Styrene — divinylbenzene copolymers,IV. Porosity changes during chloromethylation

The change in the porosity of styrene-divinylbenzene (S-DVB) copolymers during the chloromethylation reaction was investigated using apparent densities and equilibrium swelling in toluene. Maximum porosity of S-DVB copolymers does not change appreciably with the chloromethylation reaction. Only a slight decrease in the maximum porosity was observed in rigid networks, probably due to the partial destruction of the pore structure. However, with the substitution by chloromethyl groups, the degree of swelling decreases, which results in an increase in the stability of the porous structure in chloromethylated copolymers.     

Pendant vinyl group reactivity during the free-radical copolymerization of methyl methacrylate and ethylene glycol dimethacrylate

Summary Methyl methacrylate-ethylene glycol dimethacrylate (MMA-EGDM) copolymerization has been investigated in toluene at a monomer concentration of 22 w/v %. The kinetic models developed recently along with the experimental conversion curve and gel point data provided the calculation of the average reactivity of pendant vinyl groups. It was found that the pendant vinyl reactivity for intermolecular links is much less than the monomeric vinyl reactivity and it decreases further as the EGDM concentration increases. At 5–15 mol % EGDM, the average pendant reactivity is 1–2 orders of magnitude lower than the monomeric vinyl reactivity. The reduced pendant reactivity is mainly responsible for the shift of the gel point towards higher conversions.     

Removal of Turbidity from Travertine Processing Wastewaters by Coagulants,Flocculants and Natural Materials

The sedimentation behaviour of travertine-processing wastewater containing a high concentration of suspended solids was investigated using different coagulation and flocculation methods. In batch experiments, four types of coagulants [FeC1₃, Al₂(SO₄)₃, PACl, NaAlO₂], six types of flocculants (40% MMW–40% HMW cationic, 30% MMW, 40% MMW, 40% HMW anionic and nonionic) and three types of natural materials (NMs) (sepiolite, zeolite, and pumice) were used to treat wastewater with an initial turbidity of 570–880 NTU. The optimum process conditions (dosage, mixing time/speed, sedimentation time, and pH) were investigated for each. Sedimentation performance was assessed by the effluent turbidity (T _eff) values of the treated water. The best performances obtained were 99.3% (T _eff?=?4 NTU), 99.1% (T _eff?=?8 NTU), and 97.8% (T _eff?=?18 NTU) with 40% HMW anionic-cationic flocculants, zeolite, and FeCl₃, respectively. Sludge properties, including sludge settling velocity (mm/min), sludge density (g/cm³), suspended solids (SS) content (mg/L), and sludge solids (%) were determined and compared under optimized conditions. The type of additive significantly affected performance. Travertine processing wastewater flocculation with polymeric materials and NMs, especially zeolite, was more favourable than coagulants in terms of both turbidity removal and sludge quality. Since zeolite is a NM, additional studies on using and recycling of the generated sludge as an industrial feedstock would be worthwhile.     

Preparation of macroporous poly(acrylamide) hydrogels in DMSO/water mixture at subzero temperatures

The copolymerization reactions of acrylamide and N,N’-methylenebis(acrylamide) were carried out in DMSO/water mixture (1:1 by volume) at various temperatures T_prep between -18 and 22 °C. Scanning electron microscopy analysis of the networks revealed the presence of porous morphologies. All the network samples formed at or below 0 °C have relatively small pores with sizes about 10⁰ μm. In this range of T_prep, the pore size only slightly increases with the temperature. As the temperature is increased above 0 °C, both the average pore size and the degree of polydispersity of the pores rapidly increase. Between T_prep=0 and 13 °C, the microstructure gradually changes from networks having relatively small pores to those exhibiting regular assembly of polyhedral large pores of about 10¹ μm in sizes. The formation of the porous structure at or below 0 °C is as a result of the cooling-induced phase separation mechanism, while the large polyhedral pores in the networks prepared at higher temperatures form during the freeze-dry process of the hydrogels after preparation.     

Reentrant phase transition of poly(N‐isopropylacrylamide) gels in polymer solutions: Thermodynamic analysis

The swelling behavior of poly(N‐isopropylacrylamide) (PNIPA) gels in polymer solutions, particularly in aqueous solutions of poly(ethylene glycol)s, was investigated using the theory of equilibrium swelling. The volume of the PNIPA gel and the partition parameter of the macromolecules between the gel and the solution phases were calculated for various extents of the energetic interactions between the components. The simulation results were compared with the experimental data reported in the literature. It was shown that the PNIPA gel has a tendency to a reentrant phase transition in an aqueous solution of low molecular weight linear polymers. In such a transition, the gel first collapses, then reswells, if the linear polymer concentration is continuously varied. The necessary condition for the reentrant behavior of PNIPA gels was predicted in terms of the interaction parameters among the PNIPA network, the linear polymer, and water. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 801– 813, 2002     

Ethidium bromide binding to DNA cryogels

The interaction of the classical intercalator ethidium bromide (EtBr) with the double helical network strands of DNA cryogels was investigated. The cryogels were prepared starting from aqueous solutions of DNA (about 2000 base pairs long) at ?18 °C using 1,4-butanediol diglycidyl ether crosslinker under various reaction conditions. In contrast to the solubilization of DNA hydrogels in aqueous EtBr solutions, DNA cryogels remain stable even after complete saturation of their EtBr binding sites. The total binding capacity of the cryogels is 0.6 ± 0.1 EtBr per nucleotide, which is close to the theoretical maximum number of EtBr molecules that can bind to DNA. Even in very dilute solutions (down to 3 μM), cryogels remove EtBr from aqueous solutions with an efficiency of 90%. The equilibrium binding constant and the maximum number of EtBr binding sites of the cryogels almost coincide with the reported values for the secondary binding process of EtBr by DNA in aqueous solutions. At low mole ratios of bound EtBr to DNA, the cryogels swell with increasing amount of bound EtBr, most likely caused by the lengthening of DNA due to the intercalated EtBr. The response of DNA cryogels to changes in EtBr concentration between 3 and 300 μM also suggests that they can be used to detect DNA binding substrates in aqueous solutions.     

Autonomic self-healing in covalently crosslinked hydrogels containing hydrophobic domains

Self-healing hydrogels suffer from low mechanical strength due to their reversible breakable bonds which may limit their use in any stress-bearing applications. This deficiency may be improved by creating a hybrid network composed of a combination of a physical network formed via reversible crosslinks and a covalent network. Here, we prepared a series of hybrid hydrogels by the micellar copolymerization of acrylamide with 2 mol % stearyl methacrylate (C18) as a physical crosslinker and various amounts of N,N′-methylenebis(acrylamide) (BAAm) as a chemical crosslinker. Rheological measurements show that the dynamic reversible crosslinks consisting of hydrophobic associations surrounded by surfactant micelles are also effective within the covalent network of the hybrid hydrogels. A significant enhancement in the compressive mechanical properties of the hybrid gels was observed with increasing BAAm content. The existence of an autonomous self-healing process was also demonstrated in hybrid gels formed at low chemical crosslinker ratios. The largest self-healing efficiency in hybrids was observed in terms of the recovered elastic modulus, which was about 80% of the original value.     

The Historical Development and Nutritional Importance of Olive and Olive Oil Constituted an Important Part of the Mediterranean Diet

The olive tree (Olea europaea) is widely cultivated for the production of both oil and table olives and very significant because of its economic value. Olive and olive oil, a traditional food product with thousands of years of history, are the essential components of the Mediterranean diet and are largely consumed in the world. Beside of their economical contribution to national economy, these are an important food in terms of their nutritional value. Olive and olive oil may have a role in the prevention of coronary heart disease and certain cancers because of their high levels of monosaturated fatty acids and phenolic compounds. In addition, olives (Olea europaea L.) and olive oils provide a rich source of natural antioxidants. These make them both fairly stable against auto-oxidation and suitable for human health. The aim of this paper is to define the historical development and nutritional importance of olive and olive oil constituted an important part of the Mediterranean diet.     

Engineered catalyst layer design with graphene-carbon black hybrid supports for enhanced platinum utilization in PEM fuel cell

In this study, a new approach was applied to prepare platinum/reduced graphene oxide/carbon black (Pt/rGO/CB) hybrid electrocatalysts. Unlike literature firstly GO and CB in varying ratios are homogeneously mixed with a high shear mixer and then Pt was impregnated onto the hybrid support structure according to the polyol method. According to our approach CB was used as a spacer and intercalating agent in both Pt impregnation and electrode preparation to avoid restacking and increase the Pt utilization. Thus rGO/CB based hybrid support can ease the diffusion while it is promoting to the use of high electrical connectivity and surface area of graphene. The maximum power density of 645 mW cm^?2 with Pt utilization efficiency of 2.58 kW/gPt was achieved with the hybrid containing the smallest amount of CB. It seems that this small amount of CB effectively modifies the electrode structure. The enhanced fuel cell performance can be attributed to synergistic effects from graphene and CB providing better mass transport and Pt utilization in the catalyst layer.     

Dissolution kinetics of borogypsum in di-ammonium hydrogen phosphate solutions

This work examines the dissolution kinetics of borogypsum in di-ammonium hydrogen phosphate solutions ((NH₄)₂PO₄) in a batch reactor. The parameters selected were the reaction temperature (15–53 °C), di-ammonium hydrogen phosphate concentration (1–4 M), stirring speed (50–800 rpm), and solid/liquid ratio (1/50–1/5). The dissolution rate increased by increasing the temperature (from 0.32 to 0.82), di-ammonium hydrogen phosphate concentration (from 0.35 to 0.821), and by decreasing solid-to-liquid ratio (from 0.77 to 0.24). The dissolution rate increased up to stirring speed of 600 rpm (from 0.135 to 0.56), and then decreased with increasing stirring speed (from 0.56 to 0.351). The dissolution rate was described by first-order pseudo-homogeneous reaction model. The activation energy of this study was calculated as 42.103 kJ mol^?1. A kinetics model including the used parameters in this study was suggested as follows:

$?\ln \left(1?X\right)=223.63C^{0.911}{\left(S/L\right)}^{?0.7689}{W}^{0.6212}{e}^{\left(?5064.2/T\right)}t$