Showing papers by "Rosario Benavente published in 2017"

Assessment of mechanical behavior of PLA composites reinforced with Mg micro-particles through depth-sensing indentations analysis.

Abstract: This work deals with the mechanical characterization by depth-sensing indentation (DSI) of PLLA and PLDA composites reinforced with micro-particles of Mg (up to 15wt%), which is a challenging task since the indented volume must provide information of the bulk composite, i.e. contain enough reinforcement particles. The composites were fabricated by combining hot extrusion and compression moulding. Physico-chemical characterization by TGA and DSC indicates that Mg anticipates the thermal degradation of the polymers but does not compromise their stability during processing. Especial emphasis is devoted to determine the effect of strain rate and Mg content on mechanical behavior, thus important information about the visco-elastic behavior and time-dependent response of the composites is obtained. Relevant for the intended application is that Mg addition increases the elastic modulus and hardness of the polymeric matrices and induces a higher resistance to flow. The elastic modulus obtained by DSI experiments shows good agreement with that obtained by uniaxial compression tests. The results indicate that DSI experiments are a reliable method to calculate the modulus of polymeric composites reinforced with micro-particles. Taking into consideration the mechanical properties results, PLA/Mg composite could be used as substitute for biodegradable monolithic polymeric implants already in the market for orthopedics (freeform meshes, mini plates, screws, pins, …), craniomaxillofacial, or spine.

Thermal degradation mechanisms of epoxy composites filled with tin particles

Abstract: This article reports an evaluation study of the thermal degradation mechanisms of electrically insulating and conducting epoxy/Sn composites by using solid-state kinetic approaches and structural characterizations. Comparison of the thermoanalytical data of epoxy/Sn composites with pure epoxy shows that the addition of tin in epoxy catalyzes the thermal degradation of epoxy and the catalytic ability of tin depends upon its contents in epoxy. Kinetic modeling of the phenomena elaborates the thermal behaviors of epoxy/Sn composites in terms of the comparison of their activation parameters and reaction models. Friedman's differential and Arshad–Maaroufi's generalized linear integral isoconversional methods are used to obtain the variation in activation energies with the advancement of reaction. Advanced reaction model determination methodology is effectively employed to evaluate the reaction mechanisms of epoxy/Sn composites. Kinetic analysis suggests that tin increases the thermal degradation rate of epoxy by lowering the activation energy barrier of reaction. It is worth noticing that the parameters of the probable reaction model, i.e., Sestak Berggren have been found nearly the same for pure epoxy and epoxy/Sn composites, revealing weak epoxy–tin interactions in the composites. The mechanistic information obtained by kinetic analysis fairly agrees with the scanning electron microscopy and X-ray diffraction results. POLYM. COMPOS., 2015. © 2015 Society of Plastics Engineers

Kinetics of the thermal degradation mechanisms in urea-formaldehyde cellulose composites filled with zinc particles

Abstract: This paper reports a study on the structural characterization, thermal stability, and thermal degradation kinetics of urea-formaldehyde cellulose (UFC) composites filled with zinc particles. Structural characterization of UFC/Zn composites carried out by SEM, XRD and FTIR analyses reveals that the composites are fairly homogenous, and the interactions between UFC and zinc in the composites are physical in nature. Afterwards, measurements of inherent thermal stabilities, probing reaction complexity, and thermal degradation kinetics of UFC/Zn composites have been carried out. The integral procedure decompositions temperature elucidates significantly higher thermal stabilities of UFC/Zn composites. Isoconversional kinetic analysis suggests multi-step reaction pathways of UFC/Zn composites in terms of the substantial variations in their activation energies with the reaction advancement. Advanced reaction model determination methodology with the help of an innovative kinetic function F(α, T) reveals that the thermal degradation of UFC goes to completion by following complicated multi-step nucleation/growth mechanisms. A detailed account of the mechanistic information regarding to the thermal degradation processes taking place in UFC/Zn composites is given and discussed in the present study.

Thermal degradation of urea‐formaldehyde cellulose composites filled with aluminum particles: Kinetic approach to mechanisms

Abstract: This article reports a study on structural characterization and thermal degradation kinetics of insulating/conducting urea-formaldehyde cellulose (UFC) composites filled with aluminum particles. Structural characterization of UFC/Al composites carried out by SEM, XRD, and FTIR analyses reveals that composites are fairly homogenous, and the interactions between UFC and aluminum in UFC/Al composites are more probably physical in nature. Measurements of inherent thermal stabilities, probing reaction complexity, and thermal degradation kinetics of UFC and UFC/Al composites have been undertaken by thermogravimetric (TG)/differential thermogravimetric (DTG) analyses under nonisothermal conditions. The integral procedure decompositions temperature (IPDT) elucidates significant thermal stability of UFC, and higher aluminum contents in composites are capable of enhancing the thermal stability of UFC resin. TG/DTG analyses suggest highly complicated thermal degradation profiles of UFC and UFC/Al composites, which consist of various parallel/consecutive reactions. Generalized linear integral isoconversional method has been employed to determine the activation energies of thermal degradation processes. Substantial variations in activation energies of UFC and UFC/Al composites with the advancement of reaction verify their multi-step reaction pathways. Advanced reaction model determination methodology with the help of a novel kinetic function F(α,T) reveals that the multi-step thermal degradation of UFC goes to completion by principally following intricate nucleation/growth mechanisms. It is also found that aluminum more likely participates in the thermal degradation of resin and tends to alter its reaction mechanism. Detailed interpretations of the obtained kinetic parameters are given, and their probable physical significances are discussed. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 133, 44826.

The addition of aluminum nanoparticles to polypropylene increases its thermal stability

Abstract: This work was funded by the Ministerio de Ciencia e Innovacion (project MAT2010-19883) and CYTED Project 311RT0417. J. Arranz-Andres was supported by a CSIC JAE-Doc Program.

The Rheological Behavior of Wheat Starch Particulates Filled Uncured Styrene-Butadiene Rubber

Abstract: This study treats one important aspect of starch-filled rubber compounds which is their rheological behavior. Starch-based SBR1712 masterbatches resulting from various formulations were prepared using a mini two roll mill and an internal mixer (Plastograph Brabender).The content in starch was varied from 0 to 50 phr. The effect of starch content on the rheological behavior was evaluated through the flow characteristics in the temperature range (130-160 °C) which matches that used in the vulcanization process. Four experimental techniques were considered to assess the mixing and the flow behavior of the materials: 1) Brabender mixer, 2) melt flow index, 3) capillary rheometer and finally 4) dynamic rheological properties through strain sweep experiments using a plate-plate rheometer. It came out that the four techniques used in the assessment of the rheological behavior of such materials are appropriate, complementary and successful. The melt flow index and viscosity measurements indicate a resistant flow for the rubber and its starch composites. Even high temperatures do not seem to reduce the viscosity considerably. Nevertheless, small amounts of starch incorporated in the gum will ease the flow to some extent. The materials showed a pseudoplastic behavior, and storage made a slight change in their melt flow index. Morphological studies showed that the particles of starch were not destructed during the mixing and their interaction with the rubbery matrix is very poor.