Laura Contat-Rodrigo

Ultrasonication and microwave assisted extraction of degradation products from degradable polyolefin blends aged in soil

Two nonconventional extraction techniques, microwave assisted extraction (MAE) and ultrasonication, were used to extract degradation products from polyolefins with enhanced degradability. High-density polyethylene/polypropylene blends with two different biodegradable additives (a granular starch/iron oxide mixture and Mater-Bi AF05H) were subjected to outdoor soil burial tests and removed at different periods of time between 0 and 21 months. The extracted products were analyzed by gas chromatography mass spectrometry (GC-MS). Ultrasonication was found to be a more suitable technique than MAE because of better reproducibility. In addition, higher amounts of certain products (e.g., carboxylic acids) were extracted by ultrasonication than by MAE. The degradation products extracted from the two blends were basically a homologous series of alkanes, alkenes, carboxylic acids, and alcohols. The amount of hydrocarbons (saturated and unsaturated) and alcohols remained basically the same as the degradation times increased. However, carboxylic acids tended to decrease slightly with the exposure time. Their concentration remained practically unchanged until 12 months of soil burial when a more significant decrease was noted. The quantitative analysis of the degradation products revealed for both samples a decrease in the amount of carboxylic acids with the exposure time, although the trend was different according to the additive used in each sample. For blends with Mater-Bi the amount of carboxylic acids was at a minimum after 12-month exposure in soil, which coincided with a minimum in the molecular weight distribution. After blends with granular starch/iron oxide were exposed to 3 months in soil, tetradecanoic acid was no longer detectable and the amount of hexadecanoic and octadecanoic acids decreased significantly. Solid-phase microextraction, a solvent-free extraction technique, was used to extract the degradation products that could have migrated to the soil from blends with Mater-Bi. Small amounts of tetradecanoic acid and dodecanol were identified by GC-MS in the soil surrounding the sample. The degradation patterns observed here correlate with our previous results from mechanical and morphological characterization of these samples.

Viscoelastic behavior of degradable polyolefins aged in soil

Samples of polypropylene and a high density polyethylene/polypropylene blend filled with different biodegradable additives (rice starch/iron oxide mixture, Bioefect 72000 and Mater-Bi AF05H) have been subjected to an outdoor soil burial test for 21 months. Changes on the morphology of the samples have been studied by differential scanning calorimetry. The degradation process also has been analyzed in terms of the mechanical behavior of the polymers. The three characteristic relaxation zones α, β, and γ (in order of decreasing temperature) of the dynamic-mechanical relaxation spectra of the samples have been characterized according to the Fuoss–Kirkwood equation. When two relaxations were overlapped, a deconvolution method was applied. It has been observed that the degradation process affects just to a small extent the amorphous phase of the polymers. That the β relaxation is the most sensitive to the exposure time suggests that degradation starts in the crystalline–amorphous interface. However, the crystalline phase is also affected significantly by the degradation process. The mechanical results are in good agreement with the calorimetric measurements, proving that degradation takes place in two stages with different time scales depending on the additive used.

Mechanical behaviour of biodegradable polyolefins

Samples of a high density polyethylene (HDPE)/polypropylene (PP) blend with different biodegradable additives were subjected to an outdoor soil burial test. The biodegradation effects were studied in terms of viscoelastic properties and morphological changes of the polymers. An increase in the loss modulus values was observed.

TEMPERATURE FIELD RECONSTRUCTION FROM PHASE-MAP OBTAINED WITH MOIRé DEFLECTOMETRY IN DIFFUSION FLAME ON SOLIDS

Abstract Two methods of temperature field reconstruction starting from refractive index map obtained with Moiré deflectometry in downward flame spread along cylindrical PMMA samples have been compared, in order to determine their suitability in this kind of combustion problems, i.e., diffusive flames on solids. This article shows the applicability of the method based on the hypothesis of the same functional behaviour (SFB) of all the variables representing the flow, which provides a good picture of the temperature field. However, the method based on numerical solutions of the Navier–Stokes equations with simple chemical kinetics, suitable for other purposes, does not provide reliable quantitative results when it is used for the computation of the spatial variation of the Gladstone–Dale (G-D) constant and the gas constant, and for the later evaluation of the temperature from the refractive index map.

Characterization of Screen-Printed Organic Electrochemical Transistors to Detect Cations of Different Sizes.

A novel screen-printing fabrication method was used to prepare organic electrochemical transistors (OECTs) based on poly(3,4-ethylenedioxythiophene) doped with polysterene sulfonate (PEDOT:PSS). Initially, three types of these screen-printed OECTs with a different channel and gate areas ratio were compared in terms of output characteristics, transfer characteristics, and current modulation in a phosphate buffered saline (PBS) solution. Results confirm that transistors with a gate electrode larger than the channel exhibit higher modulation. OECTs with this geometry were therefore chosen to investigate their ion-sensitive properties in aqueous solutions of cations of different sizes (sodium and rhodamine B). The effect of the gate electrode was additionally studied by comparing these all-PEDOT:PSS transistors with OECTs with the same geometry but with a non-polarizable metal gate (Ag). The operation of the all-PEDOT:PSS OECTs yields a response that is not dependent on a Na+ or rhodamine concentration. The weak modulation of these transistors can be explained assuming that PEDOT:PSS behaves like a supercapacitor. In contrast, the operation of Ag-Gate OECTs yields a response that is dependent on ion concentration due to the redox reaction taking place at the gate electrode with Cl− counter-ions. This indicates that, for cation detection, the response is maximized in OECTs with non-polarizable gate electrodes.

Bologna vs non-Bologna academic outcome in BEng Mechanical Engineering within EHEA

The arising of European Higher Education Area (EHEA) brought up the implementation of new degrees throughout most of European Universities. In the realm of this upcoming environment, during 2009-2010 the School of Design Engineering (ETSID) at Universitat Politècnica de València in Spain, developed a pioneer experience in the first year of the Bachelor Engineering (BEng) degree in Mechanical Engineering, the guidelines of this innovative experience being defined in accordance with the EHEA approaches. Thus, this pioneer experience co-existed with non-Bologna teaching-learning methodology followed in the rest of groups of this BEng degree. Positive academic outcomes found in this first pioneer group encouraged to extend this experience to the second year of this degree during 2010-2011, in order to ease the upcoming full Bologna implementation. In this line, classroom activities were established so that collaborative work was promoted, autonomous tasks were developed and an assessment that took into account both classroom and autonomous activities was implemented. In this paper, we present a statistical analysis of the achieved academic outcomes of the pioneer group in the second year of the BEng degree in Mechanical Engineering, relating them to the rest of non-pioneer groups of the same year and degree.

Inexpensive Measuring System for the Characterization of Organic Transistors

A measuring module has been specifically designed for the electrical characterization of organic semiconductor devices such as organic field effect transistors (OFETs) and organic electrochemical transistors (OECTs) according to the IEEE 1620-2008 standard. This device has been tested with OFETs based on 6,13-bis(triisopropylsilylethinyl)pentacene (TIPS-pentacene). The measuring system has been constructed using a NI-PXIe-1073 chassis with integrated controller and two NI-PXI-4132 programmable high-precision source measure units (SMUs) that offer a four-quadrant ± 100 V output, with resolution down to 10 pA. LabVIEW™ has been used to develop the appropriate program. Most of the main OFET parameters included in the IEEE 1620 standard can be measured by means of this device. Although nowadays expensive devices for the characterization of Si-based transistors are available, devices for the characterization of organic transistors are not yet widespread in the market. Fabrication of a specific and flexible module that can be used to characterize this type of transistors would provide a powerful tool to researchers.

Analizing students performance in an EHEA BEng Industrial Design Engineering degree

European Universities have been exposed to major changes in order to implement the so called Bologna process. Many facets have had to be addressed in the teaching-learning system, moving from a teacher-centered model to a student-centered one, where a competence-based structure had to be facilitated, and so that the basic competences related to the integral formation of engineers should be accomplished along specific competences, making possible a professional profile and enabling the graduates to get integrated into the job market. Hence, this change has provided the opportunity to create a more active and dynamic teaching-learning model, with more personalized methods and the integration of new technologies. In the midst of this situation, a case study has been undertaken to analyze the consequences of such change in the academic results of the BEng Industrial Design Engineering degree of the School of Design Engineering ETSID (Polytechnic University of Valencia, Spain) along the first course of the European Higher Education Area (EHEA) adapted program and those obtained by the corresponding pre-EHEA course at ETSID. This paper aims to become an instrument to monitor the development and effectiveness of the teaching-learning policies adopted, thus contributing to the continuous process of educational improvement at ETSID by comparing various performance and success rates.