Chemical modification of chitin by grafting with polystyrene using ammonium persulfate initiator

Fabrication of chitin based hydrophilic hyper-crosslinked porous polymer for efficiently removing bisphenol A from water

Water pollution caused by bisphenol A (BPA) has become the world problem. Designing and preparing cost-effective and biodegradable sorbents for the effectively adsorptive removal of bisphenol A from wastewater is of immense significance. Herein, a natural polysaccharide (chitin) was used as raw materials to be grafted with styrene (GS), then crosslinked with α,α'-dichloro-p-xylene (DCX) to form the hyper-crosslinked polymer (labeled as CGS@DCX). The CGS@DCX showed high adsorptive affinity for bisphenol A, with adsorption capacity of 441 mg g-1. Various studies gave an insight into the adsorption process, demonstrating that the highly efficient adsorption of BPA by the CGS@DCX is mainly based on the π-π stacking, hydrogen-bond interaction, polar interaction and pore adsorption. Moreover, the CGS@DCX had high chemical stability, good reusability (9 cycles) and fast adsorption kinetics (10 min) for adsorption of BPA. This work provides a promising strategy for the design and synthesis of novel yet eco-friendly sorbents to solve environmental problems.

Direct and Indirect Cationization of Cellulose Nanocrystals: Structure-Properties Relationship and Virus Capture Activity

Due to increasing public concern over hygiene, there have been many studies investigating antimicrobial and antiviral agents recently. With the aim of developing biobased virucidal/virus capture agents, we report a chemical modification of the cellulose nanocrystals (CNCs) surface with poly(2-dimethylamino) ethyl acrylate) methyl chloride quaternary salt (Q-PDMAEA) to introduce the positively charged functional groups. The surface of CNCs was modified through direct and indirect graft polymerization. Subsequently, the direct and indirect cationization effect on the degree of functionalization, thermal stability, crystallinity, and antiviral activity of CNCs was investigated. Indirect cationization produced the highest degree of polymer grafting, increasing particle size and thermal stability. Further, the modified CNCs were tested for their ability to capture nonenveloped bacteriophages PhiX174 (ΦX174) and MS2. We observed a significant (>4.19 log10) reduction in total viral load by specific functionalized CNCs. However, the activity depended on the structure of functional groups, surface charge density, and the type of virus under study. Overall, the direct and indirect cationization of CNC leads to biobased agents with immobilized cationic charge, with good virus capture activity. Such agents can be used for various applications including textiles, packaging, wastewater treatment, etc.

Surface modifications of biomaterials in different applied fields

Biomaterial implantation into the human body plays a key role in the medical field and biological applications. Increasing the life expectancy of biomaterial implants, reducing the rejection reaction inside the human body and reducing the risk of infection are the problems in this field that need to be solved urgently. The surface modification of biomaterials can change the original physical, chemical and biological properties and improve the function of materials. This review focuses on the application of surface modification techniques in various fields of biomaterials reported in the past few years. The surface modification techniques include film and coating synthesis, covalent grafting, self-assembled monolayers (SAMs), plasma surface modification and other strategies. First, a brief introduction to these surface modification techniques for biomaterials is given. Subsequently, the review focuses on how these techniques change the properties of biomaterials, and evaluates the effects of modification on the cytocompatibility, antibacterial, antifouling and surface hydrophobic properties of biomaterials. In addition, the implications for the design of biomaterials with different functions are discussed. Finally, based on this review, it is expected that the biomaterials have development prospects in the medical field.

Cellulose Nanocrystal-Polyelectrolyte Hybrids for Bentonite Water-Based Drilling Fluids

Cellulose nanocrystals (CNCs), with their rodlike shape and nanoscale dimensions, greatly improve the filtration performance of bentonite-containing, water-based drilling fluids (BT-WDFs) through interactions with the BT platelets. When these WDFs are exposed to high salt concentrations, though, their fluid retention properties are greatly diminished due to reduced CNC-BT interaction and BT aggregation/flocculation. Consequently, we reduce BT-BT interaction at high salt by grafting polyelectrolytes (PE) to CNC particles (CNC-PE) to enhance CNC-BT interactions when incorporating these hybrid particles with BT-WDFs. The particles sterically and electrostatically screen BT platelets from associating, thus improving fluid filtration performance at high salt. Three types of CNC modifications were carried out: grafting from direct surface initiation, modification with vinyl-terminated glycidyl methacrylate (GMA) before grafting, and physical mixing of CNC with a polymer. These modifications were performed using three polyelectrolyte materials: anionic polystyrene sulfonate (PSS), cationic polyacrylamide (PAM), and a random copolymer of PSS and PAM (PSS-co-PAM). Formulations containing CNC-PEs prepared by covalent grafting exhibited superior filtration properties compared to those in which CNCs and PEs were physically mixed. The higher graft loading achieved with the GMA method resulted in poorer filtration results compared to the direct grafting method due to CNC-PE interparticle cross-linking. PSS-modified CNC-PEs appeared to attach to BT edges, while PAM-modified CNC-PEs attached to the BT faces. These interactions disrupted BT aggregation, with the PSS-co-PAM CNC hybrid displaying the most desired filtration properties. The results highlight the importance of steric and charge stabilization of the BT particle edges and faces to achieve high-performance WDFs for well excavation.

Double stimuli-responsive cellulose nanocrystals reinforced electrospun PHBV composites membrane for intelligent drug release

Double stimuli-responsive functionalized cellulose nanocrystal-poly[2-(dimethylamino)ethyl methacrylate] (CNC-g-PDMAEMA) reinforced poly(3-hydroxybutyrate-co-3-hydroxy valerate) (PHBV) electrospun composite membranes were explored as drug delivery vehicles using tetracycline hydrochloride (TH) as a model drug. It was found that rigid CNC-g-PDMAEMA nanoparticles enhanced thermal, crystallization and hydrophilic properties of PHBV. Moreover, great improvements in fiber diameter uniformity, crystallization ability and maximum decomposition temperature (T_max) could be achieved at 6 wt% CNC-g-PDMAEMA. Furthermore, by introducing stimuli-responsive CNC-g-PDMAEMA nanofillers, intelligent and long-term sustained release behavior of composite membranes could be achieved. The releasing mechanism of composite membranes based on zero order, first order, Higuchi and Korsmeyere-Peppas mathematical models was clearly demonstrated, giving effective technical guidance for practical drug delivery systems.

Graft modification of carboxymethyl chitosan with styrene and its biological applications

Background

Carboxymethyl chitosan (CMCh) is a water-soluble chitosan derivative and it has been widely used in biomedical applications due to its unique properties. Modification of CMCh by graft copolymerization with different monomers is done in order to enhance its applications.

Results

Graft copolymerization of styrene (S) onto CMCh using ammonium persulfate (APS) as initiator was successfully done with optimization of grafting parameters. The new materials were prepared in nano size. The antibacterial activities against Streptococcus pneumonia (RCMB 010010), Staphylococcus aureus (RCMB 010028) as Gram-positive and Escherichia coli (RCMB 010052) as Gram-negative bacteria and antifungal activity against Aspergillus fumigates (RCMB 02568), Candida albicans (RCMB 05036), Syncephalastrum racemosum (RCMB 05922), and Geotricum candidum (RCMB 05097) were examined using the diffusion agar technique. Also, the cytotoxicity effect against mammalian cell lines (MCF-7cells (human breast cancer) and HTC-116 (colon carcinoma)) was evaluated.

Conclusions

The obtained data proved that grafted carboxymethyl chitosan with styrene (CMCh-g-S) shows better antimicrobial activities, while parent carboxymethyl chitosan showed higher activity than new grafted materials. Also the nano scaled grafted CMCh showed higher activities than grafted carboxymetyl chitosan in macro scale.

Sulfonated Lignin-g-Styrene Polymer: Production and Characterization

Among sustainable alternatives for replacing fossil-based chemicals, lignin is widely available on earth, albeit the least utilized component of biomass. In this work, lignin was polymerized with styrene in aqueous emulsion systems. The reaction afforded a yield of 20 wt % under the conditions of 100 g/L lignin concentration, pH 2.5, 0.35 mol/L sodium dodecyl sulfate concentration, 5 mol/mol styrene/lignin ratio, 5 wt % initiator, 90 °C, and 2 h. The lignin-g-styrene product under the selected conditions had a grafting degree of 31 mol % of styrene, which was determined by quantitative proton nuclear magnetic resonance (NMR). The solvent addition to the reaction mixture and deoxygenation did not improve the yield of the polymerization reaction. The produced lignin-g-styrene polymer was then sulfonated using concentrated sulfuric acid. By introducing sulfonate group on the lignin-g-styrene polymers, the solubility and anionic charge density of 92 wt % (in a 10 g/L solution) and -2.4 meq/g, respectively, were obtained. Fourier-transform infrared (FTIR), static light scattering, two-dimensional COSY NMR, elemental analyses, and differential scanning calorimetry (DSC) were also employed to characterize the properties of the lignin-g-styrene and sulfonate lignin-g-styrene products. Overall, sulfonated lignin-g-styrene polymer with a high anionicity and water solubility was produced.

Chitosan Derivatives: Introducing New Functionalities with a Controlled Molecular Architecture for Innovative Materials

The functionalization of polymeric substances is of great interest for the development of innovative materials for advanced applications. For many decades, the functionalization of chitosan has been a convenient way to improve its properties with the aim of preparing new materials with specialized characteristics. In the present review, we summarize the latest methods for the modification and derivatization of chitin and chitosan under experimental conditions, which allow a control over the macromolecular architecture. This is because an understanding of the interdependence between chemical structure and properties is an important condition for proposing innovative materials. New advances in methods and strategies of functionalization such as the click chemistry approach, grafting onto copolymerization, coupling with cyclodextrins, and reactions in ionic liquids are discussed.

Fluorescence control of chitin and chitosan fabricatedviasurface functionalization using direct oxidative polymerization

The copolymer of 3-hexylthiophene (3HT) and fluorene (F) was directly grafted onto chitin and chitosan using FeCl₃ as an oxidant. The properties of the grafted chitin/chitosan were characterized by Fourier transform infrared (FT-IR) spectroscopy, UV-Vis spectroscopy, fluorescence spectroscopy, X-ray diffraction analysis, thermogravimetric analysis (TGA), transmission electron microscopy-energy dispersive X-ray spectroscopy, and quantum yield measurements. The UV-Vis absorption peaks of the chitin/chitosan grafted with 3-hexylthiophene and fluorene copolymer were increasingly blue-shifted upon increasing the fluorene content and the red-shifted emission of the grafted chitin/chitosan were controlled by varying the monomers feed of the 3HT/F units. The hypsochromic and bathochromic shifts of chitin/chitosan were ascribed to the (3HT/F) moieties grafted to their surface. The quantum yield of grafted chitin/chitosan increased upon increasing the fluorene content. The TGA and XRD analysis revealed that the thermal stability and crystallinity of chitin/chitosan decreased upon grafting the copolymer of fluorene and 3-hexylthiophene. This article represents a simple route towards the surface modification of chitin and chitosan using conducting copolymers, providing multicolor chitin and chitosan via a one-step reaction.

The copolymer of 3-hexylthiophene (3HT) and fluorene (F) was directly grafted onto chitin and chitosan using FeCl₃ as an oxidant.

The Effect of the Molecular Architecture on the Antioxidant Properties of Chitosan Gallate

To elucidate the structure-antioxidant activity relationships of chitosan gallate (CG), a series of CG derivatives with different degrees of substitution (DS's) and molecular weights (MWs) were synthesized from chitosan (CS) and gallic acid (GA) via a free radical graft reaction. A higher MW led to a lower DS of CG. The structures of CG were characterized by FT-IR and ¹H NMR, and results showed that GA was mainly conjugated to the C-2 and C-6 positions of the CS chain. The antioxidant activity (the DPPH radical scavenging activity and reducing power) were enhanced with an increased DS and a decreased MW of CG. A correlation between antioxidant activities and the DS and MW of CG was also established. In addition, a suitable concentration (0~250 μg/mL) of CG with different MWs (32.78~489.32 kDa) and DS's (0~92.89 mg·GAE/g CG) has no cytotoxicity. These results should provide a guideline to the application of CG derivatives in food or pharmacology industries.

Stimuli-Responsive Cellulose Nanocrystals for Surfactant-Free Oil Harvesting

Cellulose nanocrystals with grafted binary polymer brushes (CNC-BPB), poly(oligoethylene glycol) methacrylate (POEGMA) and poly(methacrylic acid) (PMAA), were prepared by cerium-mediated polymerization in aqueous solution. The physical properties of CNC-BPB can be controlled by external triggers, such as temperature and pH, which can be utilized to stabilize and destabilize oil-water emulsions. By virtue of the modifications, these bifunctionalized CNCs diffused to the oil-water interface and stabilized the oil droplets at high pHs. When the pH was lowered to 2, strong hydrogen bonding between POEGMA and PMAA chains grafted on the CNC induced the coalescence of the emulsion droplets, resulting in the phase separation of oil and water. For emulsions stabilized by CNC-POEGMA and free PMAA mixtures, instantaneous coalescence was not observed at low pHs. Successive stabilization-destabilization over 5 cycles was demonstrated by modulating the pH with the addition of acid or base without any loss in efficiency. This work demonstrates that functional sustainable nanomaterials can be used for small scale oil-water separations, particularly for oil droplet transportation and harvesting of lipophilic compounds.