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allows the bres that are electrospun to be more aligned and uniform [108]. Uniaxially orientated nanobers can be fabricated by electrospinning onto a rotating cylinder col-lector. Fibre alignment can improve the mechanical properties of a nanocomposite even further than randomly orientated bres. Both the needle of the syringe acts as an elec-trode causing deformation in the droplet that forms at the tip of the needle at the end of the set-up. This droplet formation is known as a Taylor cone. The solvent evaporates during the process of electrospinning, yielding a dry ber mat collected after the electro-spinning procedure. This process is illustrated in Figure 2.9.

Figure 2.9: The electrospinning procedure [109].

Other types of electrospinning procedures exist, such as ball electrospinning that allows

bres to be electrospun from multiple points due to the formation of multiple Taylor cones caused by a rotating roller within the electrospinning solution as shown in Figure 2.10.

Instead of a needle a small glass ball, called a ball spinneret, is placed in the solution and rotated while an electrical eld is applied. The bres are spun upwards which helps pre-vent polymer solution from dripping onto the bre mat that is collected on the collector plate.

Multi-needle electrospinning techniques, such as co-axial electrospinning, have also been investigated where more than one needle is used in the electrospinning system and more than one type of electrospinning solution is produced by each needle nozzle. A large working environment is required for multi-needle electrospinning so that the strong inter-ferences between adjacent solution jets can be avoided.

Figure 2.10: The procedure of ball spinning. [109]

The conventional setup (horizontal or vertical) is used widely in hundreds of labs all over the world. In this study only, the conventional horizontal setup was used. There are important parameters to consider when conducting an electrospinning procedure as discussed in Section 2.9.2.

2.9.2 Parameter eects

Electrospinning has many factors that can inuence the diameter and morphology of bres [109]. The variables and parameters are summarized in Table 2.4. The most important parameters are conductivity, viscosity, distance from the needle to base collector and ow rate. Intrinsic properties of the electrospinning solution such as the polymer type, chain conformation, viscosity, elasticity, polarity and electrical conductivity, are all important contributions to the properties of the nanobers. The surface tension of the solvent also inuences the way that the solution will electrospun. Minimization of the surface tension of the solvent causes one or more spherical droplets to form from the electrospinning solution jet. The electrostatic repulsion between the charges on the jet surface tends to increase the surface area of the droplet. This is favourable for the formation of a thin electrospinning jet rather than electrospraying. Good viscoelastic forces within the poly-mer solution prevent rapid changes in the shape of the bre and aord more support for the formation of smooth bre morphology [109]. The conditions within the lab also contribute to the product of the electrospinning process. The last two factors that can impact the morphology and diameter of the bre-mat are humidity and temperature [110].

Table 2.4: Parameter that aect electrospinning.

Solution Properties Processing Properties

1 Concentration and Viscosity 1 Applied voltage 2 Molecular Weight and Architecture 2 Flow rate

3 Conductivity 3 Tip to collector distance

4 Atmospheric Temperature and Humidity

Chapter 3

Experimental

3.1 Materials

Medium molecular weight chitosan (CTS) (deacetylation 85%) and chitin (sourced from shrimp shells) were obtained from Sigma Aldrich. Triuoroacetic acid (TFA), dichloromethane (DCM) and 37% Hydrochloric acid (HCl) were procured from MINEMA as were analytical grade Zn(NO3)2·6H2O, Ni(SO4)·7H2O, K2Cr2O7, Pb(NO4)2 and Cu(NO3)2·3H2O. Poly (ethylene-co-vinyl alcohol) (EVOH) (32 wt% ethylene content) was provided by Sigma Aldrich along with isopropanol. SnakeSkinTM dialysis tubing (10K MWCO, 22 mm) was provided by Thermo Fischer Scientic. Potassium nitrate (KNO3)(98-100%) was obtained from Barrs Industrial Enterprises. Ethylenediaminetetraacetic acid (EDTA) was obtained from Sigma Aldrich. Fluorescein isothiocyanate (FITC) was provided by Sigma Aldrich.

Glacial acetic acid (100%) was provided by Merck.

3.2 Preparation of chitin nanowhiskers

Chitin nanowhiskers (chnw) were prepared by acid hydrolysis of chitin [36]. Chitin akes (3g) were hydrolyzed in HCl (3M, 90 mL) at 100 ‰. The hydrolysis took place under reux and was terminated after 4 hours by the addition of cold deionized water (90 mL).

The hydrolysis step was then followed by centrifugation. The solution was decanted into centrifuge tubes and the initial (yellow) supernatant was discarded after which the sub-strate was washed with more deionized water and centrifuged again. These steps were repeated until the supernatant became milky (turbid) indicating the presence of chnw.

The turbid suspension was retained and dialyzed against deionized water using snakeskin dialysis tubes (20 to 25 ‰) until a neutral pH was obtained (typically after 2 weeks). The chnw suspension was then frozen with liquid nitrogen and freeze-dryed to obtain white cotton-like chnw.

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3.3 Labeling of chitin nanowhiskers, chitosan and chitosan nanoparticles

Freeze dried chnw (250 mg) was added to a round bottom ask containing NaOH (0.1 M, 25 mL). FITC (10 mg) was added to the solution. The ask was closed immediately using a stopper and covered with aluminium foil. It was stirred in darkness for three days.

After this the contents of the ask was decanted into centrifuge tubes, centrifuged twice and washed with distilled water while the solid material was collected and centrifuged again. Centrifugation was repeated until the suspension was clear. The chnw that was collected after washing was then dialyzed in distilled water for approximately a week until a neutral pH has been reached. The same procedure was used for the labeling of chitosan nanoparticles and chitosan powder.

3.4 Preparation of chitin

nanowhiskers/poly(ethylene-co-vinyl alcohol)