Adsorption of phenol on polycrystalline gold from aqueous solutions

The presence of phenolic compounds as one of the most common organic pollutants in natural water (surface and ground waters) has been detected as a worldwide problem. Very small concentrations of phenols affect the quality of both environmental and household waters, and directly or indirectly impact lives in aquatic systems and humans, as well. Most of the organic compounds, containing certain functional groups, such as amino, amines, carbonyl, hydroxyl, groups containing sulfur and others, have shown ability of adsorption on metal surfaces from aqueous solutions. Cyclic voltammetry (dE/dt = 100 mV s-1) with simultaneous monitoring of the double layer (dl) capacitance (at 100 Hz and 1 mV ac signal) was used for an adsorption study of phenol on polycrystalline gold from 0.5 mol dm-3 aqueous solutions of NaHCO3. Thus, in this study an effort was made to establish a fast method, an electrochemical procedure for qualitative and quantitative determination of phenols in natural water systems

Packaging materials and articles for food: legislation and codes of good manufacturing practice

The basic objectives of food packaging materials are to provide safety and to prevent physical damage of the product, to retain or improve sensory characteristics, to offer a pleasing appearance, to be functional, to facilitate distribution, to give dimensional stability, but also to be compatible with the requirements regulated by the law. Consumers’ demands for an extended shelf life of the product, as well as increased competition in the packaging industry, foster the need for continuous growth and application of innovative solutions for food packaging. While the traditional packaging acts as a passive barrier toward atmospheric effects, the innovative packaging systems offer “active” interactions with the foodstuff, providing increased shelf life and improved quality of the product. The selection of the appropriate packaging material is influenced by many factors, and, among many packaging materials offered on the market, polymer materials and articles have a significant place. On the other hand, some interactions occur between the plastics and the food in contact. The migration of the low-molecular-weight components from the polymer packaging to the packed food is emphasized when the socalled active and intelligent systems are used. Therefore, all the issues related to the packaging materials for food and the substances used as part of the packaging systems, are elaborated in the directives and regulations of the materials and articles intended to come in contact with the food

The Kinetics of Polyacrylamide Adsorption on Polycrystalline Gold

Fast potential step measurements (0.9 ® 1.9 ® 0.9 V, E vs. she) with simultaneous monitoring of the double layer capacity were applied in the study of the kinetics of PAA adsorption on gold from 0.5 M H2SO4, at 293 K. It was shown that the addition of PAA to the solution at 1.9 V (in the presence of a very thin oxide layer at the gold surface of 1 nm) does not affect the value of the capacity of the Au/Au2O3/PAA-solution interface, which was also confirmed by Electrochemical Impedance Spectroscopy. After the very fast cathodic reduction of the thin oxide layer (step 1.9 ® 0.9 V) for several milliseconds, the initial adsorption of PAA molecules at the bare gold surface reappeared in approx. 10 ms, causing exhaustion of the metal/solution boundary layer. The induction region (dq/dt = 0) as well as the diffusion controlled region (dq/dt = const. = f Mn((PAA); cPAA) are characteristic of low concentrations in the solution. According to the experimentally obtained linear parts of the (q / logt)-dependences, values of the diffusion coefficient of PAA-molecules with different molecular weights were calculated. These values follow fairly well the empirical equation: DPAA = 7.03 × 10–4 Mn–0.66 cm2 s–1. Using the same procedure, the diffusion coefficient of 9 × 10–6 cm2 s–1 for adsorption of »small« organic molecules, such as HMBT, was calculated

THERMAL AGING STUDY OF BIODEGRADABLE POLYMER MATERIALS BY DIELECTRIC THERMAL ANALYSIS

Two different studies of the thermal aging of polyesters based on lactic and glycolic acidswere compared. Thermal degradation of poly(L-lactic acid) (PLLA), poly(L-lactic acid-co-glycolicacid) (PLLGA) and poly(DL-lactic acid-co-glycolic acid) (PDLGA) was studied by the dielectricthermal analysis (DETA). The aging was performed at 37C in vacuum oven. The dielectric featuresi.e., dielectric permittivity,, dielectric losses,, and phase lag, tg , were determined by PL-DETAcontaining a parallel plate capacitance cell, from the room temperature to 80, 150, and 180  C,at the heating rates of 2 and 3 Cmin-1. Dielectric scans were obtained at a frequency of 1 kHz anda.c. signal of 200 mV. Different behavior of PLLA, PLLGA, and PDLGA during degradation wasobserved. As the aging of PDLGA proceeds, dielectric losses shift to the lower temperatures,indicating existence of lower molecular weights.  - T, and tg  - T dependences of PLLGA, as wellas those for PLLA show two simultaneous processes occurring, crystallization and degradation

Corrosion inhibition of iron in hydrochloric acid by polyacrylamide

The corrosion protection and/or adsorption of polyacrylamide (PAA) of number average molecular weight, , between 15,000 – 1,350,000 g mol-1 on mild steel and iron (99.99 % Fe) in 3 M HCl at room temperature was studied using spectrophotometry (the phenanthroline method), the weight loss method and EIS (Electrochemical Impedance Spectroscopy). It was found that the corrosion protect­tion efficiency of the PAA – adsorbed layers strongly depends on both the molar concentration of PAA in the solution and its molecular weight, reaching limiting values between 85 and 96 %. Simultaneously, it was also concluded that a relatively high surface coverage could be obtained with very low PAA concentrations (0.5 – 2 ppm), indicating the good adsorption characteristics of PAA on mild steel and iron in hydrochloride acid. The experimentally obtained results follow a Lan­gmuir adsorption isotherm. According to the best fitting parameters, the adsorption coef­f­i­cient B ranged between 2×107 and 4×108 mol-1 and depended strongly on the mole­cular weight of the PAA: B = k (for a ≈ 0.67 and k = 2.95×104) or the size of the polymer coil. As was found by EIS, the thickness of the adsorbed PAA layer was approx. 1.1 nm (for er = 15) and corresponded only to the polymer segments attached to the metal surface. On the other hand, as was found by ellipsometry, the limiting layer of the adsorbed PAA molecules was highly voluminous and relatively thick (100 – 200 nm), containing entangled polymer coils