Biodegradation?

A 17-year investigation on the archaeology of landfills was published by Dr William L Rathje in the National Geographic magazine on May 1991. Some of the astounding findings was that foodstuffs buried 18 years before did NOT decompose significantly in landfill. The lettuce, corn, hot dog and bread roll looked as if they were just mummified, and didn't break down into simpler or smaller substances. Newspapers which were 11 years old looked as good and completely readable as though they were just kept in the attic.

So if manufacturers claim that you can be guiltless in consuming their products because they are packaged in biodegradable plastic bottles or wrappers, which you then throw away into the garbage bin and ultimately ends up in landfill, you can now imagine what that bioplastic junk would look like in the next couple of decades or so.

Remember that bioplastics are expected to degrade only in the conditions set up in industrial composters, not in home composters nor in landfill sites. So unless there is a system for collecting back these used bioplastic packaging you can consider them as destined for the landfill.

This picture might be changing in the future, as some councils are now starting to use UR-3R waste management facilities (that stands for Urban Resource- Reduction, Recovery, Recycling) such as the one run by Global Renewables at Eastern Creek. UNSW subscribes to the UR-3R service. Under this system, recyclable paper, metal and plastic are mechanically separated; compostable materials are refined into organic growth media (it is not clear whether this system can handle bioplastics); and the rest used as a renewable energy source.

PBS Polybutylene Succinate

PBS polybutylene succinate claims to be a fully biodegradable macromolecular polymer that decomposes naturally into CO2 and H2O under specific conditions (contact with soil, light, heat, natural water).

It is used in making bioplastic films, bags, boxes, cosmetic bottles, electronic parts packing, disposable diningware, disposable medical articles.

Bionolle was one of the first PBS bioplastics.

TPS thermoplastic starch

TPS thermoplastic starch is the most important and widely used bioplastic. It is used in making capsule casings for pharmaceutical drugs. A common TPS is PSM plastarch material from corn; it biodegrades well in compost, wet soil, and water.

TPS is generally made into biodegradable bioplastic films, which are converted into shopping bags, bread bags, bait bags, over wrap, 'flushable' sanitary product backing material, and mulch film. They are also used for foamed starch loose fill packaging and injected moulded take-away containers (usually with the addition of glycerol as plasticizer and polyvinyl alcohol).

TPS blended with either PCL polycaprolactone or PVA polyvinyl alcohol yields such commercial bioplastics Mater-Bi (from Novamont, Italy) and Bioflex (from BioTech, Germany). Mater-Bi was used for biodegradable catering items and garbage bags during the Sydney 2000 Olympics.

More information at European Plastic Films and on Wikipedia.

Bioplastics

Bioplastics or organic plastics include all plastics derived from renewable plant sources, such as vegetable oil or corn starch, as opposed to petroplastics from fossil fuel sources. They are potentially biodegradable and compostable, and are now popularly used for disposable packaging (trays and containers for fruit, vegetables, eggs, meat; bottles for softdrinks and dairy products), disposable tableware (crockery, cutlery, drinkware, straws) as well as shopping bags.

Europe accounts for 60% of the biodegradable materials market. In Japan bioplastics are used not for biodegradable applications, but as a thermoplastic from renewable sources, such as for car interiors and mobile phones.

The most common bioplastics are made from
TPS thermoplastic starch
PLA polylactic acid
PBS polybutylene succinate

The European Bioplastics Association shows examples of various bioplastic products here.

More information on Wikipedia.

Note that some bioplastics are NOT designed to be biodegradable. Their avoidance of extracting non-renewable resources is their major environmental benefit, rather than their potential to reduce the bulk of solid waste.

For instance, the 2007 Mazda Premacy Hydrogen RE Hybrid vehicle used PLA fabric for its seats and rigid PLA for its lower panel, shift panel, front console, glove box lid, and hydrogen tank cover.

Mitsubishi was also developing "Green Plastics" for some of its car interiors, such as bamboo-reinforced PBS for trim material and PLA with nylon fiber for its floor mats.

There is a continuing debate on the net environmental benefits of bioplastics. While the sources are renewable, the corn or sugarcane crops do need to be intensively farmed. Moreover despite claims of biodegradability, many bioplastics degrade too slowly, some up to 100 or 1000 years!

Samples of various bioplastics can be found in the FBE Materials Library.or trim material

PLA Polylactide

Polylactic acid or polylactide (PLA) is a biodegradable polyester from fermented corn starch, cane sugar, wheat starch. It can be processed like most thermoplastics into fiber and film. PLA is often made into biodegradable plastic cups, but cannot hold hot liquids unless it is modified into PDLA or PLLA, which increases its melting and glass transition temperatures significantly.

In packaging PLA is used as biodegradable loose-fill, compost bags, sandwich packaging, and disposable cutlery. It is also used for biodegradable sutures, nappies, feminine hygiene products and disposable garments. PLA is more expensive than petroleum-based plastics, but its price has been falling as production increases.

NatureWorks is the world's biggest commercial manufacturer of PLA bioplastic. Its range of PLA consumer products can be found here. Technical data sheets, fact sheets and processing guides are available here.

Some of the Australian brands which use PLA for its bottles are

• Natures Organics haircare line
• Cool Change natural spring water

PLA is compostable and biodegradable in industrial composting conditions, but it will not degrade or disintegrate on the supermarket shelves. In order to degrade, PLA must be exposed to temperatures greater than 60°C and relative humidity greater than 90% (these heat and moisture conditions are optimal for naturally occurring microorganisms to act on the PLA) for approximately 60 to 80 days; after which it composts into carbon dioxide, water, inorganic compounds and biomass. Natureworks advises that PLA will NOT decompose in backyard or home composters (due to lack of temperature and inconsistent conditions). PLA will also not degrade in landfills, due to low oxygen and temperature drops. Industrial composters with carefully regulated temperature, moisture and turning are required.

There are some laboratory tests though which show that PLA can decompose into carbon dioxide and water, such as the one by University of Nebraska. Another study by Iowa State University and University of Costa Rica showed results of visible degradation, but did not claim complete decomposition. Suming Li & Michael Vert's chapter on biodegradation of aliphatic polyesters in the book Degradable Polymers: Principles and Applications claimed that "in particular, it is now well known that PLA polymers degrade completely and rather rapidly in a compost where the temperature is usually between 50 and 60C."

There's another discussion on this on the Greener Package knowledge exchange on sustianable packaging.