Friday, September 30, 2011

The Research behind "The Perfect Polymer"

Following up on the previous post, I did get a chance to read the paper and all I can say is "wow!". I'm going to review the paper first, and then will give some more grief to the PR blurb.

In a nutshell, the paper shows that the researchers looked at low density polyethylene (LDPE) and were able to predict flow behavior - linear, nonlinear and transient (!) - based on reaction conditions. That's plenty impressive. From the reaction conditions, they were able to predict the output material (molecular weight, molecular weight distribution, branching...) and then from that prediction, they were further able to predict the rheology. Again, that is plenty impressive. If you work with LDPE, this should be able to greatly aid in the development of new materials.

There are limitations to this work of course. First, it is limited to LDPE, although LDPE is nothing to laugh at. Given its extensive branching, modeling it is far more challenging than modelling it's linear cousin, high density polyethylene (HDPE), so I would expect similar results for HDPE sometime soon. Second, it is only predictions of the melt properties, not the properties of the final product after the polymer has cooled. Melt flow properties are plenty important, as the LDPE will have to be melted and forced to flow at some point in order to make useful products from it, but ultimately, people buy products based on the properties of the solid LDPE, not the molten LDPE.

Neither of these limitations that I just mentioned are criticisms of the work. It's great work. Papers that find universal truths for all of polymer science are very rare indeed, and nobody expects that.

But let me return to the original PR blurb. I am now even more flabbergasted by it. How they could prepare such a pile of trash is entirely beyond me. The authors never use the phase "the perfect polymer" (they do use the work "perfect" twice, but only in connection with polymer models: "Figure S1 shows an example of a time-dependent correlation map of relaxation time and priority (for LDPE 1). It also indicates the two extreme structures of perfect combs and perfect Cayley trees that constitute bounds for such maps." Emphasis added). Even within the realm of LDPE, they don't claim to have found the perfect LDPE, only that they now feel confident in making the noted predictions about it and short cutting the amount of experimentation. The reason we have so many grades of LDPE (Matweb lists 1176 grades) is that LDPE is used in so many different ways. A perfect LDPE? It doesn't exist. And the fact that the work doesn't make any predictions about the solid state properties means that experimentation is still needed.

I guess that means that, just like in the case of "The Ultimate Adhesive", we haven't reached the end of the road yet in polymer research. Our jobs are secure for a least another week (until next week's issue comes out). "Back to the lab, people!"

ResearchBlogging.orgRead, D., Auhl, D., Das, C., den Doelder, J., Kapnistos, M., Vittorias, I., & McLeish, T. (2011). Linking Models of Polymerization and Dynamics to Predict Branched Polymer Structure and Flow Science, 333 (6051), 1871-1874 DOI: 10.1126/science.1207060

Now that we have the "Perfect Plastic", you don't need me

I have read way too many PR blurbs that have categorically overhyped research discoveries, but this one is the ultimate. Truly, the ultimate as you can not ever hope to succeed it:

"Scientists and engineers create the ‘perfect plastic’ "

I am not joking about this. That is the actual title of the press release. And the idea is repeated in the second paragraph:"The breakthrough will allow experts to create the 'perfect plastic' with specific uses and properties by using a high-tech 'recipe book'. "

I really can't believe that a good university like Leeds let this out. We don't have "perfect metals", "perfect ceramics" or "perfect anything". All plastics have their strengths and weaknesses and there is not a perfect plastic that can act as an adhesive and a high temperature aerospace material and a low temperature sealant and a structural material and be biodegradable in a landfill (but only once it knows that it is in the landfill) and costs next to nothing to buy and can be processed using an E-Z bake oven and...After all, that would be the perfect plastic in my mind and the mind of many others.

Sadly, I've run into this type of mindless naming before. A person earlier in my life came up with a good adhesive with some new properties and he proceeded to name it "the Ultimate Adhesive". Everyone's response was, "well let's close up shop boys, we've got the ultimate adhesive now. There's no need to work any further in this area." Sure enough, they quickly found a new name for the adhesive that wasn't quite so egotistical.

The Perfect Plastic. Hah!

  • I discuss the actual research (it's actually pretty good) in this post.
  • While many sites ran with the "Perfect Plastic" headline, the Royal Society of Chemistry blog, Chemistry World didn't, and instead entitled it "Solving a tangled polymer problem", which is quite appropriate.

Thursday, September 29, 2011

Cool video of the day

If you have 2 minutes to spare in watching a video, check out the moving sculpture video over at the Plastics News blog. If you have 2 minutes to spare in watching a video, check out this moving sculpture video, brought to my attention by the Plastics News blog. I'm pretty much speechless to see how creative someone can be with PVC tubing.

(Updates 9/29/2014: I found a more permanent link to the video and changed the wording to reflect this. The original is still there but struck-out.)

Presenting Rheology Data

I posted a new page today that provides a very brief overview of dynamic mechanical analysis and time-temperature superposition. You can read it here if you are unfamiliar with rheology testing or want a review.

One of the most difficult aspects of rheology is that the data, particularly that generated by dynamic mechanical analysis, can be plotted in so manner different, but more or less equivalent manners.

As you saw from Monday's post, I prefer working the storage and loss moduli (G' and G" respectively) vs. frequency, although I most often supply clients with viscosity vs. frequency since that is a simpler concept to explain. Other rheologists have a built-in bias towards working with compliances, J' and J", while others are hung up on tan δ. The strangest set of plots I ever saw was from a guy who always plotted G* vs. tan delta. The information is always the same, it's just that sometimes you have to work a little bit more to figure it out.

Part of the reason I like G' and G" is that the generic shape of these curves is well established. If something is varying from it, I can immediately pick up on it to probe for further details. If you are working with tan δ, you only have the ratio of G"/G', and the only universally significant measure then is whether it is greater than, less than or equal to 1. You have a similar issue with G*, where it can hide many details that are otherwise noticeable.

In some ways, all these different plots are fun - you need to be on your toes in order to run the mental manipulations in your head to translate the data back to your preferred reference frame. I imagine that it really would be best to work within the other frameworks much like it is best to be thinking in a foreign language that you are speaking, rather than translating it all into your native tongue, preparing your response and then translating it back into the foreign language. I'm just not sure that this would happen anywhere in the rheology world as a given lab will have a given preferred format. It's only when you start working with others labs or researchers that you might start running into this issue, but those conversations don't happen all that often - you're much more likely to talk with fellow labmates than with people in other labs.

Wednesday, September 28, 2011

Hidden Problems in Heat Transfer

I get a pretty large number of trade magazine, but one that I am always excited to see is "Electronics Cooling". As you would expect, the magazine is largely oriented towards heat transfer in electronics applications, a problem that I am rarely concerned with, but there is at least one article per issue that addresses heat transfer in general, and often in very enlightening ways. This month is a terrific example with the article "Does Your Correlation Have an Imposed Slope?".

This article (combined with the editorial at the front of the issue really take engineers to task for relying excessively on those darling dimensionless numbers. For those not familiar with dimensionless numbers, these are grouping of variables that are dimensionless. The most commonly used one is the Reynolds number which is ρVL/μ, where ρ is the density of the fluid, V is the velocity of the fluid, L is an appropriate length from the test setup and μ is the viscosity of the fluid. When running fluid mechanics test, you don't need to explore the impact of all these variables over their full ranges, you only need to explore the Reynolds number of its full range and you're covered for all situations. Quite a time saver, eh? You can see why engineers love them so much.

The dimensionless numbers in heat transfer are numerous and I won't get into any of them today. Their large number would be expected since there are 4 modes of heat transfer (conduction, forced convection, natural convection and radiation). As the article points out, the numbers by themselves are not a problem. The issue arises when multiple dimensionless numbers are used in heat transfer correlations, and when the same parameters are used in multiple numbers. One example given is when the Nusselt number, Nu, is correlated to the Rayleigh number, Ra, as
Nu = C Ran
Looking at the parameters that make up these numbers, you find:
q L/(ΔT k) = C [g ΒρcpΔT L3 / k ν ]n
where ΔT (temperature difference), L (length) and k (thermal conductivity) are on both sides of the equation. This then leads to situations were random numbers can show correlations and the article gives a specific example of this.

Correlating dimensionless numbers with each other leads in other situations to an increase in the errors associated with the correlations, something that I remember well from my undergraduate days. I dug out my old heat transfer book and sure enough, I see correlations with 2, 3 or even 4 dimensionless numbers in the same equation. I am quite sure that my professor never warned us of these issues, despite their existence first being described back in 1963!

"Electronics Cooling" is free - you can get a subscription at the bottom of the first page I linked to above. If you work with heat transfer (and unless you work exclusively all day long with room temperature equipment and chemicals, you do work with heat transfer), do yourself a favor and get a subscription.

Tuesday, September 27, 2011

Plastic Rims for Cars

A plastic wheel rim, made from BASF's Ultramid (nylon) with long glass fiber reinforcement:
While the engineers in the video make some backhanded references to the mass of the rims, the point that is missed is that the moment of inertia for these wheels versus metal is much lower, so that the car will accelerate faster. Let me explain with an example.

Back when I used to race bicycles, I and the people I trained with would have two sets of wheels for our bikes: a standard set that used clincher tires and another set that used sewups. You are most likely familiar with the former - the tire had a wire edge that you had to pry off with tire levels (let's be honest.. we all used screwdrivers didn't we?) in order to access the tube. Sewups tires are a completely different beast. The tire encloses the tube entirely and is sewn shut, hence the name. The really freaky part is that the tire is then glued into a small u-shaped depression on the rim.
The sewup tire and rim is much lighter than the clincher tire and rim combination, I can't recall the exact weight difference, but back in the late 80's, it probably was about 100 g difference in weight between the two. The absolute difference of 100 g is not much, given that my bike was about 8 kg, and I was about 77 kg, but all that mass loss was at the rims so that the moment of inertia difference was big. Come race day, we would switch out the clunky clinchers for the lightweight sewups. Oh what a difference! It was so much easier to accelerate, a key factor in a bicycle race. With clinchers, it always felt like we were "wearing a showercap". We used them for training as fixing a flat was much easier than cutting open the sewup, fixing the flat, sewing the tire back together and then finally gluing it back on the rim.

Back to the car rims, the new Ultramid rims are only a 12 kg weight reduction, but for the rotational weight in a car, it is huge. 100 g in a 85 kg bike + rider combination is 0.11%, and that was a very real difference in performance. 12 kg is 0.11% of 10,200 kg, far more than any car weighs, so the ratio of mass lost is even greater far a car than it was for the bike scenario I mentioned above.i.,e if the car weighs 1000 kg, then the mass reduction is 1.2%, a much greater improvement than in the bicycle example. Even though the mass difference isn't entirely located in the outer portion of the wheel, the difference in rotational inertia should still be quite noticeable. It would expect these rims to accelerate quite a bit faster, and that's big for improving the mileage of any car in stop-and-go traffic, gas electric or hybrid. Drag racing anyone?

Monday, September 26, 2011

PET Rheology

Some serious rheology discussions today on dynamic mechanical analysis (DMA) in oscillatory shear, and to some degree, this will followup on some of the issues about the multiple requirements placed on a water bottle that I discussed a few weeks ago. Be forewarned. I ran these 'quick and dirty". PET picks up water, so measuring PET rheology is best performed on samples that are either dried or exposed to a known amount of moisture depending on what your needs are. I did neither - the PET came from recently used Fiji water bottles and a Gatorade bottle. Given this, I would assume that the bottles were at a constant and equal loading of water (although certainly not uniform throughout the walls of the bottle [1]), but I have no data to support this assumption. Both bottles had the "1" recycling code, so I took that as truth that the bottles were PET and without significant additives such as plasticizers. (Don't worry, if a customer was paying for this work, I wouldn't be working with these assumptions.)

In a nutshell, I ran temperature and frequency sweeps on the samples, then used time-temperature superposition (TTS) to generate the master curve for 280 oC (only a very small portion of it as you will see). The samples were from 2 different sizes of Fiji water (500 ml and 1 l) and also a 593 ml Gatorade bottle (G2, orange flavor if you want all the bloody details). The storage and loss moduli are shown below for the Gatorade bottle - the results for the Fiji water bottle were qualitatively similar.
Clearly this is the terminal zone. The loss modulus, G" ("liquid" component) dominates the storage modulus, G' ("solid" component). The other region of the modulus curve where there is a similar slope is the transition to glass, but there G' > G". The slope of G" is 1 which is also a good match to theory. You can also see that at the very low frequencies, the data is a little noisy.

The next plot is a little more interesting as it shows comparisons between the viscosity of the three bottles.
I went with viscosity curves for the comparison since there would only be three of them, rather than the 6 curves needed if I kept going with the G' and G" curves. The Fiji water bottles are pretty much the same, but the Gatorade bottle is much more viscous. The flatness of the curves also is what would be expected for terminal zone behavior and gives us the zero shear viscosity, although the Gatorade bottle is just beginning to show small signs of shear thinning.

I'm not surprised with these differences, as if you've touched both a Fiji water bottle and a Gatorade bottle, you know that the former has a softer feel and look to it than the Gatorade bottle does. PET is a funky polymer as it is semicrystalline, but the crystallization usually occurs as a result of orientation in the processing, and not just from temperature alone. That gives you two levers to play with in forming the bottle and creating a certain "look" with it. These characteristics are also something that the manufacturer is looking for and are additional requirements beyond the basic functionality of the bottle itself.

[1] Uniform amounts of water throughout the bottle's walls would mean that there is no concentration gradient in the bottle, meaning that there is no diffusion through the bottle and that is certainly not the case with PET.

[2] If you are not familiar with DMA, and TTS, you can get some the needed background at this site. Don't look at < a href="">the Wikipedia article - it's like most of their mathematics articles - great for a review but horrible for learning from. I've still yet to find a great site on the web for this stuff. Why can't someone explain what G' and G" are on the same page as TTS? The concepts flow (pun intended) togehter quite nicely.

Friday, September 23, 2011

Completely Off Topic Post for a Friday

I've never cared for basketball much. To me it is simply: "go up the court and shoot a basket, go down the court and shoot a basket, go up the court and shoot a basket...". Any game where each team scores 40, 50 or 60 times a game is too much [*]. And the fact that it is intelligent play to intentionally foul the other player at the end of the game puts me over the top. If it is "smart" to break the rules, then something is seriously wrong and needs to be changed. But now I have an extra argument against basketball - it's all statistical. Researchers have found that scoring in a game can be modeled as a random walk. Two thoughts on that: Yea! it's a random walk, so I can reach and say that this is in some weak way ties into polymer and rheology (since polymer configurations are modeled with random walks) and two, this is exactly what I would expect when you score 40, 50 or 60 times a game (wait, I already said that). From the conclusions:
"Thus seen through the lens of the theoretical physicist, basketball is merely a random walk (albeit in continuous time and with some additional subtleties) so that all of the observable consequences of the game that are of interest to the quantitative scientist follow from this random-walk description."
The botom line: If I'm going to look at a random walk, then I'm going to look at some polymer modeling research instead.

[*] Soccer (football to non-US based readers) [**] is quite the opposite - not enough scoring. What I really like is lacrosse - about 10 scores a game for a team, fast paced and a wide open field. Basically it's a mix of hockey and soccer, but the result has an unexpected synergy.

[**] Since Brits seem to get so upset with Americans calling the game "soccer", could one of them explain to my why the British journal publisher Taylor & Francis publishes a journal entitled "Soccer and Society"? Please?

Thursday, September 22, 2011

Another Source of Ocean Plastics - Your Clothing

Today's post, like yesterday's is also about ocean plastics, but it's about research (open access!) that identifies a disturbing new source of ocean plastic - your laundry. The researchers took samples from 18 beaches around the world and also looked at effluent from washing machines and waste-water treatment plants and found small bits of polyester and acrylic fibers everywhere.

I said this was disturbing, as this is a tough one to avoid. We can all do a better job of making sure that large pieces of waste are properly disposed of and not let loose in the environment, and personally living near the North American Pole of Inaccessibility some 1300 miles from the nearest ocean means that even if I threw all my trash out the window, exceedingly little of it would ever reach the ocean, but how can we prevent microfibers from being washed away from our clothing?

I'm not sure that clothing can be suitably modified to solve the problem. It is well known that washing machines abuse and abrade clothing, a large part of the reason that clothes age over time. I also don't think that washing machines can be suitably changed to eliminate this issue either, although I would love to be proven wrong. Changing the wastewater treatment processes might be the best shot, and certainly from a technological view, it can be done with fine enough filters. The economics of that option however are unknown to me, and the same goes for the use of new flocculants or other clarifying aids.

The open question that needs to be answered as well is does this matter negatively impact the oceans to a significant degree?

I also see that the Plastic News blog is discussing this today, with a tongue-in-cheek question about addressing the situation. Check it out.

Wednesday, September 21, 2011

A Method for Green Washing

Method Products launched a press release on the 15th headlined by "Method Unveils Breakthrough Bottle Made of Ocean Plastic"(emphasis added), and by "Ocean Plastic", they state "a bottle made out of plastic collected from the North Pacific Gyre".

The only problem is that the North Pacific Gyre, the worst of the Gyres, has a plastic density of 5.1 kg/km2 according to research cited in Wikipedia. Assuming that an empty bottle weighs 100 g (about 4 oz.), then a boat would have to trawl an entire square kilometer and collect every single piece of plastic in it in order to make 51 bottles [*]. Further, keep in mind that collecting these plastics pieces requires a very fine net and a slow moving boat.

So did Method Products and their partner Envision Plastics actually use a boat, all the while generating CO2 to collect all this plastic? No, of course not. Instead, they
"... tapped into a network of beach cleanup organizations, particularly in Hawaii. Hawaii is of the most remote land masses on the planet, and happens to sit at the southern edge of the Gyre. Because of the ocean winds and currents in the region, much of the plastic from the Gyre ends up washing up on the beaches of Hawaii."
In other words, they collected plastic on the beach, called it "Ocean Plastic from the Great Pacific Gyre" and used that instead. How is this a "breakthrough"? How is it that no one seems to be calling them out on it? Sure, it is great that the plastic is being collected and recycled, (plastic that has no business being in the ocean in the first place), but to hype it as Ocean Plastic? That's where I have to draw the line. There are plenty of people working quite hard to actually provide true "green" products (yours truly included) and to see this junk get a free pass is quite maddening.

That Method Products makes a very large line of cleaning products adds further irony to calling this PR "greenwashing".

[*] Another estimate of the plastic in the Gyre is 8 m2 per km2. Any way you look at it, it s a very small volume, but people seem to imagine it looking like this:
If it actually did look like that, the economics would be entirely different, although I certainly would prefer that the economics stink rather than having a problem truly that awful.

Tuesday, September 20, 2011

Controlling Molecular Weight and Branching

Plastics News had a recent "Ask the Extrusion Expert" webinar with Allan Griff as the expert. Most of his answers were quite fine, especially given the constraints of trying to answer in a small space questions that have many conditions and caveats. But one of his answers really needs to be commented on. The question was:"How are polymer lengths and branching controlled?" and the answer Allan gave was:
"The answers seem simple - time, temperature, pressure, co-monomers and catalysts/other active chemicals - but their application can be quite complicated. Regarding length, the longer the mass is at reaction conditions, the more of it will react, but there is a diminishing-returns principle acting when the mass is, say, 95% polymerized, and the remaining 5% of monomer is looking for a loose end to hook up with. Some polymerization, notably PVC, can be done in water suspension, which enables more free movement of monomer and short chains looking for others, but requires a draining and drying step at the end of the line.

The role of co-monomers is shown with linear-low-density PE. To get short branches, a small amount of another monomer with a double bond such as butene (4 carbons instead of the two of ethylene) is included. The butene goes into the chain with its 2-carbon double bond just like ethylene, but that leaves 2 carbons in a short chain (the branch) dangling from the main chain. Similarly, hexene (6 carbons) makes 4-carbon branches and octene (8 carbons) makes 6-carbon branches.

There are many more complications but this addresses the basics of your question."
While the question is only marginally answered (the answer doesn't really describe how to control molecular weight, and controlling branching is given in only in the context of olefin copolymerization), even within the answer itself, there are sections that I take issue with, and these were highlighted in bold.

First, to more properly answer the question: Molecular weight can be controlled by the adjusting the amount of initiator (more initiator leads to more chains with smaller molecular weight), addition of chain-transfer reagents (more of it will stop the chains short), and adjustment of reaction conditions such as time, temperature. Branching can controlled by the addition of polyfunctional monomers, appropriate catalysts, reactor design or as Allan suggested, by use of select comonomers. And also as Allan noted, "There are many more complications..."

But turning now to the answer Allan provided and the sections I bolded, the idea that the remaining monomer needs to find the growing end of the chain is correct, but this model is oriented pretty much exclusively towards free-radical (addition) reactions, and not condensation reactions. In the latter reaction such as between a diacid and a diamine to form a polyamide, the monomers disappears very quickly - one of the comonomer merely needs to find one of the other comonomer to react with and boom, they're gone. The situation of having 95% polymerized material and 5% monomer speaks to a free-radical reaction where only a certain number of monomers were initiated and the chains grow only from them. Certainly a larger volume of commercial polymers are prepared by a free-radical reaction (all the olefins and PVC for starters), but without condensation reactions, there would be no nylons, polyesters, polyurethanes and others - a group of polymers too large to ignore, even in this small space for answering.

Regarding water suspension polymerization, the water does not "enable more free movement of monomer", at least to the extent of aiding the kinetics of polymerization. The reaction kinetics of suspension polymerization are well documented as being equivalent to bulk polymerization and thus limited in the manner previously noted. The water does allow for freer movement within the reactor, but once the monomer has moved within the suspension particle, the water is absent and the diffusion of the monomer to the reactive end is again the limiting issue.

I'm not sure that clarifying any of this will help an engineer with extruding a plastic, but it certainly doesn't hurt to know (and and to know it correctly).

There is Lots of Money to be had in the Plastics Industry

I am very surprised that that one scene from the beginning of the movie "The Graduate" is still being kept alive, the one where Mr. McGuire tells Benjamin "Plastics", advice to help him make lots of money, but while the movie is now irrelevant [*], the advice might have more longevity than we think. Plastics News came out with their annual list of top-paid executives in the plastics industry, and while some of these people aren't quite as wealthy as yesterday's executive, Zhang Yin, the income of a few of the executives was eyepopping. How about the $58 million in compensation for Frank Stronach, the Chairman of Magna International, the Canadian auto parts manufacturer? Or the $20 million for Belinda Stronach (Frank's daughter), also of Magna International? Or the $16 million to Donald Walker, CEO of Magna International. Or the $15 million to Siegfried Wolf, of ... you guessed it...Magna International? That's a total of $109 million! Yes, there is lots of money to be had in the plastics industry, at least if you are in or near the corner office. Polymer scientists and engineers such as myself only make far less than 1 percent of that.

The next person on the list is the first person to break the Magna International logjam, and that is Mark Ketchum of New Rubbermaid ($9.3 million), but than we go right back to Magna International management again with Vincent Galifi ($8.9 million). One last Magna International executive is on the list at the #10 spot, Jeffrey Palmer ($6.9 million). While their certainly is plenty of doom-and-gloom to go around in the plastics industry, some small corners are doing quite fine by nearly anyone's outlook.

[*] Afterall, the movie came out 44 years ago in 1967, and it's not like everyone has seen it. It may have been an important movie back then, but it's time has come and gone. Think I'm wrong? Ask some Gen-X or Gen-Y person any question about the movie's storyline, such as "Who was Mrs. Robinson?" or "How does the movie end?", yet they all will know the line "Plastics".

Monday, September 19, 2011

Recycling Paper Around the World - Literally!

On Friday, one of our colleagues gave a "Brown Bag Seminar" (i.e., he talked at noon while the rest of us at lunch - a very informal setting as you can imagine) on recycling markets, something he was pretty familiar with from prior experience. I'm not going to go into a lot of the details, but one slide really caught our eye. It was a picture of Ms. Zhang Yin and and the question "Who is this women and what does she have in common with Oprah and J.K. Rowlings?"
The snide response was that she was filthy rich, and it turned out to be totally correct. In fact, she is richer than Oprah and Ms. Rowlings, and is regarded as the richest-self made woman in the world. She is the largest shareholder of Nine Dragons Paper Holding Company, a company that - in part - imports paper waste from the US and then makes cardboard with it for shipping products back to the US. We were all taken aback by the expense of shipping paper waste across the ocean, but then realized that it probably makes sense. The boats are empty from what the US imports and doesn't export, so putting pretty much anything in the empty containers is economical. It adds a second layer to the meaning of "recycling" as the paper cycles the globe.

Thursday, September 15, 2011

Follow Up on Yesterday's Post

Curiously, there were a couple of post yesterday on other blogs that relate closely to what I mentioned yesterday.

First, Don Loepp at the Plastics News blog discusses (and thereby amplifies my point) that passing resin increases on is not easily done.

Second, the "In the Hopper", SPI blog has a video about how PET bottles are reused in the rural areas of the Philippines and Brazil as an affordable skylight.

Lastly, here is my personal opinion about single-use plastics, be it shopping bags, water bottles,... Use your head. When you are done with the plastic bag/bottle/container, THROW IT IN THE TRASH, where it belongs, or in a recycling bin or keep it and resuse it... but dispose of it properly. Plastic in the environment is there because people put it there (directly or indirectly). Oil in the Gulf of Mexico? Sorry, but some of that is naturally there. Plastic in the Gulf of Mexico? There is nothing natural about it at all. If all the plastic were disposed of properly, I'd be blogging about something else and all these silly bans on plastic bags wouldn't be occurring.

Wednesday, September 14, 2011

Here's What Single-Use Plastic Really Does

While there certainly are people who seem to think that ALL plastic is bad, others are coming to the realization that it is really "single use" plastic that is the problem - plastic that is used to hold drinking water, for instance, or juices, yogurt,...The overwhelming perception is that the container's only purpose is to hold the food/drink item until the item is consumed, and then the plastic is thrown away.

As a product developer, I can tell you that life is not that simple. No manager or client company has ever approached me or any other product developer and said " I need something to put the food and drink in. That's it, nothing else matters." Such a situation is so far removed from reality that you can't even call it a pipe-dream.

While it is true that as far as the consumer is concerned, once the product is consumed, the container is waste, that is only looking at the last step in a long chain of events. The truth is that even a single-use disposable plastic item has to perform a wide range of tasks long before the consumer even sees it.

Let's consider just consider the object of scorn de jour, the PET water bottle. Here's what I think the requirements are and why the requirements exist:
  • It needs to seal the water in and all other contaminants out. That's pretty obvious, that's on the top of everyone's list, but for some people, they think the list stops there. It doesn't.
  • It needs to be made from materials that will not leach unsafe levels of chemicals into the water, or react with the water. The FDA monitors this, but some people are still not happy with the results.
  • It needs to not have any structural failure:
    • during shipment from the bottles' manufacturer (who is often someone different than the company filling the bottle) to the filling plant
    • while it is in the filling equipment
    • while the bottle is put into
      • the secondary packaging (often shrinkwrap)
      • into the tertiary packaging (a cardboard box)
      • additional packaging (such as to secure it to a pallet)
    • or during shipment via (multiple) trucks or boats
    • while on the shelf or rack, particularly when multiple layers of filled bottles are stacked on top of it
    • during the "normal" lifespan that the consumer has it
    Keep in mind that during shipment and in the hands of the consumer, the bottle can see temperature extremes from below freezing temperatures to 140 oF or more, as well as UV light which can degrade polymers. If there is structural failure, the water will leak from the bottle, requiring that at the very least, that bottle be thrown away or recycled. Keep in mind that that bottle's contents are then also wasted. Depending on the extent and location of the leaker, the cardboard packaging may be weakened so that handling the other bottles or even the pallet with a forklift may be a problem, and therefore many more bottles may end up being trashed.
  • The bottle needs to cost as little as possible. While you may think that this is so that the company can pocket the difference, that is not the case. With companies like Wal-Mart and others constantly asking for price concessions so that they can have a steady stream of markdowns, consumers are the only ones who can really pocket the difference. Similarly, when the price of petroleum increases, the price of the plastic increases as well, but passing such increases along is very difficult, leaving the manufacturer to pay the higher price.
  • The water can only diffuse very slowly through the bottle's walls. Once too much water has evaporated, the bottle no longer holds the volume stated on the label, say 500 ml. Now it's mislabeled, and cannot be sold, so into the wastestream it goes.
Those are the strictly technical requirements that are off the top of my head. There are still more semi-technical requirements that are related to the labeling, branding and selling - the label needs to adhere to the bottle, the bottle needs to be clear and free of visual defects, it may need to have a certain shape (for branding),.... While many consumers will shout "I don't care about that", research on consumer behavior proves otherwise, and so there are additional requirements that the bottle needs to meet.

If some of these requirements didn't exist, the bottles could be made of less durable materials or construction and the job of a product developer would be much easier, but that is not the reality of the situation. Beyond the PET bottle, a long of list of requirements exists for any product made of plastic [*], with most of these requirements completely overlooked by consumers who often only see the end result of the effort of making the bottle, filling it, and delivering it to the store. To look only at the act of buying/consuming/seeing waste and complain is to fail to see the larger issues involved.

[*] or metal, wood, fabric...

Tuesday, September 13, 2011

My Favorite Reaction

Chemical and Engineering News is hosting a Blog Carnival - a gathering of blog postings around a common theme, which in this case is "My Favorite Reaction". In my mind, you can't have a Carnival without a lion (or a lion tamer),

and so using my best barker's voice I invite you "to step right up and prepare to see the Greatest Show on Earth..."

In most cases, free-radical polymerization can be compared to a hungry lion on the Serengeti, randomly grabbing wildebeests and zebra as they scurry by. First a wildebeest, then a zebra, then maybe two or four wildebeests, then back to a zebra again, all in no particular order until the last of the herd is gone. This is what occurs in free-radical polymerization when more than one monomer is present - the result is a statistical distribution of the different comonomers. Enter the lion tamer, who is able to control the lion's appetite so it carefully alternates back and forth between the wildebeests and the zebras. The lion tamer goes by the name "thiol-ene polymerization". In this reaction, the growing chain clearly and forcibly alternates back and forth between the two monomers present, the thiol and the ene of whatever sort they may be, resulting in a perfectly formed alternating copolymer --ABABABABA--. The two main reaction steps are:

Were the formation of an alternating copolymer the only advantage of thiol-ene polymers, the lion would have been tamed, but left as a small amusement in the Carnival's sideshow and this post would never have been written. In fact the advantages of thiol-ene chemistry extend far beyond the regularity of the polymerization. Besides being a solvent-free/water-free reaction, thiol-ene systems can react fast, shockingly fast. I've developed floor coatings that under UV light have converted monomers into a hard coating, suitable for walking on, in one-tenth of a second using just a lamp plugged into a 120 VAC outlet, not a souped-up unit drawing enough electricity to power half of Tokyo.

But even better yet is that these systems do not suffer from the oxygen inhibition that commonly occurs in UV cured-acrylates. The hydrogen of the thiol group is labile enough that when oxygen adds to the chain to form peroxy radicals, the radicals are still able to abstract that hydrogen, thereby creating a new thiyl radical allowing the polymerization to continue. Acrylate polymerization comes to a standstill. In summary, you have:
  • Control of stereoregularity
  • Solvent-free reactions
  • Water-free reactions
  • Extremely fast reactions, and
  • No O2 inhibition
It is quite a set of benefits to have in a single reaction.

Monday, September 12, 2011

A Review's Dilemma

In an editorial published in Nature a few weeks back, Nai-Xing Wang of the Chinese Academy of Sciences argues against the Chinese obsession with publishing their research in journals with high impact factors. In a nutshell, the impact factor of the journal is used by the Chinese government to rate the quality of the research. Wang discusses this at length and makes many good arguments which I will not discuss here (read the editorial, it's worth the time).

I've been aware of this situation for some time, but it has always made me feel uncomfortable for an additional reason - I'm a reviewer for a number of journals published by the Royal Society of Chemistry and am increasingly reviewing more and more papers by Chinese authors. Certainly if the research is of poor quality and should not be published without rework/more data/..., I have no problem in stating so and recommending rejection. But many of the papers are more or less acceptable, but maybe should be published elsewhere, in a journal with a lower impact factor. How do I decide that, or even more importantly, should I be deciding that? A large part of me thinks that my job as a reviewer is to pore over the research and decide if it should be published, but that the publisher and their editors should be the ones deciding if it is appropriate for their journal. The editors all have technical backgrounds so the decision should not be that hard to make.

It could be argued that the reviewers are likely the readers of that same journal and could provide valuable input as to what they want to read in it. I find that argument weak. There are very few journals that I have subscriptions to - I spend most of my time scanning tables of contents from a large number of journals and seldom concern myself with the specific journal that a research article is published in. I will value an article from "Polymer" as much as one from "Soft Chemistry" or "Journal of Applied Polymer Science" or "Macromolecules" - the idea that there is a particularly brand or brand quality is lost to me [1], so I don't feel that I should be in the position of making this judgment for a journal, and now knowing that this decision could have a big impact on the career of the researchers does not help at all.

I'm sure China will eventually change it's ways (seriously, deciding a research article is more valuable because it is published in a journal where the mean impact of previously published articles was high is akin to valuing a single company's stock based on how well the Dow Jones did over the last 2 years!), but that doesn't make my job any easier in the present.

[1] Now if the article is published in the "Major Asia Minor Journal of Polymers, [2] I might not be quite as interested, or at least I would be initially more skeptical of the data, results and conclusions.

[2] I've have nothing against researchers from Asia Minor or it's present day descendants - the name Asia Minor has always hit me as funny ever since I was a child.

Thursday, September 08, 2011

Deuterated Gels

There's a new report (I only have access to the abstract, and you will too unless you have a subscription or pay to view the article) that really has a curious result. Let me cite the abstract:
"The isotopic effect of exchanging deuterium with hydrogen on the mechanical and surface properties of agar gel is examined. The elastic modulus of the D2O gels obtained by AFM nanoindentation is significantly higher (factor of ≈1.5–2) than the modulus found in H2O agar gels. Furthermore, the modulus is independent of loading rate. Surface imaging reveals that the surface roughness gets progressively smaller with increasing agar concentration. All these data suggest that the isotopic replacement of deuterium enhances the mechanical properties of the agar gel, with significant advantages in its use as a biphasic scaffold"
I think it's a poorly written abstract, as on the one hand they refer to the deuterium from the heavy water exchanging for the hydrogens in the agar [1], but then they refer again to D2O gels as well. They don't seem to be isolating the results of the exchange reaction from the heavy water itself.

Maybe this dichotomy is addressed in the paper itself (it likely is), but I still am full of wonder as to why a deuteration of the water and/or the gel would alter the mechanical properties by a factor of 1.5 or 2. Deuteration and other isotopic changes are known to alter reaction kinetics [2], but to alter equilibrium interactions is a new one, at least for me, and I am having a hard time justifying the results in my mind. Anyone?

[1] A deuterium-hydrogen exchange is probably the only way to efficiently produced deuterated agar, although the thought of growing the red algae in a pool of heavy water is an intriguing one.

[2] It is known that heavy water is toxic to animals for just this reason.

Wednesday, September 07, 2011

Coffee Ring Formation and Rheology

I wasn't able to comment much last week about the recent discovery that had quite--a bit--of buzz (pun intended) on coffee ring formation (subscription required), but I think my perspective might make it worth the wait, as just like yesterday's discussion of a topic far removed from polymers (aspirin), it will definitely be related to polymers and rheology. As any of the links above will tell you, coffee ring formation has been a puzzle for a time - the question being why does the stain form as a ring at the outer perimeter and not as a uniform stain under the entire cup? The answer involves quite a bit of transport phenomena of the three most common types - mass, momentum and heat transfer, with evaporation being greatest at the staining location, encouraging the particles in the coffee to deposit their. While this has been known for some time, the researchers here found a new key variable - that particle shape has tremendous impact on ring formation, and that elongated particles do not form a ring pattern, but rather form a uniform staining pattern. The picture below from the article shows the particle shape above the corresponding stain pattern.

The capillary forces between the different particle shape is different and that difference is enough to totally change the outcome of the drying pattern. The authors suggest in the article that surface roughness may induce strong capillary effects and these results could be relevant to ink jet printing, which I can certainly see as being an issue (a more uniformly drying drop would result in a better image), but getting back to the idea of surface roughness had me thinking another thought: painting, as in painting the walls of your house.

If you ever undertake repainting the walls of your house, you'll find that flat (matte) paints are much easier to work with. As you move from section to section, you don't need to be overly concerned about keeping the edge of the paint wet - my wife and I have stopped for long periods of time in the middle of a wall and started right up again without any issues and trust me, she is plenty picky about these issues. In the same vein, touching up the paint, even months or years later is easy. But as you go to increasingly glossier finishes (eggshell to satin to gloss), these issues become much larger - we've tried glossy paint once and will never do it again, despite the fantastic scrubability. You could easily see how each section of the wall was divided up as we move along, and I suspect that it is probably for a reason related to this research - the particles in the glossy paint favor a ring formation type mechanism is seen in coffee.

So my question is this: Could the use of modified particle shapes in paint be useful in creating glossier paints that won't show how the wall was sectioned off? The challenge of course, will be changing particle shapes without monkeying with the other rheological aspects of the paint.
Yunker, P., Still, T., Lohr, M., & Yodh, A. (2011). Suppression of the coffee-ring effect by shape-dependent capillary interactions Nature, 476 (7360), 308-311 DOI: 10.1038/nature10344

Tuesday, September 06, 2011

Polymorph Determination through Nanoindentation

Some chemicals are capable of crystallizing in more than one geometry. These forms are called polymorphs, and are usually designated with Greek letters to indicate the order of discovery. Not surprisingly, the alpha form is usually the most stable, followed by the beta,... Polymorphs do occur in some semicrystalline polymers, something that is not as widely known in the polymer community as it should be, although being able to select for a particular polymorph can be difficult. Polypropylene is probably the best example (at least it is the largest volume polymer exhibiting polymorphism) - the beta form can be prepared simply with select nucleating agents such as dibenzylidene sorbitol. Polyvinylidene fluoride and polylactic acid are two other polymorphic polymers that I can name off the top of my head.

As with all crystalline structures, determining the geometry of the unit cell requires x-ray diffraction, although the various polymorphs usually show differing physical properties as well - melting temperatures, and in the case of polymers, differing mechanical properties.

So given this background, you might be able to quickly see that a research paper (open access) examining polymorphs in a small, nonpolymeric molecule, aspirin, with a nanoindentor could be easily adaptable to polymers, but only if you knew that polymers can also be polymorphic. In the study, the nanoindentation was performed on single crystals of the aspirin and even more specifically, on previously identified faces. As expected, the different crystals showed different mechanical properties.

Applying this test directly to polymers would be more challenging for two reasons. First, unless extreme steps are taken, any polymer will be polymorphic even when processed so as to produce a dominance of any one crystalline form. Second, unless extreme steps are again taken, the orientation of the crystals in the polymer will be oriented in numerous directions so that accessing a single face repeatedly would be quite a challenge.

Nonetheless, this work raises in my mind the idea that this approach certainly could be used to study the surface of a polymorphic polymer. After looking at different samples of pure isomorphs at different angles, you could then map the entirety of the surface to see if and where one particular crystal dominates.

As I do not have access to a nanoindentor, this is beyond my capabilities, but is anyone else up for the challenge?

Thursday, September 01, 2011

My Version of the Triple Witching Hour

Despite there being plenty of fun things that I could be blogging about, I'm in the home stretch today of filing 2 patents and an SBIR grant proposal. Worse yet, they are all on the same subject, so it's not as if I get a break to think about anything else. And since the SBIR grant discusses information that is in the patents, the patents have to be filed first, and since the SBIR grant has today as a deadline, that means all three documents are being filed today.

Fun, huh?