Effect of polymerization catalyst technology on the melt processing stability of polyethylenes,Part 3: Additives blends performance

This article considers the interaction between additives that occur during the stabilization process. The simultaneous effects of the additives and associated interactions on melt processing stability and processing discoloration were of particular interest. Melt stability is an important factor to consider because physical changes in the processed polymer can occur during the compounding and fabrication steps. Furthermore, discoloration is one of the most important problems affecting commercial polymers. Most discoloration manifests itself as yellowing, especially in the case of polyolefins. Although yellowing can often be associated with degradation processes caused by various agents, such as light or heat, this is not always the case; yellowing can also be due to the interaction of additives in the stabilizer packages. Blends of primary antioxidants (AOs), secondary AOs, and hindered amine light stabilizers have been studied with the intention of further improving stabilization performance together with cost reduction of the stabilized polymer. Although synergism between AOs and a stabilizer is fairly common, antagonism was also observed in terms of melt flow protection and in color stability in some of the AOs tested. The effects of a range of thermal and light stabilizers on the melt stability (investigated via multiple pass extrusion) and color stability of three different polyethylenes (PEs) were examined. The PEs varied in terms of the catalyst system used to synthesize the polymers and included a high‐density polyethylene (HDPE) produced by using a chromium‐based Phillips catalyst and two linear low‐density polyethylenes (LLDPEs) produced via chromium‐based metallocene and titanium‐based Ziegler‐Natta catalysts. The apparent lack of influence of polymerization catalyst system on the mode of stabilizer interaction should lead to the reassessment of stabilizer formulation strategies in relation to PE type/catalyst system and associated commercial/economic considerations. J. VINYL ADDIT. TECHNOL., 22:117–127, 2016. © 2014 Society of Plastics Engineers     

Comparative evaluation of the efficiency of a series of commercial antioxidants studied by kinetic modeling in a liquid phase and during the melt processing of different polyethylenes

An antioxidant response in condensed polymeric environments is often ambiguous and may vary strongly depending on the nature of the polymer and the conditions of polymer storage, processing, and use. The impact of polymeric environments during melt processing on the intrinsic efficiency of a set of commercial antioxidants was studied. The antioxidative activity of primary antioxidants Lowinox CPL, Lowinox 22IB46, Naugard 445, hydroxylamine Genox EP, and secondary phosphite Weston TNPP were determined by using two versions of the model reaction of cumene initiated (2,2′‐azobisisobutyronitrile, AIBN, and cumyl hydroperoxide, ROOH) oxidation. The melt stabilizing efficiency of the antioxidants was also studied during multipass extrusion testing in HDPE (Phillipstype), metallocene LLDPE, and (Ziegler‐Natta) LLDPE. The kinetic measurements showed that each of the three functional hydroxyl groups of Lowinox CPL is consumed in the model reaction (version 1) with the same high inhibition rate constant (k₇), whereas the two functional groups of Lowinox 22IB46 have different activity stipulated by hydrogen bonding between the hydroxyls. All the primary stabilizers involved afforded transformation products with additional antioxidative activity. For phenolic Lowinox CPL and amine Naugard 445, these products exhibited lower inhibition rate constants than that of the main functionality, but for Lowinox 22IB46, the discrepancy was not observed. Genox EP revealed three inhibition centers with different rate constants which, however, have low values of the inhibition coefficients (f). This effect is presumably due to the versatility of the inhibition pathways for the antioxidant and its intermediates, including the path of active interception of cumylalkyl (R^?) radicals. The secondary stabilizer Weston TNPP, tested by means of the second version of the model system, along with the expected decomposition of hydroperoxide appeared to be an effective radical scavenger. Kinetic parameters of the antioxidizing activity of the stabilizers – inhibition rate constants, coefficients of the oxidation chain termination, and total antioxidative activity {A = ∑[k_7(i) (fn[InH])_(i)]} — were determined for each functional group and for the whole antioxidant molecule. The phenolic stabilizers manifested powerful antioxidative activity. Their strongest functional groups have very high inhibition rate constant values: (log k₇) = 5.4 ± 0.15 (Lowinox 22IB46) and 5.2 ± 0.1 M^?1s^?1 (Lowinox CPL). In terms of the total inhibiting activity in the liquid system the antioxidants can be ordered as: Lowinox CPL > Lowinox 22IB46 > Naugard 445 > Genox EP > Weston TNPP. The effect of stabilizers during multipass extrusion experiments was assessed via melt flow rate and yellowness index measurements conducted as a function of the number of passes. Phenolic antioxidants and Genox EP significantly improved the melt stability of the polyethylenes in terms of melt viscosity retention and in partial compliance with the data from kinetic modeling measurements. According to the melt stabilizing efficiency data, the antioxidants can be arranged as: Lowinox 22IB46 > Lowinox CPL > Genox EP > Naugard 445 > Weston TNPP. The Lowinox 22IB46 with relatively lower molecular weight exhibited the best results among the primary stabilizers because of the unrestricted molecular dynamics in the viscous‐flow state of the polymer. Yellowness index measurements made after multiple extruder passes indicated that Weston TNPP effectively decreased the color development caused by the phenolic antioxidants. Genox EP displayed high efficiency as an antioxidant and melt‐processing stabilizer and additionally provided good color protection. Generally, we received a good correlation between the activity of the antioxidants in the model system and their melt stabilization performance in HDPE, metallocene LLDPE, and LLDPE. The model reaction of cumene‐initiated oxidation has demonstrated excellent applicability as an effective tool for preliminary quantitative assessment of antioxidant radical‐scavenging efficiency. J. VINYL ADDIT. TECHNOL., 2010. © 2009 Society of Plastics Engineers     

Semantic speech recognition in the Basque context Part I: cross-lingual approaches

This work, divided into Part I and II, describes the development of GorUP a Semantic Speech Recognition System in the Basque context. Part I analyses cross-lingual approaches oriented to under-resourced languages and Part II the development of the Language Identification system. During the development, data optimization methods and Soft Computing methodologies oriented to complex environment are used in order to overcome the lack of resources. Moreover, in this context three languages coexist: French, Spanish and Basque. Indeed our main goal is the development of robust Automatic Speech Recognition (ASR) systems for Basque, but all language variability has to be analyzed. In this regard, Basque speakers mix during the speech not only sounds but also words of the three languages which results in a strong presence of cross-lingual elements. Besides, Basque is an agglutinative language with a special morpho-syntactic structure inside the words that may lead to intractable vocabularies. Nowadays, our work is oriented to Information Retrieval and mainly to small internet mass-media. In these cases the available resources for Basque in general, and for this task in particular, are very few and complex to process because of the noisy environment. Thus, the methods employed in this development (ontology-based approach or cross-lingual methodologies oriented to profit from more powerful languages) could suit the requirements of many under-resourced languages.     

Experiments for the selection of sub-word units in the Basque context for semantic tasks

The long term goal of our project is the development of robust ASR systems in the Basque context where coexist French, Spanish and Basque (a minority language). The development of ASR systems involves dealing with issues such as Acoustic Phonetic Decoding (APD), Language Modelling (LM) or the development of appropriate Language Resources (LR). Thus, these applications are generally very language-dependent and require very large resources. This work is focused on the selection of appropriate sub-word units with under-resourced and noisy conditions. Nowadays, in particular, the work is oriented to Basque Broadcast News (BN) due to the interest of digital mass-media as the trilingual Infozazpi radio (situated in French Basque Country). Thus, in order to decrease the negative impact that the lack of resources has in this issue we apply several data optimization methodologies based on Matrix Covariance Estimation and Ontology-based approaches.     

Effects of polymerization catalyst technology on the melt processing stability of polyethylenes. part 2. single stabilizer performance

The effects of a range of thermal and light stabilizers on the melt stability (investigated via multiple pass extrusion) and color stability of three different polyethylenes (PEs) were examined. The PEs varied in terms of the catalyst system used to synthesize the polymers and included an HDPE produced by using a chromium‐based Phillips catalyst and two LLDPEs produced via chromium‐based metallocene and titanium‐based Ziegler‐Natta catalysts. The additive types included a range of phenolics of different functionality, phosphites, hindered piperidines, an hydroxylamine, and Vitamin E. The results obtained for the three PEs confirmed that primary antioxidants (AOs) such as highly hindered and less, hindered phenols or hydroxylamines promoted good melt stability but in some cases tended toward yellowing. The secondary AOs such as the phosphites or thioethers behaved in the opposite way; color suppression was good, but melt stabilization was poor. It was also shown that for different types of phenols (all with similar molar activity), reducing steric hindrance to the phenolic OH enhanced the tendency to form chromophoric groups and hence color led to better efficiency than high hindrance. Those phenol with higher molar activity (mol OH/kg AO) showed the best processing performance. J. VINYL ADDIT. TECHNOL., 2012. © 2012 Society of Plastics Engineers     

The effect of doping in the electrochemical performance of (Ln1−xMx)FeO3−δ SOFC cathodes

A family of iron perovskites with the general formula AFeO_3−δ (A = Ln_1−xM_x; Ln = La, Nd and/or Pr; M = Sr or/and Ca) has been prepared keeping fixed the A cation radius 〈r_A〉 and cation size mismatch to isolate the effect of divalent dopant concentration from the A-cation steric effects. The electrochemical behaviour of these compounds for their application as SOFC cathodes was evaluated by using I-V curve measurements and ac impedance spectroscopy over three electrodes electrolyte supported cells processed under identical conditions. In contrast with the bulk behaviour, trends are more difficult to observe due to microstructural effects, but results seem to indicate that the doping level, x, does not influence in a significant way the electrochemical performance of iron perovskites with identical 〈r_A〉 and σ²(r_A).     

Semantic speech recognition in the Basque context Part II: language identification for under-resourced languages

This paper describes the development of a Language Identification (LID) system oriented to robust Multilingual Speech Recognition in the Basque context where coexist three languages: Basque, Spanish and French. The LID system is integrated in GorUP, a Semantic Speech Recognition system for industrial complex environments described in Part I. The work presents hybrid strategies for LID, based on the selection of system elements by several classifiers (Support Vector Machines and Multilayer Perceptron) and Discriminant Analysis improved with robust regularized covariance matrix estimation methods oriented to under-resourced languages and stochastic methods for speech recognition tasks (Hidden Markov Models and n-grams). The LID tool manages the main elements of the Automatic Speech Recognition system (Acoustic Phonetic Decoder, Language Model and Lexicons).     

Heat transfer through a double-glazed unit with an internal louvered blind: Determination of the thermal transmittance using a biquadratic equation

The aim of this research is to quantify the influence of a louvered blind in a double-glazed unit during night-time conditions. First, an analytical study of free convection was conducted to obtain a set of correlations for the Nusselt numbers of the cavity. Second, a parametric study was performed to calculate the total heat transfer (convective and long-wave radiative) during night-time conditions. The analysis accounted for aspect ratio, blind thermal conductivity, surface emissivity and slat angle. Using these data, a biquadratic equation was developed to calculate the U-factor of a double-glazed unit with an internal louvered blind in terms of the U-factor of the unit without the blind, slat surface emissivity and slat angle.     

Multilingual audio information management system based on semantic knowledge in complex environments

This paper proposes a multilingual audio information management system based on semantic knowledge in complex environments. The complex environment is defined by the limited resources (financial, material, human, and audio resources); the poor quality of the audio signal taken from an internet radio channel; the multilingual context (Spanish, French, and Basque that is in under-resourced situation in some areas); and the regular appearance of cross-lingual elements between the three languages. In addition to this, the system is also constrained by the requirements of the local multilingual industrial sector. We present the first evolutionary system based on a scalable architecture that is able to fulfill these specifications with automatic adaptation based on automatic semantic speech recognition, folksonomies, automatic configuration selection, machine learning, neural computing methodologies, and collaborative networks. As a result, it can be said that the initial goals have been accomplished and the usability of the final application has been tested successfully, even with non-experienced users.

     

Characterization of Ln4Al2O9 (Ln=Y,Sm, Eu,Gd, Tb) rare-earth aluminates as novel high-temperature barrier materials

A family of cuspidine-type rare-earth (RE) aluminates with the general formula Ln₄Al₂O₉ (Ln= Y, Sm, Eu, Gd, Tb) was prepared for potential use as thermal-barrier coating (TBC) materials with appropriate properties. Various trivalent lanthanides were applied to tailor the properties of the oxides for use as ceramic top coat (TC) materials intended for high-temperature applications. Following various heat treatments, the X-ray diffraction (XRD) results obtained demonstrated that Eu₄Al₂O₉ (EuAM) possessed the greatest structural stability of all the samples at 1200 and 1300?°C. Moreover, Y₄Al₂O₉ (YAM) had a long lifetime at 1000?°C, and was stable at 1100?°C. At 1200?°C, Sm₄Al₂O₉ (SmAM) and Gd₄Al₂O₉ (GdAM) were more stable than Tb₄Al₂O₉ (TbAM). However, at 300–1000?°C, the TbAM exhibited the highest thermal expansion coefficient (TEC) of all the samples. At 600?°C, the thermal diffusivity values of the five compositions were favourable, and were lower than that of yttria-stabilised zirconia (YSZ) oxides.