Week 9

Due to the variables of the electrospinning and the percentages of chemicals used, the fibers could not be tested using the tensile tester created, or a Kawabata machine.  Because they could not be tested, a Scanning Electron microscope was used instead to take a look at the fibers.  After the fibers were created and dried, high magnification pictures were taken using a scanning electron microscope, or SEM. The SEM works by using electrons and x-rays to make a picture instead of using light. The item is put in a vacuum and then an electron beam is shot at the item. When the electron beam strikes the item, electrons and x-rays are released. A detector then captures these electrons and x-rays; they are converted and then displayed as an image. There are many advantages that a SEM has over a light microscope. The SEM can have more items in focus than a light microscope. It also has a higher resolution for clearer and higher quality photos, so that some of the smallest items can still be seen clearly [5]. After the images were created and saved, they were loaded into a program called ImageJ, a program designed to count the number of fibers in an image. The number of fibers were counted and
recorded.

Figure #1: O% Carbon Black and 5%PEO

The sample with 0% carbon black (CB) and 5% PEO spun well.  It had many fibers and the white mat was thick enough to work with it. The ambient conditions benefitted the experiment. The range of the diameter is from .115 to .335 micrometers and the average diameter is .230 micrometers. It was spun at 22% humidity and 23ᵒC. When peeling off the mat it was very easy to remove the foil from the back of it.

Figure #2: 1% Carbon Black and 5%PEO

The second sample, 1% CB and 5% PEO, also spun well.  It had many fibers that had a larger diameter than the basic PEO fibers. The white mat was also thick enough. The range of the diameter is from .199 to .464 micrometers and the average diameter is .262 micrometers. This mat was easy to remove from the foil but a little bit stickier than the first sample.  For this second sample, the humidity was xxx and the temperature was xxx.  

Figure #3: 3% Carbon Black and 5%PEO

The results were the same for the third sample, 3% CB and 5% PEO.  For the third one, the humidity was 21% and the temperature 23. These conditions proved very good because when peeling off the mat it was very easy and the fiber was very thick. This percentage yielded the largest diameter and most fibers. The range of the diameter is from .210 to .547 micrometers and the average diameter is .305 micrometers.

Figure #4: 6% Carbon Black and 5%PEO

The fourth sample that was spun; 6% CB and 5% did work but it did not have a lot of fibers as the other ones. This is because the ambient conditions; humidity 38% and temperature 23 were not favorable. The range of the diameter is from .151 to .377 micrometers and the average diameter is .249 micrometers.

The last sample with 9% CB and 5% PEO did not spin correctly.  This was due to the size of the needle being too small to allow the solution to flow out of it. Furthermore, the solution was too viscous for the electrospinning to work.

Week 8:

     This week, we created a housing to hold the load cell for testing.  Using this new housing, we tested the load cell using weights.  We did this to get a line of best fit for voltage outputs vs. force.  Below are the results of the testing.

Mass (grams)	Force	Volts (in mV)
0	0	-0.088
50	.49	-0.127
100	.94	-0.185
200	1.96	-0.29
500	4.9	-0.31
700	6.86	-0.81
900	8.82	-1.02

Using this graph, the line of best fit, y = -9.3906 x - 0.7689 was found, and can be used to find the force easily.  If you plug in a voltage value x and solve, the answer will be the force.

     Also this week, a scanning electron microscope was used to photograph the carbon black and polyethylene fibers.  The fibers will not be able to be tested using a kawabata evaluation system due to their size.  The mats did not come out thick enough, making it impossible for the machine to test it.  This most likely happened from in-optimal conditions for spinning the fibers.  There are a lot of variables when electrospinning, and without the correct conditions fibers will not spin correctly.  

Week 7:


     This week we had a large setback in our design of the table top tensile strength tester.  We found that after using weights from 50-500 grams that most of the voltage results were exactly the same.  This is because the load cell is meant for a minimum 130 grams and the voltmeter does not have a more accurate result other than one decimal place.  In order to create this strength tester we would need much more sophisticated equipment to get usable results because the electrospun fibers will not put up that much resistance.  So after that had been decided, our new task is to continue creating the tensile strength tester, but instead use it as a demo with string or some other type of material like string.  We are to show that we did create a system to do the job, and that with the proper equipment it can test the strength of fibers also.
     In the Materials Science lab, the polyethylene fiber compound has been spun.  The polyethylene and 1% carbon black compound and the polyethylene and 9% carbon black have also been spun.  Next week the mixtures containing 3% and 6% carbon black will also be electrospun.  Once the fibers are finished spinning, they will be tested using Kawabata machine due to the load cell and voltmeter being used for the table top tensile strength tester.

Week 6:


     This week, our designated group members doing the electrospinning went into the Materials Engineering Department lab and mixed the chemical compounds that will be used to do electrospin polyethylene and the polyethylene and carbon black compounds.  They also learned from experienced electrospinners some of the variables needed to be set to spin polyethylene.  After the compounds have set for a while they will electrospin the fiber next week.
     In the engineering lab this week, the we figured out how to use the load cell by calling the company who created it.  We borrowed a power supply to apply 5 volts and a volt meter to read the voltage for ensuring that the load cell worked properly which it did.  We also researched how the load cell actually works.  The way it is used is through a series of resistors.  As the resistors stretch due to pulling on the load cell, the output voltage changes due to the change in resistance.  Using this output voltage, the force applied to the load cell can then be determined.  Finding this will then allow for the calculation of the stress and strain on the fibers tested.  Below is an image of the circuit board that is normally used in a load cell.  It shows how the series of resistors work to give a voltage output based on the bending of the circuit board [5].

Figure 1:  Circuit Board of a Load Cell [5]

     Now that we have figured out how the get the load cell working, the next job is to find a way to attach it to the NXT model we created.  It has to be attached in a way that it will be immobile, so the voltage reading is as accurate as possible.

Week 5:


     This week, in lab a design has been created for a table top tensile strength tester.  It was made using the Lego NXT as planned.  We did run into an issue with the load cell though.  We found a way to attach it to our design, but we do not have a way to get a reading from it.  The wires are in okay condition, but we have no clue where to plug them in.  The plan is to find a way to get a reading from the load cell next week.
     As far as the electrospinning goes, two of our group members have taken their safety tests and are ready to spin, so at the end of week 5 they are planning on going into the materials science lab and mixing the polyethylene and its mixtures to be spun the next day.
     Below is a picture of our tensile strength tester design created in Lego Digital Designer:

Figure 1:  Isometric View of the Strength tester

Week 4:


This week we received the load cells for the construction of the table top stress gauge.  There was also a discussion on what the best method of design for the gauge would be, and that is using Lego NXT.  This was decided to be the best option due to a few factors.  Using a kawabota machine would be the best option due to its great accuracy, but our group does not have access to it.  K'Nex could also be used to design the table top tester, but we have never programmed them before, and the materials would be harder to access.  Because of these reasons NXT would be the best due to the ease of acquiring parts and the familiarity with programming.

Lynn and Denisse have taken their lab safety tests online, so they can electrospin the fibers in week 5.  We have decided to create between 3-5 fibers depending on the way they spin in the lab.  The plan is to have the electrospinning done by week 6.

Week 3:

This week we finalized the plan for the project.  Polyethylene, and polyethylene compounded with carbon black will be electrospun in the Materials Science and Engineering Department within the next 2 weeks.  Two Lego NXT Mindstorms kits were signed out of the engineering lab to create the stress and strain tester.  A strain gauge and load cell were acquired from the Materials Department to be used in the Lego design of our table top strength tester for the fibers electrospun.