Javier Arranz-Andrés

Electromagnetic Shielding Features in Lightweight Pvdf-Aluminum Based Nanocomposites

Dependence of the electromagnetic shielding efiectiveness on flller volume fraction has been investigated from attenuation upon re∞ection measurements over a broad frequency range in hybrids based on Poly(vinylidene ∞uoride)-Aluminum nanoparticles. The loss of re∞ectivity with relation to the incident radiation in these nanocomposites compared with the pristine polymeric matrix shows the maximum value for the sample with an aluminum content of 10% in volume. Furthermore, the morphological aspects of all the specimens as well as their thermal properties, viscoelastic behavior and dielectric response have been evaluated. The nanocomposite that incorporates an Al content of 10% in volume exhibits the best balance in properties including, in addition to its shielding behavior, its processability and mechanical performance.

Lightweight Nanocomposites Based on Polypropylene and Aluminum Nanoparticles and Their Shielding Capability to Ionizing Radiation

Nanocomposites based on isotactic polypropylene and different contents of aluminum (Al) nanoparticles have been prepared in order to primarily analyze their electromagnetic interference shielding capability. Promising results have been attained in this area since values as high as 40 dB, which provide at least a 99% attenuation of the electromagnetic radiation, are reached. The good balance between shielding, sample weight, cost, and processability makes these lightweight materials a good alternative to replace neat metals for that application. Moreover, a complete structural and morphological characterization, as well as an evaluation of their dielectric behavior is also performed.

Mesophase Formation in Isotactic Polypropylene Copolymers

The main results related to the mesophase formation in the different isotactic polypropylene (iPP) copolymers are reviewed in this chapter. It is shown that fast scanning calorimetry (FSC) is mandatory for analyzing the process at the lower comonomer contents. On the contrary, the cooling rates required for the relatively high contents fall in the typical range of conventional DSC experiments, so that the mesophase development can be much more easily investigated (although there is an obvious decrease of the degree of order). Additionally, diffraction experiments under real time conditions (by means of synchrotron radiation) are also examined, which are used for establishing the specific character of the phases implicated. The main conclusion is that the cooling rates necessary for obtaining the mesomorphic state decrease progressively with increasing counit content, although important differences are reported depending on the comonomer type. Thus, it is shown that the content and size of the counit are influencing in a different way the rate of mesophase development and the transition temperatures. FSC experiments for studying the corresponding crystallization and mesophase rates of formation under isothermal conditions on iPP and copolymers are also reviewed.

Influence of the feeding control on the final properties of ethylene/propylene copolymers obtained in laboratory semi-batch reactor

AbstractThe slurry polymerization reactors on the industrial scale operate in continuous mode at low monomer conversion per pass to minimize mass and heat transfer limitations. Nevertheless, for the screening of catalytic systems, the laboratory tests are carried out using batch or semi-batch reactors. In this work, ethylene/propylene copolymers were synthesized in a semi-continuous reactor under similar conditions, where the only difference involves the modification of the feed ratio during the reaction. The key point of the control system is a micro-gas chromatograph (MGC), which analyzes the molar ratio ethylene (C2) to propylene (C3) in the gas phase during the reaction, and the composition in the liquid phase was calculated using the Soave-Redlich-Kwong equation of state. The effect of the ethylene/propylene copolymer microstructure has been studied using different techniques that allow us to conclude that the method of synthesis influences the comonomer distribution and the final copolymer properties.