One pot synthesis of hydrophobic nanochitin aerogel via tert-butyl alcohol/water binary solvents as antibacterial and renewable oil superabsorbent

In this study, hydrophobic nanochitin aerogels are synthesized via one-pot synthesis strategy and subsequent freeze-drying technique, employing nanochitin, hexanal and formaldehyde as primary components. The tert-butyl alcohol (TBA)/water binary solvents are found efficient for well mixing of hydrophilic nanochitin and hydrophobic hexanal, which is fundamental for fabricating hydrophobic aerogels with water contact angle as high as 105°. Schiff base reaction between amino groups in nanochitin and aldehyde groups in hexanal is believed to be the main reason for the successful hydrophobization of nanochitin aerogels. Additionally, formaldehyde is employed to enhance the mechanical properties of aerogels via ice templated crosslinking technique. Nanochitin aerogels prepared in this work possess surface area as high as 237 m2 g-1, which are believed benefiting from the TBA/water binary solvents with lower density, smaller ice crystal and convenience in freeze-drying. The ultralow density, ultrahigh porosity, and hydrophobicity nature also lead to the advanced oil adsorption (as high as 210 g g-1) of nanochitin aerogels. The simple preparation process, nature sustainability and excellent adsorption performance is believed rendering nanochitin aerogels as a viable alternative for the remediation of oil spills.

Facile preparation of re-dispersible/amphoteric nanochitin powder via choline chloride/propanedioic composite for stabilizing Pickering emulsions

Choline chloride (ChCl)/propanedioic acid (PA) based hydrated composites are synthesized for producing nanochitins from crab shell in this work. The yield of nanochitin remains higher than 75 %, even if the water content reaches 80 %. ChCl is found necessary for the successful nano-fibrillation of chitin. However, PA contributes more to the yield improvement of nanochitin. ChCl mediated PA hydrolysis leads to the successful grafting of carboxyl groups in nanochitins, contributing to its amphoteric dispersed nature. After salt-induced separation and freeze-drying treatment, dried nanochitin powder can be prepared and found to disperse well either in acidic or alkaline suspension, exhibiting efficient drying/redispersion performance. The well amphoteric and drying/redispersion nature both benefit the facile preparation of nanochitin-based Pickering emulsions. For Pickering emulsion prepared under different pH, creaming only appears under acidic conditions (pH 3) for which the creaming index reaches 10.56 % after 30 days of storage. No obvious de-emulsification can be observed under pH 7 and 10. The efficient amphoteric and drying/redispersion nature together with the simplified preparation process of nanochitins are believed to facilitate the processing and practical applications of nanochitin.

Preparation of Janus film for fog water collection via layer-by-layer assembling of nanocellulose and nanochitin on PLA

In order to explore the possibility of natural carbohydrate polymers as a biodegradable and sustainable fog water harvesting material, this work proposed an efficient substrate (hydrophobic)-transition layer (amphoteric)-coating (hydrophilic) sandwich spin-coating strategy to form all biomass-based Janus film. The oxalic acid hydrolyzed nanochitin (OAChN) was applied as a transition layer that enabled successful spin-coating of the hydrophilic nanocellulose (TEMPO-oxidized cellulose nanofiber, TOCN) and nanochitin (partially deacetylated chitin nanofibers, DEChN) on the hydrophobic polylactic acid (PLA) film substrate. In which a layer-by-layer (LBL) assembling of TOCN (carboxyl-rich negative surface charge) and DEChN (amino-rich positive surface charge) was designed to form a thickness and surface property controllable polysaccharide coating on PLA. The finally formed PLA-OAChN-TOCN/DEChN (LBL) film showed hydrophilic and hydrophobic heteromeric faces at the opposite sides and thus had improved fog water collection capacity of 90.85 mg·cm-2·h-1 (30 layers of TOCN/DEChN spin-coated on PLA), which was 276 % higher than the pure PLA film. The transition layer engaged sandwich spin-coating strategy, together with LBL assembling method proposed in this study provided a feasible fabrication of all biomass-based fog water collectors (FWC) that could contribute to alleviating water shortage.

Optimized high-yield synthesis of chitin nanocrystals from shrimp shell chitin by steam explosion

This study attempted for the first time to prepare chitin nanocrystals (ChNCs) from shrimp shell chitin using steam explosion (SE) method. Response surface methodology (RSM) approach was used to optimize the SE conditions. Optimum SE conditions to acquire a maximum yield of 76.78 % were acid concentration (2.63 N), time (23.70 min), and chitin to acid ratio (1:22). Transmission electron microscopy (TEM) revealed the ChNCs produced by SE had an irregular spherical shape with an average diameter of 55.70 ± 13.12 nm. FTIR spectra showed ChNCs were slightly different than chitin due to a shift in peak positions to higher wavenumber and higher peak intensities. XRD patterns indicated ChNCs were a typical α-chitin structure. Thermal analysis revealed ChNCs were less thermally stable than chitin. Compared to conventional acid hydrolysis, the SE approach described in this study is simple, fast, easy, and requires less acid concentration and acid quantity, making it more scalable and efficient for synthesizing ChNCs. Furthermore, the characteristics of the ChNCs will shed light on the potential industrial uses for the polymer.

Chitin nanofiber-coated biodegradable polymer microparticles via one-pot aqueous process

Tailoring the surface of biodegradable microparticles is important for various applications in the fields of cosmetics, biotechnology, and drug delivery. Chitin nanofibers (ChNFs) are one of the promising materials for surface tailoring owing to its functionality, such as biocompatibility and antibiotic properties. Here, we show biodegradable polymer microparticles densely coated with ChNFs. Cellulose acetate (CA) was used as the core material in this study, and ChNF coating was successfully carried out via a one-pot aqueous process. The average particle size of the ChNF-coated CA microparticles was approximately 6 μm, and the coating procedure had little effect on the size or shape of the original CA microparticles. The ChNF-coated CA microparticles comprised 0.2-0.4 wt% of the thin surface ChNF layers. Owing to the surface cationic ChNFs, the ζ-potential value of the ChNF-coated microparticles was +27.4 mV. The surface ChNF layer efficiently adsorbed anionic dye molecules, and repeatable adsorption/desorption behavior was exhibited owing to the coating stability of the surface ChNFs. The ChNF coating in this study was a facile aqueous process and was applicable to CA-based materials of various sizes and shapes. This versatility will open new possibilities for future biodegradable polymer materials that satisfy the increasing demand for sustainable development.

Heteroaggregation effects on Pickering stabilization using oppositely charged cellulose nanocrystal and nanochitin

Pickering emulsions are stabilized using complexes of cellulose nanocrystals (CNC) and nanochitin (NCh). The colloidal behavior and heteroaggregation in aqueous media are studied in relation to complex formation and net charge. The complexes are remarkably effective in stabilizing oil-in-water Pickering emulsions under conditions of slightly net positive or negative charges, as determined by the CNC/NCh mass ratio. Close to charge neutrality (CNC/NCh ~5), large heteroaggregates form, resulting in unstable emulsions. By contrast, under net cationic conditions, interfacial arrest of the complexes leads to non-deformable emulsion droplets with high stability (no creaming for 9 months). At given CNC/NCh concentrations, emulsions with up to 50% oil fraction are produced. This study shows how to control emulsion properties beyond consideration of the typical formulation variables, for instance, through adjusting CNC/NCh ratio or charge stoichiometry. We highlight the possibilities that are available for emulsion stabilization by using a combination of polysaccharide nanoparticles.

Immobilization of phlorotannins on nanochitin: A novel biopreservative for refrigerated sea bass (Lateolabrax japonicus) fillets

A novel biopreservative was developed by immobilizing phlorotannins into nanochitin (NCh). NCh were selected as a host complex to immobilized phlorotannins and the structural properties and antioxidant activity of the NCh-phlorotannins nanocomplex was investigated. The NCh-phlorotannins showed high antioxidant activity, as evidenced by free radical scavenging activity test. Moreover, the effects of NCh-phlorotannins on physical [color, water holding capacity (WHC), and texture], chemical [thiobarbituric acid (TBA) values, total volatile base nitrogen (TVB-N), and pH], microbiological [total viable count], changes of refrigerated sea bass (Lateolabrax japonicus) fillets were also evaluated. Sea bass fillets add with 1.5 g/kg NCh-phlorotannins had lower bacterial growth, pH, TVB-N and TBA as well as better characteristics of texture, color, and WHC than those of the control group during refrigerated storage. The efficiency of NCh-phlorotannins treatment was also better than that of phlorotannins or NCh treatment alone. Therefore, NCh-phlorotannins may be a potential biopreservative to extend the shelf-life of sea bass fillets quality during refrigerated storage.

Shape-recoverable, piezoresistive, and thermally insulated xerogels based on nanochitin-stabilized Pickering foams

Biomass-derived porous materials are promising for various fields and preferred for sustainable development. In this work, shape-recoverable nanochitin-based xerogels with porous structure and excellent mechanical strength, thermal insulation (43.23 ± 0.17 mW/m·k) and piezoresistive properties were prepared by nanochitin-stabilized Pickering foams with chemical crosslinking for the first time through simple air-drying. At the optimized ingredients of nanochitin, surfactant (T80) and crosslinker (glutaraldehyde), the Pickering foams exhibited no significant collapse after one week, and the xerogels prepared thereof achieved a mechanical strength of 0.5-2.7 MPa at 80% strain and considerable structural stability after 100 cycles at 60% strain. Moreover, the resistance of the xerogel had a high linearity in the strain range (0-10%) and could recover to the initial value after 20 cycles. Notably, this is the first time that pure bio-based conductive xerogel has been obtained. These features make nanochitin a promising candidate for biodegradable and sustainable 3D porous materials.

TEMPO-oxidized nanochitin based hydrogels and inter-structure tunable cryogels prepared by sequential chemical and physical crosslinking

Well dispersibility of 2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO)-oxidized nanochitins under alkaline conditions supports the effective chemical crosslinking between nanochitin and epichlorohydrin. The storage modulus of nanochitin hydrogels can be promoted by approximately 10 times as the nanochitin-to-epichlorohydrin mass ratio changes from 4:1 (120 Pa) to 1:4 (1200 Pa). Besides the enhanced mechanical property of hydrogels, the inter-structure of resulting cryogels is found controllable. With increasing epichlorohydrin dosage, the inter-structure of cryogels transforms from a typical fiber-like to honeycomb-like texture. The balance between chemical crosslinking effect and electrostatic repulsion between nanochitins is believed to result this controllable inter-structure. Further immersing into acetic acid solution can greatly enhance the mechanical strength of nanochitin hydrogels due to the introduction of physical crosslinking domains by shielding the electrostatic repulsion, the storage modulus becomes two times higher after immersing in 50% (w/w) acetic acid solution, while the surface area of nanochitin cryogels decreases due to the denser structure.

An optimized preparation of nanofiber hydrogels derived from natural carbohydrate polymers and their drug release capacity under different pH surroundings

Cellulose and chitin, as the two important natural carbohydrate polymers, have possibility to disassemble to biomass derived polysaccharide nanofibers. The 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) oxidized nanocellulose and nanochitin based hydrogel was fabricated via acid gas phase coagulation. It was observed that hydrogels began to form when the pH was lower than 3. When 0.1 mL of acetic acid coagulation bath was provided, 10 h were enough to form sufficient physical crosslinking. Moreover, the release time of amygdalin loaded in the hydrogel could be more than 60 h with a release amount of 80 % due to the uniform network and water-bearing structure. Meanwhile, the release capacity of hydrogels showed diversity at different pH surroundings, which was attributed to the existence of carboxyl groups on the oxidized nanofiber. The results suggested the possible application of the produced nanofiber hydrogels in some specific areas, such as drug delivery, wound dressing, and food packaging.

Associative structures formed from cellulose nanofibrils and nanochitins are pH-responsive and exhibit tunable rheology

HYPOTHESIS

Nanocellulose and nanochitin are both biobased materials with complementary structures and properties. Both exhibit pH-dependent surface charges which are opposite in sign. Hence, it should be possible to manipulate them to form complexed structures via ionic bond formation at prescribed pH conditions.

EXPERIMENT

Nanocellulose and nanochitin were mixed after exposure to acidic or neutral conditions to influence their ionization state. The heat of interaction during the introduction of nanochitin to nanocellulose was monitored via isothermal titration calorimetry. The strength and gel properties of the resulting structures were characterized via rheological measurement.

FINDINGS

The resultant gel properties in the designed hybrid systems were found to depend directly on the charge state of the starting materials, which was dictated by pH adjustment. Different interparticle interactions including ionic attraction, hydrophobic associations, and physical entanglement were identified in the systems and the influence of each was elucidated for different conditions of pH, concentration, and ratio of nanochitin to nanocellulose. Hydrophobic associations between neutralized nanochitin particles were found to contribute strongly to increased elastic modulus values. Ionic complex formation was found to provide enhanced stability under broader pH conditions, while physical entanglement of cellulose nanofibers was a substantial thickening mechanism in all systems.

Conductive biomass-based composite wires with cross-linked anionic nanocellulose and cationic nanochitin as scaffolds

In this study, a series of conductive composite wires were successfully prepared by combining dispersions of multi-wall carbon nanotubes (MWCNTs) and TEMPO-oxidized cellulose nanofibers (TOCNFs) with different MWCNTs contents into a dispersion of partially deacetylated α-chitin nanofibers (α-DECHNs) followed with a drying process. The TOCNFs/MWCNTs/α-DECHNs composite wires were prepared by extruding the negatively charged TOCNFs/MWCNTs dispersion into the positively charged α-DECHNs dispersion. The contact of the positively charged α-DECHNs and the negatively charged TOCNFs/MWCNTs triggers the electrostatic interaction (heterocoagulation) resulting in wire-shaped conductive composites. The SEM analysis indicates this conductive composite material has a wire-like shape with a rough but tight surface. The properties of samples were characterized by a zeta potential analyzer (Zetasizer Nano), a four-probe, an electrochemical workstation, a Fourier transform infrared spectroscopy (FTIR), an X-ray diffractometer (XRD), and a thermogravimetric analyzer (TG). Besides, the conductivity and the AC impedance of TOCNFs/MWCNTs/α-DECHNs composite wires with different MWCNTs contents were also analyzed. The conductivity of the composite wire increases from 9.98 × 10^-6 S∙cm^-1 to 1.56 × 10^-3 S∙cm^-1 as the MWCNTs content raises from 3.0 wt% to 14.0 wt%. When the MWCNTs content reaches 14.0 wt%, the prepared composite wire can light up LED at a voltage of 5 V, indicating the great potential of this biomass-based conductive composite in conductive material application.

Synergistic effects of nanochitin on inhibition of tobacco root rot disease

Nanomaterials have great potential for use in various fields, due to their unique properties. In order to explore the bioactivity of nanochitin on tobacco, the effects of nanochitin suspensions on tobacco seed germination, seedling growth, and synergistic effects with fungicides were studied in indoor and field trials. Results showed that 0.004% (w/v) of nanochitin improved tobacco seed germination and shortened mean time to germination significantly; 0.005% (w/v) of nanochitin increased tobacco stem length, stem girth, leaf number and leaf area, and 0.001% (w/v) of nanochitin had synergistic effects on inhibition of tobacco root rot when mixed with metalaxyl mancozeb and thiophanate methyl fungicides. This indicates that nanochitin suspensions have a strong potential to protect tobacco from tobacco root rot diseases and reduce the use of chemical fungicides in tobacco plantations.