Thursday, November 05, 2015

A Frisbee (Murder) Mystery

Fellow (retired) blogger Eric F. Brown brought to my attention an article about Frisbees, in particular, the Frisbees used playing Ultimate Frisbee. It become apparent pretty quickly in the article that the participants of the sport take it extremely seriously.

To me, a Frisbee is a Frisbee. I grew up with the Wham-O brand, but probably because there weren't any other brands to choose from. That has changed, and worse yet (for Wham-O), they are no longer the top dog. Or even the number 2 dog. And apparently, Wham-O is to blame for their own problems, and it's all because of the additives that they chose use. White Frisbees were traditionally made white by the addition of titanium dioxide. TiO2 is a great white pigment as it has great hiding power and you can add lots of it without it showing signs of yellowing (unlike, say calcium carbonate). But it is expensive and so people are always looking for alternatives.

And Wham-O found an alternative set of additives:
Comparison of Wham-O Frisbee Additive Packages
I'm not sure what type of analysis this is other than poorly done. This shows the titanium dioxide as just titanium (What type of instrumental analysis can't detect oxygen?) So while it's tempting to assume that the other metals are probably oxides as well, the aluminum is more likely to be aluminum hydroxide, a common white pigment. I can't believe that silicone was ever added (as opposed to silicon, and probably the oxide at that). The zinc could be either the oxide or the sulfide (more on this in a minute). I can't see that iron oxides would ever be used (that bloody red color is not too appealing in most applications). And what's this "other" category? (Seriously, who did this analysis? Whoever paid for it got taken good.)

Regardless, the new additive package was not accepted by the players:
"At the time, Titanium Dioxide was getting pretty scarce. So the [Wham-O] people in Mexico, when they were molding the discs, they put in some Aluminum Oxide and other fillers, instead of straight [Titanium Dioxide]. I don’t know how much you know about polymer chemistry, but the other additives were aggressive and they actually caused some degradation of the plastic and loss of performance."
Plastic degradation? Now that get's interesting. Which brings us back to the zinc. We don't know what form the zinc was in - elemental (probably not), sulfide (a white pigment, but not the greatest and it is somewhat pricey) or the oxide (another white pigment). Zinc oxide is my guess, as it is photocatalytic under mildly acidic conditions (pH ~5.5) which would lead to the degradation state. While going from 8 % zinc to 10% zinc isn't going to make that big an impact - but that's assuming that the zinc was the oxide in both formulations. What if the initial formulation was zinc sulfide while in the new formulation it was zinc oxide? This analysis can't tell the difference, so it's entirely possible and it fits the limited data.

Sadly, based on this poor analysis, we'll never know but that is my guess: the TiO2 gets the blame, while the ZnO skates free for the killing of the Wham-O Frisbee business. It's a miscarriage of justice.

Previous Years

November 5, 2012 - Job Titles and Business Cards

November 5, 2010 - Flow-Induced Crystallization

November 5, 2009 - Public to Private and Back Again

November 5, 2007 - Negative Intrinsic Viscosity and Positive Intrinsic Viscosity

Tuesday, November 03, 2015

A Novel Polymer Curing Technique

To update an old expression [*], there is more than one way to cure a polymer. The use of heat and UV-light are quite common; visible light can be used as can e-beams; moisture-/oxygen-curing are options; you could argue that 2-part silicones or urethanes are cured upon mixing (a chemical cure); and there are a few more options that escape me at the moment. Back in August however, researchers announced a new curing technology - this one is based on electricity (Open Access article).

It's one of those "why didn't I think of that" papers, although in my case, as much as I hated electrochemistry, I have an out.

The researchers used 3-[4-(bromomethyl)phenyl]-3-(trifluoromethyl)-diazirine as their crosslinking agent, due to its formation of free radicals in reductive electrochemistry. Once the free-radicals are formed, then we are in a common realm for polymer chemists and my comfort level returns. Take a look at the mechanism:
Electrocuring mechanism
The aryl-carbene can react with any of a number of atoms for crosslinking.

One limitation on this technology is pretty obvious - it is restricted to curing between conductive substrates. (Metals, indium-tin oxide coated surfaces such were used here, inherently-conductive polymers...) But what is far more concerning with this particular curing agent is that it generates N2. Gas generation in a polymer matrix is usually not desirable (unless you are making foams). It's only 1 mole per mole of diazirine, so the total amount is limited since crosslinking agents are seldom used at high levels. But still...

I recognize well that initial discoveries are seldom without issues, so consider this criticism of the nitrogen generation as a setting a direction for the mandatory "future research". But since it will involve electrochemistry, feel free to go ahead without me.

[*] That expression being "There's more than one way to skin a cat". The origins of it aren't entirely clear from what I can find online, but the meaning is: there's more than one way to get a job done. Despite the literal reading of the expression being quite gruesome, it is quite commonly said indicating that no literal intent is intended.

Previous Years

November 3, 2008 - Viscoelasticity Movies

Thursday, October 29, 2015

Dull-and-Boring News Items

Sometimes dull-and-boring is good, sometimes it is bad. Here's an example of each regarding recent news items about Dow Chemical:

1. Their latest earnings continue to look good. I especially like the poke that this article takes at the activist-investor Daniel Loeb. He's still around? When is that guy going to take his ball and go home? Regardless, a profitable earnings reports is dull, but good.

2. The Dow chemists have been working hard and have developed a new plastic for Dow to sell. With as many chemists as Dow has, you would expect it to be some gee-whiz polymer with potentially mind-blowing chemistry and great potential to replace non-plastic materials with plastic. So what is it? An LLDPE (linear low-density polyethylene). LLDPE is actually a comonomer of ethylene and α-olefins. LLDPE's have been around for decades so this is hardly exciting or novel. But as the article notes, Dow's last major product introduction was in 2013 and was also olefin-based. What else would you expect when your former Chief Technology Officer goes on the record saying that "...[no] new polymers would be discovered, since chemists already had done a thorough job in finding ways to link carbon, oxygen, hydrogen, nitrogen and sulfur atoms."

This definitely is in the dull-and-bad category. Hopefully the current CTO has a better outlook on product development.

Previous Years

October 29, 2014 - Comparing Burger Chains and Oil Companies

October 29, 2013 - A New Chemistry Lab Building, But Without New Chemistry Jobs

October 29, 2012 - More Open Access articles in Polymers and Rheology

October 29, 2010 - Garbage Patch Vacuum Cleaners

October 29, 2010 - Good Advice

October 29, 2010 - UV Scale-up

Wednesday, October 28, 2015

Elemental Sulfur as a Monomer

It's been far tooooo long since I commented on a research article, but it's time to change that. Angewandte Chemie has an open access Early View article on a new elemental sulfur/limonene polymer. The researchers are from Flinders University (South Australia) and the research has received quite a bit of press since it is able to capture mercury ions (Hg2+) from water, and as a bonus, changes color it does so. A further bonus is that sulfur is a waste product of the petroleum refining industry and limonene is a by-product of the citrus industry, (although somewhat more valuable than elemental sulfur).

The reaction is straightforward:

Simply melt the sulfur, add the limonene and wait. The sulfur rings upon heating break apart and form thiyl groups which react with the unsaturated bonds in the limonene. This is remarkably similar another sulfur/organic copolymer ($) that I blogged about 2 years ago (1, 2), which took the same approach of heat and dump. In both cases, the unsaturated organic compound needs to be low enough in volatility that the hot sulfur (> 170 oC) doesn't evaporate too much of it off.

As is shown above, there are stretches of sulfur-sulfur (sulfide) bonds between the organic segments, and these are what capture the mercury (hence the old name for thiols of "mercaptans"). I did find it somewhat surprising that the amounts of sulfur:liminone were 50:50 on a mass basis.
"An equal mass of sulfur and limonene was chosen to maximize the content of both industrial by-products in the final material."
The authors themselves note that sulfur is produced at nearly 1000x the rate of liminone, so maybe trying to incorporate a little more sulfur would be a good idea. Additionally, the formula weight for liminone is 136 g/mol while that of sulfur (S8) is 256 g/mol, which further skews the ratio of the comonomers towards the limonene.

I also wonder how long researchers are going to keep running these reactions in open flasks. The engineer in me is makes it really difficult to not scream at the monitor about running the reaction under pressure so that the volatility would no longer be a concern. Or maybe in a twin-screw extruder, for continuous production of the polymers. That would make for a great patent, wouldn't it. Or maybe I should say "would have"...

Previous Years

October 28, 2013 - SoBe, What Were You Thinking?

October 28, 2010 - A Foreign Body

October 28, 2010 - Is this safe to eat?

Tuesday, October 27, 2015

Fairlife Followup #2

Back in July I wrote about the non-recyclability of the container used by Fairlife for their chocolate milk. The recycling code says "#7 PETE" which is problematic since PETE is #1 and "Other" is for #7. Since I didn't know how to sort it, it went into the garbage. I email went off to Fairlife to explain themselves, but their reply only muddied the water further, stating that a white pigment in the PETE made it a #7. That's not right since pigments do not affect the recycling codes for any other plastic. I speculated that there was likely a barrier layer that made the container a #7.

It looks like I was right. A person [*] with access to some lab equipment cross-sectioned the container and found this:
Fairlife Milk Container - Cross-Section

Busted! There is a barrier layer in there. The identity of it is unknown, but ATR-FTIR did show the 2 main layers to be PET.

So it's time to send another letter off to Fairlife. Hopefully I'll get a more truthful reply (and not so many words in ALL CAPS!).

[*] Note: the person who did this analysis wishes to remain anonymous. I will respect that request and am very grateful for their contribution.

Previous Years

October 27, 2010 - The Coolest Thing You Can Do With a Polymer - Set Yourself Ablaze

October 27, 2010 - How to Get Around FDA Regulations - Legally!

October 27, 2008 - So when are they going to ban Scotch Tape?

Thursday, October 22, 2015

King Tut is cutting down on his BPA exposure

Earlier this year it was announced that King Tut's iconic death mask had been damaged by some incompetent curators - the beard had been knocked off! - and then hastily repaired using epoxy that ended up getting everywhere. My take at the time was that the epoxy most likely contained BPA (bisphenol A) and thus the mask was being exposed to BPA for all eternity. But that concern is now being addressed, as a German expert has been assigned to repair the mask [*]. Since the depth of penetration of the epoxy is unknown, the time for the repair is vague, with 2 months being the outer limit at present.

Apparently the construction of the mask is unknown (other what is on the surface) and so the repair team will take advantage of this opportunity to study it further. The details of the construction will then drive what approach will be taken to reattach the beard in a more suitable manner than the "Dumb and Dumber" approach taken last time.

I can't imagine what would be done to reattached the beard. A mechanical approach would stand up the longest and duration has to be a great concern. After all, this object will be retained for millenia into the future and adhesives - organic, silicone or any other chemistry - will not have that durability. If they are used, it would likely be with the view that any adhesive would have to be removable at some future date so that it could be refreshened. (No more scraping off epoxies with a wooden stick.) But a mechanical approach would also be the most invasive and damaging, even if the outer aesthetics are immaculate.

It possible that some good may come from the epoxy disaster. If epoxy did in fact penetrate the mask to some degree and then hardened, that material could then serve as a barrier to penetration from adhesives applied now and in the future. And that could put the adhesives option back on the list. We'll just have to wait and see what is approach is decided upon and what the justification is.

[*] How do you get a job like that? Is it a free-lance position and what are the hourly rates?

Previous Years

October 22, 2014 - Dow Chemical's Earnings Keep Improving

October 22, 2013 - October 22, 2013 -

October 22, 2012 - White Isn't Always White

October 22, 2010 - Thoughts on Losing Electricity

October 22, 2010 - Plastics - They Have a Future, but no Futures

October 22, 2010 - It's Not Easy Being Green