Pramanik, Professor, Department of Biotechnological Engineering, National Institute of Technology, Rourkela, for giving me this wonderful opportunity to work under her guidance during this work. Electrospinning is currently one of the best fiber forming technologies with many advantages over previously available methods. Although this electrospinning has been widely used for the production of nanofibers, the exploitation of technologies based on electrospinning is still very limited due to poor understanding of the process and the resulting limitation in process control, reproducibility and productivity.
The digital thermometer monitors the temperature of the environment at a regular interval inside the electrospinning box, which is later used as part of the temperature control of the electrospinning process by the heat exchange method. 10 The entire electronic rotation setup is housed in a Plexiglas box that helps limit exposure of the entire system to the outside. The inside of the Plexiglas box also contains the acetone bath used to saturate the electrospinning medium with acetone.
The syringe is driven by a syringe pump which is used to control the flow rate and volume of the polymer ejected. Basically, electrospinning process can be broadly explained by 5 steps, such as: a) Loading of the polymer liquid. Beyond a critical charge density, Taylor cone becomes unstable and a jet of liquid id is emitted from the tip of the cone.
Thinning of the jet
In the polymer solution, the repulsion between the similar charges in the free electric double layer now acts against the surface tension and fluid elasticity to deform the droplet into a conically shaped structure known as Taylor cone.
Instability of the jet:-
Fibre collection:-
CHAPTER -3
POLYMER SOLUTION PARAMETERS
- Molecular weight and solution viscosity
- Dielectric effect of solvent
Higher the molecular weight of the polymer dissolved in the solvent, higher is the viscosity of the solution, because with higher molecular weight, the polymer chain length is higher, and therefore the molecular entanglement increases, which causes increase in viscosity. Higher viscosity prevents the electrospun jet from breaking during its stretch up to the collector electrode, leading to continuous fiber generation. However, very high viscosity can make pumping the solution difficult and can also lead to drying of the solution at the needle tip, lowering the yield of the process. Very low viscosity can also lead to beading in the resulting electrospun fiber. High viscosity also lead to the formation of fiber with increased diameter due to the solution's resistance to stretching.
The higher viscosity also accounts for a smaller deposition area because it prevents bending of the resultant fiber. At higher viscosities there is a steady formation of the secondary current which carries the smaller diameter fibers along with the larger diameter fibers breaking off from the main current. At lower viscosity, the surface tension leads to the formation of beads along the length of the fiber because it leads to a reduction in surface area. But at higher viscosity the surface tension effect cancels out due to the uniform distribution of the polymer solution over the entangled polymer molecules. Low surface tension leads to smooth fiber formation.
Lower surface tension can be achieved by adding surfactant to the polymer solution. 3.2.3 Conductivity of the solution. Increased solution conductivity leads to higher charge distribution in the electrospinning current leading to increased solution stretch during fiber formation leading to the production of smaller diameter smooth fiber. Increasing the conductivity of the polymer solution also lowers the critical voltage for electrospinning.
A higher load leads to a higher bending instability, which leads to a larger deposition area of the fiber being formed; as a result, the beam path is increased, leading to the formation of finer fibers. It can also be increased by the addition of drugs and proteins that dissociate into ions upon solution, increasing the conductivity of the solution. When smaller diameter polymers are dissolved, due to their greater mobility under an external electrostatic field, there is a greater stretching force leading to the formation of smaller diameter fibers.
The higher the dielectric property of the solution, the less likely it is to bead and the smaller the diameter of the electrospun fiber. With an increase in the dielectric property there is an increase in the bending instability of the beam leading the larger deposition area of fibers.
PROCESSING CONDITION PARAMETERS
- VOLTAGE
- FEEDRATE
- EFFECT OF COLLECTOR
- DIAMETER OF PIPETTE ORIFICE
At higher temperature, the fiber produced has uniform cross-section due to lower viscosity and higher solubility which allows greater stretch of the solution. In electrospinning, collector material is made of conductive material that is electrically grounded to create stable potential difference between needle and collector. If a non-conductive material had been used, the charges on the electrospinning beam would have developed an opposite charge on the collector reducing the amount of fiber deposited with a lower packing density.
But in the case of a conductive collector, there is accumulation of closely packed fibers with higher packing density. A porous collector produces fibers with a lower packing density compared to a non-porous collector plate. In a porous collector plate, the surface area is increased so that residual solvent molecules evaporate quickly compared to a non-porous collector, where residual solvent builds up around the fibers, leading to a densely packed structure.
On a porous surface, residual charges remain on the fiber, which reflects each fiber, leading to a lower packing density, but in the case of a uniform surface, the residual charges lead away to the collector, leading to less reflection and thus a higher packing density. A rotary collector is useful in obtaining dry fibers as it allows more time for the solvents to evaporate. A smaller inner diameter opening reduces the clogging effect due to less exposure of the solution to the atmosphere.
However, a very small opening has the disadvantage of creating problems in extruding a drop of solution at the tip of the opening.
CHAPTER-4
TEMPERATURE SENSOR
- PIN CONFIGURATION AND CONNECTION Vcc = 4 Volt – 20 volt
- OPERTING PRINCIPLE OF LM35
The LM35 temperature sensor is a precision integrated circuit temperature sensor whose output voltage is linearly proportional to the Celsius temperature. It can be used to measure the ambient temperature in degrees Celsius with an accuracy of 0.5 degrees Celsius. The LM35 temperature sensor has an advantage over other temperature sensors because it does not use mercury (like old thermometers), bimetallic strips (like in some home thermometers or ovens), nor does it use thermistors (temperature sensitive resistors).
For this, the output pin of the LM35 is connected to A0 of port A (ADC port) of the At mega 32 microcontroller, where it is converted to the appropriate digital values so that the MCU can read them. In the LM35 temperature sensor, as the temperature increases, the voltage across the diode increases at a constant rate due to the voltage drop between the base and the emitter. The analog output of the LM35 temperature sensor is converted to the corresponding digital values using the ADC port of the ATMEGA 32 microcontroller.
ANALOG TO DIGITAL CONVERTION
CALIBRATION AND SIGNAL PROCESSING
Seven segment display is divided into 7 different segments which can be switched on or off independently according to a user defined program. The one common point of all the LEDs is connected while the rest are available. Depending on whether anode or cathode of all the LEDs are connected, they are of 2 types, - . a) Common cathode seven segment display b) Common anode seven segment display.
The two middle pins are connected internally and the rest of the pins are the free end of each LED. Then the second is activated keeping the other two off and the same for the third seven segment display.
CHAPTER-5
RESULTS AND DISCUSSIONS
- RESULT
- PARAMETERS FOR OPTIMIZTION OF ELECTROSPINNIN PROCESS
- TO INCREASE THE FIBER DIAMETER
- DECRESE IN BEAD FORMATION
- OUTLOOK
- CONCLUSION
Then, according to the calibration and formula in Chapter 4, we can measure the temperature in degrees Celsius. To be able to maintain the internal temperature of the Electrospinnin box at an optimal value so that the fiber morphology can be used. In the future, we can surround the entire electrospinning box with pipes through which hot or cold water can flow according to our need to increase or decrease the internal temperature of the electrospinning box to get the optimal temperature value.,.
However, care should be taken when dealing with biological substances such as enzymes and proteins, because this may be the cause of loss of functionality. But the temperature should not be kept very high, because this can lead to the electrospun fibers melting. From Chapter 3, we came to know about various parameters that affect the electrospinning process.
The conductivity of the polymer solution must be increased by the addition of polyelectrolyte or by the addition of drugs and proteins. The conductivity of the solution must be increased by adding polyelectrolyte or by adding drugs and proteins. A rotating or moving collector can be used to increase flight time and reduce bead size.
Because if the deposition area is larger, the fibers may not be completely collected at the electrode, leading to waste of fiber and also the fiber diameter decreases due to increased flight time. No surfactant should be added, so the surface tension must be kept to a minimum. Further different modification of the existing electrospinning machine can be achieved by different methods.
Use of heat exchanger system around the electrospinning box to regulate the temperature of the electrospinning process and thereby regulate fiber morphology B). Using rack and pinion mechanism to control the distance between TIP and collector .. so the fiber morphology can be adjusted according to parameters and our needs. The study reports the various parameters to be modified according to the process needs for the production of nanofibers with high yield and optimum quality according to the use.
This can further be used for the real-time temperature measurement during the electrospinning process, so that the electrospinning temperature can be adjusted to an optimal value through the temperature feedback method.
WEB REFERENCES
