Monday, January 26, 2015

King Tut and BPA

King Tut was in the news last week, or more correctly, his burial mask was (although I bet most people don't really know the difference). The breaking news is over a polymeric material and the incompetence of some conservators to do the right thing. Specifically, it is reported that his iconic beard broke off, and was hastily repaired with an epoxy.
"Three of the museum's conservators reached by telephone gave differing accounts of when the incident occurred last year, and whether the beard was knocked off by accident while the mask's case was being cleaned, or was removed because it was loose. They agree however that orders came from above to fix it quickly and that an inappropriate adhesive was used. All spoke on condition of anonymity for fear of professional reprisals. 'Unfortunately he used a very irreversible material — epoxy has a very high property for attaching and is used on metal or stone but I think it wasn't suitable for an outstanding object like Tutankhamun's golden mask,' one conservator said."
But it gets worse. The three conservators really made a mess of things, so much so that you have to wonder if they were possibly named Larry, Moe and Curly.
"The conservator said that the mask now shows a gap between the face and the beard, whereas before it was directly attached: 'Now you can see a layer of transparent yellow.' Another museum conservator, who was present at the time of the repair, said that epoxy had dried on the face of the boy king's mask and that a colleague used a spatula to remove it, leaving scratches."
Take a look at this picture and see the damage yourself:
That is one bad glue job on ol' King Tut
Source
That is an awful patch job - it looks like something I would do puttering around in the garage on the weekend. And that would include getting excess adhesive all over the place. Look closely and you can also see freshly scratched gold in numerous areas of the chin where the excess was removed. King Tut's burial mask, damaged for all eternity.

Fortunately, the chemophobic missed out on a big story here regarding the chemistry of epoxy adhesives. They are usually two-part adhesives, with part A having molecules with multiple, terminal epoxide rings, and part B being a hydrogen-donating molecule, such an amine. Mixed together, the two parts react to form a crosslinked material - "irreversible" to quote one of the conservators. For part A, the most commonly used compound is DGEBA, an abbreviation for diglycidyl ester of bisphenol A. Yes, bisphenol A, that chemical that the chemophobic so love to fear for causing everything awful to our bodies and our children's bodies. While we cannot be certain at this point what the chemistry of the epoxy was, the most likely scenario is that it did contain DGEBA so that now King Tut is being exposed to BPA for his eternal afterlife.

To which I can only say:
King Tut  - exposed to BPA


Previous Years

January 26, 2012 - Viewing History through an Oil Refinery

January 26, 2011 - My Most Embarrassing Moment at Work

January 26, 2010 - Phosgene Death

January 26, 2009 - More on Dow and Rohm & Haas

January 26, 2009 - Biodegradation of Polymers

Friday, January 23, 2015

The Dastardly Death Ray vs. The Snowman

Please forgive my absence in posting this week. My thoughts have been elsewhere - on
WORLD DOMINATION!
I've written in the past about the Death Ray that I possess. It is the natural result of sunlight reflecting off the thin, curved window glass on the south side of my house. The curvature is enough to concentrate the sunlight so that it can burn the lawn and melt snow. Egged on by a comment from Chemjobber, I decided to put the Death Ray to the test and use it to sever a Snowman.

Once the world sees the destructive force of my Death Ray, it will bow before me and I will be unstoppable!

Conditions were ideal this last weekend for the construction of my victim - warm and cloudy. I had planned for weeks the exact location. My plan was perfect! The snowman was in the ideal location, now all I needed was sunshine. And that came yesterday. Here is the setup from yesterday morning before the sun was high enough to cause havoc:
The house faces due south. In just a few hours, the sunlight would bounce off the windows, becoming concentrated and unleash it full photonic fury upon the snowman.

Just before noon, the first of the caustics crossed the snowman's body. Goodbye Mr. Frosty:
But alas! My plan was a complete failure. The Death Ray barely affected the snowman at all! In fact, the sunshine that fell on the back of the snowman was far more destructive, creating the extensive cratering that is all so common on sunstruck snow. Oh cruel world!. My hopes for world domination are dashed. And worse yet, I now have a snowman right outside my kitchen window that each day will mock me. Instead of having results worthy of publication in both Science and Nature [*], I now can only publish them in a third-rate blog. Oh, why have the Fates seen fit to punish me so?

(The explanation for my failure is fairly simple. The Death Ray is able to cut tracks in the snow field (see the photos in the 2nd link above) while the sun can't because the grade of the yard in that area is away from the sun and towards the house. For Frosty, the slope of his back was facing nearly directly at the sun. Additionally, the sun was able to shine on Frosty for a number of continuous hours, while the caustic crossed the snowman in just a few minutes.)

And so it is back to the drawing board, but that is how science and engineering often is. Now matter how appealing a hypothesis is ("I can sever a snowman with the Death Ray"), we need to run the experiment to prove it, and in this case, face the difficult fact that the Death Ray cannot sever the snowman's body (or even make a noticeable dent). I'm glad I tried, but I think this will be the last time I write about the Death Ray. I'll get back to more normal topics next week.



[*] With a fully functional Death Ray, who was going to stop me? Certainly not Reviewer #3




Previous Years

January 23, 2014 - Dow Chemical Under Attack From Its Own Investors

Friday, January 16, 2015

BPA and BPS

As much as I would like to brag, or say "I told you so", I really don't feel that I'm prescient in the least. Any scientist with a little appreciation for their field would instantly recognize that when somebody says "Chemical X is poisonous! We need to stop using it!", the immediate follow-up questions should be:
  • OK, so what should we replace it with?
and
  • Why do you think the replacement is any better?
And yet that is what we face with the chemical bisphenol A, also known as BPA. It is the condensation product of 2 moles of phenol (hence the bisphenol) and 1 mole of acetone (hence the A). It is used to make the polycarbonate that is used for making Blu-ray/DVD/CD discs (other polycarbonate do exist as well). It is also used for making epoxies, some of which are used as adhesives, but others of which are used for lining steel cans to prevent their rusting.

Once the BPA has reacted and formed the polymer, there is very little reason to be concerned about it. The polymer is good and stable. The concern over BPA arises from unreacted BPA in the polymer, not from the reacted BPA (although chemophobes will try and convince you otherwise). As much as the FDA and regulatory bodies around the world have looked at the available data and said that there is no reason for concern (see the link above), some people are concerned and want to avoid any contact with BPA.

One popular suggestion as an alternative is BPS, made by reacting two moles of phenol with one mole of sulfuric acid (hence the "S"). (If you are curious, there is a whole alphabet of bisphenols out there, even a BPZ.) But now we have a report that in zebrafish embryos, BPS appears to causing at least as much hormonal damage as BPA. While I don't ever want to create problems for any animal, let alone zebrafish, for us humans, well, we have to wait and see if the effects of BPS are the same in humans.

While the biological aspects of the research are beyond my understanding, the interpretation and conclusions are not. The researchers contradict themselves and don't even see it. Near the end of the article they state
"...manufacturers have turned to BPS with little proper toxicology testing to produce the “BPA-free” products demanded by society..."
and yet the authors have no problem with proposing their own open-ended experiment:
"These findings...support a societal push to remove all structurally similar bisphenol analogues..."
And the alternative compounds (that of course have been "properly" tested) are...?

That last statement quoted above is shockingly overreaching just by itself. So because BPS didn't work out in one (unreplicated) study on fish (and not humans), we need to toss out all bisphenol compounds, even the ones that are safe (such as BPA)? Wow. What an overstatement. Could the researchers take themselves and their results even more seriously? It's only January 16th, but I'm ready to predict that this quote will easily win the "Overstatement of the Year 2015 " Award.


Previous Years


January 16, 2014 - Recycling Plastics for the Do-It-Yourselfer


January 16, 2013 - Does Going Public Kill Innovation?


January 16, 2012 - Flying Cupcake Update


January 16, 2009 - The Pitch Drop Experiment





Thursday, January 15, 2015

Falling Oil Prices and ExxonMobil

I've been preaching for a while about how ExxonMobil is incorrectly blamed for any and all possible problems around the world that can be connected to our modern petroleum-consuming economies. While ExxonMobil may indeed be at fault for many of these accused problems either directly or indirectly, I again want to emphasize that they are a small fish in a large ocean.

Look at the recent price drop in petroleum around the world. ExxonMobil has nothing to do with this, and in fact, the low prices are hurting them. Revenues are dropping, investments are dropping and their stock price is dropping. Is anyone saying ExxonMobil is responsible for the low prices? Or si the blame being put on Saudi Arabia, whose National Oil Company, Saudi Aramco, has the largest reserves in the world, and who isn't cutting production?

People being people, ExxonMobil will again be vilified when prices do increase and their profits follow. No one will blame Saudi Aramco, and our profound, collective ignorance of the true dynamics of the petroleum industry will continue.



Previous Years

January 15, 2013 - Assault with a Deadly Hair Removal Gel


Wednesday, January 14, 2015

Monkey see, monkey do

Back in November, Dow Chemical was able to reach a truce with their "activist investor" Daniel Loeb of Third Point LLC., by letting Third Point put two of their people on the Dow Chemical Board of Directors. (In a rather intelligent move, Dow Chemical also added 2 additional directors so there are now 14 total. Had Loeb won his proxy fight, his 2 directors would have been 2/10 = 20% of the board. Now they are 2/14 = 14%. It may have been awhile since Dow's CEO was at the bench, but he certainly understands dilution to this day.)

The other large US-based chemical company whose name also starts with with the letter "D" is now in a similar fight with an activist investor, in this case Nelson Peltz and his company Trian Investors. No doubt emboldened by Loeb's (dubious) success, guess what Peltz wants? You got it - he wants to put directors on Dupont's board! Peltz obviously has a little more time on his hands than Loeb does, as Peltz wants to be one of the directors, while Loeb was quite content to let his cohorts have that role.

Dupont's Board is already 14 members and Peltz is running a slate of four candidates. If they all win, they would make up almost 4/14 = 29% of the Board. Or maybe Dupont can copy what Dow did and let Peltz put two on the board while Dupont adds two more, in which case Peltz will only control 2/18 = 11% of the Board. That would be a significant swing.

I've not followed Dupont's business closely, so they may or may not be deserving of a kick in the pants to wake them up, but activist investors never sit well with me. They strike me as too much grandstanding and publicity seeking and not having enough focus on rational thought. Such behavior is typical for politicians. I don't approve of it from either group.



Previous Years




Tuesday, January 13, 2015

Kinetics, Thermodynamics and Polymer Phase Transitions

Polymers appear to break many rules of thermodynamics on a regular basis, when in actuality nothing of the sort occurs. I bring this up after reading an article in the Guardian yesterday about glass transitions in polymers that has too many errors to just let slide. I don't think that these errors are acceptable. While explaining the glass transition of polymers can run you afoul of numerous difficulties, The Wall Street Journal did an admirable job a few years back, so I don't think my standards are too high.

Consider this excerpt, which really is logically incoherent:
"Every polymer locks up ...at its own particular temperature, known as the glass transition temperature, usually denoted Tg. This is the temperature at which the chains can no longer move fast enough to respond to any external forces to allow deformation to occur. If you hit the polymer fast with a hammer this means that a higher glass transition temperature is recorded than if you slowly pull on it."
If that last sentence came to you as out of nowhere, or maybe better, as a sudden blow to the head with a hammer, you're not alone. It's quite a non sequitur The discussion starts on Tg as a temperature, but then a hammer enters the picture and that changes everything about that temperature? And how is that change in temperature "recorded" when the hammer comes down? This is horribly unclear but I understand where the author wants to go.

A polymer can act glassy in two entirely different manners. First, it will behave as a glass when it is cooled below its glass transition temperature. But it can also act glassy (and the emphasis here in on "act") even if it is above its Tg when too great a stress is applied too quickly. In this latter case, the polymer strands do not have the time to relax and flow past each other and so they have to stay in place and take the stress without moving - just like a glass. I'm guessing that that is where the "hammer" comes from - a short, sharp blow from a hammer can shatter some polymers like glass. But to suggest that this glasslike behavior "changes" the Tg is entirely incorrect. And it contradicts the first sentence - "Every polymer locks up...at its own particular temperature...."

Then consider this:
"The glass transition temperature is quite different: its value depends on how you measure it. This makes it something of a thermodynamic oddity; it isn’t a true phase transition at all. "
Oh boy, them's fighting words [*]. The glass transition temperature is a true phase transition, but it is a 2nd-order phase transition, not a first order phase transition such as the boiling of water that the author compares it to.

Measuring any phase transition (1st- or 2nd-order) in a polymer takes patience, at least if you want to measure a true equilibrium value. Ideally you need to cool down the sample very slowly so that the polymer chains can relax any internal stresses and reach a true equilibrium configuration. But the cooler you go, the longer it takes since the viscosity of the polymers increase rapidly. And so compromises between cooling speed and data accuracy need to be made. By looking at data from multiple tests, it is possible to extrapolate an equilibrium value which is why we can have tables of glass transition temperatures. Extrapolations like this a very common in science. Think about absolute zero. We've never been able to cool a sample to 0 K, but we still know that the temperature exists and we can extrapolate numerous thermodynamic data to it as well. And so it is with the glass transition temperature.

I stated that patience is need for measuring any phase transition in polymer. For even a 1st-order phase transition such as melting, the values you record will depend on the heating rate. Because polymers are such poor thermal conductors, measuring the melting transition at higher rates would increase the "thermal lag" between the transition and the applied temperature. Measurements are typically made at 10 oC per minute, a completely arbitrary value (since the rate has dimensions, it is arbitrary) that is a compromise between accuracy and measurement rate. If that rate is changed, the temperature of the transition would be reported differently. To requote the article, "...its value depends on how you measure it". No, the values don't vary in this case either. It is an experimental error, nothing more, and results from our impatience in waiting for equilibrium data.

You may have noticed the two main points here both rely on the balance between kinetics and thermodynamics.
  • Because of the sometimes slow kinetics polymer have in relaxing internal stresses, they can be glasslike in appearance. This can appear at conditions well removed from the equilibrium glass transition temperature, but it does not mean that the glass transition temperature has changed.
  • Because of the slow rate at which polymers conduct heat, measuring any phase transition for a polymer is a compromise between getting the data at a reasonable rate and the accuracy of the data.



[*] Three times in my professional life I have witness arguments get so heated that I thought it would break out into a barehanded brawl. Two of those arguments were over the glass transition and statements just like this.


Previous Years