Entries tagged with “Injection Molding” from Hawk Talk - Guthrie

So this past weekend I began working on my research project. As I have previously mentioned in my blogs; my project is to mix a commodity plastic, polypropylene, with recycled rubber material from tires. These materials were compounded using a twin screw extruder in the basement of Ball Hall on North campus. Me and a grad student were in the laboratory from 9am until 9pm.


Polypropylene was mixed with two varieties of the recycled rubber, 140 mesh and 200 mesh. What that means is that the tires were ground down and fed through a sieve, where 140 mesh has 140 openings per square inch. So larger particles get caught in smaller meshes where finer particles fall through. Batches of 80% PP, 20% rubber; 60% PP, 40% rubber; and 40% PP and 60% rubber, were compounded for each of the two mesh sizes. We are also testing the effect of compatiblilizers, which are materials that are supposed to make the plastic and rubber cooperate better. We used an aliphatic and aromatic compatibilizer. The batches were 76.5% PP, 3.5% compatibilizer, and 20% rubber, for each compatibilizer and each mesh size. All of these gave a total of 10 samples.


This was the plan for Saturday, to make enough material for each batch to perform all of the tests we are planning to perform. However the actual processing was not as easy to perform as it was to describe. First, mixing ratios needed to be found, as you cannot just set the machine to a percentage. Both of the mixers were independent of each other, so their output needed to be measured. The material extruded had to be fed through a water bath to be cooled and into a pellitizer. Many times the strand broke and needed to be re-strung.


The worst part of this time consuming process was the smell of the burning rubber. It was almost like sitting in a car that was doing a 12 hour burnout, and spilling extremely strong black coffee all over yourself. However, the worst is now over, and the rest of the project should be easier.


The next step in this project is to injection mold these batches of material made this past weekend. They will be molded into tensile bars, flex bars, and impact disks for further testing. Some of the material will be tested in the pellet form it is in now. The light at the end of the tunnel will be a trip to a rubber conference in Pittsburg, PA this upcoming October. I will be sure to keep you posted on my progress.

My Research Project...


This semester I volunteered to take part in a non-funded undergraduate research project. I am working with one other undergraduate student, and a grad student is working as our advisor. The scope of this project is to test the mechanical properties of plastics with different amounts of rubber filler. The filler being used is reground tires. If the mechanical properties see a significant increase, we may find a successful way to recycle car tires.  

The first step was to have a meeting with the professor in charge of the project, and lay out a plan. In this meeting we determined what the batches of material and filler we would use. The material being used is polypropylene, and the fillers are measured by different mesh sizes, which are 140 and 200. We will also be using compatibilizers in some of the batches.

The next step in this project is to compound these materials using a twin screw extruder. This means, the two different materials will be melted, and extruded into one strand, then reground to make one batch of material. These different batches of material will be injection molded into tensile bars, flexural bars, and impact disks. We are going to try and find a family mold that has all three. Once these samples are made, they will be undergoing numerous tests to determine mechanical properties.

The results of this project are going to be presented next winter at the ACS rubber show in Pittsburgh, PA. So far, we have determined the batches of material, located our base material, and cleaned and programmed the twin screw extruder. I will let you know how this project is going once we get closer to the presentation date.

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