Dr Jim Lunt, MD of Jim Lunt & Associates LLC differentiated bio-based and bio-degradable products. The former must test positive for carbon 14, proving that new plant matter had been used, but need not be biodegradable. The latter must meet recognised biodegradation standards but can be free of C14, i.e. made from fossil fuels.
The most common feedstocks for bio-based plastics are food crops: corn, sugar beet, sugar cane, sorghum, sweet potato, wheat, coconut oil, palm oil, and soy beans along with the non-edible castor beans and jatropha.
Conversion of food to fuel transportation is becoming unacceptable so lignocellulosics (wood and agricultural residues) algae and food waste are being considered. Currently, the major routes to “drop-in” monomers for today’s polymers are:
1. Sugar cane -> ethanol -> ethylene ->ethylene glycol
2. Sugar or corn -> paraxylene (Virent process) -> terephthalic acid
3. Sugar or corn -> succinic acid -> butanediol or adipic acid
4. Corn à glycerol -> propane diol
5. Sugar or corn -> furan 2,5 dicarboxylic acid (YXY Technology)
First generation bioplastics such as Polylactic acid, starch PLA blends and Poly hydroxyl alkanoates all have problems with hydrolytic stability because they were designed to be biodegradable when that seemed to be a good idea. Now the second-generation bioplastics are identical to the non-degradable petro-polymers but are made using some monomer from biomass e.g
- Braskem's Polyethylene (route 1 above),
- Syncom’s Polyester (combining monomers from Routes 1 and 2),
- Rennovia’s Nylon 6,6 (Route 3 monomer with some of the glucose converted to hexamethylene diamine).
- Dupont’s Sorona, Poly trimethylene terephthalate, a nylon substitute, combines monomers from routes 2 and 4).