Environmentally acceptable bioplastics - ISO Standards play key role

Issue 41 – August 2012

This article by Dr Ramani Narayan first appeared in ISO Focus+ July 2012 and is summarised here with permission from ISO.

Plastics are everywhere, and used in all parts of our lives – from agriculture to electronics to medical devices to packaging. Growing from 1.5 million tonnes in 1950 to 232 million tonnes in 2010, worldwide plastics use is expected to increase further by 3 – 4% a year.

In particular, rapid industrialisation in populated countries such as India and China has resulted in increasing demand.

Plastics are popular as they are lightweight, energy saving, low cost, readily processable, and have unique and versatile properties that can be tailored for specific applications.

However, concern about the sustainability and environmental impact of plastics is driving the development of new 'green plastics'. Plastics are therefore being increasingly re-engineered:

  • To use biobased feedstocks (agricultural crops, residues, and biomass) rather than the current petro/fossil feedstock

  • With the traditional petro/fossil carbon replaced completely or partly by biobased carbon

  • With a reduced carbon footprint and in harmony with the rates and timescale of the biological carbon cycle

  • To consider the carbon dioxide and environmental footprint from converting feedstock to product (the manufacturing process footprint), by using the life cycle assessment (LCA) methodology in ISO 14040:2006 Environmental management – Life cycle assessment – Principles and framework and ISO 14044:2006 Environmental management – Life cycle assessment – Requirements and guidelines

  • To offer end-of-life options such as recycling and complete biodegradability in selected disposal environments like composting, soil, and anaerobic digestors.

ISO Standards play key role

With the introduction of more environmentally acceptable bioplastics, International Organization for Standardization (ISO) Standards play a key role in the regulatory and market acceptance of bioplastics, and contribute to the plastic industry's long-term growth.

For the plastics industry to respond to these new sustainability requirements, Standards were needed. ISO technical committee (TC) 61, Plastics, developed two Standards that provide a platform for future work in the area:

ISO 17422:2002 Plastics – Environmental aspects – General guidelines for their inclusion in standards. ISO 17422 provides guidance on the inclusion of environmental attributes in plastics Standards. It is written primarily for Standards writers planning to incorporate environmental provisions and includes guidance on aspects such as LCA, minimising environmental impact, and balancing product performance with environmental impacts.

ISO 15270:2008 Plastics – Guidelines for the recovery and recycling of plastics waste. ISO 15270 provides guidance to the plastics industry in developing sustainable global infrastructure for plastics recovery and recycling, and markets for recovered plastics. The Standard includes guidance on mechanical, chemical/feedstock and biological-organic recycling, and on energy recovery.

Biodegradability explained

As an end-of-life option, biodegradability uses the power of micro-organisms in the selected disposal environment to remove true biodegradable plastic products. This takes place through the microbial food chain – promptly, safely, and effectively.

When discussing or reporting the biodegradability of a product, the 'disposal environment' must be clearly defined. These frameworks include the composting (compostable plastic), soil, anaerobic digester, and marine environments.

'Reporting time to complete biodegradation' is the time required for complete microbial assimilation of the plastic in the selected disposal environment.

Micro-organisms use carbon substrates as 'food' to extract chemical energy for their life processes. Under aerobic conditions, the carbon is biologically oxidised to carbon dioxide inside the cell, releasing energy that is harnessed by the micro-organisms.

Under anaerobic conditions, carbon dioxide and methane are produced. Thus, a measure of the rate and amount of carbon or carbon dioxide and methane evolved is a direct measure of the amount of carbon substrate being used by the micro-organism (percent biodegradation). This fundamental, basic biology forms the basis for the various ISO/TC 61 Standards.

Within ISO/TC 61, subcommittee (SC) 5, Physical-chemical properties, working group (WG) 22, Biodegradability, has developed a series of standard test methods that teach readers how to measure and report percent biodegradability (percent carbon of the test substrate utilised by the microorganisms) in a targeted end-of-life disposal environment like:

  • composting:

    • ISO 14855-1:2007 Determination of the ultimate aerobic biodegradability of plastic materials under controlled composting conditions – Method by analysis of evolved carbon dioxide – Part 1:2005 General method

    • ISO 14855-2:2007 Determination of the ultimate aerobic biodegradability of plastic materials under controlled composting conditions – Method by analysis of evolved carbon dioxide – Part 2: Gravimetric measurement of carbon dioxide evolved in a laboratory-scale test

    • ISO 16929:2002 Plastics – Determination of the degree of disintegration of plastic materials under defined composting conditions in a pilot-scale test
  • soil:

    • ISO 17556:2003 Plastics – Determination of the ultimate aerobic biodegradability in soil by measuring the oxygen demand in a respirometer or the amount of carbon dioxide evolved
  • and anaerobic digestion

    • ISO 15985:2004 Plastics – Determination of the ultimate anaerobic biodegradation and disintegration under high-solids anaerobic-digestion conditions – Method by analysis of released biogas

Specification for compostable plastics (ISO 17088:2012 Specifications for compostable plastics) provides criteria to be met to make claims of compostability for plastics and is used by certification organisations worldwide.

Biobased plastics

As discussed earlier, replacing petro/fossil carbon with biocarbon offers the intrinsic value proposition of a neutral or zero material carbon footprint. This arises from the short in-balance carbon cycle in which the rate and timescale of carbon sequestration into plants (agricultural crops, residues, or biomass) is in balance (1 to 10 year cycle) with the rate and time scale of use and ultimate disposal of product – a zero material carbon footprint. In contrast, the petroleum or natural gas feedstocks form over millions of years and are not in balance with the use cycle.

Already in the market are biobased resins – polyethylene (PE), polyethylene terephthalate (PET), polyamides (nylons), polyurethanes (PU) and polyesters. New biobased resins include poly(lactic) acid (PLA); and also accepted in the market are PHAs (polyhydroxy alkanoates) and starch, cellulosic derivatives, and blends.

WG 23, Test methods for bioplastics, under SC 5, was formed to provide comprehensive, harmonised ISO Standards for measuring and reporting biobased carbon and biomass content, and the carbon and environmental footprint data of biobased plastics.

The future ISO 16620 Plastics – Determination of biobased content, will consist of three parts:

  • Part 1: Test methods for determining the biobased-carbon content

  • Part 2: Calculating and reporting biobased-carbon content

  • Part 3: Determination and reporting of biobased-plastic content.

Biobased plastics are not necessarily biodegradable-compostable. For example, biobased polyurethane (PE), polyethylene terephthalate (PET), or polyurethanes (PU) are not biodegradable-compostable. The end-of-life strategy for these biobased plastics is recycling.

Poly(lactic) acid (PLA), polyhydroxyalkanoate (PHA), starch, and cellulosic plastics are 100% biobased and fully compostable (biodegradable under composting conditions).

However, not all biodegradable-compostable plastics are biobased. Examples are polybutylene adipate-co-terephthalate (PBAT), and aliphatic polyesters, which are fully biodegradable under composting conditions but derived from petroleum/natural gas feedstocks.

The author Dr Ramani Narayan is Chair of ISO technical committee (TC) ISO/TC 61, Plastics, subcommittee (SC) 1, Terminology; Convenor of working group (WG) 23, Test methods for bioplastics, of SC 5, Physical-chemical properties; technical expert on SC 5/WG 22, Biodegradability and WG 24, Guidance on environmental provisions in plastics Standards; and Convenor of ISO/TC 122, Packaging, SC 4, Packaging and environment, WG 7, Organic recovery.

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Convenor of ISO/TC 122, Packaging, SC 4, Packaging and environment, WG 7, Organic recovery.

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