Control of Molecular weight and polydispersity in polyethylene/needle-like shaped clay nanocomposites obtained by in situ polymerization with metallocene catalysts

Producción CientíficaIn an effort to understand the influence of the shape and area of the nanoclay type used in the in situ polymerization process, two different types of clays (fibrillar and laminar) were employed to obtain nanocomposites. The preliminary results demonstrated that a needlelike shaped clay promotes higher molar mass and better mechanical properties compared with laminar clay. The ultra-high molecular weight of sepiolite/nanocomposites introduces significant problems with processability. Therefore, a new method of polymerization was designed to include two significant changes. The first change was related to the use of a non-isothermal temperature profile and the second to the addition of an additional amount of non-anchored co-catalyst leading to materials with higher fluidity.Ministerio de Economía y Competitivida

Rheological modification of recycled poly(ethylene terephthalate): Blending and reactive extrusion

The use of recycled PET (rPET) in long-term applications, such as composites, may provide an environmentally friendly solution for PET wastes. Main problem to overcome to use rPET in composites is its high viscosity which compromises the impregnation with the fibers during the consolidation process. As it is well known, PET undergoes thermo-mechanical and hydrolytic degradation during its mechanical recycling decreasing its viscosity and causing a loss of mechanical properties. For this reason, this paper takes into consideration a rheological modification during mechanical recycling to achieve the necessary fluidity for composites while maintaining the mechanical properties. Rheological modification was carried out by physical and chemical methods. Physical method was realized through blending with virgin PET (vPET) of low melt viscosity. Chemical method was performed on rPET, vPET and its blends by reactive extrusion. The effect of rheological modifications on the final thermal and mechanical properties was studied. Main results showed that both methods are able to decrease the viscosity without compromising mechanical properties. In addition, the chemical method during the reactive extrusion provided higher Elastic Modulus values.Ministerio de Economía, industria y Competitividad (Project MAT2017-85101-C2-1-R)Junta de Castilla y León-Instituto para la Competitividad Empresarial de Castilla y León (projects VA071G18 and CCTT2/18/VA/0002)Ministerio de Ciencia, Innovación y Universidades (project PTQ-16-0844

Optimization of injection parameters to obtain selected properties on foamed PP with hollow glass microspheres and thermally expandable microspheres using Taguchi method

Se utilizó un sistema de espumación compuesto por microesferas de vidrio huecas (HGM) y microesferas térmicamente expandibles (EM) para lograr un equilibrio entre las propiedades seleccionadas de polipropileno (PP) espumado mediante moldeo por inyección, combinando las mayores propiedades de flexión y menor densidad requeridas en las piezas interiores de los automóviles. El L16 de Taguchi (44.23) se empleó para el plan experimental y la relación señal/ruido (S/N) para la optimización del sistema planteado. Los dos parámetros importantes de moldeo por inyección que afectan a las propiedades seleccionadas fueron la temperatura de la masa fundida y del molde. El efecto más importante efecto sobre el módulo de flexión fue la cantidad de HGM, y para la densidad la cantidad de EM.Ministerio de Economía, Industria y Competitividad (project MAT2017-85101-C2-1-R

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements