Chitin Nanowhiskers Research Articles

1H NMR and 1H–13C HSQC surface characterization of chitosan–chitin sheath-core nanowhiskers

Surface deacetylation of chitin nanowhiskers (CtNWs) to chitosan–sheath/chitin-core nanowhiskers (CsNWs) was successfully monitored by liquid-state high-resolution NMR of colloidal suspensions of these never-dried nanowhiskers. CtNWs were derived from acid hydrolysis (3N HCl, 30mL/g, 90min, 104°C) of chitin at 65% yield and 86% CrI. Deacetylation (50% NaOH, 48h, 50°C) of CtNWs generated CsNWs with unchanged nanowhisker morphology and overall length and width dimensions, but a reduced CrI of 54%. Successful step-wise exchanging the aqueous media with acetone, then D2O prevented agglomeration of nanowhiskers and enabled NMR detection of individual nanowhiskers. The crystalline structure of CtNWs and CsNWs provided different chemical environments for the glucosamine hydrogen atom H2, splitting the NMR signals into 2 peaks (δ 3.0 and δ 3.35ppm) which differed from that reported for soluble chitosan (δ 3.2ppm). Besides, 1H–13C HSQC was only possible for CsNWs indicating the NMR phenomenon observed to represent that of the surfaces where the outer layers were highly mobile and less crystalline. The degree of acetylation at the surfaces was determined from 1H NMR data to be 56% and 9% for CtNWs and CsNWs, respectively.

Physically Crosslinked Composite Hydrogels of Hemicelluloses with Poly(vinyl alcohol phosphate) and Chitin Nanowhiskers

Hydrogels have been widely studied as tissue engineering scaffolds due to their swelling capabilities in water and other physical properties. In this study, phosphatized PVAs of varying degrees were prepared by esterification of phosphoric acid, and a freeze-thaw technique was introduced to fabricate hydrogels from hemicelluloses, poly(vinyl alcohol phosphate) (P-PVA), and chitin nanowhiskers. The obtained hydrogels were characterized by Fourier transform infrared (FT-IR) spectrometry, scanning electron microscopy (SEM), X-ray diffraction (XRD), and CP/MAS 13C nuclear magnetic resonance; their swelling properties and compressive strength were also determined. The repeated freeze-thaw cycles induced physically crosslinked chain packing among the three polymers by hydrogen bonds. The results showed that the hydrogels possessed higher swelling ratio and mechanical strength when the PVA was phosphatized by phosphoric acid and urea and more hydroxyl groups were introduced into the polymer matrices. This suggested that hydrogels with good mechanical properties were prepared successfully by the freeze-thaw technique.

Chitin nanowhiskers as alternative antimicrobial controlled release carriers

Antimicrobial finishings protect users from pathogenic and odor-generating microorganisms, which are of medical and hygiene concerns.

Preparation of sterically stabilized chitin nanowhisker dispersions by grafting of poly(ethylene glycol) and evaluation of their dispersion stability.

Sterically stabilized chitin nanowhiskers (ChNWs) were prepared by surface grafting monomethoxy poly(ethylene glycol) (mPEG) via reductive amination of primary amino groups on ChNWs and terminal aldehydes on mPEG. The amount of grafted mPEG was determined to be 0.2-0.3 g/g ChNWs, by conductometric titration, from the decrease in amino groups after grafting. ChNWs with controlled amounts of surface amino groups were obtained by deacetylation; however, this did not cause a drastic change in the amount of grafted mPEG. Grafting was confirmed by Fourier-transform infrared spectroscopy; however, X-ray diffractometry indicated no sign of mPEG. Thermogravimetry indicated a higher amount of mPEG than that from titration, suggesting an overestimation due to the facilitated combustion of grafted samples. In contrast to ungrafted samples, all grafted samples were stable in the presence of electrolytes. However, liquid-crystalline phase separation of grafted ChNWs was not observed, possibly owing to the high viscosity of the concentrated sample.

Mechanical Properties of Polylactic Acid/Treated Fermented Chitin Nanowhiskers Biocomposites

The market share of biodegradable polymers from renewable sources has grown rapidly in the plastic industry. Properties of the polymers from renewable resources can be enhanced through blending and composite formation. Fermented chitin is a by-product in a bacterial prawn waste fermentation for protein recovery which has undergone mild chemical treatment producing treated fermented chitin (TFC). TFC was further acid hydrolysed to produce chitin nanowhiskers (TFCNW). The chitin nanowhiskers was used as filler in polylactic acid (PLA) through solution casting method. Atomic Force Microscopy showed TFCNW particles are uniformly dispersed in PLA matrix but tends to agglomerate as TFCNW loading increased. Tensile strength of the biocomposite film increased up to 12.4 MPa at 2 phr TFCNW which it decreased with further addition of TFCNW. The Young’s modulus increased with increasing of TFCNW content up to 3.69 GPa. However, elongation at break of the biocomposite film decreased by 66 % upon addition of TFCNW when compared to pure PLA.

Anionic and cationic nanocomposite hydrogels reinforced with cellulose and chitin nanowhiskers: effect of electrolyte concentration on mechanical properties and swelling behaviors

Various nanocomposite gels were prepared using cellulose nanowhiskers (CNWs) or chitin nanowhiskers (ChNWs) as reinforcing fillers and hydroxypropyl cellulose (HPC), carboxymethyl cellulose (CMC), or chitosan as network polymers. The use of CNWs with low surface charge induced significant CNWs aggregations, which were well explained by depletion effect. Young's modulus E and swelling ratio Q of CNWs/HPC · CMC gels were highest at zero electrolyte concentration and decreased above 0.01 M electrolyte, whereas stress at break σ of the gels showed its minimum at zero electrolytes and increased with an addition of electrolytes. In the case of ChNWs/chitosan gels, maximum of E and Q was located at 0.01 M electrolyte concentration, and σ did not indicate clear tendency with electrolyte concentration. Although all gels indicated an increase in E and a decrease in Q with an increase in whisker content, the most remarkable changes were observed under an absence of electrolytes, whereas the changes under the presence of electrolytes were somewhat negligible. Copyright © 2014 John Wiley & Sons, Ltd.

Nanoreinforced hemicellulose-based hydrogels prepared by freeze–thaw treatment

A novel hybrid hydrogel was prepared from hemicelluloses, polyvinyl alcohol, and chitin nanowhiskers by the freeze–thaw technique. The hydrogel was characterized by Fourier-transform infrared (FT-IR) spectrometry, scanning electron microscopy, X-ray diffraction analysis, cross-polarization (CP)/magic-angle spinning (MAS) 13C nuclear magnetic resonance (NMR), and swelling property and compressive strength measurements. Atomic force microscopy images of chitin implied that the size of whiskers reached nanometer level with average length of about 200 nm and width of 40 nm. The FT-IR and NMR results indicated that physical cross-linking rather than chemical reaction occurred during the gelation process. The mechanical properties of the hydrogels were significantly improved with increasing proportion of chitin nanowhiskers, with the highest compressive stress of 9.6 MPa being found for Gel-0.5. The results showed that the repeated freeze–thaw cycles induced physical cross-linking of packed chains by hydrogen bonds among the polymers, and the concentration of chitin nanowhiskers affected the hydrogel morphology and properties. It is suggested that hydrogels with good mechanical properties can be successfully prepared by this physical method, offering promise for tissue engineering applications.

Chitosan-sheath and chitin-core nanowhiskers

Chitosan-sheath and α-chitin-core nanowhiskers (CsNWs) have been successfully generated by surface deacetylation of chitin nanowhiskers (CtNWs) in the never-dried state. Acid hydrolysis (3N HCl, 30mL/g, 104°C) of pure chitin derived from crab shell yielded 65% 4–10nm thick, 16nm wide and 214nm long chitin whiskers (CtNWs) that were 86% crystalline and 81% acetylated. Surface deacetylation of CtNWs was robust in their never-dried state in 50% NaOH at a moderate 50°C for 6h, yielding 92% CsNWs. All deacetylated CsNWs retain the same α-chitin crystalline core at reduced 50% crystallinity and similar dimensions (4–12nm thick, 15nm wide, 247 long) as CtNWs, but reduced 60% acetylation reflecting the deacetylated surface layers. Progressive surface deacetylation was evident by the increased IP as well as increased positive charges under acidic pH and reduced negative charges at alkaline pH with increasing reaction time.

Fabrication and Characterization of PLA/PHBV-Chitin Nanocomposites and Their Foams

This paper examines the effect of biobased chitin nanowhisker fillers on the thermal, rheological, physical, mechanical and morphological properties of biobased polylactic acid (PLA) and PLA/polyhydroxybutyrate-co-valerate (PHBV) blended nanocomposites as well as the physical, mechanical and morphological properties of porous PLA and PLA/PHBV nanocomposite foams. Solid nanocomposites of PLA, PLA/PHBV and chitin nanowhiskers were manufactured through melt blending while porous nanocomposites foams were fabricated through a batch foaming process with the aid of CO2 as blowing agent. It was found that by incorporating small quantities of chitin nanowhiskers (<2 wt%) the mechanical properties of solid specimens are improved while strength and expandability of the foam can be significantly improved, yielding a homogenously distributed cell morphology with average cell size of 1.5 μm.

High strength of hemicelluloses based hydrogels by freeze/thaw technique

Novel hydrogels were prepared from hemicelluloses, polyvinyl alcohol (PVA), and chitin nanowhiskers through 0, 1, 3, 5, 7, and 9 times of freeze/thaw cycle. These hydrogels were characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), swelling property, and compressive strength. The repeated freeze/thaw cycles induced physically crosslinked chains packing among these polymers, and a phase separation caused by the hydrogen bonds. Larger pores led to a high swelling degree, whereas the formation of compact structure after multiple freeze/thaw cycles resulted in high mechanical strength and thermal stability. The highest compressive strength of these hydrogels was achieved by the 9 times of freeze/thaw cycles with compressive stress of 10.5MPa. This work provides a remarkable way for the preparation of hydrogels with good mechanical properties by physical method.

Chitin nanowhisker aerogels.

Chitin nanowhiskers are structured into mesoporous aerogels by using the same benign process used previously in our group to make cellulose nanowhisker aerogels. The nanowhiskers are sonicated in water to form a hydrogel before solvent-exchange with ethanol and drying under supercritical CO2 (scCO2). Aerogels are prepared with various densities and porosities, relating directly to the initial chitin nanowhisker content. scCO2 drying enables the mesoporous network structure to be retained as well as allowing the gel to retain its initial dimensions. The chitin aerogels have low densities (0.043–0.113 g cm−3), high porosities (up to 97 %), surface areas of up to 261 m2 g−1, and mechanical properties at the high end of other reported values (modulus between 7 and 9.3 MPa). The aerogels were further characterized by using X-ray diffraction, BET analysis, electron microscopy, FTIR, and thermogravimetric analysis. Characterization showed that the rod-like crystalline nature of the nanowhiskers was retained during the aerogel production process, making the aerogel truly an assembled structure of chitin nanocrystals. These aerogels also showed the lowest reported shrinkage during drying to date, with an average shrinkage of only 4 %.

Chitin-chitosan nanocomposite gels: reinforcement of chitosan hydrogels with rod-like chitin nanowhiskers

Nanocomposite gels containing chitosan as a network polymer and chitin nanowhiskers as reinforcing fillers were successfully prepared by cross-linking with the blocked isocyanate, HDS. Young’s modulus and stress at break of the nanocomposite gels increased to maximum values of 169 and 135 kPa, respectively, with increase in whisker content up to 13.3%, whereas the degree of swelling decreased from 357 to 33.0.

Fabrication and characterization of melt-blended polylactide-chitin composites and their foams

This study details the fabrication and foaming of melt-blended polylactide (PLA) and chitin composites. The chitin used for compounding was as-received, as chitin nanowhiskers and as chitin nanowhiskers with a compatibilizing agent. The chitin nanowhiskers were produced by an acid-hydrolysis technique and their morphology was examined with transmission electron microscopy. The composite morphology was characterized with scanning electron microscopy and was related to the observed thermal, rheological, and mechanical behaviors of the composites. Chitin was found to decrease the thermal stability of the composites. Addition of chitin was also found to reduce the viscosity of the composites, which is believed to be because of the hydrolysis of PLA during melt blending of chitin in suspension. The stiffness of the composites was found to increase with increasing chitin content while the strength was found to decrease. Porous PLA—chitin composites were produced by a two-step batch-foaming technique, and the expansion behavior was correlated with the visco-elastic observations. The statistical significance of chitin type and composition dependence on the mechanical properties and foam morphologies were evaluated.

Preparation of chitin nanowhiskers using an ionic liquid and their composite materials with poly(vinyl alcohol)

The preparation of chitin nanowhiskers using an ionic liquid, 1-allyl-3-methylimidazolium bromide (AMIMBr) was performed. First, chitin was swollen with AMIMBr by soaking at room temperature, followed by heating at 100°C. Soaking the resulting gel in methanol and subsequent sonication gave a chitin dispersion. The SEM image of the dispersion showed the formation of chitin nanowhiskers. Then, filtration of the dispersion was carried out to give a chitin film. Composite films of the chitin nanowhiskers with poly(vinyl alcohol) were prepared by a similar procedure to the chitin film. They were characterized by SEM and DSC measurements and their mechanical properties were evaluated by tensile testing.

Chitin Nanowhiskers Mediate Transformation of Escherichia coli by Exogenous Plasmid DNA

A colloidal solution of chitin nanowhiskers containing pUC18 plasmid DNA and cells of Escherichia coli was placed on an agar hydrogel and stimulated by sliding friction applied between the agar hydrogel and polystyrene stir stick, leading to transformation of the bacteria to antibiotic resistance. The combination of chitin nanowhiskers and sliding friction was necessary for genetic transformation, indicating that the chitin nanowhiskers induced the Yoshida effect, resulting in the formation of E. coli cells penetration-intermediates. The pUC18 adsorbed onto the chitin nanowhiskers is presumably taken up through the penetration-intermediates, leading to transformation. The transformation efficiency changed when the number of recipient cells and amount of chitin nanowhiskers were varied. The maximum number of penetration-intermediates acquiring pUC18 DNA was obtained with concentrations of agar hydrogel, chitin nanowhiskers, and recipient E. coli cells of 2.5%, 5.0 ?g/ml, and 4.8 x 108 cells/ml, respectively. Optimal transformation efficiency with pUC18 was achieved with 2.1 x 1066 colony forming units/?g of pUC18. Induction of the Yoshida effect with chitin nanowhiskers represents a simpler alternative for introducing genes into bacteria.

CaCO3/chitin-whisker hybrids: formation of CaCO3 crystals in chitin-based liquid-crystalline suspension

CaCO3/chitin-whisker hybrids were prepared using the liquid-crystalline suspension of the chitin whisker. Suspensions of chitin nanowhiskers were obtained by acid hydrolysis of chitin powder. The suspension containing about 5 wt% of whiskers exhibited lyotropic liquid-crystalline behavior. The suspension was converted to a gel form when it was exposed to ammonium carbonate vapor. CaCO3 crystals were formed for 30 days in chitin gels as templates. The nucleation of CaCO3 occurred in the liquid-crystalline chitin matrix and the CaCO3 crystals deposited in the chitin gels to form hybrids with an interpenetrated three-dimensional structure. Scanning electron microscopy image of the fractured sample of the hybrid showed that the gel matrix was filled with CaCO3 crystals. Thermogravimetric analysis revealed that the composition of CaCO3/polymer/H2O is about 2:6:2 in weight. This approach inspired by biomineralization may be useful for the development of inorganic/organic hybrid materials. CaCO3/chitin-whisker hybrids were prepared by deposition of CaCO3 crystals in ordered chitin gel matrices. The gels were prepared by conversion of lyotropic liquid crystals of chitin whiskers.

Individual chitin nano-whiskers prepared from partially deacetylated α-chitin by fibril surface cationization

α-Chitin was partially deacetylated to degrees of N-acetylation (DNAc) 0.74–0.70 by 33% NaOH treatment at 90 °C for 2–4 h. Solid recovery ratios or yields of the products were 85–90%. Crystallinity index and crystal size of the original α-chitin were maintained, showing that the partial deacetylation mostly occurred on the α-chitin crystallite surfaces. Transparent and highly viscous liquids were obtained by disintegration of the partially deacetylated chitins in water at pH 3–4. Transmission electron microscopy (TEM) revealed that the liquids consisted mostly of individual nano-whiskers with average width and length 6.2 ± 1.1 and 250 ± 140 nm, respectively. Some α-chitin nano-fibrils of more than 500 nm in length were also detected in TEM images. Because the DNAc values 0.74–0.70 correspond to 1.34–1.56 mmol g −1 C2-amino group contents, high cationic charges might be formed on the α-chitin fibril surfaces in high density by protonation in water at pH 3–4.

Microwave technique for efficient deacetylation of chitin nanowhiskers to a chitosan nanoscaffold

A chitosan nanoscaffold in the form of a colloidal solution was obtained from the deacetylation of chitin whiskers under alkaline conditions by using a microwave technique in only 1/7 of the treatment time of the conventional method. Fourier-transform infrared spectroscopy (FTIR) and nuclear magnetic resonance ( 1H NMR) techniques confirm the degree of deacetylation to be above 90% within 3 h. The wide-angle X-ray diffraction (WAXD) pattern clearly shows that the highly crystalline chitin whiskers are changed to amorphous chitosan. SEM micrographs show the aggregation of branched nanofibers, whereas the TEM micrographs reveal the scaffold morphology.