Monday, March 30, 2009

Yeah...what he said...

While I've always maintained that rheology is a pretty daunting subject in full, many of the concepts are easily grasped by 6th graders - which explains the presence of multiple containers of Silly Putty on my desk and in the lab. But this definition of the subject is just a wee bit abstruse:

"The line activity of fluids much as liquid plastics, natural fluids, and paints is much more multifarious and Byzantine than that of tralatitious physicist fluids. The persona of nonverbal help in the think of much flows has accumulated staggeringly over the time cardinal years, and the phenomena and nonverbal difficulties in Byzantine flows hit led to newborn and hard mathematical questions.

Studying much flows presents a patron of problems, as substantially as opportunities for mathematical analysis, including questions of asymptotics, qualitative dynamics, and quality of nonverbal methods. Mathematical Analysis of Viscoelastic Flows presents an overview of mathematical problems, methods, and results relating to investigate on viscoelastic flows. This monograph is supported on a program of lectures presented at the 1999 NSF-CBMS Regional Research Conference on Mathematical Analysis of Viscoelastic Flows. It begins with an launching to phenomena observed in viscoelastic flows, the compound of mathematical equations to help much flows, and the activity of different models in ultimate flows. It also discusses the asymptotics of the broad Weissenberg limit, the psychotherapy of line instabilities, the equations of viscoelastic flows, jets and filaments and their breakup, as substantially as individual another topics."


Source

Somehow I have this mild feeling that this was translated without any human intervention in the process. I like the use of Byzantine, but was thoroughly unaware that line instabilities are in need of psychotherapy. As I said at the beginning, rheology is can be pretty difficult at time so unless you want to end up in the loony bin, leave it to the professionals!

Recycled News on Recycling of Plastics

Certainly this is not surprising, but a new SRI report shows that plastics recycling is still have a negligible impact in displacing virgin resins. I certainly don't see that changing anytime soon either.

I've worked for 4 different companies in various industries for nearly 20 years now, and in my current job I've worked with dozens of additional companies. I've yet to encounter a single example of using post-consumer waste in any product. (Post-industrial waste?. Now that's a different story. See below.)

So what circumstances would need to change in order to reach this eco-utopia where industry uses a significant amount of post-consumer waste? I don't think that that is possible. Post-consumer waste is far too variable in color, rheology, and quantity (i.e., the available quantity is not always constant, and many end-uses require more resin than is available). Many applications have very high performance standards, such as healthcare devices, (I don't expect the FDA to approve recycled HDPE resins in implant situations anytime soon). When people's safety is involved, no company is going to want to take the risk.

Post-industrial recycling is far more common, as it avoids most of the problems listed above. Many processors will simple grind up their own waste and add it to their own feedstream instead of paying for the waste disposal, but even in that has limitations. There are plenty of examples where even in such a controlled situation, the processor will not use the recycle because the polymer has been damaged (by heat and mechanical stresses) too much for it to not significantly degrade the performance of a product.

Thursday, March 26, 2009

The Ongoing Saga of Open Access

MIT is taking a provocative stand - the faculty is now required to retain copyrights indefinitely on their published research. This may be challenging for those journals that do not offer any option of open access, and other universities/research institutions may feel compelled to keep up. Open access can but not necessarily will lead to greater citation of those papers, so I can certainly see other institutions following suit. At least the prestigious ones that have the big buck grants that can buy the open access option. Researchers at the Northern campus of Southeastern State College will be struggle to keep up.

Misc.

Just some various links of varying degrees of interest

- The New York Times Magazine has an article on Dyson Freeman. If you are not familiar with him, this is a pretty good introduction, although it spends way too much time on global warming and not enough on previous pursuits, such as are highlighted in the Wikipedia article.

- The Wall Street Journal looks a little more carefully at the numbers behind the massive mass of plastic floating in the Pacific. Not surprisingly (as is always the case when a political statement is being made from "science" based data), the numbers are a little bit fuzzy and not as exact as they appear.

- This is a just plain weird way to sell polymer resins. I can certainly appreciate off-beat humor, - maybe my sense of humor is out of wack.

Monday, March 23, 2009

Natureworks is expanding

In this economy, that's always a good thing. Demand for their biosourced polymers is growing, and so they are expanding.

These polymers are polylactic acid - PLA - with the lactic acid produced from corn.
PLA can be made with great difficulty by polyermizing lactic acid, but the water is a byproduct and degrades the polymer. A clever way around this problem is to use lactide instead of lactic acid as a feedstock. Lactide is a dimer of lactic acid minus a couple of water molecules. Polymerizing the lactide is much simpler without the condensation byproducts floating around.



This is another example where the name of the polymer is not descriptive of the monomer(s) use to prepare it. Polyvinyl alcohol is the most famous example. Vinyl alcohol, if ever formed, immediately undergoes a keto-enol rearrangement to form acetaldhyde. Instead, polyvinyl acetate is hydrolysed to form polyvinyl alcohol.

Thursday, March 19, 2009

Nitrogen Enriched Gasoline???

I'm assuming that anybody reading this blog (both of you) would have had the same reaction as me - total shock that anybody would thing that nitrogen in gasoline would do anything of any value. Besides, nitrogen is already the largest component in the cylinder when ignited (the inlet air is ~ 79/21 nitrogen/oxygen, and the oxygen/gasoline ratio is about 13:1) so whatever small amount that could be solubilized and/or dispersed in gasoline would be a very small amount indeed. (Now nitromethane, that's a different story.) Nonetheless, Shell has just introduced nitrogen enriched gasoline.

Reading the press releases, you eventually find that the nitrogen is part of a (new) cleaning system. That's all fine and nice, but how does that become "nitrogen enriched gasoline"? Note that there is not a trademark on the "nitrogen enriched gasoline", it is simply the generic "nitrogen".

Is the Shell marketing department really so technically inept? Why not claim instead "hydrogen enriched gasoline"? The mind reels from it all.

Wednesday, March 18, 2009

So you want to win an race of Epic proportions?

Just be sure you're named Lance and also a cancer survivor.


Lance Mackey (on the left) is about to win the Itidarod for the third straight time after surviving throat cancer. As of 1 PM CDT, he is past the last checkpoint and has less than 22 miles to go, while the closest competition is 50 miles behind. It's all over but the celebrating. A very impressive win based on shear teamwork and superior ability.

Lance Armstrong (on the right) won the Tour de France seven straight times after surviving testicular cancer. Despite all the focus on the man wearing the yellow jersey, all wins in the Tour are also based on teamwork and superior ability.

Chaos Theory and the Big Three

Edward Lapham at "The Auto News" raises an interesting question. Could the bankruptcy of a small parts supplier set off a ripple effect that takes down the Big 3 automakers? I don't like the analogy with pre-WWI Europe, but the result could be comparable - someone small (possibly even a Tier-2 supplier) getting in trouble, setting in motion a progressively larger chain of events. Suppliers to the Big 3 (and the Big 3 themselves) have been under tremendous pressure the last decade (and more) so the current downturn is even that much worse.

Keep your fingers crossed. All economies do not take well to sudden changes, so if anyone in Detroit were to disappear, it would be better if they would just fade away.

Monday, March 16, 2009

First they came for BPA...

but I didn't use BPA so I didn't stop them. Then they came for PET...

From Science News: "Bottled mineral water may deliver more than a no-calorie thirst quencher. If dispensed in bottles made from a type of plastic known as PET, for polyethylene terephthalate, this water may also pack a substantial quantity of estrogen-mimicking pollution, according to researchers at Johann Wolfgang Goethe University in Frankfurt.".

At present, the science behind this doesn't look too good. They didn't actually test (quantitatively) for any estrogen-mimicking compound, or even identify what it is. Instead they placed estrogen-sensitive snails into the bottle and saw a response that correlates with increased estrogen levels.

Apparently they seem to have forgotten that correlation is not causation, something can all scientists know but are prone to forgetting on occasion (more occasions for some than for others).

The full article is open access.

Spring Time in Minnesota

To really appreciated Spring, you have to live through Winter. There is no other way. This last weekend was spectacular. After a fairly hard winter, we finally had two days of real warmth - 50 F on Saturday and 56 F on Sunday. Certainly not warm by most people's scale, but with a foot a snow on the ground, many were moved to wearing shorts. Moving water is always beautiful, but seeing moving water against a snow bank is even more so.

Don't worry about calling anyone in the upper Midwest today. We are all in a great mood.

Friday, March 13, 2009

The New Investment Diversification

Just a small thought on investing: In the past, it was solid investment advice to diversify one's protfolio across a range of stocks (large/medium/small cap), bonds, international ventures, precious metals, real estate... In light of the scam of Bernie Madoff and other Ponzi artists, it now seems prudent to diversify across investment companies as well.

Depressing News

In the same way that news on the economy is both depressing but not surprising, the California Academy of Sciences has found that American's knowledge of basic science facts (such as how long it takes the Earth to orbit the sun) is appallingly low. I find no comfort in the fact that it is valued as being important. That is simply empty talk less enlightning than a late night interview of some new starlet.

Wednesday, March 11, 2009

The "Most Admired" Chemical Company

Fortune has reassembled their "Most Admired Companies" list. BASF was atop the chemical company list, but I don't think that is then accurate to call it the "Most Admired Chemical Company". Maybe I'm splitting hairs, but I don't think you would get much of a list if you asked people (business leaders or otherwise) "What is the most admired chemical company?" Public perception of the industry is just too low to assemble much of a list. It would be like asking for "most admired politician" or "most admired lawyer". I would write the headline differently: Amongst chemical companies, BASF is most respected.

I mean no disrespect towards BASF or anyone else on the list, but this is a case of reinterpreting results.

Dow and Rohm & Haas - The Last Word?

Both sides seem to have been able to kiss and make up. And their still closing at $78 a share. And Wall Street seems to be happy about it too. Today. But since they always have a "what have you done for me lately" (i.e., in the last quarter) prospective, I don't think the long term perspective will be as rosy.

It's ironic that Dow is able to progress on this by selling assets since it was by attempting to sell assets to the Kuwaitis that they got themselves into this pickle. They're obviously believing that selling this set of plants and equipment will proceed a little bit smoother. And they're cutting jobs too.

The New York Times has an excellent look at all the details of this deal by someone with much more information than I can gather by just reading news articles.

Yet another rant

Since my previous post was motivated by irritation, I might as well continue the trend and post another.

Thixotropy is a real poster child for an abused rheological term. Beside the previously mentioned issues, there is an even more fundamental misunderstanding of the word - that thixotropic materials are MORE viscous than non-thixotropic materials.

The best I can gather is this: many thixotropic agents, such as silica, when added to a polymer create a mixture that is more viscous than the initial polymer was (in an unstressed state). Since an unstressed state is the condition that most people view them (unless you are prone to sticking your hand into an operating mixer) and since the first syllable in the word sounds like "thick", I can see that one could make the conclusion that "thixotropic" is fancy jargon for "thicker". But this is clearly wrong, since if you start to shear the material, the viscosity will quickly drop.

For filled materials - such as when silica is added - the polymer chains, running willy-nilly are adsorbed onto the surface of the filler. This makes it more difficult for the polymer to relax and flow when a stress is applied, since the filler is effectively an entanglement preventing a chain from moving. The drop in viscosity over time is associated with a breakdown in this network. The strength of the adsorbtive bonds is low enough that the stress applied by the shear can remove them from the surface of the filler so that they are freer to move relative to each other. i.e., flow.

Monday, March 09, 2009

Abusing the Poiseuille equation

The abuse has always existed, but now it seems to be on the uptick and it's got to stop.

The eponymic Poiseuille equation (don't even begin to ask me about pronouncing the name) shows the relationship between the important variables when a fluid is flowing through a pipe. The volumetric flow rate, Q, is related to the pressure drop, DP, the pipe diameter, d, the pipe length, l, and the viscosity, h, by

Q =(p d4 DP)/(8 h l)



In getting to this result, there are TWO (2) assumptions. Violate either assumption and the results you get from the equation are useless.

1) The first assumption is that the flow field is fully developed, meaning that the liquid has been moving for a long enough time period in the tube that its velocity profile is not changing. Fully developed flow typically requires that l/d is at least 20.

2) The second is that the viscosity, h, is constant at all shear rates. This is a good assumption for low molecular weight fluids, but not for polymers and other non-Newtonian fluids where the viscosity typically decreases as the shear rate increases, although numerous other possibilities exist.

Given these two assumptions, it is clear that if you are looking at polymer flow through a short pipe (l/d < 20), YOU CANNOT USE THE POISEUILLE EQUATION. Instead, you need to rederive the equation using an appropriate function for the viscosity. (Power law or 8-constant Oldroyd or whatever.)

And yet this abuse is getting more and more common all the time. I saw this misuse in a major trade magazine for the plastics magazine where the author, who really should have known better, was attempting to quantitate melt-flow-index data. A melt flow index has a short die (l/d ~ 4) so that the flow profile never fully develops. All the numbers the author generated (and there were a lot) are meaningless.

I also ran across it on another blog. The worst part was that the blog seemed to be well read (based on the number of comments) and that the readers also were being lead down the wrong path.

Please stop it.

Friday, March 06, 2009

Lumpy Gravy

I'm getting a chance to work again with some water soluble polymers. For some reason, preparing aqueous solutions of these is always more difficult than dissolving any other polymer in a non-aqueous solvent. If you dump the powder in too fast, without adequate mixing, you end up with clumps that never dissolve - hence the title of this post.



(Obligatory Frank Zappa reference).

What's happening is that the water is quickly swelling and softening the surface of the powder. The grains then are easily able to stick together in a mass greatly slowing the uptake of further water and preventing complete dissolution. Certainly this could happen with solvents, but it never seems to. Only with water soluble polymers. (And this truly is what happens when you make lumpy gravy.)

An easy trick around this is to put some crushed ice in the water (being sure to incorporate the mass of the ice into the final concentration calculations). The cold water doesn't swell the polymer particles nearly as fast, thereby allowing for a complete dispersion of the powder. Once it is all dispersed, some heat melts the ice and the complete dissolution rapidly follows.

Dow and Rohm & Haas - The Saga continues

Marketplace is now reporting that the two parties are talking after all about still trying to close the deal. Given how Dow's chart is remarkably similar to that of another Michagan-based, industrial giant, and so different from Rohm and Haas's, I can't imagine that Dow is paying for it with any stock without convincing R & H that it is seriously undervalued and will be a "sure thing" to rise a lot in the future. They certainly don't have the cash or they never would have been in this mess in the first place (as previously discussed here and here and here).

Maybe they are hoping to become "too big to fail"?

Thursday, March 05, 2009

Some hints on the Rheology of Ketchup

The most common interactions people have with rheologically complex materials is in their food. Having a few moments of free time, I sampled some of the ketchup sitting in the company cafeteria refridgerator, which as you would expect, has been sitting in there for who-knows-how-long, enduring who-knows-what-temperature-cycles and surviving countless power outages of verying lengths. It passed the SOS test (sight-odor-slime) so I'd eat it, and therefore it's good enough to test in the dynamic mechanical analyzer.

While it seems that endless rheologist-wanna-be's endlessly state that ketchup is "thixotropic", it is far more complex than that simple statement. Let's define terms: thixotropic: "A material that shows a decrease in viscosity over time while being exposed to a constant shear rate." This is commonly confused with shear thinning (aka pseudoplasticity): "A material that shows a decrease in viscosity when the shear rate increases." Got it? In one case (thixotropy) you measure the viscosity at a constant shear rate and look for changes over time. In the other case (shear-thinning), you make measurements at a variety of shear rates and look for a negative correlation.

The plot below shows that the sampled ketchup is shear-thinning. The viscosity decreases as the shear rate increases.

It also shows the storage and loss moduli with the latter begin less than the former, but both are non-zero. This means that the ketchup shows both solid and liquid characteristics, but that the solid-like characteristics are greater than those of the liquid. The moduli are also pretty insensitive to the shear rate.

The next figure shows what happens as ever increasing strains are applied to the sauce. Between a strain of 1 and about 20, very little happens, but after that, things get interesting. All three curves drop, but the storage modulus drops faster than the loss modulus, eventually crossing over at about 60. All the while the viscosity keeps dropping too.


That's all for today, but more will be on the way.

Monday, March 02, 2009

Mylar -What it isn't


Mylar.

What it is: Dupont's tradename for biaxially oriented polyethylene terephthalate film, i.e., PET unless you the SPI making up recycling codes, in which case it is PETE. It is transparent. Now you know.

But here's the catch. PET is commonly metalized with an aluminum vapor coat, and for some reason, this has caught on with the general public as being the only type of Mylar, so that any and all examples of metalized films, PET or not, are called Mylar, and non-metalized examples are not.

Why? This is not an example of a trademark becoming a generic, such as nylon. This a trademark becoming generic but only in a certain embodiment. I can't think of any other examples of this. It would be like lotion-soaked tissues being known as "Kleenex", but all other Kleenexes would be known as facial tissues.

Polymers and their Solubility

Th' Gaussling posted a question a few weeks about about polymer compatibility. Being that Th' Gaussling and I have exchanged emails in the past, I shot him back (or so I thought) a quick reply. Not hearing a simple "thanks" is uncharacteristic of the fellow, so after additional follow-up mails were unanswered, I became suspicious. It now appears that my emails have never arrived. That is certainly understandable as our IT department loves to play tricks on us (replacing networks servers over the weekend without prior notification AND supplying the new server with a new name so that all of our old shortcuts need to be edited...) so the fault is clearly on this end. Since most of what I attempted to send to Th' Gaussling is suitable for public viewing, here is what I attempted to communicate earlier.

This is one of areas of polymer science that is not as well known as it should be. There has been quite a bit of work done in the area, but mostly by paint chemists so it just isn’t very broadly known. As you would expect, it is a horribly complex area, full of endless exceptions-to-the-rules, so here are what I see as general guidelines.

The concerns you have all closely related: as a polymer dissolves, swelling increases, migration increases… Avoid one, and you avoid them all.

Most of the focus is on polarity of the polymer and the solvent, but it’s more complicated than in organic chemistry. Start with the Hildebrand cohesive energy density which is the heat of evaporation divided by the molar volume. The square root of this is the solubility parameter. You get weird units, such as (cal/cc)1/2. This number will range from about 6 to 24 or so, with the higher numbers indicating greater polarity. You can run into problems if the solubility parameter of the polymer and the chemical are too close, as they are then too compatible.

It has been found that this one-dimensional approach falls short in many cases, and that a two-dimensional approach is needed. Introducing the hydrogen bonding parameter, which is measured by looking at shifts in the IR spectra following deuteration.Using two parameters allows you to differentiate between chlorinated solvents for example, which have high polarity but negligible hydrogen bonding.

There are a couple of other bonding parameters as well to carry this to further dimensions, but they are much more difficult to measure and I’ve never found that they greatly increase the usefulness.

Working with these two parameters, people have prepared 2-D maps showing the regions where solubility occurs. The regions are big amorphous blobs often with one or more arms. Like something from a low budget sci-fi movie. (“The Blob that Ate Boise.”) Given this, you can then imagine situations where a polymer dissolves in some solvents with a given solubility parameter, but not all of them, since the hydrogen bonding also need to be given heed.

A big wrench in the workings is crystallinity of the polymers. Based on the arguments above, xylene is a good solvent for polyethylene, but for it to solvate, you need to more or less melt the resin. The thermodynamic well for the crystallization is that deep. Too bad, as a RT solvent for PE would be a godsend.

So that’s it in a nutshell. Going forward, there are a number of options for getting more detailed information. Alan F. M Barton has a couple of authoritative books in the area (“CRC Handbook of Solubility Parameters and Other Cohesion Parameters”, and “CRC Handbook of Polymer-Liquid Interaction Parameters and Solubility Parameters) that have tabulations of the parameters and some solubility maps. Unfortunately, they are published by CRC, which to me has always meant “Costly, Really Costly”. The coverage is not as broad as I would like, but measurement and tabulation of basic physical properties has never been sexy. Google Books also has some sections online too. Lastly, now that you know the terminology, you might be able to locate appropriate journal articles as well.