羧甲基纤维素-壳聚糖水凝胶球的制备及性能

采用物理交联法制备了羧甲基纤维素(CMC)-壳聚糖(CS)共混水凝胶球;研究了共混球的耐酸碱性、溶胀性及对亚甲基蓝的吸附性能.结果表明,水凝胶球在弱酸和弱碱中具有一定的稳定性;随着羧甲基纤维素与壳聚糖质量比的增大,水凝胶的吸水溶胀率增加.在CMC与CS质量比为1∶4时制备的水凝胶呈规则球状.     

Effect of crosslinker functionality on swelling and network parameters of copolymeric hydrogels

Crosslinked xerogels comprising N-vinyl-2-pyrrolidone (VP) and butyl acrylate (BA) with different weight fractions of BA ranging between 0.1 and 0.3 were prepared by γ-ray initiation copolymerization using different concentrations of either hexa- or tetrafunctional crosslinking agents. Methylene bisacrylamide (MBA) was selected as tetrafunctional crosslinker, while 1,1,1-trimethylolpropane trimethacrylate (TPT) was used as a hexafunctional crosslinker. The concentration of both crosslinkers ranged between 0.5% and 2%. Thin disks of the prepared copolymers were swollen in deionized water at 294 K. The final equilibrium water content, volume fraction of polymer and swelling capacity were determined. The effective crosslinking density V_e, the average molecular weight between the crosslinks M_c and the polymer–water interaction parameter were determined from stress–strain measurements. For different compositions of VP/BA, the linear relations between theoretical crosslinking densities V_t and V_e were established. The efficiencies of MBA and TPT crosslinking agents towards VP–BA copolymers were determined. © 1998 John Wiley & Sons, Ltd.     

Sucrose diacrylate: A unique chemically and biologically degradable crosslinker for polymeric hydrogels

A series of degradable hydrogels based on different vinyl monomers such as acrylamide, sucrose-1′-acrylate, and acrylic acid were synthesized using sucrose-6,1′-diacrylate (SDA) as a crosslinking agent. SDA was prepared by enzymatic transesterification of vinyl acrylate with sucrose in pyridine. Base catalyzed hydrolysis of SDA in aqueous solution was studied as a function of pH. As expected, hydrolysis of SDA was faster at higher pHs such that poly(acrylamide), poly(sucrose 1′-acrylate), and poly(acrylic acid) hydrogels underwent substantial degradation at and above pH 7, 9, and 13, respectively. The degradation was characterized by changes in the swelling ratios of the hydrogels indicating breakage of the crosslinking agent. Degradation of the hydrogels at their chemically stable pHs was studied in presence of enzymes. Enzymes, including pepsin and a fungal Lipase, were able to degrade the poly(acrylamide) hydrogel at pH 4 and 5, respectively. Poly(acrylic acid) hydrogel was degraded in presence of a fungal protease at pH 7.8. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2221–2229, 1997     

Synthesis of fast-swelling superabsorbent hydrogels: effect of crosslinker type and concentration on porosity and absorption rate

Fast-swelling highly porous superabsorbent hydrogels were synthesized through a rapid solution polymerization of concentrated partially neutralized acrylic acid under normal atmospheric conditions. Acetone and sodium bicarbonate were used as porosity generators (porogens) during polymerization process for porosity generation. N,N^′-methylenebisacrylamide (MBA) and 1,4-butanedioldiacrylate were used as the water- and the oil-soluble crosslinkers, respectively. The temperature changing of the reaction mixture during polymerization and foam formation process was monitored and investigated in details. Time and sequence of addition of the porogens and gelation time were recognized to be important to increase efficiency of the porogens. The concentration of the crosslinkers on gelation time was optimized to achieve highly porous products. It was found that higher crosslinker concentration, especially in the case of MBA, causes decreased gelation times. Shorter gelation time resulted in more porogen bubbles trapped in the viscose reaction mixture led to products with higher porosity. The effect of type and concentration of the crosslinking agents on the process and swelling behavior of the hydrogels (in water and saline solutions) were investigated. Power law relationships were found for the variation of swelling in terms of either crosslinker or saline concentration. Less sensitivity to the change of salinity was achieved by employing higher amount of crosslinker.     

Metal adsorption of carboxymethyl cellulose/carboxymethyl chitosan blend hydrogels prepared by Gamma irradiation

Blend hydrogels based on the carboxymethyl cellulose (CMC) and carboxymethyl chitosan (CMCts) were prepared by γ-irradiation of a high concentrated CMC/CMCts aqueous solution. Properties of the hydrogels, such as gel fraction, swelling ratio, gel strength, and metal adsorption for Pb and Au were investigated. The gel fraction increased with increasing dose, while the swelling ratio decreased with increasing it. The obtained blend hydrogels had high adsorption performance which was controlled by adjusting the composition of CMC/CMCts.     

Effect of the amount and type of the crosslinker on the swelling behavior of temperature-sensitive poly(N-tert-butylacrylamide-co-acrylamide) hydrogels

Temperature-sensitive poly(N-tert-butylacrylamide-co-acrylamide) [P(NTBA-co-AAm)] hydrogels were synthesized by free-radical copolymerization in a water–methanol mixture using three types of crosslinkers: 1,2-ethyleneglycol dimethacrylate, N,N-methylenebisacrylamide, and 1,3-butandiol dimethacrylate. These thermosensitive hydrogels were swollen to equilibrium in water at 20°C and examined by gravimetric measurements. The influence of type and content of crosslinkers on the swelling ratio, the polymer–solvent interaction parameter (χ), the average molecular mass between crosslinks and the effective crosslinking density (ν _E) of the hydrogels were reported and discussed. The swelling process in water was found to be non-Fickian diffusion. The enthalpy (ΔH) and entropy (ΔS) changes appearing in the χ parameter for the hydrogels were determined by using the Flory–Rehner theory based on the phantom network model of swelling equilibrium. Negative values for ΔH and ΔS indicated that the hydrogels had a negative temperature-sensitive property in water; that is, swelling at a lower temperature and shrinking at a higher temperature. The temperature-reversibility and on–off switching properties of the P(NTBA-co-AAm) hydrogels may be considered as good candidates for designing novel drug-delivery systems.     

Magnetic cellulose-chitosan hydrogels prepared from ionic liquids as reusable adsorbent for removal of heavy metal ions

Magnetic hybrid hydrogels with a novel polymeric coating consisting of chitosan and cellulose were prepared. By coating cellulose and chitosan, we combined the renewability and biocompatibility of cellulose and chitosan as well as the magnetic properties of Fe(3)O(4) to create a hybrid system to adsorb heavy metals.     

Radiation preparation and swelling behavior of sodium carboxymethyl cellulose hydrogels

Sodium carboxymethyl cellulose (CMC) is a kind of degraded polymer under γ-irradiation. However, in this work, it has been found that CMC crosslinks partially to form hydrogel by radiation technique at more than 20% CMC aqueous solution. The gel fraction increases with the dose. The crosslinking reaction of CMC is promoted in the presence of N₂ or N₂O due to the increase of free radicals on CMC backbone, but gel fraction of CMC hydrogel is not high (<40%). Some important values related to this kind of new CMC hydrogel synthesized under different conditions, such as radiation yield of crosslinking G(x), gelation dose R_g, number average molecular weight of network M_c were calculated according to the Charlesby–Pinner equation. The results indicated that although crosslinked CMC hydrogel could be prepared by radiation method, the rate of radiation degradation of CMC was faster than that of radiation crosslinking due to the character of CMC itself. Swelling dynamics of CMC hydrogel and its swelling behavior at different conditions, such as acidic, basic, inorganic salt as well as temperature were also investigated. Strong acidity, strong basicity, small amount of inorganic salts and lower temperature can reduce swelling ratio.     

Effect of filler networking on the response of thermosensitive composite hydrogels

Several composite hydrogels of poly(N-isopropylacrylamide) (pNIPAAm) with sodium montmorillonite (NaMM) have been synthesized using a fixed polymer/NaMM ratio (4:1 wt./wt.), but various monomer concentrations, in order to obtain hydrogels with different degrees of swelling, and thus different clay contents in the swollen state. For comparison, unfilled pNIPAAm gels have been also prepared at the same concentrations. The equilibrium swelling behaviour of the gels has been studied both in the swollen and in the shrunk state. In the swollen state, the polymer volume fraction increases with the initial monomer concentration C₀. In the shrunk state, the polymer fraction in pNIPAAm hydrogels is dependent on the specimen size and on C₀, whereas in the composite gels a constant polymer content is observed. When subjected to stepwise heating from 25 to 45 °C, unfilled gels undergo only poor deswelling. By contrast, complete deswelling takes place in composite gels. The latter show half-shrinking times varying over two orders of magnitude, depending on the monomer concentration and on the procedure followed to disperse NaMM, which determine the overall dispersion state of the filler, as evidenced by transmission electron microscopy (TEM). In particular, TEM observations show clay networking above a percolation threshold near 2.5 wt.% of NaMM. The effect of the incorporation of clay on the response to thermal stimuli is discussed in terms of the ability of NaMM to hinder the hydrophobic association of pNIPAAm segments and in terms of its dispersion state. It is suggested that, above the percolation threshold, NaMM forms a hydrophilic, physical network, through which water can flow also above the volume transition temperature, where pNIPAAm acquires a hydrophobic character.     

A novel crosslinker for UV copolymerization of N-vinyl pyrrolidone and methacrylates to give hydrogels

Methacryloxyethyl vinyl carbonate, a novel crosslinker containing a vinyl carbonate and a methacrylate group which is capable of copolymerizing N-vinyl pyrrolidone and methacrylates, was prepared. With this crosslinker, N-vinyl pyrrolidone (NVP) and methacrylates can copolymerize efficiently under strictly UV conditions. It was found that this crosslinker was able to give hydrogels with higher water content, higher tear strength, and lower modulus, compared to a traditional dimethacrylate crosslinker. In addition, hydrogel lenses fabricated by UV curing of formulations using this crosslinker were found to be superior to those fabricated with established process in terms of optical quality. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1039–1046, 1997     

Synthesis and characterization of novel carboxymethyl chitosan grafted polylactide hydrogels for controlled drug delivery

Novel carboxymethyl chitosan‐polylactide (CMCS‐g‐PLA) hydrogels were prepared by using 1‐(3‐dimethylaminopropyl)‐3‐ethylcarbodiimide hydrochloride/N‐hydroxysuccinimide (EDC/NHS) as crosslinking agent and catalyst at room temperature. Solid‐state ¹³C‐NMR, SEM, and FT‐IR measurements showed that PLA blocks are successfully grafted onto the CMCS main chains. DSC measurements confirmed the effective crosslinking of carboxymethyl chitosan. With increasing the amount of EDC/NHS, the crosslink destiny of CMCS‐g‐PLA copolymers is improved. The swelling ratio of CMCS‐g‐PLA hydrogels is pH dependent, showing a minimum in the pH range of 3 to 5. Rheological studies confirmed the formation of hydrogels. The higher the crosslinking density, the higher the storage modulus of hydrogels. CMCS‐g‐PLA hydrogels only slightly degrade in PBS for 10 days. In the presence of lysozyme, however, hydrogels with low crosslink density are totally degraded in 10 days. Drug release studies show that after 96 h, 95% of thymopentin is released under in vitro conditions. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis and characterization of antibacterial semi-interpenetrating carboxymethyl chitosan/poly (acrylonitrile) hydrogels

Blend hydrogels composed of carboxymethyl chitosan (CMCh) and poly (acrylonitrile) (PAN) were synthesized via crosslinking method. Several analyses were made to investigate both physical and thermal properties of CMCh/PAN hydrogels like; FTIR, scanning electron microscope, XRD and thermogravimetric analysis (TGA). TGA results showed that CMCh/PAN hydrogels are thermally more stable than CMCh and their thermal stability increases as PAN content increases in the hydrogel. Moreover, the swelling behavior of CMCh/PAN hydrogels was studied in different buffer solutions. It was found that CMCh/PAN hydrogels swell much more than PAN especially at pH 9. The hydrogels sorption for different dyestuff and various metal ions like; Cu²⁺, Cd²⁺ and Co²⁺ were also studied. In this work, antibacterial characteristic of hydrogels was mainly investigated towards Escherichia coli (E. coli) as a serious disease-leading bacterium. All tested hydrogels have clearly presented good antibacterial activity as CMCh content increases in the hydrogels.     

Comparative rheological study of ionic semi-IPN composite hydrogels based on polyacrylamide and dextran sulphate and of polyacrylamide hydrogels

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.     

Effect of crosslinker multiplicity on the gel point in ATRP

The experimental gelation was studied in atom transfer radical polymerization (ATRP) of methyl acrylate (MA) with various branching reagents that structurally differ by the number of vinyl groups (multiplicity). MA was copolymerized with branching reagents containing 2, 3, 4, 5, or 6 acrylate moieties per molecule, respectively. Reactions with a constant concentration of branching vinyl groups (the same molar ratio of [Vinyl_branch]₀/[Initiator]₀) revealed a different gelation behavior when ethylene glycol diacrylate (2A) and trimethylolpropane triacrylate (3A) were used as crosslinkers, whereas the reactions using pentaerythritol tetraacrylate (4A) showed similar gelation behavior as compared to reactions using 3A. Additional reactions with dipentaerythritol pentaacrylate (5A) and hexafunctional acrylate crosslinkers (6A) revealed the presence of a concentration‐dependant gelation behavior. On the other hand, in reactions with the same molar concentration of various crosslinkers, gelation occurred at progressively lower MA conversions for reactions with an increasing number of vinyl groups per crosslinker. In addition, the number of unreacted pendant vinyl groups in the sols was compared for reactions with different multiplicity of the crosslinker and various ratios of [Vinyl_branch]₀/[Initiator]₀. Finally, a linear oligomeric crosslinker containing multiple branching vinyl groups along the side chain was used as the branching reagent for gelation. The gelation behavior during the ATRP of MA with the linear crosslinker was different as compared to the use of the aforementioned crosslinkers with a star‐like architecture. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2016–2023, 2010     

Equilibrium partitioning of Ficoll in composite hydrogels

Equilibrium partition coefficients (phi, the concentration in the gel divided by that in free solution) of fluorescein-labeled Ficolls in pure agarose and agarose-dextran composite gels were measured as a function of gel composition and Ficoll size. The four narrow fractions of Ficoll, a spherical polysaccharide, had Stokes-Einstein radii ranging from 2.7 to 5.9 nm. Gels with agarose volume fractions of 0.040 and 0.080 were studied, with dextran volume fractions (calculated as if the chain were a long fiber) up to 0.011. As expected, phi generally decreased as the Ficoll size increased (for a given gel composition) or as the amount of dextran incorporated into the gel increased (for a given agarose concentration and Ficoll size). The decrease in phi that accompanied dextran addition was predicted well by an excluded volume theory in which agarose and dextran were both treated as rigid, straight, randomly positioned and oriented fibers. Modeling dextran as a spherical coil within a fibrous agarose gel produced much less accurate predictions. The diffusional permeabilities of these gels were assessed by combining the current partitioning data with relative diffusivities (Kd, the diffusivity in the gel divided by that in free solution) reported previously. The values of phi Kd for a synthetic gel with 8.0% agarose and 1.1% dextran (by volume) were found to be very similar to those for the glomerular basement membrane, a physiologically important material which also has a total solids content of approximately 10%.     

Effect of local microstructure on the indentation induced damage of a fiber reinforced composite

Multicycle grid nanoindentation tests, combined with high resolution Scanning Electron Microscopy (SEM) and Scanning Probe Microscopy (SPM) observations, were applied on a commercial Carbon Fiber (CF) reinforced epoxy matrix composite in order to study the induced damage mechanisms with respect to: (a) the orientation of the CFs relative to the surface and (b) the CF packing density. Normal to the surface CFs showed a multiple cracking pattern, those forming 45° showed distinct cracking, while CFs parallel to the surface did not suffer cracking. CF detachment from the epoxy matrix was observed in all cases. Pop-in type discontinuities were observed only in the samples where cracking ensued, as revealed through SEM and SPM observations. The load to induce CF cracking increased with increase of the matrix pocket area. Elastic modulus, hardness and significance of elastic deformation as an indentation energy absorbing mechanism, were reduced right after pop-in.     

Modification of cellulose nanocrystal-reinforced composite hydrogels: effects of co-crosslinked and drying treatment

The synthesis platform of composite hydrogels containing rigid reinforcing filler cellulose nanocrystals (CNCs) and polymer matrix polyacrylamide (PAM) has been proposed (Yang et al. in Cellulose 20:227–237, 2013). The features of CNCs as multifunctional crosslinkers and flexible polymer chain entanglements contributed to the unique arrangement of CNC/PAM clusters with reversible network structures. In this article, the chemical crosslinking agent N,N′-methylene-bisacrylamide (BIS) was added to obtain the dual crosslinked networks, and the mechanical properties of the resulting co-crosslinked hydrogels were examined by tailoring the CNC and BIS concentrations. The results indicated that the homogeneous dispersion of CNCs throughout the polymer matrix was disturbed in the presence of BIS, and the covalent crosslinkers led to weakness and brittleness of the hydrogels. Some new entanglements within the networks were formed after a simple drying treatment, which was verified by the greater tensile strength compared with the as-prepared ones. The mechanism for the formation of these new entanglements was ascribed to the irreversible rearrangement of the CNC/PAM network structure, whereas for co-crosslinked hydrogels no strength increment was observed after the drying treatment.     

Effects of crosslinker density on the polymer network structure in poly‐N,N‐dimethylacrylamide hydrogels

To investigate the effects of crosslinker density on the properties of hydrogels, compression tests, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and Raman measurements were performed on poly‐N,N‐dimethylacrylamide hydrogels. The results of the compression tests showed that the Young's modulus increases as the crosslinker density increases. To understand the mechanism of the change in the mechanical properties, the structures of the polymer networks and water and the molecular vibrations were analyzed using SEM, DSC, and Raman methods. From the SEM images, it was found that the porosity estimated from the mesh size and cell density increases with increasing crosslinker density. In addition, the DSC and Raman results show that the thickness of the bound water increases as the porosity increases, although the density of the polymer chains in the porous wall remains nearly constant. The increase in the number density of polymer chains can be one of the mechanisms contributing to the increase in the mechanical strength of the hydrogels at lower crosslinker density below 5 mol %, as proposed by previous studies. At higher crosslinker density, however, the number density of polymer chains does not increase with increasing crosslinker density. The present results suggest that the bound water plays an important role in strengthening the hydrogel. The water structure may be one of the dominant factors governing the chemical and physical properties of hydrogels. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1017–1027