How is plastic made?

RobertN · Dec 7, 2004

I wondered if anyone here could give a description of how plastic is made?

If I had a gallon jug of crude oil sitting on my desk, how would it be processed to make a plastic broom handle, or plastic garbage sack for instance?

I have but not a clue /forums/images/graemlins/shocked.gif

rdln · Dec 7, 2004

ABRACADDABRA!

That class was 15 years ago, I killed alot of brain cells since then. Someone will know.

RobertN · Dec 7, 2004

/forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif

Glenn9643 · Dec 7, 2004

A good starting point would be to investigate "polymer science". The various characteristics of plastics are achieved by their molecular structure. It was interesting but an elective in my senior year and I never learned anything beyond basic introduction.

DocHeb · Dec 7, 2004

A gallon jug of petroleum would slowly break down, oxidize and randomly polymerize, with the key word being randomly. It would slowly deteriorate into tar-like substances that are disorganized polymers. For useful plastics, we need organized polymers, that is, very repititious and predictable chemical reactions to make the polymers (plastics).

Petroleum products are related to plastics since petroleum contains many long molecules made of chains of carbon atoms that can be used as starting blocks. Depending on the shape of the molecules and the types of atoms at the ends of the molecules, as the molecules react with each other the plastic will form. In some plastics, the molecules react with identical molecules to make even longer chains (think of a bunch of identical snakes each biting the tail of another snake). This would be a very simple polymer plastic, threadlike - good for long things like broom handles. Varying the structure of the molecules can give varying properties (think of a bunch of two-headed snakes biting the tails of another snakes). This would give a branching polymer, stronger and able to cover area better (such as a plastic bag).

A summary, but more importantly, more links, can be found at:

HowStuffWorks

ByronBob · Dec 8, 2004

I'm a Quality Engineer for an injection molding company and have worked in the plastics industry for 15 years. Your question is a little more complicated then it sounds.

For starters plastics can be made in many different ways. And with that their are many different polymers on the market. Because of this I will try to answer your question the best I can.

Start with the gallon jug, or for that matter any plastic bottle. The process that makes that is called blow molding. A slug of liquified material is injected with a gas to form the hollow chamber. Most plastic jugs are made of polypropylene which has a lot of lubricants in it. It's the elastic polymer which makes it flexible to withstand breaking. These are low melt materials.

Injection molding heats the resin into a soft liquid to be injected into a mold and form a shape. This process allows solid parts to be formed. It also allows you to mold harder and higher tensile materials such as nylon and other materials made for your car. Some resins have glass fibers in them which make them hard and it's the glass fiber which gives it a grainy look to it. Melt temperature here can go up to 750 degrees.

Not all plastics have carbon in them. Most do but not all. There are materials which melt like plastic, inject like liquid and after being baked act like metal. (MIM) is metal injection molding and it's expensive.

Garbage bags for instance are made like paper from pulp. The plastics are rolled through a press to a thin material and then bonded into garbage bags. You can't take a gallon jug and make it into a garbage bag. It's like apples to oranges. All different technique to it.

Everything is biodegradeable but the length of time to decompose can vary on the materials chemical property.

chucko · Dec 8, 2004

I think he ment how to turn the "crude oil" in the jug into plastic.
But I have been wrong before

RobertN · Dec 8, 2004

You are right /forums/images/graemlins/grin.gif

But, I find all this information very interesting /forums/images/graemlins/wink.gif

ByronBob · Dec 9, 2004

Oops. I misunderstood you.
Oil is a product in making resin but it's not the only one. When you think of oil in the making of plastic it's the lubricity of the resin which gets it's properties from oil. You also have such things as teflon in resins which give it the flow characterisitics.

As with metal plastics loose their bonding abilities when you heat them up. Because of this recycled plastics such as a milk jug can be used several times but their comes a point where oils, polymers and the like fatigue to the point where their no good. So recycling is a good idea in that respect. It's come a long way in the 20 or so years I remember when we used to just throw everything in a landfill.