Increase In Crosslinker Concentration Research Articles

Characteristics of Weak-Gel Flooding and Its Application in LD10-1 Oilfield.

Weak gel is a kind of three-dimensional cross-linking system with low polymer concentration and appropriate cross-linking agents, dominated by intermolecular cross-linking, supplemented by intramolecular cross-linking, and with a weak cross-linking degree. In this paper, the microstructure and properties of the weak gel were observed and evaluated under different conditions. Seepage behavior experiments and parallel core displacement experiments were carried out to evaluate profile control and flooding performance of the weak gel. Under a certain polymer concentration, with the increase in cross-linker concentration, the reticular structure of the weak gel becomes more uniform and the strength of the weak gel was further enhanced. Weak gel has more retention in porous media and greater strength. The profile control and flooding performance of the weak gel are much better than those of the polymer. A field test of weak-gel flooding was successfully carried out in LD10-1 oilfield. Most of the production wells around the weak gel injection wells responded after weak-gel injection and the accumulative oil incremental oil production of the test area was 57.8 × 104 m3 up to December 2018.

Fabrication and characterization of collagen-oxidized pullulan scaffold for biomedical applications

Pullulan, a naturally occurring polysaccharide was oxidized using sodium periodate and converted into its aldehyde derivative and used as a bio crosslinker for stabilizing collagen. The crosslinking mainly occurred due to Schiff's base reaction between amino group of lysine or hydroxylysine present in collagen with the aldehyde groups of oxidized pullulan. A known concentration of collagen was crosslinked with different concentrations of oxidized pullulan and scaffolds were prepared by freeze drying method. The crosslinking efficiency and biodegradation of the crosslinked scaffolds showed higher degree of crosslinking and slower degradation rate with increase in cross linker concentration. The surface morphology of scaffolds using SEM showed that the scaffolds with 3% concentration of crosslinker (Col-OxP-3) exhibited highly porous nature with interconnecting pores of 66.35 μm size compared to other groups, which was also supported by porosity and tensile strength measurement. The tensile strength was 10 times higher in Col-OxP-3 scaffold compared to native collagen. The swelling capacity of the scaffolds increased with increase in crosslinker concentration and the equilibrium was retained up to 60 min. The crosslinked scaffolds were non-toxic to 3T3 fibroblast cell line proving their biocompatible nature. Thus, this new class of bio-crosslinker can be used in replacement of synthetic crosslinkers for biomaterial synthesis.

Formulation and evaluation of interpenetrating network of xanthan gum and polyvinylpyrrolidone as a hydrophilic matrix for controlled drug delivery system

The prime objective of the present study was to develop novel colon targeting xanthan gum/polyvinylpyrrolidone-co-poly acrylic acid hydrogels for controlled delivery of 5-fluorouracil at colon-specific site by combining the properties of natural and synthetic polymers. Xanthan gum (XG) and polyvinylpyrrolidone (PVP) polymer have been chemically cross-linked with acrylic acid (AA) monomer using ethylene glycol dimethacrylate and ammonium per sulfate/sodium hydrogen sulfite as a cross-linker and initiator, respectively. Different proportions of XG, PVP, acrylic acid and ethylene glycol dimethacrylate were blended with each other to fabricate pH-sensitive hydrogels by free radical polymerization. SEM, FTIR, TGA, DSC, XRD and sol−gel fraction analysis were carried out for characterization and structural analysis of polymeric system. pH-responsive behavior of fabricated hydrogels was investigated by performing swelling studies and in vitro drug release studies at both pH 1.2 and pH 7.4. Toxicity studies were performed on rabbits to evaluate cytotoxicity and biocompatibility. TGA and DSC confirmed that formulations were thermodynamically stable, while FTIR, SEM and XRD revealed the successful grafting of components. By increasing the content of polymer, monomer and cross-linker, gel fraction was found to be increased. Swelling capacity of hydrogels increases with the increase in concentration of monomer, while swelling capacity tends to decreases with the increase in concentration of cross-linker and polymer in hydrogel composition. pH sensitivity of hydrogels was confirmed by swelling dynamic and drug release behavior in simulated gastrointestinal fluids. Toxicity studies confirmed that hydrogels were non-toxic. Drug release kinetics revealed the controlled release pattern of 5-fluorouracil in developed polymeric network. Cross-linked XG/PVP-co-poly (AA) hydrogels can be used as promising candidate for controlled delivery of 5-FU for prolonged treatment period at colon-specific site.

Characterization of Biodegradable Microsphere-Hydrogel Ocular Drug Delivery System for Controlled and Extended Release of Ranibizumab.

PurposeTo characterize a biodegradable microsphere-hydrogel drug delivery system (DDS) for controlled and extended release of ranibizumab.MethodsThe degradable microsphere-hydrogel DDSs were fabricated by suspending ranibizumab-loaded or blank poly(lactic-co-glycolic acid) microspheres within a poly(ethylene glycol)-co-(L-lactic-acid) diacrylate/N-isopropylacrylamide (PEG-PLLA-DA/NIPAAm) hydrogel. The thermal responsive behavior of various DDS formulations was characterized in terms of volume phase transition temperature (VPTT) and swelling ratios changes from 22°C to 42°C. The mechanical properties were characterized using rheological methods. Degradability of hydrogels were also examined via wet weight loss. Finally, Iodine-125 was used to radiolabel ranibizumab for characterization of encapsulation efficiency and in vitro release.ResultsAll DDS formulations investigated were injectable through a 28-gauge needle at room temperature. The VPTT increased with increase of cross-linker concentration. The swelling ratios decreased as temperature increased and were not influenced by presence of microspheres. Rheology data confirmed that increase of cross-linker concentration and microsphere loading made DDS stiffer. Increase of degradable cross-linker concentration facilitated hydrogel in vitro degradation. Controlled release of ranibizumab were achieved for investigated DDS formulations for 6 months; and increased degradable cross-linker concentration produced faster and more complete release.ConclusionsThe biodegradable DDSs are suitable for sustained release of ranibizumab. Considering ease of injection, degradability and release of ranibizumab, DDS with 3 mM cross-linker concentration and less than 20 mg/mL microsphere loadings is more favorable for future application.Translational RelevanceThe investigated DDS is promising for controlled and extended release of anti-VEGF therapeutics to achieve better treatment regimen in ocular neovascularizations.

Synthesis, Applications and Swelling Properties of Poly (Sodium Acrylate-Coacrylamide) Based Superabsorbent Hydrogels

Superabsorbent hydrogels constitute a group of polymeric materials with three-dimensional network structure, which can swell to absorb an enormous amount of water or aqueous solutions. This property enables various commercial applications of hydrogels such as water holding capability in agriculture and superabsorbent material for baby diapers. Several novel superabsorbent hydrogels based on acrylic acid-co-acrylamide copolymers were synthesized under variation of copolymer compositions through free radical polymerization. N,N’methylenebisacrylamide (MBA) was used as a water soluble crosslinker and potassium persulphate (KPS) as an initiator. Effect of varying the copolymer composition, change in crosslinker concentration, and effect of environmental parameters (pH, temperature, and ion concentration) on both swelling capacity and swelling rate were examined. These gel shows maximum swelling at neutral pH-7, whereas increasing salt concentration in water decrease the swelling capacity. It was found interesting that an increase in crosslinker concentration from 0.020% to 0.16%, the swelling capacity decreases up to 70% while the swelling rate increases from 0.007g water/g dry hydrogel sec to 0.024g water/g dry hydrogel sec, respectively because there is a compromise exists between entropic spring forces between network connection points and the hydrostatic pressure of the water diffusing into the gels. Dynamic swelling curve obtained were fitted to the three different kinetic models namely Peleg’s kinetic model, pseudo 1st order as proposed by Lagergen and pseudo 2nd order kinetics. All these models provided a good agreement with the experimental data; However on the bases of statistical parameters (RMSE, R2 and X2) the Peleg’s model was selected as the most appropriate model for this study. Analyzing rate constant for Peleg’s models at different swelling temperatures disclosed that increasing temperature could only increase the swelling rate without affecting the swelling capacity of the hydrogels. Experimental values for rate constant k1 of Peleg’s model at different temperature shows a sharp decrease from 0.57545 at 30 oC to 0.1535 at 75 oC that contemplated the rate of swelling at 75 oC was 65% faster than that of 30 oC. The diffusion mechanisms in hydrogels were proven to be tailorable by increasing cross-linker concentration and temperature, leading towards the Fickian type diffusion behavior. The synthesized superabsorbent hydrogels were also tested for water retention applications in agriculture.

Synthesis and evaluation of pH dependent hydrogels for controlled release of Venlafaxine HCl

pH dependent hydrogel formulations of venlafexine HCl were prepared by free radical polymerization method using polyethylene glycol as polymer. Various samples were prepared with varying concentration of polymer, monomer and cross-linker to study their effect on gel swelling, diffusion characteristics and drug release. Swelling was found to be increased with increase in pH. Increase in acrylic acid concentration increases swelling while increase in cross-linker concentration has an opposite effect on swelling. Drug release study was performed in pH 1.2, 5.5 and 7.5 for 12 hours at 37 oC and drug release was found to increase in higher pH. Prepared hydrogel preparations were also characterized by PXRD, TGA, SEM and FTIR.

Synthesis and evaluation of pH dependent polyethylene glycol-co-acrylic acid hydrogels for controlled release of venlafaxine HCl

pH dependent polyethylene glycol/acrylic acid(AA/PEG) hydrogels of an anti-depressant, venlafaxine hydrochloride were prepared by free-radical co-polymerization method, using benzyl peroxide (BPO) as initiator and methylene bisacrylamide (MBA) as cross-linker. Different formulations were prepared with varying concentration of polymer, monomer and cross-linker to study their effect on gel swelling, diffusion characteristics and subsequent drug release. Structural parameters of AA/PEG hydrogels were investigated by measuring diffusion co-efficient, volume fraction of polymer in the swollen state, effective molecular weight of polymer chain between cross-linking points, the number of links between two crosslink and solvent interaction parameters. Swelling coefficients were found to be increased with increase in pH i.e. minimum at pH 1.2 and maximum at pH 7.5. Increase in acrylic acid concentration increases swelling while increase in cross-linker concentration has an opposite effect due to denser structure. AA/PEG hydrogels were characterized by fourier-transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), X-Ray diffraction (XRD), thermo gravimetric analysis (TGA) to determine the polymer structure, its morphology and strength. Drug release studies performed at pH 1.2, 5.5 and 7.5 shows higher release at higher pH. Drug release was increased by increasing acrylic acid concentration and decreasing cross-linker concentration.

Interpenetrating networks of carboxymethyl tamarind gum and chitosan for sustained delivery of aceclofenac

The aim of present investigation was to characterize carboxymethyl tamarind gum (CMTG) based interpenetrating networks (IPNs) of aceclofenac for site specific sustained delivery. The drug loaded IPNs were prepared by using chitosan and CMTG as polymers and gluteraldehyde as crosslinking agent. The IPNs were characterized by Attenuated total reflectance- Fourier transform infrared (ATR-FTIR) spectroscopy, thermal analysis, X-ray powder diffraction and solid state 13C-nuclear magnetic resonance spectroscopy. The prepared IPNs were evaluated for the drug entrapment efficiency and equilibrium swelling. The drug release from IPNs was studied in 0.1NHCl for 2h followed by phosphate buffer pH 6.8 for further 10h and compared with commercial tablet. The results of ATR-FTIR and thermal analysis for blank IPNs indicated intercalation of polymeric chains of crosslinked CMTG and chitosan. The results of solid state characterization revealed that the aceclofenac is compatible with IPNs. Entrapment efficiency of IPNs was found to be increased with increase in crosslinker concentration as well as amount of CMTG. The equilibrium swelling study indicated pH dependent swelling of IPNs. The drug release by IPNs showed sustained release of aceclofenac upto 12h while commercial formulation showed fast release within 8h. From the results, it can be concluded that the IPNs of CMTG and chitosan has potential in development of site specific sustained drug delivery.

Graphene oxide–enriched double network hydrogel with tunable physico-mechanical properties and performance

An emerging approach to obtain polymeric hydrogels with superior properties is integrating carbon-based nanomaterials within their network structure. On the other hand, hydrogels with tailored physical and mechanical characteristics are desirable class of materials which have extensive application in drug delivery and tissue engineering. This study presents a strategy to achieve graphene oxide (GO)-enriched hydrogels with modulated physico-mechanical properties and performance. GO/poly acrylic acid (PAA)/gelatin hydrogels are fabricated via in situ polymerization method followed by chemical crosslinking of gelatin molecules. N,N′-Methylenebisacrylamide (BIS) in a various concentrations is used within the prepolymer composition as cross-linking agent to prepare a set of nanocomposite hydrogels. Fourier transform infrared (FTIR), X-ray diffraction (XRD), and atomic force microscopy (AFM) are utilized to characterize the fabricated hydrogel samples. The microstructure of samples is analyzed with scanning electron microscopy (SEM). The mechanical properties of the specimens are evaluated by rheometry. The swelling behavior, degradation kinetic and porosity of the hydrogels as well as their in vitro cytotoxicity are also assessed. The results show successful synthesis of nano GO sheets and polymer composites. The increase of cross-linker concentration is decreased the swelling ratio and increased the porosity of hydrogel samples. A wide range of pore diameters (70–300μm) and mechanical stiffness (storage modulus of 2000–25,000Pa) is obtained. Through manipulation of cross-linking density the degradation rate of nanocomposite hydrogels is controlled. Finally, no toxicity is detected by exposure of the hydrogel extracts to osteoblast osteosarcoma cells. The optimized hydrogel samples having appropriate range of physical characteristics and functionality suggest the application of the 3D structures as scaffold material for hard tissue construction.

Novel cross linked guar gum-g-poly(acrylate) porous superabsorbent hydrogels: Characterization and swelling behaviour in different environments

A new series of eco-friendly cross linked guar gum-g-poly(acrylate) porous superabsorbent hydrogels was prepared by in situ grafting polymerization and cross-linking on to a natural guar gum employing N,N-methylene bis acrylamide as cross linker. Morphological and structural characterization of the prepared hydrogels (SPHs) done by Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and solid state C13 NMR spectroscopy confirmed formation of porous grafted and crosslinked hydrogel structure. Increase in cross linker concentration in the feed mass exhibited decrease in porosity and increase in density of the hydrogels. Swelling of an optimized hydrogel (SPH) in response to external stimuli namely, salt solutions, fertilizer solutions, temperature, and pH exhibited high swelling ratios in various environments. Swelling rate of the SPH was faster than the corresponding nonporous superabsorbent hydrogel. The prepared hydrogels can serve as excellent carriers of pesticides, fertilizers and agriculturally important microbes. Biocontrol formulations based on a representative SPH exhibited excellent shelf-life characteristics and bioefficacy against phytopathogenic fungus Pythium aphanidermatum.

Designing galacturonic acid /arabinogalactan crosslinked poly(vinyl pyrrolidone)- co-poly(2-acrylamido-2-methylpropane sulfonic acid) polymers: Synthesis, characterization and drug delivery application

The polysaccharide tragacanth gum (TG) is generally recognized as safe by the Food and Drug Administration and it has been used as folk medicine in various gastrointestinal problems and has good adhesive property. In the present work attempt has been made to explore its potential in designing amoxicillin loaded slow delivery system for GIT infections based on galacturonic acid/arabinogalactan crosslinked poly(vinyl pyrrolidone)- co-poly(2-acrylamido-2-methylpropane sulfonic acid) polymers. These mucoadhesive polymer networks have been prepared by using poly(vinyl pyrrolidone) (PVP) and poly(2-acrylamido-2-methylpropane sulfonic acid) Poly(AMPSA). These polymers have been characterized by SEMs, FTIR, 13C NMR, XRD, TGA/DTA/DTG, DSC and swelling studies. Different kinetic models (i.e. zero order, first order, Higuchi square root law, Korsmeyer–Peppas model and Hixson–Crowell cube root) have been applied for drug release profile. The mechanical, biocompatible and mucoadhesive properties of polymers have also been determined. The polymer network parameters such as polymer volume fraction in the swollen state, Flory–Huggins interaction parameter, molecular weight of polymer chain between two cross-links, crosslink density and mesh size have been evaluated. Both, mesh size and molecular weight of the polymer chain between two neighboring cross links of hydrogels decreased with increase in crosslinker concentration. The drug release occurred through non-Fickian diffusion mechanism and release profile best fitted in the Higuchi square root model. The polymers have been observed as non-thrombogenic and mucoadhesive in nature and may be used in slow drug delivery applications to GIT.

Development of Mechanically Stable Polymer-Based Silica Aerogel

Silica aerogels have attracted attention for many applications due to their unique properties such as low density (0.003 g/cm), mesoporosity (pore size 2–50 nm), high thermal insulation and high surface area (500–1200 m2/g). However, their fragility and environmental sensitivity restricts the use of monolithic silica aerogel. In this paper, silica aerogel that is crosslinked with diisocyanate is introduced and the effects of polymer concentration on aerogel properties, especially mechanical strength are discussed. Fracture of silica aerogel mainly occurs at the interface of secondary particles that are formed during aging. It is believed that if the surface of silica aerogel is covalently bonded to nanocast polymer coating, the interparticle necks become wider and can reinforce the structure of the aerogel. In this study, several characterizations are performed to investigate the properties of the aerogel. First, bulk density is measured to visualize the change in density with increase in crosslinker concentration. Brunauer Emmett and Teller (BET) illustrated the pore size, bulk density and surface area. The critical temperature up to which polymer crosslinked aerogel decompose was investigated by Thermogravimetric Analysis (TGA). The phase change in the aerogel was studied with Differential Scanning Calorimetry (DSC) testing. Using Scanning Electron Microscope (SEM), the nanoscale pore size and pore distribution throughout the aerogel surface were investigated. Furthermore, compression tests were performed to study the effect of crosslinking polymer on mechanical strength over non-crosslinked framework.

Effect of crosslinker concentration on characteristics of superporous hydrogel

Aim:Synthesis of superporous hydrogel with different concentrations of crosslinker was carried out using solution polymerization to study its effect on characteristics of superporous hydrogel. Methylene-bis-acrylamide was used as a crosslinker.Materials and Methods:The characterization studies were performed by measurement of apparent density, porosity, swelling studies, mechanical strength studies, and scanning electron microscopy analysis. Results and Discussion: As the concentration of crosslinker increased from 7.37% to 14.36 % the porosities decreased. In double distilled water, superporous hydrogels showed good increase in equilibrium swelling capacity compared to that in simulated gastric fluid. Scanning electron microscopic images clearly indicated the formation of interconnected pore and capillary channels. Characterization studies revealed that the increase in crosslinker concentration is beneficial from the mechanical stability point of view, but at the same time the decrease in porosity may lead to decrease in drug release rate by diffusion through these capillary channels. Batches B1 and B2 with low concentrations of crosslinker provide good porous structure, swelling characteristics, and mechanical strength appropriate for further applications of superporous hydrogel-based drug delivery systems.Conclusion:The concentration of crosslinker affects the porous structure, swelling characteristics and mechanical strength. By setting appropriate degree of crosslinking it is possible to prepare superporous hydrogel having desired characteristics, which will provide a platform to design the drug delivery systems based on it.

Controlled release formulations of carbaryl based on copper alginate, barium alginate, and alginic acid beads

AbstractA controlled release system for reducing environmental impact was produced by encapsulating the pesticide carbaryl (Carb) in the alginate beads. The various bead formulations were prepared by using sodium alginate (NaAlg) as a polymer, CuCl2, BaCl2 as a crosslinking agent, and HCl as a linking agent. The surface morphology of prepared beads was characterized with scanning electron microscopy (SEM). SEM confirmed the spherical nature and surface morphology of the particles. Bead characteristics, such as Carb entrapment efficiency, particle size, swelling degree, and Carb release kinetics, were determined. The effects of crosslinker or linker concentration, type, and carbaryl/sodium alginate (Carb/NaAlg) ratio on Carb release from the beads were investigated for 20 days at 25°C. It was observed that Carb release from the beads increased with the increase of Carb/NaAlg ratio whereas decreased with the increase of crosslinker concentration. At the end of 20 days, the Carb release from alginic acid beads was found to be higher than that of copper alginate (Cu‐Alg) and barium alginate (Ba‐Alg) beads. The swelling measurements of the beads supported the release results. Release kinetics were described by Fickian and non‐Fickian approaches. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4245–4253, 2006

Studies of crosslinked poly(AM-MSAS-AA) gels. I. Synthesis and characterization

Novel superabsorbent copolymers were prepared from acrylamide (AM), sodium methallylsulfonate (MSAS), sodium acrylate (AA), and N,N′-methylenebisacrylamide (BisA) in aqueous solution using potassium persulfate (KPS)/N,N,N′,N′-tetramethylethylenediamine (TMEDA) as the redox initiator. The copolymers were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The experimental results show that absorbency increases with an increase in crosslinker concentration but decreases with excessive crosslinking. The ionic groups in the polymer network significantly increase the equilibrium swelling. Water retention at pressures of 1–10 kg/cm2 and temperatures of 60 and 100°C are also reported. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1001–1007, 1997

Study on the morphology and properties of interpenetrating polymer networks of poly (zinc acrylate) and polyacrylonitrile

A series of semi-interpenetrating polymer networks (IPNs) based on poly(zinc acrylate) and polyacrylonitrile were synthesized by a sequential mode of synthesis. The IPNs were characterized by scanning electron microscopy, i.r. spectroscopy and by measuring crosslink density. Divinyl benzene was used as the crosslinking agent for acrylonitrile, and azobisisobutyronitrile as initiator. Variation in composition of the IPN was achieved by varying the concentration of polymer, monomer, crosslinker, initiator and the viscosity average molecular weight of polymer, and their effects on morphology and crosslinking were examined. The increase in concentration of linear polymer and initiator decreases crosslinking were examined. The increase in concentration of linear polymer and initiator decreases crosslinking and increases incompatibility, while the increase in concentration of crosslinker increases both crosslinking and phase separation.