Buenos Aires, Argentina
Buenos Aires, Argentina
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Garcia N.L.,LPyMC | Garcia N.L.,National University of San Martín of Argentina | Lamanna M.,CONICET | D'Accorso N.,CONICET | And 3 more authors.
Polymer Degradation and Stability | Year: 2012

PLA was grafted onto starch nanoparticles using a novel synthetic strategy consisting of three reaction steps. The first step was aimed to protect the hydroxyl groups of PLA by benzoylation (PLABz), the second one involved the activation of carboxyl groups using thionyl chloride and the last reaction was the grafting of the modified PLA onto the starch nanoparticles (PLASTARCH). The thermal behavior of the composite obtained by this method was very different from that displayed by the physical mixture of PLA and the starch nanoparticles (PLA-NC blend). The benzoylation step that leads to PLABz produces an increase of the molecular mobility, resulting in lower glass transition temperature, Tg, than that of the original PLA; a change that was observed in the DSC thermograms of the samples. On the other hand, the Tg of the PLASTARCH was similar to that of the PLA as a consequence of two opposite effects acting simultaneously: a free volume increase due to the presence of benzoyl groups and a confinement of the polymer chain, originating from the grafting onto NC. The material obtained by chemical modification (PLASTARCH) has a degradation temperature slightly lower than that of PLA, which does not affect its potential use in the packaging industry. © 2012 Elsevier Ltd. All rights reserved.

Mansilla M.A.,IFIMAT | Mansilla M.A.,CONICET | Rodriguez Garraza A.L.,LPyMC | Silva L.,IFIMAT | And 8 more authors.
Polymer Testing | Year: 2013

An investigation of the influence of the cure time on the glass transition temperature and nanostructure for two isomers of polybutadiene rubbers, CB25 (97% cis) and CB55 (38% cis), vulcanized at 433 K is presented. The samples were prepared with sulphur and TBBS (N-t-butyl-2-benzothiazole sulfenamide), and several crosslink densities were achieved at the different selected cure times. The studies on the samples were carried out using differential scanning calorimetry and positron annihilation lifetime spectroscopy. The variation of the glass transition temperature with the degree of cure and its relation with the crosslink density is analyzed for each type of isomer. A correlation between the free nanohole volume and the crosslink density is also analyzed. From swelling tests, the absorbed solvent at room temperature is discussed in terms of the obtained free nanohole volumes, showing a correspondence between these parameters. In the frame of the obtained results, the cis to trans isomerisation of the elastomer with high cis content during the vulcanization is discussed. © 2013 Elsevier Ltd. All rights reserved.

Morales Mendoza N.,CONICET | Goyanes S.,LPyMC | Chiliotte C.,LBT | Bekeris V.,LBT | And 3 more authors.
Physica B: Condensed Matter | Year: 2012

Magnetic binary nanofillers containing multiwall carbon nanotubes (MWCNT) and hercynite were synthesized by Chemical Vapor Deposition (CVD) on Fe/AlOOH prepared by the sol-gel method. The catalyst precursor was fired at 450 °C, ground and sifted through different meshes. Two powders were obtained with different particle sizes: sample A (50-75 μm) and sample B (smaller than 50 μm). These powders are composed of iron oxide particles widely dispersed in the non-crystalline matrix of aluminum oxide and they are not ferromagnetic. After reduction process the powders are composed of α-Fe nanoparticles inside hercynite matrix. These nanofillers are composed of hercynite containing α-Fe nanoparticles and MWCNT. The binary magnetic nanofillers were slightly ferromagnetic. The saturation magnetization of the nanofillers depended on the powder particle size. The nanofiller obtained from powder particles in the range 50-75 μm showed a saturation magnetization 36% higher than the one formed from powder particles smaller than 50 μm. The phenomenon is explained in terms of changes in the magnetic environment of the particles as consequence of the presence of MWCNT. © 2011 Elsevier B.V. All rights reserved.

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