Nadeeka D. Tissera

A method for top down preparation of chitosan nanoparticles and nanofibers

A method of top down preparation of chitosan nanoparticles and nanofibers is proposed. Chitin nanofibrils (chitin NFs) were prepared using ultrasonic assisted method from crab shells with an average diameter of 5 nm and the length less than 3 μm as analyzed by atomic force microscopy and transmission electron microscopy. These chitin nanofibers were used as the precursor material for the preparation of chitosan nanoparticles and nanofibers. The degree of deacetylation of these prepared chitosan nanostructures were found to be approximately 98%. In addition these chitosan nanostructures showed amorphous crystallinity. Transmission electron microscopic studies revealed that chitosan nanoparticles were roughly spherical in nature and had diameters less than 300 nm. These larger particles formed through self-assembly of much smaller 25 nm particles as evidenced by the TEM imaging. The diameter and the length of the chitosan nanofibers were found to be less than 100 nm and 3 μm respectively. It is envisaged that due to the cavitation effect, the deacetylated chitin nanofibers were broken down to small pieces to form seed particles. These seed particles can then be self-assembled to form larger chitosan nanoparticles.

Ultrasound energy to accelerate dye uptake and dye–fiber interaction of reactive dye on knitted cotton fabric at low temperatures

Acoustic cavitation formed due to propagation of ultrasound wave inside a dye bath was successfully used to dye cotton fabric with a reactive dye at lower temperatures. The energy input to the system during sonication was 0.7 W/cm(2). This was within the energy range that contributes towards forming cavitation during ultra-sonication. The influence of ultrasound treatment on dye particle size and fiber morphology is discussed. Particle size analysis of the dye bath revealed ultra-sonication energy was capable of de-agglomeration of hydrolyzed dye molecules during dyeing. SEM micrograph and AFM topographical image of the fiber surface revealed fiber morphology remains unchanged after the sonication. The study was extended in understanding the contribution of ultrasound method of dyeing towards achieving good color strength on the fabric, compared to the normal heating method of dyeing. Study showed color strength obtained using ultra sound method of dyeing is higher compared to normal heating dyeing. Ultrasound energy was able to achieve the good color strength on cotton fabric at very low temperature such as 30 °C, which was approximately 230% more than the color strength achieved in normal heating method of dyeing. This indicates that energy input to the system using ultrasound was capable of acting as an effective alternative method of dyeing knitted cotton fabrics with reactive dye.

Side selective surface modification of chitin nanofibers on anionically modified cotton fabrics

Chitin nanofibers have been prepared from crab shell as a chitin source using ultrasound assisted fibrillation. Atomic force microscopy (AFM) study showed that the prepared nanofibers were having diameters and lengths primarily in the range of 2-20 nm and 0.3-4 μm respectively. These nanofibers were selectively grafted on one side of a 100% cotton fabric using a special apparatus. Prior to the grafting, cotton fabrics were modified with partial carboxymethylation to encourage cotton fiber nanofiber interactions. The surface modification was confirmed by Fourier transform infrared spectroscopy (FT-IR) peaks at 1,594 cm(-1) and 1,735 cm(-1) due to the presence of carboxylic acid functionality in modified cotton fabrics. Scanning electron microscope (SEM) study of the nanofiber grafted cotton fabrics showed that nanofibers were adhered to the cotton fabrics. Elemental analysis confirmed that side selective grafting of nanofiber has taken place due to the peak at 0.394 keV which attributes to the presence of nitrogen element in chitin nanofibers. This peak was absent in the other side of the fabric which was not coated with chitin nanofibers. Amount of adhered nanofibers was seen to increase with the increase of nanofiber concentration used in grafting as confirmed by Kjeldahl analysis. A possible mechanism of cotton fiber-nanofiber interactions is introduced.

Coloration of cotton fibers using nano chitosan.

A method of coloration of cotton fabrics with nano chitosan is proposed. Nano chitosan were prepared using crab shell chitin nanofibers through alkaline deacetylation process. Average nano fiber diameters of nano chitosan were 18 nm to 35 nm and the lengths were in the range of 0.2-1.3 μm according to the atomic force microscope study. The degree of deacetylation of the material was found to be 97.3%. The prepared nano chitosan dyed using acid blue 25 (2-anthraquinonesulfonic acid) and used as the coloration agent for cotton fibers. Simple wet immersion method was used to color the cotton fabrics by nano chitosan dispersion followed by acid vapor treatment. Scanning electron microscope and atomic force microscope study of the treated cotton fiber revealed that the nano chitosan were consistently deposited on the cotton fiber surface and transformed in to a thin polymer layer upon the acid vapor treatment. The color strength of the dyed fabrics could be changed by changing the concentration of dyed nano chitosan dispersion.

Heterogeneous in situ polymerization of polyaniline (PANI) nanofibers on cotton textiles: Improved electrical conductivity, electrical switching, and tuning properties

Electrically conductive cotton fabric was fabricated by in situ one pot oxidative polymerization of aniline. Using a simple heterogeneous polymerization method, polyaniline (PANI) nano fibers with an average fiber diameter of 40-75 nm were grafted in situ onto cotton fabric. The electrical conductivity of the PANI nanofiber grafted fabric was improved 10 fold compared to fabric grafted with PANI nanoclusters having an average cluster size of 145-315 nm. The surface morphology of the cotton fibers was characterized using SEM and AFM. Electrical conductivity of PANI nanofibers on the cotton textile was further improved from 76 kΏ/cm to 1 kΏ/cm by increasing the HCl concentration from 1 M to 3 M in the polymerization medium. PANI grafted cotton fabrics were analyzed using FTIR, and the data showed the presence of polyaniline functional groups on the treated fabric. Further evidence was present for the chemical interaction of PANI with cellulose. Dopant level and morphology dependent electron transition behavior of PANI nanostructures grafted on cotton fabric was further characterized using UV-vis spectroscopy. The electrical conductivity of the PANI nano fiber grafted cotton fabric can be tuned by immersing the fabric in pH 2 and pH 6 solutions for multiple cycles.

Carbon black functionalized stretchable conductive fabrics for wearable heating applications

There is an increasing interest on robust electrically conductive textiles with light weight and flexibility to meet the applications in wearable electronics. Current challenge is to fabricate such structures with feasible application strategies that can be readily scalable and provide higher mechanical stability of the conductive media on the textile matrix to withstand constant stretch and shear forces. We report a strategy to address these challenges, by using a “screen printing process” employing conductive carbon black ink. We produced conductive fabrics with liner resistance of less than 71 Ω cm−1. These textile materials showed stable conductivity up to 25% strain. Microscopic studies revealed that at strains lower than 25%, percolation pathways in the conductive media increases resulting lowering of the liner resistance. However, further stretching of over 25% resulted increase of resistance due to separation of conductive pathways. Ohmic heating application of the resulted fabrics showed fast response rate and no significant hysteresis. The conductive print was stable over long period of heating over number of cycles. These feasible conductive fabric fabrication pathways can provide new avenues in designing and manufacturing of wearable heat management and electronic applications.

In-situ formation of supramolecular aggregates between chitin nanofibers and silver nanoparticles

Chitin and chitin derivatives have gained significant research interest over the years due to a number of beneficial properties that can be exploited in various application fields. Particularly, interactions between their nanostructures and other nanomaterials are of great interest. In situ photo-reduction of AgCl in chitin nanofiber aqueous dispersions resulted in significant loss of colloidal stability of both chitin nanofibers (CNF) and silver nanoparticles. UV-vis spectroscopy was used to characterize the extinction profiles of in-situ prepared CNF and several silver nanoparticle mixtures over the reaction steps. High resolution TEM characterization of the resulting structures indicated the presence of the aggregated form of nanofiber and nanoparticles. Energy filtered TEM analysis confirmed the existence of both CNF and silver nano particles in the aggregate, with silver in its chemically reduced state (Ag(0)). FT-IR, and 13C solid state NMR revealed the presence of strong interactions between Ag and CNF through hydroxyl and carbonyl moieties of the CNF structure. It was concluded that these interactions led to the formation of a supramolecular aggregate in the in-situ mixture as a result of wrapping of CNF around photo-reduced silver nanoparticles which resulted in the colloidal instability.