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Glass transition is a relevant property for performance definition in rubber products. For extrapolation to high frequency behavior, time-temperature superposition is usually assumed, although most complex rubber compounds might be outside of its area of validity. Fast differential scanning calorimetry (FDSC) up to 1500 K/s and broadband dielectric spectroscopy (BDS) up to 20 MHz are applied here to directly access both kinetics and dynamics of glass formation in a wide frequency range. For the first time, the relation between the thermal vitrification and the dielectric relaxation is studied on vulcanized styrene-butadiene rubber, showing that both cooling rate and frequency dependence of its glass transition can be described by one single Vogel-Fulcher-Tammann-Hesse equation. The results indicate the validity of the Frenkel-Kobeko-Reiner equation. Another focus is the sample preparation of vulcanized elastomers for FDSC and BDS as well as the temperature calibration below 0 °C.

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International audience; Polymer materials with antimicrobial activity are prepared by UV polymerization of acrylate and methacrylate mixture at room temperature. The antimicrobials are silver acetate and copper (II) acetate, used without pretreatment. Their chemical stability in the acrylate matrix and their effect on the thermal and mechanical properties of the polymer matrix are investigated as a function of their concentration up to 15 wt%. Physico-chemical, thermal, rheological, and morphological analyses as well as the surveillance of metal salts release in aqueous medium are conducted. A significant decrease in the thermal stability of the salts introduced into the acrylate matrix is observed after UV treatment. The metal salts also have significant effects on the properties of the matrix. A plasticization and densification of the material associated with an aggregation of salts up to the percolation at the highest concentration are highlighted. At equal concentrations, the effects are more pronounced in the presence of copper salts. The latter was released more slowly than silver salts from acrylate material.

The spectroscopic and thermal properties of swollen Nafion membranes in methanol aqueous mixtures were investigated to understand the behavior of commercial electrolytes in the presence of polar solvents. Several differences were observed in the absorption processes depending on the composition of the solvent. Deconvolution methods were applied to study specific contributions of solvents and polymer groups based on Fourier transform infrared spectroscopy and thermogravimetric analysis. The results evidence compositional effects on the interactions between solvents and Nafion. A major influence of the nonpolar domains (hydrophobic regions) in the absorption of methanol together with a reduction of the interactions with sulfonate groups was observed. Such changes are accompanied by a modification of the cluster morphology of the equilibrated membranes evaluated by differential scanning calorimetry. These findings can be useful to improve the knowledge on Nafion’s microstructure in the presence of polar solvents, The authors thank the financial support of the Generalitat Valenciana, through the Grisolia and Forteza programs, and the Spanish Ministry of Science and Innovation, through the Research Projects ENE2007-67584-C03, UPOV08-3E-013, IT2009-0074, ENE2011-28735-C02-01 and the awarding of two FPI and FPU predoctoral grants.

The miscibility of poly(butylene succinate) (PBS)/poly(butylene thiodiglycolate) (PBTDG) blends was investigated by DSC technique. PBS and PBTDG were completely immiscible in as blended-state, as evidenced by the presence of two Tgs at −34 and −48°C, respectively. The miscibility changes upon mixing at elevated temperature: the original two phases merged into a single one because of transesterification reactions. Poly(butylene succinate/thiodiglycolate) block copolymers, prepared by reactive blending of the parent homopolymers, were studied to investigate the effects of transesterification reactions on the molecular structure and solid-state properties. 13C-NMR analysis evidenced the formation of copolymers whose degree of randomness increased with mixing time. Thermal characterization results showed that all the samples were semicrystalline, with a soft rubbery amorphous phase and a rigid crystal phase whose amount decreased by introducing BTDG units into the PBS chain (20 ≤ χc ≤ 41). Lastly, the mechanical properties were found strictly related to crystallinity degree (χc), the random copolymer, exhibiting the lowest elastic modulus (E = 61 MPa) and the highest deformation at break (eb (%) = 713). © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Poly(lactic acid) (PLA), a physical blend of PLA and thermoplastic cassava starch (TPCS) (PLA-TPCS), and reactive blends of PLA with TPCS using maleic anhydride as compatibilizer with two different peroxide initiators [i.e., 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane (L101) and dicumyl peroxide (DCP)] PLA-g-TPCS-L101 and PLA-g-TPCS-DCP were produced and characterized. Blends were produced using either a mixer unit or twin-screw extruder. Films for testing were produced by compression molding and cast film extrusion. Morphological, mechanical, thermomechanical, thermal, and optical properties of the samples were assessed. Blends produced with the twin-screw extruder resulted in a better grade of mixing than blends produced with the mixer. Reactive compatibilization improved the interfacial adhesion of PLA and TPCS. Scanning electron microscopy images of the physical blend showed larger TPCS domains in the PLA matrix due to poor compatibilization. However, reactive blends revealed smaller TPCS domains and better interfacial adhesion of TPCS to the PLA matrix when DCP was used as initiator. Reactive blends exhibited high values for elongation at break without an improvement in tensile strength. PLA-g-TPCS-DCP provides promising properties as a tougher biodegradable film. Fil: Bher, Anibal Ricardo. Michigan State University; Estados Unidos. Universidad Nacional de San Martín; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Materiales de Misiones. Universidad Nacional de Misiones. Facultad de Ciencias Exactas Químicas y Naturales. Instituto de Materiales de Misiones; Argentina Fil: Auras, Rafael. Michigan State University; Estados Unidos Fil: Schvezov, Carlos Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Materiales de Misiones. Universidad Nacional de Misiones. Facultad de Ciencias Exactas Químicas y Naturales. Instituto de Materiales de Misiones; Argentina

Non-medical-grade industrial nets are often implemented in developing countries as affordable alternative to surgical meshes for hernia repair. Even if there is clear evidence about their repairing reliability, their physicochemical and mechanical properties have been not fully investigated. This works compares three industrial nets with different textile patterns, and a surgical mesh of the same polymer. Nets are autoclave-sterilized and characterized through scanning electron microscope, Raman spectroscopy, thermogravimetric analysis , differential scanning calorimetry, and uniaxial tensile tests. Spectral and thermal analyses reveal that all samples are based on poly(ethylene terephthalate). Differences are found in phase conformations with modifications in amorphous, ordered amorphous, and crystalline domains. Changes in material characteristics do not affect mechanical properties, which are mainly ascribable to the textile pattern. Industrial nets show a stiffening behavior different from the almost linear anisotropic response of surgical mesh. However, non-medical-grade nets could be potentially applied for surgeries once their biocompatibility and in vivo stability have been evaluated. Non-medical-grade industrial nets are used as low-cost alternative to surgical meshes for hernia repair in less developed countries. Nets sterilization modifies their phase conformation, due to the interaction with water, but do not affect mechanical properties. Even tough industrial nets show a different stiffening behavior, physicochemical characterization confirms a similarity to standard surgical meshes.

Linear low-density polyethylene (LLDPE)/polybutadiene (PB) and LLDPE/poly(styrene-b-butadiene-b-styrene) (SBS) binary blends were prepared by simple melt mixing or by reactive blending in the presence of a free-radical initiator, and for comparison, pure LLDPE was treated under the same conditions with a comparable free-radical initiator concentration. The effect of the reactive melt mixing on the morphology of the blends was studied with transmission electron microscopy, and the corresponding particle size distributions were analyzed and compared to highlight the effects of the crosslinking and grafting phenomena. Thermal properties of the obtained materials were investigated with differential scanning calorimetry and dynamic mechanical thermal analysis (DMTA). In particular, the effect of the reactive mixing parameters on the amorphous phase mobility was investigated. The influence of the chemical modification on the crystallization behavior of LLDPE, neat and blended with PB and SBS, was also studied with dynamic and isothermal differential scanning calorimetry tests, and the isothermal thermograms were analyzed in light of the Avrami equation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Received 27 February 2007; accepted 1 June 2007DOI 10.1002/app.27408Published online 30 November 2007 in Wiley InterScience (www.interscience.wiley.com).ABSTRACT: The effect of inert gases, nitrogen and car-bon dioxide, on the oxidative degradation of low-densitypolyethylene appearing as colored spots has been studiedduring an extrusion process in competition with an anti-oxidant. Extrusion under inert gases significantlydecreases the degradation level in the critical region of theprocess in comparison with classical extrusion under air.The effect of antioxidants on degradation during extrusionat a high temperature is weak. The main processes actingon this reduction of polymer oxidation and the origin ofthe color of degraded domains have been investigated.Energy-dispersive spectra of particles have confirmed thatdegradation is caused by thermooxidation. The nature ofchromophore groups in degraded areas has been identi-fied by IR microscopy. We found that b-conjugated keto-enols are present inside colored spots and seem to beresponsible for the color of degraded parts. Quantum cal-culations have confirmed that such chemical structuresabsorb visible light and create reddish and browncolors.

A poly(vinyl alcohol) (PVA)/silica (SiO2) nanocomposite was prepared with a novel self-assembled monolayer technique, and its morphology and thermal properties were studied with different material characterization instruments. The treated SiO2 nanoparticles were dispersed in the PVA matrix homogeneously, and the thermal properties of the nanocomposite were markedly improved in comparison with those of pure PVA. Under the same isothermal heating conditions, the decomposition of the nanocomposite was delayed significantly in comparison with that of PVA. The thermal degradation of the nanocomposite was a two-step reaction, including the degradation of the side chain and main chain. The products of side-chain degradation were mainly carboxylic acid, whereas main-chain degradation primarily produced carbon dioxide and low-molecular-weight conjugated polyene. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1436–1442, 2005

Author(s): Le, Anh V; Wang, Meng; Noelle, Daniel J; Shi, Yang; Yoon, Hyojung; Zhang, Minghao; Meng, Y Shirley; Qiao, Yu