Investigation of the degradation of commercial polyoxymethylene copolymer in water service applications

An investigation has been carried out on the influence of degradation on various properties of commercial polyoxymethylene (POM) copolymer fittings in chlorinated cold water service lines. Scanning electron microscope (SEM) was used to document interior bulk morphological changes and typical defects. The various types of irregular cracks and pits were observed at the innerface of the samples. DSC and intrinsic viscosity determination were carried out for investigation of crystallinity and molecular weight changes. It was seen that the crystallinity of the POM increases at a much higher rate at the inner surface layers than the outer layer in the used samples. The FT-IR spectra of the new and used samples indicate the extent of degradation of the samples.     

Characterization of methanol extracts from <Emphasis Type="Italic">Quercus hartwissiana</Emphasis> wood and bark

The MeOH extracts of wood and bark from Quercus hartwissiana have been investigated by GC-MS after derivatization, as well as by classical spectroscopic methods. The results for the free compounds revealed that ellagic acid, catechin, gallic acid, quercitol, and also long chain fatty acids, sugars, and sitosterol were the essential compounds in wood and bark, most of them being present in differing amounts. Quercitol, a characteristic compound for the oak wood tannin, was also recognized and determined in oak bark extracts in this study. Amounting to 1/4^th to 1/3^rd of the free compounds, the bark had the highest catechin content. While the content of sugars, such as fructose and glucose, increased in sapwood and bark extracts remarkably, the amounts of these compounds decreased in extracts of heartwood. The profile of the bound compounds contained sugars (i.e., arabinose, xylose, and, above all, glucose), ellagic and gallic acids, quercitols, and inositols. Compared with the composition of free compounds, the hydrolyzed extracts showed relatively higher amounts of sugars, especially glucose, gallic acid and quercitol.     

The effects of polyelectrolytes on the inhibition and aggregation of calcium oxalate crystallization

The influence of polyelectrolytes with different architecture on spontaneous batch crystallization of calcium oxalate was investigated. A series of acidic acrylate block copolymers were been made, by radical polymerization, with defined molecular weight and structure. Radical polymerization of acrylic acid (AA) was carried out in the presence of α‐thiopolyethylene glycol monomethylether as a chain transfer agent to produce poly(ethylene glycolblockacrylic acid) copolymers. Poly(ethylene glycol) (PEG) block length in the copolymers was controlled by using three different molecular weight chain transfer agents (M_n = 350, 750 and 2000 g/mol). The presence of copolymers inhibited the crystal growth of calcium oxalate possibly through adsorption onto the active growth sites for crystal growth due to the charge and hydrophilic effects. Copyright © 2006 John Wiley & Sons, Ltd.     

Biomimetic mineralization of hydroxyapatite crystals on the copolymers of vinylphosphonic acid and 4-vinilyimidazole

In the present work, copolymers of vinylphosphonic acid and 4-vinilyimidazole (poly(4-VIm-co-VPA)) were found to be substrates favoring the precipitation of nanohydroxyapatite (HAP) crystals from stable supersaturated solutions at pH 7.4 and 37 degrees C. Deposition kinetics were studied by the constant composition technique. The rates of crystallization both on HAP seed crystals as reference and on the copolymer in powder form were investigated at constant supersaturation conditions. The rates of HAP crystal growth on the polymeric substrate were found to depend on the amount of seed material and on the phosphate content of the copolymer.     

Solution Properties of Poly(ethylene Oxide) as Determined by Viscometric Measurements in Aqueous Salt Solutions

The properties of dilute solutions of poly(ethylene oxide) (PEO) in aqueous salt solutions are studied by measurements of intrinsic viscosity [n] in theta and nontheta solvents. The unperturbed dimensions in various salt solutions were found larger than those in pure water. These results are attributed to a change in the polymer hydration sheath, in the uche-transilibrium in the PEO chain in aqueous solutions, and in the water structure because of the added salt. Also, for carboxylic anions, similar behavior is expected due to the interaction of the ether oxygens of PEO with the weak acids through hydrogen bonding. The enthalpy and entropy dilution parameters XHand XS were observed to take on negative and positive values, respectively.     

Aqueous pathways for formation of zinc oxide particles in the presence of carboxymethyl inulin

In this study, zinc oxide (ZnO) crystals were obtained by a simple wet chemical method using zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O) and hexamethylenetetramine as the starting materials in the presence of the water-soluble biopolymer carboxymethyl inulin (CMI). We investigated the effect of reaction temperature and CMI concentration on the morphology, surface area, particle size, and size distribution of zinc oxide. X-ray diffraction analysis showed the XRD patterns for all the samples were similar to that of ZnO with the wurtzite structure, irrespective of the geometric shape of the particle. The ZnO rod grows preferentially along the [001] direction in the absence of the CMI. The biopolymer affects the ZnO crystals in a concentration-dependent manner by altering the growth rate of the particles along the c-axis and a-axis. The vast majority of the crystals have a central grain boundary in the presence of CMI. The precipitate consisted of micrometer-sized hexagonally shaped bipyramidal ZnO crystals and nanocrystals.     

Effect of ethyl acetate on carbohydrate components and crystalline structure of pulp produced in aqueous acetic acid pulping

The aim of this study was to investigate the changes in carbohydrate components and the crystalline structure in hemp bast fibers by adding ethyl acetate to acetic acid/water pulping processes. It was found that ethyl acetate added to acetic acid/water process had a positive effect on yield, viscosity and carbohydrate components in pulp. It was assumed that the delignification ratio increased by adding ethyl acetate to aqueous acetic acid pulping. Xylose content in hemp bast fibers was affected more negatively in the ethyl acetate/acetic acid/water process than in the acetic acid/water one. Crystallinity and crystallite size were higher in pulp sample obtained by the acetic acid/water process without ethyl acetate.