Physical Crosslinking Research Articles

Dual cross‐linked self‐healing temperature and pressure sensor based on PAM/ENR/h‐BN composite

AbstractSensor of monitor of temperature and pressure changes are garnering constant attention due to their wide applications. It is a challenge to synthesize dual‐functional material with the well‐balanced performance to temperature response and pressure changes. In this work, we have proposed a facile way to fabricate tough, flexible, and self‐healing composite with dually synergistic networks for pressure and temperature sensors, which are composed of polyacrylamide (PAM) and elastic epoxidized natural rubber (ENR). PAM networks are crosslinked by N,N‐methylenebisacrylamide (MBA) and physical crosslinking of hydrophilic hexagonal boron nitride (h‐BN) nanosheets, ENR network is further interlocked and PAM by physical entanglements, hydrogen bonds. It is found that the ternary PAM/ENR/h‐BN (PEB) composite is highly sensitive to temperature, making it can be exploited as a thermistor. This thermistor possesses high flexibility and appealing mechanical performance, with the sensitivity as high as 1.87%/°C at temperature range of −13 to 90°C. Furtherly, the PEB composite also can work as a flexible pressure sensor at operating range of ~80% strain and ~540 KPa. Our research work provides a guideline for the preparation of temperature monitor, piezoresistive pressure sensors, as well as flexible electronic products.

Dual dynamic bonds approach for polyurethane recycling and self-healing of emulsified asphalt

To recycle polyurethane and extend the service life of polyurethane-modified emulsified asphalt, this study developed novel perspectives for a lower carbon-footprint and cleaner preparation of recyclable polyurethane (RWPU) and its modified emulsified asphalt (RPUA-x) by using self-emulsification and dual dynamic bonds. Particle dispersion and zeta potential tests reflected that the emulsions of RWPU and RPUA-x existed excellent dispersion and storage stability. Microscopic and thermal analyses indicated that RWPU possessed dynamic bonds and maintained thermal stability below 250 °C as anticipated. Concurrently, RWPU provided RPUA-x with a strong physical cross-linking network, and a homogeneous phase was observed in RPUA-x after drying. Self-healing and mechanical evaluation results revealed that the regeneration efficiencies of RWPU were 72.3 % (stress) and 100 % (strain), respectively, and the stress-strain healing efficiency of RPUA-x was >73 %. The energy dissipation performance and plastic damage principle of RWPU were investigated using cyclic tensile loading. The multiple self-healing mechanisms of RPUA-x were revealed through microexamination. Furthermore, the viscoelasticity of RPUA-x and variations in flow activation energy were determined based on Arrhenius fitting from dynamic shear rheometer tests. In conclusion, disulfide bonds and hydrogen bonds endow RWPU with remarkable regenerative properties and grant RPUA-x with both asphalt diffusion self-healing and dynamic reversible self-healing capabilities.

Interfacing reduced graphene oxide with an adipose-derived extracellular matrix as a regulating milieu for neural tissue engineering.

Enthralling evidence of the potential of graphene-based materials for neural tissue engineering is motivating the development of scaffolds using various structures related to graphene such as graphene oxide (GO) or its reduced form. Here, we investigated a strategy based on reduced graphene oxide (rGO) combined with a decellularized extracellular matrix from adipose tissue (adECM), which is still unexplored for neural repair and regeneration. Scaffolds containing up to 50wt% rGO relative to adECM were prepared by thermally induced phase separation assisted by carbodiimide (EDC) crosslinking. Using partially reduced GO enables fine-tuning of the structural interaction between rGO and adECM. As the concentration of rGO increased, non-covalent bonding gradually prevailed over EDC-induced covalent conjugation with the adECM. Edge-to-edge aggregation of rGO favours adECM to act as a biomolecular physical crosslinker to rGO, leading to the softening of the scaffolds. The unique biochemistry of adECM allows neural stem cells to adhere and grow. Importantly, high rGO concentrations directly control cell fate by inducing the differentiation of both NE-4C cells and embryonic neural progenitor cells into neurons. Furthermore, primary astrocyte fate is also modulated as increasing rGO boosts the expression of reactivity markers while unaltering the expression of scar-forming ones.

Hydrogel Drug Delivery Systems for Bone Regeneration.

With the in-depth understanding of bone regeneration mechanisms and the development of bone tissue engineering, a variety of scaffold carrier materials with desirable physicochemical properties and biological functions have recently emerged in the field of bone regeneration. Hydrogels are being increasingly used in the field of bone regeneration and tissue engineering because of their biocompatibility, unique swelling properties, and relative ease of fabrication. Hydrogel drug delivery systems comprise cells, cytokines, an extracellular matrix, and small molecule nucleotides, which have different properties depending on their chemical or physical cross-linking. Additionally, hydrogels can be designed for different types of drug delivery for specific applications. In this paper, we summarize recent research in the field of bone regeneration using hydrogels as delivery carriers, detail the application of hydrogels in bone defect diseases and their mechanisms, and discuss future research directions of hydrogel drug delivery systems in bone tissue engineering.

Intrinsically Healable Fabrics

AbstractWearable electronics with healability have been extensively researched recently. To provide wearing comfort, fabrics are often adopted as the base materials. Intrinsic healability, however, is challenging for fabrics because of the inability to retain the fibrous morphologies. Herein, an unprecedented strategy is presented for producing electrospun fabrics that are intrinsically healable by carefully balancing the crystalline structural support and healing ability. Fluorocarbon polymers with different crystallinities are mixed with ionic liquids to form ionogels, which are spun into fabrics using a unique wet electrospinning apparatus. Importantly, the introduction of the crystalline domains prevents the fusion of the electrospun fibers; even after 1 year, no significant morphological change is observed. The nonwoven fabrics are not only stretchable and waterproof but also intrinsically healable. The ion–dipole interactions between the polar copolymers and ionic liquids provide the reversible physical crosslinking essential to the healing capability. When damaged, the fabrics can be overlapped and healed after applying pressure. Moreover, the fabrics demonstrate healability underwater. Healable sensing devices, pressure, and tensile sensors are also designed by printing ion‐conductive gels as electrodes. Both devices show good stability before and after healing. This work demonstrates the first example of intrinsically healable electrospun fabrics, which are promising for fabric‐based wearable electronics and smart clothing.

Isolating the Effect of Crosslink Densities on Mechanical Properties of Isotactic Polypropylene Using Dissipative Particle Dynamics

AbstractGiven the importance of preserving the mechanical properties of recycled isotactic polypropylene (iPP) during its processing, this work provides an improved understanding of the contribution of introducing physical or chemical crosslinks using the dissipative particle dynamics (DPD) method, which makes it possible to model iPP structures with a realistic range of crosslink densities. First, the protocol to build a coarse‐grained model of iPP from an all‐atom expression by Bayesian optimization is described. A Bayesian optimization procedure employing two different cutoff distances successfully provides optimal DPD parameters reproducing iPP's properties compared to the all‐atom system. Then, the coarse‐grained iPP model with optimal DPD parameters is applied to study structures containing a realistic range of crosslink densities to evaluate their mechanical properties. These calculations demonstrate that the mechanical properties such as the Young's modulus and ultimate strength increase while the fracture strain decreases with an increase in the crosslink density, which is consistent with experimental observations. The results also show that there is a critical crosslink density above which these properties start to be improved due to the introduction of crosslinks. These findings can help us to obtain targeted properties of recycled iPP by introducing physical or chemical crosslinks.

Mechanically robust, creep resistant and malleability retentive elastomer vitrimer enabled by integrating hydrogen bonds and boronic easters

Vitrimer, featured with many fascinating properties, is a novel class of polymer, since their network topologies can be rearranged at elevated temperatures without the loss of crosslinking density. Although remarkable advances have been achieved in vitrimers, some of the published vitrimers are liable to creep and their mechanical strength are not always satisfied the specific applications. Herein, toward this issue, dual-crosslinked elastomer vitrimer was prepared by implanting supramolecular hydrogen bonds and exchangeable boronic esters into one single network. In detail, commercialized styrene butadiene rubber was firstly modified by N-Acetylglycine (NAg) to implant building blocks of hydrogen bonds, and subsequently crosslinked by dimercaptoborate (BDB) to introduce exchangeable boronic esters into vitrimer networks. The hydrogen bonds arisen between the grafted NAg moieties can function as physical crosslinks, thereby improve the overall mechanical properties remarkably by reversible breaking and reformation events. Besides, the hydrogen bonds crosslinks impose additional constraints on network strand diffusion, resulting in an improve the creep resistance. Moreover, the malleability and reprocessibility were not deteriorated by hydrogen bonds, as they can dissociate at high temperatures.

Mussel‐mimetic chitosan based injectable hydrogel with fast-crosslinking and water-resistance as tissue adhesive

It is very crucial to develop ideal tissue adhesive materials with high toughness, super tissue adhesion, biodegradability and biocompatibility for the treatment of accidental trauma and surgery. Inspired by mussels, a novel injectable bioadhesive chitosan-based hydrogel was developed by dual-ionic crosslinking in this paper, which was composed of catechol-modified chitosan (Cat-CS), thermosensitive polymer (PNAM) and NaHCO3. The gelation time of Cat–CS–PNAM/NaHCO3 hydrogel is 50 s at 37 °C, showing good sol-gel transition under different temperatures. The prepared hydrogels have the ability to adhere to a variety of materials surface, wherein the adhesion strength to metal surface is 126.20 ± 15.17 kPa. They also possess compact microstructure and excellent dry/wet adhesion to tissues due to the interaction between catechol/amino groups and tissues, combined with physical crosslinking. In addition, the hydrogels can be completely degraded after 14 days in vitro and show good cytocompatibility. This newly designed mussel-inspired chitosan hydrogels have the characteristics of injectability, fast gelation, bioadhesion and biocompatibility, with great potential for application in biomedical fields.

Glutathione-Responsive Tannic Acid-Assisted FRET Nanomedicine for Cancer Therapy.

In cancer combination therapy, a multimodal delivery vector is used to improve the bioavailability of multiple anti-cancer hydrophobic drugs. Further, targeted delivery of therapeutics along with simultaneous monitoring of the drug release at the tumor site without normal organ toxicity is an emerging and effective strategy for cancer treatment. However, the lack of a smart nano-delivery system limits the application of this therapeutic strategy. To overcome this issue, a PEGylated dual drug, conjugated amphiphilic polymer (CPT-S-S-PEG-CUR), has been successfully synthesized by conjugating two hydrophobic fluorescent anti-cancer drugs, curcumin (CUR) and camptothecin (CPT), through an ester and a redox-sensitive disulfide (-S-S-) linkage, respectively, with a PEG chain via in situ two-step reactions. CPT-S-S-PEG-CUR is spontaneously self-assembled in the presence of tannic acid (TA, a physical crosslinker) into anionic, comparatively smaller-sized (~100 nm), stable nano-assemblies in water in comparison to only polymer due to stronger H-bond formation between polymer and TA. Further, due to the spectral overlap between CPT and CUR and a stable, smaller nano-assembly formation by the pro-drug polymer in water in presence of TA, a successful Fluorescence Resonance Energy Transfer (FRET) signal was generated between the conjugated CPT (FRET donor) and conjugated CUR (FRET acceptor). Interestingly, these stable nano-assemblies showed a preferential breakdown and release of CPT in a tumor-relevant redox environment (in the presence of 50 mM glutathione), leading to the disappearance of the FRET signal. These nano-assemblies exhibited a successful cellular uptake by the cancer cells and an enhanced antiproliferative effect in comparison to the individual drugs in cancer cells (AsPC1 and SW480). Such promising in vitro results with a novel redox-responsive, dual-drug conjugated, FRET pair-based nanosized multimodal delivery vector can be highly useful as an advanced theranostic system towards effective cancer treatment.

Immunoregulatory hydrogel decorated with Tannic acid/Ferric ion accelerates diabetic wound healing via regulating Macrophage polarization

Diabetic wound management still faces great challenges mainly due to immune disorders at wound area. Especially, macrophage polarization toward M2 phenotype is severely inhibited at the inflammatory stage. Thus, targeted regulation of macrophage polarization could be a useful approach to normalize the immune environment of diabetic wound to accelerate wound healing. Herein, a composited hydrogel derived from natural polymers, as an immunoregulatory dressing, was fabricated to treat diabetic wound. The composited hydrogel (GBTF) was synthesized by one step photo-polymerization of gelatin methacrylate (GelMA), Bletilla Striata polysaccharide (BSP) and tannic acid/ferric iron complex (TA/Fe3+). Attributed to the chemical and physical cross-linking, the GBTF hydrogel exhibited adequate mechanical properties. Thanks to the photothermal transition of TA/Fe3+ in GBTF, good antibacterial capacity was achieved. Meanwhile, the polyphenol in TA could help to attenuate excessive ROS and induce macrophage polarization toward M2 phenotype. Furthermore, the potential immunoregulatory mechanism of the GBTF hydrogel was investigated through RNA sequencing in vitro. In addition, BSP showed positive contribution in vascularization. In vivo, results from diabetic wound model showed that the wound treated by GBTF hydrogel presented the fastest closure rate, superior granulation tissue regeneration, re-epithelialization and collagen deposition. These results indicated GBTF hydrogel rapidly promoted wound healing through anti-inflammation and pro-angiogenesis. The GBTF hydrogel showed great potential to serve as promising dressing for treatment of diabetic wounds in clinic.

Characterization and formation mechanisms of high tensile strength gliadin films prepared by bi-crosslinking and blending

Different methods have been used to fabricate gliadin (Gli) films with high tensile strength (TS) and functional performances. In this study, the bi-crosslinked Gli-films were fabricated by Schiff base bonds and disulfide bonds crosslinking to improve their TS and other properties, which were also blended by chitosan (CS). The overall performances of mechanics, water-resistance and stability, barrier, as well as their formation mechanisms, were fully investigated. Results showed that the Gli-films possessed excellent mechanical performances, and CS further improved the TS of Gli-films but decreased their elongation. The bi-crosslinking effect also enhanced the water vapor barrier performance, CO2 barrier performance, water-resistance, and long-term stability in water of Gli-films via both chemical (Schiff base bonds and disulfide bonds) and physical (hydrophobic bonds) crosslinking. These will highlight the applications of plant proteins and provide a theoretical and practical foundation for the fabrication of protein-based packaging with high TS.

High-Expansion Open-Cell Polylactide Foams Prepared by Microcellular Foaming Based on Stereocomplexation Mechanism with Outstanding Oil-Water Separation.

Biodegradable polylactic acid (PLA) foams with open-cell structures are good candidates for oil-water separation. However, the foaming of PLA with high-expansion and uniform cell morphology by the traditional supercritical carbon dioxide microcellular foaming method remains a big challenge due to its low melting strength. Herein, a green facile strategy for the fabrication of open-cell fully biodegradable PLA-based foams is proposed by introducing the unique stereocomplexation mechanism between PLLA and synthesized star-shaped PDLA for the first time. A series of star-shaped PDLA with eight arms (8-s-PDLA) was synthesized with different molecular weights and added into the PLLA as modifiers. PLLA/8-s-PDLA foams with open-cells structure and high expansion ratios were fabricated by microcellular foaming with green supercritical carbon dioxide. In detail, the influences of induced 8-s-PDLA on the crystallization behavior, rheological properties, cell morphology and consequential oil-water separation performance of PLA-based foam were investigated systemically. The addition of 8-s-PDLA induced the formation of SC-PLA, enhancing crystallization by acting as nucleation sites and improving the melting strength through acting as physical cross-linking points. The further microcellular foaming of PLLA/8-s-PDLA resulted in open-cell foams of high porosity and high expansion ratios. With an optimized foaming condition, the PLLA/8-s-PDLA-13K foam exhibited an average cell size of about 61.7 μm and expansion ratio of 24. Furthermore, due to the high porosity of the interconnected open cells, the high-absorption performance of the carbon tetrachloride was up to 37 g/g. This work provides a facile green fabrication strategy for the development of environmentally friendly PLA foams with stable open-cell structures and high expansion ratios for oil-water separation.

Fabrication of high-strength and multi-recyclable supramolecular polysiloxane by incorporating quadruple hydrogen bonds into main-chains for adhesive and oil-water separation

Studies are currently exploring strategies for development of recyclable materials that do not rely on petrochemical resources to alleviate increased environmental pollution. Polysiloxane is a non-toxic and non-hazardous polymeric material that is not produced from petrochemical resources, but has limited application due to its poor mechanical properties. In the present study, a novel supramolecular polysiloxane (SPSO) with excellent mechanical properties, exceptional reprocessing molding, and superior multiple recyclability was fabricated through incorporation of 2-ureido-4[1H]-pyrimidinone (UPy) into the main chains. The quadruple hydrogen bond interaction of UPy induces the aggregation of UPy, leading to phase separation and physical crosslinking in the SPSO. The rigid hard phase region acts as a reinforcing filler to further enhance the mechanical strength of the SPSO. The maximum tensile strength of the material was 7.28 MPa, which was significantly higher than that of traditional silicone rubber at 0.5 MPa. The mechanical properties of the SPSO retained 100% of the original properties even after three generations of recycling, indicating excellent multiple recyclability. The material exhibited excellent adhesive properties due to the high number of hydrogen bonds. The maximum adhesive strength of the SPSO to wood was 4.8 MPa. SPSO composite sponge was prepared by adding chopped carbon fiber reinforcement. The superhydrophobic SPSO composite sponge had a high water contact angle of 153°, indicating that it can be used for oil-water separation. The maximum separation efficiency of the material was 96%. A simple and versatile approach was used to introduce hydrogen bonds into the backbone of polysiloxane to form physical cross-links and enhance microphase separation. The findings from this study provide a basis for constructing polysiloxane materials with high recyclability and strong mechanical properties.

Temperature Responsive Diblock Polymer Brushes as Nanoreactors for Silver Nanoparticles Catalysis.

Metal nanoparticles are widely used in catalysis. Loading metal nanoparticles into polymer brushes has aroused wide attention, but regulation of catalytic performance still needs to be improved. The novel diblock polymer brushes, polystyrene@sodium polystyrene sulfonate-b-poly (N-isopropylacrylamide) (PSV@PSS-b-PNIPA) and PSV@PNIPA-b-PSS with reversed block sequence, were prepared by surface initiated photoiniferter-mediated polymerization (SI-PIMP) and used as nanoreactors to load silver nanoparticles (AgNPs). The block sequence caused the difference of conformation and further affected the catalytic performance. PSV@PNIPA-b-PSS@Ag was found to be able to control the amount of AgNPs exposed to external reactant of 4-nitrophenol at different temperatures to achieve regulation of the reaction rate due to the hydrogen bonds and further physical crosslinking between PNIPA and PSS.

Chitosan particles modulate the properties of cellulose nanocrystals through interparticle interactions: Effect of concentration

The physical and chemical properties of cellulose nanocrystals (CNC) were regulated by physical crosslinking with chitosan particles (CSp). At a fixed concentration (0.5 wt%) of CNC, varying CSp concentration (0.02–0.5 wt%) influenced the morphologies and chemical properties of the obtained complex particles (CNC-CSp). The results of Fourier transform infrared spectroscopy (FTIR) and zeta potential confirmed the electrostatic and hydrogen bonding interactions between CSp and CNC. At a low CSp concentration (0.02–0.05 wt%), the charge shielding effect induced the formation of particle aggregation networks, thus showing increased viscosity, turbidity and size (153.4–2605.7 nm). At a higher CSp concentration (0.1–0.5 wt%), the hydrogen bonding interaction promoted CSp adsorption onto the surface of CNC, thus facilitating the dispersion of CNC-CSp due to electrostatic repulsion caused by surface-adsorbed CSp. In addition, CSp improved the thermal stability, hydrophobicity (41.87–60.02°) and rheological properties of CNC. Compared with CNC, CNC-CSp displayed a better emulsifying ability and emulsion stability, in which CSp could play a dual role (i.e., charge regulator and stabilizer). This study suggests that introducing CSp can improve the properties and application potentials of CNC as food colloids.

Multifunctional edible chitin nanofibers/ferulic acid composite coating for fruit preservation

AbstractAbout one‐third of the world's entire food production is lost or wasted every year, in which the perishables such as fruits and vegetables account for the largest proportion due to their short shelf life. Therefore, it has attracted great attention to the development of food preservation. In this paper, a simple strategy for food preservation is developed. Chitin nanofiber aqueous suspension is used as the substrate, and ferulic acid (FA) acts as the physical crosslinker to obtain a multifunctional composite protective coating for fruits. The results of Zeta potential, X‐ray photoelectron spectroscopy (XPS) and X‐ray diffraction (XRD) indicate that there are multiple noncovalent interactions between FA and chitin nanofibers. The chitin/FA coating films show superior mechanical properties, water and oxygen resistance. They could effectively reduce the water loss rate, delay ripening, and resist oxidation and microbial invasion for the fresh strawberries and fresh‐cut apples, indicating the potential in food preservation.

Synthesis and Characterization of Biodegradable Poly(vinyl alcohol)-Chitosan/Cellulose Hydrogel Beads for Efficient Removal of Pb(II), Cd(II), Zn(II), and Co(II) from Water

Globally, water contamination by heavy metals is a serious problem that affects the environment and human health. Adsorption is the most efficient way of water treatment for eliminating heavy metals. Various hydrogels have been prepared and used as adsorbents to remove heavy metals. By taking advantage of poly(vinyl alcohol) (PVA), chitosan (CS), cellulose (CE), and the process for physical crosslinking, we propose a simple method to prepare a PVA-CS/CE composite hydrogel adsorbent for the removal of Pb(II), Cd(II), Zn(II) and Co(II) from water. Structural analyses of the adsorbent were examined by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy-energy dispersive X-ray (SEM-EDX) analysis, and X-ray diffraction (XRD). PVA-CS/CE hydrogel beads had a good spherical shape together with a robust structure and suitable functional groups for the adsorption of heavy metals. The effects of adsorption parameters such as pH, contact time, adsorbent dose, initial concentration of metal ions, and temperature on the adsorption capacity of PVA-CS/CE adsorbent were studied. The adsorption characteristics of PVA-CS/CE for heavy metals may be completely explained by pseudo-second-order adsorption and the Langmuir adsorption model. The removal efficiency of PVA-CS/CE adsorbent for Pb(II), Cd(II), Zn(II), and Co(II) was 99, 95, 92, and 84%, respectively, within 60 min. The heavy metal's hydrated ionic radius may be crucial in determining the adsorption preference. After five consecutive adsorption-desorption cycles, the removal efficiency remained over 80%. As a result, the outstanding adsorption-desorption properties of PVA-CS/CE can potentially be extended to industrial wastewater for heavy metal ion removal.

Nonlinear Viscoelasticity and Toughening Mechanisms in Nanoclay-PNIPAAm Double Network Hydrogels.

We investigate the mechanical properties of a magnetic temperature-sensitive hydrogel at varying concentrations of covalent and physical cross-linking. The hydrogel consists of covalently cross-linked poly(N-isopropylacrylamide) (PNIPAAm), physically interacting nanoclay particles, and magnetic ferric oxide nanoparticles. The physical nanoclay network exhibits strong viscoplastic behavior, and we find that increasing nanoclay content improves both strength and toughness in the double network materials. We investigate the behavior of the gels using a nonlinear viscoplasticity model with a modified rule of mixtures approach and attribute the observed trends to two factors: (a) the yield-stress behavior of the nanoclay network and (b) load-sharing interactions between the PNIPAAm and the nanoclay. Our findings indicate a strong correlation between the mass ratio of covalent cross-linker used and fractional percolation of the PNIPAAm network.

Highly Stretchable, Repairable, and Tough Nanocomposite Hydrogel Physically Cross-linked by Hydrophobic Interactions and Reinforced by Surface-Grafted Hydrophobized Cellulose Nanocrystals.

Highly stretchable, repairable, and tough nanocomposite hydrogels are designed by incorporating hydrophobic carbon chains to create first-layer cross-linking among the polymer matrix and monomer-modified polymerizable yet hydrophobic nanofillers to create second-layer strong polymer-nanofiller clusters involving mostly covalent bonds and electrostatic interactions. The hydrogels are synthesized from three main components: hydrophobic monomer DMAPMA-C18 by reacting N-[3-(dimethylamino)propyl]methacrylamide] (DMAPMA) with 1-bromooctadecane, monomer N,N-dimethylacrylamide (DMAc), and monomer-modified polymerizable hydrophobized cellulose nanocrystal(CNC-G) obtained by reacting CNC with 3-trimethoxysily propyl methacrylate. The polymerization of DMAPMA-C18 and DMAc and physical cross-linking due to the hydrophobic interactions between C18 chains make DMAPMA-C18/DMAc hydrogel. The additional introduction of CNC-G brings more interactions into the final hydrogel (DMAPMA-C18/DMAc/CNC-G): the covalent bonds between CNC-G and DMAPMA-C18/DMAc, hydrophobic interactions, electrostatic interactions between negatively charged CNC-G and positively charged DMAPMA-C18, and hydrogen bonds. The optimum DMAPMA-C18/DMAc/CNC-G hydrogel exhibits excellent mechanical performance with elongation stress of 1085 ± 14kPa, strain of 4106 ± 311%, toughness of 3.35×104 kJ m-3 , Young's modulus of 844kPa, and compression stress of 5.18MPa at 85% strain. Besides, the hydrogel exhibits good repairability and promising adhesive ability (83-260kN m-2 toward various surfaces).

An ultralight and flexible nanofibrillated cellulose/chitosan aerogel for efficient chromium removal: Adsorption-reduction process and mechanism

Heavy metals in water are critical global environmental problems. In particular, the anionic heavy metal chromium (Cr) has carcinogenic and genotoxic risks on human health. To this end, an ultralight and flexible nanofibrillated cellulose (NFC)/chitosan (CS) aerogel was developed only by freeze-drying combined with physical thermal cross-linking for efficient one step co-removal of Cr(VI) and Cr(III). The maximum adsorption capacity of Cr(VI) and total Cr calculated according to the Langmuir model was 197.33 and 134.12 mg/g, respectively. Even in the presence of competing soluble organics, anions and oil contaminants, the resulting NFC/CS-5 aerogels showed excellent selectivity. The aerogel exhibited outstanding mechanical integrity, remaining intact after 17 compressions in air and underwater. Meanwhile, after 5 adsorption-desorption cycles, the aerogel was easy to regenerate and maintained a high regeneration efficiency of 80.25%. Importantly, self-assembled NFC/CS-5 aerogel filter connected with the peristaltic pump could purify 752 mL of industrial wastewater with Cr(VI) pre-concentration capacity of 49.71 mg/g. XPS and FT-IR verified that electrostatic interactions, reduction and complexation acted as the main driving forces for the adsorption process. Moreover, such aerogel possessed broad application prospects for alleviating heavy metal pollution in agriculture.