Other Plastics ♹

Although the BIG 6 are really important and have a fairly well know path to the recycling bin, the "other" category has everything else that is possibly recyclable as well. Here we cover some of these "others".

Nylon

Nylon is a copolymer just like PET. However, instead of a polyester like PET, Nylon is a polyamide. It reacts in a similar manner - a condensation polymer. It also uses a dicarboxylic acid as one monomer - in this case, adipic acid which is a 6-carbon chain with a carboxylic acid function on the two end carbons. The other monomer is hexamethylenediamine. These come together and make an amide link which happens to be a very tough link as well. This is the same reaction that amino acids in your body undergo to make proteins. Only in proteins the link is called a peptide link.


properties: Higher melting point than many other plastics, 256 °C. Due to highly ordered chains and H-bonding, nylon is highly crystalline which allows for very strong tensile strength (strong fibers). It is easily dyed and retains color exceptionally well. Due to the nature of the amide link, nylons are hydroscopic (attracts water). The absorption of water does tend to change some of the properties as well. Strong acids will hydrolyze (pretty much the opposite of the condensation reaction that made it) the amide link and should be avoided. Resistant to mold, mildew, and fungi. Tends to melt more so than burn.

uses: Nylon stockings - one of the first big hits of plastics. All kinds of fabrics - very resilient (easy-care). Carpeting. Machine parts - gears. Used as framing material for many items - the Glock pistol has a nylon-based frame. Classical guitar strings - replaced catgut.

Bakelite

Bakelite is a copolymer which happens to also be a thermoset. A thermoset is a polymer that does not melt - if you heat it, it will char and start to burn, but not melt. So to make a thermoset into a molded shape, you must mix the two monomers and pour it into a mold. Once in the mold, you then heat it to trigger the polymerization and then you have your "set" polymer. And when bakelite sets, it really sets and doesn't yield much at all. It was used as a replacement back in the day for ivory - pool balls were first wood, then ivory, then bakelite. Bowling balls were also bakelite for a while. It wasn't really until the '70's and '80's that other more modern polymers took over from bakelite.

Bakelite is made from phenol (C6H5-OH) and formaldehyde (CH2O). The structure for each is shown below.

     

Once the reaction starts, the monomers can link in 3 different positions on the phenol ring and you get a lot of cross-linking. Pretty much the entire structure is cross-linked giving it great strength and rigidity.

As you can see, the formaldehyde becomes the methylene (-CH2-) links between all the phenols. Depending on your screen size, the above polymer will wrap accordingly but should still "link" up correctly. Want to see a lot more linked up? Check out this page.

Teflon

Teflon is an addition polymer and is a derivative of good ol' ethylene. However, unlike all those Big 6 plastics, the monomer for Teflon is tetrafluoroethene which means all 4 hydrogens are swapped out for fluorines.

Very tough and slick stuff. The C-F bonds are quite hardy - the strongest of all carbon single bonds coming in at close to 500 kJ/mol. It is used as the still popular non-stick coating on many items - especially cookware. The biggest challenge in making that non-stick cookware is getting the teflon to stick/glue to the pan surface itself. Teflon is very hydrophobic which means water will bead up on it and not want to wet it. Teflon can also act as a type of solid lubricant due to the fact that there is very little friction between it and other surfaces.


Kevlar

Like Nylon, this is a polyamide - but instead of straight chain carbons in between the amide links, there are benzenes (ok, phenyl groups). This increases the intermolecular forces and makes an even stronger polymer strand. It is 5× stronger than the same mass of steel as a fiber. The most known use is in bulletproof vests. Other uses are making incredibly strong sails for racing sailboats (America's Cup type of thing - although carbon-fiber is also in there). Kevlar (and similar polymers) has replaced the steel in "steel-belted" radial tires. As a fabric, it can provide great strength and flexibility for many applications.

The two monomers are terephthaloyl chloride (kin to terephthalic acid of PET fame) and para phenylenediamine. The "para" in that name defines where the amine groups are on the ring - para in this sense means opposite or the two positions 180° across from each other. In numbering you'd number starting on one amine (1) and number around the ring. So para is a 1,4 substitution on the ring. For point of reference the 1,2 positions (adjacent) are called ortho, and the 1,3 positions are called meta. Below is the reaction to make Kevlar.



previous back to top next

© 2019-2021 · mccord