Most polymers are compounded with a small amount of functional additives to help their performance in certain, critical manners, such as antioxidants, UV absorbers, slip agents, antimicrobials, antifungals, etc, These are added in small amounts (generally less than 2 wt%) for two reasons. First, they are much more expensive than the base compounds, and secondly, they generally work so effectively that that only small amounts are needed. This two characteristics still don't prevent some people from pushing this too far and not adding enough of the additives (usually as a cost reduction effort [*] but that is another issue for another day.
Polyvinyl chloride (PVC) is nothing without additives, albeit the most common additives for PVC are plasticizers which added in much higher levels than noted above. But the other additives noted above are also commonly incorporated in PVC as needed. There is a new report out yesterday (subscription require) that some newly developed additives, amide derivatives of ethylene glycol-bis(2-aminoethylether)-N,N,N′,N′-tetraacetic acid, that were originally designed as antimicrobials, but were also found to have UV absoprtion properties as well. That is big. You now have one additive that can do the job of two. While UV absorbers are typically added at higher levels than antimicrobials, the use of this additive will decrease the amount of proper UV absorber that is needed, an approach that every processor can get behind.
[*] ...and even more usually combined with obtaining these additives from a low cost producer whose quality is also low
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