Crack growth behavior of SBR, NR and BR rubber compounds: comparison of Pure-Shear versus Strip Tensile test

Fatigue crack growth experiments on different carbon black–filled rubber compounds have been carried out to evaluate the influence of pure-shear and strip tensile testing mode by using sine and pulse as waveforms. In a previous set of experimental investigations regarding the influence of both waveform and tested material, it was found that the mode I of crack opening sometimes propagates too quickly to be properly monitored in tests involving strip-tensile specimens. An alternative test methodology based on pure-shear test mode has been investigated, optimizing both the shape of the specimen and the test equipment. Data obtained from the different compound formulations were consistent with the theoretical background and resulted in similar ranking of compound crack growth resistance for the two testing modes; in addition, pure-shear mode showed a higher sensitivity to formula variations

Comparison of sine versus pulse waveform effects on fatigue crack growth behavior on Nr, SBR, and BR compounds

Fatigue crack growth experiments on carbon black-filled rubber compounds have been carried out to evaluate the influence of testing conditions over different compound formulations. Investigations on the influence of waveform, data acquisition, and compound formulation have been performed on strip-tensile specimens reproducing the mode I of crack opening. The response of three different compound formulations (based on either natural rubber, butadiene rubber, or styrene-butadiene rubber) to the application of two different waveforms, pulse and sine, has been analyzed, showing significant differences in fatigue behavior and ranking of the various compounds. Compared to the sinusoidal waveform, the use of a pulse waveform provided an improved correlation of the tearing energy with the crack propagation speed. This difference was particularly evident in the case of natural rubber and butadiene rubber, while it resulted negligible in the case of styrene-butadiene rubber. Such a different behavior could be attributed to differences in macromolecular chains orientation. Fine-tuning of video acquisition parameters provided an accurate observation of the crack growth process, as confirmed by the low standard deviation of the estimated tearing energy and crack growth rate

COMPARISON OF SINE VERSUS PULSE WAVEFORM EFFECTS ON FATIGUE CRACK GROWTH BEHAVIOR OF NR, SBR, AND BR COMPOUNDS

Fatigue crack growth experiments on carbon black-filled rubber compounds have been carried out to evaluate the influence of testing conditions over different compound formulations. Investigations on the influence of waveform, data acquisition, and compound formulation have been performed on strip-tensile specimens reproducing the model of crack opening. The response of three different compound formulations (based on either natural rubber, butadiene rubber, or styrene-butadiene rubber) to the application of two different waveforms, pulse and sine, has been analyzed, showing significant differences in fatigue behavior and ranking of the various compounds. Compared to the sinusoidal waveform, the use of a pulse waveform provided an improved correlation of the tearing energy with the crack propagation speed. This difference was particularly evident in the case of natural rubber and butadiene rubber, while it resulted negligible in the case of styrene-butadiene rubber. Such a different behavior could be attributed to differences in macromolecular chains orientation. Fine-tuning of video acquisition parameters provided an accurate observation of the crack growth process, as confirmed by the low standard deviation of the estimated tearing energy and crack growth rate

Produzione in fed-batch ripetuto di acido citrico da Yarrowia lipolytica con riciclo di biomassa per microfiltrazione tangenziale

In this work, citric acid production by Yarrowia lipolytica ATCC 20346 was studied in a laboratory-scale Membrane Recycle Bioreactor composed of a stirred fermenter coupled to a flat-membrane cross-flow microfiltration (CFMF) unit. By increasing the number of production cycles, citrate productivity (R-p) tended to reduce in spite of the fact that the production medium had been integrated with vitamins, whereas the yield factor for citric acid production on glucose was found to be approximately constant. By operating with partial cell discharge (when using either the production media enriched with amounts of nitrogen and essential nutrients equivalent to the mass of cells disposed of, or the growth medium), it was possible to obtain the expected microbial biomass with no or very limited citrate excretion. To minimise the contribution of the cell growth phase to the overall citrate productivity and yield on glucose, it would be convenient to subdivide the process into the following stages: growth phase, yeast recovery by CFMF; Ist prolunged fed-batch production using a pi-I-controller as an indirect feedback of simultaneous substrate and alkaline reagent feeding; yeast recovery by CFMF; 2nd prolunged fed-batch production

Confocal Raman imaging, FTIR spectroscopy and kinetic modelling of the zinc oxide/stearic acid reaction in a vulcanizing rubber

The reaction of zinc oxide (ZnO) with stearic acid (StA) to form zinc stearate (ZnSt) has been investigated experimentally in a model matrix (unvulcanized styreneebutadiene rubber) by using confocal Raman microscopy and FTIR transmission spectroscopy. The heterogeneous nature of the reacting system has been confirmed. The Raman analysis has revealed the coreeshell structure of the product, which is formed via the gradual shrinkage of the ZnO core and the concurrent formation of a surrounding ZnSt shell of increasing thickness. FTIR spectroscopy has provided information about the molecular state of aggregation of StA when dissolved in the rubber, as well as quantitative information on the reaction kinetics. The kinetic behaviour of the system has been interpreted using a semi-quantitative heterogeneous reaction model grounded on the Raman imaging results, which was able to catch the essential features of the phenomenon and to simulate reliably the experimental conversion vs time data at three different temperatures

Neat and GNPs loaded natural rubber fibers by electrospinning: Manufacturing and characterization

The interest towards natural rubber (NR) is progressively increasing due to its sustainable production and remarkable mechanical properties, presenting a wide application range in the automotive industry and civil engineering. In this paper we report, for the first time, the use of electrospinning technique to produce neat and graphene nanoplatelets (GNPs, 1 wt.%) loaded natural rubber fibers. Both randomly distributed and aligned fibers (average diameter size ~ 1 μm) mats were obtained, resulting uniform and defect-free. A detailed characterization of these fibers is reported, including field emission-scanning electron microscopy (FEG-SEM), X-Ray diffraction (XRD) and infrared spectroscopy (FTIR-ATR) techniques. It has been demonstrated that the electrospinning process is able to induce a strong orientation of the polymeric chains in the case of aligned fibers, with respect to the randomly oriented fibers and solvent cast films

Clinical and MRI predictors of response to interferon-beta and glatiramer acetate in relapsing-remitting multiple sclerosis patients

Background and purpose: It is still unclear which patients benefit more from available disease-modifying treatments (DMTs) in multiple sclerosis (MS). Our objective is to identify the baseline clinical and magnetic resonance imaging (MRI) predictors of response to first-line DMTs in a cohort of relapsing-remitting (RR) MS patients in a real-world clinical setting. Methods: Consecutive na\uc3\uafve RRMS patients treated with interferon-beta or glatiramer acetate have been included and followed for 2years. Patients were grouped into responders (R) in case of absence of clinical and MRI activity, and non-responders (NR) if the on-treatment annualized relapse rate (ARR) reduction was <50% of the ARR in the 2years before treatment or in the presence of MRI activity (\ue2\u89\ua52 active lesions at 1-year MRI or \ue2\u89\ua54 active lesions at 1+2-year MRI). Results: At 2-year follow-up, 272 patients were R (34.6%) and 322 NR (40.9%), and multivariate analysis revealed that a later age at onset of the disease (P<0.0001), a lower disability (P<0.0001) and a lower number of gadolinium-enhancing lesions at baseline MRI (P=0.002) were predictors of efficacy of DMTs. Moreover, the first year response had a good predictive power on the second year, as 73.7% of 1-year R had no evidence of clinical and MRI activity within the ensuing year. Conclusion: A lower baseline MRI and clinical activity have been identified as predictors of DMT efficacy in patients with RRMS in routine clinical practice. Evaluation of clinical and MRI activity at 1year is recommended to monitor patients over time