1,721,127 research outputs found
Polyvinyl chloride biodegradation by Pseudomonas citronellolis and Bacillus flexus
Full text linkThe accumulation of high amounts of petroleum-derived plastics in the environment has raised ecological and health concerns. The aim of this work was to study the biodegradative abilities of five bacterial strains, namely Pseudomonas chlororaphis, Pseudomonas citronellolis, Bacillus subtilis, Bacillus flexus and Chelatococcus daeguensis, towards polyethylene, polypropylene, polystyrene and polyvinyl chloride films under aerobic conditions. Preliminary screening resulted in the selection of P. citronellolis and B. flexus as potential PVC film degraders. Both strains were able to form a biofilm on the plastic film surface and to cause some modifications to the FTIR spectra of biomass-free PVC films. The two strains were then used to set up a PVC film biodegradation assay in 2-liter flasks. After 45 days incubation, fragmentation of the film was observed, suggesting that PVC biodegradative activity took place. Gel permeation chromatography analysis showed a reduction in average molecular weight of 10% for PVC incubated with P. citronellolis, with PVC polymer chains apparently attacked. Based on these results, the P. citronellolis strain was selected for biodegradation assays of two waste PVC films, used either nonsterile or subjected to ethanol sterilization. Chemical analyses on the incubated films confirmed the biodegradation of waste PVC plastics as shown by a gravimetric weight loss of up to about 19% after 30 days incubation. In summary, this work reports the biodegradation of PVC films by P. citronellolis and B. flexus. Both strains were shown to act mainly against PVC additives, exhibiting a low biodegradation rate of PVC polymer
Cold-crystallization of poly(butylene 2,6-naphthalate) following Ostwald's rule of stages
No full textMelt-crystallization of poly (butylene 2,6-naphthalate) (PBN) at temperatures lower than about 160 °C follows Ostwald's rule of stages, leading first to formation of a transient smectic liquid crystalline phase (LC) which then may convert in a second step into crystals, controlled by kinetics. In the present work, the PBN melt was cooled at different rates in a fast scanning chip calorimeter to below the glass transition temperature, to obtain different structural states before analysis of the cold-crystallization behavior on heating. It was found that heating of fully amorphous PBN at 1000 K/s leads to a similar two-step crystallization process as on cooling the quiescent melt, with LC-formation occurring slightly above Tg and their transformation into crystals at their stability limit close to 200 °C. In-situ polarized-light optical microscopy provided information that the transition of the LC-phase into crystals on slow heating is not connected with a change of the micrometer-scale superstructure, as the recently found Schlieren texture remains unchanged
Bio-based poly(propylene 2,5-furandicarboxylate/cyclohexanedicarboxylate) multiblock copolymers for food packaging applications
No full textEnthalpy of formation and disordering temperature of transient monotropic liquid crystals of poly(butylene 2,6-naphthalate)
No full textMelt-crystallization of poly(butylene 2,6-naphthalate) (PBN) at temperatures lower than about 160 °C follows Ostwald's rule of stages via intermediate formation of a smectic liquid crystalline phase (LC-phase). The transient LC-phase has been isolated by interruption of the isothermal crystallization process at 140 °C at sub-second timescale, and then its disordering was analyzed on heating at a rate of 2000 K/s, which suppresses the transition into α-crystals. The disordering temperature of the LC-mesophase is slightly lower than 200 °C, and as such 20–30 K lower than the melting temperature of α-crystals formed from the LC-phase at 140 °C. Analysis of the bulk enthalpy of formation of the LC-phase revealed that it covers only 20–25% of the total bulk enthalpy of crystallization, which is considered further proof of its smectic nature
New elastomeric biocompatible PLLA-based triblock copolymers for vascular tissue engineering applications
No full textNew nano and microparticles from PLLA-based triblock copolymers for controlled drug release
No full textReactive blending of poly(propylene 2,5-furandicarboxylate) and poly(propylene cyclohexanedicarboxylate). Bio-based multiblock copolymers for food packaging applications
No full textCrystallization of poly(butylene 2,6‐naphthalate) containing diethylene 2,6‐naphthalate constitutional defects
No full textDoes the glass transition of polymers change upon 3D confinement?
Full text linkThe calorimetric trace of polymer spheres shows an increase of the glass-transition temperature (Tg), with respect to its bulk value. This increase is evaluated by means of an entropy model, where the 3D confinement leads to a limiting number of repeating polymer units in the sphere, and thus to a reduction of the possible configuration states of the polymer chains. This is ultimately related to variations in the bulk value of the T g. Also, the way the polymer nature affects how confinement takes place and how restrictions imposed affect the way a polymer forms cooperative rearranging regions at Tg are presented. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.This work has been funden by the Spanish Ministry of Science (Projects Mat2011-23455 and CTQ2010-16457). D.M.T. acknowledges CSIC and Fondo Social Europeo for the tenure of a JAE Pre-fellowship.Peer Reviewe
Chain arrangement and glass transition temperature variations in polymer nanoparticles under 3D-confinement
Full text linkPolymer nanospheres with different size distributions of poly(ethyl methacrylate) are prepared by two different methods, with and without the aid of a surfactant. The calorimetric trace of these spheres shows an increase of the glass transition temperature that has been evaluated by means of an entropy model. This 3D-confinement, imposed by the nanospheres, leads to a limiting number of repeating polymer units in the sphere and thus to a reduction of the possible configuration states of the polymer chains, which is ultimately related to variations in the bulk value of the glass transition temperature. Our model is evaluated against our calorimetric measurements as well as with the data available in the literature. Good agreement between data and model is found for many cases, proving that confinement is related to reductions in entropy for these systems. © 2013 American Chemical Society.Financial support by MAT2008-03232, MAT2011-23455, and MAT2012-33517 from MINECO. JAE-Doc contract, Fondo Social Europeo (FSE) for cofinancing the JAE Program.Peer Reviewe
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