Biodegradable polymers; Nylon and Teflon

Biodegradable polymers

Biodegradable polymers are polymers that can be broken down by the action of microorganisms (bacteria, fungi) and enzymes in the environment into CO₂, water and biomass. They contain links such as ester or amide groups that enzymes can attack.

Examples: PHBV (poly-β-hydroxybutyrate-co-β-hydroxyvalerate; from 3-hydroxybutanoic and 3-hydroxypentanoic acids), polylactic acid (PLA), polycaprolactone, starch- and cellulose-based plastics, and nylon-2-nylon-6 (glycine + aminocaproic acid). Uses: packaging, carry bags, disposable cutlery, surgical sutures, implants, and controlled drug delivery capsules.

Nylon 6,6

Nylon 6,6 is a polyamide made by condensation polymerisation of hexamethylenediamine (6 carbons) and adipic acid (6 carbons) at about 250 °C under pressure:

n H₂N(CH₂)₆NH₂ + n HOOC(CH₂)₄COOH → [–NH(CH₂)₆NH–CO(CH₂)₄CO–]ₙ + 2n H₂O

The repeating unit has the amide (–CONH–) link. (Nylon 6 is made from caprolactam by ring-opening polymerisation.)

Uses: Nylon is strong, tough, elastic and abrasion resistant, so it is used for fibres for ropes, fishing nets, socks, stockings and clothes, tyre cord, parachutes, carpets, brush bristles, and moulded gears and bearings.

Teflon

Teflon (PTFE, polytetrafluoroethylene) is made by free-radical addition polymerisation of tetrafluoroethylene (TFE) using a persulphate initiator under pressure:

n CF₂=CF₂ → [–CF₂–CF₂–]ₙ

TFE itself is obtained by heating chlorodifluoromethane (CHClF₂) at 600–800 °C.

Uses: PTFE is chemically inert, heat resistant (up to 260 °C, m.p. 327 °C), has a very low coefficient of friction and is an excellent electrical insulator. It is used for non-stick coating on cookware, gaskets and seals, insulation of wires and cables, lining of chemical equipment, bearings, valves and surgical implants.