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Poly(acrylic acid) (PAAc) hydrogels are essential functional materials. However, their mechanical properties do not meet the required standards. In this study, a one‐pot method is employed to prepare cellulose‐reinforced PAAc hydrogels by dissolving allyl cellulose (AC) in acrylic acid (AAc) solutions. Fourier transform infrared (FTIR), solid‐state 13C nuclear magnetic resonance (NMR), and thermogravimetric (TG) analysis are used to demonstrate that the incorporation of AC results in the formation of covalent and hydrogen bonds, which contribute to the crosslink network of the PAAc hydrogels. Significantly, by modifying the ratio of AC to AAc in the pre‐polymerization solution, the prepared AC–PAAc hydrogels exhibit a transition from transparent to opaque. This suggests that phase separation is induced by hydrogen bonding. The occurrence of phase separation is verified by observing the hydrogel microstructures using scanning electron microscopy. Phase separation leads to enhanced polymer–polymer interactions in the hydrogels, resulting in a maximum fracture stress of 2.34 MPa. The AC–PAAc hydrogels display distinct swelling behavior under various pH conditions. Moreover, they demonstrate differences in transparency and mechanical properties when exposed to dimethyl sulfoxide (DMSO) and water, indicating their responsiveness to solvents. This work demonstrates the great potential of enhancing the mechanical performance and responsiveness of PAAc hydrogels. A one‐pot method is employed to prepare cellulose‐reinforced poly(acrylic acid) (PAAc) hydrogels by dissolving allyl cellulose (AC) in acrylic acid solutions. Both covalent interactions and hydrogen bonding are formed between AC and PAAC, and a maximum fracture stress of 2.34 MPa is obtained for the hydrogels.

To prepare superabsorbent hydrogels, starch-graft-poly(acrylic acid) reinforced by cellulose nanofibers (CNF), was synthesized through free radical graft polymerization. The results of its biocompatibility tests exhibited that by increasing incubation time from 1 to 5 days, the numbers of living cells were increased on both reinforced and unreinforced hydrogels. However, the fraction of cells on the surfaces of the reinforced hydrogel is comparable to unreinforced samples. The swelling amounts in NaCl, CaCl2, and AlCl3 solutions were 193 ± 9, 110 ± 8, and 99 ± 7 (gwater/gabsorbent) for 5 wt% CNF-reinforced hydrogels and 109 ± 8, 62 ± 7, and 56 ± 6 (gwater/gabsorbent) for unreinforced hydrogels, respectively. Compressive strength and Young’s modulus of 5 wt% CNF-assisted hydrogels were also 63.3 and 31.6 kPa corresponding to 69% and 140% improvements compared with unreinforced one. The graft polymerization of acrylic acid monomer was controlled by monomer content and cross-linking percentage, in order to achieve the highest swelling capacity for hydrogels. Hydrogel swelling in water was 312 gwater/gabsorbent for unreinforced hydrogel and 523 gwater/gabsorbent for 5 wt% CNF-reinforced sample and water absorption kinetics results was in agreement with the pseudo-second-order model. The prepared CNF-reinforced starch-graft-poly(acrylic acid) hydrogels can be used in a wide range of medical application due to the enhanced hydrophilicity, mechanical strength, and biocompatibility.Graphic abstract

Iron-based magnetic nanoparticles (MNPs) have attracted considerable attention as promising draw solutes in forward osmosis processes due to various advantages. In the present study, magnetite (Fe 3 O 4 ) nanoparticles (MNPs) with diameters in the range of 12 ± 2 nm were synthesized by applying the coprecipitation method and stabilized using (3-aminopropyl)triethoxysilane (APTES). The amino groups of APTES were further functionalized with various amounts of citric acid (CA) and poly(acrylic acid) (PAA) to achieve higher osmotic pressure. The as-prepared and functionalized nanoparticles were characterized using different methods: Fourier-transform infrared spectroscopy (FTIR) confirmed the binding of APTES and CA/PAA on the surface of the MNPs, while the size of the particles was determined by transmission electron microscopy (TEM) and X-ray powder diffraction. The isoelectric point, zeta potential, and the particle size in suspension were determined by dynamic light scattering (DLS)/zeta potential measuring system. The amount of free –COOH groups was determined by conductometric titrations. The amount of organic matter (APTES, CA, and PAA) bound on the surface was determined by thermogravimetric analysis (TG), giving results between 7.6% for samples stabilized with APTES only and 17.5% for samples functionalized with APTES + PAA. TG provides a simple and efficient method for determining the amount of organic compounds bound to the surface of MNPs. The osmotic pressure measurements of double-layer coated MNPs provided encouraging results of up to 28 bar, enabling using the samples as draw solutions in an experimental forward osmosis system.

Heavy metal contaminants have attracted widespread attention due to their severe toxicity and bioaccumulation. In this study, a novel graphene (EG)/molybdenum disulfide (MoS 2 ) modified with poly (acrylic acid) (PAA) composites (EG/MoS 2 /PAA) were successfully synthesized via a one-step hydrothermal method and effectively removed Pb(II) , Zn(II) , and Cd(II) ions from wastewater. The incorporation of PAA within the EG/MoS 2 significantly improved sorption ability. The EG/MoS 2 /PAA composite was characterized using XRD, FTIR, TEM, Raman, SEM–EDS, EIS, and cyclic voltammetry, which confirmed the successful synthesis of the EG/MoS 2 /PAA composite. The adsorption isotherm and kinetic of Pb(II), Zn(II), and Cd(II) were fitted with the Temkin isotherm and pseudo-second-order model, respectively. The maximum adsorption capacities (q max ) obtained using the Langmuir model were 47.13 mg/g for Pb(II) at pH 5, while 12.59 and 12.89 mg/g for Zn(II) and Cd(II) at pH 7. In the presence of interfering cations (i.e., Na + , Cu 2+ , Co 2+ , Fe 3+ , and Mg 2+ ), the EG/MoS 2 /PAA adsorbent exhibited high selectivity and excellent reusability after three cycles. The adsorption mechanism of Pb(II), Zn(II), and Cd(II) onto the EG/MoS 2 /PAA composite surface was found to be primarily controlled by complexation and electrostatic interaction. This novel EG/MoS 2 /PAA adsorbent has excellent suitability for practical application in the treatment of highly contaminated wastewater.

pH-sensitive polyampholyte microgels of poly(acrylic acid-co-vinylamine) (P(AA-co-VAm)) were developed as an injectable hydrogel for controlled drug release. The microgels of P(AA-co-VAm) were prepared via inverse suspension polymerization of acrylic acid and N-vinylformamide followed by hydrolysis of poly(N-vinylformamide) (PNVF) chains of the resultant microgels under basic condition. The pH-sensitivity of the P(AA-co-VAm) microgels in zeta potential and swelling ratio were investigated using a zeta potential analyzer and optical microscope. The results showed that both the zeta potential and the swelling ratio of the microgels were highly affected by the solution pH. By changing the pH of P(AA-co-VAm) microgel dispersion, the interparticle interaction and the swelling ratio of the microgels could be well adjusted and a colloidal hydrogel could be fabricated at moderate pH, showing a pH-triggered reversible fluid-gel transition. Using the polyampholyte P(AA-co-VAm) microgels as an injectable hydrogel drug release system, a sustained drug release could be achieved, indicating the great potentials of the pH-sensitive P(AA-co-VAm) microgels for controlled drug delivery.

Global challenges in agriculture, in terms of water and nutrient loss control, require new approaches to maintaining or even increasing crop production. Promising materials, such as superabsorbent hydrogels of hybrid types obtained from natural polymers grafted with synthetic polymers, represent a viable solution to solve these problems and maintain a clean environment. In view of this, two types of hydrogels based on sodium alginate, acrylic acid and polyethylene oxide obtained using 5.5 MeV electron-beam irradiation were subjected to degradation through burial in the soil. Swollen hydrogels in two types of water (distilled and tap) and two types of nutrient solutions (synthetic nutrient solution and 100% natural organic nutrient solution), with different pHs of 5.40, 6.05, 7.45 and 7.66, were buried in soil for 30 and 60 days and then extracted and analyzed in terms of their mass loss, swelling behavior and cross-linking structure. The highest mass losses after both 30 and 60 days were recorded for the hydrogels buried in soils whose humidity was maintained by watering them with the basic solutions (tap water and the organic nutrient solution). Structural modifications associated with the degradation process were highlighted by decreases in the cross-link densities and increases in the mesh sizes and swelling. These results were confirmed using FTIR and SEM techniques.

Nettle and the sage herbs were used to obtain carbonaceous adsorbents. For the biochar preparation the precursors were dried and subjected to conventional pyrolysis. Activated carbons were obtained during precursor impregnation with phosphoric(V) acid and multistep pyrolysis. The textural parameters and acidic-basic properties of the obtained adsorbents were studied. The activated carbons prepared from the above herbs were characterized by the largely developed specific surface area. The obtained carbonaceous adsorbents were used for polymer removal from aqueous solution. Poly(acrylic acid) (PAA) and polyethylenimine (PEI) were chosen, due to their frequent presence in wastewater resulting from their extensive usage in many industrial fields. The influence of polymers on the electrokinetic properties of activated carbon were considered. PAA adsorption caused a decrease in the zeta potential and the surface charge density, whereas PEI increased these values. The activated carbons and biochars were used as polymer adsorbents from their single and binary solutions. Both polymers showed the greatest adsorption at pH 3. Poly (acrylic acid) had no significant effect on the polyethylenimine adsorbed amount, whereas PEI presence decreased the amount of PAA adsorption. Both polymers could be successfully desorbed from the activated carbons and biochar surfaces. The presented studies are innovatory and greatly required for the development of new environment protection procedures.

Concrete is vital for the development of modern buildings. However, they suffer from the high viscosity problem in their application process due to the use of a low water–cement ratio in order to maintain their high strength. Developing PCEs with the presence of ester functional groups in their molecular structure is one of the most effective measures to improve the flowability of concrete. Here, three PCEs with different alkyl densities of acrylic acid ester: PCE-M, PCE-E, and PCE-B were designed to explore their viscosity-reducing effect on the performance of cement and concrete. The structures of the three PCEs were characterized via Fourier transform infrared (FTIR) spectra, proton nuclear magnetic resonance (1H NMR), and gel permeation chromatography (GPC). Their properties were also determined via zeta potential, surface tension, and rheological experiments. It was found that PCE-M had the best performance, with the lowest surface tension, highest zeta potential, and therefore highest charge density on the cement particles, lowest viscosity, and highest flowability of cement paste, and exhibited the best performance of concrete in terms of workability. The best performance of PCE-M in reducing the viscosity of cement and concrete can be ascribed to the smallest amount of water-repellent alkyl groups, enhancing the electrostatic repulsion and reducing the viscosity, thereby boosting the dispersion and stabilization of cement pastes and concrete. This study shed lights on designing other PCEs with high viscosity-reducing effects via an ester group control.

Background: Poly(acrylic acid) (PAA) is a water-soluble synthetic polymer with tissue-adhesive properties. When PAA is mixed with polyvinylpyrrolidone (PVP) in water, it forms a water-insoluble precipitate that neither swells nor adheres to tissues. Methods and Results: We developed a novel solid/solution interface complexation method to obtain a water-swellable PAA/PVP complex. First, PAA solution was dried up in a vessel to form a film. The PAA film was then immersed in an aqueous PVP solution to obtain a highly swollen PAA/PVP hydrogel. Heat drying of the hydrogel yielded a transparent film, while freeze-drying the hydrogel provided a soft sponge. Both the PAA/PVP film and sponge could be re-swelled by water to obtain a bioadhesive gel. A relatively larger specific surface area of the sponge than that of the film led to a more rapid swelling and water absorption behavior and quick adhesion to tissues. The addition of hyaluronic acid (HA) improved the mechanical characteristics of the sponges. PAA/PVP/HA sponges had low cytotoxicity, and they exhibited high hemostatic efficiency in clinical studies after dialysis treatment or tooth extraction, even in patients on antithrombotic drugs. Conclusions: Such bioadhesive materials consisting of low-toxicity polymers have a high potential for use in medical hemostatic devices.

In this study, simultaneous adsorption of cationic dyes was investigated by using binary component solutions. Thiourea-modified poly(acrylonitrile-co-acrylic acid) (TMPAA) polymer was used as an adsorbent for uptake of cationic dyes (malachite green, MG and methylene blue, MB) from aqueous solution in a binary system. Adsorption tests revealed that TMPAA presented high adsorption of MG and MB at higher pH and higher dye concentrations. It suggested that there are strong electrostatic attractions between the surface functional groups of the adsorbent and cationic dyes. The equilibrium analyses explain that both extended Langmuir and extended models are suitable for the description of adsorption data in the binary system. An antagonistic effect was found, probably due to triangular (MG) and linear (MB) molecular structures that mutually hinder the adsorption of both dyes on TMPAA. Besides, the kinetic studies for sorption of MG and MB dyes onto adsorbent were better represented by a pseudo-second-order model, which demonstrates chemisorption between the polymeric TMPAA adsorbent and dye molecules. According to experimental findings, TMPAA is an attractive adsorbent for treatment of wastewater containing multiple cationic dyes.