Superabsorbent hydrogels from poly(aspartic acid) with salt-, temperature- and pH-responsiveness properties

Polyaspartic acid (PAsp) resin was synthesized by polysuccinimide (PSI), through chemical cross-linking using the cross-linking agent (diamine). The effects of reaction variables, such as PSI concentration and terminal pH on the water absorbent capacity have been studied. These phenomena were discussed according to structural parameters, which were confirmed by SEM. Water absorbencies were compared for the hydrogels at terminal pH 8 and 10. The water absorbent capacity enhanced with increasing terminal pH and decreasing PSI concentration. The swelling/deswelling kinetics of the super-absorbent hydrogels was investigated as well. It is found that the hydrogels showed ampholytic and reversible pH-responsiveness properties. The variational water absorbencies were attributed to swelling theory based on the hydrogel physical and chemical structure. The swelling was also extremely sensitive to the temperature, ionic strength and cationic kind. The reversible pH-responsiveness, salt- and temperature-sensitivity of the hydrogels make this intelligentized polymer had wider applications.     

玉米淀粉接枝丙烯酰胺制备高吸水性树脂

用硝酸铈铵作引发剂,通过水溶液聚合法制得了玉米淀粉接枝丙烯酰胺高吸水性树脂。研究了交联剂及引发剂用量、碱用量、反应温度以及反应时间等对吸水率的影响。得到的最佳反应条件为:交联剂和引发剂与丙烯酰胺的摩尔比分别为1.0×10-5和3.0×10-3,碱与丙烯酰胺的摩尔比为1.50,反应温度60℃,反应时间2 h。在室温下制得的高吸水树脂,30 m in每克吸蒸馏水和自来水分别约为其自身质量的600和170倍。     

Cold crystallization of water in hydrated poly(2‐methoxyethyl acrylate) (PMEA)

The structure of water associated with poly(2‐methoxyethyl acrylate) (PMEA), which is known to exhibit excellent blood compatibility, has been investigated using differential scanning calorimetry (DSC). The total equilibrium water content (EWC) of PMEA was 9.0 wt%. Water in the PMEA could be classified into three types: non‐freezing, freezing‐bound and free water. Cold crystallization of water was clearly observed at about −42 °C on heating when the water content was more than 3.0 wt%. Cold crystallization is attributed to the phase transition from the amorphous ice to the crystal ice in PMEA. The relative proportions of freezing‐bound water at the EWC is 48 % of all the water in hydrated PMEA. © 2000 Society of Chemical Industry     

Chemical cross-linking of conducting poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) using poly(ethylene oxide) (PEO)

Hybrid films of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) were prepared with different molecular weights of poly(ethylene oxide) (PEO). The cross-linking reaction between PEO and PEDOT:PSS was performed at high temperature and confirmed by using differential scanning calorimeter (DSC), contact angle measurement, and solid-state ¹H NMR. The effect of chemical reaction on the conductivity and morphology of these hybrid films was studied by using 4-point probe and atomic force microscope (AFM), respectively. As-spun PEO/PEDOT:PSS films have lower electric conductivity due to the addition of nonconductive PEO, and exhibits no molecular weight dependence on conductivity. After chemical cross-linking reaction at high temperature, only PEDOT:PSS films with lowest molecular weight PEO additives show enhanced conductivity with increasing reaction time. AFM result indicates that the heat-treated PEO/PEDOT:PSS hybrid films show grain-like morphology compared to ethylene glycol treated PEDOT:PSS films which shows continuous PEDOT domain. In the present work we demonstrate that the cross-linking reaction can be used to improve the wet stability of PEDOT:PSS nanofiber, showing good water resistance and excellent dimensional stability.     

An FTIR/ATR in situ study of sorption and transport in corrosion protective organic coatings: 1. Water sorption and the role of inhibitor anions

Both sorption and desorption transport coefficients of water and the inhibitor (HPO₄²⁻) in a series of epoxy resins (model paints) of different cross-linking density have been reported. Water diffusion is unaffected by low electrolyte concentrations (0.1 μm) but is retarded at 0.6 M chloride ion levels, presumably due to water–polymer–polymer interaction shielding. Swelling is small, but may be significant for polymer chain relaxation. The FTIR data have been used to add a molecular level interpretation of the four different pseudo-Fickian processes observed at room temperature. These data are consistent with rapid sorption onto polymer active (OH, NH), sites followed by slower incorporation of water into polymer microvoids where cluster sizes are smaller. The reverse process (on desorption) is also evident from the water, ν(OH), spectral distribution. No evidence of significant accumulation of ‘bulk’ water at the polymer–substrate interface was found.     

膜集成技术在药用纯化水制备中的应用

兰州市某高校医学院以兰州市自来水为水源,采用预处理+二级反渗透(RO)+连续电除盐技术(EDI)+后处理的膜集成技术制取药用超纯水。运行结果表明,采用二级RO+EDI的膜集成技术制取药用超纯水是可行的,产品水达到分析实验室用水国家标准(GB/T 6682—2000)和中国药典(2010版)纯化水标准。     

Effect of water and tri(ethylene) glycol on the rheological properties of zein

Before conducting larger scale studies utilizing highly concentrated zein blends on an extruder, it is advisable to carry out experiments on a torque rheometer. Water and tri(ethylene glycol) (TEG) are known plasticizers for zein, however, the effects these materials have on zein rheology has not been studied using a torque rheometer. The amount of each plasticizer in zein was varied between 5 and 30%. It was demonstrated that water and TEG interact differently with zein. When the amount of water was above 10% at 90 °C, torque increased rapidly. With TEG, torque increased linearly with time and only at 120 °C did the rapid torque increase occur. Multiple torque increases for zein mixtures were observed, suggesting that processes that increase viscosity are an on-going process. Significant cross-linking is not the main source for the increased torque. The energy of activation of flow was determined when using 20% TEG. A model was developed relating %water, %TEG, temperature and rpm with initial torque.     

Water sorption in cross-linked poly(vinyl alcohol) networks

Poly(vinyl alcohol) (PVA) networks of different cross-linking densities were prepared by reaction with hexamethylene diisocyanate in solution and casting. The dynamic-mechanical properties of PVA films have been investigated in the temperature range of −150 to +150 °C. Two relaxations processes labeled α and β in order of decreasing temperature were observed. The α-relaxation shifts to lower temperature and the average molecular weight between cross-links decreases with increasing cross-linking density. Isothermal sorption from vapor and liquid water allowed determination of the Flory-Huggins interaction parameter between water and the polymer chain segments, which decreased with the water activity in the hydrogel and increased with the cross-linking density as a consequence of the hydrophobic character of the cross-linking agent. The water diffusion coefficients, D, in the networks obtained by means of dynamic sorption experiments increased with increasing water activity. This behavior is interpreted in terms of plasticization of the polymer by water molecules.     

Preparation of Silane-Grafted and Moisture Cross-Linked Low Density Polyethylene: Part I: Factors Affecting Performance of Grafting and Cross-Linking

In the present work, the silane grafting and water cross-linking of low density polyethylene (LDPE) were investigated. The grafting reaction was carried out in an internal mixer and polyethylene cross-linking was done in hot water. The effect of silane, peroxide, catalyst, carbon black, cross-linking time, and cross-linking temperature on the grafting and cross-linking processes are reported. Vinyl trimethoxy silane (VTMO) and di-cumyl peroxide (DCP) were selected as grafting agent and initiator respectively. Silane grafting on polyethylene was determined using Fourier transform infrared (FTIR) spectroscopy and torque monitoring of the mixer. Absorption peak due to –Si–OCH₃ groups in FTIR and torque increasing due to silane grafting in the mixer illustrated that silane-grafting reactions occurred. The FTIR data demonstrated that the extent of silane grafting was increased as the concentration of silane and peroxide was increased. Thermogravimetry analysis (TGA) determined that the thermal stability of LDPE increased by increasing the amount of silane grafting. Gel fraction increased with silane and peroxide concentration. As the percent of of catalyst increase the time scale for specified gel content shifted to shorter times. Incorporation of carbon black into LDPE decreased the extent of silane grafting and gel fraction. Water temperature increasing in cross-linking stage reduced the time to maximum degree of cross-linking.     

The occurrence of priority PAHs, nonylphenol and octylphenol in inland and coastal waters of Central Greece and the Island of Lesvos

Polycyclic aromatic hydrocarbons (PAHs) as well as nonylphenol (NP) and octylphenol (OP) are substances of major environmental concern because of their adverse health effects on organisms, including endocrine disrupting activity. Seven PAHs, NP and OP have been included in the priority list of substances regulated by 2000/60/EC Water Framework Directive. The present work concerns the investigation of the occurrence of the seven priority PAHs, NP and OP in surface and coastal waters in Central Greece and the Island of Lesvos. Samples were collected and analyzed seasonally for one year from the four reservoirs that supply water to Athens: Mornos, Marathonas, Yliki and Evinos. Samples were also collected from inland waters of the Lesvos Island (the rivers Mylopotamos and Evergetoulas), and from coastal waters (five sampling points) of the Mytilene area, which is the capital city of the Island of Lesvos. The results have shown that in most cases the water samples that were analyzed are free from PAHs, possibly because of lack of PAHs release sources nearby the particular areas, or due to the adsorption of PAHs on sediments. NP occurred at low levels in several cases, while OP was detected only in one sample.     

Sorption equilibria and diffusion coefficients of ethanol and water in the PVA membranes containing cyclodextrin

Effects of cyclodextrin (CD) on the pervaporation characteristics for water/ethanol through the PVA/CD membranes (PVA membranes containing β-CD oligomer) have been investigated in terms of sorption equilibria and diffusion coefficients based on the sorption–diffusion theory. The increase in water selectivity through the pervaporation by CD was due mainly to the changes in the diffusion coefficients by CD, which depended on the feed composition and the cross-linking time. The water selectivity through the sorption equilibria was not increased by the addition of CD, and the ethanol-sorption amount was increased by CD. These effects of CD were interpreted by the inclusion strength in the CD cavity and the cross-linking density of the PVA phase. © 1994 John Wiley & Sons, Inc.     

Enhanced forward osmosis from chemically modified polybenzimidazole (PBI) nanofiltration hollow fiber membranes with a thin wall

To develop high-flux and high-rejection forward osmosis (FO) membranes for water reuses and seawater desalination, we have fabricated polybenzimidazole (PBI) nanofiltration (NF) hollow fiber membranes with a thin wall and a desired pore size via non-solvent induced phase inversion and chemically cross-linking modification. The cross-linking by p-xylylene dichloride can finely tune the mean pore size and enhance the salt selectivity. High water permeation flux and improved salt selectivity for water reuses were achieved by using the 2-h modified PBI NF membrane which has a narrow pore size distribution. Cross-linking at a longer time produces even a lower salt permeation flux potentially suitable for desalination but at the expense of permeation flux due to tightened pore sizes. It is found that draw solution concentration and membrane orientations are main factors determining the water permeation flux. In addition, effects of membrane morphology and operation conditions on water and salt transport through membrane have been investigated.     

Ground water leaching resistance of high and ultra high performance concretes in relation to the testing convection regime

The stability of concrete in contact with water is an issue of great concern if long-term service-life is needed. High and ultra high performance concretes have been developed to enhance the durability of concretes structures, but the great differences in composition and microstructure of these concretes with regard to the traditional concrete mean that previous experience may be inapplicable.Ground water leaching resistance of high and ultra high performance concretes has been studied employing two leaching methods based on different convection regimes of the leachant: Tank Water Test (TWT) and Running Water Test (RWT). The leachability of calcium has been used to monitor leaching.     

The Effect of Degree of Impregnation in Amberlite Resins with Organophosphorous Extractants for Y(III), La(III), Ce(III), Th(IV) and U(VI) Ions

Abstract

Background: The sorption of Y(III), La(III), Ce(III), U(VI) and Th(IV) ions with solvent impregnated resins using diphenylphosphate (DPP), and diphenylphosphinic acid (DPPA) as extractant and Amberlite XAD 16 and Amberlite XAD 2000 as a polymeric support has been studied. The impregnated resins containing various amounts of extractants (10/90, 20/80, 50/50, 60/40) have been prepared by a dry method. The effects of pH, types of extractant, extractant content, surface area of polymeric support and contact time have been investigated by batch method.

Results: The impregnation for DPP on XAD‐16 and XAD‐2000 was 111 and 46% at 60/40 extractant/resin mass ratio, respectively. The impregnation of DPPA at all ratios on both resins was found constant and lower than DPP. The sorption percentage of studied metal ions was within 90‐99% for DPP and DPPA on both resins after 20/80 extractant/resin mass ratio.

Conclusions: The sorption of DPP on Amberlite XAD 16 and XAD 2000 resins is rather more than DPPA. It could be seen that 20/80 extractant/resin mass ratio is generally adequate for single metal analysis where 60/40 could be suitable for multi‐metal analysis.     

The flocculating properties of chitosan‐graft‐polyacrylamide flocculants (II)—Test in pilot scale

In this study, the flocculating properties of chitosan‐graft‐polyacrylamide (PAM) copolymer flocculants have been investigated in pilot scale, and the raw water from Zhenjiang part of Yangtse river in China was used as simulated waste water. The influences of dose, mechanical mixing rate, and sedimentation time to the flocculating effects have been investigated in different seasons: summer and winter, respectively. The optimal experimental conditions have been studied by orthogonal test. In addition, the structure effects of the flocculants: the grafting ratio, on the flocculating properties have been also investigated in pilot scale, which results were fully consistent to those from the beaker experiment in laboratory scale using kaolin suspension as simulated waste water. Compared to poly ferric sulfate, current used flocculants in Jinxi Water Factory, chitosan‐g‐PAM copolymer flocculants showed better flocculating properties, which was ascribed to the cooperative effects of the charge neutralization and bridging flocculating mechanisms of polymer flocculants. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Polymer-metal complexes: Synthesis, characterization, and properties of poly(maleic acid) metal complexes with Cu(II), Co(II), Ni(II), and Zn(II)

SUMMARY Polymer metal complexes of poly(maleic acid) and Cu(II), Co(II), Ni(II), and Zn(II) were synthesized. Elemental analysis, as well as magnetic, spectral and thermal properties, in addition to electrical conductivities of the chelates were investigated, and possible structures have been assigned to the polychelates. Semi-empirical calculations at the PM3 level were carried out on the geometrical arrangement of the polychelates. Received: 19 November 1999/Revised version: 22 March 2000/Accepted: 31 March 2000     

Cross-linking and foaming behavior of elastomers with water based blowing agents

Physiologically hazardous chemical blowing agents are state of the art for the foaming of extruded rubber profiles. Water is a potential alternative to these blowing agents and is incorporated into rubber compounds in the form of water-loaded hygroscopic substances such silica or hydrates. To achieve an optimum foaming result, the water desorption and cross-linking reaction has to be coordinated. Studies of the foaming behavior in the salt bath of the Sponge Rubber Analyzer show, that the density of an ethylene propylene diene monomer (EPDM) rubber compound is reduced to about 60% and a nitrile butadiene rubber (NBR) compound to approximately 70%. The low reference densities of chemically foamed EPDM of 30% and NBR of 45% are not achieved. This is attributed to the premature foaming when using water-loaded silica as blowing agent. Due to the low resistance of the rubber matrix, large cells are formed by coalescence, which collapse at low cross-linking densities. Investigations of the cross-linking behavior of EPDM and NBR with water-loaded silica as blowing agent state, that the cross-linking density is reduced to about 65% for EPDM and 50% for NBR when water is present. Furthermore, the incubation time is shortened by inhibition of the CBS retarder in the cross-linking system of the NBR. However, this is not sufficient to fix the foamed cells.     

The effect of preparation temperature on the swelling behavior of poly (N-isopropylacrylamide) gels

Summary The role of the preparation temperature of poly(N-isopropylacrylamide) (PNIPA) gels on their swelling behavior in water and in aqueous solutions of sodium dodecylbenzenesulfonate was investigated. PNIPA gels were prepared by free-radical crosslinking copolymerization of N-isopropylacrylamide and N,N'-methylene(bis) acrylamide in water at fixed monomer and crosslinker concentrations. The equilibrium swelling ratio of the gels increases first slightly up to about 20°C then rapidly with increasing gel preparation temperature. Magnitude of the collapse transition in water at 34°C becomes larger as the gel preparation temperature increases. Calculations indicate a decrease in the effective crosslink density of PNIPA gels with increasing preparation temperature. The gels prepared at temperatures higher then 20°C were heterogeneous consisting of highly crosslinked regions interconnected by the PNIPA chains. Received: 3 May 2000/Revised version: 3 July 2000/Accepted: 17 July 2000     

Water vapour permeability,diffusion and solubility in latex films

Water vapour diffusion D, solubility S and permeability P coefficients have been determined for films obtained from carboxylated styrene-butadiene (SB) copolymer latexes. The experimental method is water vapour sorption performed in the range 30–60d?C. Using the small angle neutron scattering (SANS) method and a selective labelling with D₂O vapour, it has been shown that water molecules mainly diffuse in the films through the particle-particle interfaces, which consist of a polar carboxyl-rich copolymer. It has been shown that the degree of cross-linking of the particles does not significantly affect the values of D and S. Moreover, the effect of neutralization conditions, regarding both the pH value of the initial latex and the nature of the neutralizing agent, has also been investigated. It has been found that D does not depend on these parameters, whereas S appears to be very sensitive to them. The results have been interpreted on the basis of the structural modifications of the films induced by neutralization. Finally, the hydrophilicity (or hydrophobicity) of the neutralizing agent has been identified as one of the key features for controlling the affinity of the latex film for water vapour and hence its permeability properties.     

Synthesis and water absorbency of the copolymer of acrylamide with anionic monomers

A series of novel copolymer superabsorbents based on acrylamide, sodium allylsulfonate, sodium acrylate, and N,N′-methylenebisacrylamide were prepared by copolymerization. The resulting superabsorbents have a fast swelling rate. The experimental results show that absorbency increases to a maximum as the cross-linking increases, but an excess of cross-linking leads to a swelling decrease. Their water retention was observed at pressures of 1–10 kg/cm² and temperatures of 60 and 100°C, respectively. The water retention of soil has been enhanced by using the poly(acrylamide–sodium allysulfonate–sodium acrylate) superabsorbent; its use for bean growth was also investigated. © 1994 John Wiley & Sons, Inc.