Schiff Base Structure Research Articles

Novel Biomass-Based Polymeric Dyes: Preparation and Performance Assessment in the Dyeing of Biomass-Derived Aldehyde-Tanned Leather.

High-performance chrome-free leather production is currently one of the most concerning needs to warrant the sustainable development of the leather industry due to the serious chrome pollution. Driven by these research challenges, this work explores using biobased polymeric dyes (BPDs) based on dialdehyde starch and reactive small-molecule dye (reactive red 180, RD-180) as novel dyeing agents for leather tanned using a chrome-free, biomass-derived aldehyde tanning agent (BAT). FTIR, 1H NMR, XPS, and UV-visible spectrometry analyses indicated that a Schiff base structure was generated between the aldehyde group of dialdehyde starch (DST) and the amino group of RD-180, resulting in the successful load of RD-180 on DST to produce BPD. The BPD could first penetrate the BAT-tanned leather efficiently and then be deposited on the leather matrix, thus exhibiting a high uptake ratio. Compared with the crust leathers prepared using a conventional anionic dye (CAD), dyeing, and RD-180 dyeing, the BPD-dyed crust leather not only had better coloring uniformity and fastness but it also showed a higher tensile strength, elongation at break, and fullness. These data suggest that BPD has the potential to be used as a novel sustainable polymeric dye for the high-performance dyeing of organically tanned chrome-free leather, which is paramount to ensuring and promoting the sustainable development of the leather industry.

A novel functional fluorescent probe based on a pyrene derivative for the detection of multiple pollutants

In regards to environmental protection, the detection of metal ions and pesticide residues remains meaningful and challenging. Herein, we report a novel multifunctional fluorescent probe based on a pyrene derivative, 4-[(pyren-1-ylimino)methyl]benzene-1,3-diol (PBD), that can recognize Al3+, Cr3+, Fe3+ and mesotrione with quantification of the sample being tested. In addition, the PBD probe can detect Hg2+ in a “turn-off” fluorescent mode. It is worth noting that the hydrolysis of carbon–nitrogen double bonds in the PBD Schiff base structure is targeted and catalyzed by Fe3+, Al3+ and Cr3+ cations, while mesotrione can also promote the hydrolysis of Schiff bases through the formation of intermolecular hydrogen bonds. Consequently, the PBD probe with weak fluorescence was converted to 1-aminopyrene in a localized state, showing stronger fluorescence. In addition, chelation may lead to fluorescence quenching of the PBD probe in the presence of Hg2+. The quantitative determination of Fe3+, Al3+, Cr3+ and mesotrione is achieved in which the limit of detection (LOD) is calculated to be 0.52, 0.30, 0.32 and 0.70 μM, respectively. Hg2+ detection is realized with an LOD of 1.93 μM. Moreover, the sensitive PBD probe is utilized to determine the amount mesotrione in actual water samples, demonstrating its potential practical applications. In addition, the multifunctional PBD probe can be employed for intracellular imaging of Fe3+ and Hg2+ based on its low cytotoxicity and certain water solubility. The present work describes a very competitive fluorescent probe for the detection of different types of pollutants, which is relevant to future research regarding environmental contaminant monitoring.

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.

Synthesis of a “Turn-On” Mg2+ fluorescent probe and its application in hydrogel adsorption

A compound with a Schiff base structure, (E)-3-hydroxy-N'-(2-hydroxybenzaldehyde) (HMN), was synthesized using 3‑hydroxy-2-naphthoic acid hydrazine and 2-hydroxy-4-methoxybenzaldehyde as raw materials. The structure of probe HMN was characterized by 1H NMR, 13C NMR, HR-MS, IR and X-ray single crystal diffraction. This study found that the probe HMN can rapidly and highly selectively recognize Mg2+ in a water system with DMSO=1:9 (water system: 20% triethanolamine + 0.1 mol•L−1 L-cysteine). We used fluorescence spectroscopy and ultraviolet-visible spectroscopy to study the spectral properties of the probe HMN. The results showed that the combination of probe HMN and Mg2+ produced an obvious fluorescence enhancement effect which was negligibly affected by other metals and anions. After that, we used Job's curve, NMR titration, MS and DFT calculations to explore the binding mechanism of probe HMN and Mg2+, and found that they were coordinated in a 1:1 manner. We fitted a linear equation to different Mg2+ concentrations and fluorescence intensities, and the calculated detection limit (LOD) was 8.4802×10−8 mol/L. The standard addition and recovery experiments showed that the probe can be used for the qualitative detection of Mg2+ in water samples. A hydrogel (PAM-HMN) was prepared by doping HMN into polyacrylamide (PAM). We found that PAM-HMN had an efficient absorption performance for Mg2+, and the removal rate of Mg2+ from water reached 97.99%. The color change before and after adsorption of Mg2+ was easily identified by the naked eye under UV light. The microstructure and composition of PAM-HMN before and after adsorption were analysed by SEM-EDS. The probe and hydrogel derivatives have potential application value in environmental detection and pollution prevention. The experimental study of standard addition recovery showed that probe HMN could be used for the quantitative detection of Mg2+in actual water samples.

A pH-Responsive Charge-Convertible Drug Delivery Nanocarrier for Precise Starvation and Chemo Synergistic Oncotherapy.

A pH-responsive charge-convertible drug delivery nanocarrier (MSN-TPZ-GOx@ZnO@PAH-PEG-DMMA, abbreviated as MTGZ@PPD) was prepared, which could specifically release hypoxia-activated chemotherapeutic Tirapazamine (TPZ) and glucose oxidase (GOx) in the tumor site for precise starvation and chemo synergistic oncotherapy. Acid-responsive Schiff base structure modified mesoporous silica nanoparticles (MSN) co-load with GOx and TPZ, then link with ZnO quantum dots (QDs). PAH-PEG-DMMA (PPD) polymer makes MTGZ@PPD with biocompatibility and charge-convertible feature. MTGZ@PPD is negatively charged at physiological pH, and the charge reversal of PPD and acidolysis of the Schiff base structure under the acidic tumor microenvironment (TME) induce a positively charged surface, which could potentiate the cell internalization. ZnO QDs could decompose at acidic TME, achieving controllable drug release. GOx could starve the tumor cells and enhance hypoxia level, thus initiates the activation of TPZ to realize synergistic starvation therapy and chemotherapy. This intelligent MTGZ@PPD has shown great potential for starvation and chemo synergistic oncotherapy.

A self-healing and conductive ionic hydrogel based on polysaccharides for flexible sensors

An ionic hydrogel based on polysaccharides with self-healing and conductive properties serves as the flexible sensors to record the information of pressing Morse codes and browsing web pages with a mobile phone. In this study, we proposed a self-healing conductive hydrogel based on polysaccharides and Li + to serve as flexible sensors. At first, the oxidized sodium alginate (OSA) was obtained through the oxidation reaction of sodium alginate (SA). Then OSA, carboxymethyl chitosan (CMC), and agarose (AGO) were dissolved in LiCl solution, respectively. Finally, the hydrogel was obtained through heating, mixing, and cooling processes. Because of the Schiff base structure and hydrogen bonding, the hydrogel demonstrates good mechanical and self-healing properties. The presence of Li + provides good conductivity for the hydrogel. In addition, we demonstrated the application of the hydrogel as the flexible sensors. It can perceive the process of pressing Morse code with the index finger as a pressure sensor and monitor sliding movement of the thumb as the strain sensor to browse the web with the mobile phone. Thus, the self-healing conductive hydrogel may have potential applications in flexible wearable sensors.

Equilibria of complexes in the aqueous cobalt(II)–N-(2-hydroxybenzyl)phenylalanine system and their biological activity compared to analogous Schiff base structures

Due to their excellent prospects in biological applications, Schiff bases and their complexes are a source of continuing interest. The present study examines the formation of four cobalt(II) complexes with the reduced Schiff base N-(2-hydroxybenzyl)phenylalanine (PhAlaSal) in alkaline aqueous solution by pH-metry. UV–Vis and ESI–MS studies confirmed the model of proposed species. Kinetic analysis indicated that the single- and bi-ligand cobalt(II) complexes transitioned from octahedral to tetrahedral structures. The Schiff base and its complexes detected under physiological pH were tested for antimicrobial abilities and compared with analogous structures of the Schiff base derivative, N-(2-hydroxybenzyl)alanine (AlaSal). The ability of these structures to influence cell growth was tested on L929 mouse fibroblasts and on cervix and gastric adenocarcinoma cancer cell lines. N-(2-hydroxybenzyl)phenylalanine demonstrates greater antimicrobial efficacy than N-(2-hydroxybenzyl)alanine but also higher cytotoxicity; however, it is nonetheless effective against cancer cells. In turn, AlaSal demonstrates low cytotoxicity for fibroblasts and high cytotoxicity for gastric adenocarcinoma epithelial cells at bacteriostatic concentration for Helicobacter pylori and Candida strains. The presence of these microorganisms in the gastric milieu supports the development of gastritis and gastric cancer; AlaSal therapy may be simultaneously effective against both. Due to their cytotoxicity, Schiff base complexes are not suitable for use against fungal and bacterial infections, but may effectively prevent cancer cell growth. Data availabilityData will be made available on request.

Amino modified cellulose fibers loaded zinc oxide nanoparticles via paper-making wet-forming for antibacterial materials

Bacterial infection has become one of the major threats to human health all over the world, and the development and application of antibacterial materials has drawn great attention. Based on the Schiff-base structure, ZnONPs@ACFs are obtained by loading zinc oxide nanoparticles (ZnONPs) on amino cellulose fibers (ACFs) in-situ through the coordination of amino groups with metal ions. The results of FT-IR, XRD and UV-vis demonstrate that ZnONPs are successfully loaded and uniformly dispersed on ACF surface, and the ACFs maintain intact morphology observed by SEM. Furthermore, the zero-span tensile strength of ZnONPs@ACFs is 66.48 N/cm (ROL: 24.98 N/cm/s) under the optimum conditions, which indicates that ZnONPs@ACFs have a certain strength and can be used to make antibacterial sheet materials via paper-making wet-forming process. Accordingly, the ZnONPs@ACF composites show inhibition zones of 4.95 mm and 1.10 mm against E. coli and S. aureus, respectively. The new cellulose-based antibacterial materials demonstrate potential applications in the field of food packaging and biological medicine etc.

Vanillin-based liquid crystalline polyimine thermosets and their composites for recyclable thermal management application

The development of bio-based thermosets with favorable mechanical properties, high glass transition temperature (Tg), and recyclability for thermal management applications remains a huge challenge. In this study, a trifunctional aldehydes monomer was prepared from vanillin followed by curing with two kinds of diamine for novel polyimine networks. The results showed that the polyimine networks cured with 4,4′-diaminodiphenyl methane demonstrated the liquid crystalline polyimine thermosets with a high Tg of 193 °C, a high tensile strength up to 84 MPa, and excellent thermal stability (the values of degradation temperature for 5 wt% weight loss, Td5 = 373 °C), while the polyimine networks cured with 4,4′-methylenebis(cyclohexylamine) demonstrated amorphous polyimine thermosets with inferior mechanical and thermos-physical performances, due to the crosslinked liquid crystal structure, the rigid benzene ring and the π-π stacking effect of the former. Furthermore, the polyimine nanocomposites were constructed by incorporating graphene nanoplatelets (GnPs) into these bio-based thermosets. With only 8 wt% GnPs, the nanocomposites showed a remarkable thermal conductivity of 1.8 W m−1 K−1. Interestingly, both the polyimine networks and their composites demonstrated complete recyclability in mild acid conditions owing to the existence of dynamical Schiff-base structures. The bio-based polyimines and nanocomposites reported here offer various advantages, including high mechanical properties and Tg, excellent thermal stability, remarkable thermal conductivity, and recyclability, which provides a new direction for the development of high-performance base composite networks.

A novel pyrene-based fluorescent probe for Al3+ detection

Based on the classical Schiff base reaction, fluorescent probe dimethyl 5-((pyren-1-ylmethylene)amino)isophthalate (PAI) is designed and synthesized through introducing Schiff base structure to pyrene unit for structural modification. The structure of the synthesized probe PAI is determined and characterized by FT-IR, 1H NMR, 13C NMR and HRMS. PAI is a type of “turn-on” probe which can specifically recognize Al3+ ion with high selectivity. The limit of detection is calculated to be 3.07 × 10−8 M, which proves the probe’s high sensitivity and is lower than that of many efficient reported probes. The probe PAI is intrinsically non-fluorescent due to the photoinduced electron transfer (PET) process. However, the addition of Al3+ ion leads to the breakage of the carbon–nitrogen double bond of Schiff base in PAI resulting in the product without PET property, which shows a typical localized state with enhanced fluorescence and blue color. In addition, PAI can recognize Al3+ ion through test papers, which is in favor of the future research regarding to Al3+ ion sensing.

Salicylaldehyde and D-(+)-galactose functionalized chitosan oligosaccharide nanoparticles as carriers for sustained release of pesticide with enhanced UV stability

Sustainable food consumption is intertwined with sustainable agriculture development, which focuses on the production and protection of agricultural crops in a safe and effective fashion. Herein, amphiphilic functionalized chitosan oligosaccharide nanoparticles (CSD) were formed by a Schiff base reaction grafted with salicylaldehyde and D-(+)-galactose (D-Gal). Avermectin (AVM) was used as a model pesticide and self-assembled onto CSD to obtain AVM@CSD nanoparticles with an encapsulation efficiency of 74.94%. AVM@CSD nanocarrier exhibited excellent anti-UV property to retain more AVM, due to their Schiff base structure and salicylaldehyde for UV shielding. Compared with bare AVM and commercial AVM emulsifiable concentrates, AVM@CSD preserved high insecticidal activity after UV irradiation. Additionally, CSD carrier promoted cucumber seed germination and seedling growth. These data suggested the potential utilization of the amphiphilic chitosan oligosaccharide as carriers for pesticides to improve their delivery and release properties and opens a novel avenue towards the application of water-dispersible and biological CSD in the field of pest management and plant growth.

Renewable Vanillin-Based Thermoplastic Polybutadiene Rubber: High Strength, Recyclability, Self-Welding, Shape Memory, and Antibacterial Properties.

The vast majority of traditional vulcanized rubber products are insoluble and infusible, which is difficult to reprocess and biodegrade, resulting in black pollution. In addition, although most rubber materials based on covalent adaptive networks (CANs) can achieve structural reconstruction, the lack of traditional vulcanization system leads to a decline in strength. In this study, biobased vanillin derivatives (PV) were synthesized to cross-link the commercially available 1,2-polybutadiene rubber precursor to construct imine-based CANs, thereby fabricating a resource-renewable, recyclable, and degradable high-performance rubber material. Due to the rigid tripod structure of the PV, the tensile strength of the material can achieve as high as 16.24 MPa, ranking among the best in the field of recyclable polybutadiene-based materials. Benefiting from the dynamic imine unit, the "dynamic covalent bridge" can be re-established to repair the damaged network and endow the material with excellent weldability. And, shape memory faculty of the material was proved and depicted. Moreover, this material displayed excellent antibacterial property originates from the introduced Schiff-base structure. By mixing with graphene, the application of action sensors can also be achieved.

Facile and scalable preparation of carbon dots with Schiff base structures toward an efficient corrosion inhibitor

Carbon dots (CDs) have been demonstrated to be a novel, green and effective corrosion inhibitor. Nevertheless, it still remains an enormous challenge to obtain CDs corrosion inhibitors by an energy-efficient and time-saving way. Meanwhile, there is no investigation to evaluate the inhibition effect of CDs with Schiff base structures. To surmount the barrier, a facile and scalable approach is elaborately designed to prepare CDs with Schiff base structures (Sc-CDs) by Schiff base reaction using o-phenylenediamine (o-PD) and p-benzoquinone (p-BQ) as precursors at 50 °C for 2 h, and their corrosion inhibiting properties for Q235 carbon steel in 1 M HCl solution are systematacially investigated by weight loss test, electrochemical impedance spectra (EIS) and potentiodynamic polarization (PDP) measurement for the first time. Significantly, Sc-CDs with a long-term dispersion stability in HCl solution reveal a prominent inhibition efficiency of >96 % only at 200 mg/L incorporation. And according to the analyses of electrochemistry, adsorption isotherm and corrosion morphology, the inhibition mechanism of Sc-CDs is rationally attributed to the protective film established by Sc-CDs chemical and physical adsorptions. This work not only provides a facile, scalable, energy-efficient and time-saving approach to synthesize CDs, but also firstly evidences significant inhibition capacities of CDs with Schiff base structures. These findings would dramatically stimulate the development of truly low-cost and high-efficiency CDs corrosion inhibitors.

Synthesis of a novel bis Schiff base chelating resin for adsorption of heavy metal ions and catalytic reduction of 4-NP

A novel CPS-AA chelating resin containing bis Schiff base was prepared by the CPS with synthetic small molecular ligands. It has been used for the adsorption of heavy metal ions in wastewater. Ft-IR spectroscopy and the 1H NMR spectrum proved the successful synthesis of Schiff base structure on the chelating resin. The results of adsorption experiments showed the maximum adsorption capacities for Cu (II), Pb (II) and Ni (II) were 3.74, 1.02, and 2.87 mmol/g respectively. The adsorption condition experiment proves that the material has excellent adsorption selectivity and reusability. The possible chelation mechanism was inferred to be four-tooth coordination, which is beneficial to the stretching of molecular chain and increases the adsorption capacity and stability of heavy metal ions. Finally, Cu-adsorbed composites (CPS-AA-Cu) were used as catalysts to explore the reduction and removal of 4-NP in an aqueous solution, and the results showed excellent catalytic performance.

Versatile levulinic acid-derived dynamic covalent thermosets enabled by in situ generated imine and multiple hydrogen bonds

Bio-based dynamic covalent thermosets have attracted extensive attention as they are expected to break conventional thermosets' reliance on fossil resources and address the recycling issue after disposal. However, there has always been a contradiction between using bio-based feedstocks and possessing high properties, as well as a conflict between high performance and rapid recycling (reprocessing and degradation). In this work, a simple approach was developed to prepare bio-based thermosets with high performance, rapid reprocessing, high flame retardancy, and antibacterial properties enabled by in-situ generated dynamic covalent imine (Schiff base) bonds and multiple hydrogen bonds. The levulinic acid epoxy (ELA) was successfully synthesized and cured with 2-(4-aminophenyl)-1H-benzimidazol-5-amine (BIA) containing benzimidazole structures. The high concentration of Schiff bases and multiple hydrogen bonds of ELA-BIA endowed it with high glass transition temperature and mechanical properties, as well as satisfactory catalyst-free malleability, rapid reprocessing and repairing. Furthermore, due to the combined effect of the in-situ Schiff base and benzimidazole structure, ELA-BIA exhibited excellent condensed phase char formation ability, resulting in intrinsic flame retardancy with a limiting oxygen index of 33.8 % and a UL-94 V-0 rating, both of which were significantly higher than 4, 4′-diaminodiphenyl methane (DDM) cured ELA or DDM cured bisphenol A epoxy. Moreover, the Schiff bases bonded in the networks provided 100 % of the intrinsic antibacterial rates. This work provides a feasible and simple strategy for the preparation of high-performance and versatile bio-based dynamic covalent thermosets.

Effect of novel silicone/vanillin monomer on the thermal stability and adhesion properties of UV-curable polyurethane pressure sensitive adhesive and its application in functional glass

At present, the energy crisis is becoming increasingly outstanding, and the expanding market of pressure sensitive adhesives (PSAs) puts forward higher requirements for biomass materials. Vanillin comes from biomass raw materials, and it has been widely used in related research fields. So far, there are few reports on the preparation of novel monomers containing Schiff base structure from silicone and vanillin. In this work, vanillin reacts with methacrylic anhydride to prepare monomers with double bond structure, and furthermore a fresh type of silicone/vanillin monomer is prepared by aldehyde-amine condensation reaction. Finally, the novel monomer is introduced into polyurethane matrix, and a series of silicone/vanillin-based PSAs are prepared under UV conditions. The results show that the introduction of silicone/vanillin monomer can improve the residual carbon rate of PSAs, and the residual carbon rate of PUPG-C is as high as 12 wt%. Moreover, by comparison to the control group PUPG-0, the ball number, 180° peel strength and shear strength of PUPG-A are increased by 120.0 %, 215.0 % and 49.8 %, respectively. It is worth noting that the 180° peel strength of PSAs on functionalized glass has been strengthened, which greatly promotes the application of PSAs on functionalized glass. In short, this work provides a simple, versatile and extensible method for designing PSAs with silicone/vanillin structure in the future.

Preparation of novel bio-based imine-containing phthalonitrile resin through the nucleophilic reaction in green solvent

Nucleophilic reactions, as extensive and easily implementable reactions in organic chemistry, play a significant role in the molecular design of organic compounds and polymer materials. In current sustainable development strategies, nucleophilic reactions are also being shifted towards green chemistry. In this paper, phthalonitrile (PN) resin, a thermoset prepared by nucleophilic substitution reaction, was selected for a case study to investigate the application and reusability of the ‘green solvent’ dimethyl carbonate (DMC) in the nucleophilic substitution reaction. This research employed naturally existing vanillin and tyramine for the synthesis of a fully bio-based bisphenol bearing a Schiff base structure (VTBP). Then VTBP was converted to a novel bio-based PN (VTPN) through a nucleophilic substitution reaction in DMC, and the DMC was recovered and reused through a rotary evaporation. The structure, curing behavior, and performance of the cured resin of the synthesized VTPN were characterized. The results suggest that the Schiff base may promote and participate in the crosslinking of nitrile, with a relatively high performance achieved under moderate curing conditions. This study provides a new green implementation scheme for high-performance polymers prepared through nucleophilic reactions, as well as for the high-performance and efficient utilization of widely existing bio-based aldehydes and amines. • Bio-based phthalonitrile resin was synthesized in green solvent dimethylcarbonate. • Dimethylcarbonate was recovered and reused in the synthesis. • Imine unit was proved to promote the polymerization of phthalonitrile.

A red-emission iridium (Ⅲ) complex-based fluorescent probe with Schiff base structure for selection detection HOCl and its application in water sample

Hypochlorous acid (HOCl), a kind of reactive oxygen species (ROS), has been reported to be related to many human diseases, such as Parkinson's diseases, arthritis and cancers. Herein, a red-emission Ir(III) complex-based probe 1 for quantitative detection of HOCl was prepared and characterized by 1H and 13C NMR, IR and HRMS. For probe 1, benzenesulfonylhydrazine group was introduced to the main N^C ligands phenylpyridine to quench fluorescence due to the isomerization of C = N bond. After reaction with HOCl in 30% DMF/PBS solution, the benzenesulfonylhydrazine group was taken off and fluorescent complex Ir-CHO was generated. The fluorescence intensity at 625 nm was significantly enhanced, and finally increased by 23 times. The experiment results demonstrated that probe 1 possessed large Stokes shift (ca. 195 nm), low detection limit (1.3728 × 10−6 M), fast response (25 s), and high selectivity toward HOCl without interference from other ions and bio-related species. In addition, probe 1 exhibited good stability and water solubility. Moreover, it could be further applied in actual water for quantitative detection of HOCl with high recovery rate (95% − 101%).

Synthesis of an aromatic amine derived from biomass and its use as a feedstock for versatile epoxy thermoset

Innovative bio-based monomers and polymers are required as substitutes for limited fossil resources. Aromatic amines as an important class of chemicals are currently mostly formulated from petroleum. In this paper, a guaiacol derivative aromatic amine (5-aminoguaiacol) was designed and successfully synthesized, which was employed together with vanillin to build a high bio-based bisphenol compound. Following by glycidylation and cross-linking with 4,4′-diaminodiphenyl methane (DDM), we presented an epoxy resin network (GV-EP/DDM) bearing dynamic Schiff base bonds with high glass transition temperature of 220 °C, char yield (in N2 at 800 °C) of 44.9%, storage modulus at 30 °C of 3602 MPa, and Young’s modulus of 4489 MPa, which was 33 °C, 2.5-fold, 38% and 28% higher than those of bisphenol A epoxy resin, respectively. Furthermore, the introduction of Schiff base structure endowed the GV-EP/DDM system with shape memory, degradability, reprocessability at 230 °C under 10 MPa, as well as satisfactory antibacterial property. Notably, the higher crosslinking density made GV-EP/DDM have stronger acid resistance than the other epoxy resins with Schiff base bonds. This work provides a feasible toolbox for production of bio-based aromatic amine compounds, and a strategy to construct high performance and versatile bio-based polymer materials.

A novel biomass-derived Schiff base waterborne epoxy coating for flame retardation and anti-bacteria

Flammability and pollution of solvent-based epoxy resin coatings are thorny issues that brings series of adverse factors to the daily life and industrial manufacture. Therefore, the coatings from waterborne bio-renewable alternatives are one of the most popular topics. A novel biobased waterborne epoxy resin (WPDE) with flame retardancy and antibacterial ability was synthesized from a biomass-derived Schiff base compound [4,4′-(1E,1′E-(methylenebis(4,1-phenylene))bis(azanylylidene))bis(methanylylidene)) bis(benzene-1,2-diol), PH-DDM], followed by the reaction with epichlorohydrin and diethanolamine. The resultant WPDE was characterized by FTIR and 1 H NMR analyses. After curing reaction of WPDE with long chain fatty amine curing agent (BC919), the cured WPDE epoxy thermoset (WPDE/BC919) possessed excellent flame retardancy due to the introduction of Schiff base structure, showing a 57.3% and 25.6% decrease in peak heat release rate and total heat release value, respectively, compared with cured waterborne bisphenol A type epoxy thermoset (WE51/BC919). WPDE/BC919 also showed a superior antibacterial performance due to the formation of hydration layer and the lone pair electrons in an SP (Ahmadi et al.) hybridized nitrogen atom of Schiff base structure. Moreover, WPDE/BC919 possessed a higher glass transition temperature (Tg) of 79.6 °C and showed a 40% and 268.2% increase in storage modulus (at 20 °C) (1506.8 MPa vs. 1084.4 MPa) and Young′s modulus (306.0 MPa vs. 83.1 MPa), respectively, compared with WE51/BC919. The paper provides a novel strategy for further investigation on biobased waterborne epoxy resins as a multifunctional coating.