilizer to replace synthetic surfactants in emulsion polymerization opens new avenues for the application of SNCs as biobased Pickering stabilizers to produce latex for coatings, adhesives, inks, and textiles.

Water-In-Water Emulsion Gels Stabilized by Cellulose Nanocrystals.

Particle-stabilized water-in-water emulsions were prepared by mixing dextran and poly(ethylene oxide) (PEO) in water and adding cellulose nanocrystals (CNC). The CNC formed a layer at the surface of the dispersed droplets formed by the PEO-rich phase. Excess CNC partitioned to the continuous dextran phase. Aggregation of CNC at different rates was induced by adding NaCl between 10 and 100 mM. In the presence of more than 2 g/L CNC, fast aggregation led to the formation of an emulsion gel showing no signs of creaming. Confocal laser scanning microscopy showed that the emulgels were formed by a continuous network of CNC in which the randomly distributed droplets were embedded. The gel stiffness was measured with oscillatory shear rheology and found to increase strongly with increasing CNC concentration ( C). The dispersed droplets were elastically active and increased the gel stiffness at low C. However, up to C = 10 g/L, the yield stress was too small to inhibit the flow when the gels were tilted. At C < 2 g/L, creaming was observed until the network of connected droplets became sufficiently dense to be strong enough to resist buoyancy.