Chemistry 101

[freeztar]

Originally Posted by Lwelson

Hi any chance in giving me an understanding of how plastics are made? i have to do a presentation on 'plastic' and everything about it.

I highly recommend visiting your local library and obtaining as many books as possible on the subject of plastics.

I might be able to recommend some sources. What class is this for? What style presentation do you plan to give (ie posterboard, lecture, powerpoint, etc.)? Does your presentation have any time constraints?

[HydrogenBond]

Plastics are polymers or long molecules made up of repeat units. For example, polyethylene is long molecule made of ethylene units. The repeat unit is called a monomer. The long chain of monomers, like cars in a train, is called a polymer. Some plastics have two or more different repeat or monomer units allowing a wide range of properties. Proteins are natural polymers, sort of natural plastics, using animo acids as monomers.

There are different ways to make common plastics. Many use a thing called an initiator, which reacts to or grabs one of the monomers and turns the other end into an active site. This allows the next monomer unit to attach, with it then ending up with the active site, etc. The chain reaction is like cars being added to a train.

One way to adjust some properties of any given polymer is by adjusting the concentration of initiator. If there is only a little there will only be a few very long chains forming. This version is very viscous tough plastics. If we add extra initiator, there are more little chains forming at the same time before we use up all the monomer. The result are more smaller chains. This makes the plastic less viscous or more pliable. Depending on what kind of properties we need to make we can adjust the plastic this way.

One of the most used plastics is acrylic. This is polymethymethacrylate. This is made with a process called emulsion polymerization. One of the initiators often used, is the active ingredient in some acne medications; Benzoyl peroxide. The monomer unit is soluble in water. But once the acrylic plastic forms it is not soluble and begin to separate out. You need to stir real good so the little active ends can find the monomers. The result is like mixing water and oil (plastic) to get an emulsion. Typically, you add the monomer and water. Then carefully calculate the amount of initiator needed to get the chains long enough to give the properties you want. Once you add that you stir the heck out of it and its gets thicker and thicker until it is done. With paint they will add other ingredients. Contact lenses like it pure.

Once a plastic is made if often dried and transported as a powder. Next, we need to shape it into something useful like a plastic cup. One technique is called extrusion. The plastic powder is fed into a machine that has worm screws that convey, grid and pressurize the powder until it becomes a fluid. At the end of this machine are molds in the shape you need to make the product. The plastic is squeezed under pressure into the mold, the mold is then cooled and the part released. The result can be a plastic cup, dish, pipe, or computer case, depending on mold and plastic chosen.

The extruder sounds simple, but is complicated because plastics are weird because they are not newtonian fluids. As you add pressure the material doesn't act normally but has strange compression properties. It takes the study called rheology to figure out how to balance the feed rate and the pressure to make the material flow out right for zero defects.

[Lwelson]

I have a 5 minute power point presentation slot in a construction course to explain where plastics come from and where they are used in construction, the bit i'm not so clued up on is how they are made, right from the 'non renewable resource'. I dont need to go into too much detail, but enough for me to show that i understand about it.
Cheers
Luke

[modest]

Originally Posted by Lwelson

I have a 5 minute power point presentation slot in a construction course to explain where plastics come from and where they are used in construction, the bit i'm not so clued up on is how they are made, right from the 'non renewable resource'. I dont need to go into too much detail, but enough for me to show that i understand about it.
Cheers
Luke

Because most plastics are made very differently from one another it would be best if we had a clear idea of which will fit into your presentation.

Polystyrene is an obvious choice if you're talking about construction. Then again, Polyvinyl chloride might be better because they make PVC pipes and vinyl siding. The point is, even these two examples are made differently and to tell you how one is made is not going to be the same as the other.

Plastics are not really a substance that has an overall manufacturing outline to it. It would be hard to try and present one. Can we focus on a particular example?

-modest

[Lwelson]

In the presentation i need to cover thermoplastics also thermosetting plastics. I will focus on PVC, but i think also need to mention HDPE and ABS also briefly mentioning how they are made.
The assignment question itself is quite brief. 'How are plastics made and where are they used in construction?'
Cheers
Luke

[freeztar]

plastics in construction - Google Search

how is plastic made - Google Search

The type of information you are seeking is readily available. Research the google links provided above.

[modest]

Originally Posted by Lwelson

In the presentation i need to cover thermoplastics

"thermoplastic" is not specific. If you are looking for general information wikipedia's page on thermoplastics is impressive.

Originally Posted by Lwelson

also thermosetting plastics.

Also again, wikipedia.

Thermosetting plastic - Wikipedia, the free encyclopedia

Originally Posted by Lwelson

I will focus on PVC, but i think also need to mention HDPE and ABS also briefly mentioning how they are made.

A general manufacturing process with chemistry involved can be found here:
Vinyl Council Australia - Making PVC

and more with diagrams can be found here:

http://www.pall.com/pdf/HCP-8c.pdf

Originally Posted by Lwelson

The assignment question itself is quite brief. 'How are plastics made and where are they used in construction?'
Cheers
Luke

I would start by talking about the history of natural plastics such as cellulose then get into synthetic plastics and just what a polymer is. But, it really isn't our style here to write someone's report. If in the course of writing your report you find you do not understand something or have a specific question then we can help you work out the problem.

Good luck,

-modest

[Galapagos]

I have a question about gasoline/power steering fluid. I have seen both of these chemicals spilled or leaked out onto the asphalt street, and when the sun is shining on them(especially when they have mixed with water) they appear to be glistening in many bands of metallic colors. Why does this occur?

[Mercedes Benzene]

Originally Posted by Galapagos

I have a question about gasoline/power steering fluid. I have seen both of these chemicals spilled or leaked out onto the asphalt street, and when the sun is shining on them(especially when they have mixed with water) they appear to be glistening in many bands of metallic colors. Why does this occur?

I actually had to look this up myself, and it's really more physics than chemistry.

But apparently a couple of things play into that effect, just as in "regular" rainbows that you see in the sky or when a sprinkler is turned on. Here's a pretty good explanation:
Why oil on water looks like a rainbow@Everything2.com

[Galapagos]

Originally Posted by Mercedes Benzene

I actually had to look this up myself, and it's really more physics than chemistry.

But apparently a couple of things play into that effect, just as in "regular" rainbows that you see in the sky or when a sprinkler is turned on. Here's a pretty good explanation:
Why oil on water looks like a rainbow@Everything2.com

That's what I figured. It just seemed like the kind of question that didn't deserve it's own thread. Thanks for the quick answer!!