Thermal characterization of the oxo-degradation of polypropylene containing a pro-oxidant/pro-degradant additive

The oxo-degradation process of polypropylene (PP) samples containing different concentrations (4% and 10% w/w) of pro-oxidant/pro-degradant additive Envirocare AG1000C was investigated under accelerated test conditions. Samples were initially exposed to UV radiation for 300 h. The tendency to biodegradation in soil medium of these UV-aged samples was then indirectly assessed by an indirect method for a period of 6 months. The entire degradation process of these materials was first examined by monitoring changes in their morphological properties (melting temperature, maximum lamellar thickness and crystallinity) with the ageing time, by Differential Scanning Calorimetry (DSC). Then, changes in the thermal properties (onset temperature and maximum decomposition temperature) of these materials with the ageing time were analysed by Thermogravimetric Analysis (TGA). Furthermore, the kinetics of the thermal decomposition of these PP samples with pro-oxidant/pro-degradant was also studied during the oxo-degradation process, by means of the Chang differential method. During exposure to UV radiation, the more significant changes in the morphological and thermal properties that were detected in PP samples containing pro-oxidant/pro-degradant additive compared to pure PP, clearly suggest a higher level of oxidation in these samples, confirming the effectiveness of this pro-oxidant/prodegradant additive in promoting the abiotic oxidation of polypropylene during UV-irradiation. Moreover, the level of oxidation observed in UV-aged samples seems to be dependent on the additive load. On the other hand, during incubation in soil medium, changes in the morphological and thermal properties of previously photo-oxidized PP samples with pro-oxidant/pro-degradant were detected that indirectly support a certain progress of oxidation, indicating that previous abiotic oxidation can promote further degradation of the polypropylene matrix by soil microorganisms. In general, both morphological and thermal properties exhibit a non-linear dependency with the incubation time in soil, supporting the idea that biodegradation is a complex process that occurs in different stages. Furthermore, the extent of the changes in these properties during soil incubation was found to be proportional to the pro-oxidant/pro-degradant load and the previous photo-oxidation level.The author is grateful to the Generalitat Valenciana for financial support from the research project: GV/2007/220.Contat Rodrigo, L. (2013). Thermal characterization of the oxo-degradation of polypropylene containing a pro-oxidant/pro-degradant additive. Polymer Degradation and Stability. 98(11):2117-2124. https://doi.org/10.1016/j.polymdegradstab.2013.09.011S21172124981

Screen-printed Organic Electrochemical Transistors for the detection of ascorbic acid in food

[EN] Methods traditionally used for ascorbic acid (AA) detection in food are often expensive and complex, making them unsuitable for day-to-day determinations. In this work, we report on the use of all- PEDOT:PSS Organic Electrochemical Transistors (OECTs) for fast, simple and low-cost determination of AA in food. The performance of these OECTs was tested first with in lab-prepared solutions of AA with different concentrations. The effect of the geometry on the transistors performance for AA sensing was also investigated by comparing the response of two OECTs with different channel and gate areas ratio (g), in terms of current modulation, sensitivity, background signal and limit of detection (LOD). OECTs with smaller gate electrode than the channel (large g) show the best performance for AA sensing: these devices display smaller background signal, higher sensitivity, larger modulation and better LOD value (80.10^-6 M). Since the AA content in food rich in Vitamin C is in the mM range, these transistors can be considered sensitive enough for quantitatively monitoring AA in food. In order to demonstrate the reliability of the proposed sensors in real food samples, the response of these transistors was additionally measured in a commercial orange juice. The amount of AA obtained with the OECTs is in good agreement with that determined by HPLC and with values reported in the literature for orange juices. Furthermore, these OECTs can be considered promising candidates for the selective detection of AA in the presence of other interfering antioxidants.This work was supported by Spanish Government/FEDER funds (grant number MAT2015-64139-C4-3-R (MINECO/FEDER)) and Generalitat Valenciana funds (grant number AICO/2015/103).Contat-Rodrigo, L.; Pérez Fuster, C.; Lidon-Roger, JV.; Bonfiglio, A.; Garcia-Breijo, E. (2017). Screen-printed Organic Electrochemical Transistors for the detection of ascorbic acid in food. Organic Electronics. 45:89-96. https://doi.org/10.1016/j.orgel.2017.02.03789964

A Rapid Electrochemical Impedance Spectroscopy and Sensor-Based Method for Monitoring Freeze-Damage in Tangerines

[EN] This study focuses on the analysis and early detection of freeze-damage in tangerines using a specific double-needle sensor and Electrochemical Impedance Spectroscopy (EIS). Freeze damage may appear in citrus fruits both in the field and in postharvest processes resulting in quality loss and a difficult commercialization of the fruit. EIS has been used to test a set of homogeneous tangerine samples both fresh and later frozen to analyze electrochemical and biological differences. A double-needle electrode associated to a specifically designed electronic device and software has been designed and used to send an AC electric sinusoidal signal 1 V in amplitude and frequency range [100Hz to 1MHz] to the analyzed samples and then receive the electrochemical impedance response. EIS measurements lead to distinct values of both impedance module and phase of fresh and frozen samples over a wide frequency range. Statistical treatment of the received data set by Principal Components Analysis (PCA) and Partial Least Squares Discriminant Analysis (PLS-DA) shows a clear classification of the samples depending on the experienced freeze phenomenon, with high sensitivity (1.00), specificity (>= 0.95) and confidence level (95%). Later Artificial Neural Networks (ANN) analysis based on 20-3-1 architecture has allowed to create a mathematical prediction model able to correctly classify 100% of the analyzed samples (CCR =100% for training, validation and test phases, and overall classification), being fast, easy, robust and reliable, and an interesting alternative method to the traditional laboratory analyses.This work was supported by the Spanish Government/FEDER funds [Ministerio de Economia y Empresa (MINECO)/Fondo Europeo de Desarrollo Regional (FEDER)] under Grant RTI2018-100910-B-C43 and in part by the Conselleria d'Educacio, Investigacio, Cultura i Esport de la Generalitat Valenciana under Grant GV/2018/090.Albelda Aparisi, P.; Fortes Sánchez, E.; Contat-Rodrigo, L.; Masot Peris, R.; Laguarda-Miro, N. (2021). A Rapid Electrochemical Impedance Spectroscopy and Sensor-Based Method for Monitoring Freeze-Damage in Tangerines. IEEE Sensors Journal. 21(10):12009-12018. https://doi.org/10.1109/JSEN.2021.3065846S1200912018211

Low-Temperature Soldering of Surface Mount Devices on Screen-Printed Silver Tracks on Fabrics for Flexible Textile Hybrid Electronics

[EN] The combination of flexible-printed substrates and conventional electronics leads to flexible hybrid electronics. When fabrics are used as flexible substrates, two kinds of problems arise. The first type is related to the printing of the tracks of the corresponding circuit. The second one concerns the incorporation of conventional electronic devices, such as integrated circuits, on the textile substrate. Regarding the printing of tracks, this work studies the optimal design parameters of screen-printed silver tracks on textiles focused on printing an electronic circuit on a textile substrate. Several patterns of different widths and gaps between tracks were tested in order to find the best design parameters for some footprint configurations. With respect to the incorporation of devices on textile substrates, the paper analyzes the soldering of surface mount devices on fabric substrates. Due to the substrate's nature, low soldering temperatures must be used to avoid deformations or damage to the substrate caused by the higher temperatures used in conventional soldering. Several solder pastes used for low-temperature soldering are analyzed in terms of joint resistance and shear force application. The results obtained are satisfactory, demonstrating the viability of using flexible hybrid electronics with fabrics. As a practical result, a simple single-layer circuit was implemented to check the results of the research.This work was supported by the Spanish Government FEDER funds (RTI2018-100910B-C43) (MINECO/FEDER). The work presented is also funded by the Conselleria d'Economia Sostenible, Sectors Productius i Treball, through IVACE (Instituto Valenciano de Competitividad Empresarial) and cofunded by ERDF funding from the EU Stretch Project, application No.: IMAMCA/2022/6.Silvestre, R.; Llinares Llopis, R.; Contat-Rodrigo, L.; Serrano Martínez, V.; Ferri, J.; Garcia-Breijo, E. (2022). Low-Temperature Soldering of Surface Mount Devices on Screen-Printed Silver Tracks on Fabrics for Flexible Textile Hybrid Electronics. Sensors. 22(15):1-23. https://doi.org/10.3390/s22155766123221

Influence of potential pulses amplitude sequence in a voltammetric electronic tongue (VET) applied to assess antioxidant capacity in aliso

[EN] Four signals configurations were studied, two of them built by small increases of potential and two with bigger increments. The highest current values were obtained when pulses with bigger change of potential were used although the best results were shown by the pulse sequence which included an intermediate pulse before the relevant pulse. A mathematical model based on trolox pattern was developed to predict antioxidant capacity of aliso, employing information obtained from all the electrodes, although model validation could be done only employing the information from gold electrode.Fuentes-Pérez, EM.; Alcañiz Fillol, M.; Contat-Rodrigo, L.; Baldeon-Chamorro, E.; Barat Baviera, JM.; Grau Meló, R. (2017). Influence of potential pulses amplitude sequence in a voltammetric electronic tongue (VET) applied to assess antioxidant capacity in aliso. Food Chemistry. 224:233-241. doi:10.1016/j.foodchem.2016.12.076S23324122

Inexpensive Measuring System for the Characterization of Organic Transistors

[EN] 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 +/- 100V output, with resolution down to 10 pA. LabVIEW (TM) 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.All financial support from the Spanish Government and FEDER funds (MAT2015-64139-C4-3-R (MINECO/FEDER)) and the Generalitat Valenciana (GVA funds) (AICO/2015/103) is gratefully acknowledged.Pérez Fuster, C.; Lidon-Roger, JV.; Contat-Rodrigo, L.; Garcia-Breijo, E. (2018). Inexpensive Measuring System for the Characterization of Organic Transistors. Journal of Sensors. 2018:1-9. https://doi.org/10.1155/2018/4286894S19201

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

[EN] 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.Financial support from FEDER and Spanish Government funds (MAT2015-64139-C4-3-R (MINECO/FEDER)) and GVA funds (AICO/2015/103) are gratefully acknowledged.Contat-Rodrigo, L.; Pérez Fuster, C.; Lidon-Roger, JV.; Bonfiglio, A.; Garcia-Breijo, E. (2016). Characterization of Screen-Printed Organic Electrochemical Transistors to Detect Cations of Different Sizes. Sensors. 16(10). https://doi.org/10.3390/s16101599S15991610Shirakawa, H., Louis, E. J., MacDiarmid, A. 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