Monday, January 31, 2011

Real Time IV Measurement? Nah!

This blurb produced a spontaneous eyebrow lift for me. How about you?
"The unique technology represented in PTi's real-time IV Monitoring System is based on precise measurement of melt temperature and capillary piping pressures such that the viscosity and subsequent IV can be accurately calculated. These results are benchmarked against the ASTM D4603 Solution Test Method for measuring IV and possess an accuracy of +/- 0.02 dl/g."
I.V. measurement (I.V. meaning inherent viscosity, not be confused with intrinsic viscosity [*]) involves dissolution of the PET into a solvent at high temperature and then measuring the drain time of the solution through a glass capillary. The whole process takes quite some time. While I don't doubt that this new technique can make viscometric measurements on a PET melt and correlate them to IV, call this Real Time IV Monitoring is factually incorrect. A correlation to another measurement is never the same as the other measurement, and like all correlations, is fraught with potential errors being introduced by uncontrolled variables.

To me it would be far more helpful to look at the raw data that is actually being measured and track/monitor that. There would be a significant learning curve to understanding the data, and PTi has certainly gone through it. When multiple input measurements are being reduced to a single output, there will be situations were increases in one or more variables are offset by decreases in one or more other variables, all of which makes me more leery of the IV output. If you are measuring multiple inputs, why not study all of them? It's like working with just the average of a distribution.

I also find it strange that it is the IV that is being correlated since it has no scientific basis unlike the intrinsic viscosity. Well, maybe not. MFI is an awful test with no scientific basis, and yet is still used to buy and sell billions of pounds of polymer a year, so why should IV be any different?

[*] Don't worry, IUPAC nomenclature is far worse. Inherent viscosity is called logrithmic viscosity (not so bad), but the intrinsic viscosity is call the limiting viscosity number - what a mouthful, and how can a "number" have units?

Friday, January 28, 2011

Designing a Crematorium

Today's entry is on the depressing side. I ran across a link to a site that discusses the German companies and engineers that were involved in the design and construction of the crematoria used in the Holocaust, something that most of us as engineers and scientists have probably never thought about. I think it is perversely ironic that they even applied for a patent on the design.

While that part of the article is disturbing at face value, it also disturbs me in a way that probably differs from most, in that it repeatedly refers to the users of the ovens as "Nazis". That is at least partially true, but also misleading. It gives too much power to the tag; it creates the idea that the Nazis were a separate group of people, almost like invaders from another planet that came and took over the government and were all killed in the war (or at the Nuremburg trials) and that they are gone forever. The history of mankind (even since WWII) has shown that that is not the case, and that people in all parts of the world can become demons capable of unleashing unimaginable harm to other people. Such situations do have a few demons at the top, but rely on an ever increasing array of support from people below, people who are brought in slowly to the situation, perhaps with some subtle pressure. If dropped into the final environment, the people would strongly fight back, but when the changes occur slowly, pliability can be found and taken advantage of. Maybe these engineers believed in the cause and maybe they didn't. In this case, it was probably quite clear what the intended use was and that there wouldn't be other uses, in contrast with the manufacture of other items that can be both harmful to people but also beneficial (guns, drugs, pesticides..).

But to me, the bottom line is clear. The authors are trying to put too much separation between this aspect of humanity that we wish we did not have inside ourselves, but we do.


Broken Plastics, Silicone Dreams Nice name for a blog, although it has nothing to do with plastics (or silicones either).

The headline says it all. "Calculating the intrinsic viscosity of PET resin? There’s an app for that."

Thursday, January 27, 2011


I ran across the concept of "baroplastics" yesterday [*], something that I had not heard before, although given their discovery occur in the 2003 timeframe, I personally understand why. These are polymers that can be processed at room temperature while under (significant) pressure, roughly around 5000 psi (35 MPa). There is nice letter in Nature (open access) that shows examples of materials being reprocessed up to 10 times without a noticeable loss of properties. All the materials are diblock copolymers, and the pressure is able to change the thermodynamic compatibility of the two blocks so that they are compatible.

It's a neat concept, and given that 8 years have passed and nothing seems to have commercialized from it, a concept is all that it may end up being. Still, I find it pleasing that something so simple could be discovered from a rather commonplace material.

[*] Rather sadly, as it was mentioned in the obituary for the MIT professor, Anne Mayers, who discovered these polymers.

Wednesday, January 26, 2011

My Most Embarrassing Moment at Work

Plastics News is accumulating a list of such accomplishment, but most of the items there so far are quite short. This story needs more of a setup.

My first job after school was at the Hercules film plant in Terre Haute. There was a group of about 4 of us that were part of the R & D group, and we reported to the R & D headquarters in Wilmington, but Hercules was trying to make sure that their R & D people had some experience with manufacturing so they located us at the plant. My supervisor and I were the only Ph.D.'s at the site that employed several hundred people.

One day the tenter plant was having a problem, and my supervisor and I walked into the oven to look at something (I don't recall the details of exactly what) and the door closed behind us. We pushed against it and kicked the door to no avail; we were locked in the oven. We started banging on the door and in about 10 seconds, one of the wisecracking engineers opened the door and snidely said "How many Ph. D.'s does it take to lock themselves in an oven?"

I've since suspected that the engineer may have been behind the door closing and being "locked". Regardless, I've yet to come close to anything else like that in the last 20 years. Give the Plastic News site a look and please post your stories there as I certainly don't want to be the only one with a story.

Tuesday, January 25, 2011

Reuse that PET bottle, please!

I try and minimize the time I spend at websites that cater to a "all plastic is evil" philosophy, (or anything close to it), but this one made me laugh (thank goodness, as doing so prevented me from crying). Like many blogs out there, the post was more or less a cut-and-paste of something from somewhere else that keeps getting posting around the web ad infinitum. [*] The title appears to be quite real however, because it is so meaningless: "Plastics Part 2: The world’s most popular PET" ???? To have a "most popular" item implies that one is choosing from a list of options, but unfortunately PET is not a list of options, it is only PET. Maybe the author thought that PET is an abbreviation for "polyester" and are unaware that is stands for "polyethylene terephthalate".

The post continues along nicely with generic information about PET and its uses. The last two paragraphs however, have some uninformed ideas that are repeated way too much. Like this one:
"One common way that plastic leaches (phthalates) is through heat and sun exposure–for example, leaving a bottle of water in the car, using a container or bottle multiple times (like when refilling a disposable water bottle, and/or using a bottle that has contained a food or beverage product for months or years, like a shelved bottle of mayonnaise or honey)."
Fine, diffusion (i.e., migration) of pretty much anything increases with heat, but if this is a concern, then reusing a bottle it the ideal way to go. The bottle has only a limited amount of whatever nasty in it, and the initial fill will remove some of it, maybe a lot of it if the product spent a long time between manufacture and consumption. When the bottle is refilled, there is potentially less material available for diffusion, and decrease in potential means that less will diffuse into the fill each time. Reuse the bottle enough and you will see exceedingly low levels of whatever the concern is. Considering that an objective of reducing plastic usage is to reuse when possible, I don't see why this so many people are against resue of a plastic bottle.

And then the last paragraph leads off with a misleading statement
"There has also been concern with the compound Bisphenol-A, which is regularly used in plastic products."
Since the rest of the post has been about PET, this makes it appear that BPA is a concern in PET, certainly not the case.

So much misinformation, so little time.

[*] In many cases, these seem to be autogenerated, probably with the idea of making money off the ads. The blog discussed here does not fit into this classification, as there real contributors listed on it.

Monday, January 24, 2011

How about a Deborah Number for Durability?

As we've all seen, plastics have lifetimes of anywhere between "eternity" (Plastics are Forever [1])and zero (?!?).

We certainly will see increasing amounts of biodegradable and compostable materials in the coming decades, and as every engineer will immediately recognize, the challenge is to ensure that the degradation does not occur during the intended lifetime of the product [2]. This is very comparable to the the Deborah number in that we need to compare the degradation time to the product lifetime. (You will recall that the Deborah number is the ratio of the relaxation time to the observation time.) How about we call it the Deborah Degradation Number?

It obviously can't be listed on a spec sheet anymore than a Deborah number can be, but still, the concept needs to be understood and better communicated, don't you think?

[1] Sure they are forever. That's why they keep failing and breaking down into the ever small pieces that fill the various oceanic garbage patches and whale burps.

[2] Sadly, this is a challenge for too many engineers even today in a world of nondegradable polymers. (Notice that I said engineers, and not the materials themselves?)

Friday, January 21, 2011

Benefits(?) to Plastic Bags in the Environment

This is truly strange. A new report (subscription/pay-per-view) in todays Science has found that birds are using pieces of platic bags to their benefit. In this study, the birds (black kites, a European raptor) were found to use the pieces to decorate their nests, which by itself, it not novel. Such decorations are common, and have been ignored. But this new study concluded that the decorations actually serve a purpose, in that fitter birds used more decorative materials than less fit birds.

So are other animals doing the same or similar thing - using pieces of plastics for their gain? And what are the longer term, evolutionary issues with this? What would happen if in the extreme all plastic bags were banned world wide? I have no answers, but am just fascinated by all of this.

The article is also discussed at

Wednesday, January 19, 2011

What's in a Name?

CR-39 is the pseudo-polycarbonate [*] which stands for Columbia Resin #39, the first 38 being failures. (What a lucky developer. There is no way I've ever developed anything in just 39 efforts.)

But what does SU-8 stand for? This is the famous photoresist, so famous that its referred to without any introduction. Please don't get me depressed and tell me that the developer was successful after only 8 attempts.

[*] I say "pseudo" because the polycarbonate linkages are already existant in the monomer. The backbones are built through free-radical polymerization of the telomeric enes

Tuesday, January 18, 2011

Plastic Debris in the Great Lakes

Being located pretty close to North America's Continental Pole of Inaccessibility [1], I can sleep well at night knowing that my trash is not ending up in the oceans, adding to any of the various "Garbage Patches" that are constantly in the news. (Besides, most of the trash here in town is incinerated and used to generate electricity.) Getting to the ocean is a major trip and not something that I think of other than as a distant environment.

Lake Superior and the other Great Lakes are quite the opposite. Superior is just a two hour drive from here and I've been along its shores many times, truly a beautiful shoreline. Lake Michigan is about 5 hours from here and I've been to its shore quite a bit for business and pleasure, and is a beautiful front yard for the city of Chicago. It also serves as a major obstacle in travel to the state of Michigan. All of which builds to my point here: that the Great Lakes are very much part of my semi)-immediate environment. As such, I was saddened to hear that people are finding balls of natural and synthetic materials washing up on the shoreline in Duluth.
Affectionately known as "whale burps" (even though there are no whales in the Great Lakes) [2], they occur in oceans and are formed by the action of waves on these materials while in the lake.

I don't think anyone is going to be imagining a "Great Lakes Garbage Patch" anytime soon, but regardless, plastic garbage has no business being in the lakes (or anywhere else in the natural environment).

[1] And we pay the price by the near impossibility of finding fresh fish at the grocery store.

[2] Names are not the strong point for Minnesotans. Aspen Research is located in the city of White Bear Lake, and there are no polar bears to be found here.

Monday, January 17, 2011

More on Cyanoacrylates

Another thought occurred to me regarding cyanoacrylate adhesives that is nowhere near as widely known as it should be. The polymerization of this adhesive is catalyzed by hydroxide ions or other bases. It is often stated that water is the catalyst (the Wikipedia article tiptoes along this line) but this is definitely not true. You can prove it for yourself by adding water to the monomers and watching nothing occur. Instead, it is the hydroxide ion that always exist in water that catalyzes the polymerization, and what a pretty powerful catalyst it is! Neutral water has a hydroxide ion concentration of 10-7 moles/l, and with moisture making up about a few percent of the air, you can knock that number down further by a couple orders of magnitude, call it 10-9 moles/l. Truly a catalyst!

That the polymerization is catalyzed by a component of moisture is easy to confirm here in Minnesota. In the summers, we have high humidity. Dewpoints are often in the 60's or 70's and our superglues work just wonderfully. But then comes winter, when dewpoints become frostpoints and the air inside most buildings is dryer than in the lab's desiccators. Just getting a cyanoacrylate to work is then quite challenging. I've found that exhaling a big breath of warm humid air right before I jam the two pieces together helps, although even that is not guaranteed.

Why was he measuring RI?

The story is often told of discovery of poly(cyanoacrylates) aka Superglue. Harry Cover had recently synthesized some of the stuff and went to measure the refractive index of it. As he was using an Abbe refractometer, the liquid quickly adhered the prisms together [*], ruining the instrument.

The question I always have had was why was he measuring the RI? I've synthesized a nice amount of polymers and have never measured RI for any of them. I always figured that because it is such a trivial test to run even back in the 1940's, it was routine because the many other tests that we now take from granted (FTIR, NMR,...) didn't exist back then (or were difficult to carry out/analyze...)

I think I was finally able to hypothesize an answer when I was reading about Mr. Coover receiving the National Medal of Technology last year: he was trying to develop materials for gun sights. And then suddenly I gathered the rest of the story. Gun sights are lenses, and lenses function based on refractive index and that would then be perfectly logical reason to measure RI, even today.

The other question I have is what was the numerical value of the measurement? Gluing the prisms together certianly would not prevent making the measurement; it would only hinder making subsequent measurements.

[*] For those not familiar with this device, a few drops of the liquid being measured are placed on the lower prism, and then the upper prism is lowered on top of it. The measurement is actually of the angle of total internal reflection, and details can be found elsewhere, but NOT the Wikipedia article which is really poorly written and refers to nonexistent illustrations.

Wednesday, January 12, 2011

My Polymer Chemistry Hero

Following in the vein of the Chemistry World Blog's celebration of the International Year of Chemistry, I'm submitting my contribution: Hermann Staudinger. This was the man who first established the existence of polymeric molecules, but that in itself is really a lame introduction, so let me back up. To be a true "Hero" in my book requires courage and taking risks. The was certainly the case with Hermann. We certainly take the existence of polymer molecules as an accepted fact, so much so that we wonder how their existence could have ever been questioned, but that was not always the case. From the Wikipedia article:
"At the time leading organic chemists such as Emil Fischer and Heinrich Wieland believed that the measured high molecular weights were only apparent values caused by the aggregation of small molecules into colloids. At first the majority of Staudinger’s colleagues refused to accept the possibility that small molecules could link together covalently to form high-molecular weight compounds. As Mülhaupt aptly notes, this is due in part to the fact that molecular structure and bonding theory were not fully understood in the early 20th century.
Keep in mind that this is the same Fischer who established the relative sterochemistry of sugars (and was lucky(!) enough to actually be correctly identify the absolute chemistry). Staudinger caught quite a bit of heat for a couple of decades for the whole idea of such large molecules as chemists were not comfortable with the idea, let alone the idea that a given polymer would have a distribution of molecular weights. (All that discomfort still exists today for many chemists. You've seen it, right? Chemists who just ignore polymers, despite the fact that many of them are trivial to synthesize.) And so that's the basis for my choice.

I briefly considered Paul Flory, as he was able to provide tremendous contributions to the science across a vast range of areas, both chemical and physical. And Carothers would be another option, somewhat appealing by the tragic life he lead, and being hounded by depression certainly requires courage that most of us cannot understand. And there are certainly others that have made important contributions, but on the basis of my (personal) definition of hero, I'm sticking with Staudinger.

Wednesday, January 05, 2011


I found out over the New Year's break that my paper I submitted to ANTEC was accepted. Hoop yeah!! The reviewer only had a brief comment about how "heavy" the paper was and that the industrial designers might not be happy with it, so if you're an industrial designer, considered yourself forewarned. For the rest of you, if you're in Boston in the first week of May, feel free to stop by and give me a listen. If you're not, I strongly suspect that Aspen Research will make a video of the practice session and post that on YouTube (as was done last year).

This looks like it might be a banner year for Aspen, as it looks like we are 5 for 5 as company for papers accepted.

Tuesday, January 04, 2011

Extruder Philosophy

Extruders come in quite a range of configurations (single screw, twin screw, octascrews of all types...), an even larger range of geometries (L/D's all over the map, intermeshing twin screws, non-intermeshing twin screws...), all of which have a purpose.

The puzzle to me that I've noticed over my career and client visits is that companies tend to fixate on using just one type. Some companies only use single screws ("twin screws are too expensive and we can modify the screw to do what we need") while others use only twin screws ("can't do a blasted thing with a single screw"). And then at that, they only seem to run in a single dirction, either counter- or co-rotating, but not both. What is really funny is that I've seen "twin-screw companies", when they do have a single screw, run it like it's a twin-screw: starve-fed, instead of flooded as is typical for single screws.

I can understand a company locking into a business model and following it religously, but extruders?