3.1 Introduction

This chapter begins with an examination of the mechanisms of polymer biodegradation, how biodegradation mechanisms are measured and the factors affecting biodegradation. This is followed by a review of the different classes of biodegradable polymers, their chemical composition, properties, performance characteristics and processing technologies.

3.2 Definitions of Biodegradable Polymers

Biodegradability and compostability are clearly defined by the scientific community and were legally incorporated into a Standard by the American Society for Testing and Materials (ASTM), under reference ASTM D 6400 - 99, in July 1999. Similar definitions have been recognised in several countries around the world, the most significant being DIN CERTCO 54900 in Germany. Harmonisation of the definitions was carried out through the International Biodegradable Products Institute (BPI), which signed a memorandum of understanding with the Japanese Biodegradable Plastics Society and the German DIN CERTCO.

The ASTM defines a biodegradable plastic as a degradable plastic in which the degradation results from the action of naturally occurring microorganisms such as bacteria, fungi and algae.

Composting is defined as a managed process that controls the biological decomposition of biodegradable materials into a humus-like substance called compost; the aerobic and mesophilic and thermophilic degradation of organic matter to make compost; the transformation of biologically decomposable materials through a controlled process of bio-oxidation that proceeds through mesophilic and thermophilic phases and results in the production of carbon dioxide, water, minerals and stabilised organic matter (compost or humus).

Following the international agreement on definitions for biodegradable plastics, specified periods of time, disposal...