Ning Lin

Supramolecular hydrogels from in situ host-guest inclusion between chemically modified cellulose nanocrystals and cyclodextrin.

When grafted β-cyclodextrin is used as targeting sites, Pluronic polymers have been introduced on the surface of cellulose nanocrystals by means of inclusion interaction between β-cyclodextrin and hydrophobic segment of the polymer. Because of the steric stabilization effect, surface poly(ethylene glycol) chains facilitate the dispersion and compatibility of nanocrystals, which also enhance the loading levels of nanocrystals in the hydrogel system. Meanwhile, uncovered poly(ethylene glycol) segments render the participating inclusion of α-cyclodextrin for the architecture of in situ hydrogels. Surface grafting and inclusion reactions were proved by solid (13)C NMR and FTIR. Grafting efficiency of β-cyclodextrin and inclusion efficiency of Pluronic on the surface of nanocrystals were confirmed by UV spectroscopy and elemental analysis. A significant enhancement of the structural and thermal stability of in situ hydrogels with high loading levels of modified nanocrystals (>5.77 wt %) was observed by rheological analysis. Further study reveals the performance and behavior of hydrogels under a different pH environment. Finally, in situ hydrogels were used as drug carrier for in vitro release of doxorubicin and exhibit the behavior of prolonged drug release with special release kinetics.

Effect of polysaccharide nanocrystals on structure, properties, and drug release kinetics of alginate-based microspheres

Polysaccharide nanocrystals, such as rod-like cellulose nanocrystals and chitin whiskers and platelet-like starch nanocrystals, were incorporated into alginate-based nanocomposite microspheres with the aim of enhancing mechanical strength and regulating drug release behavior. The structures and properties of the sols and the resultant nanocomposite microspheres were characterized by rheological testing, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The presence of polysaccharide nanocrystals increased the stability of the crosslinked network structure, and the nanocomposite microspheres consequently exhibited prominent sustained release profiles, as demonstrated by inhibited diffusion of theophylline. Furthermore, based on the drug release results, the release kinetics and transport mechanisms were analyzed and discussed.

Preparation, modification, and application of starch nanocrystals in nanomaterials: a review

During the past decade, much work has been devoted to the preparation of nanomaterials by blending starch nanocrystals from different sources with various polymer matrices. The following paper summarizes the most up-to-date information available relating to starch nanocrystals and their contribution to research, application, and advancement of diversified nanomaterials. This paper provides an overview of aspects related to starch nanocrystals, including methods for extraction and preparation, chemical modification (with particular emphasis on the modification methods and strategies), reinforcing effects and mechanisms, and applications and prospects.

Reinforcement and nucleation of acetylated cellulose nanocrystals in foamed polyester composites.

The biodegradable foamed nanocomposites were developed from the reinforcement of surface acetylated cellulose nanocrystals (ACNC) as bionanofillers and the poly(butylene succinate) (PBS) as polymeric matrix. The surface modification of high-efficiency acetylation on the cellulose nanocrystals converted the hydrophilic hydroxyl groups to hydrophobic acetyl groups, which improved the compatibility between rigid nanoparticles and polyester matrix through the similar ester groups of two components. With the introduction of 5 wt% ACNC, the specific flexural strength (σ/ρf) and the specific flexural modulus (E/ρf) of the foamed composites significantly increased by 75.7% and 57.2% in comparison with those of the neat PBS foamed material. Meanwhile, with the change of the ACNC concentrations, the cell size and cell density of the foamed composites can be regulated and achieved the high cell density of 1.95 × 10(5)cells/cm(3) bearing the small average cell size of 178.84 μm (5 wt% ACNC). The microstructure observation of the foamed composites indicated the moderate loading levels of rigid ACNC can serve as the reinforcing phase for the stress transfer and promote the crystallinity advancement of the foamed composites.

Highly alkynyl-functionalization of cellulose nanocrystals and advanced nanocomposites thereof via Click chemistry

A series of reactive GAP (glycidyl azide polymer)/PTPB (propargyl-terminated polybutadiene) nanocomposites reinforced by alkynylated cellulose nanocrystals (ACNC) were synthesized by Huisgen click chemistry. High-efficiency substitution (more than 80%) of the hydroxyl groups by alkynyl groups on the surface of CNC was realized through the esterification reaction between the alkynylated anhydride compound and the cellulose nanocrystals. The covalent bonding from the alkynyl groups of ACNC and the azide groups of GAP was proved by Fourier transform infrared spectroscopy, which indicated the possible participation of the click reactions among the ACNC, GAP, and PTPB components in the composites. The nanoreinforcing effect of the rigid ACNC on the GAP/PTPB matrix and the strong interfacial interaction through the covalent grafting between nanoparticles and the matrix significantly improved the mechanical properties of the prepared nanocomposites. In comparison with the neat GAP/PTPB (GP2) material, the tensile strength, Youngs modulus, and the elongation at break of the GP2/ACNC-1.0 nanocomposite (containing only 1.0 wt% ACNC) were increased by 103.3%, 100.0% and 12.4%, respectively. This study is a promising attempt to develop advanced polymeric composites reinforced with biomass-based nanoparticles with the simultaneous improvement of strength, modulus and toughness.

Green bionanocomposites from high-elasticity “soft” polyurethane and high-crystallinity “rigid” chitin nanocrystals with controlled surface acetylation

Castor oil-based polyurethane bionanocomposites with improved mechanical properties were prepared by the introduction of crab chitin nanocrystals from partial surface acetylation. Through controlled acetylation, some of the hydrophilic hydroxyl groups on the nanocrystals were replaced by hydrophobic acetyl groups in order to enhance the compatibility between the chitin nanoparticles and polyurethane; and some of the hydroxyl groups were preserved on the surface of nanocrystals for the purpose of rigid network formation among chitin nanoparticles. The presence of acetylated chitin nanocrystals at moderate concentration (6 wt%) will significantly promote the nano-reinforcing effect in composites, and simultaneously improved the strength, stiffness and toughness of thermoplastic polyurethane-based nanocomposites. Meanwhile, derived from the restriction of rigid nanocrystals to soft segments, the glass transition temperatures of the nanocomposites surprisingly increased with the higher loading levels of acetylated chitin nanocrystals. More importantly, this study provided a strategy for the discussion of synergistic effects and “trade-off” of adequate dispersion, network formation and interfacial adhesion of rigid nanoparticles in soft polymeric matrices, by means of structure and properties analysis of semi-transparent polyurethane/acetylated chitin nanocrystals composites.

Advances in cellulose nanomaterials

Research on nanocellulose has significantly increased over the past few decades, owing to the various attractive characteristics of this material, such as renewability, widespread availability, low density, excellent mechanical properties, economic value, biocompatibility, and biodegradability. Nanocellulose categorized into two main types, namely cellulose nanofibrils (CNFs) and cellulose nanocrystals (CNCs). In this review, we present the recent advances made in the production of CNFs and CNCs. In addition to the conventional mechanical and chemical treatments used to prepare CNFs and CNCs, respectively, other promising techniques as well as pretreatment processes have been also proposed in recent times, in an effort to design an economically efficient and eco-friendly production route for nanocellulose. Further, while the hydrophilic nature of nanocellulose limits its use in polymeric matrices and in some industrial applications, the large number of hydroxyl groups on the surface of nanocellulose provides a suitable platform for various kinds of modification treatments. The various chemical and physical surface treatment procedures reported for nanocellulose have been reviewed in this paper. Finally, in this review, we summarize the life cycle assessment studies conducted so far on nanocellulose, which quantify the environmental impact of nanocellulose products. The current paper is a comprehensive review of the recent literature on nanostructured cellulose.

Preparation of fungus-derived chitin nanocrystals and their dispersion stability evaluation in aqueous media

The chitin nanocrystal is a promising nano-reinforcing agent, but the parasitic pathogens carried on crabs and shrimp shells as main sources limit its application in some fields. In this study, the ChNs which avoided possible safety risks were extracted from mushrooms via protein/mineral-purification and subsequent HCl-hydrolysis. Such fungus-derived ChNs presented an α-chitin crystalline structure with a length of 143±24nm and a diameter of 10±2nm. Since the dispersion stability of ChNs suspension determines their further applications, this present study emphasized the dispersity of ChNs in aqueous media evaluated by the viscosity under steady-shear flow and UV-vis absorption, whose results indicated that ChNs in dispersion would aggregate when the concentration of homogeneous dispersion reached 0.5-0.6wt%. To explore the effect of electrostatic repulsion on interactions between nanoparticles, the maximum energy barriers for parallel and crossed orientations of ChNs in suspension were analyzed using a traditional DLVO theory with additions of NaCl solutions.

Focus on Gradientwise Control of the Surface Acetylation of Cellulose Nanocrystals to Optimize Mechanical Reinforcement for Hydrophobic Polyester-Based Nanocomposites

Surface acetylation of cellulose nanocrystals (CNCs) imposes an important effect on CNC-related mechanical enhancement of hydrophobic polyester-based composites, of which interfacial properties still need optimization. In the present work, the surface acetylation of CNCs was adjusted as a gradient of above ca. 10%. Then, we found that the surface energy of acetylated CNCs (ACNs) decreased and thus their hydrophobicity increased as the surface acetylation degree increased. Hence, the ACNs with varied degrees of acetyl substitution (DSsurface-acetyl) values were attempted to reinforce a kind of hydrophobic polyester, poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (PHB). The results indicated that a smaller discrepancy in the surface energy between the CNC surface and the PHB matrix was obtained, as the surface acetylation degree increased, and then, the affinity and interaction between the two components increased, which improved the homogeneous distribution of ACNs in the PHB matrix. Besides, in comparison to the nanocomposites filled with 15 wt % unmodified CNCs, the tensile strength of those with ACNs of 62.9% DSsurface-acetyl was 43.3% higher. This study was the first attempt to adjust the surface substitution degrees with a gradient profile for the surface modification of CNCs and prove that acetylation gradient control is an effective and facile strategy to optimize the mechanical properties.

Simultaneous enhancement of elasticity and strength of Al2O3-based ceramics body from cellulose nanocrystals via gel-casting process

A green gel-casting method was developed by the combination of rod-like cellulose nanocrystals (CNC) and low toxicity monomer N, N-dimethylacrylamide (DMAA), which was proved to be a promising substitute of traditional neurotoxin monomer acrylamide (AM). The hydrophilic nature and homogeneous dispersion of CNC in aqueous suspension ensured the essential compatibility with the hydrosoluble polymerization system, and therefore provided remarkable mechanical enhancement of green body. The bending strength of the green body was highly increased by 68% with the introduction of 0.9 wt‰ CNC. Meanwhile, the fabricated green body exhibited significant improvement in flexibility and elasticity, with the unique bendable and recovery performances after drying treatment at room temperature for 1h. The computer stimulation by the COMSOL Multiphysics confirmed the special mechanical enhancement effect induced by the presence of highly-crystalline and rigid CNC.