Low-swelling chitosan derivatives as biosorbents for basic dyes

In this study, three different chitosan microsphere derivatives were prepared as sorbents for basic dyes. Preparation was succeeded by a novel cross-linking method based on ionic gelation with tripolyphosphate and subsequent covalent cross-linking with glutaraldheyde in order to address the large amount of swelling of the powdered form of the respective derivatives. Basic blue 3G (dye) was selected as the sorbate, and chitosan microsheres grafted with acrylamide and acrylic acid were used as biosorbents. Techniques such as FTIR spectroscopy, SEM, and swelling measurements facilitated the evaluation of the materials. Sorption-desorption experiments over the whole pH range were carried out to reveal the optimum value of sorption-desorption. The Langmuir isotherm model was used to fit the equilibrium experimental data, giving a maximum sorption capacity of 0.808 mmol/g at 338 K. An intraparticle diffusion model was employed to fit the kinetic data, and the resulting diffusion coefficients were in the range of (1-10) x 10(-11) m(2)/s. Thermodynamic analysis showed that the sorption process was spontaneous and endothermic with an increased randomness. In addition, sorption experiments were realized with a mixture of three basic dyes at various concentrations of sorbents.     

Poly(ammonium/ pyridinium)-chitosan Schiff base as a smart biosorbent for scavenging of Cu2+ ions from aqueous effluents

Chitosan Schiff bases (CSBs) decorated with ammonium or pyridinium motifs for recyclable biosorption of Cu²⁺ ions from aqueous effluents were tailored by grafting of salicylaldehyde ionic liquids (Sal-ILs) onto chitosan surface. Biosorption capacity of poly(ionic-salicylidene) CSBs (PISCSB_1,2) was compared with chitosan and poly(neural-salicylidene) CSBs (PSCSB). The ionic salicylidene-functionalized chitosan, poly(pyridinium)-salicylidene chitosan Schiff base (PISCSB₂), exhibited excellent adsorption capacity (99.1%), in comparison to chitosan (85%) and PSCSB (95%). Biosorption of Cu²⁺ ions onto PSCSB followed pseudo-first-order kinetic model while onto chitosan (CS) and PISCSB_1,2 followed pseudo-second-order kinetic model. However, Cu²⁺ ions biosorption onto all biosorbents fitted Langmuir adsorption isotherm model. Negative values of ΔG^o and ΔH^o confirmed the spontaneity and exothermic behavior of adsorption process. The new biosorbents could be successfully regenerated in aqueous 0.01 M EDTA solution with negligible loss in their adsorption capacity. Consequently, our new chitosan-based biosorbents may offer promising green and renewable scavengers for Cu²⁺ ions from wastewater.     

Modification of chitosan via grafting of glycolic acid followed by polycondensation during heat treatment

The modification of chitosan via grafting of glycolic acid and subsequent polycondensation during heat treatment have been studied. The formation of copolymers, the degree of amidization of amino groups, and the length of side polyglycolide chains are investigated by IR spectroscopy and gravimetry. The structural features and surface behavior of the films based on chitosan modified by poly(glycolic acid) are examined by X-ray diffraction and AFM. The grafting of side polyglycolide chains leads to marked changes in the chitosan structure. The study of the sorption behavior of the films based on the modified chitosan confirms the hydrophobization of chitosan via grafting of poly(glycolic acid).     

Effect of polar modifications on cure characteristics, solvent resistance and thermo-mechanical properties of metallocene-based polyolefinic elastomers

Metallocene-based poly(ethylene-octene) and poly(ethylene-butene) elastomers were polar modified through sulfonation and grafting of acrylic acid. The impact of polar modifications on the oil and solvent resistance, curing characteristics and various thermo-mechanical properties of the cured elastomers was thoroughly investigated. Greater solvent resistance was observed due to grafting of acrylic acid in comparison to sulfonation. Thermo-mechanical properties were significantly improved after polar modifications.     

Interaction of indigo carmine dye with chitosan evaluated by adsorption and thermochemical data

Chitosan can use its protonated amine groups to adsorb strongly anionic species from diluted solutions. In this work, adsorption and thermochemical data on the interaction of the dye indigo carmine with chitosan in aqueous medium were found, in order to obtain new adsorption data on this relatively unexplored chitosan field. The studies were carried out by the batch method from 35 to 50 degrees C. The adsorption results were well fitted to both Langmuir and Freundlich adsorption models. The increase in the temperature decreased the adsorption of the dye. The enthalpy of interaction, when a monolayer of the dye was formed on the chitosan surface, delta(int)H, of -23.2 kJ mol(-1) was encountered for all temperature ranges studied. The spontaneity of the interaction is indicated by the delta(int)G values from -9.1 to -8.2 kJ mol(-1). Other thermodynamic quantities were also calculated and are discussed.     

Adsorption of polymers at the solution-solid interface. VI. Polyacids on nylon powder

The adsorption of some polyacids, principally poly(acrylic acid), on nylon powder has been studied. In aqueous solutions at low pH the adsorption behavior of poly(acrylic acid) is controlled by adsorbate coil dimensions rather than by electrostatic effects. Less adsorption takes place from methanol solutions but the process is much more rapid than from water. Above a critical value, increase of adsorbate molecular weight leads to a reduced adsorption, the effect being particularly evidenced by aqueous solutions. Model compounds (propionic and glutaric acids) are rapidly adsorbed from both methanol and water, but give low specific absorptions. Adsorption of poly(acrylic acids) and model compounds, is reduced, but not eliminated, by modification of the nylon adsorbent through acetylation or methoxymethylation. The adsorption of poly(acrylic acid) on nylon is not readily reversible; however, partial neutralization will release preadsorbed poly(acrylic acid) from nylon powder. The adsorption behavior of copolymers of acrylic acid with N-vinylpyrrolidone is reported, as are brief studies on some other homopolyacids. The results are generally interpreted on the basis of sorption of the macromolecules into a swollen, flexible adsorbent.     

Effect of heat and solvent treatment on radiation grafting of acrylic acid to poly(ethylene terpehthalate)

Direct radiation graft polymerization of acrylic acid onto oriented poly(ethylene terephthalate) films and fibers subjected to thermal treatment and treated with structure-active solvents, such as dichloroethane and dioxane, was studied. Based on the results of thermomechanical analysis, X-ray diffraction, sorption, and acrylic acid grafting, conclusions were drawn concerning the character of structural changes in poly(ethylene terephthalate) exposed to structure-active solvents. The physicochemical properties of the graft copolymers obtained were examined, including the resistance against γ-radiation.     

Radiation synthesis of chitosan beads grafted with acrylic acid for metal ions sorption

Radiation-induced grafting of acrylic acid onto chitosan beads was performed in solution at a dose rate of 20.6 Gy/min of cobalt-60 gamma rays. The effect of absorbed dose on grafting yield was investigated. The characterization of the grafted material was performed by FTIR spectroscopy and the swelling measurements at different pHs. The grafting yield increased with the increase in dose, it reached 80% at 40 kGy irradiation dose.The removal of Pb and Cd ions from aqueous solutions was investigated with both ungrafted and grafted chitosan beads. The sorption behavior of the sorbents was examined through pH, kinetics and equilibrium measurements. Grafted chitosan beads presented higher sorption capacity for both metal ions than unmodified chitosan beads.     

Studies on the graft copolymerization of cellulosic materials

Graft copolymers of acrylic acid on cellulosic materials were obtained by use of ceric ion in aqueous medium at various temperatures. The level of incorporation of poly(acrylic acid) grafts and the efficiency of grafting were significantly reduced as the temperature of polymerization was increased from 35° to 60°C. The uptake of cadmium and copperions from aqueous solution by the cellulose-g-poly(acrylic acid) copolymer was examined by equilibrium and dynamic sorption studies. The amount of metal ions removed from solution depended on the metal ion type, initial concentration of the metal ion solution, level of incorporation of poly(acrylic acid) in the graft copolymer and the temperature of the metal ion solution.     

电化法研究壳聚糖树脂与游离酸的相互作用

利用电化实验技术，跟踪观察交联壳聚糖树脂吸附低浓度游离酸的行为，讨论了酸和甲醇浓度等因素对吸附的影响，利用固-液相互作用方程，求取吸附剂一吸附质相互作用能。实验结果表明，交联壳聚糖树脂吸附低浓度游离酸的过程是遵循单分子层机制进行的，表观吸附速率常数随着吸附质浓度和外加甲醇含量的增大而减小，表观吸附速率常数与吸附剂一吸附质相互作用能（U）存在线性相关。     

Comparative adsorption studies of indigo carmine dye on chitin and chitosan

The adsorption of indigo carmine dye onto chitin and chitosan from aqueous solutions was followed in a batch system. The ability of these materials to adsorb indigo carmine dye from aqueous solution was followed through a series of adsorption isotherms adjusted to a modified Langmuir equation. The maximum number of moles adsorbed was 1.24 +/- 0.16 x 10(-5) and 1.54 +/- 0.03 x 10(-4) mol g(-1) for chitin and chitosan, respectively. The same interactions were calorimetrically followed and the thermodynamic data showed exothermic enthalpic values of -40.12 +/- 3.52 and -29.25 +/- 1.93 kJ mol(-1) for chitin and chitosan, respectively. Gibbs free energies for the two adsorption processes of indigo carmine dye presented a positive value for chitin and a negative one for chitosan, reflecting that dye/surface interactions are thermodynamic favorable for chitosan and nonspontaneous for chitin at 298.15 K. The interaction processes were accompanied by an increase of entropy value for chitosan (90 +/- 6 J mol(-1)K(-1)) and a decrease for chitin (-145 +/- 13 J mol(-1)K(-1)). Thus, dye/chitosan interaction showed favorable enthalpic and entropic processes, reflecting thermodynamic stability of the formed complex, while dye/chitin interaction showed an exothermic enthalpic value and a highly nonfavorable entropic effect, resulting in a nonspontaneous thermodynamic system.     

Facile tailoring of film morphology and release properties using layer-by-layer assembly of thermoresponsive materials

Layer-by-layer self-assembly was used to prepare thermoresponsive thin films of poly(N-isopropylacrylamide) (PNIPAAm) and poly(acrylic acid) (PAA) based on hydrogen bonding. The temperature of PNIPAAm adsorption was shown to significantly affect both the mass proportion of PNIPAAm in the film and the film surface morphology. When the adsorption was conducted at temperatures close to the lower critical solubility temperature of PNIPAAm, the amount of PNIPAAm in the film increased significantly (from 51 to 59%), and the total film mass increased by 30-40%. The films prepared at 30 degrees C also exhibited a lower surface roughness (1-2 nm) compared with 5-8 nm when prepared at 10 or 21 degrees C. The resulting multilayer films ([PAA/PNIPAAm]10) were capable of being reversibly loaded and unloaded with dye (Rhodamine B) by exposure to solutions at elevated temperatures. The rate of loading and release was shown to depend on both the solution temperature and film preparation temperature, leading to tunable loading/release properties.     

Radiation grafting of ionically crosslinked alginate/chitosan beads with acrylic acid for lead sorption

Radiation-induced grafting of acrylic acid onto alginate/chitosan beads was performed in solution at a dose rate of 20.6 Gy/min of Co-60 gamma rays. The effect of absorbed dose on grafting yield was investigated. The characterization of the grafted and un-grafted beads was performed by FTIR spectroscopy and the swelling measurements at different pHs was studied. It is found that as the pH value increases the swelling degree increases up to pH 6 but with further increase in pH value the swelling decreases. Also, it is noticed that the grafting yield increased with increase the irradiation dose. Both un-grafted and grafted alginate/chitosan beads were examined as sorbents for the removal of Pb ions from aqueous solutions. The sorption behavior of the sorbents was examined through pH, and equilibrium measurements. Grafted alginate/chitosan beads presented higher sorption capacity for Pb ions than un-grafted beads.     

Structure and protein binding capacity of a planar PAA brush

We performed neutron reflectometry (NR) and total internal reflection fluorescence (TIRF) spectroscopy to characterize the structure and the protein binding capacity of a planar poly(acrylic acid) (PAA) brush at different temperatures. A PAA brush was prepared by spin-coating planar quartz or silicon wafers with a thin film of poly(styrene). Then, the diblock copolymer poly(styrene)-poly(acrylic acid) was deposited on these modified wafers using the Langmuir-Sch?fer or Langmuir-Blodgett technique. PAA grafting densities of about 0.1 chains per nm2 were obtained. The NR experiments indicate a remarkable swelling of the PAA brush in contact with a buffer solution, when it is heated to 40 degrees C for several hours. The swollen brush structure remains upon cooling back to 20 degrees C suggesting a disentanglement of the initially formed PAA brush by the temporary heating. At pD = 6.7, the protein bovine serum albumin (BSA) with a negative net charge is strongly adsorbed to the swollen PAA brush. From the scattering length density profiles obtained from the NR curves, an almost homogeneous filling of the whole PAA brush space with BSA molecules can be deduced corresponding to an average BSA volume fraction of about 7-10% and an adsorbed protein mass of about 1.4 mg m-2. By analyzing the TIRF experiments, it is found that BSA adsorption is enhanced when increasing the temperature which represents an evidence for an entropic driving force for protein adsorption. However, the mechanism of BSA adsorption at a PAA brush appears to be different at 20 and 40 degrees C.     

Modification of porous silica particles with poly(acrylic acid)

The surface of porous silica particles was modified with poly(acrylic acid) by reacting the carboxyl groups on poly(acrylic acid) with the amino groups of pregrafted aminopropyltriethoxysilane (APS). The chemical modifications by APS and polymer were characterized by infrared spectroscopy and the amount of APS and poly(acrylic acid) grafted to the surface were determined by thermal gravimetric analyses. The wettability of the modified silica particles, based on the rate of water penetration, was pH‐dependent with PAA; at pH 1.5 the wettability increased but at pH 5.5 it decreased dramatically. The pore size and size distribution of the silica particles decreased with APS and polymer grafting. Copyright © 2000 John Wiley & Sons, Ltd.     

Simple and fast method for the fabrication of switchable bicomponent micropatterned polymer surfaces

We report on the fabrication of micropatterned polymer surfaces that allow the reversible inversion of surface topography, charge, and wettability. Micropatterned surfaces were prepared by grafting two oppositely charged polyelectrolytes (poly(acrylic acid) and poly(2-vinylpyridine)) using a combination of photolithography, "lift off", and "grafting to" techniques. The switchable surfaces are of interest in microprinting and for the design of microfluidic devices and programmed protein adsorption.     

Blood compatibility of thermoplastic polyurethane membrane immobilized with water-soluble chitosan/dextran sulfate

Water-soluble chitosan (WSC)/dextran sulfate (DS) was immobilized onto the surface of thermoplastic polyurethane (TPU) membrane after ozone-induced graft polymerization of poly(acrylic acid) (PAA). The surface was characterized with contact angle measurement and X-ray photoelectron spectroscopy (XPS). The adsorption of human plasma fibrinogen (HPF) followed the Langmuir adsorption isotherm. The results showed that the surface density of peroxides generated and poly(acrylic acid) (PAA) grafted reached the maximum value at 20 min of ozone treatment. It was found that the WSC- and DS-immobilized amount increased with pH and the molecular weight of WSC. The membrane/water interfacial free energy increased with PAA-grafting and WSC/DS-immobilization, indicating the increasing wettability of TPU membrane. The adsorption of HPF on TPU-WSC/DS membranes could be effectively curtailed and exhibited unfavorable adsorption. Moreover, WSC/DS immobilization could effectively reduce platelet adhesion and prolong the blood coagulation time, thereby membrane improving blood compatibility of TPU membrane. In addition, the in vitro cytotoxicity test of PEC modification was non-cytotoxic according to much low growth inhibition of L929 fibroblasts. Furthermore, TPU-WSC/DS membranes exhibited higher cell viability than native TPU membrane.     

Grafting of poly(acrylic acid) onto nonporous glass bead surfaces

The surface of glass beads were modified with covalently bonded poly(acrylic acid). The optimum reaction conditions were determined to graft poly(acrylic acid) effectively onto the glass surface. The dependence of the graft polymer molecular weight, grafting percentage and monomer weight conversion based on these reaction conditions were consistent with free radical kinetics. Grafting efficiency for azobisisobutyronitrile was more complex compared with the benzyl peroxide initiator system © 1997 John Wiley & Sons, Ltd.     

Multilayer film assembled from charged derivatives of chitosan: physical characteristics and biological responses

Polyelectrolyte multilayer films were successfully assembled from each of the three charged derivatives of chitosan; N-[(2-hydroxyl-3-trimethylammonium)propyl]chitosan chloride (HTACC), N-succinyl chitosan (SCC) and N-sulfofurfuryl chitosan (SFC), paired with one of the two oppositely charged polyelectrolytes, poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) on surface-treated poly(ethylene terephthalate) (treated PET) substrates by alternate layer-by-layer adsorption. Surface coverage and wettability of the multilayer films were determined by AFM and water contact angle measurements, respectively. Analysis by quartz crystal balance with dissipation (QCM-D) has suggested that all multilayer films are relatively rigid and have a high water content associated within their structures, accounting for up to 85-90% (w/w) for films having 7-10 layers. In vitro cytocompatibility tests for the fibroblast-like L929 cell line revealed a slight dependency for cell adhesion and proliferation on the outermost layer. The multilayer film containing HTACC exhibited moderate antibacterial activity against E. coli and S. aureus. Bearing negative charges, the multilayer films terminating with SFC and having at least 10 layers were capable of suppressing the adsorption of plasma proteins and platelet adhesion at a comparable level to the multilayer film assembled from heparin, a well-known antithrombogenic polymer.     

Adsorption thermodynamics of short-chain peptides on charged and uncharged nanothin polymer films

The present work describes experimental measurements of submolecular-level interaction energies involved in the process of peptide adsorption on polymer films using surface plasmon resonance spectroscopy. Gibbs energy change on adsorption (DeltaG(ad)) for tyrosine, phenylalanine, and glycine homopeptides were measured at 25 degrees C and pH 7 on highly uniform, nanothin polymer films, and the results were used to predict DeltaG(ad) for homologous homopeptides with a larger number of residue units. Nanothin poly(2-vinylpyridine), poly(styrene), and poly(1-benzyl-2-vinylpyridinium bromide) films were used for the adsorption studies; they were prepared using a graft polymerization methodology. In-situ swelling experiments were done with ellipsometry to examine the uniformity of the surfaces and to ensure that the graft densities of the different polymer films were similar to facilitate the comparison of adsorption results on these surfaces. The swelling experiments showed that the films were uniform, and the grafting densities were found to be 0.14-0.17 chains/nm(2). For uncharged surfaces, predicted and measured DeltaG(ads) values for homopeptides deviated by < or =4.9%. To extend this approach to a mixed-residue peptide, measurements were made for glycine, phenylalanine, and tyrosine-leucine subunits found in leucine enkephalin. The predicted DeltaG(ads) values for leucine enkephalin deviated by 3.0% and -9.1% for poly(2-vinylpyridine) and poly(styrene) films, respectively. Deviations between measured and predicted adsorption energies were larger for the charged poly(1-benzyl-2-vinylpyridinium bromide) surface relative to uncharged surfaces. While the adsorption energies were found to be additive within experimental uncertainties for the charged surface, generally speaking, measured uncertainty values were also larger for the charged surface.