Chitin Whiskers Research Articles

Preparation and Characterization of Nanocomposite Films from Chitin Whisker and Waterborne Poly(ester-urethane) With or Without Ultra-Sonification Treatment

Two series of nanocomposite films were prepared from waterborne poly(ester-urethane) and chitin whisker with and without ultrasound treatment coded as CW/WPU and CHW/WPU, respectively. The effects of ultra-sonification method and chitin whisker content on the chemical compositions, crystallization behavior and miscibility were studied by attenuated total reflection Fourier transform infrared (ATR-FTIR), wide-angle X-ray diffraction (WXRD), dynamic mechanical analysis (DMA) and scanning electron microscopy (SEM). Thermal stability and mechanical properties of the films were measured by thermogravimetric analysis (TGA) and tensile test, respectively. The results revealed that both nanocomposite films exhibited a certain degree of miscibility when chitin whisker content was lower than 30 wt%, resulting in higher thermal stability and tensile strength than the pure waterborne poly(ester-urethane) film. Interestingly, the composite films CW/WPU with ultrasound treatment possessed better miscibility, storage modulus, thermal stability and tensile strength than those without ultrasound treatment over the entire composition range studied here. The difference can be attributed to the relatively higher dispersion level of whisker within poly(ester-urethane) matrix resulting in relatively stronger entanglement and interaction between both components. The ultrasound treatment can effectively improve the miscibility and mechanical properties of the casting nanocomposite films with nano-meter size chitin whisker added. This indicated that the structure, miscibility and mechanical properties of the nanocomposite films depended significantly on the preparation method.

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.

Starch-based composites reinforced with novel chitin nanoparticles

Contrary to the most recognizable whiskers of slender parallelepiped rods, unique nanoparticles of about 50–100 nm were obtained from chitin after consecutive acid hydrolysis and mechanical ultrasonication treatments. Chitin nanoparticles (CNP) exhibited lower crystallinity when compared to conventional chitin whisker. Glycerol plasticized-potato starch (GPS) was combined with CNP to prepare all-natural nanocomposites by casting and evaporation. The morphology, structural, thermal and mechanical properties of the nanocomposites were evaluated by electron microscopy, X-ray diffraction, dynamic mechanical thermal analysis, and tensile tests. At low loading levels, CNP were uniformly dispersed in the GPS matrix and had good interaction between the filler and matrix, which led to improvements in tensile strength, storage modulus, glass transition temperature, and water vapor barrier properties of the GPS/CNP composites. However, at higher loading (greater than 5 wt.%), aggregation of CNP had a negative effect on these properties.

X‐ray diffraction and dynamic mechanical analyses of α‐chitin whisker‐reinforced poly(vinyl alcohol) nanocomposite nanofibers

AbstractElectrospinning is a facile method for preparing nanocomposite materials in fiber form. Nanomaterials that have been incorporated within such fibers are usually inorganic in nature. Recently, nanocomposite nanofibers based on poly(vinyl alcohol) (PVA) as the matrix and nanocrystals of α‐chitin (i.e. chitin whiskers; ca 31 nm in width and ca 549 nm in length on average) as the nanofiller have been successfully prepared. In the study reported here, the fibers were further investigated using X‐ray diffraction (XRD) and dynamic mechanical analyses in comparison with the corresponding solvent‐cast films. The average diameters of the PVA/chitin whiskers fibers ranged between 175 and 218 nm. Careful analysis of the wide‐angle XRD patterns of the fiber mats and the films showed that PVA was partially crystalline, and the incorporation of the whiskers within the fibers was confirmed by peaks characteristic to α‐chitin crystals. Dynamic mechanical analysis showed that the fiber mats were weaker than the films and that the relaxation temperatures associated with the glass transition (Tg) of the fiber mats were greater than those of the films. The addition and increasing the amount of the whiskers caused the crystallinity of PVA within the nanocomposite materials to decrease and Tg to increase. The present study shows that the geometry of nanocomposite materials plays a major role in determining their properties. Copyright © 2009 Society of Chemical Industry

Wet-spun alginate/chitosan whiskers nanocomposite fibers: Preparation, characterization and release characteristic of the whiskers

Incorporation of chitosan whiskers in alginate fibers was achieved by mixing homogenized chitosan whisker colloidal suspension with 6% w/v sodium alginate aqueous solution, followed by extrusion into fiber form by wet spinning. The chitosan whiskers were prepared by deacetylation of chitin whiskers which had been obtained by acid hydrolysis of chitin flakes from shrimp shells. The average length and width of the whiskers were 309 and 64 nm, respectively, with the average aspect ratio being ∼4.8. Study on the mechanical properties of the neat alginate and the alginate/chitosan whiskers nanocomposite yarns (30 individual fibers) revealed that, at 1.0% w/w, noticeable improvement in the tensile strength of the nanocomposite yarns was observed, at the expense of the elongation at break. The release of the whiskers from the nanocomposite yarns was dose-dependent and it occurred based on the surface erosion phenomenon. The release half-lives of the nanocomposite yarns containing 0.2% and 0.6% w/w of the whiskers were about 6 h and less than 1 h, respectively. Incorporation of the chitosan whiskers within the alginate yarns imparted the antibacterial activity against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli to the resulting alginate/chitosan whiskers nanocomposite yarns, which rendered them as effectual wound dressing materials.

Cross-Linked Chitosan/Chitin Crystal Nanocomposites with Improved Permeation Selectivity and pH Stability

This study is aimed at developing and characterizing cross-linked bionanocomposites for membrane applications using chitosan as the matrix, chitin nanocrystals as the functional phase, and gluteraldehyde as the cross-linker. The nanocomposites' chemistry and morphology were examined by estimation of gel content, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and atomic force microscopy (AFM), whereby the occurrence of cross-linking and nanoscale dispersion of chitin in the matrix was confirmed. Besides, cross-linking and chitin whiskers content were both found to impact the water uptake mechanism. Cross-linking provided dimensional stability in acidic medium and significantly decreased the equilibrium water uptake. Incorporation of chitin nanocrystals provided increased permeation selectivity to chitosan in neutral and acidic medium.

Direct chitosan scaffold formation via chitin whiskers by a supercritical carbon dioxide method: a green approach

The wide array of tissue-engineering applications enhances the need for biodegradable materials with broad potential. Chitosan, the partially deacetylated derivative of chitin, may be one such material. This research studies the morphology and characterization of porous structures produced from chitin for use as a scaffold for cell culture. The chitosan scaffold was prepared by reaction of chitin with alkali using supercritical carbon dioxide (scCO2). The prepared hydrogel was subjected to solvent exchange. The material was characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM). Nitrogen porosimetry was applied to evaluate the scaffold for its porosity and surface area. With this scCO2 method, a porous chitosan scaffold was successfully fabricated.

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.

Fabrication, structure, and properties of chitin whisker‐reinforced alginate nanocomposite fibers

AbstractCalcium alginate yarn (30 fibers) and calcium alginate nanocomposite yarn (30 fibers) containing 0.05–2.00% w/w chitin whiskers were both prepared by wet spinning process. The whiskers were prepared by acid hydrolysis of chitin from shrimp shells. The average length and width of the whiskers were 343 and 46 nm, with the aspect ratio being ∼ 7.5. Incorporation of a low amount of the whiskers in the nanocomposite fibers improved both the mechanical and the thermal properties of the fibers significantly, possibly a result of the specific interactions, i.e., hydrogen bonding and electrostatic interactions, between the alginate molecules and the homogeneously dispersed chitin whiskers. Biodegradation of the calcium alginate fibers and the nanocomposite fibers was tested in Tris‐HCl buffer solution and the same buffer solution that contained lysozyme. The addition of the chitin whiskers in the nanocomposites fibers accelerated the biodegradation process of the fibers in the presence of lysozyme, whereas the presence of Ca2+ ions in the Tris‐HCl buffer solution helped to improve the tenacity of both the alginate and the nanocomposite fibers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Polysaccharide nano crystal reinforced nanocomposites

There are numerous examples of animals or plants that synthesize extracellular high-performance skeletal biocomposites consisting of a matrix reinforced by nano sized crystalline domains. Cellulose and chitin are classical examples of these reinforcing elements, which occur as whisker-like microfibrils that are biosynthesized and deposited in a continuous fashion. In many cases, this mode of biogenesis leads to crystalline microfibrils that are almost defect-free, and whose axial physical properties therefore approach those of perfect crystals. During the last decade we have attempted to mimic biocomposites by blending cellulose or chitin whiskers from different sources with polymer matrices. Aqueous suspensions of such nano crystals can be prepared by acid hydrolysis of the substrate. The object of this treatment is to dissolve away regions of low lateral order so that the water-insoluble, highly crystalline residue may be converted into a stable suspensoid by subsequent vigorous mechanical shearing action. The resulting nano crystals occur as rod-like particles or whiskers, whose dimensions depend on the nature of the substrate. They are typically a few hundred nm long and between 5 and 20 nm in diameter. Starch can also be used as a source for the production of nano crystals. The constitutive nano crystals appear as platelet-like nano particles with a length ranging between 20 and 40 nm, a width ranging between 15 and 30 nm, and a thickness ranging between 5 and 7 nm. Since the first announcement of using cellulose whiskers as a reinforcing phase, they have been used extensively as model fillers in several kinds of polymeric matrices, including synthetic and natural ones. Casting mixtures of polysaccharide nano crystals and lattices led to the production of nano composite materials with drastically enhanced mechanical properties, especially at T > Tg of the matrix, by virtue of the formation of a whiskers network, even when the whisker volume fraction was only a few percent. The formation of this rigid network, resulting from strong interactions between whiskers, was assumed to be governed by a percolation mechanism. This hydrogen-bonded network induced a thermal stabilization of the composite up to 500 K, the temperature at which polysaccharides start to decompose. Any factors that perturb the formation of this percolating network directly affect the reinforcing effect of polysaccharide nano crystals. In addition to some practical applications, the study of these nano composite materials can help researchers understand such physical properties as the geometric and mechanical percolation effect.Key words: nano composites, polysaccharide, polymer, cellulose, nano crystal.

Influence of the Processing Conditions on the Mechanical Properties of Chitin Whisker Reinforced Poly(caprolactone) Nanocomposites

Influence of the Processing Conditions on the Mechanical Properties of Chitin Whisker Reinforced Poly(caprolactone) Nanocomposites

Preparation and characterization of chitin whisker-reinforced silk fibroin nanocomposite sponges

For highly porous form such as sponges or scaffolds, the induction of the β-sheet formation of silk fibroin to make the water-stable materials usually results in their high shrinkage leading to a difficulty in controlling shape and size of materials. Thus, the objective of this study was to improve dimensional stability of silk fibroin sponge by incorporating chitin whiskers as nanofiller. Chitin whiskers exhibited the average length and width of 427 and 43 nm, respectively. Nanocomposite sponges at chitin whiskers to silk fibroin weight ratio (C/S ratio) of 0, 1/8, 2/8, or 4/8 were prepared by using a freeze-drying technique. The dispersion of chitin whiskers embedded in the silk fibroin matrix was found to be homogeneous. The presence of chitin whiskers embedded into silk fibroin sponge not only improved its dimensional stability but also enhanced its compression strength. Regardless of the chitin whisker content, SEM micrographs showed that all samples possessed an interconnected pore network with an average pore size of 150 μm. To investigate the feasibility of the nanocomposites for tissue engineering applications, L929 cells were seeded onto their surfaces, the results indicated that silk fibroin sponges both with and without chitin whiskers were cytocompatible. Moreover, when compared to the neat silk fibroin sponge, the incorporation of chitin whiskers into the silk fibroin matrix was found to promote cell spreading.

Direct chitosan nanoscaffold formation via chitin whiskers

Chitosan nanoscaffold obtained directly from chitin whiskers is proposed. The structural analysis by nuclear magnetic resonance (1H NMR) confirms that the alkaline treatment changes chitin whisker to chitosan nanoscaffold with as high as 98% degree of deacetylation. The micrographs from scanning electron microscope (SEM) and transmission electron microscope (TEM) confirm that the short fiber of chitin whiskers develop itself to be a network in nano-scale of chitosan or chitosan nanoscaffold. The increase in viscosity of chitosan nanoscaffold as compared to that of the chitin whiskers suggests that the scaffold network performs as a polymer bulk in the solution. The increases in surface area, pore volume, and pore size as studied by the Brunauer–Emmett–Teller (BET) gas adsorption inform the development of porous structure in chitosan. The well dispersion of nanoscaffold in the solution is easily controlled by the solvent polarity and salt concentration.

Fabrication of α-chitin whisker-reinforced poly(vinyl alcohol) nanocomposite nanofibres by electrospinning

The present contribution reports, for the first time, the successful fabrication ofα-chitin whisker-reinforced poly(vinyl alcohol) (PVA) nanocomposite nanofibres by electrospinning. Theα-chitin whiskerswere prepared from α-chitin flakes from shrimp shells by acid hydrolysis. The as-prepared chitin whiskersexhibited lengths in the range 231–969 nm and widths in the range 12–65 nm, with theaverage length and width being about 549 and 31 nm, respectively. Successful incorporationof the chitin whiskers within the as-spun PVA/chitin whisker nanocomposite nanofibreswas verified by infrared spectroscopic and thermogravimetric methods. The incorporationof chitin whiskers within the as-spun nanocomposite fibre mats increased theYoung’s modulus by about 4–8 times over that of the neat as-spun PVA fibremat.

A novel soft and cotton‐like chitosan‐sugar nanoscaffold

A novel type of chitosan nanoscaffold with a soft and cotton-like appearance is proposed. The key to success is based on two points: (i) the change in morphology of chitin whisker to chitosan nanoscaffold and (ii) the surface modification of the nanoscaffold chitosan with a sugar unit. Simple deacetylation of chitin whisker gives a colloidal solution of chitosan, of which the chitosan is in a nanoscaled scaffold. Surface functionalization of the chitosan nanoscaffold with lactose or maltose via a heterogeneous system in water at room temperature results in a soft and cotton-like chitosan containing mesopores. As all steps are organic solvent free, this chitosan-sugar nanoscaffold might be a promising material for biopolymer-supported tissue engineering.

Morphology and properties of soy protein isolate thermoplastics reinforced with chitin whiskers.

Environmentally friendly thermoplastic nanocomposites were successfully developed using a colloidal suspension of chitin whiskers as a filler to reinforce soy protein isolate (SPI) plastics. The chitin whiskers, having lengths of 500 +/- 50 nm and diameters of 50 +/- 10 nm on average, were prepared from commercial chitin by acid hydrolysis. The dependence of morphology and properties on the chitin whiskers content in the range from 0 to 30 wt % for the glycerol plasticized SPI nanocomposites was investigated by dynamic mechanical thermal analysis, scanning electron microscopy, swelling experiment, and tensile testing. The results indicate that the strong interactions between fillers and between the filler and SPI matrix play an important role in reinforcing the composites without interfering with their biodegradability. The SPI/chitin whisker nanocomposites at 43% relative humidity increased in both tensile strength and Young's modulus from 3.3 MPa for the SPI sheet to 8.4 MPa and from 26 MPa for the SPI sheet to 158 MPa, respectively. Further, incorporating chitin whisker into the SPI matrix leads to an improvement in water resistance for the SPI based nanocomposites.

Crab Shell Chitin Whiskers Reinforced Natural Rubber Nanocomposites. 3. Effect of Chemical Modification of Chitin Whiskers

The purpose of this study was to chemically modify the surface of chitin whiskers and to investigate the effect of the incorporation of these modified whiskers into a natural rubber (NR) matrix on the properties of the ensuing nanocomposite. Different chemical coupling agents were tested, namely, phenyl isocyanate (PI), alkenyl succinic anhydride (ASA) (Accosize 18 from American Cyanamid), and 3-isopropenyl-alpha,alpha'-dimethylbenzyl isocyanate (TMI). The extent of chemical modification was evaluated by Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), and surface energy analysis. After chemical modification, nanocomposite films were obtained using a toluene natural rubber solution in which the whiskers were dispersed. Their mechanical properties were found to be inferior to those of unmodified chitin/NR composites presented in our previous study. In fact, even though there is an increase in filler-matrix interaction as a result of chemical modification of the chitin whiskers, this does not contribute to the improvement in the mechanical properties of the resulting nanocomposite. It is concluded that this loss of performance is due to the partial destruction of the three-dimensional network of chitin whiskers assumed to be present in the unmodified composites.

Crab shell chitin whisker reinforced natural rubber nanocomposites. 2. Mechanical behavior.

In a previous work (part 1), nanocomposite materials were obtained using a latex of either unvulcanized or prevulcanized natural rubber as the matrix and a colloidal suspension of crab chitin whiskers as the reinforcing phase. The mechanical behavior of the resulting nanocomposite films was analyzed in both the linear and the nonlinear range in the present study. The effects of the filler and processing technique were evaluated, and the results are discussed based on the knowledge of the structural morphology and swelling behavior reported in our previous work. The reinforcing effect of chitin whiskers strongly depended on their ability to form a rigid three-dimensional network, resulting from strong interactions such as hydrogen bonds between the whiskers. The results emanating from the successive tensile test experiments give clear evidence for the presence of a three-dimensional chitin network within the evaporated samples. Cross-linking of the matrix was found to interfere with the formation of this network.

Crab shell chitin whisker reinforced natural rubber nanocomposites. 1. Processing and swelling behavior.

Nanocomposite materials were obtained from a colloidal suspension of chitin whiskers as the reinforcing phase and latex of both unvulcanized and prevulcanized natural rubber as the matrix. The chitin whiskers, prepared by acid hydrolysis of chitin from crab shell, consisted of slender parallelepiped rods with an aspect ratio close to 16. After the two aqueous suspensions were mixed and strirred, solid composite films were obtained either by freeze-drying and hot-pressing or by casting and evaporating the preparations. The processing and swelling behavior of composite films were evaluated. It was concluded that the whiskers form a rigid network assumed to be governed by a percolation mechanism in the evaporated samples only. Comparatively, better resistance of evaporated samples than hot-pressed ones against swelling in an organic solvent medium is good evidence for the existence of a rigid chitin network. The values of diffusion coefficient, bound rubber content, and relative weight loss also supported the presence of a three-dimensional chitin network within the evaporated samples. The mechanical behavior of the composites gives additional insight and evidence for this fact (part 2).

Nanocomposites of Chitin Whiskers from Riftia Tubes and Poly(caprolactone)

Nanocomposite materials were obtained from a colloidal suspension of high aspect ratio β chitin whiskers as the reinforcing phase and poly(caprolactone) as the matrix. The chitin whiskers, prepared by acid hydrolysis of Riftia tubes, consisted of slender parallelepiped rods with an aspect ratio close to 120. A procedure was optimized to prepare a latex of poly(caprolactone). After mixing and stirring the two aqueous suspensions, solid films were obtained by either freeze-drying and hot-pressing or casting and evaporating the preparations. An amorphous poly(styrene-co-butyl acrylate) latex was also used as a model matrix. The thermal and mechanical properties of the resulting films were evaluated. The reinforcing effect of chitin whiskers is discussed on the basis of different types of mechanical models, and it is concluded that these whiskers form a rigid network assumed to be governed by a percolation mechanism. The formation of this network allows the thermal stabilization of the material for temperatur...