Whenever you buy a polymer, you are never buying just the polymer. There are always additives of some sort, even if just enough so that the manufacturer can get the resin through his equipment to pelletize it. But I have never, ever seen any manufacturer state exactly what additives are in a resin.
Right now and personally, I'm not complaining about this. The secrecy results in some good business for my employer. Extracting all those additives and running them through the MS is good for business, although providing quantitative results is a real challenge. It can be done, but it's too expensive for most clients.
But all this is changing with a new grade of PLA from Natureworks. Natureworks is going the full disclosure route:
"In answer to questions from MPW, Steve Davies, director of communications and public affairs, explained, 'Until now NatureWorks has offered the market the finished resin grade...The difference now is that, for the injection molding market specifically, we've 'drawn back the curtain' on how we've developed this grade, and shared exactly what the technology is (the resin modifiers, the nucleants, the additives package, etc), so that we're not offering just a 'black-box' finished solution, but we've also been completely transparent with how we arrived at that solution (what we used to tailor the resin properties and processing characteristics, and why).'"
I can't believe that this won't help Natureworks in getting this resin into more applications. Too often all the secrecy of the resin suppliers ends up getting in the way instead of providing the competitive advantage expected by maintaining the information internally.