April 18, 2011
Here’s a green route to poly(butylene terephthalate). Increasingly, traditional petrochemical companies and entrepreneurial biotech startup companies are developing environmentally responsible process technologies for the production of polymers and plastics. This technology can take various directions, including
- converting renewable feedstocks to products that would normally be considered petrochemical-based (e.g., producing so-called green polyethylene from bioethanol);
- converting renewables to biodegradable plastics that have no analogue made from oil or gas; and
- converting a petrochemical-based plastic waste that would normally be taken to a landfill to a useful new product.
P. Agarwal and co-inventors used the first and third scenarios to make an environmentally friendly version of poly(1,4-butylene terephthalate) (PBT). In their method, scrap poly(ethylene terephthalate) (PET) is depolymerized in the presence of 1,4-butanediol (BDO), and ethylene glycol is removed under vacuum.
In one example, 100 g of green recycled PET pellets, with an intrinsic viscosity of 0.68–0.78, is combined with 134 g BDO (2.9:1 mol ratio) in a 500-mL reaction kettle. The temperature is ramped up to 225 °C, and the agitator is set at 20 rpm. At this point, 0.2 mL of catalyst, an organic titanate, is added, and the reaction mass reaches a temperature of 227 °C, the BDO boiling point. The mixture is maintained at reflux for 2 h.
To allow polymerization, the reflux condenser is removed, and a vacuum of 0.199 kPa is applied. The polymer molecular weight increases rapidly under these conditions. Analysis of the resulting polymer shows 49.1 mol% repeat terephthalate units and 47.0 mol% repeat BDO units. The concentration of ethylene glycol repeat units is only 2.3 mol%.
This PBT production method represents the third category. The inventors also give examples in which BDO is made by hydrogenolyzing biologically derived succinic acid—a process that combines the first and third methods to produce PBT. (Sabic Innovative Plastics [Bergen op Zoom, The Netherlands.] US Patent 7,902,263, March 8, 2011; Jeffrey S. Plotkin)