Even if they do it on television, don't expect a resin testing lab to pinpoint something as specific as a material's manufacturer.
I admit to being a huge fan of shows like CSI and NCIS. The multiple investigative tracks that run through any given show, with the backdrop of the analytical people, many of them as quirky as they come, feeding information to the field, makes for great entertainment. But it is an indisputable fact that these shows have made my professional life more challenging.
The reason is simple. When people watch week after week as television characters bring in odd pieces of clothing, paint, and other debris, feed it into an analytical instrument, and within the hour are given a positive identification of the material as well as a narrative history of where it had been for the last six weeks, sooner or later those same people are going to start believing that this is possible in the real world.
Recently I watched a field agent bring in a remnant of a small gas tank that had been involved in a fire. Gasoline residue was still present and this individual was trying to determine where the gasoline had been purchased. Before the next commercial break, a print out was spitting results from an expensive-looking piece of equipment into the waiting hands of an analyst wearing a self-satisfied smile and a suitably impressive lab coat. This person then called the field agent and proceeded to tell him not only at which station the gasoline was purchased but also which pump it came from.
Apparently, this constant bombardment of images of extreme competence in the lab also goes to the heads of some analytical services professionals. Perhaps they do not want to disappoint a clientele that has come to expect that these miracles can happen in the real world. How else to explain why analytical services companies would accept money from customers to answer the unanswerable questions?
WHOSE POLYCARBONATE IS THIS?
One of the prime examples of an analysis that is almost guaranteed to fail is the one whose objective is to determine the commercial source of a particular compound. It is fairly common for a customer to send in a material that it already knows is, for example, a nylon 6/6, and request confirmation that it is a particular grade of Zytel or Ultramid.
A responsible analyst will explain to the customer, before the order is placed, that without some inside information regarding trace ingredients, this is rarely possible. The best that can be done is to perform tests that will produce a fingerprint, which can then be established as consistent with that of a particular material. Nevertheless, every year we review lengthy reports covering expensive testing programs designed to identify a specific vendor's product. They almost never achieve their objective.
The simple and sometimes not-so-simple tests that can be done on a material can reveal a lot of information about composition. In fact, with enough money and time, it is possible to break a material down to the last bit of additive that may be present at levels of tens of parts per million. But as impressive as this might be, it still does not help distinguish a Bayer polycarbonate from a GE polycarbonate or an Equistar polyethylene from a Dow polyethylene unless there is prior knowledge regarding a unique aspect of composition.
Most of the time, this inside information is a closely guarded secret. It is true that materials from a certain supplier will likely contain unique markers that are distinctive to that product line. These markers may be placed into materials intentionally so that a material manufacturer can determine if an unknown product is made from their material. But these markers are typically present at very low levels and without some previous knowledge of what to look for, even finding the mystery component does not ensure that the analyst will be able to attach any significance to it.
WASTING TIME
Recently, we were asked to review a report that involved five types of tests designed to identify a particular manufacturer of an elastomer. Some of the tests, like hardness, are simple and inexpensive. Others that involved the extraction and identification of additives using methods like gas chromatography and mass spectroscopy (GC-MS) can take time and are costly.
The resulting report was more than 30 pages long. The appropriate certifications and signatures were provided. But no answers were found. In fact, it was not even possible to determine from reading the report what the purpose of the analysis had been. The fact that the analysis failed was not due to a lack of skill on the part of the analysts. It was because this type of problem is almost always unsolvable unless the lab has an impressive library of known standards that pertain to the problem at hand.
This is not to say that these types of projects are always dead ends. Sometimes the compound turns out to be unique. Identifying the chemical composition of the base polymer can automatically bring with it a positive identification of the compound and the associated manufacturer. For example, there is only one compound that employs a blend of ABS and PET polyester. There are six polybenzimidazoles (PBI), but the same manufacturer produces them all. Identifying the material as a PBI automatically identifies the manufacturer. Additional tests should be able to easily designate the specific grade according to distinguishing features such as filler type and amount, determinations that are easily made.
Suppose an analysis of polymer composition turns up a syndiotactic polystyrene (SPS) that contains PTFE. There are several suppliers of SPS, but at this point only one compounder provides grades modified with PTFE. That's today. With the rapid changes in the global economy, it is important to note that new suppliers can enter the market at any time, sometimes in remote corners of the world. So part of the ability of a lab to provide the needed information to a client hinges on their awareness of the commercial environment.
BE REALISTIC
Sometimes a limited scope of inquiry can also be productive. For example, polyphthalamides (PPA) are made by several primary manufacturers. However, they are slightly different in chemistry and this influences their melting points. So an infrared spectrum that identifies a material as a PPA, followed by a DSC to determine the melting point, can distinguish, for example, a Grivory from an Amodel. Additional tests can then be run to check for distinguishing features such as filler type, filler content, flame retardants, and impact modifiers. Here again, some knowledge of the commercial landscape is helpful if not required.
Other projects are much less likely to succeed if the objective is a match to a specific compound. There are thousands of polyethylenes, thousands of nylon 6 compounds, and thousands of flexible PVC grades. These are materials where identification of a specific compound from a particular manufacturer is unlikely. The client should be advised of this low probability of success before the project starts and a large sum of money is committed.
The opinion of the general public regarding what is possible and not possible in a laboratory has been changed by shows like CSI. This may be partially responsible for the pressure that labs feel to say yes to a speculative project. But as impressive as the experts in fiction may appear to be, a close look at their expertise in the area of resins has been shown to be suspect.
Devotees of the original CSI may remember an episode where plastic fragments were found in a shooting victim. The lab director, Grissom, delivered a stirring analysis of how the particles came to be there, explaining that the shooter used a carbonated beverage bottle as a silencer, which was responsible for the presence of polyethylene shards. But almost everyone in the plastics industry knows that soda bottles these days are made of polyethylene terephthalate. Oops.
About
Michael Sepe Michael Sepe has worked in the plastics industry since 1975 in a variety of roles involving both manufacturing and research and development. He is an independent consultant based in Arizona with clients throughout North America. He assists clients with material selection, designing for manufacturability, process optimization, troubleshooting, and failure analysis. Learn
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