Study of polypropylene/ethylene‐propylene‐diene monomer blends reinforced with sisal fibers

Thermoplastics reinforced with natural fibers have attracted much attention from researchers because of their advantages, especially regarding environmental aspects. However, poor impact strength, particularly at low temperatures, limits the application of some thermoplastics, such as polypropylene (PP). To minimize this drawback, impact modifiers have been used, including the terpolymer of ethylene‐propylene‐diene (EPDM). In this work, PP/EPDM/sisal composites of distinct compositions were investigated focusing on the effect of the alkali (NaOH) treatment of the vegetable fiber on the composites properties regarding physical, mechanical, thermal, and morphological behavior. The results indicated that flow rate decreases at higher fiber content due to flow hindering by the presence of the fibers. The addition of the fiber, in general, increased Young's modulus and strength (tensile and flexural), whereas impact strength increased for higher EPDM content. The alkali treatment was considered generally efficient in terms of mechanical properties, even though this was not found in the dynamic mechanical analysis. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

The ForeMoSt approach to building valid model-based safety arguments

Software and Systems Modeling - Safety assurance cases (ACs) are structured arguments designed to comprehensively show that a system is safe. ACs are often model-based, meaning that a model of the...     

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.