Thursday, April 30, 2015

Living Hinges

One mechanical entity that is almost exclusively limited to being constructed from polymers is a "living hinge". Trying to describe a living hinge can be difficult, so let me provide a few pictures of living hinges you might have around the house:
Living Hinge - Ketchup bottle
What American home doesn't have a ketchup bottle or two?

Fish sauce bottle

The common feature in all cases is that there is a thin strip of the polymer that provides a flexible, continuous (usually) hinge between two other more substantial parts. Trying to make such a hinge from metal would be pretty challenging (let alone ceramics or other rigid materials).

Living hinges are most commonly produced from polypropylene (PP) and polypropylene copolymers, not only because that material is plenty cheap, but also because when properly made, the hinges can last for years. I have a large polypropylene tub that originally was used for dog food some 12 years ago. It has since been repurposed for storing bird seed in an icy-cold/sultry-hot Minnesota garage. It has been flexed two or three times a week for its entire life, and other than where mice tried chewing through it last winter looking for some free seeds, it still works beautifully.

Last week when helping out with the laundry, I ran into a living hinge that I thought was a little unusual. It's a container for Tide Pods:
Living Hinge - Tide Pods
Tide Pods Container

I say it is unusual because the container is polyester. While polyester (PET) is used for living hinges, it's usually for food packaging such as this:
Living Hinge - Fresh Herb Container
Fresh Mint
or other items at the grocery store. PET is much more expensive that PP, but it is used in food packaging because its clarity shows off the food so well. But that argument doesn't hold up with the PET used for the Tide Pods as it is not clear at all. Additionally, the hinge will be flexed quite a bit - the container holds 72 pods so that is at least 72 cycles of opening and shutting. So why does P & G use PET instead of PP? I have no idea. Perhaps some other aspect of the molding (cycle time for instance) dominates and allows for the use of a more expensive resin.

The term "living" hinge has always bothered me as there is nothing alive about the hinge. It's a hinge. A thin plastic hinge. But misuse of the word "living" in polymer science and engineering is nothing new. Look at "living" polymerizations. In a living polymerization, the polymerization reaction runs until the monomer is depleted, but unlike with more common reactions, the termination reaction never kicks in to permanently halt the polymerization. If more monomer is added to a depleted living polymerization, the reaction can pick up right where it left off, even if the newly added monomer is different that what was used previously. But is the living polymerization still "alive" while it is in that paused, deplete state, or is it more like a dormant state? (Or maybe even a "zombie" state as was discussed yesterday?) I guess polymer scientists and engineers have a hard time distinguishing between "live" and "dead". But then again, I have wondered that about my colleagues themselves at times too, so perhaps the misuse is understandable.



Previous Years

April 30, 2014 - Dow Chemical Keeps Plodding Along and Silencing Critics

April 30, 2012 - Another Set of Rants about a Rejected SBIR Grant

April 30, 2010 - Natureworks

April 30, 2010 - This Changes Everything!

April 30, 2009 - Skip the ER for potential heart attacks and find a spectroscopist instead

April 30, 2009 - This isn't even peer-reviewed


Tuesday, April 28, 2015

The Antibacterial Properties of Silver can be "Long Lived"

While polymeric materials are seldom consumed by bacteria, the surfaces can still provide a location for bacteria to live on, especially if the surface is contaminated with substances that can sustain bacterial life. One common way to prevent this is to add various toxic metals to the polymers such as silver or copper. The use of these metals to control bacteria has been known for centuries, but a new research report (OPEN ACCESS!) puts a new twist on just how effective silver can be: the bacteria that have been killed by silver nitrate are themselves capable of killing additional bacteria. Apparently the silver in the dead bacteria serves as a reservoir to kill additional bacteria. The researchers believe that copper would be able to act in a similar fashion.

The researchers provide an "interesting" take on what they observed: Dead animals are able to kill living animals of their same species. There is one and only one word for this type of behavior: ZOMBIES! And that's exactly the word that the researchers used. It's a little bit of a stretch as the dead bacteria are not actively pursuing the live ones, but it certainly draws your attention in.



Previous Years

April 28, 2010 - Overqualified?

April 28, 2010 - The Cox-Merz Rule Rules

April 28, 2009 - More Science Funding



Monday, April 27, 2015

Using Drones to Find Ocean Plastic?

Hardly a day goes by without someone suggesting a new use for drones. But using them to study ocean plastic? I doubt that that will work well at all.

Glancing at the article, you would think otherwise, especially with a picture like:
Ocean Plastic - NOT!
leading off the article. If the plastic pieces were actually that visible, drones would be helpful.

But the reality of ocean plastic is quite different. A researcher from the Scripps Research Institute recently took a picture from the middle of the eastern Garbage Patch. This is what she saw:
The Middle of the Eastern Ocean Gyre - Where's all the plastic?
Quite a different perspective, isn't it.

This is not a denial of the Garbage Patches and Ocean Plastic. The plastic is there alright. But you have to look closer and concentrate to see it since it looks like this:
What ocean plastic really looks like
It's mostly small particles and not very closely clustered together. Which is most unfortunate, as that dilution prevents the plastic from being recovered.

Unless these new drones have super powerful magnification and a smooth ocean surface, they aren't going to useful at seeing much of any except the big stuff. Certain groups of people are okay with finding just the big stuff, because that can then be used to paint the evocative images of "Garbage Patches" and "Floating Islands" "the size of Texas". But that is not the least bit representative of reality.



Previous Years

April 27, 2011 - Closing the Loop in Biotechnology

April 27, 2010 - Adhesives vs. Rivots

April 27, 2010 - Strange Math

Tuesday, April 21, 2015

Using a Reusable Bag isn't so good for the Waistline

The issues surrounding the use of reusable bags at the grocery store just got a little more complicated. That's because Harvard and Duke researchers found out that using a reusable bag changes your behavior, and not all for the good. People toting around a reusable bag did buy more organic foods, but they also felt good enough about themselves and their helping-the-environment that rewarded themselves with junk food:
"It was clear that shoppers who brought their own bags were more likely to replace nonorganic versions of goods like milk with organic versions. So one green action led to another. But those same people were also more likely to buy foods like ice cream, chips, candy bars, and cookies. They weren’t replacing other items with junk food, as they did with organic food. They were just adding it to their carts."
Maybe we need to update the old saying "A moment on the lips, a lifetime on the hips" to "Don't bring your own bag or your butt will start to drag"?


Hattip to Don Loepp at PlasticsNews for this item.


Previous Years

April 21, 2014 - The Week That Was(n't)

April 21, 2011 - Small is not Necessarily Better (with Plastics)

April 21, 2010 - Visible Light Photocatalysis - Even in the Dark

April 21, 2009 - The Double-Edged Sword of UV Light


Wednesday, April 15, 2015

So just how many polymer chemists are there?

While polymers have touched just about all aspects of our lives, you might be tempted to think that most chemists work with them. While it is true that all working chemists do to some degree, i.e., they wear plastic safety glasses and rubber gloves, I want to probe the subject just a little more deeply and ask: what percentage of chemists work in the development and/or manufacturing of polymers?

This is surprisingly difficult to answer. My own personal perspective sans data is that very few do. If social media is representative at all of chemists, then the fact that there are very few bloggers and tweeters on polymers compared to the number of chemists involved in those media supports my position. Also compare the size of their readership and/or followers. Further, look at how few polymer research articles are published in general chemistry journals such as JACS or Angewandte Chemie. Or how few polymer talks are given at the ACS national convention.

As I've said in the past,
"If you want to feel like an outcast chemist, take up polymer chemistry."
Googling for an answer doesn't help much. Typing in the question outright doesn't provide any answer, so I took a different approach and searched on "X% of chemists work with polymers", and went with X from 10 to 110. (Yes, 110% since we all know that polymer chemists always give 110%. More on that in a minute.) The only hits I got were at 50% and 70% from the ACS and the University of Oregon respectively. Those numbers are preposterous. No citations are provided (not surprisingly).

I finally hit some real paydirt when I looked at the federal government's tabulations. The Bureau of Labor Statistic (BLS) has collected all the relevant data and provides an accurate picture (open up the spreadsheet for chemists if you to see all the details). In 2012, there were just under 88,000 chemists. Of that number, 2100 worked in "Resin, synthetic rubber, and artificial synthetic fibers and filaments manufacturing", 1900 worked in "Paint, coating, and adhesive manufacturing", and 600 in "Plastics and rubber products manufacturing". That's 4600 in manufacturing. There are some broader categories that undoubtedly include polymer chemists, such as the nearly 18,000 that work in "Scientific research and development services", and the 4600 that work in "Educational services; state, local, and private". Even if everyone of these last two groups were all polymer chemists, that would still only total to 27,200 chemists, not even 31% of the total workforce. I think a more realistic number would be just 10% of those last two groups, which would be 2260 more for a grand total of 6860 chemist. This is not quite 8% of the workforce.

Keep in mind that this is just "chemists". Chemical engineers, materials scientists etc. are not part of the numbers. It could be argued that the ACS pages includes a disclaimer:"As many as 50% of all chemists will work in polymer science in some capacity during their career."(emphasis added), but I'm not buying that either. Jumping fields and going into polymer chemistry is no more likely than an organiker becoming an analytical chemist or a computational chemist become a bench inorganic chemist. It can be done, but that is the exception, not the rule.

Also, it needs no mention that these are numbers for the US only but I would expect similar percentages for other countries. If some international readers have different numbers (or even anecdotes), please feel free to provide feedback either in the comments below or via email (address is on the upper left side of this page).

One final closing thought: If a mere 8% of chemists are able to provide the incredible bounty of polymers that the US and much of the world enjoys, I can't help but think that we are the James Brown of chemists - the hardest working people in chemistry!
James Brown - Papa's Got a Brand New Plastic Bag

Previous Years

April 15, 2013 - A Novel Flame Retardant Coating for PU Foams

April 15, 2011 - Show me a picture, please!

April 15, 2010 - More Olefin Polymer Oxidation

April 15, 2009 - Self-Healing Polymers