Exceptionally Fast Temperature-Responsive, Mechanically Strong and Extensible Monolithic Non-Porous Hydrogels: Poly(N-isopropylacrylamide) Intercalated with Hydroxypropyl Methylcellulose

Exceptionally fast temperature-responsive, mechanically strong, tough and extensible monolithic non-porous hydrogels were synthesized. They are based on divinyl-crosslinked poly(N-isopropyl-acrylamide) (PNIPAm) intercalated by hydroxypropyl methylcellulose (HPMC). HPMC was largely extracted after polymerization, thus yielding a 'template-modified' PNIPAm network intercalated with a modest residue of HPMC. High contents of divinyl crosslinker and of HPMC caused a varying degree of micro-phase-separation in some products, but without detriment to mechanical or tensile properties. After extraction of non-fixed HPMC, the micro-phase-separated products combine superior mechanical properties with ultra-fast T-response (in 30 s). Their PNIPAm network was highly regular and extensible (intercalation effect), toughened by hydrogen bonds to HPMC, and interpenetrated by a network of nano-channels (left behind by extracted HPMC), which ensured the water transport rates needed for ultra-fast deswelling. Moreover, the T-response rate could be widely tuned by the degree of heterogeneity during synthesis. The fastest-responsive among our hydrogels could be of practical interest as soft actuators with very good mechanical properties (soft robotics), while the slower ones offer applications in drug delivery systems (as tested on the example of Theophylline), or in related biomedical engineering applications.

Biobased Epoxy Composites Reinforced with Acetylated Corn Straw

Corn straw/epoxy resin composites (CS/ECs) and maleic anhydride acetylated CS/ECs (MA-CS/ECs) were prepared through dry mixing and high-temperature curing. Corn straw is a kind of abundant, eco-friendly, and low-cost biomass material. Unmodified and modified corn straws were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The interfacial affinity of the composite was testified by the contact angle. The results of XPS and SEM demonstrated that maleic anhydride had been successfully bonded onto the structure of corn straw. Corn straw particle-reinforced epoxy resin composites were prepared using a casting and molding process. Results showed that the MA-CS/EC had better impact and flexural resistance than the unmodified corn straw/epoxy resin composites when the corn straw addition was 15 wt %. The result of the contact angle showed that the interfacial compatibility between composites is also stronger than that of CS/EC.

Cellulose/nanocellulose superabsorbent hydrogels as a sustainable platform for materials applications: A mini-review and perspective

Superabsorbent hydrogels (SAH) are crosslinked three-dimensional networks distinguished by their super capacity to stabilize a large quantity of water without dissolving. Such behavior enables them to engage in various applications. Cellulose and its derived nanocellulose can become SAHs as an appealing, versatile, and sustainable platform because of abundance, biodegradability, and renewability compared to petroleum-based materials. In this review, a synthetic strategy that reflects starting cellulosic resources to their associated synthons, crosslinking types, and synthetic controlling factors was highlighted. Representative examples of cellulose and nanocellulose SAH and an in-depth discussion of structure-absorption relationships were listed. Finally, various applications of cellulose and nanocellulose SAH, challenges and existing problems, and proposed future research pathways were listed.

BiFeO3 immobilized within liquid natural rubber-based hydrogel with enhanced adsorption-photocatalytic performance

Semiconductor materials have shown a good photocatalytic behaviour for the photodegradation of organic pollutants. In this work, maleated liquid natural rubber (MLNR) based hydrogel supported bismuth ferrite (BiFeO₃) as photocatalyst was successfully synthesized by crosslinking with acrylic acid (AAc) assisted by the ultrasonication method to study the efficiency for the removal of methylene blue (MB) dye in wastewater. Response surface methodology (RSM) was used to optimize the parameters for adsorption of the methylene blue (MB) dye compound, whereby the effects of the initial concentration of MB and the adsorption time were examined to obtain a quadratic model for the respective hydrogel composite. The prepared composite sample was characterized by Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy-Energy Dispersive X-ray (SEM-EDX) and X-ray Diffraction (XRD) analysis. Remarkable improvement for removal of methylene blue (99% removal) was found within 3 h adsorption time with a MLNR/AAc-BiFeO₃ hydrogel composite as compared to the pristine hydrogel. A synergistic mode of dye removal by adsorption and photodegradation is proposed. Based on the isotherm and kinetic study conducted, it was found that Freundlich isotherm model and a pseudo second-order kinetic model was best fitted for adsorption of MB dye. The MLNR/AAc-BiFeO₃ composite maintains its removal efficiency after 5 cycles without the necessity of post-treatment separation. Therefore, it is crucial to note that the resultant low-cost MLNR/AAc-BiFeO₃ hydrogel composite in this study offers excellent potential for water and wastewater treatment applications with improved recyclability and recovery.

Synthesis and application of eco-friendly superabsorbent composites based on xanthan gum and semi-coke

An eco-friendly superabsorbent composites of xanthan gum-g-polyacrylic acid/semi-coke (XG-g-PAA/SC) were fabricated via grafting of polyacrylic acid onto the XG in the presence of SC. The obtained products were characterized in combination with Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The result indicated that the SC interacted with the polymeric network by hydrogen bond or electrostatic interaction. The swelling ratio of the best sample XG-g-PAA/SC (15 wt%) in distilled water and 0.9 wt% NaCl solution was 410.8 and 61.5 g/g by optimizing the polymerization conditions. In addition, compared with the blank sample (only containing soil), it can be found that adding a certain amount of XG-g-PAA/SC can significantly improve the soil water retention efficiency, which can be further proved by the results of plant pot experiment. Based on the above excellent swelling capacity, water holding capacity and plant growth promoting performance, it can be inferred that the XG-g-PAA/SC is expected to become a water retaining agent or soil regulator for plant growth.

Preparation and Characterization of Superabsorbent Polymers Based on Sawdust

Sawdust, a cheap by-product of the timber and forestry industry, was considered as a framework structure to prepare superabsorbent polymer with acrylic acid (AA) and acrylamide (AM), the synthetic monomers. The effects of initiator content, crosslinker content, AA content, AM content, degree of neutralization of AA, and reaction temperature on the swelling rate of superabsorbent polymer were investigated. The synthesized polymer was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). Under optimal synthesis conditions, the results showed that the swelling rate of the polymer in deionized water and 0.9% NaCl solution reached 738.12 and 90.18 g/g, respectively. The polymer exhibits excellent swelling ability, thermal stability, and reusability. After the polymer was introduced into the samples (soil or coal), the water evaporation rate of the samples was significantly reduced, and the saturated water holding capacity and pore structure were also significantly improved.

Lauric Acid-Modified Nitraria Seed Meal Composite as Green Carrier Material for Pesticide Controlled Release

To alleviate the adverse effects of pesticide residues on the environment, development of a more safe, economical, and reliable usage approach of pesticides is critically urgent. In the present study, a novel pesticide carrier LA-NSM (lauric acid-modified Nitraria seed meal) with controlled release property was prepared through grafting esterification of lauric acid onto Nitraria seed meal substrates. The structure of the obtained samples was characterized by Fourier-transform infrared spectroscopy, scanning electron microscopy, and contact angle measurements. The results indicated that LA-NSM products had a well-defined hydrophobic surface and irregular holes for efficient loading of pesticide molecules. Deltamethrin (DEL), a representative insoluble pyrethroid insecticide in water, was deliberately selected as the index pesticide to evaluate the loading and releasing efficiency of LA-NSM. The loading capacity of LA-NSM for DEL can reach about 1068 mg/g. pH, humidity of soil, and temperature had a significant influence on controlled release performance of LA-NSM@DEL. Moreover, the releasing kinetics of LA-NSM@DEL composites could be fitted well with the Higuchi model. Overall, the highly hydrophobic property, excellent loading, and controlled release ability of LA-NSM made it a promising candidate in agricultural applications.

Cellulose-Based Absorbent Production from Bacterial Cellulose and Acrylic Acid: Synthesis and Performance

Cellulose-based superabsorbent was synthesized by bacterial cellulose (BC) grafting acrylic acid (AA) in the presence of N,N′-methylenebisacrylamide (NMBA) as a crosslinker and ammonium persulfate (APS) as an initiator. The influence of different factors on composite synthesis, including the weight ratio of the monomer to BC, initiator content, crosslinker content, AA neutralization degree, reaction temperature, and reaction time on the water absorbency of the composite, were systematically learned. Under the optimized conditions, the maximum water absorbency of the composite was 322 ± 23 g/g distilled water. However, the water absorbency was much less for the different salt solutions and the absorption capacity of the composite decreased as the concentration of the salt solutions increased. The pH value had a significant influence on water absorption performance, and with the increase of temperature, the water retention rate of the composite decreased. Additionally, the structure of this composite was characterized with nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The results of NMR and FT-IR provided evidence that the composite was synthesized by BC and AA, and the microstructure showed that it had good performance for water absorption. In addition, the composite possessed suitable thermal stability, and that it could be used in a few high-temperature environments. Overall, this composite is promising for application in water absorption.

Ultrasonic-assisted synthesis of superabsorbent hydrogels based on sodium lignosulfonate and their adsorption properties for Ni2

Nowadays, the attention of both academic and industrial research is paid to the novel materials based on renewable organic resources. Sodium lignosulphonate (SLS) is selected in this study to synthesize novel superabsorbent hydrogels by ultrasonic polymerization. The structure, morphology and stability of SLS-based hydrogel were confirmed by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). Under the optimal condition, SLS-based hydrogel possesses the water absorbency of 1328g·g^-1 in distilled water and 110g·g^-1 in 0.9wt% NaCl solution. In addition, the prepared SLS-hydrogel as an adsorbent was applied to remove Ni²⁺ from an aqueous solution in virtue of its low cost and favorable adsorption capacity. The various experimental conditions that influence the adsorption capacity were investigated such as temperature (20-60°C), pH (2.0-7.0), contact time (0-360min) and initial concentration of the Ni²⁺ solution (100-600mg·L^-1). Then the adsorption capability could reach 293mg·g^-1 under optimal conditions. The results revealed that the adsorption behavior is spontaneous and endothermic. Furthermore, it was observed that the adsorption mechanism and adsorption equilibrium data obeyed pseudo-second-order kinetic and Freundlich models.

Fabrication of phytic acid-modified wheat straw platform and its pH-responsive release performance for the pesticide imidacloprid

For the effective utilization of pesticides and the treatment of abundant waste wheat straw (WS) resources, an eco-friendly composite PA-WS platform was prepared by modification of WS with phytic acid (PA).

Microwave-assisted one-step synthesis and characterization of a slow release nitrogen fertilizer with inorganic and organic composites

Microwave-assisted one-step synthesis of a novel high-performance slow release nitrogen fertilizer with inorganic and organic composites.

Synthesis of adipic acid dihydrazide-decorated coco peat powder-based superabsorbent for controlled release of soil nutrients

We firstly employ adipic acid dihydrazide as an outstanding decoration substrate for the pretreatment of CP, and then synthesis a novel superabsorbent through grafting AA onto MA modified CP@ADH surface.

Facile fabrication of sea buckthorn biocarbon (SB)@α-Fe2O3 composite catalysts and their applications for adsorptive removal of doxycycline wastewater through a cohesive heterogeneous Fenton-like regeneration

Novel SB@α-Fe₂O₃ composite catalysts were fabricated through a simple thermal conversion process from SB@β-FeOOH precursor, which maintained good adsorption capacity after five successive adsorption/heterogeneous Fenton-like regeneration cycles.

Synthesis and properties of the rapeseed meal-grafted-poly(methyl methacrylate-co-butyl acrylate) oil-absorbents

Economical RSMs-g-P(MMA-co-BA) oil-absorbents with 3D network structures were prepared through free radical graft copolymerization, which exhibited good oil absorbency, reusability and were applied to oil/water separation.

Synthesis, characterization, and swelling behaviors of salt-sensitive maize bran-poly(acrylic acid) superabsorbent hydrogel

A novel composite hydrogel was prepared via UV irradiation copolymerization of acrylic acid and maize bran (MB) in the presence of composite initiator (2,2-dimethoxy-2-phenylacetophenone and ammonium persulfate) and cross-linker (N,N'-methylenebis(acrylamide)). Under the optimized conditions, maize bran-poly(acrylic acid) was obtained (2507 g g(-1) in distilled water and 658 g g(-1) in 0.9 wt % NaCl solution). Effects of granularity, salt concentration, and various cations and anions on water absorbency were investigated. It was found that swelling was extremely sensitive to the ionic strength and cation and anion type. Swelling kinetics and water diffusion mechanism in distilled water were also discussed. Moreover, the product showed excellent water retention capability under the condition of high temperature or high pressure. The salt sensitivity, good water absorbency, and excellent water retention capability of the hydrogels give this intelligentized polymer wide potential applications.

Boronic acid shell-crosslinked dextran-b-PLA micelles for acid-responsive drug delivery

Herein, 3-carboxy-5-nitrophenylboronic acid (CNPBA) shell-crosslinked micelles based on amphiphilic dextran-block-polylactide (Dex-b-PLA) are prepared and used for efficient intracellular drug deliveries. Due to the reversible pH-dependent binding with diols to form boronate esters, CNPBA modified Dex-b-PLA shows excellent pH-sensitivity. In neutral aqueous conditions, CNPBA-Dex-b-PLA forms shell-crosslinked micelles to enable DOX loading, while in acid conditions, the boronate esters hydrolyze and the micelles de-crosslink to release loaded DOX. In vitro release studies indicate that the release of the DOX cargo is minimized at physiological conditions, while there is a burst release in response to low pHs. The cell viability of CNPBA-Dex-b-PLA investigated by MTT assay was more than 90%, indicating that, as a drug delivery system, CNPBA-Dex-b-PLA has good cytocompatibility. These features suggest that the pH-responsive biodegradable CNPBA-Dex-b-PLA can efficiently load and deliver DOX into tumor cells and enhance the inhibition of cellular proliferation in vitro, providing a favorable platform as a drug delivery system for cancer therapy.

Ultrasonic synthesis and properties of a sodium lignosulfonate–grafted poly(acrylic acid-co-acryl amide) composite super absorbent polymer

We presented a quick and efficient way (ultrasonic method) to prepare a green and high quality superabsorbent.