Morphology,thermal, and electrical properties of polypropylene hybrid composites co‐filled with multi‐walled carbon nanotubes and graphene nanoplatelets

In this study, nanocomposites of polypropylene (PP) with various loadings of multi‐wall carbon nanotubes (MWCNT) and graphene nanoplatelets (GnP) were formed by masterbatch dilution/mixing approach from individual masterbatches PP‐MWCNT and PP‐GnP. Melt mixing on a twin‐screw extruder at two different processing temperatures was followed by characterization of morphology by transmitted‐light microscopy including the statistical analysis of agglomeration behavior. The influence of processing temperature and weight fractions of both nanofillers on the dispersion quality is reported. Thermal properties of the nanocomposites investigated by DSC and TGA show sensitivity to the nanofillers weight fraction ratio and to processing conditions. Electrical conductivity is observed to increase up to an order of magnitude with the concentration of each nanofiller increasing from 0.5 wt % to 1.0 wt %. This is related with a decrease of electrical conductivity observed for unequal concentration of both nanofillers. This particular behavior shows the increase of electrical properties for higher MWCNT loadings and the increase of thermo‐mechanical properties for higher GnP loadings. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42793.     

Biochemical changes of fresh-cut pineapple slices treated with antibrowning agents

The effectiveness of ascorbic acid (AA), isoascorbic acid (IAA) and N‐acetyl‐cysteine (AC) in inhibiting browning of fresh‐cut pineapple slices that were stored for up to 14 days at 10 °C, were studied. Slices treated with IAA and AA maintained higher levels of sugars and vitamin C than AC and controls. A low reduction of total phenolic content in treated slices was correlated with a lower polyphenol oxidase activity. IAA and AA slowed the degradation rates of sugars, vitamin C, and phenolic content, whereas AC was less effective in affecting these processes. A higher content of AA and IAA was associated with better compositional quality parameters and appearance of the pineapple slices during the storage period.     

Thermodynamic equation of state approach for the choice of working fluids of absorption cooling cycles

A methodology is developed for the application of thermodynamic equations of state of fluids and fluid mixtures in evaluating working fluid combinations of absorption cooling cycles. Thermodynamic phase equilibrium formulation of this methodology is presented. In the application of this approach for the comparitive study and choice of working fluids, the Redlich-Kwong equation of state is used for a number of possible working fluid combinations for solar absorption cooling cycles. It is demonstrated that when limited experimental data are at hand this approach could be a useful screening technique for potential working fluid combinations.     

Evaluation of partial pressure CO2 change in the dialyzer blood inlet during hemodialysis as a measure of vascular access recirculation

Introduction

Vascular access recirculation during hemodialysis is associated with reduced effectiveness and worse survival outcomes. To evaluate recirculation, an increase in pCO₂ in the blood of the arterial line during hemodialysis (threshold of 4.5 mmHg) was proposed. The blood returning from the dialyzer in the venous line has significantly higher pCO₂, so in the presence of recirculation, pCO2 in the arterial blood line may increase (ΔpCO₂) during hemodialysis sessions. The aim of our study was to evaluate ΔpCO₂ as a diagnostic tool for vascular access recirculation in chronic hemodialysis patients.

Methods

We evaluated vascular access recirculation with ΔpCO₂ and compared it with the results of a urea recirculation test, which is the gold standard. ΔpCO₂ was obtained from the difference in pCO₂ in the arterial line at baseline (pCO₂T1) and after 5 min of hemodialysis (pCO₂T2). ∆pCO₂ = pCO₂T2–pCO₂T1.

Findings

In 70 hemodialysis patients (mean age: 70.52 ± 13.97 years; hemodialysis vintage of 41.36 ± 34.54, KT/V 1.4 ± 0.3), ∆pCO₂ was 4 ± 4 mmHg, and urea recirculation was 7% ± 9%. Vascular access recirculation was identified using both methods in 17 of 70 patients, who showed a ∆pCO₂ of 10 ± 5 mmHg and urea recirculation of 20% ± 9%; time in months of hemodialysis was the only difference between vascular access recirculation and non-vascular access recirculation patients (22 ± 19 vs. 46 ± 36, p: 0.05). In the non-vascular access recirculation group, the average ΔpCO₂ was 1.9 ± 2 (p: 0.001), and the urea recirculation % was 2.8 ± 3 (p: 0.001). The ΔpCO₂ correlated with the urea recirculation % (R: 0.728; p < 0.001).

Discussion

ΔpCO₂ in the arterial blood line during hemodialysis is an effective and reliable diagnostic tool for identifying recirculation of the vascular access but not its magnitude. The ΔpCO₂ test application is simple and economical and does not require special equipment.