Foreword

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This document was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 14, Environmental aspects, in collaboration with the European Committee for Standardization (CEN) Technical Committee CEN/TC 249, Plastics, in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).

This third edition cancels and replaces the second edition (ISO 14855-2:2018), which has been technically revised.

The main changes are as follows:

the NDIR method to the measurement of evolved carbon dioxide in addition to the conventional gravimetric method has been added;
a schematic diagram of the measurement device and an example of biodegradability measurement using an NDIR sensor have been added to Annex D.

A list of all parts in the ISO 14855 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A complete listing of these bodies can be found at www.iso.org/members.html.

Introduction

Management of plastics waste is a serious problem in the world. Plastics recovery technologies include material recovery (mechanical recycling, chemical or feedstock recycling, and biological or organic recycling) and energy recovery (heat, steam or electricity as a substitute for fossil fuels or other fuel resources). The use of biodegradable plastics is one valuable recovery option (biological or organic recycling).

Several ISO standards for determining the ultimate aerobic/anaerobic biodegradability of plastic materials have been published. In particular, ISO 14855-1 is a common test method that measures the amount of carbon dioxide evolved using methods such as continuous infrared analysis, gas chromatography or titration.

Compared with ISO 14855-1, the amounts of compost inoculum and test sample used in this document are one-tenth the size. In order to ensure the activity of the compost inoculum, inert material that gives the mixture the same texture as soil is mixed into the inoculum. The carbon dioxide evolved from the test vessel is determined by absorbing it in a carbon dioxide trap and carrying out gravimetric analysis of the absorbent. The method described in this document, which uses a closed system to capture the carbon dioxide evolved, can also be used to obtain valuable information, by means of isotopic-labelling studies, on the way in which the molecular structure of co-polymers degrades.

In addition to traditional gravimetric methods, this test method adds a new way to measure carbon dioxide using spectroscopic non-dispersive infrared (NDIR) technology, significantly reducing the routine work and chemical use required for quantitative measurement without compromising the quantitative accuracy of chemical methods.

1 Scope

This document specifies a method for determining the ultimate aerobic biodegradability of plastic materials under controlled composting conditions by gravimetric measurement of the amount of carbon dioxide evolved. The method is designed to yield an optimum rate of biodegradation by adjusting the humidity, aeration and temperature of the composting vessel.

The method applies to the following materials:

natural and/or synthetic polymers and copolymers, and mixtures of these;
plastic materials that contain additives such as plasticizers or colorants;
water-soluble polymers;
materials that, under the test conditions, do not inhibit the activity of microorganisms present in the inoculum.

NOTE If the test material inhibits microorganisms in the inoculum, another type of mature compost or pre-exposure compost can be used.

2 Normative references

3 Terms and definitions

4 Principle

5 Reagents

5.1

5.2

5.3

5.4

5.5

5.6

6 Apparatus

6.1

6.2

6.3

6.4

6.5

6.6

6.7

6.8

6.9

7 Procedure

7.1 Preparation of the inoculum

7.2 Preparation of the sea sand

7.3 Preparation of test material and reference material

7.4 Starting up the test

7.5 Measurement of the evolved carbon dioxide

7.6 Incubation period

7.7 Termination of the test

8 Calculation

8.1 Theoretical amount of carbon dioxide evolved by test material

8.2 Percentage biodegradation

9 Expression and interpretation of results

10 Validity of results

11 Test report

Bibliography