Masterbatches

As predicted last week, Retraction Watch has now posted a third retraction notice from the Journal of Applied Polymer Science, and even found a 4th one! One of the retracted papers was about masterbatches. The authors of the Retraction Watch blog have bio/life sciences backgrounds, so they probably are unfamiliar with the term masterbatch, not only because they are seldom if ever used in that field, but also because they a) made a joke about the term using it's similarity to a word describing a self-satisfying activity, and b) linked to the Wikipedia article on masterbatchs, which is a horrible article incapable of leading to any understanding about the subject whatsoever.

So let me speak a little about masterbatches. Simply put, a masterbatch is a polymer with an unusually high level of additive(s) in it, such as pigments or antioxidants. It is designed to be added to another polymer (usually of the same base material, i.e., a polypropylene masterbatch will be added to a polypropylene polymer) at a ratio that lowers the additives to the final, desired concentration. The addition is done in continuous or semi-continuous process equipment such as extruders or injection molders. Masterbatches can be up to around 40 wt% of the additive, while the final product may have only 1 wt% of the additive.

Masterbatches are used for a variety of reasons. Adding a single masterbatch to a polymer requires much less equipment ($), manpower ($) and maintenance ($) than would be needed for adding multiple components individually. Masterbatches are also easier to blend into the base polymer than just the additives would be since much of the initial distributing and dispersing has already been completed. This can mean less thermomechanical degradation of the base polymer since the screws in the equipment can be designed for less intensive mixing. And some sites just don't want to deal with the mess of additives. Such is often the case with carbon black. If you've never dealt with carbon black, then let me assure you from personal experience that it gets everywhere, no matter what controls you take. You would be best off just painting everything in sight black, (mcuh like bakers wear white to hide the flour on their clothing). If you are trying to make a black plastic for a medical device, the FDA inspectors won't be happy about your housekeeping, so you would be strongly advised to use a black masterbatch and let someone else deal with the mess.