Re: Styron


soolinehistory <destorzek@...>
 

--- In STMFC@..., "Gatwood, Elden J SAD " <elden.j.gatwood@...> wrote:

Dennis;

The only resin operation I was familiar with was the old Pennsylvania
Industrial Chemical Corp that was taken over in the mid-70's by Hercules.
They made PICCOLASTIC among others, lots of it used in the rubber and
plastics industry, among what I understand were literally hundreds of varied
end users... I would love to know more about how the
industry, and they in particular, got and shipped their products. Do you
know how that end of the industry worked and how and when it evolved?...
Elden,

It turns out Eastman Chemical still makes the stuff:

http://www.eastman.com/Brands/piccolastic/Pages/Overview.aspx

We need a bit of discussion about the term resin, a generic term that covers a lot of territory. Since the original question was about Styron polystyrene, I wanted to correct the impression that it was a liquid. Almost all thermoPLASTIC resins (that's the PLASTICS that Dustin Hoffman was advised to get into in the movie The Graduate) are reacted during manufacture so they become fully polymerized, and are delivered to the "processor" (molder, extruder, etc.) as a solid, either pellets or powder. The processor simply melts it to make it change shape; no further chemical reaction takes place at this stage.

But the broader use of the term includes the material in the un-reacted state, and this is typically a liquid. These are used in paints and coatings, for adhesives, and as a binder for some molding processes. They can be naturally occurring compounds, such as linseed oil, or synthetics, such as polyester. In use, the chemical reaction that turns the resin into a polymer occurs at the point of use. That is the common thread that ties all these together; enamel paints technically don't dry, they cure, same for most adhesives and THERMOSET molding compounds. The defining feature of all these is once reacted, they can't be undone; the paint or glue or molded parts can't be dissolved in solvent to return to the virgin material. Paint may dissolve in some solvent, but it won't become paint again.

There is a sub-set of the molding industry that deals with thermosets, indeed, one of the earliest synthetic molding compounds, Bakelite, is a thermosetting resin. The resins used are typically endothermic, that is, they need to absorb heat to cure. The "BMC" Bulk Molding Compound as it is known, is made by blending resin, catalyst, fillers and reinforcements to a putty-like consistency, catalysis to a level that that won't react at normal temperatures. This is then fed into an extruder and forced into a heated mold, the temperature of which is high enough to "kick off" the polymerization. The process is the exact opposite of thermoplastic molding, which uses a heated extruder and chilled mold; thermosets require a chilled extruder, to keep it from reacting prematurely, and a heated mold to drive the reaction.

I don't have enough experience with the thermoset molding industry to say whether it is common to blend BMC in the same facility that molds it; the company next door to Accurail used to compound BMC and ship it out in boxes with plastic liners to another facility where it was molded. There was no rail service, but inbound was tank trailers of resin and solvents for cleaning equipment, and van trailers of powdered clay fillers and chopped glass fiber for reinforcement. The boxes of BMC went out in van trailers.

Dennis

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