Wednesday, July 28, 2010

Gelators - Part II

This is the week of the gelators. Here's another one:

This gelator is part of some new research (open access) showing a creative use for hydrogels.

As a quick aside following up on yesterday's comments, I can't rationalize the gel-forming ability of this one at all - at least not until I see some x-ray data or other structural test results (and then my hindsight would be 20/20). Regardless, this one has some very important properties that would be of interest for up to half the population of the earth - the men. Or at least those men suffering from prostate cancer.

Prostrate cancer cells give off an antigen known as PSA [*]. When the gel is prepared, a second molecule is added. This second molecule has two parts, one of which is degrade by the PSA. When the degradation occurs, the remaining fragment of the second molecule no longer stays in the gel. With appropriate choices, that fragment can then be taken up by the prostrate cancer, a very effective way to deliver therapeutics to the prostrate and basically no where else.

[*] "Prostate specific antigen". No relation to pressure-sensitive adhesive. Don't ever do a patent or lit search for PSA or you will get hits from both fields. I know. Been there, done that. And googling it is even worse as then you can get all the public services announcements.

Update 8/2/2010. Eric Brown of "The Rheol World" commented that I had used "prostrate" instead of "prostate". This misuse has been corrected, although the cancer can certainly leave you prostrate.

Also, I added an additional meaning for the abbreviation "PSA".

Tuesday, July 27, 2010

Gelators - Part I

I've always been fascinated by low molecular weight gelators. These are small, non-polymeric molecules that easily outperform the long-chained cousins when it comes to making gels. They are surfactant-like molecules that because of intermolecular interactions, build large networks at low concentrations, maybe just a few percent. Here's one that I've worked with in the past: 12-hydroxy stearic acid (12-HSA).

Stearic acid is already well known as a surfactant of sorts capable of forming micelles with the acid groups all aligned up at one end and thereby forming a 3-D structure of limited strength. The associations and hydrogen bonding are all located only at one end of the molecule. By adding the hydroxyl groups along the chain, hydrogen bonds can now form further away from the head of the molecule and stabilize the entire system of molecules, much like nailing a board in two spots is better than in just one.

I have seen ultrahigh molecular weight PE gel mineral oil at low percentages, but that is clearly an exceptional polymer. Any non-crosslinked polymer of normal molecular weight can't make gels at such low concentrations.

C & E News has a report of a sugar-based gelator that is able to selectively gel just the oil phase of a diesel/water mixture. (There's a video at the site to watch as well.) It's worth a look. Here's a look at the molecule:

As with the 12-HSA, there is a polar segment and a non-polar segment - in this case, 2 of them [*].

The article has the usual hype of how this can be used in oil spill cleanup... completely overlooking that this material has never been evaluated for environmental toxicity or other effects, or even used with crude petroleum, let alone any of the other short comings already mentioned in the article. Still, it is a neat molecule capable of rheological changes that polymers can only dream of.

[*] Looking at the structure of a molecule and attempting to predict its gel-forming abilities is challenging. There are no sites for hydrogen bonding away from the center of the molecule. Since there isn't, I mentally rationalize this gelator as being akin to some of the poloxamers (Tradename Pluronics) such as the PPO-PEO-PPO block copolymers. Only the mid-block is water soluble, but this can still form gels at ~ 20 wt% concentration

Monday, July 26, 2010

Extreme rheology

Extreme physics can intersect with polymers and rheology in odd manners. I mentioned last year some high-energy physics experiments of polymers being probed with muon entanglements. That is quite tame however, to what I ran across this weekend: the rheology of neutron stars.

Tautologically speaking, neutron stars are composed of neutrons. They are remnants of supernovae and are extremely dense, so much so that the gravity from the star itself bends the light from its surface enough that more than half of the surface can be viewed at one time. Given the immense distance to these stars it is quite surprising that much can be known of their nature, let alone the rheology of them.

This is a pretty crazy intersection of two diverse areas, isn't it?

Friday, July 23, 2010

Isn't this Obvious??

Maybe because it's a Friday afternoon in late July that research like this counts are news, but I see this as something that even a first year undergrad (and many higher schoolers) know: "Sampling frequency affects the reproducibility of results and if not properly done, introduces sampling artifacts".

Somehow that is news and worth highlighting. C & E News is reporting on research in wastewater and sewage sampling. There's a bit of a growing trend in this area. Analytical techniques have now become sensitive enough to find all sorts of chemicals, drugs (both legal and illegal)... in the sewer pipes, and more and more papers are being published using this data.

Somehow a researcher in Australia was able to publish a paper (paid subscription) showing that sampling frequency matters since the sewers are a dynamic system. I know it sounds like I am picking on the researcher, but my vitriol is aimed at:

1) all the previous researchers that overlooked this simple fact making this new paper necessary,
2) all the reviewers of those papers that overlooked this simple fact making this new paper necessary, and
3) C & E News for thinking this is worth highlighting.

A New Nano-Clay for Polymer Reinforcement

There's a report in Macromolecules about new way to nano-size common clay particles and make them compatible with a wide range of polymers.

This looks to me like it might be worth getting excited about. The researchers used a new exfoliating agent [*], a resorcinol bis(diphenyl phosphate) with montmorillonite. Not only did they get good exfoliation, but by using a phosphate, they also achieved (at least partial) fire protection. And then perhaps best of all, they were able to make compatible blends with PMMA, PC and PS, the last one supposedly not being possible with standard exfoliation. The report (open access) is quite extensive and well documented.

[*] Clays consist of layers of various silcates. The key to creating a good nanocomposite is to break these layers up - exfoliate them - by adding various chemicals to neutralize the charges between the layers. Once broken up, proper dispersion then is possible - still no small challenge, but certainly impossible without exfoliation.

Thursday, July 22, 2010

A Bio-based Acrylic

The Bio-Pol Blog has a post about the pending development of a bioacrylic. Personally I am more excited about this than about the bio-polyesters (i.e, PLA) that have been developed to date - I've spent far more time playing around with acrylic polymers than with polyesters given the ease of polymerizing acrylics.

Tuesday, July 20, 2010

The Limits of Peel Testing

In a peel test, energy is applied to the system in order to separate the adhesive (and its backing) from the substrate. Ideally, all this energy is applied to the adhesive-substrate interface, so that by measuring the applied energy, you then have a value of the strength of that adhesive bond. That however, is not the case in any real system.

Some of the energy applied to the system is spread to other components of the system and does not go to the adhesive-substrate interface. These other components include the part of the adhesive not at the adhesive-substrate interface and also the backing.

Adhesives in general and pressure-sensitive adhesives in particular are made from soft materials which absorb energy. In a peel test, a good amount of the applied energy will be used to first deform the bulk of the adhesive prior to any energy being applied to the adhesive-substrate interface. This is the reason that thicker layers of adhesive have stronger bonds – the actual bond at the interface is identical, but the extra amount of adhesive adsorbs more applied energy. More energy is needed to break the bond. More energy = stronger bond.

Foam adhesives (whether the adhesive is foamed itself or applied to both sides of a layer of foam) are another example of this. The foam absorbs a terrific amount of energy so that the interface doesn't.

A similar issue occurs with the backing – it too must be deformed during the peel test and this deformation requires energy. The stiffer the backing, the more energy that must be applied to deform it.

Both of these deformations then represent energy sinks that make it more difficult to understand the results of any peel test. If a consistent backing is used, and if the adhesive thickness is the same, then it is possible to make comparisons between different adhesives. The energy sinks still exist, but they have become standardized.

Additionally, it is possible with very stiff substrates that the energy sinks will consume such a large fraction of the applied energy (90% +) that the energy applied to breaking the adhesive-substrate interface will be lost in the noise of the measurements. That's when you need to find another test.

Monday, July 19, 2010

Self-Healing Polymers - Maybe getting better

Over the last year I've discussed self-healing polymers a number of times (1, 2, 3) and have always been underwhelmed. I understand the challenges of technology development and how ugly prototypes can look (having done all this myself numerous times), but this area has struck me as not even being close to viable. Partly because the "rehealed" material loses a significant fraction of the original strength, but also because the self healing particles use up volume in the original material reducing its initial strength. It's a double whammy - you start out weak and only get weaker.

A new report in Smart Materials and Structures (open access but see [*] below) discusses an approach that in my mind is much more viable - name to have the reactants flow through a network of small tubes, akin to blood moving through your body. At least for the samples prepared in this work, the internal tubing (glass) did not significantly reduce the initial strength of the original material - a carbon fiber /epoxy composite. They did not take the next step of incorporating a reactive system, but it is a good first step that I've not seen before. Work of this nature would make me much more inclined to believe in the potential of the field.

[*] IOP has open access to most of their journal articles for the first 30 days after the article. Registration is required, commercial uses are prohibitted...

Now this is Dreaming

A couple of weeks ago, Electrolux revealed their plans for creating vacuum cleaners from resin in the various gyres. A challenging project no doubt, but probably doable. Now comes the most over-the-top-pie-in-the-sky-what-were-they-smoking-and-not-sharing proposal yet: take all the plastic and make a floating island with it.

Kinda neat how that the wildlife even likes the island - notice the osprey circling above it.

But this would be far more than just an island; it would be home for living creatures, like people.

Looks like something out of SimCity.

This can't be serious. The first tropical storm through the area would toss this around like the plastic bags it would be made from.

Friday, July 16, 2010

No Death Knell for PVC

Think PVC might be dropping in useage, going the way of the dinosaurs, adios, good riddance? Think again. Plastics and Rubber Weekly is reporting on the groundbreaking of the world's largest PVC plant - 330,000 tpa with possible expansion to 500,000 tpa. Just think of all the plasticizers that are going to be needed, and lubricants and heat stabilizers and... everything else I've ranted on in the past.

Curiously (at least to uninformed me) the plant will be located near Nizhny Novgorod (previously known as Gorky), about a couple hours east of Moscow. I'm wondering where the customers will be. That is an odd spot to be supplying China, India or anywhere in Asia. If the smaller European states were a target, I would have thought it would be built west of Moscow. But since Sibur (a Russian company), Solvay and BASF are involved, I'm sure they have thought things out.

Thursday, July 15, 2010

Blow Molding on a Small Scale

Blow molding, like most polymer processing operations, is not something that can be easily done by garage tinkerers. All the equipment, extruders, molds...all have high costs even for "lab scale" equipment. But that has all changed. George Fereday has invented a "personal blow molding gun", even taking the time to snap pictures of the short shots.

Small, lightweight and run by just 1 person - the perfect gift for the do-it-yourselfer.

Wednesday, July 14, 2010

No RDA on BPA in the EU

Given the extensive efforts here in the US to reduce/eliminate BPA in food/water contact situations, I was surprised to find that Europe is still at the same point that the FDA is: more time and studies are needed. Plastics News (Europe) is reporting that the European Food Safety Authority has again delayed publishing an opinion on the maximum acceptable level of BPA consumption.

I found this paragraph as particularly interesting:

"The panel is understood to have dismissed the Stump study’s conclusions over BPA affecting neuro-behaviour, which had led Denmark to ban BPA in materials in contact with food for children aged 0-3 years. It has also ruled out DTU’s claim that low doses damage learning ability. "

Allowing for children to contact BPA and also ruling out the claim of damaged learning ability? I would have thought that the fearmongers would have won the day.

Chemistry and Music

Most scientists are well aware that people astute in math are commonly talented in music and vice versa. Philip Ball has a post on a few musicians (composers in particular) who also enjoyed chemistry.

Tuesday, July 13, 2010

Betrayal by a Polymer Scientist

Update: 3/13/20

This post has been removed. I have been provided new information that makes me question the validity of the original claims of impropriety by the researcher and so I have decided to remove the post entirely.

This is not an action that I take likely, but I feel that it is the most appropriate action at this time.

Physicists Can't Get Anything Right something so basic as the size of a proton. Sure, they can build the LHC and look for the Higgs boson and spend 30+ years developing String Theory without yet even devising a single experiment to test it, so then how come it is so difficult to find out the size of a proton, one of the three most elemental subatomic particles?

C & E News is reporting on a new experiment that concluded the proton is 0.84184 femtometers across, down 4% from the currently agreed upon value of 0.8768 fm. Such a change would apparently cascade causing wide swaths of physics to be re-examined.

As has been pointed out elsewhere, Emil Fischer had a 1:16 chance of correctly identify the stereoisomers of the sugars and he nailed it. Ben Franklin had a 1:1 chance of correctly identify the direction of current flow and got it wrong. When it counts, go with a chemist.

Monday, July 12, 2010

Frito-Lays PLA Bag #2

I mentioned this bag back in April. I bought a bag of the chips this weekend and what I didn't mention earlier was this: it is a seriously LOUD bag. There is no chance that you will be able to sneak a few chips from this without anyone knowing.

The noise reminds me very much of the noise that you get from a polyester blister pack - minus the cussing from the individual attempting to open the package! Polylactic acid (PLA) is a polyester (aliphatic instead of aromatic) but still, polyester linkages unite the monomers along the backbone. I'm not sure that I want to go out on a limb and attempt to correlate noise profiles with specific linkages however.

How much plastic is in the ocean? (Reposted)

Nobody knows for sure, but the new estimate - 315 billion pounds - posted at 5 Gyres is surely wrong.

You know that the estimate is going to be bad when the author, Stiv Wilson, starts out with this sentence: "If we were to attempt to quantify how much is out there, we need to do some big math." Watch out! Big math is coming! Danger! Danger!

Stiv starts with a measurement of 5 kg/km2, derived from drag net measurements taken in the North Atlantic Gyre, and also states that plastic pieces can be found 90 feet down. Good. Data is always a good spot to start with.

However, Stiv takes this value of 5 kg/km2, taken from a gyre, an known area of concentration and multiplies it by the entire surface area of oceans on the earth, completely overlooking that most of the areas are of lower concentration, since they are not gyres or "garbage patches".

But it get worse. 90 feet worse. Stiv further makes that assumption that the concentration above is for the first foot and then multiples it by 90, as if the plastic is uniformly distributed for all 90 feet. The assumption of uniformity is not rationalized at all. I would strongly propose that the uniform assumption is going to be inaccurate and overstates the amount of plastic. Just the fact that a number exists as a lower limit strongly suggests that it is an asymptote, a depth below which plastic is so seldom seen as to be nonexistent. If 90 feet were not an asymptote, there is no reason why 90 feet would be a cutoff at all. Plastic should be found at all depths if it were uniformly dispersed. Lacking data, all sorts of concentration-depth profiles could be proposed - linear, exponential decay, a power law fit or whatever. Regardless of the model, the end result is again that Stiv has overestimated the amount of plastic.

Now the real kicker: Stiv calls these "conservative estimates". Opps, sorry, I misquoted him. Shame on me. He doesn't call them conservative estimates afterall. Instead, he calls them"extremely conservative estimates".

So know we all know how bad "big math" can be, which in the end turned out to be merely the product of 3 numbers.

Look, plastic has no business being in the ocean, but to overinflate estimates of how much their is has no value to anybody.

Friday, July 09, 2010

Non-Stick Chewing Gum

Revolymer, a British company has announced the FDA approval of a new chewing gum that will not stick to surfaces - or at least will stick at a greatly reduced level.

They have a few videos on their home page. I only have looked at one so far - "Why Things Stick" and have made a few guesses about what is going on. I was also dissappointed, in that the title of the movie is misleading - they barely touch on why things stick [*]. He also made references to cohesive strength vs. adhesive strength.

One tidbit the speaker did give away is that they have added a polymeric surfactant to the gum. I would have to guess that it is a Pluronic - a PEO-PPO-PEO block copolymer. They are already used as surfactant (and being nonionic, they are low foaming, always a good thing for chewing gum), and they have pharmaceutical approval. I'm curious if the surfactant changes the cohesive strength at all either.

[*] During a recent client visit, I gave an overview of why things stick as a lead into why cleaning things is so difficult. The Leonard-Jones 6-12 potential energy well is short and deep, and I was pleased to see even the non-technical people in attendence understanding the concept. Plus I told them that at their next cocktail party and can toss around the term "Leonard-Jone 6-12 potential" and impress the other attendees.

Thursday, July 08, 2010

Metathesis and Polymers

"Psst! Hey Buddy, you want some double bonds moved around?"

In a nutshell, that is metathesis [*]. Since olefins are involved, polymerization can soon follow. The most common example is ROMP - Ring Opening Metathsis Polymerization, but I discovered yesterday REMP - Ring Expanding Metathsis Polymerization. This discovery comes courtesy of a blog devoted to metathesis: "All Things Metathesis".

Making a ring of a polymerizing chain is always a challenge as the two free ends aren't necessarily close to each other most of the time. It's more likely that the chain will extend itself by reacting with another linear chain (if there are 100 chains in the mix, that means there are 200 free ends, 198 of which are not the ones you are trying to react. Not good odds.) To steal an old slogan: "Dilution is the solution". If the mix is diluted enough, then each chain will be so far from any other chain that it will only be able to react with itself - eventually.

In the case of REMP, the catalysis is able to confine the two ends of the chain to a small space all the while allowing the ring to grow. Since the ends are close together, it is easier for achieve ring closure without having to go to high dilution.

[*] The term also has uses outside of chemistry. In linguistics, metathesis is the rearrangement of the letters in a word when it is pronounced - such as when President Bush (W) would say "nuke-you-lure".

New Pressure-Sensitive Adhesives from Tree Byproducts

Most press blurbs from academia are begging for disbelief - endless claims of never-before [1] innovations that will revolutionize industry or cancer treatments [2] and will be on the market in 2 - 5 years [3].

The challenge then is to find out what exactly is the discovery. Let me give you an example. Yesterday, Oregon State University issued one such blurb. Apparently they have discovered a new pressure-sensitive adhesive based on vegie oils. Details on the chemistry are completely lacking, undoubtedly because the legal department is trying to patent this. Hopefully there will be some publication soon as I am intrigued not by the feedstock but by the polymerization process:

"There have been previous attempts to make pressure-sensitive adhesives from vegetable oils, Li said, but they used the same type of polymerization chemistry as the acrylate-based petrochemicals now used to make tape. They didn’t cost much less or perform as well, he said.

The new approach used at OSU is based on a different type of polymerization process and produces pressure-sensitive adhesives that could be adapted for a wide range of uses, perform well, cost much less, and would be made from renewable crops such as soy beans, corn or canola oil, instead of petroleum-based polymers."

So that is the interesting part of the blurb. The rest is quite obnoxious. Consider this:

"This adhesive is incredibly simple to make, doesn’t use any organic solvents or toxic chemicals, and is based on vegetable oils that would be completely renewable, not petrochemicals. It should be about half the cost of existing technologies and appears to work just as well."

A typical cost structure for a product is the raw materials costing 25% of the final cost. Even zeroing this out will only reduce total cost by 25%, not the 50% cited.

Also consider these sentences:

"The new adhesive can be produced from a range of vegetable oils, and may find applications for duct tape, packaging tape, stick-on notes, labels, even postage stamps – almost any type of product requiring a pressure-sensitive adhesive. There are thousands of pressure-sensitive tape products, and analysts say it’s a $26 billion global industry."

Kinda gives you the impression that there is $26 billion available for the taking since they are all more or less the same adhesive, right?

Again, I am curious about the polymerization process, but will have to withhold judgement as to it's level of innovation. But why must there be so much junk in these blurbs?

[1] Meaning only if you look at the last 10 years of technical literature. Go back further or look at patents (hint: the US is not the only country to issue patents) and you find that it has been done before.
[2] Since every known cancer and all other diseases have been cured in rats, how come we don't have immortal rats? Whatever it is that is killing them, we have the cure for; why doesn't someone just go for it a keep a rat alive forever? Maybe it would show the cures have shortfalls way beyond the mere fact that they work in rats and not humans?
[3] If only there were a way to place a short on these predictions, those of us in industry could all all retire at a very young age.

Tuesday, July 06, 2010

Ruminations on a Furnace Filter

Time for the quarterly replacement: out with the old electrets, in with the new. Looking at the old filter with the naked eye, there is an impressive amount of dirt. Certainly enough to keep the furance clean, but I just have to trust the testing labs that the allergens are removed as claimed. Not that I doubt it, but I certainly understand the difference between what the naked eye can see and what it can't. (Akin to what a nose can smell and how dangerous it is.)

Electrets have always struck me in a funny way. I understand the phyics behind them (the placement of a near permanent charge on a polymer, or most typically a polymer) and having worked in tape, film and netting plants, I know to never, ever touch a roll stored in the warehouse unless someone else have been foolish enough to touch it first (charges on some rolls can reach thousands of volt!). But I have never been able to get a good explanation of why the electret can't be grounded.

Friday, July 02, 2010

A Unique Composite Bicycle Frame

The Tour de France starts tomorrow, so it is perfectly appropriate to discuss a bicycle: the Delta 7 Isotruss open tube frame. This doesn't look like anything I ever raced on:
and I've yet to see a European pro ride one either. Besides looking like an expensive cheese grater, it doesn't seem to provide any significant weight reduction. The frame is listed at 1000 g /2.1 lb (who's doing the conversions here? That should be 2.2 lb!) and is compared to the carbon composite frame Lance Armstrong rode in the uphill time trial in the 2004 TdF, which weighed 907 g / 2 lb. Granted, time trial bikes can be stripped down extensively as they are only ridden for relatively short distances (50 km or less), and in the case of an uphill time trial (up the infamous L'Alpe d' Huez no less), I'm sure every conceivable microgram of extra material was eliminated, so this is probably not a completely fair comparison.

More important than weight considerations however, is the issue of drag. Run this through a windtunnel, ideally with and without a ride and see if all those exposed edges don't cause a big increase in drag. Keep in mind that drag is far more important than dead weight. The mass of a nonrotating part is only an issue in acceleration (or on an uphill). Once the acceleration is over, the magnitude of the mass doesn't matter, and can even be helpful on a downhill. On the other hand, drag is always there, constantly resisting any forward movement - uphill, downhill, accelerating or even at constant velocity. Drag is the true enemy, not mass.

You can read more in the March 2010 issue of High-Performance Composites, which is also the source of the picture.

Thursday, July 01, 2010

You're Never Alone on the Internet

On Monday I (and others) were lamenting the sorry state of the blogosphere for polymers and such. We are not alone. Apparently biologists and astrophysicists have the same problem.

It still doesn't make the current state more acceptable however.

Great Injection Molding Resources

Compared to other polymer processes, injection molding can be pretty complicated. Deciding where to inject, where to set the ejector pins, runner and gate sizing, shrinkage, warping, and then there is the whole design aspect - making sure that the part can even be molded in the first place, or maybe more correctly, making sure that the molded part can be removed from the mold. Designing an extrusion die is much easier, even in the case of multilayers.

Protomold has a wonderful set of resources on their website regarding injection molding. I know of no equivalent site on the internet. The resources are no substitute for an experienced moldmaker - woe to anyone who reads the stuff and think they know everything, but by becoming a smarter customer, the relationship with the mold builder can't help but be improved.

Full Disclosure: Neither I nor my employer has any financial relationship with Protomold. This post is simply me pointing out a useful website.