Bioplastics – what does it all mean?

Materials World magazine
,
1 Apr 2010
Compostable bioplastic packaging

Jan Czerski is an expert in polymer materials and part of the IOM3 Materials Information Service. He discusses bioplastics.

No other subject than bioplastics is so hotly debated in the plastics industry, and yet, it is not always clear what the term means.

If a plastic is bio-based then it is made from biomass. However, bioplastic is a collective term for a plastic which is either partially or completely made from a renewable raw material or is degradable due to naturally occurring microorganisms (biodegradable).

The common bio-based polymers are polylactic acid (PLA) and polyhydroxybutyrate (PHB). Polylactic acid is produced by polycondensation from lactic acid, which in turn is obtained by the fermentation of starch. Polyhydroxybutyrates are polyesters formed from bio-based sugar using microorganisms.

Another category of bio-derived plastics replaces a chemical usually obtained from the petrolchemical industry with a plant-based unit. Examples are bio-based polyethylene derived from ethanol produced by the fermentation of plant sugar, a nylon 6 produced from sebacic acid derived from castor oil and polyurethane produced from a polyol also made from castor oil.

Ecoflex, manufactured by global chemical company BASF, is a biodegradable plastic produced like conventional polymers, but it is completely biodegradable. It is similar to polyethylene but can be disposed of by industrial composting and is reduced to CO2 and water.

This material also offers advantages in application because of its tear and water resistance – it can also be printed so is useful in packaging fruit and vegetables. Other applications include carrier bags that at the end of their life are used as biowaste bags and agricultural sheeting that can be ploughed into the soil after use.

Currently 65% of bioplastics are used in packaging and food applications but new uses and innovations are predicted in the automotive and electronic industries.

There are, however, some practical issues to be overcome. One is cost as generally film manufactured from bioplastic is more expensive than that from a traditional polyolefin. Also the presence of a bioplastic in mixed plastics waste affects the recycling by lowering the molecular weight of PET and making the recycled product unsuitable for reuse.

Seperation of bioplastics from the mixed plastics waste stream is sometimes feasible prior to recycling, but this is expensive.