Systematic Evaluation of a Novel Self-Healing Poly(acrylamide-co-vinyl acetate)/Alginate Polymer Gel for Fluid Flow Control in High Temperature and High Salinity Reservoirs

Preferential fluid flow often occurs when water and CO₂ is injected into mature oilfields, significantly reducing their injection efficiency. Particle gels have been evaluated and applied to control the short circulation problems. This study systematically investigated a novel poly(acrylamide-co-vinyl acetate)/alginate-based interpenetrated gel system (Alg-IPNG) which is designed to control the preferential fluid flow problems in high-temperature reservoirs. Chromium acetate was incorporated into the gel system to provide the delayed crosslinking feature of the particle gels. The alginate polymer system can also take advantage of the Ca²⁺ ions in the formation water, which exist in most reservoirs, to reinforce its strength by capturing the Ca²⁺ to form Ca–alginate bonds. In this paper, various characterizations for the Alg-IPNGs before and after the self-healing process were introduced: (1) the elastic modulus is set at up to 1890 Pa, and (2) the water uptake ratio is set at up to 20. In addition, we also discuss their possible self-healing and reinforcement mechanisms. In particular, the self-healing starting time of the Alg-IPNG particles are modified between 38 to 60 h, which is related to the water uptake ratio, Ca²⁺ concentration, and temperature. The reinforced Alg-IPNG gel has an enhanced thermal stability (180 days) at the temperature up to 110 °C.

Chitosan modifications for adsorption of pollutants - A review

In recent times, research interest into the development of biodegradable, cost-effective and environmental friendly adsorbents with favourable properties for adsorption of pollutants is a challenge. Modification of chitosan via different physical and chemical methods have gained attention as a promising approach for removing organic (such as dyes and pharmaceuticals) and inorganic (such as metal/metal ions) pollutants from aqueous medium. In this regard, researchers have reported grafting and cross-linking approach among others as a potentially useful method for chitosan's modification for improved adsorption efficiency with respect to pollutant uptake. This article reviews the trend in chitosan modification, with regards to the summary of some recently published works on modification of chitosan and their adsorption application in pollutants (metal ion, dyes and pharmaceuticals) removal from aqueous medium. The review uniquely highlights some common cross-linkers and grafting procedures for chitosan modification, their influence on structure and adsorption capacity of modified-chitosan with respect to pollutants removal. Findings revealed that the performance of modified chitosan for adsorption of pollutants depends largely on the modification method adopted, materials used for the modification and adsorption experimental conditions. Cross-linking is commonly utilized for improving the chemical and mechanical stabilities of chitosan but usually decreases adsorption capacity of chitosan/modified-chitosan for adsorption of pollutants. However, literature survey revealed that adsorption capacity of cross-linked chitosan based materials have been enhanced in recently published works either by grafting, incorporation of solid adsorbents (e.g metals, clays and activated carbon) or combination of both prior to cross-linking.

Preparation of Chitosan-grafted-Polyvinyl acetate Metal Nanocomposite for producing Multifunctional Textile Cotton Fabrics

Chitosan-g-polyvinyl acetate (Cs-g-PVAc) was synthesized successfully using redox copolymerization using potassium persulfate as initiator. TiO₂ and TiO₂ doped ZnO which previously prepared by sol-gel technique added for preparing emulsion from polymer - metal oxide nanocomposites. Cotton fabrics were treated with prepared emulsions using citric acid and sodium hypophosphite. XRD measurements prove that the prepared TiO₂ nanoparticles corresponded to anatase phase with average crystallite size d = 15.98 nm where the crystallinity and crystallite size decreased for Zn doped TiO₂ where d = 11.7 nm. FTIR indicates that the exhibition of grafting process and formation polymer metal oxide nanocomposite. Samples treated with Copolymer showed the highest antibacterial properties. However, the copolymer doped with TiO₂ and TiO₂/ZnO showed lowest contact angle and affects positively on its photocatalytic performance. SEM and TEM micrographs confirmed that the prepared metal oxides are in nano scales, where TiO₂ is smaller than TiO₂/ZnO which effects on the band gap of TiO₂/ZnO to be larger than TiO₂ and consequently decreased on the photocatalytic properties TiO₂/ZnO of samples compared to TiO₂ sample under the halogen lamp.

Preparation and Properties of Copolymer of Methacrylic Acid and Acrylamide onto Degraded Chitosan Initiated by HRP/H2O2/ACAC

The chitosan was degraded by hydrochloric acid and the effects of concentration of chitosan, amount of hydrochloric acid, reaction temperature and reaction time on the viscosity of chitosan were investigated. The results showed that the degraded chitosan with low viscosity could be prepared when chitosan (wt 6%) was dissolved in acetic acid solution and hydrochloric acid (wt 3%) at 90°C for 6 h to decrease the viscosity from 7.52 mPa·s to 2.48 mPa·s. Then, a graft copolymer was synthesized by copolymerization of degraded chitosan with methacrylic acid (MAA) and acrylamide (AAM) by using horseradish peroxidase (HRP)/H2O2/acetylacetone (ACAC) as initiator. The structures of original chitosan, degraded chitosan and the copolymer were characterized by FTIR. The copolymer was applied to the leather industry as an amphoteric retanning agent. The applied results showed that the retanned leather had the merits of good uniformity fullness softness, strong selecting filling properties, good dyeing ability and antimicrobial activity.

Chromium (VI) ion adsorption features of chitosan film and its chitosan/zeolite conjugate 13X film

This research evaluated the importance of the adsorption properties of chitosan a chitosan/zeolite conjugate film for the removal of Cr(VI) ions from solutions in the 5–260 mg/L concentration range, when the pH was adjusted to 4.0 and 6.0. The uptake capacities of the films formed by chitosan and by the chitosan/zeolite conjugate were calculated by mass balance. The equilibrium isotherms were fitted to the Langmuir, Freundlich and Redlich-Peterson models. The chitosan film seems to be a good sorbent for Cr(VI) at pH 4, but its physical instability suggests the need for a more resilient support. Due to this fact zeolite was added to the chitosan matrix in solution and a chitosan/zeolite (CS/Zeo) film was thus formed. The solubility of the film and the characterization of the different matrices by FTIR, TGA and X-Ray showed that a cross-linked structure was formed between the chitosan and zeolite and the solubility of the film increased. In this study, the low manufacturing cost of the CS/Zeo matrix, the good uptake of Cr(VI) at acidic pH (17.28 mg/g) and the non desorption of Cr(VI) from the film in water suggests this combination should be tested in industrial environment.