Preparation of nanofibers from natural cellulose by electrospinning method

Nanotechnology involves the development of nanoscale materials with superior properties and performance in surface applications, electrical-computer technology, medical fields, aerospace-space research, biotechnology-agriculture and environment-energy industries. Because the nanofibers diameter is at the nanometer level, it increases the surface / volume ratio of the material and the mechanical properties of the fibers. Nanotechnology has begun to show interest, in renewable reserves as a raw material for the creation of value-added products for the increasing global energy demand in environmental and energy research for the environmental ethics. Plastics and composites derived from renewable biomass raw materials are seen as promising materials for replacing synthetic polymers and reducing global dependence on fossil fuels. Among renewable materials, cellulose is considered to be the strongest potential candidate for the recruitment of petroleum-based polymers due to environmental friendliness such as biodegradability, biocompatibility and renewability. Thanks to its superior properties such as high thermal stability and desirable mechanical strength, it is used in various fields such as textile engineering, food science and biomedical engineering. Cellulose is the most abundant natural organic chemical substance of the world produced by living organisms on earth and produces about 180 billion tons of cellulose per year. Among the most primitive plants, high organized trees, even in some animal sources, cellulose is present. Cellulose is regarded as an almost inexhaustible source of raw material, with an increase in demand for friendly biocompatible materials. While the chemical structure properties of the cellulose from different sources are similar to those of the building stone, there are significant differences between them physically (crystal structure, polymerization degree, etc.). From here we aim to, dissolve the cellulose that we use in our daily life, in suitable solvents and then electrospinning. To demonstrate the operability of the electrospinning device and proving the gathering of the nanofibers, cellulose acetate solution is used. Cellulose acetate solution is dissolved in acetone/DMAc. Electrospinning process is done for the cellulose acetate solution and then for the characterization of the nanofibers, SEM is used. The average fiber diameter for cellulose acetate is 126.9土12 nm. In the first part of the experimental study, a suitable solvent is searched for the breaking down the hydrogen bonds of the toilet paper (cellulose) which is the main raw material we use in this study and then tried to electrospin the solution. Firstly, before the dissolving process is carried out; cellulose in DMAc/LiCl always requires a pre-activation process. The main purpose for activation process is to weaken the polymer chain interaction to get a relaxed conformation. There are two main methods for cellulose activation process; high temperature activation and polar medium exchange activation. The high temperature activation method degrades cellulose notably by the effect of high temperature. Besides, polar medium exchange activation; without any degradation of cellulose, achieved better, faster and more reproducible dissolution. In our first part of study, we used polar medium activation. For the activation process before dissolution water x2 (45 min) + methanol x2 (45 min) + DMAc (45 min. + overnight) are used. Activated cellulose with concentrations of 2-3% in DMAc / LiCl of 8% are prepared, but the viscosity of the obtained solution is very high for the electrospinning process. Electrospinning has not been made successfully due to high viscosity. Later, heating of the solution was tried, but until starting the electrospinning process, the solution returned to room temperature. As a second system, a heat gun was used but due to the limits of the electrospinning device, the heat gun also did not give the desired result. As the last system infrared heater was used, it was attached to the top of the electrospining device. Although the temperature was set at 60oC, due to the limits of the electrospinning device, the infrared heater also did not give the desired result. In the second part of the experimental work, the solvent was changed to TFA. Since TFA is volatile, it should be used immediately after opening the lid or it is starting to lose its effect. The cellulose solution with concentrations of 2-2.5% was prepared and the viscosity was lower than the first used solvent. Electrospinning was made successfully with this effect. The obtained fibers were examined by SEM, FTIR and XRD. From the 2.5% toilet paper, 2.5% long fiber and 2.5% short fiber, nanofibers were obtained. When the solution concentration is above 2.5%, the solution becomes very viscous and takes bulk consistency. As a result of the different experiments, the concentration of optimum solution is determined as 2.5% for long fiber. At concentrations below 2.5%, no nanofibers were obtained. The optimum concentration for Short Fiber is 2.5%. Working with high concentrations results poor conductivity between nanofibers. When concentration is reduced, more nanofibres are obtained. The optimum concentration for toilet paper is 2.5%. As the concentration decreases, the diameters of the fibers obtained increase. The best and optimum working conditions for the toilet paper, long and short fibers are; 5 ml/hr for the flow rate, for the voltage 25-27 kV, for the distance between needle and the collector is around 12 cm and the relative humidity is Rh 60 %. As a result of the obtained FTIR, most of the cellulosic peaks were seen in FTIR analysis, as toilet paper consisted of pure cellulose. Before the FTIR analysis the cast film was exposed to air for a long time and the band of 1790 cm-1 indicating the TFA peak was not observed. After exposure of the nanofibers to air, FTIR analysis showed that the ester groups were partially removed from the TFA trough by hydration with air humidity and, at the same time, natural evaporation. It has been seen that these peaks disappear completely when exposed to air for longer periods. In nanofibers, the peak at 1426 cm-1, known as crystallinity peak, disappeared, indicating that the structure has a amorphous phase. FT-IR results showed an almost complete removal of the TFA by the exposure of air; thus, contact with or consumption for humans is safe. Therefore, the idea of an application in materials such as food industry can be reasonable. From the results of XRD, the nanofibers produced from the toilet paper exhibited an amorphous state. This cellulose suggests that the tensile properties of the nanofiber are lower than that of the conventional solution spinning. The resulting cellulose nanofiber, which has amorphous properties and can be completely purified from TFA, cellulose may provide an advantage for rapid biodegradation and may be intended to be used as a biocompatible and biodegradable material.