Rubber Compounds from Devulcanized Ground Tire Rubber: Recipe Formulation and Characterization.

In this study, our focus was on developing and investigating rubber recipes that are suitable for devulcanized ground tire rubber (dGTR). Devulcanized rubber has a powdery or sticky uncured rubber-like appearance depending on the extent of main-chain degradation that occurs with selective crosslinking scission. Still, it has a significantly shorter scorch time than a new rubber compound. Therefore, our primary goal was to slow down the vulcanization process of dGTR and improve its mechanical properties via recipe development. We formulated several recipes (sulfur-, peroxide-, and phenolic resin-based) and studied the vulcanization process and the main properties of the revulcanized rubber sheets. We observed that the vulcanization process could be altered with different vulcanization methods: using peroxide and vulcanizing resin extended the process significantly. Peroxide vulcanization also provided enhanced elongation compared to sulfuric systems. With a balance of properties in mind, we selected a semi-efficient sulfur-based recipe and studied the characteristics of natural rubber/dGTR mixtures with the help of plasticizer oils. We successfully replaced a notable portion of natural rubber with dGTR, maintaining its properties without much compromise.

Development of nanoparticle-filled polypropylene-based single polymer composite foams.

In this study, our focus was on developing and investigating nanoparticle-filled polypropylene-based single polymer composite foams. These composites had porous and nanotube-reinforced matrices, with plain woven polypropylene (PP) fabric as reinforcement. Our main objective was to enhance the energy absorption and stiffness of the single polymer composites (SPCs) by modifying their matrices. We produced SPCs with two different matrices: one of amorphous poly-alpha-olefin (APAO) and one of thermoplastic elastomer (TPE) blended with APAO. We observed that the APAO matrix exhibited better impregnation of the fabric due to its low viscosity, while the composites with the TPE matrix showed significantly better tensile properties. The foaming process applied to the matrices resulted in a substantial increase in energy absorption for the SPCs, while preserving their tensile properties relative to their density. Scanning electron microscope images confirmed that foaming of the APAO matrix was notably more effective, primarily due to its low viscosity. Furthermore, we successfully enhanced the stiffness and tensile properties of the SPCs by nano-reinforcing the matrices with multi-wall carbon nanotubes (MWCNTs). Due to the size of the nanotubes, this reinforcement did not compromise the impact properties of the SPCs. Scanning electron microscope images also demonstrated improved dispersion of the nanotubes within the APAO matrices.

Polypropylene Blends for Highly Drawn Tapes with Improved Toughness.

In this study, we used four amorphous poly-alpha-olefin (APAO) grades to improve the toughness of drawn polypropylene (PP) tapes. The samples containing different amounts of APAOs were drawn in a heat chamber of a tensile testing machine. The APAOs reduced the work of drawing and increased the melting enthalpy of the drawn specimens, as they facilitated the movement of the PP molecules. The APAO with the highest molecular weight and with a low level of crystallinity increased both the tensile strength and the strain-at-break of the specimens, so we also produced drawn tapes from that PP/APAO blend on a continuous-operation stretching line. The continuously drawn tapes also showed improved toughness.

The effect of the heat used during composite processing on the mechanical properties of fibrous reinforcement of polypropylene-based single-polymer composites.

In this study, we investigated the effect of heat treatment on the mechanical properties of high-tenacity polypropylene (PP) fibers. An application field of versatile polypropylene as fibers and tapes is the reinforcement of single-polymer composites. During consolidation at an elevated temperature, typically near the melt temperature of PP, the heat causes molecular relaxation of the strongly oriented molecular chains, which impairs mechanical properties. We investigated the shrinkage of PP single fibers isothermally and anisothermally, and heat-treated PP single fibers and multifilament rovings in a temperature range of 120-190 °C for 5-20 min in a constrained and an unconstrained arrangement. The heat-treated fibers and rovings were then tensile tested and their residual mechanical properties were determined and compared to the as-received rovings. We analyzed the tensile characteristics mathematically, applying the statistical fiber-bundle-cell modeling method, and described the measured and averaged stress-strain curves with fitted E-bundles having fibers with nonlinear tensile characteristics. The tensile modulus of the constrained fibers treated for 5 min decreased less in the whole heat treatment temperature range but considerably decreased further with increasing treatment time. Conversely, their tensile strength decreased only slightly, and treatment time had a minor effect up to 180-190 °C (above the melting temperature of the fiber). The results proved that constraining is a useful tool for preserving the reinforcing ability of high-tenacity polymer fibers.

Predictors of Hospital Mortality in Patients with Acute Coronary Syndrome Complicated by Cardiogenic Shock.

As demonstrated by earlier studies, pre-hospital triage with trans-telephonic electrocardiogram (TTECG) and direct referral for catheter therapy shows great value in the management of out-of-hospital chest pain emergencies. It does not only improve in-hospital mortality in ST-segment elevation myocardial infarction, but it has also been identified as an independent predictor of higher in-hospital survival rate. Since TTECG-facilitated triage shortens both transport time and percutaneous coronary intervention (PCI)-related procedural time intervals, it was hypothesized that even high-risk patients with acute coronary syndrome (ACS) and cardiogenic shock (CS) might also benefit from TTECG-based triage. Here, we decided to examine our database for new triage- and left ventricular (LV) function-related parameters that can influence in-hospital mortality in ACS complicated by CS. ACS patients were divided into two groups, namely, (1) hospital death patients (n = 77), and (2) hospital survivors (control, n = 210). Interestingly, TTECG-based consultation and triage of CS and ACS patients were confirmed as significant independent predictors of lower hospital mortality risk (odds ratio (OR) 0.40, confidence interval (CI) 0.21-0.76, p = 0.0049). Regarding LV function and blood chemistry, a good myocardial reperfusion after PCI (high area at risk (AAR) blush score/AAR LV segment number; OR 0.85, CI 0.78-0.98, p = 0.0178) and high glomerular filtration rate (GFR) value at the time of hospital admission (OR 0.97, CI 0.96-0.99, p = 0.0042) were the most crucial independent predictors of a decreased risk of in-hospital mortality in this model. At the same time, a prolonged time interval between symptom onset and hospital admission, successful resuscitation, and higher peak creatine kinase activity were the most important independent predictors for an increased risk of in-hospital mortality. In ACS patients with CS, (1) an early TTECG-based teleconsultation and triage, as well as (2) good myocardial perfusion after PCI and a high GFR value at the time of hospital admission, appear as major independent predictors of a lower in-hospital mortality rate.

Enhanced Fatigue and Durability Properties of Natural Rubber Composites Reinforced with Carbon Nanotubes and Graphene Oxide.

Fibrous carbon nanotubes (CNTs) and lamellar graphene oxide (GO) exhibit significant advantages for improving the fatigue properties of rubber composites. In this work, the synergistic effect of CNTs and GO on the modification of the microstructure and fatigue properties of natural rubber (NR) was comprehensively investigated. Results showed that CNTs and GO were interspersed, and they formed a strong filler network in the NR matrix. Compared with those of CNT/NR and GO/NR composites, the CNT-GO/NR composites showed the smallest crack precursor sizes, the lowest crack growth rates, more branching and deflections, and the longest fatigue life.

Devulcanization of ground tire rubber: microwave and thermomechanical approaches.

We devulcanized ground tire rubber (GTR) in a laboratory microwave oven and an internal mixer, measured the soluble content and the cross-link density of the samples, and then used Horikx's analysis. The results showed that microwave treatment caused severe degradation of the polymer chains, while in the case of thermomechanical devulcanization, the selective scission of covalent cross-links is more common. Four devulcanized ground tire rubber (dGTR) samples were chosen for further study and three groups of samples were produced: dGTR samples containing vulcanizing agents and different amounts of paraffin oil (dGTR-based mixtures), natural rubber-based rubber mixtures with different dGTR contents and reference rubber mixtures with dGTR-based mixtures (increased vulcanizing agent contents). Cure characteristics showed a plasticizer-like effect of dGTR. Tensile and tear strength decreased drastically with increasing dGTR content; however, elongation at break values did not follow such a trend. Mechanical properties improved with increased vulcanizing agent contents. The examined properties of the samples improved even further with the use of thermomechanically devulcanized samples. Horikx's analysis showed that this is attributable to moderate polymer chain scission.

Development of Polypropylene-Based Single-Polymer Composites With Blends of Amorphous Poly-Alpha-Olefin and Random Polypropylene Copolymer.

We developed polypropylene-based single-polymer composites (PP-SPC) with blends of amorphous poly-alpha-olefin (APAO) and random polypropylene copolymer (rPP) as matrix material and polypropylene (PP) woven fabric as reinforcement. Our goal was to utilize the lower melting temperature of APAO/rPP blends to increase the consolidation of the composites and decrease the heat load of the PP reinforcement. We produced the composites by film-stacking at 160 °C, and characterized the composites with density, peel, static tensile and dynamic falling weight impact tests, and by scanning electron microscopy. The results indicate that consolidation can be enhanced by increasing the APAO content of the matrix. We found that the APAO content of 50% is optimal for tensile properties. With increasing APAO content, the perforation energy decreased, but even the well-consolidated composites showed very high perforation energy. In the case of a pure APAO matrix, fiber content can be increased up to 80 wt% without a severe loss of consolidation, resulting in good tensile properties. The PP-SPCs developed possessed excellent mechanical properties, and well-consolidated composites can be produced with APAO/rPP blends as a matrix with high fiber content.

The transtelephonic electrocardiogram-based triage is an independent predictor of decreased hospital mortality in patients with ST-segment elevation myocardial infarction treated with primary percutaneous coronary intervention.

INTRODUCTION: The transtelephonic electrocardiogram has been shown to have a great value in the management of out-of-hospital chest pain emergencies. In our previous study it not only improved the pre-hospital medical therapy and time to intervention, but also the in-hospital mortality in ST-segment elevation myocardial infarction. It was hypothesised that the higher in-hospital survival rate could be due to improved transtelephonic electrocardiogram-based pre-hospital management (electrocardiogram interpretation and teleconsultation) and consequently, better coronary perfusion of patients at the time of hospital admission. To test this hypothesis, our database of ST-segment elevation myocardial infarction patients was evaluated retrospectively for predictors (including transtelephonic electrocardiogram) that may influence in-hospital survival. METHODS AND RESULTS: The ST-segment elevation myocardial infarction patients were divided into two groups, namely (a) hospital death patients (n = 49) and (b) hospital survivors (control, n = 726). Regarding pre-hospital medical management, the transtelephonic electrocardiogram-based triage (odds ratio 0.48, confidence interval 0.25-0.92, p = 0.0261) and the administration of optimal pre-hospital medical therapy (acetylsalicylic acid and/or clopidogrel and glycoprotein IIb/IIIa inhibitor) were the most important independent predictors for a decreased risk in our model. At the same time, age, acute heart failure (Killip class >2), successful pre-hospital resuscitation and total occlusion of the infarct-related coronary artery before percutaneous coronary intervention were the most important independent predictors for an increased risk of in-hospital mortality. DISCUSSION: In ST-segment elevation myocardial infarction patients, (a) an early transtelephonic electrocardiogram-based teleconsultation and triage, (b) optimal pre-hospital antithrombotic medical therapy and (c) the patency and better perfusion of the infarct-related coronary artery on hospital admission are important predictors of a lower in-hospital mortality rate.

Corrigendum to "Oxidative Stress-Related Parthanatos of Circulating Mononuclear Leukocytes in Heart Failure".

[This corrects the article DOI: 10.1155/2017/1249614.].

Thermoplastic Dynamic Vulcanizates with In Situ Synthesized Segmented Polyurethane Matrix.

The aim of this paper was the detailed investigation of the properties of one-shot bulk polymerized thermoplastic polyurethanes (TPUs) produced with different processing temperatures and the properties of thermoplastic dynamic vulcanizates (TDVs) made by utilizing such in situ synthetized TPUs as their matrix polymer. We combined TPUs and conventional crosslinked rubbers in order to create TDVs by dynamic vulcanization in an internal mixer. The rubber phase was based on three different rubber types: acrylonitrile butadiene rubber (NBR), carboxylated acrylonitrile butadiene rubber (XNBR), and epoxidized natural rubber (ENR). Our goal was to investigate the effect of different processing conditions and material combinations on the properties of the resulting TDVs with the opportunity of improving the interfacial connection between the two phases by chemically bonding the crosslinked rubber phase to the TPU matrix. Therefore, the matrix TPU was synthesized in situ during compounding from diisocyanate, diol, and polyol in parallel with the dynamic vulcanization of the rubber mixture. The mechanical properties were examined by tensile and dynamical mechanical analysis (DMTA) tests. The morphology of the resulting TDVs was studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM) and the thermal properties by differential scanning calorimetry (DSC). Based on these results, the initial temperature of 125 °C is the most suitable for the production of TDVs. Based on the atomic force micrographs, it can be assumed that phase separation occurred in the TPU matrix and we managed to evenly distribute the rubber phase in the TDVs. However, based on the SEM images, these dispersed rubber particles tended to agglomerate and form a quasi-continuous secondary phase where rubber particles were held together by secondary forces (dipole-dipole and hydrogen bonding) and can be broken up reversibly by heat and/or shear. In terms of mechanical properties, the TDVs we produced are on a par with commercially available TDVs with similar hardness.

Microwave Devulcanized Crumb Rubbers in Polypropylene Based Thermoplastic Dynamic Vulcanizates.

Because of the chemically crosslinked 3D molecular structure of rubbers, their recycling is a challenging task, especially when cost efficiency is also considered. One of the most straightforward procedures is the grinding of discarded rubber products with subsequent devulcanization. The devulcanized rubber can be used as a feedstock for fresh rubber compounds or can be blended with uncured virgin rubber and thermoplastic polymers to form thermoplastic dynamic vulcanizates (TDVs). TDVs combine the beneficial (re)processability of thermoplastics and the elastic properties of rubbers. Our current work focuses on the development of polypropylene (PP)-based TDVs with the use of a tire model rubber (MR) composed of natural rubber (NR) and styrene-butadiene rubber (SBR) in a ratio of 70/30. The research target was the partial substitution of the above fresh MR by microwave devulcanized crumb rubber (dCR). TDVs were produced by continuous extrusion, and the effects of composition (PP/MR/dCR = 40/60/0…50/35/15) and processing parameters (different screw configurations, temperature profiles, the feeding method of PP) were investigated. Results showed that the fresh rubber compound can be replaced up to 10 wt % without compromising the mechanical properties of the resulting TDV.

Oxidative Stress-Related Parthanatos of Circulating Mononuclear Leukocytes in Heart Failure.

BACKGROUND: The present study aims to examine the oxidative stress-related activation of poly(ADP-ribose) polymerase (PARP), a cause of parthanatos in circulating mononuclear leukocytes of patients with chronic heart failure (CHF), that was rarely investigated in the human setting yet. METHODS: Patients with CHF (n = 20) and age- and body mass index-matched volunteers (n = 15) with a normal heart function were enrolled. C-reactive protein, N-terminal probrain-type natriuretic peptide (pro-BNP), plasma total peroxide level (PRX), plasma total antioxidant capacity (TAC), oxidative stress index (OSI), leukocyte lipid peroxidation (4-hydroxynonenal; HNE), protein tyrosine nitration (NT), poly(ADP-ribosyl)ation (PARylation), and apoptosis-inducing factor (AIF) translocation were measured in blood samples of fasting subjects. RESULTS: Plasma PRX, leukocyte HNE, NT, PARylation, and AIF translocation were significantly higher in the heart failure group. Pro-BNP levels in all study subjects showed a significant positive correlation to PRX, OSI, leukocyte HNE, NT, PARylation, and AIF translocation. Ejection fraction negatively correlated with the same parameters. Among HF patients, a positive correlation of pro-BNP with PRX, OSI, and PARylation was still present. CONCLUSIONS: Markers of oxidative-nitrative stress, PARP activation, and AIF translocation in blood components showed correlation to reduced cardiac function and the clinical appearance of CHF. These results may reinforce the consideration of PARP inhibition as a potential therapeutic target in CHF.

Key Role of Reinforcing Structures in the Flame Retardant Performance of Self-Reinforced Polypropylene Composites.

The flame retardant synergism between highly stretched polymer fibres and intumescent flame retardant systems was investigated in self-reinforced polypropylene composites. It was found that the structure of reinforcement, such as degree of molecular orientation, fibre alignment and weave type, has a particular effect on the fire performance of the intumescent system. As little as 7.2 wt % additive content, one third of the amount needed in non-reinforced polypropylene matrix, was sufficient to reach a UL-94 V-0 rating. The best result was found in self-reinforced polypropylene composites reinforced with unidirectional fibres. In addition to the fire retardant performance, the mechanical properties were also evaluated. The maximum was found at optimal consolidation temperature, while the flame retardant additive in the matrix did not influence the mechanical performance up to the investigated 13 wt % concentration.

Phase Morphology and Mechanical Properties of Cyclic Butylene Terephthalate Oligomer-Containing Rubbers: Effect of Mixing Temperature.

In this work, the effect of mixing temperature (Tmix) on the mechanical, rheological, and morphological properties of rubber/cyclic butylene terephthalate (CBT) oligomer compounds was studied. Apolar (styrene butadiene rubber, SBR) and polar (acrylonitrile butadiene rubber, NBR) rubbers were modified by CBT (20 phr) for reinforcement and viscosity reduction. The mechanical properties were determined in tensile, tear, and dynamical mechanical analysis (DMTA) tests. The CBT-caused viscosity changes were assessed by parallel-plate rheometry. The morphology was studied by scanning electron microscopy (SEM). CBT became better dispersed in the rubber matrices with elevated mixing temperatures (at which CBT was in partially molten state), which resulted in improved tensile properties. With increasing mixing temperature the size of the CBT particles in the compounds decreased significantly, from few hundred microns to 5-10 microns. Compounding at temperatures above 120 °C and 140 °C for NBR and SBR, respectively, yielded reduced tensile mechanical properties most likely due to the degradation of the base rubber. The viscosity reduction by CBT was more pronounced in mixes with coarser CBT dispersions prepared at lower mixing temperatures.

Role of stent selection in the incidence of persisting hemodynamic depression after carotid artery stenting.

PURPOSE: To investigate the possible role of stent selection and procedure-related vessel diameter changes in the development of persisting hemodynamic depression (PHD) and to demonstrate the effectiveness and safety of permanent pacemaker implantation in patients with refractory PHD. METHODS: Data from 584 procedures performed in 542 patients (398 men; mean age 67.3 years) between 2008 and 2011 using Wallstent, Precise, and Xact stents in a nonrandomized fashion were analyzed retrospectively. Cardiovascular risk factors and lesion, stent, and balloon characteristics were collected, and the pre- and postprocedure diameters of the common carotid artery (CCA) and internal carotid artery were measured. PHD was defined as any episode of hypotension (systolic blood pressure <90 mm Hg) and/or bradycardia (heart rate <60/min) lasting >6 hours. Risk factors for PHD were sought using logistic regression analyses; the results are presented as the odds ratio (OR) and 95% confidence interval (CI). RESULTS: The incidence of PHD was 37.0% (216/584). Refractory PHD was encountered in 9 patients; among these, 6 were successfully treated with pacemaker implantation. A history of prior ipsilateral carotid endarterectomy (OR 0.44, 95% CI 0.22 to 0.87, p=0.019) and the presence of a contralateral high-grade stenosis (OR 0.12, 95% CI 0.02 to 0.95, p=0.045) were independent protective factors, while calcification (OR 1.5, 95% CI 1.03 to 2.18, p=0.034), involvement of the carotid bulb (OR 2.56, 95% 1.62 to 4.03, p<0.001), and implantation of a nitinol stent (adjusted OR 1.62, 95% CI 1.12 to 2.34, p=0.011) were independent risk factors for developing PHD after carotid artery stenting. The ratio of the post-/preprocedure CCA diameter (p=0.002), the stent to CCA diameter ratio (p=0.009), and the presence of residual stenosis (p=0.009) were significantly higher in the PHD group. CONCLUSION: Stent selection and procedure-related changes in vessel diameter may have an influence on the development of PHD. Permanent pacemaker implantation is an effective treatment option in patients with refractory PHD.

Water-Assisted Production of Thermoplastic Nanocomposites: A Review.

Water-assisted, or more generally liquid-mediated, melt compounding of nanocomposites is basically a combination of solution-assisted and traditional melt mixing methods. It is an emerging technique to overcome several disadvantages of the above two. Water or aqueous liquids with additives, do not work merely as temporary carrier materials of suitable nanofillers. During batchwise and continuous compounding, these liquids are fully or partly evaporated. In the latter case, the residual liquid is working as a plasticizer. This processing technique contributes to a better dispersion of the nanofillers and affects markedly the morphology and properties of the resulting nanocomposites. A survey is given below on the present praxis and possible future developments of water-assisted melt mixing techniques for the production of thermoplastic nanocomposites.

Activation of poly(ADP-ribose) polymerase by myocardial ischemia and coronary reperfusion in human circulating leukocytes.

Reactive free radical and oxidant production leads to DNA damage during myocardial ischemia/reperfusion. Consequent overactivation of poly(ADP-ribose) polymerase (PARP) promotes cellular energy deficit and necrosis. We hypothesized that PARP is activated in circulating leukocytes in patients with myocardial infarction and reperfusion during primary percutaneous coronary intervention (PCI). In 15 patients with ST segment elevation acute myocardial infarction, before and after primary PCI and 24 and 96 h later, we determined serum hydrogen peroxide concentrations, plasma levels of the oxidative DNA adduct 8-hydroxy-2'-deoxyguanosine (8OHdG), tyrosine nitration, PARP activation, and translocation of apoptosis-inducing factor (AIF) in circulating leukocytes. Plasma 8OHdG levels and leukocyte tyrosine nitration were rapidly increased by PCI. Similarly, poly(ADP-ribose) content of the leukocytes increased in cells isolated just after PCI, indicating immediate PARP activation triggered by reperfusion of the myocardium. In contrast, serum hydrogen peroxide concentrations and the translocation of AIF gradually increased over time and were most pronounced at 96 h. Reperfusion-related oxidative/nitrosative stress triggers DNA damage, which leads to PARP activation in circulating leukocytes. Translocation of AIF and lipid peroxidation occurs at a later stage. These results represent the first direct demonstration of PARP activation in human myocardial infarction. Future work is required to test whether pharmacological inhibition of PARP may offer myocardial protection during primary PCI.