Publications

Biodegradable Plastics - Developments and Environmental Impacts

Nolan-ITU Pty Ltd
Prepared in assocation with ExcelPlas Australia
October, 2002

Potential Positive Environmental Impacts

Full life-cycle assessment studies of biodegradable plastics in comparison to conventional petroleum-based plastics are required. However, environmental benefits that may be derived from the use of biodegradable plastics compared to conventional materials are outlined below.

9.1 Composting

Compost derived from biodegradable plastics along with other organic products increase soil organic carbon, water and nutrient retention, while reducing fertiliser inputs and suppressing plant disease. The composting of biodegradable plastics also cycles matter rather than 'locking' it up in persistent materials, particularly when the non-degradable plastics are destined for landfill.

9.2 Landfill Degradation

The use of biodegradable shopping and waste bags may have the potential to increase the rate of food degradation in landfills, and therefore have the potential to enhance methane harvesting potential where infrastructure is in place and decrease landfill space usage. The use of biodegradable plastic film as daily landfill covers has the potential to considerably extend landfill life, as they could replace traditional soil cover material which use approximately 25% of landfill space.

9.3 Energy Use

The energy required to synthesise and manufacture biodegradable plastics is shown in Table 9.1, along with values for high density and low density polyethylene. PHA biopolymers presently consume similar energy inputs to polyethylenes. New feedstocks for PHA (see Section 3.1) should lower the energy required for their production.

Source: 'Review of Life Cycle Assessments for Bioplastics' by Dr. Martin Patel, Utrecht University, Netherlands, Nov. 2001.

9.4 Greenhouse Gas Emissions

An important environmental impact of biodegradable plastics is their contribution to greenhouse gas (GHG) generation when they biodegrade.

In the manufacture of hydrocarbon polymers, carbon is taken from one carbon sink (e.g. an oil deposit) to another carbon sink (plastic) with no net production of atmospheric carbon other than that generated during energy production for the conversion process.

Carbon in the form of carbon dioxide is 'fixed' during the growth of the plants, and can be used in the production of some biodegradable polymers. This carbon is then returned to the air when the polymers degrade. The EPI polymers on the other hand, convert carbon from petroleum deposits ultimately into atmospheric carbon. In this case, they are removing carbon from a carbon sink and contributing to greenhouse gases. Greenhouse gas emissions include manufacturing emissions as well as emissions from end-of-life waste treatment of biodegradable plastics are shown in Table 9.2.

Source: 'Review of Life Cycle Assessments for Bioplastics' by Dr. Martin Patel, Department of Science, Technology and Society, Utrecht University, Netherlands, Nov. 2001.

As shown in Table 9.2, biodegradable plastics result in relatively low greenhouse gas emissions in comparison to some polyethylenes. This is particularly obvious for starch-based plastics.