Poly(benzoxazine-f-chitosan) films: The role of aldehyde neighboring groups on chemical interaction of benzoxazine precursors with chitosan

Reactive oxygen species-responsive hydrophobic crosslinked chitosan films based on triple-function crosslinkers

Chitosan is widely used in reactive oxygen species (ROS)-responsive films but remains great challenges owing to its weak mechanical strength and strong hydrophilicity. Herein, we synthesized novel hydrophobic crosslinked CS films with ROS-responsive properties and excellent physicochemical properties. A novel crosslinker, 2-((10-carboxydecyl)thio)succinic acid, with long-chain alkanes, three carboxyl groups, and sulfhydryl groups was synthesized and then used to produce thioether-containing crosslinked CS membranes. The results suggested that crosslinking could significantly increase the tensile strength of the film from 15.67 MPa to 24.32 MPa. The compact structure of crosslinked chitosan film improved the hydrophobicity and degradability, reduced the thermal stability and swelling rates, exhibited excellent non- cytotoxicity. The in vitro release studies revealed that crosslinked chitosan films could displayed the highest flux about 1.40 mg/ (cm2 h) and significant NR fluorescence change over 80 %. Collectively, our results demonstrate the applicability of these films as ROS-responsive drug delivery systems.

Benzoxazine-grafted-chitosan biopolymer films with inherent disulfide linkage: Antimicrobial properties

Synthesis and fabrication of naturally sourced biopolymers, especially chitosan, grafted with renewable small molecules have recently attracted attention as efficient antimicrobial agents and are highly desired for sustainable material development. Advantageous inherent functionalities in biobased benzoxazine extend the possibility of crosslinking with chitosan which holds immense potential. Herein, a low-temperature, greener facile methodology is adopted for the covalent confinement of benzoxazine monomers bearing aldehyde and disulfide linkages within chitosan to form benzoxazine-grafted-chitosan copolymer films. The association of benzoxazine as Schiff base, hydrogen bonding, and ring-opened structures enabled the exfoliation of chitosan galleries, and such host-guest mediated interactions demonstrated outstanding properties like hydrophobicity, good thermal, and solution stability due to the synergistic effects. Furthermore, the structures empowered excellent bactericidal properties against both E. coli and S. aureus as investigated by GSH loss, live/dead fluorescence microscopy, and morphological alteration on the cell surface by SEM. The work provides the benefits of disulfide-linked benzoxazines on chitosan, offering a promising avenue for general and eco-friendly usage in wound-healing and packaging material.

Chitosan-pullulan films enriched with Artemisia annua essential oil: Characterization and application in grape preservation

Composite films were prepared using a flow casting method, with chitosan and pullulan as film-forming agents and Artemisia annua essential oil as the UV absorber. The utility of the composite films for preserving grape berries was assessed. The effect of the added Artemisia annua essential oil on the physicochemical properties of the composite film was investigated to determine the optimal amount of essential oil that should be added to the composite film. When the Artemisia annua essential oil content was 0.8 %, the elongation at break of the composite film increased to 71.25 ± 2.87 % and the water vapor transmission rate decreased to 0.378 ± 0.007 g‧mm/(m²‧h‧kpa). The transmittance of the composite film was almost 0 % in the UV region (200-280 nm) and <30 % in the visible light region (380-800 nm), reflecting the UV absorption by the composite film. Additionally, the composite film extended the storage time of the grape berries. Therefore, the composite film containing Artemisia annua essential oil may be a promising fruit packaging material.

ZnO nanoparticles coated and stearic acid modified superhydrophobic chitosan film for self-cleaning and oil-water separation

The aim of this study was to prepare superhydrophobic chitosan films using a ZnO nanoparticle coating and stearic acid hydrophobic modification. A 1 % concentration of ZnO nanoparticles and a 1 % concentration of stearic acid generated a superhydrophobic film with the largest contact angle (WCA) of 156°, which was attributed to the synergy of micro/nano-level hierarchical structure and low surface energy modification. The superhydrophobic film showed better stability to acid, alkali, heat, and UV irradiation than a neat chitosan film and a reduction in light transmittance of 14.4 % at 354 nm. The superhydrophobic chitosan film also showed excellent self-cleaning and oil-water separation performance. Our findings will expand the application of chitosan films in food packaging, outdoor self-cleaning materials and oil-water separations.

Two high toughness and flame retardant DOPO-containing polybenzoxazines based on polyether-urea

In this current work, two new-style DOPO-containing benzoxazines based on polyether-urea were successfully synthesized by a modified version via three-step procedures, and the corresponding polybenzoxazines with high toughness and flame retardancy were obtained by thermal activated polymerization. The single and double DOPO-containing benzoxazines were named as BzD1 and BzD2, respectively. The corresponding polymers followed were named as PBzD1 and PBzD2, respectively. The curing behaviors of the two new benzoxazines were investigated by differential scanning calorimetry. The thermal and mechanical properties of the materials were evaluated by TGA and dynamic mechanical analysis. The flame retardant properties were elucidated via limiting oxygen index (LOI). The toughness properties were expressed by bending tests. The results showed that the Yc for PBzD1 and PBzD2 were approximately 22.2% and 24%, respectively, distinctively higher than the value 2.57% of pristine polybenzoxazine PBz1, at 800 °C in N2 atmosphere. The Tgs of PBzD1 and PBzD2 distinctly increased by 42.8 °C and 20 °C, respectively, in comparison to −35 °C for pristine PBz1. The LOI values of PBzD1 and PBzD2 were 28.5 and 31, respectively. The length and weight-loss of PBzD1 and PBzD2 samples were significantly less than that of PBz1 when they were burned in the air environmental condition. The burning behavior demonstrated that the flame retardant properties was obviously improved as DOPO was introduced. All of the three specimens of PBz1, PBzD1 and PBzD2 presented excellent flexible property.

Metal Ion-Catalyzed Low-Temperature Curing of Urushiol-Based Polybenzoxazine

In this work, urushiol-based polybenzoxazine is cured by the Lewis acid (FeCl₃, AlCl_3, and CuCl₂) at low temperature instead of high thermal curing temperature. The effect of the Lewis acid on structures and properties of the polymers is revealed. The relating urushiol-based benzoxazine monomer (BZ) was synthesized by natural urushiol, formaldehyde, and n-octylamine. The monomer was reacted with the Lewis acid with a molar ratio of 6:1 (N_monomer: N_Metal) at 80°C to obtain films that can be cured at room temperature. The chemical structures of benzoxazine monomers were identified by Fourier-transform infrared spectroscopy (FTIR) and ¹H nuclear magnetic resonance spectroscopy (¹H-NMR). The interaction between the metal ion and the polymers is revealed by X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance-FTIR (ATR-FTIR). The effect of the Lewis acid on the mechanical properties, wettability, and thermal stability was investigated. The results show that the benzoxazine cured by Cu²⁺ has a better performance than that cured by Al³⁺ and Fe³⁺.

Chitosan/pullulan based films incorporated with clove essential oil loaded chitosan-ZnO hybrid nanoparticles for active food packaging

Herein, we developed clove essential oil (CEO) loaded Chitosan-ZnO hybrid nanoparticles (CS-ZnO@CEO (CZC NPs)) integrated chitosan/pullulan (CS/PL) nanocomposite films. SEM images revealed a homogenous distribution of CZC NPs with minimum aggregation in nanocomposite films. The incorporation of CZC NPs led to enhanced tensile strength (~39.82%), film hydrophobicity (~35.36%), UV light blocking ability, water vapor barrier (~84.64%), and oxygen barrier (~57.66%) compared to the bare CS/PL film and overall migration limit of CPCZC films were found below the permitted limit of 1000 μg/dm². Besides, incorporation of CZC NPs into the CS/PL films enhanced antioxidant activity and showed strong antibacterial activity against P. aeruginosa, S. aureus, and E. coli. Also, the CPCZC films displayed potential to extend the shelf-life of chicken meat by up to 5 days when stored at 8 ± 2 °C. These results suggest that the prepared CPCZC films acquire the ideal prerequisites for potential active packaging materials.

Preparation of a superhydrophilic SiO2 nanoparticles coated chitosan-sodium phytate film by a simple ethanol soaking process

The development of environmentally friendly and transparent superhydrophilic food packaging materials is essential in our daily lives. The objective of this study was to develop a simple method of preparing a superhydrophilic, transparent, and biodegradable composite film. The composite film was obtained by soaking a chitosan-sodium phytate film in an ethanol solution of SiO₂ nanoparticles. The results showed that when the chitosan-sodium phytate film was coated with SiO₂ nanoparticles that were dissolved in 75% ethanol, its water contact angle (WCA) was reduced from 100° to 3°, and the film surface was changed from a hydrophobic to a superhydrophilic. Furthermore, the oxygen transmission rate (OTR) was significantly reduced, and the mechanical properties of the film were improved. The method is easy to carry out and can be used for the potential production of superhydrophilic materials.

Glyceraldehyde as an Efficient Chemical Crosslinker Agent for the Formation of Chitosan Hydrogels

The rheological changes that occur during the chemical gelation of semidilute solutions of chitosan in the presence of the low-toxicity agent glyceraldehyde (GCA) are presented and discussed in detail. The entanglement concentration for chitosan solutions was found to be approximately 0.2 wt.% and the rheological experiments were carried out on 1 wt.% chitosan solutions with various amounts of GCA at different temperatures (25 °C and 40 °C) and pH values (4.8 and 5.8). High crosslinker concentration, as well as elevated temperature and pH close to the pKa value (pH ≈ 6.3-7) of chitosan are three parameters that all accelerate the gelation process. These conditions also promote a faster solid-like response of the gel-network in the post-gel region after long curing times. The mesh size of the gel-network after a very long (18 h) curing time was found to contract with increasing level of crosslinker addition and elevated temperature. The gelation of chitosan in the presence of other chemical crosslinker agents (glutaraldehyde and genipin) is discussed and a comparison with GCA is made. Small angle neutron scattering (SANS) results reveal structural changes between chitosan solutions, incipient gels, and mature gels.

Chitosan functionalized with heptadentate dinucleating ligand applied to removal of nickel, copper and zinc

The preconcentration of metal ions present at low concentration levels in aqueous systems and the selective removal of potentially toxic metals are important applications of adsorption processes. In this study, a heptadentate dinucleating ligand was anchored to chitosan for use in adsorption studies on Zn(II), Cu(II) and Ni(II) ions. The novel adsorbent was characterized by ¹³C NMR and FT-IR spectroscopy, TGA and BET surface area analysis. The degree of substitution of the ligand in chitosan, obtained from CHN analysis, was 0.73. The adsorption kinetics followed a pseudo-second-order model. The rate constants and the adsorption capacities for multicomponent systems decreased in the order Cu(II) >> Ni(II) ∼ Zn(II), indicating the preferential adsorption of Cu(II). For Cu(II) ions, the Langmuir model provided the best fitting to the experimental data, and the monolayer Cu(II) adsorption capacity was 0.404 mmol g^-1, while the linear isotherm described Zn(II) and Ni(II) ion adsorption.

Design of High-Performance Polybenzoxazines with Tunable Extended Networks Based on Resveratrol and Allyl Functional Benzoxazine

A novel resveratrol-based bio-benzoxazine monomer (RES-al) containing an allyl group has been synthesized using resveratrol, allylamine, and paraformaldehyde via Mannich condensation reaction, and its chemical structures have been characterized by FT-IR spectroscopy and NMR techniques. The polymerization behavior of this benzoxazine resin has been investigated using in situ FT-IR and differential scanning calorimeter (DSC) measurements, and the thermal-mechanical properties of its corresponding polybenzoxazines are evaluated by DMA and TGA. We show that by controlling the curing process of the oxazine ring, the C=C bond in resveratrol, and the allyl group in RES-al, the cross-linking network of the polybenzoxazine can be manipulated, giving rise to tunable performance of thermosets. As all curable functionalities in RES-al are polymerized, the resulted polybenzoxazine exhibits a good thermal stability with a Tg temperature of 313 °C, a T_d5 value of 352 °C, and char yield of 53% at 800 °C under N₂.

Antibacterial performance of fully biobased chitosan-grafted-polybenzoxazine films: Elaboration and properties of released material

A fully biobased benzoxazine monomer, V-fa (using vanillin and furfurylamine) was grafted onto chitosan (CS) at different weight ratios (C_XV_Y) using "grafting to" benign Schiff base chemistry. Incorporation of V-fa onto CS increased the tensile strength and improved chemical resistance of the CS-graft-V-fa films. Reversible labile linkages, expansion of CS galleries and leaching out of phenolic species from biobased polymer films led to an improved antibacterial activity against Staphylococcus aureus, which is ∼125 times higher than the bare CS film, V-fa and oligomeric V-fa. The leached out species from films were analyzed extensively by NMR, FTIR, GPC, ABTS and HRMS analysis. Oxidative-stress seems to be responsible for antibacterial activity. Current work illustrates an attractive synthetic approach and the improved antibacterial performance of biobased CS-graft-poly(V-fa) films which may hold as a potential alternative for wound-healing and implant applications in future.

Synthesis and characterisation of novel Cu(ii)-anchored biopolymer complexes as reusable materials for the photocatalytic degradation of methylene blue

This study focused on the synthesis, photocatalytic degradation of organic dyes and biological activity of novel N, N, O-donor tridentate water soluble 4-hydroxy benzohydrazide-grafted biopolymer Schiff base Cu(ii) complexes. The eco-friendly catalysts were designed for potential application in the degradation of organic dyes. The photocatalytic degradation of methylene blue was investigated with various irradiation times (30, 60, 90 and 120 min), catalytic dosages (5, 10, 15 and 20 mg) and pH (3, 7 and 12). The as-prepared compounds were characterised via various techniques including FT-IR and FT-NMR spectroscopy; TGA-DTA, XRD, SEM-EDAX; ESR and UV-vis spectroscopy; photoluminescence, magnetic moment, and conductivity measurements; and elemental and thermal analysis. The crystallinity of the Schiff base ligands, chitosan, and their Cu(ii) complexes was analysed via X-ray diffraction (XRD) studies. The XRD patterns revealed that the polymer chitosan was more crystalline than the Schiff base ligands and their complexes. The surface morphological analysis by scanning electron microscopy (SEM) revealed that the Cu(ii) complexes were amorphous in nature compared to chitosan and the ligands. The anti-inflammatory and anti-diabetic studies of the biopolymer Cu(ii) complexes were performed using the albumin denaturation technique and McCue and Shetty method, respectively. The as-synthesized 4-hydroxy benzohydrazide-grafted O-carboxymethyl chitosan Schiff base ligands and their Cu(ii) complexes showed a good anti-inflammatory and antidiabetic effect. The photocatalytic activity proved that the aryl-substituted complex was more efficient than the aliphatic-substituted complex.

The effect of chitosan and PEG polymers on stabilization of GF-17 structure: A molecular dynamics study

We examine the interactions of chitosan and polyethylene glycol (PEG) with antimicrobial peptide GF-17 to identify a suitable carrier to improve the peptide drug delivery systems. To this end, the molecular dynamics simulations are used to determine the interactions of a typical antimicrobial peptide GF-17 with the chitosan and PEG polymers. The findings indicate the great potential of the peptide to maintain its secondary structure in the adjacent to chitosan polymers. During the interaction with chitosan polymers, the structure of the peptide has smaller fluctuations compared to the PEG polymers. Also, in the presence of both the polymers, the PEG polymers are situated closer to the peptide than chitosan polymers. Moreover, the analysis indicates that the acidic residues and phenylalanine play a crucial role in peptide-polymer interactions. This research provides a valuable insight into the design of polymer surfaces for drug delivery applications such as controlled-release peptide delivery systems.