Citric Acid Crosslinking Research Articles

Cellulose fiber drainage improvement via citric acid crosslinking

Wheat straw, as a non-wood fiber waste, is available worldwide and can be used in cellulosic matric production, promoting the application of sustainable materials. However, poor fiber properties and water drainage are the primary obstacles to its utilization. In this study, wheat straw pulp fibers were chemically crosslinked by citric acid (CA) in an environmentally friendly process. X-ray photoelectron spectroscopy and Fourier transform infrared spectra confirmed that the chemical treatment introduced carboxylic groups to cellulose fibers. Meanwhile, X-ray diffraction patterns showed that the crystallinity of cellulose was reduced. The average fiber length and water retention value of the pulp decreased with increasing CA dosage under the conditions of 3 mL/g CA4 (4 wt% CA), and the drainage performance of the cellulose pulp improved by 21 %. Also, the crosslinking of fibers contributed to the mechanical properties of the cellulosic matrix, increasing the dry and wet strength by 21 % and 282 %, respectively. These results demonstrated that citric acid could be a sustainable method for improving the properties of wheat straw fibers, thereby promoting its application in fabricating sustainable materials.

Effective synthesis and characterization of citric acid cross-linking of modified ferrous metal-organic framework and chitosan nanocomposite sponge for Th(IV) elimination: Adsorption isotherms, kinetic analysis, and optimization by Box-Behnken design

This research presents a novel nanocomposite of ferrous metal-organic framework (Fe(II)-MOF) that has been encapsulated with chitosan matrix, leading to the development of a new adsorbent referred to as NH2-Fe(II)-MOF@CSC composite sponge. This composite sponge has shown effectiveness in removing radioactive thorium (IV) contamination from water sources. The adsorbent underwent characterization using techniques including FTIR, PXRD, BET analysis, and SEM. The adsorbent has a high surface area of 1360.8 m2/g. The most effective conditions for adsorbing Th(IV) were found to be a pH of 5, using 0.02 g of adsorbent dose per 25 mL, and maintaining a contact time of 100 min. The composite sponge demonstrated an impressive maximum adsorption capacity of 618.8 mg/g for Th(IV). The adsorption process was fitted to Langmuir isothermally and kinetically fitted to pseudo-second-order. Nonetheless, the relatively low adsorption energy of 6.22 kJ/mol suggests that the main adsorption mechanism is physisorption, which is marked by weaker van der Waals forces. This discovery could have implications for the material's potential for easy regeneration. In the analysis of the influence of temperature on the adsorption of Th(IV), it was discovered that the adsorption process is endothermic because the positive ΔHo value was 24.48 kJ.mol−1. Furthermore, a positive ΔSo value of 87.46 J.mol−1 K−1 suggests the existence of disorder at the solid-solution interface. Conversely, a temperature rise resulted in a higher negatively charged ΔGo, indicating that the adsorption process is spontaneous. The research also examined the mechanism of interaction, such as π-π interaction, hydrogen bonding, pore filling, and electrostatic interaction. It was noted that the adsorbent can be efficiently used for a maximum of six cycles, demonstrating its economic viability. The adsorption outcomes were optimized using the Box Behnken design (BBD).

A Nontoxic and Biocompatible Method for Augmenting Mechanical Strength of Acellular Matrix by Silk Fibroin Impregnation.

Biological scaffolds are plagued by poor biomechanical properties and untimely degradation. These limitations have yet to be addressed without compromising their biocompatibility. It is desirable to avoid inflammation and have degradation with concomitant host collagen deposition or even site-appropriate in situ regeneration for the successful outcome of an implanted biological scaffold. This work aims to achieve this by utilizing a biocompatible method to modify acellular scaffolds by impregnating alkaline-catalyzed citric acid (CA) cross-linking between the extracellular matrix proteins and silk fibroin (SF)/SF-gelatin (SFG) blends. Combinatorial detergent decellularization was employed to prepare a decellularized porcine liver scaffold (DPL). After proving the decellularization efficiency, the scaffold underwent modification by vacuum impregnation with CA containing SF (SF100DPL) and SFG blends (SFG5050DPL and SFG3070DPL) following pre-cross-linking, drying, and post-cross-linking. The subsequent strength augmentation was demonstrated by significant improvement in tensile strength from 2.4 ± 0.4 MPa (DPL) to, 3.8 ± 0.7 MPa (SF100DPL), 3.4 ± 0.7 MPa (SFG5050DPL), and 3.5 ± 0.2 MPa (SFG3070DPL); Young's modulus from 8.7 ± 1.8 MPa (DPL) to 20 ± 1.9 MPa (SF100DPL), 13.3 ± 2.6 MPa (SFG5050DPL), and 16 ± 1.2 MPa (SFG3070DPL); and suture retention strength from 0.9 ± 0.08 MPa (DPL) to 2.3 ± 0.2 MPa (SF100DPL), 2.8 ± 1.2 MPa (SFG5050DPL), and 2.6 ± 0.9 MPa (SFG3070DPL). The degradation resistance of the modified scaffolds was also markedly improved. Being cytocompatible, its ability to incite tolerable inflammatory and immune responses was confirmed by rat subcutaneous implantation for 14, 30, and 90 days, in terms of inflammatory cell infiltration, neoangiogenesis, and in vitro cytokine release to assess B-cell and T-cell activation. Such ECM composite scaffolds with appropriate strength and biocompatibility offer great promise in soft tissue repair applications such as skin grafting.

Tuning the Properties of Xylan/Chitosan-Based Films by Temperature and Citric Acid Crosslinking Agent.

Petroleum-based food packaging causes environmental problems such as waste accumulation and microplastic generation. In this work, biobased films from stable polyelectrolyte complex suspensions (PECs) of xylan and chitosan (70 Xyl/30 Ch wt% mass ratio), at different concentrations of citric acid (CA) (0, 2.5, 5, 7.5 wt%), were prepared and characterized. Films were treated at two temperatures (135 °C, 155 °C) and times (30 min, 60 min) to promote covalent crosslinking. Esterification and amidation reactions were confirmed by Fourier Transform Infrared Spectroscopy and Confocal Raman Microscopy. Water resistance and dry and wet stress-strain results were markedly increased by thermal treatment, mainly at 155 °C. The presence of 5 wt% CA tended to increase dry and wet stress-strain values further, up to 88 MPa-10% (155 °C for 60 min), and 5.6 MPa-40% (155 °C for 30 min), respectively. The UV-blocking performance of the films was improved by all treatments, as was thermal stability (up to Tonset: 230 °C). Contact angle values were between 73 and 84°, indicating partly wettable surfaces. Thus, thermal treatment at low CA concentrations represents a good alternative for improving the performance of Xyl/Ch films.

Influence of Crosslinking Concentration on the Properties of Biodegradable Modified Cassava Starch-Based Films for Packaging Applications.

Chitosan/modified cassava starch/curcumin (CS/S/Cur) films with a crosslinker were developed via the solvent casting technique for the application of food packaging. The effects of citric acid (CA) as a natural crosslinker were assessed at different concentrations (0-10.0%, w/w, on a dry base on CS and S content). To measure the most favorable film, chemical structure and physical, mechanical, and thermal properties were investigated. Successful crosslinking between CS and S was seen clearly in the Fourier Transform Infrared (FTIR) spectra. The properties of the water resistance of the CS/S/Cur films crosslinked with CA were enhanced when compared to those without CA. Furthermore, it was found that the addition of CA crosslinking would improve the mechanical properties of composite films to some extent. It had been reported that the CA crosslinking level of 7.5 wt% of CS/S/Cur film demonstrated high performance in terms of physical properties. The tensile strength of the crosslinked film increased from 8 ± 1 MPa to 12 ± 1 MPa with the increasing content of CA, while water vapor permeability (WVP), swelling degree (SD), and water solubility (WS) decreased. An effective antioxidant scavenging activity of the CS/S/Cur film decreased with an increase in CA concentrations. This study provides an effective pathway for the development of active films based on polysaccharide-based film for food packaging applications.

Caffeic Acid Encapsulated Centrifugally Spun Antioxidant Fibers: Characterization and Incorporation in Cakes

AbstractThe primary aim of this study was to formulate a cake with high antioxidant activity through the incorporation of centrifugally spun gelatin-based fiber which was enriched with caffeic acid. Characterization analyses were conducted to evaluate fibers with different concentrations of caffeic acid (2% and 4%), while simultaneously the effects of thermal and citric acid crosslinking on the physical and functional properties of the encapsulated fibers were investigated. The study revealed varying encapsulation efficiencies of caffeic acid in gelatin fibers (56.34–94.55%), markedly affected by substantial reduction of thermal crosslinking, contrasting with citric acid’s minimal impact. Additionally, citric acid increased total phenolic content (TPC), but thermal treatment notably decreased antioxidant activity (AOA) due to its impact on radical scavenging and phenolic group dissociation. The addition of citric acid significantly reduced water vapor permeability by 22% suggesting an induced crosslinking in both thermal-treated caffeic acid and citric acid samples. The study highlighted reduced AOA and phenolic content in thermally treated fibers (thermally treated gelatin with 2% caffeic acid vs thermally treated gelatin with 4% caffeic acid), suggesting lower water solubility and improved thermal stability with approximately 24% remaining weight after thermogravimetric analysis. Despite this, cakes with thermally treated fibers had higher AOA due to improved heat resistance of fibers. Generally, adding fibers to cakes decreased hardness and pH while increasing TPC, AOA, and volume index, showing a novel approach using centrifugally spun fibers to enrich foods with antioxidants.

Sustainable foams from hemp, lignin, xylan, pectin, and glycerol: tunable via reversible citric acid crosslinking for absorption and insulation applications

This study investigates the development of sustainable multifunctional foams utilizing hemp stalk waste, lignin, xylan, pectin, glycerol, and citric acid. Using the freeze-drying method for foam formation in combination with industrial waste products and renewable resources, we emphasize a green, scalable material development approach. In total, 25 distinct formulations were prepared and methodically examined, mainly focusing on the roles of citric acid, pectin, and glycerol. Thermal crosslinking, conducted at 140°C, was analyzed using FTIR, confirming the formation of ester bonds. The microstructural characterization of the foams revealed distinct variations from nanofibrillar to microfibrillar structures based on composition. The bulk density of the foams ranged from 13 to 152 mg/cm3, and porosity values varied from 97 % to 99 % for most of the compositions. Foams showed up to 50 g/g water, 51 g/g rapeseed oil, and 46 g/g kerosine absorption. Foam absorption capacity changes were examined through 10 iterative cycles in water, demonstrating that most compositions retained near-original absorption capacities. Adding glycerol conferred exceptional hydrophobic properties to the foam surfaces, as evidenced by water contact angles ranging between 140° and 150°. The thermal conductivity of foams ranged from 0.040 to 0.046 W/mK. The mechanical properties of foams were assessed using compression testing, which showed highly tunable structures ranging from soft to rigid. This study illustrates the broad applicability of these foams, emphasizing their utility in thermal insulation, filtration systems, and environmental cleanup, among other potential uses.

Chitosan/teff flour active films incorporated with citric acid and beetroot leaf extract: Physicochemical properties and mathematical modeling of phenolic release

Active compounds are integrated into food packaging films to enhance their food protection capabilities. Understanding the release of these components in films, particularly in crosslinking scenarios, is crucial. This study aimed to mathematically model the release of phenolic compounds from chitosan/teff flour films to understand how active compounds gradually release. Moreover, it was aimed to study the effects of incorporation of beetroot leaf extract and citric acid crosslinking. The collective observations, encompassing increased density and thermal stability, alongside concurrent reductions in moisture content, water solubility, water vapor permeability and swelling index following citric acid addition, strongly suggested the presence of crosslinking. Applying Fick's law and the finite element method revealed a substantial influence of the crosslinking agent on diffusion coefficients. The model exhibited strong agreement with experimental data, as reflected in low root mean square error values ranging from 3.02 to 8.50 mmol/m3 for films. Furthermore, the influence of citric acid crosslinking on the release of TPC was evident, as indicated by a decrease in average diffusion coefficient values from 3.499 × 10−13 m2 s−1 to 1.770 × 10−13 m2 s−1 with the formula with 1.5 % citric acid and 0.5 % beetroot leaf extract. This showcases the impact of various parameters on controlled release in food packaging.

Enhanced probiotic viability in innovative double-network emulsion gels: Synergistic effects of the whey protein concentrate-xanthan gum complex and κ-carrageenan

In this study, the whey protein concentrate and xanthan gum complex obtained by specific pH treatment, along with κ-carrageenan (KC), were used to encapsulate Lactobacillus acidophilus JYLA-191 in an emulsion gel system. The effects of crosslinking and KC concentration on the visual characteristics, stability, mechanical properties, and formation mechanism of emulsion gels were investigated. The results of optical imaging, particle size distribution, and rheology exhibited that with the addition of crosslinking agents, denser and more homogeneous emulsion gels were formed, along with a relative decrease in the droplet size and a gradual increase in viscosity. Especially when the concentration of citric acid (CA) was 0.09 wt%, KC was 0.8 wt%, and K+ was present in the system, the double-network emulsion gel was stable at high temperatures and in freezing environments, and the swelling ratio was the lowest (9.41%). Gastrointestinal tract digestive treatments and pasteurization revealed that the probiotics encapsulated in the double-network emulsion gel had a higher survival rate, which was attributed to the synergistic cross-linking of CA and K+ biopolymers to construct the emulsion gels. Overall, this study highlights the potential of emulsion gels to maintain probiotic vitality and provides valuable insights for developing inventive functional foods.

Hydrogel derived from hybrid water hyacinth carboxymethyl cellulose and banana peels pectin hydrogel via citric acid crosslinking

Water hyacinth (WH) is a major pest in aquifer and likewise of banana peel waste that pollutes the environment. WH and banana peels have potential to produce carboxymethyl cellulose (CMC) as well as pectin. Both CMC and pectin are applicable for fabrication of hydrogels that focus on the natural ingredients for their use as food packaging materials. The application of CMC and pectin as a hydrogel material are splendid for increasing its mechanical, biodegradable and environment-friendly properties. This study determined the effect of citric acid as a cross-linking agent on the swelling properties of CMC-pectin based hydrogels and investigated their functional groups. Preparation of hybrid CMCpectin hydrogels was started by extracting WH cellulose. Through bleaching and dehemicellulose process. Cellulose was modified into CMC in two steps, alkalization and carboxymethylation. At the alkalization stage, the cellulose was mixed with NaOH 10% solution. For carboxymethylation, natrium chloroacetate (Na-CA) was added and stirred at 55°C for 3.5 hrs. Fabrication of hydrogel was mixed with 5% ratio 70:30 (w/w.%) of CMC:pectin. Citric acid (CA) was added as the cross-linking agent with concentrations of 5%, 10%, and 15% on heat treatment. The result of hybrid bio-hydrogels (HBH) was a sheet form film of semi-transparent, and brownish in color. HBH CMC/pectin with the addition of a cross-linking agent in the form of citric acid (5%) gave the highest swelling ability (6.64 wt., within 1 hr). Also, the presence of carboxyl bonds with hydroxyl groups was observed via Fourier transformed infrared spectrometry (FTIR) analysis.

Advancing sustainable bioplastics: chemical and physical modification of starch films for enhanced thermal and barrier properties.

This study addresses the urgent need for sustainable alternatives to conventional plastics by focusing on modification of thermoplastic starch (TPS) derived from renewable biomass sources. Despite TPS's biodegradability and cost advantages, its limitations in mechanical strength and water resistance prompted the investigation of physical and chemical modifications. Ultrasonication, autoclaving, and cross-linking with substances like citric acid and STMP (sodium trimetaphosphate)/STPP (sodium tripolyphosphate) were employed, with citric acid crosslinking standing out for its significant enhancement of transparency, especially beneficial for packaging applications. Film thickness varied with modification methods, with ultrasonicated films exhibiting thinner structures. Differential scanning calorimetry revealed insights into molecular interactions, with citric acid crosslinked film showing a substantial increase in thermal stability of the polymer at 164 °C, while moisture content analysis showed the impact of ultrasonication on reducing water absorption and citric acid crosslinking enhancing dimensional stability. Water vapor transmission rate data highlighted the effectiveness of ultrasonication in creating films with reduced permeability, and citric acid cross-linked films demonstrated potential for tailored water vapor barrier properties. Static water contact angle results indicated the hydrophobicity of films, with citric acid crosslinked films showing significantly more hydrophobic surfaces. The study also delved into water solubility, emphasizing the influence of depolymerization in ultrasonicated films and strengthened starch networks in crosslinked films, affecting their biodegradability. In conclusion, this comprehensive exploration demonstrates the feasibility of producing robust starch films with improved physicochemical properties through physical and chemical modifications, offering potential solutions in the quest for environmentally friendly alternatives to traditional plastics.

Evaluation of physicochemical properties of citric acid crosslinked starch elastomers reinforced with silicon dioxide.

Thermoplastic starch (TPS), derived from renewable resources, offers advantages such as biodegradability and lower production costs compared to petroleum-based plastics. However, its limited mechanical properties pose a challenge for broader applications. This research aims to explore the potential of enhancing the mechanical and barrier properties of TPS films through the incorporation of silicon dioxide as a reinforcement filler and citric acid as a crosslinking agent. By introducing silicon dioxide as a reinforcement filler, the mechanical strength of the TPS films is expected to be improved. Additionally, the incorporation of citric acid as a crosslinking agent is anticipated to enhance the barrier properties of the films. The combination of these additives holds promise for creating TPS films with improved performance, contributing to the development of sustainable and environmentally friendly materials in various industries. The results reveal that SiO2 improves the stiffness of the films at lower concentrations but causes brittleness at higher concentrations. In contrast, citric acid crosslinked films exhibit improved flexibility and density. Scanning electron microscopy demonstrates the morphological changes in the films, with SiO2 affecting surface roughness and aggregate formation. SiO2 reduces film thickness and transparency, while citric acid enhances water resistance and barrier properties. X-ray diffraction analysis shows a reduction in crystallinity due to the plasticization process. Fourier-transform infrared spectroscopy highlights chemical changes and antimicrobial activity is observed with citric acid against specific bacteria. The soil burial test reveals that citric acid crosslinked films exhibit slower degradation due to antimicrobial properties. The combination of SiO2 reinforcement and citric acid crosslinking enhances the overall performance of the films, promising sustainable and environmentally friendly materials for various applications.

Water Reduction of Biodegradable Plastic From Bagasse By‐Product With Synergistic Effect of Graphene Oxide Reinforcement and Citric Acid Crosslinking

In today’s world, plastics are vital as they are used in a wide range of applications although packaging is the most prevalent. Most of the plastics that are used for packaging applications are derived from petrochemicals. These plastics meet most of the requirements for good packing applications. However, they are not completely biodegradable. This consequently pollutes the environment. As a result, biodegradable plastics have emerged as an alternative to conventional plastics. Cellulose is one of the potential materials that are used for making biodegradable plastics. However, making plastic from cellulose causes deforestation. In this work, plastic was produced from cellulose bagasse, which is an industrial waste. Since bagasse is an industrial by‐product, it causes neither deforestation nor scarcity of food. However, the plastic made from bagasse showed high water absorption and low tensile strength. To overcome this problem, the plastic, which is made from bagasse, was reinforced with various concentrations of graphene oxide (GO) and crosslinked with various concentrations of citric acid (CA) at different crosslinking temperatures and crosslinking times. The water absorption and biodegradability of the films were studied. Furthermore, the synergistic effect of crosslinking and reinforcement was used to improve the interfacial bonding between the two. The water absorption of pure cellulose, cellulose crosslinked with 10% CA, cellulose reinforced with 15% GO reinforcement, and synergy of 10% CA crosslinking and 15% GO reinforcement at crosslinking temperature of 130°C and crosslinking time of 25 min was found to be 99.02%, 56.4%, 44.275%, and 36.78%, respectively. The biodegradability at the optimal values of crosslinker concentration, crosslinking time, and crosslinking temperature of pure cellulose of bagasse, 10% CA crosslinked bagasse, and 10% CA crosslinked bagasse with 15% GO reinforcement in 30 days were found to be 94.0397%, 56.91%, and 40.81%, respectively. The result of the study shows that water‐resistant biodegradable plastic can be produced with the synergistic effect of crosslinking and reinforcement.

Citric acid cross-linking of a hydrogel from Aloe vera (Aloe barbadensis M.) engenders a pH-responsive, superporous, and smart material for drug delivery.

The current research work is based on the evaluation of a citric acid (CA) cross-linked Aloe vera (Aloe barbadensis M.) leaf hydrogel (CL-ALH) for pH-dependent and sustained drug release application. The CA was used in different concentrations (1.25, 2.5, 5.0, and 10.0%) to cross-link the ALH using homogenous reaction conditions. The synthesis of CL-ALH was confirmed through Fourier transform and nuclear magnetic resonance spectroscopic studies. The thermal analysis indicated that the ALH and CL-ALH were stable and decomposed in two steps. The scanning electron microscopic images of CL-ALH confirmed its porous nature due to the presence of interconnected channeling. The swelling of CL-ALH was evaluated at pH 1.2, 6.8, and 7.4 as well as in deionized water (DW). High swelling of CL-ALH was observed in DW, and at pH 7.4 and 6.8 whereas, less swelling of CL-ALH was witnessed at pH 1.2. CL-ALH also exhibited swelling/deswelling behavior in DW and ethanol, DW and normal saline, and at pH 7.4 and 1.2. Tablets were prepared from CL-ALH as a release retarding agent demonstrating the sustained release of venlafaxine hydrochloride (VFX) for 8 h. Whereas, VFX was released within 4 h from the ALH-based tablet formulation (un-cross-linked material) indicating the prolonged and sustained release behavior of CL-ALH. The VFX was released from CL-ALH tablets and followed zero-order kinetics. The mechanism followed by VFX release from CL-ALH tablets was non-Fickian diffusion. The in vivo fate of the tablet formulation was observed through an X-ray study. The CL-ALH-based tablet safely passed through the stomach of a stray dog without any significant erosion and then disintegrated in the small intestine and colon. These findings confirmed that the CL-ALH is an effective excipient for designing a sustained-release drug delivery system for the small intestine and colon.

Antioxidant water-resistant fish gelatin nanofibers: A comparative analysis of fructose and citric acid crosslinking and investigation of chlorogenic acid release kinetics

The use of bio-based and biodegradable electrospun mats encapsulating antioxidants is a promising strategy for creating innovative multi-layered food packaging materials, since the nanometric size of the fibers forming the mat maximizes the availability of the active compound. However, the development of water-resistant active electrospun mats using only non-toxic natural components remains a challenge. In this paper, water-resistant fish gelatin (FG) nanofibers incorporating chlorogenic acid (CGA), a natural antioxidant, were developed using either citric acid (CA) or fructose (F) as crosslinking agents. The CA-crosslinked fibers had a mean diameter of (200 ± 50) nm and a solubility in cold water of (28 ± 2)%, while F-crosslinked fibers were obtained with a mean diameter of (300 ± 50) nm and a solubility of (5 ± 3)%. CGA was quickly released when the mats were immersed in several food simulants, achieving equilibrium in less than 30 min for both materials. ABTS scavenging activity did not show significant differences (p > 0.05) regardless of the crosslinker, but DPPH activity was significantly higher (p < 0.05) in those samples crosslinked with CA. Physico-chemical properties of the developed materials were studied by FTIR, DSC, and TGA tests. Results demonstrate the release kinetics and antioxidant activity of electrospinning-fabricated water-resistant FG nanofibers.

Novel cross-linking of toxic-free biopolymers for cellulose-gelatin films from avocado seed waste

Renewable, low-cost, and environmentally friendly processes have been continuously developed to produce biopolymers for various functional materials. This study aims to develop cellulose-gelatin film as a toxic-free biopolymer. Combining the excellent properties of cellulose and gelatin offers a promising alternative for improving the desirable properties. Herein, avocado seed waste was chemically treated and used as a cellulose-rich filler for gelatin-based film synthesis. Furthermore, different influences were examined with- and without- citric acid addition as a cross-linker agent. The citric acid cross-linked film has cellulose trapped in gelatin matrix structure with a smooth surface, good elasticity, sufficient flexibility, and free-toxic substance. Moreover, this study demonstrated that citric acid cross-linking design successfully improved the percent elongation film from 2.47 to 68.04 %, enhanced the water absorption capacity to 99.71 % at 24 h, and revealed high antibacterial activity, implying potential future application, especially for wound dressing.

Cellulose nanofiber aerogels modified with titanium dioxide nanoparticles as high-performance nanofiltration materials

Air pollution is a major environmental and public health issue. Each year, large amounts of particulate matter (PM) and other harmful pollutants are released into the atmosphere. Conventional polymer nanofiber filters lack the functionality to capture ultrafine PM. As a sustainable alternative, this work developed titanium dioxide (TiO2) nanoparticle surface-modified cellulose nanofiber (CNF) aerogels for PM2.5 filtration. CNFs were extracted via mechanical disintegration to diameters below 100 nm. The nanofibers were functionalized with 1.0–2.5 wt% TiO2 nanoparticles using citric acid cross-linking. Cylindrical aerogels were fabricated by freezing and lyophilizing aqueous suspensions. Structural, morphological, thermal, and mechanical properties were characterized. TiO2 modification increased density (11.8–19.7 mg/cm3), specific surface area (287–370 m2/g), and Young's modulus (33.5–125.5 kPa) but decreased porosity (99.6 %–97.7 %), pore size (20.2–15.6 nm) and thermal stability compared to unmodified cellulose aerogels. At 2.5 wt% loading, the optimized aerogels achieved 100 % absorption of 0.1–5 μm particulates owing to reduced pore size. Despite enhanced filtration capabilities, the modified CNF aerogels retained inherent biodegradability, degrading over 70 % within one month of soil burial. This pioneering research establishes TiO2 functionalized CNF aerogels as promising sustainable alternatives to traditional petroleum-based air filters, representing an innovative approach to creating next-generation nanofiltration materials capable of effectively capturing fine and ultrafine particulate matter pollutants.

Citric acid crosslinked soluble soybean polysaccharide films for active food packaging applications

In this work, a nontoxic crosslinking agent, citric acid (CA), was used to crosslink glycerol-plasticized SSPS films via a heat activated reaction. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy results confirmed the occurrence of esterification reaction between CA and SSPS. Microstructure of the CA-crosslinked SSPS films were characterized by scanning electron microscopy, atomic force microscopy and X-ray diffraction. The water resistance, mechanical, UV-barrier, water vapor barrier, antioxidant and thermal properties of SSPS films were enhanced by CA crosslinking. The SSPS film crosslinked with 5 % CA exhibited a maximum tensile strength of 6.5 MPa and a minimum water solubility of 34.3 %. The CA-crosslinked SSPS film also presented superior antibacterial properties against Gram-positive and Gram-negative bacteria. Application test results showed that the CA-crosslinked SSPS film can effectively delay the oxidative deterioration of lard during storage, suggesting that the developed CA-crosslinked SSPS film could be a promising candidate for active food packaging.

Preparation of crosslinked starches with enhanced and tunable gel properties by the cooperative crosslinking-extrusion combined modification

Due to its safety and palatability, the citric acid crosslinking modification is an excellent way to modify the properties of starch gels. However, the application of this method is restricted by the low degree of crosslinking of gels produced by this method in the hydrogel system. To produce citric acid-crosslinked starch with improved strength and tunable gel characteristics, a novel ion-esterification cooperative crosslinking-extrusion combined (CCEC) modification approach is presented in this study. The linear and nonlinear rheological characteristics of the samples were measured to evaluate the effectiveness of CCEC modification. Findings disclosed that at 0.1 % strain, the elastic modulus of the CCEC-modified starch (SC-0.5Zn2+, G' = 1522.29 ± 36.31) exhibited a significant rise of 387.27 % as compared to the elastic modulus of citric acid-crosslinked starch (SC, G' = 318.29 ± 11.62). Furthermore, changing the cation concentration allowed for efficient control of the gel's rheological characteristics. The samples were characterized by SEM, FTIR, XRD, and XPS. The CCEC-modified gels had a smaller pore size distribution and a denser honeycomb porous structure. The CCEC modification reaction involves ester bonds and electrostatic attraction. This research is essential to elucidate how coupled physicochemical modification techniques affect the manipulation of starch gel characteristics.

Cellulose acetate-based smart gating membrane with pH/thermal response for flux control

Inspired by the stomatal opening and closing mechanism of plants, a cellulose acetate-based pH/thermal response smart gating membrane was designed through surface segregation mechanism by embedding stimulation-responsive poly(N- isopropylacrylaminde) (PNIPAM)/poly(acrylic acid) (PAAc) microgels in the membrane pore channels. The water flux of the optimized smart membrane (CAM1.5) is 0.420 L/m2·h at 20 ℃/pH= 11 and changes to 121 L/m2·h at 65 ℃/pH= 1 with the highest gating ratio of 174. Meanwhile, the membrane gating ratio can be further improved to 216 when citric acid is used as coagulation bath. The carboxyl group content in the PAAc side chain is decreased and the interaction between water and microgels is improved under acid environment, which promotes the surface segregation of microgel. In addition, there is significant increase in the wet strength owing to the covalent crosslinking of citric acid. A fluid control system was designed based on the tunable membrane pore structure. According to the change of temperature and pH of the reaction system, the membrane can be opened and closed independently to precisely control the flow of reactants. This smart membrane shows promising applications in micro/nano fluid valves and temperature/pH sensitive biochemical reactors.