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Catalytically active porous and hollow titania nanofibers encapsulating gold nanoparticles were fabricated using a combination of sol-gel chemistry and coaxial electrospinning technique. We report the fabrication of catalytically active porous and hollow titania nanofibers encapsulating gold nanoparticles (AuNPs) using a combination of sol-gel chemistry and coaxial electrospinning technique. The coaxial electrospinning involved the use of a mixture of poly(vinyl pyrrolidone) (PVP) and titania sol as the shell forming component, whereas a mixture of poly(4-vinyl pyridine) (P4VP) and pre-synthesized AuNPs constituted the core forming component. The core-shell nanofibers were calcined stepwise up to 600 °C which resulted in decomposition and removal of the organic constituents of the nanofibers. This led to the formation of porous and hollow titania nanofibers, where the catalytic AuNPs were embedded in the inner wall of the titania shell. The catalytic activity of the prepared Au@TiO2 porous nanofibers was investigated using a model reaction of catalytic reduction of 4-nitrophenol and Congo red dye in the presence of NaBH4. The Au@TiO2 porous and hollow nanofibers exhibited excellent catalytic activity and recyclability, and the morphology of the nanofibers remained intact after repeated usage. The presented approach could be a promising route for immobilizing various nanosized catalysts in hollow titania supports for the design of stable catalytic systems where the added photocatalytic activity of titania could further be of significance.

The separation of toxic pollutants such as Pb2+, Cd2+, and Al3+ from water is a constant challenge as contamination of natural water bodies is increasing. Al3+ and especially Pb2+ and Cd2+ are ecotoxic and highly toxic for humans, even in ppb concentrations, and therefore removal below a dangerous level is demanding. Herein, the potential adsorber material starch, being ecofriendly, cheap, and abundantly available, was investigated. Thus, four different native starch samples (potato, corn, waxy corn, and wheat starch) and two oxidized starches (oxidized potato and corn starch) were comprehensively analyzed with streaming potential and charge density measurements, SEM-EDX, ATR-FTIR, 1H-NMR, and TGA. Subsequently, the starch samples were tested for the adsorption of Pb2+, Cd2+, and Al3+ from the respective sulfate salt solution. The adsorption process was analyzed by ICP-OES and SEM-EDX, and the adsorption isotherms were fitted comparing Langmuir, Sips, and Dubinin-Radushkevich models. Oxidized starch, for which chemical modification is one of the simplest, and also native potato starch were excellent natural adsorber materials for Al3+, Cd2+, and especially Pb2+ in the low concentration range, exhibiting maximum adsorption capacities of 84, 71, and 104 µmol/g for oxidized potato starch, respectively.

Flocculation is still one of the most important and efficient processes for water treatment. However, most industrial processes, such as in water treatment plants, still use huge amounts of synthetic polyelectrolytes for the flocculation process. Here we compare the flocculation of two different suspended particles, i.e., silica particles and china clay, with the biopolymer chitosan and two common strong synthetic polyelectrolytes. As a flocculant, chitosan featured a minimum uptake rate of 0.05 mg/g for silica and 1.8 mg/g for china clay. Polydiallyldimethylammonium chloride (PDADMAC) for comparison possessed a minimum uptake rate of 0.05 mg/g for silica and 2.2 mg/g for china clay. Chitosan as an environmentally friendly biopolymer competes with the synthetic polyelectrolytes and thus represents a beneficial economic alternative to synthetic flocculants.

The modification of the biobased polymer chitosan is a broad and widely studied field. Herein, an insight into the hydrophobization of low-molecular-weight chitosan by substitution of amino functionalities with hexanoyl chloride is reported. Thereby, the influence of the pH of the reaction media was investigated. Further, methods for the determination of the degree of substitution based on 1H-NMR, FTIR, and potentiometric titration were compared and discussed regarding their accuracy and precision. 1H-NMR was the most accurate method, while FTIR and the potentiometric titration, though precise and reproducible, underlie the influence of complete protonation and solubility issues. Additionally, the impact of the pH variation during the synthesis on the properties of the samples was investigated by Cd2+ sorption experiments. The adjusted pH values during the synthesis and, therefore, the obtained degrees of substitution possessed a strong impact on the adsorption properties of the final material.

In this study, low molecular weight chitosan salt (LMWC-HCl) highly soluble in water was prepared from low molecular weight chitosan (LMWC) in the solid state exposed to hydrogen chloride gas as a reagent. The effects of chitosan particle size, exposure conditions, reaction temperature and reaction time were investigated on the solubility and the molecular weight of obtained products. The formation of the chloride salt was observed after 3 h in a range of temperatures from 4 to 50 °C. The solubility of prepared LMWC-HCl was over 98% for all samples, much higher than that of the original LMWC. The average molecular weight of the LMWC-HCl was about 20–90 kDa with a quite narrow distribution and lower compared to the LMWC. LMWC-HCl and LMWC showed the same high antibacterial activity against Bacillus cereus and Vibrio parahaemolyticus. This facile and efficient process for solubilization of LMWC has potential for industrial application of chitosan.

Polyethyleneimine (PEI) cryogels have been fabricated using poly(ethylene glycol) diglycidyl ether (DGE-PEG), 1,4-butanediol diglycidyl ether (DGE-1,4-BD), and glutaric aldehyde (GA) as cross-linking agents. The rate of PEI cross-linking changes in the order GA > DGE-1,4-BD > DGE-PEG. The established correlations between the modification degree, swelling, and static ion-exchange capacity revealed a tendency of diglycidyl ethers, especially DGE-1,4-BD, to graft as a side chain to PEI in alkaline media. Low reactivity of cross-linkers at temperatures below zero resulted in lower modification degree and higher sorption capacities of PEI cryogels in comparison with PEI cross-linked at room temperature. Due to the difference in mechanisms of sorption of metal cations and anions, PEI cryogels cross-linked with DGE-1,4-BD and DGE-PEG were the most efficient for sorption of Hg(II) as [HgCl4]2− complex and Cu(II) ions, respectively. The morphology of PEI cryogels depends on the type of the cross-linking agent, cross-linker/PEI molar ratio, and concentration of PEI solution; the pore volume of cryogels obtained under the same conditions decreased in the order GA > DGE-1,4-BD > DGE-PEG.

Due to the existence-threatening risk to aquatic life and entire ecosystems, the removal of oxyanions such as sulfate and phosphate from anthropogenic wastewaters, such as municipal effluents and acid mine drainage, is inevitable. Furthermore, phosphorus is an indispensable resource for worldwide plant fertilization, which cannot be replaced by any other substance. This raises phosphate to one of the most important mineral resources worldwide. Thus, efficient recovery of phosphate is essential for ecosystems and the economy. To face the harsh acidic conditions, such as for acid mine drainage, an adsorber material with a high chemical resistivity is beneficial. Poly(melamine-co-formaldehyde) (PMF) sustains these conditions whilst its very high amount of nitrogen functionalities (up to 53.7 wt.%) act as efficient adsorption sides. To increase adsorption capacities, PMF was synthesized in the form of mesoporous particles using a hard-templating approach yielding specific surface areas up to 409 m2/g. Different amounts of silica nanospheres were utilized as template and evaluated for the adsorption of sulfate and phosphate ions. The adsorption isotherms were validated by the Langmuir model. Due to their properties, the PMF particles possessed outperforming maximum adsorption capacities of 341 and 251 mg/g for phosphate and sulfate, respectively. Furthermore, selective adsorption of sulfate from mixed solutions of phosphate and sulfate was found for silica/PMF hybrid particles.

The immobilisation of silica nanoparticles on the surface of a flowing polymer melt is studied during injection moulding. We use silica nanoparticles of identical size of about 200 nm, but with different surface functionalities: plain unmodified particles with silanole groups as well as amino- and hydrocarbon modified particles. The particles were brought in contact with a polycarbonate melt at a temperature of 300 °C. In our investigation, we show that particles with polar surfaces are more embedded than those with non-polar surfaces. Immobilised polar particles exhibited also a higher adhesion, tested with an adhesive tape, whereas the non-polar particles can be easily removed by peeling off the adhesive tape. This paper reveals that surface properties have a larger influence on embedding of nanoparticles than thermal conditions due to cooling of the melt.

In this work, the flocculation efficiency of reacetylated chitosans were compared with those of commercially available chitosans. The flocculation properties were investigated in dispersion of clay by means of turbidity measurements, colloid titration and measurements of the floc size. Reacetylated chitosan dissolves in deionized water without any additives and exhibits good flocculation properties like a wider flocculation window but a higher amount of polymer. For commercial chitosan lower amounts of polymer were required for the flocculation of clay dispersion. Flocculation with commercial chitosan is possible even in basic range.

New types of composites were obtained by an autotemplate method for assembling hollow CaCO3 capsules by using pH-sensitive polymers. Five pectin samples, which differ in the methylation degree and/or amide content, and some nonstoichiometric polyelectrolyte complex dispersions, prepared with the pectin samples and poly(allylamine hydrochloride), were used to control the crystal growth. The morphology of the composites was investigated by scanning electron microscopy, and the polymorphs characteristics were investigated by FTIR spectroscopy. The presence of the polymer in the composite particles was evidenced by X-ray photoelectron spectroscopy, particle charge density, and zeta-potential. The new CaCO3/pectin hollow capsules were tested as a possible matrix for a tetracycline hydrochloride carrier. The kinetics of the drug release mechanism was followed using Higuchi and Korsmeyer–Peppas mathematical models.

Copper(II) as a heavy metal ion is posing risk to aquatic ecosystems including algae, fish, mollusks, and bacteria, negatively affecting human life because of bioaccumulation and non-biodegradability. In this study, two thermoresponsive PNIPAM-b-PAA block copolymers with different characteristics in terms of molecular weight and PAA composition were investigated to remove copper ions from simulated water. We chose to utilize those block copolymers in CuSO4 adsorption experiments in order to comprehend how the combination of the thermoresponsive PNIPAM block and the binding ability that PAA block offers, affects the adsorption of Cu2+ and SO42− and provides eventually their removal from aqueous solutions. The adsorption protocol includes simple mixing of the copolymer and CuSO4 aqueous solutions under stirring. Dynamic and electrophoretic light scattering, pH, UV–vis, turbidity and ICP-OES measurements were conducted to verify the PNIPAM-b-PAA ability as smart adsorbents. The results showed that the PNIPAM-b-PAA_50−50 sample offers the possibility of Cu2+ and SO42- adsorption of greater percentage especially when temperature increases to 60 °C. Therefore, PNIPAM-b-PAA block copolymers comprise efficient and smart Cu2+ and SO42- adsorbents.

Chitosan in the solid state has been degraded in a controlled way by treatment with hydrogen peroxide at room temperature. Chitosan was swollen in diluted NaOH, making it more susceptible to the peroxide treatment. The product has been characterized by intrinsic viscosity, FTIR infrared spectroscopy and roentgen diffraction. The molecular weight and the intrinsic viscosity were reduced significantly (about tenfold). The degree of deacetylation did not change. The chitosan product has a low viscosity (about 100 cP), a lower molecular weight (1.4 × 102 kDa), a high purity and a high crystallinity. It can be used in many potential applications. This method is easy and suitable for a large-scale process.

Chitosan (flakes with a degree of deacetylation of 90%) was used as adsorbent for heavy metal ions in solution (copper, iron, nickel). The adsorption capacities were determined in dependence on the adsorption time and the initial metal salt concentration. With increasing adsorption time as well as the initial metal salt concentration the adsorption capacities increased. Highest adsorption capacity was achieved for copper(II)ions with 110 mg/L. Iron(II)- and nickel(II)ions adsorbed with an adsorption capacity of 80 mg/L. The surface of chitosan flakes were investigated before and after the adsorption process by SEM and SEM-EDX, respectively. The formation of crystal-like structures was observed by SEM analysis for the investigation of copper(II)sulfate and iron(II)sulfate. It has been noticed that iron(II)ions oxidized before the adsorption on chitosan occurs. In comparison, the adsorption of nickel salt resulted in a smooth layer on the chitosan surface. SEM-EDX analysis revealed that sulfate adsorbs on the chitosan surface besides the metal cations used.

The modification of silica microparticles surface with a high number of amino/carboxylic groups of polymer chains represent an interesting route to obtain nanostructured composite materials aiming different applications. Herein, four weak polycations (PC) [polyethyleneimine (PEI), polylysine (PLL), polyvinylamine (PVAm), polyallylamine hydrochloride (PAH)] and one weak polyanion [polyacrylic acid (PAA)] were layer-by-layer deposited onto spherical silica to form composite microparticles. A strategy where each deposited polycation layer was chemically cross-linked with glutaraldehyde (GA) prior to the deposition of PAA layer was used, forming at the end silica//(PC GA/PAA)n composite microparticles. Finally, we investigated the particles towards their adsorption properties on metal ions (Cu2+, Pb2+, Ni2+, and Fe2+) from simulated and real surface water, as a potential application for the composite particles.

The biopolymer chitosan is a very efficient adsorber material for the removal of heavy metal ions from aqueous solutions. Due to the solubility properties of chitosan it can be used as both a liquid adsorber and a solid flocculant for water treatment reaching outstanding adsorption capacities for a number of heavy metal ions. However, the type of anion corresponding to the investigated heavy metal ions has a strong influence on the adsorption capacity and sorption mechanism on chitosan. In this work, the adsorption capacity of the heavy metal ions manganese, iron, cobalt, nickel, copper, and zinc were investigated in dependence on their corresponding anions sulfate, chloride, and nitrate by batch experiments. The selectivity of the different heavy metal ions was analyzed by column experiments.

The study confirms the interaction of sulfate ions (SO42−) into the polymer chains of chitosan under acidic conditions. As a result the crystallinity of chitosan decreases with (1) increasing protonation of the amino groups and (2) increasing SO42− concentration. The adsorption of iron ions (Fe2+/3+) resulting from (FeSO4)aq onto the chitosan surface takes place incidentally by the oxidative effect of Fe2+/3+ with formation of orthorhombic α-FeOOH and γ-FeOOH. The separation of iron and sulfate ions correlates stoichiometrically. Chitosan with different degrees of deacetylation (DD) were used in order to investigate the influence of DD on the adsorption behavior of iron and sulfate ions. The higher the DD of chitosan, the more iron and sulfate ions can be adsorbed. Langmuir isotherms showed good agreement with the adsorption data obtained (qDD=90 %(Fe) = 2.36 mmol g-1; qDD=90 %(SO42−) = 2.58 mmol g-1). After adsorption process, the adsorber was analyzed extensively via X-ray diffraction, FTIR, 13C-NMR, SEM/EDX measurements and Mossbauer spectroscopy.

Polymers 10(7), - (2018). doi:10.3390/polym10070791 special issue: "Special Issue "Microgels and Hydrogels at Interfaces" / Guest Editor Dr. Patrick van Rijn, Department of BioMedical Engineering FB-40, University of Groningen/University Medical Center Groningen; Dr. Felix Plamper, Institute of Physical Chemistry, RWTH Aachen University", Published by MDPI, Basel

Composite microparticles of CaCO3 and two pectin samples (which differ by the functional group ratio) or corresponding nonstoichiometric polyelectrolyte complexes with different molar ratios (0.5, 0.9 and 1.2) are obtained, characterized and tested for loading and release of streptomycin and kanamycin sulphate. The synthesized carriers were characterized before and after drug loading in terms of morphology (by SEM using secondary electron and energy selective backscattered electron detectors), porosity (by water sorption isotherms) and elemental composition (by elemental mapping using energy dispersive X-ray and FTIR spectroscopy). The kinetics of the release mechanism from the microparticles was investigated using Higuchi and Korsmeyer–Peppas mathematical models.

The biodegradable polysaccharide chitosan possesses protonated and natural amino groups at medium pH values and has therefore been used as an adsorbing material for nickel salts in water treatment. Nickel is a problematic heavy metal ion which can cause various diseases and disorders in living organisms. Here, we show the influence of oxyanions (e.g., nitrate and sulfate) to the adsorption of nickel ions. Hence, simultaneously we are addressing the increasing global problem of nitrate and sulfate ion pollution in groundwater and surface water. A series of adsorption experiments was carried out in order to determine (i) the adsorption equilibrium, (ii) the adsorption capacity in dependence on the initial nickel ion concentration, and (iii) the influence of the anion presented in solution for the adsorption capacity. Surface morphology of chitosan flakes before and after the adsorption process has been studied with SEM-EDX analysis. The chitosan flakes exhibited promising adsorption capacities of 81.9 mg·g−1 and 21.2 mg·g−1 for nickel (sulfate) and nickel (nitrate), respectively. The calculated values of Gibbs free energy change ΔG0 confirm the higher adsorption of nickel ions in presence of sulfate ions. Hence, higher anion valence leads to a higher adsorption capacity.

As a consequence of mining, heavy metal ions can be exposed to the environment hence contaminate ground water and surface water amongst others. The natural polymer chitosan was proved to be an excellent adsorber material for the effective removal of iron and sulfate ions in batch as well as in column experiments. The adsorption behavior of iron ions, as well as sulfate ions was investigated by utilizing chitosan flakes as a natural adsorbent. The removal was studied using adsorbance measurements, SEM and SEM-EDX. The adsorption capacity of chitosan was determined at different times. The received adsorption capacities for iron ions were very promising with a maximum adsorption capacity of 85 mg/g and a rate of separation of 100%. The maximum adsorption capacity obtained for sulfate ions was 188.8 mg/g and a rate of 80%.

Five pectin samples – which differ by the methylation degree and/or amide content – were used to prepare inorganic/organic composites by CaCO3 mineralization from supersaturated solutions. The pectin chemical structure and concentration could control the composite superstructure by induction or orientation of crystal growth. The inorganic materials may also control CaCO3 polymorphism and morphologies and therefore different carbonate sources, such as Na2CO3, diethylcarbonate or ammonium carbonates, were used as modulators for crystal growth. The morphology of the new CaCO3/pectin composites was investigated by SEM and the polymorphs content by X-ray diffraction, as compared to bare CaCO3 samples prepared in similar conditions. The composites were tested as sorbents for Cu(II) and Ni(II) ions. Keywords: Pectin, CaCO3, Composite, Polymorph, Sorbent

Biologically degradable polymers based on renewable raw materials, such as polysaccharides, represent promising alternatives to synthetic polymers used as flocculants or stabilizing agents. Polysaccharides derived from potato starch have been modified with benzyl- and additionally cationic hydroxypropyl trimethyl ammonium groups of different degrees of substitution (DS). In this work these amphiphilic starch derivatives have been used to remove substances which impact negatively the paper production process when using recycled paper, so called stickies. Model suspensions have been studied using a multitude of different measurement techniques with the aim to predict a “sticky potential” and to reduce dissolved and colloidal substances such as micro-stickies. Systematic experiments studying the interactions between the novel amphiphilic starch derivatives and the model suspension have shown that dynamic surface tension is a very suitable property to characterize the surface active compounds in the model suspension giving additional information about the sticky potential of waste water, e.g. white water and offering a new and sensitive way to describe the parameter “hydrophobicity”. Moderately cationic and hydrophobic starch derivatives proved to be the most effective ones for sticky removal.

“Adsorption deinking” is a new concept for ink removal from suspensions using polymer particles instead of air bubbles (flotation) in a process with high efficiency, concerning the consumption of energy and water. We studied the influence of different papers and inks, of the deinking solution (compared with water), and of the duration of deinking. The process is characterized not only by the colour of polymer particles, but also by the properties in suspension such as charge, turbidity or particle size. Further it is shown, that dynamic surface tension is a useful tool to characterize not only the surfactant in suspension, but also its interaction with other substances (cellulose and ink). The efficiency of adsorption deinking is strongly influenced by the properties in suspension which depend on the type of paper.

Chitosan steht seit einigen Jahren im Fokus biologisch orientierter Forschung sowohl in der Modifizierung als auch in der Anwendung. Es hat eine Vielzahl von Vorteilen gegenüber synthetischen Produkten, es ist z. B. nicht toxisch. In dieser Arbeit wurden die Chitosane reacetyliert und charakterisiert. Reacetylierte Chitosane lösen sich ohne Zusätze in Wasser und zeigen gute Flockungseigenschaften. Die Flockung von reacetylierten und kommerziellen Chitosanen wurde verglichen. Molmasse, pH‐Wert und der Salzgehalt im System nehmen großen Einfluss auf die Lage und Breite der Flockungsfenster.

For different practical applications, it is cardinal to maintain the stability of nanoparticles in aqueous suspension. The theoretical impact of pH and ultrasonication time on surface charge, particle size distribution and the dispersion stability of AEROSIL®OX 50 in water were evaluated, and a practical (centrifugal sedimentation analysis) test was used to determine the effects of concentration and molar mass of the polymer polyvinylpyrrolidone (PVP) at different pHs. It was observed that the size distribution of silica remains almost unaffected, but the surface charge increased with ultrasonication time up to 20 min and then leveled off. This increase in surface charge was proportional to the molar mass of the added polymer. The zeta potential increased with the increasing concentration of PVP in the silica suspension. This behavior is attributed to the adsorption of polymer over the surface of the particles. The suspensions were found to be the most stable, up to 36 %, at concentration (1 %) of PVP having higher molar masses. Furthermore, the addition of polymer strengthened the available agglomerates in the dispersion which resulted in the widening of the particles’ size distribution.

This study describes the effects of mixed anionic/cationic polyelectrolytes on the crystallization of calcium carbonate in supersaturated solutions in comparison with polyanion-based CaCO3 composite structures. Two simple methods of introducing the polycation in the crystallogenesis of calcium carbonate are proposed: preformed nonstoichiometric polyelectrolyte complexes (NPECs) or in situ mixing of complementary polyelectrolytes, with a very large range of ratios between complementary polyions. For this purpose three polyanions—poly(acrylic acid) sodium salt, poly(sodium 4-styrenesulfonate) and poly(sodium vinylsulfonate)—and poly(diallyl-dimethylammonium chloride) as polycation were used. The molar ratio between complementary polyelectrolytes used in CaCO3 composite synthesis varied between 0 (just polyanions) up to 0.95 (close to the equimolar ratio between ionic charges of complementary polyelectrolytes). The polymer presence into the composite particles, as a function of polyanion structure and the pr...

Flocculation properties of amphiphilic starch derivatives of varying degrees of substitution (DS) of benzyl- and 2-hydroxypropyl-trimethylammonium moieties have been investigated in dispersions of kaolin, calcium carbonate, and silica. Moderate hydrophobic substitution leads to a decrease of efficient flocculant dose and increase of flocculation window width. Samples with high DS of hydrophobic moieties are effective only at significantly higher doses but in a broader concentration range compared to solely cationic ones of the same DS. Joint analysis of adsorption isotherms and flocculation test data has revealed that the surface coverage required to induce phase separation ranges between 10–25% and is minimal for amphiphiles, whose floc sizes are moreover less dependent on the flocculant dose.

A novel strategy for faster and better flocculation in solid-liquid separation processes is reported: the use of the natural polyelectrolyte chitosan (CH2500) in combination with the biocompatible thermosensitive polymer poly(N-vinylcaprolactam) (PNVCL). Silica dispersions (Aerosil OX50) were used as model and evaluated by means of analytical centrifuge, laser diffraction, and turbidimetry studies. Results show that the sedimentation velocity is doubled by addition of PNVCL and that at 45°C the density of the sediment is 33% higher, as compared to the use of CH2500 only. This results from the temperature sensitive behavior of PNVCL that phase-separate expelling water at temperatures higher than its LCST (32–34°C) leading to compaction of the flocs. By using this strategy the sediment is more compact, contains less water, and contains a very small amount of biodegradable CH2500 and biocompatible PNVCL.

The crystallization characteristics of calcium carbonate microparticles grown from supersaturated aqueous solutions in the presence of a double hydrophilic block copolymer poly(p-hydroxystyrene-b-methacrylic acid), PHOS-b-PMAA, have been investigated. The studies aim to highlight both the possibilities and the limitations of CaCO3/PHOS-b-PMAA microparticle formation under different relative inorganic/polymer ratio conditions, varying the initial solution supersaturation or the polymer concentration. Scanning electron microscopy and atomic force microscopy were used to provide high-resolution images of particles and thereby information on the particle morphology, while X-ray diffraction analysis was used to determine the polymorph type and crystallite characteristics. The presence of the polymer in the composite particles was shown by thermogravimetric, particle charge density and zeta potential analysis. The polymer-induced sensitivity of the new composites to environmental pH variations has been followed by streaming potential variation.

The characteristics of calcium carbonate microparticles formed in supersaturated aqueous solutions, in the presence of some strong/weak anionic polymers or with nonstoichiometric polyelectrolyte complexes with negative charges in excess (NPEC-n), have been investigated under different relative inorganic/polymer ratios, tuned by initial solution supersaturation and polymer concentration. For this purpose two polyanions which contain the carboxylic and sulfonic ionic groups, poly(2-acrylamido-2-methylpropanesulfonic acid-co-acrylic acid) and chondroitin-4-sulfate, were used. NPEC-n dispersions prepared with the same polyanions and chitosan as a polycation were also used as templates for calcium carbonate crystallization. Scanning electron microscopy was used to provide the particle morphologies and flow particle image analysis to evidence their mean sizes and sphericities. The polymer presence in the composite particles was evidenced by X-ray photoelectron spectroscopy, particle charge densities, and zeta p...

This study follows the possibility to tune the thermal stability of some CaCO3/polymer composites by crystal growth from supersaturated solutions controlled by polymer structure or by using nonstoichiometric polyelectrolyte complexes (NPECs). As the ratio between the organic and inorganic parts in the composites controls the Ca2+/polymer network crosslinking density, the CaCO3/polymer weight ratio was kept constant at 50/1, varying the initial concentration of the polyanions solutions (0.05 or 0.06 wt.%), the NPECs molar ratio , n+/n- (0.2 or 0.4), or the inorganic precursors concentration (0.25 or 0.3 M). Poly(2-acrylamido-2-methylpropanesulfonic acid-co-acrylic acid) (PSA) and chondroitin-4-sulfate (CSA) were used as polyanions. Some NPEC dispersions, prepared with the same polyanions and poly(allylamine hydrochloride) (PAH), were also used for calcium carbonate crystallization. The characteristics of the prepared composites were investigated by scanning electron microscopy (SEM), flow particle image analysis (FPIA), particles charge density (CD), zeta-potential (ZP). The thermal stability of the composite particles was investigated as compared to bare CaCO3 microparticles prepared at the same initial inorganic concentrations.

The adsorption of water-soluble polymer, polyvinylpyrrolidone having molecular mass 9.1 ± 1.43 × 103Kg mole−1 on kaolin has been investigated. The effect of different parameters like pH, molecular mass of polymer and pre-heat treatment on the adsorption of PVP has been deliberated. The 20.7% decrease in adsorption in pH ranging from 2–10 have been found, which was an indication of the fact that with the increase in pH the kaolin surfaces sites charge amount and ultimately sign changes. Maximum adsorption was observed at pH 5.6 that was also molecular mass dependent. By increasing the pretreatment temperature, the amount of polymer adsorbed was also increased. However, above the specific temperature adsorption of PVP was decreased and attributed to decrease in specific surface area of kaolin.

Modified starch with cationic as well as hydrophobic units can be used to remove negatively charged substances due to recycling processes of paper, so called stickies. The interactions between different types of starch and a negatively charged model suspension, obtained by heating up common newspaper, have been studied using polyelectrolyte titration, nephelometric turbidity measurement, and determination of the carbon content. In addition, we were able to show that the dynamic interface tension is a very suitable property to characterize the surface active compounds in the model suspension which allows receiving additional information about the sticky content of the waste water. Polyelectrolyte complexes were formed by adding cationic starch to the anionically charged model suspension. At a certain mixing ratio their precipitation leads to a significant reduction of the turbidity and the carbon content, whereas the surface tension increases due to sticky removal. Among starches with the same degree of cationic charge, those with the highest hydrophobicity were the most effective.

A novel strategy for faster and better flocculation in solid–liquid separation processes is reported: the use of a natural polyelectrolyte (chitosan) in combination with a biocompatible thermosensitive polymer [poly(N-vinylcaprolactam) (PNVCL)]. Clay dispersions were used as model and evaluated by means of analytical centrifuge, laser diffraction, streaming potential and turbidimetry studies. Results show that at 45 °C the density of the sediment is up to 15% higher, as compared to the use of chitosan only. This results from the temperature sensitive behaviour of PNVCL that phase separate expelling water at temperatures higher than it's LCST (32–34 °C). By using this strategy the sediment is more compact, contains less water, and contains a very small amount of biodegradable chitosan and biocompatible PNVCL.

A new polymer–drug conjugate based on poly( N -vinylpyrrolidone-co-maleic anhydride) as support and 2-amino-5-(4-methoxy-phenyl)-1,3,4-oxadiazole, having antimicrobial and antifungal activity, was synthesized by Higashi–Yamazaki reaction. The functionalized copolymer having a substitution degree of 29% was fully characterized in terms of chemical structure by 1 H NMR, FTIR and UV–Vis spectroscopy, and by molecular weight measurements. The crystallization of CaCO 3 particles from saturate aqueous solutions in the presence of the newly synthesized conjugate copolymer, comparative with particles prepared in similar conditions but without polymer, has been investigated. The obtained particles were characterized by scanning electron and polarized optical microscopy, X-ray diffraction, particles charge density, and electrophoresis. These new composite materials are excellent candidates for use in biomedical applications, particularly for drug delivery.

The crystallization characteristics of CaCO3 microparticles from supersaturate aqueous solutions in the presence of a conjugate drug-copolymer has been investigated, comparative with particles prepared in similar conditions but without polymer. The polymer conjugate, P(NVP-MA-Ox), is based on poly(N-vinylpyrrolidone-co-maleic anhydride) as support and 2-amino-5-(4-methoxy-phenyl)-1,3,4-oxadiazole. The influence of the polymer/CaCO3 ratio on the microparticles' characteristics and the particles' pH stability was deeply investigated by scanning electron microscopy, X-ray diffraction, flow particle image analysis, particles charge density, and electrophoresis. The presence of P(NVP-MA-Ox) as a template in the CaCO3 crystallization process induced the particles stability increase up to the polymer isoelectric point located at pH = 3.4, irrespective of carbonate content in composite particles. The adsorption capacity of the microparticles as a function of their characteristics was tested using methylene blue. ...

The crystallization of CaCO 3 particles from aqueous solutions in the absence and presence of a strong/weak anionic copolymer, poly(2-acrylamido-2-methylpropanesulfonic acid–co-acrylic acid) (PAMPSAA) is discussed in this paper. Vaterite/calcite polymorphs with different sizes and spherical shapes were obtained. The products were characterized by infrared spectroscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, flow particle image analysis, laser diffraction technology, and SEM and optical microscopy. Oppositely charged chitosan and PAMPSAA were assembled onto carbonate colloidal particles in a layer-by-layer manner to yield core–shell structures.

The dissociation behaviour of poly(acrylic acid) and poly(ethylene-alt-maleic acid) has been investigated by both classical potentiometric titration and colloid titration as an alternative way. In the case of colloid titration, the monovalent counterions are assumed to be replaced by the oppositely charged polycation in the course of titration, so that the total concentration of anionic groups of the polycarboxylic acid is determined. As a consequence the apparent dissociation constants determined by polyelectrolyte complex formation do not depend on the degree of dissociation. In contrast to this finding, potentiometric titration is known to result in apparent dissociation constants which decrease with increasing degree of dissociation. The release of protons from the acid groups of the polycarboxylic acids is promoted by the complex formation with the strong cationic polyelectrolyte.

Ionic semi-interpenetrating polymer networks composite hydrogels were synthesized by free-radical polymerization using dextran sulphate (DxS), acrylamide as monomer and N,N′-methylene(bis)acrylamide as cross-linking agent. The viscoelastic properties of these composite hydrogels were investigated by oscillatory shear measurements under small deformation conditions comparative with those of polyacrylamide gels. Changes of the rheological properties of composite hydrogels have been studied in terms of polymerization temperature, cross-linker ratio, initial monomer concentration and molar mass of DxS. The results showed that the stability of the composite hydrogels obtained at room temperature (22 °C) was relatively low because the storage modulus (G′) was only eight times higher than the loss modulus (G″), while for those obtained by cryopolymerization (−18 °C), the stability was improved, the G′ values being about 30 times higher than those of G″. This behaviour indicated that, by conducting the synthesis of hydrogels below the freezing point of the reaction solutions, an enhancement of the hydrogels elasticity was achieved. The network parameters, i.e. the average molecular weight between two cross-links and the cross-link density of the composite hydrogels prepared at −18 °C, were estimated from rheological data.

Reversible addition-fragmentation chain transfer (RAFT) polymerization is used to prepare temperature- and pH-sensitive statistical copolymers with lower critical solution temperature (LCST) close to 38 °C at pH 7.4 based on N-isopropylacrylamide and methacrylic acid derivative comonomers with a pKa close to 6. Statistical copolymers are re-activated to prepare amphiphilic block copolymers and star polymers with cross-linked core. The LCST is maintained by varying the architecture; however, the LCST originated behaviour changes due to self-aggregation. Statistical copolymers and short block copolymers show complex aggregation, whereas mid-size block copolymers and star polymers show shrinkage of aggregate dimensions. The pH of the medium has a profound impact on the self-assembling behaviour of the different polymer architectures.

This study aims to evidence the influence of polyelectrolytes structure and the number of double layers on the properties of some new nanostructured architectures formed by layer-by-layer self-assembly of complementary weak polyelectrolytes on planar surfaces. For this purpose, we used chitosan and poly(allylamine hydrochloride) as polycations, and poly(acrylic acid) and poly(2-acrylamido-2-methylpropanesulfonic acid–co-acrylic acid) as polyanions. To get a direct image on the polyelectrolyte multilayers formation and properties, gravimetry, infrared spectroscopy, and atomic force microscopy have been used. The capacity of the polyions to overcompensate the complementary polyions charges, and thus to influence the swelling degree in water of thin films, was strongly influenced by the chain structure and flexibility. A special attention was paid to the responsiveness of the new composite materials to the pH of the swelling environment.

The growth and properties of the polycation/azo dye multilayer thin films as a function of specific effects of the counterion (Cl−, Br−, SO42−), and the counterion concentration on the polycation conformation, the pure dye being always adsorbed from salt-free aqueous solution, have been investigated. A strong polycation containing 95 mol% of N,N-dimethyl-2-hydroxypropyleneammonium chloride units in the backbone and the azo dye Direct Red 80 were used as building blocks. An almost linear increase of the absorbance at 558 nm and of the layer pair thickness, measured by spectroscopic ellipsometry in wet state, with the increase of the layer pair number, were observed for all electrolytes. The specific effects of counterion type and concentration have been manifested in the amount of the dye adsorbed on each polycation layer, the thickness of the layer pair, and the surface morphology.

Aim of this work was to evaluate the flocculation efficiency of a modified, water soluble chitosan versus various commercial products such as: chitosan, PolyDADMAC and positively charged polyacrylamide. The flocculation properties were investigated in dispersions of the clay type “Blauton” by means of turbidity measurements, colloid titration and measurements of the floc size. It was found that flocculation occurs even before the Blauton surface charge neutralization is achieved. The modified chitosan was more effective than the commercial one in Blauton's settling. Modified chitosan in comparison to the commercial products demonstrated not only a wider flocculation window, but also a higher efficiency since lower amounts of polymer were required for the flocculation of Blauton. Finally, the use of modified chitosan resulted in an increase of the critical polymer concentration above which restabilization of Blauton occurs.

The stability of Aerosil-silica dispersions is analyzed in dependence on the addition of polycations with different charge density and hydrophobic modification using the analytical centrifuge LUMiSizer. This novel centrifugal sedimentation method allows the direct calculation of the stability parameters like sedimentation velocity and prediction of the shelf life. The highly charged polycation poly (diallyl-dimethylammonium chloride) (PDADMAC) is compared with tailored cationic polyelectrolytes of equal degree of polymerization but lower and different charge density as well as various hydrophobic substitutions. The used technique allows to accelerate demixing and to quantify the stability of dispersions in a direct way. All polymers under study are able to stabilize aerosil dispersions, but the shelf life strongly depends on the polymer concentration. Typically for polycations, the stability increases with the polymer concentration whereas at low-polymer content flocculation can be detected. In this context, the behavior of PDADMAC and three cationic PVB derivatives is similar, but, whereas the stability of PDADMAC containing dispersions decreases at higher polymer concentrations, PVB derivatives are effective stabilizers at higher concentrations too. The highest increase of the stability with increasing polymer concentration is obtained with the ampholytic terpolymer TP that has the lowest cationic charge. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

This work describes the application relevant characterization of eight commercially available silica powders dependent on dispersing procedure using different instruments: photon correlation spectroscopy, nitrogen adsorption, and particle charge detector. The particle size of silica was found to be different in dispersion from that of all types of fumed silica, where, after proper dispersion, the measured average particle size is similar and much higher than the primary particle size. The different properties of these two silica types will be discussed.