Thursday, October 18, 2012

Plastic Precursors

Oh plastic, how you both simplify and complicate our lives. We don't use it in baby bottles anymore because maybe it leaches hormone-mimicking chemicals. But it's still the chassis of virtually every electronic device, and certainly every portable radio. People are going back to glassware for food storage over similar fears, but it still coats all electrical wiring everywhere. Where would I be without saran-wrap and wiffle bats?  From the aglets of our shoe laces to the bezel of the car stereo... plastic is everywhere. Real modern plastics are over 100 years old. Below is a list of landmarks in plastics for better or worse.

The modern word plastic originates in the Latin word "plasticus" from the Greek "plastikos" meaning moldable in the sense that clay and mud are moldable. The modern definition of the word plastic dates to 1905 from it's use by Leo Baekeland the inventor of Bakelite. Interestingly source cite his use prior to his invention...  The idea surely came from the popular use of vulcanized rubber invented by Goodyear in 1839. Before that little in the home was elastic. Thomas Hancock stole his patent in the UK. But we didn't coat wires in it. We only had started using gutta-percha after it's 1843 discovery by William Montgomerie. Nothing else was even slightly flexible. All we had was shellac and lacquer (cellulose acetate). More here.

The first real plastic was Polystyrene. It was discovered in 1839 by Eduard Simon. His early attempt rendered it from a natural resin. But it's commercial scale manufacture was only developed by BASF in the 1930s. Xylonite and Parkesine were invented in the 1860s and reinvented as Celluloid in 1863 by John Wesley Hyatt. But it wasn't a good insulator; too flammable. real modern plastics start in 1872 with PVC. Below is a list of the highlights.
  • 1839 - Ploystyrene - Eduard Simon (first sold in the US in 1937)
  • 1872 - PVC (Polyvinyl Chloride) - first created by Eugen Baumann 
  • 1894 - Rayon - Charles Frederick Cross, Edward John Bevan 
  • 1908 - Cellophane - Jacques E. Brandenberger 
  • 1909 - Bakelite (Phenol-Formaldehyde) - Leo Hendrik Baekeland 
  • 1926 - Vinyl (plasticized PVC) - Walter Semo
  • 1933 - Saran Wrap (Polyvinylidene chloride)  - Ralph Wiley, at Dow
  • 1935 - LDPE (Low-density polyethylene)- Reginald Gibson and Eric Fawcett
  • 1936 - Acrylic (Polymethyl Methacrylate) -Otto Rohm
  • 1937 - Polyurethane - Otto Bayer
  • 1938 - Teflon (Tetrafluoroethylene) - Roy Plunkett, at DuPont
  • 1939 - Nylon and Neoprene - Wallace Hume Carothers
  • 1941 - PET (Polyethylene Terephthalate) - Whinfield and Dickson 
  • 1951 - Polypropylene - Paul Hogan and Robert Banks 
  • 1954 - Styrofoam - Ray McIntire, at Dow
  • 1970 - Mylar (Thermoplastic Polyester) - DuPont
  • 1978 - LLDP (Linear Low Density Polyethylene) - ICI corp.
  • 1985 - Kevlar (Liquid Crystal Polymer) - Stephanie Kwolek, at DuPont
The plastic we use in electrical insulation in wiring is PVC, aka vinyl. This is not because it is best at resisting the electrical potential. There are quantifiable qualities to electrical wiring that pushed the world into PVC. Firstly, wiring has to be flexible. A rigid wire would never be able to get from the circuit breaker to your stereo on the 2nd floor. A rigid wire would also be impossible to loop across a circuit board. It's nice for it to be fire resistant too.

But after that we quickly get to electrical qualities. We measure it's electrical insulating properties as volume resistivity or dielectric strength. Volume resistivity is expressed in terms of sample resistance, which is measured in ohms. All very dry and scientific. Dielectric strength is more fun. It is expressed in terms of destruction of test samples by various voltage magnitudes. Ceramic has excellent dielectric strength, but is entirely inflexible. Polypropylene, Polystyrene and Polyethylene all have superior resistivity but fail on the fire test. Teflon is superior to all of them in resistivity but it's famous non-stick slipperiness allows things like gaskets to creep out of position. the result is that each application has an ideal plastic with no sole single right answer. More here.