Polymers
moleculeoftheday | August 28, 2007Formaldehyde's funny stuff. It's naturally a gas. If you put too much of it in solution, it will polymerize and form a polyacetal, "paraformaldehyde," which is just -O-CH2- repeating over and over.
Because of this tendency towards polymerization, formaldehyde of commerce is sold with a little methanol added to keep it in solution. Interestingly, formaldehyde polymer is used as a plastic - and it's food approved! In some ways, it stands to reason - the stuff won't dissolve in much of anything so it's pretty chemically resistant. On the other hand, you can actually "crack" paraformaldehyde just…
moleculeoftheday | April 18, 2007Inulin is polymeric fructose:
Unlike cellulose (another sugar polymer, which comprises such indigestibles as wood), inulin is quite soluble. To you, it's almost entirely undigestible, and so is one of the "soluble fibers" in your diet.
You can find inulin in various plants, such as jicama, onions, and the Jerusalem artichoke. Because of its relative indigestibility, enzymes in your gut often take advantage of its ready availability and digest it. This can increase the population of bacteria in your GI; because of this, inulin is often termed a "probiotic." This is something of a euphemism;…
moleculeoftheday | April 5, 2007The pet food recall scare continues unabated; a couple weeks ago, people were pointing at aminopterin, a folic acid analogue, which was covered here. Now, people are pointing fingers at melamine as a potential contaminant.
Melamine is a pretty simple compound, with a number of uses. Here, it's being reported that it's used as a fertilizer, which contaminated some wheat gluten, which ended up in the pet food. Despite the fact that you mostly get carbohydrate from wheat flour; gluten is actually a pretty inexpensive protein source. It's mostly eaten in Asia, but some vegans have picked it up…
moleculeoftheday | March 22, 2007Yesterday's entry on epichlorohydrin got us halfway to an epoxy resin, with the aid of good old bisphenol A. In that other tube, you'll often find some sort of amine, which, when mixed with a prepolymer like that formed with epichlorohydrin-bisphenol A, heats up and hardens.
This triamino-phenol is one hardener found in epoxy adhesives. It reacts further with the epichlorohydrin, giving a cross-linked, hard (or just firm) epoxy resin. It's also responsible for the smell you probably associate with epoxy.
moleculeoftheday | March 21, 2007Yesterday's entry on epoxides may have brought to mind epoxies. The similarity isn't a coincidence. Chloromethylepoxide, or "epichlorohydrin," is the basis for many epoxy adhexives.
One tube contains some epoxide, such as epichlorohydrin, along with some bisphenol A - the very same stuff you find in polycarbonate. This is actually partially polymerized ("oligomers") - the degree of polymerization and ratio of epichlorohydrin to bisphenol A can determine how hard an epoxy you get - this is often the basis for "soft" epoxies.
It's not over yet, though. Tomorrow I'll cover what's in that other…
moleculeoftheday | October 17, 2006PET is an ubiquitous plastic. You've heard it referred to as "dacron", "mylar," or just "polyester."
It it produced by (among other methods) the condensation of terephthalic acid and ethylene glycol:
PET is all over, from soft drink bottles to fabrics. Perhaps the neatest use is as mylar; an oriented form of PET. Back in the fifties we stumbled across it and we haven't looked back. There aren't many applications for a plastic mylar hasn't found its way into.
Awhile ago, my friend sent me a link to the Prelinger Archives, an amazing public-domain repository of gee-whiz video from the past…
moleculeoftheday | September 28, 2006(Oops, this should have been published on Tuesday. I didn't click publish. Sorry!)
Certain bacteria, under certain conditions, will excrete plastic.
The one above is a polybutyrate, but many are possible.
This is neat, first of all, because it's bizzare. Can you imagine being able to excrete plastic?:
To produce PHB a culture of a micro-organism such as Alcaligenes eutrophus is placed in a suitable medium and fed appropriate nutrients so that it multiplies rapidly. Once the population has reached a substancial level, the 'diet' is changed to force the micro-organism to create PHB. Harvested…
moleculeoftheday | September 27, 2006Inspired by Keith's comment on polylactic acid's tendency to deform under heat, and procrastination, I just did a quickie test of the heat-deformation characteristics of my polylactic acid bottle.
I took my PLA bottle and a cute little PET bottle I had lying around. I put some tap-hot water in the microwave and heated it up for awhile. After stirring to equilibrate the temperature, I measured it with my oh-so-cool noncontact thermometer, a Raytek Raynger ST-6, which I wouldn't own if it weren't for Jeffrey Steingarten's unintentional salesmanship (fortunately, by the time I got one, the model…
moleculeoftheday | September 25, 2006This weekend I came across Biota brand spring water, which is the normal expensive kind of spring water (the kind where they make a point of saying where in the earth it came from rather than obfuscating the "municipal source" text). It was pretty good - maybe even one of the better waters I've had.
I'm not here to talk water, though. What's unique about this is the bottle. Most water bottles are PET, a polyester of terephthalic acid and ethylene glycol. These bottles are made of PLA, or polylactic acid.
Esters are pretty labile, and will break down pretty easily into their components. The…
moleculeoftheday | August 22, 2006It's hard to overemphasize the effect WW2 had on science. I'm not just talking about atomic bombs or the ensuing cold war. A huge part of WW2 was shortages of just about everything. Textiles were especially susceptible, because their civilian and military uses are ubiquitous, and, at the time, we pretty much had wool, silk, and cotton (pretty much all you get as far as natural fibers go, save some exotic stuff like processed bamboo and modified celluloses). Obviously, planting things and waiting is kind of hard during the (relatively) short timeline of global war. This shot the young polymer…