Fabrication of zirconium(IV) cross-linked alginate/kaolin hybrid beads for nitrate and phosphate retention

The extreme nitrate (NO₃⁻) species in drinking water leads to methemoglobinemia (blue baby syndrome) disease in new born toddlers whereas the excess phosphate (PO₄³⁻) and NO₃⁻ contents lead to the eutrophication (algae growth) problem of water sources. Upto date, the environmental researchers have developing the suitable adsorbent materials for providing NO₃⁻ and PO₄³⁻ free water system. In present study, a low-cost alginate (Alg) assisted kaolin (KN) (AlgKN) composite beads were prepared and utilized for the removal of NO₃⁻ and PO₄³⁻. To improve the sorption capacity (SC) and stability, Zr⁴⁺ ions were coated onto AlgKN to get Zr@AlgKN composite beads which were prepared via., hydrothermal (Hydro) and in situ precipitation (In situ) methods. The hydro assisted Zr@AlgKN composite beads possess an enhanced SC than the in situ assisted adsorbents. In batch scale, the parameters responsible for the adsorption process such as contact time, co-ions, adsorbent dosage, pH, initial ions concentration and temperature were optimized. The adsorbents were characterized by XRD, FTIR, BET, EDAX and SEM analysis. The adsorption experimental data was fitted with isotherms, kinetics and thermodynamic parameters. The regeneration and field applicability study of the Zr@AlgKN composite beads were also investigated.     

Drug release of pH/temperature-responsive calcium alginate/poly(N-isopropylacrylamide) semi-IPN beads

A series of semi-interpenetrating, polymer network (semi-IPN), hydrogel beads, composed of calcium alginate (Ca-alginate) and poly(N-isopropylacrylamide) (PNIPAAM), were prepared for a pH/temperature-sensitive drug delivery study. The equilibrium swelling showed the independent pH- and thermo- responsive nature of the developed materials. At pH=2.1, the release amount of indomethacin incorporated into these beads was about 10% within 400 min, while this value approached to 95% at pH=7.4. The release rate of the drug was higher at 37 degrees C than that at 25 degrees C and increased slightly with increasing PNIPAAM content. These results suggest that the Ca-alginate/PNIPAAM beads have the potential to be used as an effective pH/temperature sustainable delivery system of bioactive agents. [GRAPHS: SEE TEXT] A summary of the temperature- and pH-dependence on the release of the drug over a period of 450 min. The effect of the temperature on the swelling of the beads is shown in the inset.     

Entrapment and release of sodium polystyrene sulfonate (SPS) from calcium alginate gel beads

The release of sodium polystyrene sulfonate (SPS) from calcium alginate hydrogel beads has been studied. It has been shown that the structure of the cross-linked calcium alginate network is of primary importance in the retention and/or release of the SPS. This has been evidenced by studying the influence of Ca²⁺ concentration, molar masses (M_n) and the ratio of mannuronic acid/guluronic acid components. A minimum in the SPS release is observed in relation with the organization of the network structure. Conditions inducing the organization of a strong gel (e.g. high Ca²⁺ concentration for example) are not always related to a low release. A good control of release is found when a compromise between a well-structured hydrogel and sterical consideration of SPS is reached.     

Effects of intercalated hydrotalcite on drug release behavior for poly(acrylic acid-co-N-isopropyl acrylamide)/intercalated hydrotalcite hydrogels

The influence of positively charged intercalated hydrotalcite (IHT) in the anionic poly(acrylic acid-co-N-isopropyl acrylamide), poly(AA-co-NIPAAm)/hydrotalcite nanocomposite hydrogels on the drug release behavior for the drugs with different charges was investigated in this study. Results show that the loading amount and release ratio of indomethacin are affected by the swelling ratio in saline solution and related to the affinity in the alcohol solution, respectively. The loading amount and release ratio of caffeine are affected by the swelling ratio. The loading amount of crystal violet (CV) increased with an increase of the content of intercalating agent in IHT of the gel but the fractional release of CV in the gels decreases with increase in intercalating agent content. The result of release and loading for phenol red in the hydrogels is contrary to CV.     

Thermomechanical properties and crystallization behavior of layered double hydroxide/poly(ethylene terephthalate) nanocomposites prepared by in‐situ polymerization

Thermomechanical properties and crystallization behavior of poly(ethylene terephthalate) (PET) nanocomposites containing layered double hydroxide (LDH) were investigated. To enhance the compatibility between PET matrix and LDH, dimethyl 5‐sulfoisophthalate (DMSI) anion intercalated LDH (LDH‐DMSI) was synthesized by coprecipitation method, and its structure was confirmed by Fourier transform infrared (FTIR) spectrometer and X‐ray diffraction (XRD) measurements. Then, PET nanocomposites with LDH‐DMSI content of 0, 0.5, 1.0, and 2.0 wt% were prepared by in‐situ polymerization. The dispersion morphologies were observed by transmission electron microscopy (TEM) and XRD, showing that LDH‐DMSI was exfoliated in PET matrix. Thermal and mechanical properties, such as thermal stability, tensile modulus, and tensile yield strength of nanocomposites, were enhanced by exfoliated LDH‐DMSI nanolayers. However, elongation at break was drastically decreased with LDH loading owing to the increased stiffness and microvoids. The effect of exfoliated nanolayers, which acted as a nucleating agent confirmed by differential scanning calorimeter (DSC), on the microstructural parameters during isothermal crystallization, was analyzed by synchrotron small‐angle X‐ray scattering (SAXS). It is believed that nanocomposites could be crystallized more easily owing to the increased nucleation sites, which lead to the decrease of average amorphous region size and the long period with the increase of LDH‐DMSI content. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 28–40, 2007     

Controlled release of atenolol from freeze/thawed poly(vinyl alcohol) hydrogel

Physically crosslinked polymeric films containing atenolol drug were formulated and the release of the drug was evaluated with view to investigate the feasibility of these films as drug delivery systems. Freezing and thawing process for PVA was used to prepare a controlled release device for atenolol drug. The process included incorporation of the drug into PVA film during the freezing and thawing process. The PVA has used a molecular weight of 125 k and degree of saponification of 98. Various amounts of the atenolol drug were incorporated into the freeze/thawed PVA. The in vitro release behavior of atenolol from these films was investigated. The drug release profiles from the polymeric formulations indicated initial high rate of release followed by slow rate of the release. The release of atenolol increased with increasing drug concentration in the film. The results showed the feasibility of the use of freezing and thawing technique to control the release of atenolol drug from PVA.     

Controlled release of acetochlor from poly (butyl methacrylate-diacetone acrylamide) based formulation prepared by nanoemulsion polymerisation method and evaluation of the efficacy

Acetochlor is an important herbicide for gramineous weeds and some small seed broadleaf weeds. Controlled-release formulations of herbicide are highly desirable not only for attaining the most effective utilisation of the weed control, but also for reducing environmental pollution. Acetochlor was incorporated in poly (butyl methacrylate-diacetone acrylamide) based formulation to obtain controlled release properties. The acetochlor nanocapsules were characterised by size distribution, infrared spectroscopy (IR) and field emission scanning electron microscopy (FESEM), and factors related to loading efficiency, swelling behaviour of the formulation were investigated. For this controlled-release formulation, the loading efficiency could reach about 50% (w/w). n, the diffusion parameter was indicative of the transport mechanism, and the values for ‘n’ were in the range of 0.28–0.61, which indicated that the release of acetochlor was diffusion-controlled. The time taken for 50% of the active ingredient to be released into water, t₅₀, was also calculated for the comparison of formulations in different conditions. The formulation with higher temperature and more diacetone acrylamide had lower value of t₅₀, which means a quicker release of the active ingredient. This study highlighted some pieces of evidence that improved herbicide incorporation and slower release were linked to potential interactions between the herbicide and the polymer.     

The controlled release behavior and pH‐ and thermo‐sensitivity of alginate/poly(vinyl alcohol) blended hydrogels

Poly(vinyl alcohol) (PVA) was blended with sodium alginate (Alg) in various ratios and crosslinked with calcium chloride and made into hydrogel membranes. The dependence of the swelling behavior of these Alg‐Ca/PVA hydrogels on pH was investigated. The temperature‐dependent swelling behavior of the semi‐interpenetrating network (semi‐IPN) hydrogels was examined at temperatures from 2 to 45°C and the enthalpy of mixing (ΔH_mix) was determined at various temperatures. The molecular structure of the hydrogels was studied by infrared spectroscopy and their water structure in the semi‐IPN hydrogels was measured by differential scanning calorimetry (DSC). The influence of Ca²⁺ content on the network structure of Alg‐Ca/PVA hydrogels was investigated in terms of the compressive elastic modulus, effective crosslinking density, and the polymer–solvent interaction parameter based on the Flory theory. The loading of alizarin red S (ARS) followed the Langmuir isotherm mechanism and the release kinetics of ARS from the Alg‐Ca/PVA hydrogels followed the Fickian diffusion mechanism. Copyright © 2008 John Wiley & Sons, Ltd.     

Preparation and drug release property of CO2 stimulus-sensitive poly(N, N-dimethylaminoethyl methacrylate)-b-polystyrene nanoparticles

The CO₂ stimulus-sensitive nanoparticles based on poly(N, N-dimethylaminoethyl methacrylate)-b-poly styrene (PDMAEMA-b-PS) were prepared via surfactant-free miniemulsion reversible addition–fragmentation chain transfer (RAFT) polymerization. The as-prepared nanoparticles exhibited core–shell structure with about 120 nm in diameter. Their dispersion/aggregation in water can be adjusted by alternatively bubbling of CO₂ and N₂. Drug release from these nanoparticles can be accelerated (or delayed) by bubbling (or removing) of CO₂.     

Polymerization of propylene catalyzed over highly active and stereospecific catalysts synthesized with Mg(OEt)2/benzoyl chloride/TiCl4

A series of monoester catalysts has been studied, each catalyst prepared by the reaction of magnesium diethoxide with benzoyl chloride [BzCOCl, to produce ethyl benzoate (EB) in situ] in the presence of excess titanium tetrachloride. Solid product and catalysts obtained by subsequent treatments with titanium tetrachloride were characterized by elemental analysis, IR spectroscopy, x-ray diffraction, BET measurement, and thermal gravimetric analysis. The catalysts yielded very high activity (above 20 kg polymer/g Ti h atm) for the polymerization of propylene in slurry reactions. From the results of polymerization as well as catalyst characterization, the effects of internal and external Lewis bases on the isospecificity and stability of catalysts are discussed in detail. © 1992 John Wiley & Sons, Inc.     

Controlled loading and release of methylene blue from LbL polyurethane/poly(acrylic acid) film

The layer‐by‐layer (LbL) assembled multilayer films are widely used in the biomedical field for the controlled drug delivery. Here, multilayer films were assembled by LbL technique through alternating deposition of cationic polyurethane (PU) and poly(acrylic acid) (PAA) on glass slides. Methylene blue (MB) was used as a model drug to investigate the loading and release ability of the prepared multilayer film. The results showed that the loading rate and loading amount of MB were greatly influenced by pH value of the dye solution, and the release rate of MB was controlled both by ionic strength and pH value of immersing solution. The result also indicated that the film had a good reversibility of drug loading and release. It suggested that the PU/PAA multilayer film had potential applications in drug delivery and controlled release. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis and characterization of poly(urethane‐benzoxazine) films as novel type of polyurethane/phenolic resin composites

Poly(urethane‐benzoxazine) films as novel polyurethane ( PU )/phenolic resin composites were prepared by blending a benzoxazine monomer ( Ba ) and PU prepolymer that was synthesized from 2,4‐tolylene diisocyanate (TDI) and polyethylene adipate polyol (MW ca. 1000) in 2 : 1 molar ratio. DSC of PU/Ba blend showed an exotherm with maximum at ca. 246 °C due to the ring‐opening polymerization of Ba, giving phenolic OH functionalities that react with isocyanate groups in the PU prepolymer. The poly(urethane‐benzoxazine) films obtained by thermal cure were transparent, with color ranging from yellow to pale wine with increase of Ba content. All the films have only one glass transition temperature (T_g ) from viscoelastic measurements, indicating no phase separation in poly(urethane‐benzoxazine) due to in situ polymerization. The T_g increased with the increase of Ba content. The films containing 10 and 15% of Ba have characteristics of an elastomer, with elongation at break at 244 and 182%, respectively. These elastic films exhibit good resilience with excellent reinstating behavior. The films containing more than 20% of Ba have characteristics of plastics. The poly(urethane‐benzoxazine) films showed excellent resistance to the solvents such as tetrahydrofuran, N,N‐dimethyl formamide, and N‐methyl‐2‐pyrrolidinone that easily dissolve PU s. Thermal stability of PU was greatly enhanced even with the incorporation of a small amount of Ba . © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4165–4176, 2000     

The role of polymer/drug interactions on the sustained release from poly(dl-lactic acid) tablets

The release profiles of model drugs (propranolol HCl, diclofenac sodium, salicylic acid and sulfasalazine) from low molecular weight poly(d,l-lactic acid) [d,l-PLA] tablets immersed in buffer solutions were investigated in an attempt to explore the mechanism of the related phenomena. It was confirmed that drug release is controlled by diffusion through the polymer matrix and by the erosion of the polymer. The pH of the surrounding medium influences the drug solubility as well as swelling and degradation rate of the polymer and therefore the overall drug release process. Physicochemical interaction between d,l-PLA and drug is an additional factor which influences the degree of matrix swelling and therefore its porosity and diffusion release process. Propranolol HCl shows extended delivery time at both examined pH values (5.4 and 7.4) and especially at pH 7.4 where release was accomplished in 190 days, most probably due to its decreased solubility at higher pH values. The acidic drugs gave shorter delivery times especially at pH 7.4. A slower drug release rate and more extended delivery time at pH 7.4 in comparison with that at pH 5.4 was recorded for tablets loaded with diclofenac sodium and salicylic acid. The opposite effect was observed with samples loaded with propranolol HCl.     

Controlled drug release behavior of metformin hydrogen chloride from biodegradable films based on chitosan/poly(ethylene glycol) methyl ether blend

In this study, novel smart drug release films were prepared by blending chitosan with polyethylene glycol methyl ether (PEGME), also named as methoxy polyethylene glycol (mPEG), for controlled drug release applications. The polymeric films were characterized by Fourier transform infra-red for functional groups analysis, scanning electron microscopy for morphology and X-ray photoelectron spectroscopy for chemical and surface analysis followed by mechanical and thermal analysis. The mechanical properties showed that with the addition of PEGME (40%), the tensile strength and elongation break were increased up to 34.14 MPa and 26.40%, respectively as compared to the controlled sample (without PEGME). The developed biodegradable films were tested for Metformin hydrogen chloride release ability at a particular rate in phosphate buffer saline solution at pH 7.4. The results showed that chitosan/PEGME blends could be employed for controlled drug release and other biomedical applications.     

Polyelectrolyte microcapsules templated on poly(styrene sulfonate)-doped CaCO3 particles for loading and sustained release of daunorubicin and doxorubicin

A strategy to incorporate and release anti-cancer drugs of daunorubicin (DNR) and doxorubicin (DOX) in preformed microcapsules is introduced, which is based on charge interaction mechanism. Oppositely charged poly(allylamine hydrochloride) (PAH) and poly(styrene sulfonate) (PSS) were assembled onto PSS doped-CaCO₃ colloidal particles in a layer-by-layer manner to yield core-shell particles. After removal of the carbonate cores, hollow microcapsules with entrapped PSS were fabricated, which showed spontaneous loading ability of positively charged DNR and DOX. The drug loading was confirmed quantitatively by observations under confocal laser scanning microscopy, transmission electron microscopy and scanning force microscopy. Quantification of the drug loading was performed under different conditions, revealing that a larger amount of drugs could be incorporated at higher drug feeding concentrations and higher salt concentrations. However, putting additional polyelectrolyte layers on the microcapsules after core removal resulted in weaker drug loading efficiency. The drug release behaviors from the microcapsules with different layer numbers were studied too, revealing a diffusion controlled release mechanism at the initial stage (4 h).     

Drug release and biocompatibility of self‐assembled micelles prepared from poly (ɛ‐caprolactone/glycolide)‐poly (ethylene glycol) block copolymers

A series of poly(?‐caprolactone/glycolide)‐poly(ethylene glycol) (P(CL/GA)‐PEG) diblock copolymers were prepared by ring opening polymerization of a mixture of ?‐caprolactone and glycolide using mPEG as macro‐initiator and stannous octoate as catalyst. Self‐assembled micelles were prepared from the copolymers using nanoprecipitation method. The micelles were spherical in shape. The micelle size was larger for copolymers with longer PEG blocks. In contrast, the critical micelle concentration of copolymers increased with decreasing the overall hydrophobic block length. Drug loading and drug release studies were performed under in vitro conditions, using paclitaxel as a hydrophobic model drug. Higher drug loading was obtained for micelles with longer poly(ε‐caprolactone) blocks. Faster drug release was obtained for micelles of mPEG2000 initiated copolymers than those of mPEG5000 initiated ones. Higher GA content in the copolymers led to faster drug release. Moreover, drug release rate was enhanced in the presence of lipase from Pseudomonas sp., indicating that drug release is facilitated by copolymer degradation. The biocompatibility of copolymers was evaluated from hemolysis, dynamic clotting time, and plasma recalcification time tests, as well as MTT assay and agar diffusion test. Data showed that copolymer micelles present outstanding hemocompatibility and cytocompatibility, thus suggesting that P(CL/GA)‐PEG micelles are promising for prolonged release of hydrophobic drugs.     

In situ polymerization and characterization of graphene oxide‐co‐poly(phenylene benzobisoxazole) copolymer fibers derived from composite inner salts

A facile and efficient strategy for preparing well dispersed graphene oxide (GO)‐co‐Poly(phenylene benzobisoxazole) (PBO) copolymer fibers was carried out by direct in situ polycondensation of composite inner salts. The composite inner salts were achieved to improve the dispersivity, solubility, reactivity, and interfacial adhesion of GO in PBO polymer matrix. The structure and morphology of GO‐co‐PBO copolymer fibers have been characterized. It was demonstrated that GO were covalently incorporated with PBO molecular chains and dispersed considerably well in PBO fiber even the GO reach to 3 wt %. Meanwhile, the tensile modulus, tensile strength and thermal stability of GO‐co‐PBO copolymer fibers increased considerably with GO. The mechanism and theoretical calculation of GO enhanced PBO fiber were also discussed. The main reasons for the improvement on performance of PBO fiber should be attributed to good dispersion GO in PBO matrix and covalent bonding networks at the interface between GO and PBO molecular chains. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Electrospun zeolitic imidazolate framework-8/poly(lactic acid) nanofibers for pipette-tip micro-solid phase extraction of carbamate insecticides from environmental samples

In the present study, electrospun zeolitic imidazolate framework-8/poly(lactic acid) nanofibers were successfully synthesized and characterized as a potential nanosorbent for the pipette-tip micro-solid phase extraction of chlorpropham, pirimicarb, carbaryl, and methiocarb carbamate insecticides from environmental water samples. The extraction procedure was followed by gas chromatography/mass spectrometry separation and determination of the target analytes. All the effective parameters of the extraction procedure were optimized through the one variable at-a-time method. Thanks to the very simple extraction procedure as well as the application of electrospun nanofibers with high surface area, the four analytes were efficiently extracted with as lowest extraction times as practicable. Under the optimal conditions, the calibration plots of the analytes were obtained within broad linear dynamic ranges of 0.5 – 150 ng mL^?1 for chlorpropham and pirimicarb plus 1.0 – 175 ng mL^?1 for carbaryl and methiocarb, respectively. Besides, limits of detection as low as 0.2 and 0.15 ng mL^?1 for chlorpropham and pirimicarb, respectively, as well as 0.5 ng mL^?1 for carbaryl and methiocarb indicate the favorable sensitivity of the analytical procedure. The applicability of the developed method was evaluated by quantitative determination of the target analytes in four different environmental water samples. Relative recoveries higher than 88.0% shows the acceptable accuracy of the method in the quantitative determination of the four carbamate insecticides.     

N,N-Dichloro poly(styrene-co-divinyl benzene) sulfonamide polymeric beads: an efficient and recyclable reagent for the synthesis of dialkyl chlorophosphates from dialkylphosphites at room temperature

An efficient and operationally simple method is developed for the synthesis of dialkyl chlorophosphates from dialkylphosphites using a new chlorine bearing reagent, N,N-dichloro poly(styrene-co-divinyl benzene) sulfonamide in the form of polymeric beads. The reagent afforded dialkyl chlorophosphates at room temperature, and is recyclable.