Design Proposal

Project Overview

Problem Overview

          The plan is to create a stronger compound of polyethylene.  Polyethylene is one of the most commonly used plastics in the world today and is the main ingredient in most plastic grocery bags created today.  Most of the plastic grocery bags used to bring heavy groceries into people's homes do not stand up to much weight.  With the creation of a stronger compound of polyethylene, grocery bags would be able to withstand more weight.  To test this newly created polyethylene and black carbon compound, there will be the creation of a table top device to test stress and strain using Lego NXT technology. 

Design Constraints

         The first constraint on the design is obtaining the materials for the project.  The polyethylene mixture used to make the fiber compound will be created  and electrospun with materials and machinery found in the Drexel Materials Science and Engineering Department.  The materials being used to fill the polyethylene compound to increase tensile strength will be limited.  Carbon Black, the material filler will be provided by the Materials Science Department.  The efficiency of the electrospinner used will change the results of the fiber strength.  The next constraint is the ability to make polyethylene using different methods other than electrospinning.  Compression molding is another good way of compounding polyethylene, but there is no access to the machinery to do it.  There is also a time constraint to the amount of different polyethylene and carbon black compounds created and to the number of tensile strength tests done on them, due to the project lasting only ten weeks and the polyethylene compounds will take approximately a week to dry.  
          The machine used to test the strength of the polyethylene compounds will be built from a Lego NXT Mindstorms kit, so the design is constrained to the parts included.  The kit comes with one programmable Mindstorms Brick, three motors, and an assorted amount of Lego pieces.  It was decided that this would be the best option due to many factors.  A kawabota machine would be used for its great accuracy, but for this project there is no access to that machinery.  K'Nex could also be used for designing a table top stress and strain cage, but the materials are harder to access.  Because of this NXT would be the best decision due to the ease of acquiring the parts, and the familiarity of programming NXT bricks.

Pre-Existing Solutions

           Other research on electropinning describes the difference between the stress and strain on Nonwoven fibers vs. electrospun fibers of soft elastomers. The fibers were tested by increasing strain and then plotting the stress on the fibers.  Nonwoven fibers had a small deformation of 53%. After the fibers were electrospun, the deformation greatly increased to 360% (Figure 29). This was because the fibers gained the properties of the soft elastomers [1].

            Research with an alternate method, mixing heated polymers and compression molding, describes changes in tensile strength and tear strength. The first paper, using mixed heated polymers, uses polyethylene separately mixed with talc, dolomite, mica, and wollastonite. All of these lowered the price of the polyethylene, with different effects to tensile strength. Talc and dolomite increased the tensile strength, while mica had no effect on it. Wollastonite, however, had a negative effect, decreasing the tensile strength to about half its original strength. These same compression molds were tested for tear strength as well. Talc and dolomite increased the tear strength a large amount while mica had a very small increase on the tear strength [2].

            The second paper, describes changes in the tensile strength of polyethylene compression molded with wood flour and then coated. The entire mixture first was coated with silane (172 and 174) and then separately with PMPPIC. The tensile strength increased by 20% when coated with both silane types. The PMPPIC also increased the tensile strength, but no specific value was given [3].

Design Goal

          The main design goal is to create a stronger tensile strength polyethylene compound.  This will be achieved using carbon black, a filler that will make the electrospun polyethylene have more tensile strength.  Then the goal is to create a working table top strength tester for the   polyethylene compounds that will measure the stress and strain on the fibers.  The tester will be created from an NXT Lego Mindstorms kit.

Project Deliverables

Items we need	Why we need them	How much or how long
Electro spinner	To mix our materials together. Electro spinner works by creating an electric field, used to draw a charged polymer solution from a syringe tip to a collector.  The electric field is increased until the polymer can overcome surface tension and as they dry the polymers form solids.	We need to use an electro spinner with a power supply of25 kV, the electro spinner needs a needle that is .21mm and the collector that is 20cm from the needle. The polymer solution needs to be fed at a rate of 80µL/min.  The material made must dry for a week.
Carbon Black	We will strengthen our polymer with the use of Carbon Black.  Carbon Black is characterized by high-structure Carbon Black consists of many primary nanoparticles fused together in a grapelike aggregate.	We will need a small concentration of carbon black. Carbon black is characterized by a high-structure carbon black consists of many primary nanoparticles fused together in a Grapelike aggregate.
Polyethylene	This is our polymer.  We will mix with carbon black to make a stronger polymer.  This polymer will be stronger because of the new carbon bonds that carbon black will create.	We will need more polyethylene than carbon black but not too much.  We need more polyethylene than carbon black because the polymers we are going to create will only have 1-9% carbon black.
Table Top Stress and Strain Tester	This will be created to test the strength of the polyethylene and carbon black fibers created.	It will be created out of a Lego NXT Mindstorms kit.

[4]

Project Schedule

Week Number	Goals
3	·         Finish design proposal ·         Plan time to create the polymer compounds ·         Research where the materials that are needed can be found and find out if the company is willing to give some away for the experiment ·         Find out what lab is available for use.
4	·         Gather the materials that were requested ·         Finalize the exact amount of the carbon black is going to be electrospun with the polyethylene. ·         Start a Draft Design for the strength tester
5	·         Use the electrospinner to create the polymer compounds ·         Allow the fibers to dry for one week ·         Continue working on the strength tester design
6	·         Test the tensile strength of all the different fibers using the strength tester ·         If one there are any issues with the electrospun fibers, this week the electrospinner will be used again to create new ones
7	·         Test the tensile strength of any fibers that could not be tested in week six, or any fibers electrospun again in week six
8	·         Analyze that data that was collected during the tensile strength tests
9	·         Begin working on the final lab report and brainstorm ideas for the presentation ·         Submit the lab report to the Drexel Writing Center to have it edited
10	·         Submit the final lab report ·         Practice for the presentation

Projected Budget

For this project, we are expecting to use polyethylene which is the most common plastic in the industry and it is frequently used in plastic bags, plastic films and geomembranes. And carbon black which comes from the incomplete combustion of petroleum and it is commonly used as a pigment in inks, coatings and plastics. Approximately, the required quantity for polyethylene is 60 grams and for carbon black is 10 grams. The approximate costs are: for 2.2 pounds of high density polyethylene, $13.06 dollars, for 1 pound of low density polyethylene, $11.49 dollars and for 10 grams of carbon black, $8.95 dollars.  The tester for determining the amount of stress and strain the fibers can withstand will be from a Lego NXT Mindstorms Kit, signed out of the Drexel University Engineering Department.