Biodegradable composites with improved barrier properties and transparency from the impregnation of PLA to bacterial cellulose membranes

Poly(lactic acid) (PLA) was impregnated in bacterial cellulose (BC) membranes. BC/PLA films were prepared by solvent casting and mechanical, optical and barrier properties, and biodegradation process were investigated. The transparency of processed films was higher than that of neat BC and increased with PLA content. Moreover, the incorporation of PLA to BC enhanced significantly the water vapor barrier properties of the BC membranes. The bionanocomposites contained a high percentage of cellulose due to the impregnation method that leads to the film with a BC content of 94%, which practically maintains the excellent mechanical properties of BC. However, when increasing the PLA content in the bionanocomposites the mechanical properties decreased slightly with respect to BC. Biodegradation under real soil conditions was determined indirectly through the study of the visual degradation and disintegration, demonstrating that the bionanocomposites were degraded faster than the neat PLA. The successful production of BC/PLA bionanocomposites suggested the possible application of them for active food packaging. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43669.     

Nitrogen-doped graphene with enhanced oxygen reduction activity produced by pyrolysis of graphene functionalized with imidazole derivatives

Nitrogen-doped graphene nanoplatelets (N-GNP) with 1.6–3.3 at.% nitrogen content were synthesized by thermal annealing of GNP functionalized with a series of imidazole-based nitrogen-containing precursors of different nature, charge and nitrogen content. The imidazole derivatives included one ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate (BMIBF4) and two polymers, a neutral one, poly(vinylimidazole) (PVI) and a poly(ionic liquid), poly(3-butyl-1-vinylimidazolium bromide) (PBVIBr). N-GNP showed enhanced electrocatalytic activity for oxygen reduction reaction (ORR) in alkaline media compared to pristine GNP, with the number of electrons transferred in oxygen-saturated KOH at low overpotentials following the trend: 2.5 (pristine GNP) < 2.9 (N-GNP from PVI–GNP) < 3.3 (N-GNP from BMIBF₄–GNP) < 3.5 (N-GNP from PBVIBr-GNP). Interestingly, ORR catalytic activity did not correlate with total nitrogen content but was more affected by Brunauer–Emmett–Teller (BET) surface area. The most active materials were N-GNP with lowest doping levels and highest surface area resulting from the ionic (imidazolium-based) nitrogen precursors.     

Carbon nanotubes/chitin nanowhiskers aerogel achieved by quaternization‐induced gelation

Organic aerogels from polysaccharides such as cellulose and chitin are of particular importance because they utilize renewable feedstocks. In this article, the aerogels were prepared through the self‐assembly of chitin nanowhiskers previously modified. The surface of chitin nanowhiskers was rendered cationic through two reactions. A first reaction between hydroxyl groups of chitin and 2‐chloroethyl isocyanate and a second reaction between the chloride groups of isocyanate anchored to the surface and 1‐methylimidazole. This modification led to stable aqueous suspensions of the chitin nanowhiskers with gelation and rheological properties. Additionally, chitin nanowhiskers aerogels containing modified carbon nanotubes were obtained. The addition of modified carbon nanotubes provoked a change in the morphology of the hydrogels and as a consequence, the rheological properties of the hydrogel are modified as well. In contrast from previous procedures, this method has not required any kind of solvent exchange or high pressure in order to obtain the final materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42547.     

PVC/PBA random copolymers obtained by SET–DTLRP: Pressure effect on glass transition,rheology, and processing

A study of the effect of pressure on the glass transition and viscosity of poly(vinyl chloride) (PVC)–poly(butyl acrylate) random copolymers prepared by Single Electron Transfer–Degenerative Chain Transfer Living Radical Polymerization and able to act as self‐plasticized PVCs, is presented. The research has a dual purpose, as it focuses on polymer physics, as well as on applied polymer processing. Results of dynamic mechanical thermal analysis, pressure–volume–temperature (PVT), and extrusion capillary tests were combined, to analyze the additivity of the free volume and the effect of frequency and pressure on the glass transition of the copolymers, T_g. Free volume additivity, which is on the basis of self‐plasticization, was revealed by T_g and activation energy of flow, E_a, results. dT_g/dP results were linked to the number of segments involved in the glass transition temperature. Using an ad hoc model, which involves parameters obtained by PVT and the activation energy of flow, the pressure‐viscosity coefficient was determined. This allowed estimating the viscosity as a function of the shear rate, the temperature and the pressure, offering suitable data to be employed in virtual injection molding. J. VINYL ADDIT. TECHNOL., 25:76–84, 2019. © 2018 Society of Plastics Engineers     

Molecular characterization of alkyd/acrylic latexes prepared by miniemulsion polymerization

The molecular characterization of alkyd/acrylic hybrid latexes produced by miniemulsion polymerization was characterized in terms of the resin degree of grafting, acrylic degree of grafting, reacted double bonds in the alkyd, gel content, and molecular weight distribution of the sol part. A simple method based on conventional size exclusion chromatography measurements was developed to estimate the fraction of alkyd resin grafted to the acrylic polymer. The method could be applied to completely soluble hybrids and to hybrids containing gel. Also, the limits of the extraction method used in the literature to estimate the fraction of acrylic polymer grafted to the alkyd was investigated; we found that this technique only provided accurate results at high values of the acrylic degree of grafting. The combination of this information with the reacted double bonds of the alkyd (determined by iodine titration) and the molecular weight distribution of the sol polymer provided a detailed characterization of the alkyd–acrylic hybrid polymer. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Pineapple agroindustrial residues for the production of high value bacterial cellulose with different morphologies

Bacterial cellulose (BC) with different morphologies was biosynthesized by Gluconacetobacter medellinensis strain under static and dynamic culture conditions using sugar cane juice and pineapple residues as sources of carbon and other nutrients. Hestrin and Schramm's standard culture medium was used as reference. The fermentation condition and resulting yield, physico‐chemical properties, and morphology relationships of obtained cellulose were analyzed. Pineapple agroindustrial residues can be envisaged as an inexpensive and sustainable alternative resource for the production of different BC morphologies. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41237.     

Transformation of waterborne hybrid polymer particles into films: Morphology development and modeling

Films cast from multiphase polymer particles have the potential to combine the properties of their components synergistically. The properties of the film depend on the hybrid polymer architecture and the film morphology. However, how the polymer microstructure and particle morphology are transformed during film formation to determine the film morphology is not well understood. Here, using waterborne alkyd-acrylic nanocomposite particles in a case study, it was found that phase migration leading to the formation of aggregates occurred during film formation. A coarse-grained Monte Carlo model was developed to account for the effects of polymer microstructure and particle morphology on the morphology of the film. The model was validated by comparing its predictions with the observed effects, and then used to explore combinations of polymer microstructure and particle morphology not attainable with the system used as a case study. Significantly, the compatibility of the phases was found to have a greater influence than the morphology of the particles in determining the film structure.