Nuclear Waste Glass Durability: I, Predicting Environmental Response from Thermodynamic (Pourbaix) Diagrams

Pourbaix diagrams are shown to conceptually explain dissolution of glasses in terms of their thermodynamic stability and surface layer formation. To predict the long-term effects of ground-water contact on the durability of nuclear waste glass in a geologic repository, the nature of the glass dissolution process has been extensively examined. Hydration thermodynamics has been used to quantify the role of glass composition and the effect of solution pH. The glass compositions examined vary widely in composition and include natural, lunar, medieval, and nuclear waste glasses, as well as some glass-ceramics. The known effects of solution pH and oxidation potential (Eh) on glass dissolution are empirically described by thermodynamically calculated Pourbaix diagrams. Statistical analysis of over 300 glass durability tests demonstrates that the Pourbaix diagram can be quantified because of (1) the colinearity of the hydration free energy with solution pH defined by the Nernst equation and (2) the colinearity of the solution pH with the concentration of dissolved silicon and boron in the solution defined by the pH dependence of the ion activities. Construction of Pourbaix diagrams to describe glass dissolution serves to unify and categorize various existing experimental glass dissolution data.     

Modification of cellulose/chitin mix fibers with N‐isopropylacrylamide and poly(N‐isopropylacrylamide) under cold plasma conditions

A two‐step grafting procedure was applied to cellulose/chitin (CC) mix fibers, namely: activation under the action of cold plasma discharges, followed by reaction with N‐isopropylacrylamide (NIPAAm) and poly(N‐isopropylacrylamide) (PNIPAAm) to obtain fibers with responsiveness to external stimuli. The graft samples were characterized using attenuated total reflection Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy (XPS), X‐ray diffraction, scanning electron microscopy coupled with energy‐dispersive X‐ray microanalysis and antimicrobial testing. All obtained results confirm the morphological and structural changes after plasma treatment which determine the modification of cellulose fiber properties. It was estimated from XPS data that the degrees of modification/grafting were about 23% for CC/NIPAAm and 13% for CC/PNIPAAm. Such treatment could be transferred to practical technologies, particularly in textile applications and special applications in the medical field. Copyright © 2012 Society of Chemical Industry     

Epidemiology of end‐stage renal disease and hemodialysis treatment in Serbia at the turn of the millennium

The study presents the epidemiological features of patients treated with renal replacement therapy (RRT) in Serbia from 1997 to 2009 and compares the results of hemodialysis treatment in 1999 and 2009. Epidemiological data were obtained from the National Registry of RRT patients and data on hemodialysis treatment from special surveys conducted in 1999 and 2009. Within the period 1997–2009 the incidence of patients on RRT increased from 108 to 179 per million population (pmp), prevalence rose from 435 to 699 pmp, while mortality rate fell from 20.7% to 16.7%. The frequency of patients with glomerulonephritis decreased, while that of patients with diabetes and hypertensive nephropathy increased. In late 2009 there were 5208 patients receiving RRT in Serbia. Within the examined period new hemodialysis and reverse osmosis equipment were purchased, high‐flux dialyzers with synthetic membranes were increasingly used and the number of patients receiving hemodiafiltration increased to 17.6%. Kt/V greater than 1.2 was recorded in 16% of the patients in 1999 but 52% in 2009. Options for correction of anemia and mineral disorders have also improved. The percentage of patients with HbsAg (13.8% vs. 4.8%) as well as anti‐hepatitis C virus antibodies positive patients (23.2% vs. 12.7%) was significantly lower in 2009 than in 1999. Both the incidence and prevalence of RRT patients in Serbia are rising continuously, while the mortality rate is falling. More favorable conditions for dialysis treatment have brought about significant improvement in the results over the last 10 years.     

Polymer Microcapsules with Carbohydrate‐Sensitive Properties

Carbohydrate‐sensitive polymer multilayers are assembled onto flat substrates and colloidal CaCO₃ particles via reversible covalent ester formation between the polysaccharide mannan and phenylboronic acid moieties grafted onto poly(acrylic acid) (PAA). The resulting multilayer films are sensitive to several carbohydrates, and show the highest sensitivity to fructose. The response to carbohydrates arises from the competitive binding of small molecular weight sugars and mannan to boronic acid groups within the films, and is observed as a rapid dissolution of the multilayers upon contact with a sugar‐containing solution above a critical concentration. In addition, carbohydrate‐sensitive multilayer capsules are prepared, and their sugar‐dependent stability is investigated by following the release of encapsulated tetramethylrhodamine isothiocyanate‐bovine serum albumin (TRITC‐BSA).     

Unmodified and esterified Kraft lignin‐filled polyethylene composites: Compatibilization by free‐radical grafting

In this study, the effectiveness of free‐radical grafting as a compatibilization method applied to composites containing Kraft lignin (KL) and esterified lignin was comparatively investigated. Maleated lignin (ML) was first obtained via esterification of KL with maleic anhydride. KL and ML were respectively incorporated into high density polyethylene (HDPE) up to 60% wt and dicumyl peroxide was used as a free‐radical generator. The influence of lignin esterification and free‐radical grafting on the morphological, mechanical, and thermal properties of lignin‐based composites was studied. The incorporation of lignins into HDPE resulted in poor mechanical strength because of low compatibility. Morphological and mechanical evidences indicate improved compatibility between lignins and HDPE following free‐radical grafting. The free‐radical scavenging properties of KL allowed better compatibilization of KL‐based composites compared with ML‐based composites. In addition, thermal analysis results showed that free‐radical grafting increases the thermal stability of ML‐based composites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41484.     

The kinetics of isothermal nicotinamide release from poly(acrylic‐co‐methacrylic acid) loaded xerogel

The isothermal kinetics of in vitro nicotinamide release from poly(acrylic‐co‐methacrylic acid) loaded xerogel into water was evaluated. The isothermal kinetics curves of nicotinamide release from poly(acrylic‐co‐methacrylic acid) xerogel were measured at different temperatures ranging from 296 K to 315 K. It was proven that the kinetics of nicotinamide release from poly(acrylic‐co‐methacrylic acid) xerogel was a kinetically complex process which was neither controlled by the processes of drug diffusion nor with the relaxation of the xerogel. The kinetic of nicotinamide release from poly(acrylic‐co‐methacrylic acid) may be described by the kinetics model of reversible first order chemical reaction and the apparent activation energy have value of E_a,M = 14.1 kJ mol^?1 and preexponential factor ln(A_M min^?1) = 2.3. The rate constants of nicotinamide release ( ) and the rate constants of its reversible absorption reaction ( ) were calculated and found to fall within the range 0.019 min^?1?0.033 min^?1 for and 0.014 min^?1?0.016 min^?1 for . The value of activation energy for the nicotinamide releas, E_a.R =21.25 kJ mol^?1, is significantly higher than the value for the process of nicotinamide absorption (E_a,A = 2.6 kJ mol^?1). The rate of nicotinamide release was predetermined with the rate of nicotinamide molecules distribution between the hydrogel and surrounding solution. POLYM. ENG. SCI., 55:60–69, 2015. © 2014 Society of Plastics Engineers