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Martin-Alfonso J.E.,University of Huelva | Martin-Alfonso J.E.,Pro2Tecemical Process and Product Technology Research Center | Franco J.M.,University of Huelva | Franco J.M.,Pro2Tecemical Process and Product Technology Research Center
Polymer Engineering and Science | Year: 2015

New oleogel formulations based on high-oleic sunflower oil (HOSO) and ethylene vinyl acetate copolymer (EVA)/polypropylene (PP) blends were prepared using the mixing rheometry technique and further characterized. The effects of PP tacticity and EVA vinyl acetate (VAc) content on the rheological, morphological, and thermal behavior of derived oleogels were investigated. Differential scanning calorimetry (DSC) and polarized-light optical microscopy (PLOM) observations indicated that VAc segments markedly influence the crystalline structure of polymeric fractions and phase morphology of oleogels. The normalized crystallinity of isotactic polypropylene (iPP) phase increased linearly with its concentration whereas syndiotactic polypropylene (sPP) content does not exert a significant influence. PLOM observations showed that VAc content plays an important role in the phase morphology of PP frictions (size and shape of crystals). The viscoelastic response of oleogels depended on PP tacticity and VAc content, which may be explained attending to the different microstructures attained. © 2015 Society of Plastics Engineers. Source


Martin-Alfonso J.E.,University of Huelva | Martin-Alfonso J.E.,Pro2Tecemical Process and Product Technology Research Center | Franco J.M.,University of Huelva | Franco J.M.,Pro2Tecemical Process and Product Technology Research Center
Polymer Testing | Year: 2015

Abstract The overall objective of this work was to study the effect of reprocessing cycles of isotactic polypropylene (PP) on the rheological behavior and microstructure of gel-like dispersions in mineral oil. PP was subjected to 10 reprocessing cycles and oleogel samples were further prepared by using the mixing rheometry technique and characterized from a rheological point of view and polarized light optical microscopy (PLOM). Recycled polymer samples were also characterized by means of rheological measurements, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) to evaluate the property changes induced by reprocessing. The values of different linear viscoelastic functions (elastic modulus and complex viscosity) of recycled PP decrease with the number of reprocessing cycles, which influences oleogel rheological response. An empirical exponential correlation between the storage modulus (G′) of PP samples and the plateau modulus (GNo) of oleogels has been proposed to predict the rheological behavior of oleogels. Results were explained considering the scission of PP chains induced by the thermomechanical reprocessing treatment applied. © 2015 Elsevier Ltd. Source


Martin-Alfonso J.E.,University of Huelva | Martin-Alfonso J.E.,Pro2Tecemical Process and Product Technology Research Center | Franco J.M.,University of Huelva | Franco J.M.,Pro2Tecemical Process and Product Technology Research Center
Polymer Testing | Year: 2014

The overall objective of this work was to study the influence of vinyl acetate (VAc) content on the rheological properties and microstructure of polymer gels based on conventional and high-oleic sunflower vegetable oils and ethylene-vinyl acetate copolymer (EVA). The mechanical properties during gel preparation can be in situ monitored through the evolution of torque with processing time by using the mixing rheometry technique. Linear viscoelastic measurements, as well as differential scanning calorimetry (DSC) tests and morphological observations, were performed on the resulting gels. From the experimental results, it can be concluded that VAc content and melt flow index of the EVA copolymer significantly affect the rheological and thermal responses of polymer gels. VAc content, mainly affecting EVA degree of crystallinity, and melt flow index influence the linear viscoelastic behaviour in opposite directions. On the contrary, the extension of the linear viscoelastic regime and gel-like to liquid-like response transition temperatures are mainly dominated by EVA degree of crystallinity, as confirmed through calorimetry tests and microscopy observations. The different fatty acid profile in sunflower oils tested does not exert an important influence on process rheokinetics and rheological behaviour. © 2014 Elsevier Ltd. All rights reserved. Source


Martin-Alfonso J.E.,University of Huelva | Martin-Alfonso J.E.,Pro2Tecemical Process and Product Technology Research Center | Valencia C.,University of Huelva | Valencia C.,Pro2Tecemical Process and Product Technology Research Center
Tribology International | Year: 2015

This work deals with the development of oleogels based on conventional (SO) and high-oleic sunflower (HOSO) vegetable oils and ethylene-vinyl acetate copolymer (EVA) for lubricant applications. Particularly, the influence of EVA concentration on the tribological, rheological properties and microstructure of these oleogels was analyzed. The results showed that the evolution of linear viscoelasticity functions was similar to that found for lithium greases. The different fatty acid profile in vegetable oils tested exerted an important influence on friction and wear in the ball-on-plates contact. The friction coefficient values became lower when EVA content was decreased. The wear marks obtained after the frictional tests for EVA-SO oleogels significantly reduced the wear scars versus EVA-HOSO oleogels and it was similar to commercial grease. © 2015 Elsevier Ltd. All rights reserved. Source

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