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. 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