Thursday, June 23, 2016

Olefin metathesis - as a degradation route for PE?

Normally when I hear of olefin metathesis in connection with polymers, it is regarding polymerization (such as ring-opening metathesis polymerization (ROMP)). So I was surprised the other day to read a paper where metathesis was used to depolymerize a polymer, and not just any polymer, but a polymer lacking in olefin groups - polyethylene.

The report appears in Science Advances (open access) and shows off some clever tricks. The polyethylene is dissolved in a light alkane (naptha or similar) and then a dehydrogenation is carried out on both the polyethylene and the solvent. After that, the metathesis can happen.

A metathesis reaction is one where there a cross-exchange between two different chemicals. An example would be A-X + B-Y → A-Y + B-X. For olefin metathesis, the A and Y are on either side of a double bond, as are the B and X. And the same is true for the A-Y and the B-X, so the reaction is A=X + B=Y → A=Y + B=X. where A=X is the partially dehydrogenated polyethylene and B=Y is the partially hydrogenated light alkane. If the double bond is near the center of the PE molecule, you are able to pretty much cut the molecular weight in half in just one reaction. Since the molecules are dehydrogenated in multiple locations, the PE can quickly be reduced to very short chains by allowing the reaction to repeatedly occur. And all the while, the degradation products are completely soluble in the solvent.

The technique works for the whole spectrum of PE, from Mw = 3350 daltons to ultra-high molecular weight (Mv = 1.7 x 106 daltons), as well as LDPE and LLDPE (no surprise there, but glad they checked) as well as on PE that had antioxidants compounded into it. Would it work for polypropylene? Polystyrene? PVC? Inquiring minds want to know!

The statistics of this reaction are intriguing to think about. This degradation reaction is actually more akin to a condensation reaction (run in reverse, of course) than the addition reaction that created the PE, but there is so much more. Is there an optimal level of dehydrogenation (as a function of MW, MWD, branching...)? Is there is an optimal light alkane mix? Would having alkenes already in it help or hurt? Modeling this could be quite a bit of fun.

The use of the end product as a fuel is suggested by the authors, who strongly believe that it is an economically feasible route, much better than anaerobic pyrolysis. No numbers are provided however. I won't get into criticizing them at this point, since this is just a first discovery and with just 56% yield, there is a lot of work ahead for someone. But this process and its simplicity seems promising and I would encourage the researchers to push on.



Previous Years

June 23, 2011 - Older workers

June 23, 2010 - Skewing the results - heavily

June 23, 2009 - If anybody dares quote Paul Simon...








Monday, June 20, 2016

Some advice to companies looking for employees

  • Don't ask for my social security number as part of the application. Seriously? Why could you possibly need it at this point in time, since most likely 95% of the applications are going to be rejected out-of-hand. If you make me a tentative offer and I tentatively accept it, then you can have my SSN. But up front? Not a chance.
  • Don't ask for an electronic version of my resume and then ask me to complete an online application which includes me having to re-enter my employment history. Why? You just got my resume. For someone with my experiences, it can take the better part of an hour, even using cut-and-paste to complete the online application.
  • I really question that I should have to register on your website, but fine whatever. And maybe you even do need me to establish a password. But can you please let me know up front what rules you have for the password? Why waste everyone's time by telling them later when you could have told them upfront that the password needs to be at least 18 characters long, must include at least 1 uppercase astrological symbol, 1 Roman numeral and at least one cuneform?
And academic positions can have their own inner-circle of hell
  • Fingerprints? To teach chemistry? If I'm applying for a security clearance position with the government, fine, but I'm not and I'm not applying to your position either.
  • Letters of references, upfront? Again, 95% of the applications will be rejected out-of-hand. Don't you already have more than enough paperwork to look at having gotten my 8-page CV, my cover letter, my research proposal(s), my teaching philosophy, my ethics statement/statement of faith, my graduate transcript and my undergraduate transcript? Do you really have that much time to go through all of that for each applicant? I've gotten most of my industrial positions without having to even list references, let alone supply letters up front.

And to industry and academia alike, is it really that difficult to send out an email saying that someone else got the job?



Previous Years

June 20, 2104 - Will we finally see less packaging when ordering lab chemicals?

June 20, 2013 - Polylactic Acid - from Methane?

June 20, 2012 - A Vinyl Window with a Great R-Value

June 20, 2011 - Viscosity


Thursday, June 16, 2016

Polymers and Soccer Balls

One of the things that I don't understand about soccer/football/futbol [*] is never ending changes in the design of the ball. You can read a little bit about the construction at Compound Interest, which briefly discusses some of the polymers used (urethane for the skin, butyl rubber for the bladder...). Every time there is a World Cup, out comes a new ball design. The 2014 World Cup had the Bazuca, which was used because nobody liked the knuckle ball characteristics of the Jabulani which was used in the 2010 World Cup. Before that, there was the Teamgeist and the Fevernova.

It's not just the World Cup that switches things up. The Euro Cup for instance, used the Tango 12 back in 2012 and this year is using the Beau Jeu.

Just the fact that these ball have names has me shaking my head. Can you imagine a baseball having a name and its design being changed every few years? Or an (American) football with a name? Part of the beauty of those sports is that the designs are so constant. Unless partially deflated, a football is a football is a football. Why would such an well established game as this need to keep changing the ball? (Obviously Adidas is making some money off of all this, but it can't be that much.)

The differences in these balls are not just the color, but the actual construction. The number of pieces in the skin and their joints are always in play and that translates into different aerodynamics, such as how the player can bend the ball when it is kicked. That means that every few years or so, or maybe even just between different competitions, the players have to adjust to a different ball.

Since FIFA is fine with such adjustments, why not start adjusting other things. Let's make the goal a couple of meters taller in all international competitions (that way guys wide open with the ball in front of the net with a sterling chance to score will have a harder time sailing it clear over the top). Don't worry - the keepers will adjust.



[*] Other things I don't understand include:
  • Why can't the players do a better job of drawing a foul? You can see better acting at a 6th grade school play. Surely there must be some actors who are soccer fans that would be thrilled to help coach that skill
  • Why don't they have retractable/removable flags in the corners? There are no other obstructions anywhere on the field except in the corners. I think we could devise a simple solution.
  • Hooliganism



Previous Years

June 16, 2015 - When does the "chemistry" disappear in a polymerization?

June 16, 2011 - UV Abosrption and Sun Protection Factors

June 16, 2009 - A sign of economic turnaround?


Wednesday, June 15, 2016

Throwing the baby (fish) out with the (ocean) water

Concerns about oceans plastics first focused on just the existence of a trillion pieces of plastic floating around. Now concerns are switching to the impact of the plastic on the ocean environment and the entities living there. A recent report in Science which got a lot of free publicity (since it was in Science after all) found that ocean perch hatchlings prefer microparticles to their regular food, gain less weight and don't respond as well to danger signals, meaning they are more likely to be eaten by predators. And this is all on top of have a reduced hatching rate in the first place.

Rather than studying fish in the natural environment, this was all done in a lab. Ocean water was filtered and put into 1 L bottles that had an aeration system. Plastic particles were added at a low concentration (10,000 particle/m3) and high concentration (80,000 particle/m3). Water without any particles was the control.

I'm amazed that all the results can be attributed to a physical entity - a microplastic particle. After all, a plastic particle is too large to induce much in the way of a (bio)chemical reaction, and even plastic molecules themselves are too large to induce a reaction either. So how does this happen strictly via physics?

It doesn't. There is some chemistry involved, but it is not chemistry with plastic as a starting reagent. Something else such as unreacted monomer, residual catalyst, etc. is the real culprit and that rogue actor was never identified. Since we are now talking chemistry, the universality of the results is called into question.

Surprisingly, the researchers used polystyrene microspheres that they got off the shelf from Polysciences. Why?

Why polystyrene, with a specific gravity of 1.04? In the Supplemental Information (SI), the researchers noted that about 60 - 70% of the particles settled to the bottom. First off, how did they come up with that number? No information is provided. But secondly, is that value the same for both the high concentration tanks and the low concentration tanks? Really? Because as an engineer, I seriously question how a simply designed tank could achieve that same degree of flotation/separation across a multitude of concentrations.

In the main article, the authors infer that the low hatch rates with higher concentration of plastic is due to an unnamed chemical:"
"This suggests that polystyrene particles may be chemically affecting larvae in both average and high concentrations, as exposure potentially reduces hatching rates of fertilized P. fluviatilis eggs."
But then they remark in the SI:
"Thus, fertilized eggs may have been in direct contact with some of the polystyrene microparticles and that is why the authors are unable to say that the reduced hatching success of larvae exposed to microplastic particles are solely due to a chemical effect."
In other words, the reduced hatching results may be due to nothing more than the eggs being buried by the settling particles?

Would the results be different with polyethylene and polypropylene, both of which are far more common in oceans (having been produced in much larger quantities and more often as single-use articles) and both of which have an specific gravity less than one. Flotation would eliminate the burying-the-eggs-alive problem and any leachates from the olefin plastics would be quite different chemically than that of the polystyrene.

And why not run a set of experiments with unfiltered ocean water - a real control (adding more plastic as needed). Then there would be some idea of how well these results mimic reality.

Sorry, but I'm just not impressed much with this report. The authors took a rather complicated system and threw out so much of it that there is likely little chance that the results will ever translate back into the real world. Reducing a complicated system is often a good idea, but you have to take care to not overly reduce it. Unfortunately, that is what happened here.






Previous Years

June 15 - 2015 - Is a Vegan Tesla even Possible?

June 15, 2011 - Sustainability

June 15, 2007 - PVA - Err, is that alcohol or acetate?



Friday, June 10, 2016

Some Friday Fun with the Leidenfrost effect (or maybe something that just looks like it )

Here's a fun video with some Orbeez added to a hot fry pan. I can't find an exact description of what Orbeez are, although they are a water-swellable polymer so they must be crosslinked. However, they are not the usual superabsorbant polymer (SAP) or polyacrylamide. More on that in a minute. First, the video:
As I said above, the chemistry of Orbeez is clearly not that of an SAP or a polyacrylamide. Similar "toys" made from those compounds, such as Waterbalz have been pulled from the market after they caused internal obstructions from children swallowing them. Orbeez have been allowed to continue being sold, largely because research has shown [*] that their swelling in water and gastric fluids is so much less. What I find most interesting is that Orbeez swell to the greatest extent in vodka. Vokda is less polar than water and so the base polymer must be less polar too, or at least have fewer options for hydrogen bonding. This also makes them inherently safer - at least from an ingestion viewpoint - as long as you aren't drinking straights shots of Stolichnaya.

The videomaker states that the activity is a result of the Leidenfrost effect, although strictly speaking, that is highly unlikely since the temperature of the pan's surface was so highly uncontrolled. Film boiling, such as was observed here, is actually a fairly complicated affair. Here's a plot showing all the different boiling regimes that can occur with water in an open pan:
Boiling regimes
(Source - Credit)

The x-axis is the temperature excess between the heated surface and the boiling point of the liquid, and the y-axis is the amount of heat transferred. For people seeing this plot for the first time, it is actually surprising. It is intuitively expected that heat transfer would monotonically increase with excess temperature. While this does occur initially, as the excess temperature is further increased beyond a certain critical value, the heat transferred actually drops. This drop continues to a minimum, which is known as the Leidenfrost point, after which increases in excess temperature lead to increases in heat transfer. This last region of increasing heat transfer is known as the film boiling regime as there is a continuous layer of gas/vapor that keeps the liquid from making direct contact with the heated surface, hence the relatively inefficient heat transfer. (You can see why engineers prefer to use columnar boiling for heat transfer - you can get a good amount of heat transfer without having to excessively heat the surface.)

The Leidenfrost effect and film boiling are visually similar, but as you can see from the curve, the amount of heat transfer can be drastically different (that is a logarithmic y-axis after all). And as I mentioned earlier, the fact that the excess temperature of the pan was so uncontrolled, the bounciness of the Orbeez was likely the result of film boiling and not the Leidenfrost effect.

Overly pedantic? Maybe so, but maybe not. Think about this: plenty of people claim the Leidenfrost effect saves them such as when they immerse their hands in liquid nitrogen or molten lead. The effect (or a low order film-boiling effect in the immediate vicinity) certainly does. There are plenty of videos to prove it. But by such logic, the same could be tried with liquid helium and molten titanium. However, both those situations would put you firmly into the extreme right-hand-side of the boiling curve - the part where the takes off to infinity, never to return.

So be careful with the Leidenfrost effect and what you ascribe to it. It may well be film boiling and you can't tell the difference just by visual inspection. Now that you know how the two phenomenon work and how they differ, you can see that you literally could be playing with fire.



[*] The poster could use a do-over, namely so that all the plots have the same scale on the y-axis, rather than relying on their software to autoscale to the data.


Previous Years

June 10, 2015 - What's in a Name? Marketing Gobbledygook #2

June 10, 2014 - Hillary woos the plastics industry

June 10, 2013 - The Future of Sustainable Polymers: Bio-based Monomers or Polymers?

June 10, 2011 - Have You Considered a Career in Plastics?

June 10, 2011 - The Supreme Court Decides On Freebase Cocaine

June 10, 2010 - Pull Up a Chair

June 10, 2009 - Another Journal Scandal


Wednesday, June 08, 2016

Senator Flake's List and the Importance of Justifying Research

US Senator Jeff Flake recently released a hardcopy of his list of 20 "highly questionable" research projects funded by the US government. Professor David L. Hu of Georgia Tech was associated with 3 of them and wrote a very polite response, "Confessions of a Wasteful Scientist", describing potential benefits of the research and also noting his failures to communicate with the public more clearly about the research and its value. I would highly recommend you read his response.

All of this lead to a number of divergent thoughts:

  1. It's this type of political haymaking by Sen. Flake that is in large part responsible for researchers (and their associated University PR offices) having to overhype any little research result. It's why each week we have a new cure for cancer/heart disease/Alzheimer's (all at the same time for some really revolutionary cases), a new green chemistry that will get us completely off our petroleum based economy and a pill that will help us lose weight/look young forever/give us the hair that we always wanted (but only in the places that we want it). Researchers are having to sell the results of all they do so that they don't appear on some senator's list and the national news.

    While taxpayers certainly have a right to accountability for all government spending, this opportunistic politicking is NOT a responsible inquiry.
  2. Professor Paul Baran of the Scripps Institute recently spoke about increasing the private (corporate) funding of academic research. I see this as "meet the new boss - same as the old boss". The private funding sources, even philanthropies, are going to want to know that their money is being well spent. They certainly aren't going to publicly humiliate you or attempt to leverage your "inane" project to gain a competitive advantage, but they are paying the piper and so they will want to call the tune (or least the band and the album - you can pick the tune). I experienced this first hand back in grad school when my adviser took a small amount of some corporate money."Never again!" he was heard to cry.

    The idea that corporate money will fund basic research is especially laughable, given that corporations such as DuPont have been downsizing their corporate labs and assigning the staff to frontline divisions. (Other corporations are as guilty of this as well - they just are doing it more subtly and not making headlines.)
  3. Something that always seems to be overlooked when criticizing academic research are the side benefits, specifically the training of new researchers. Doing research in graduate school (and as a post doc) is critical to becoming a researcher - a bachelors degree just won't cut it very much. It doesn't matter how "applied" the research is, as long as the research field is deep enough and challenging enough, the end result will be one or more newly trained researchers, who can then go into industry, academia, the public sector...and be comfortable in doing independent research.
  4. This doesn't mean that basic research is dead (despite the comments from Baran highlighted in the article I linked to above). Over $13 billion dollars was spent finding the Higgs boson and the US contributed over half a billion of that. What this really means is that physics (and astrology/cosmology...) have done a far better job of selling their research than chemists ever have (and maybe ever will). When quarks have charm and flavor, the Higgs boson is "the God particle" and the Hubble telescope provides breathtaking pictures of nebulae, the public is captivated. In contrast, we chemists have supramolecular objects, ylides and ToFSIMS - not the same thing at all. Buckyballs were a good start, but ultimately flamed out. Even the personalities associated with physics (Einstein and Hawking) are popularized while our champions (Woodward, Hoffann,...) are completely unknown to the public.

    Much of this is the ability of physicists to work together on "big physics". The Manhattan Project started it all, and it is continuing with the various particle colliders, NASA/ESO, etc. "Big chemistry"? It doesn't exist and no one is proposing any such projects. And if if proposed, who would the field turn to to help sell the project to the public?
We can pine all we want for the good old days when money for basic chemistry research flowed easily and was unquestioned, but they're gone and not coming back. We need to justify our research now and into the future. Professor Hu, who I started this article with, gets it.

Previous Years
June 8, 2011 - It's a Bloody Good Mystery to Me

June 8, 2011 - A New Journal in Polymer Science

June 8, 2010 - Polymer Physics

June 8, 2009 - Memory Foam