Handbook of Biodegradable Polymers

Catia Bastioli

• Publisher: De Gruyter
• Year: 2020
• Print ISBN: 9781501519215
• eBook ISBN: 9781501511981
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Environmental Science

This handbook covers characteristics, processability and application areas of biodegradable polymers, with key polymer family groups discussed. It explores the role of biodegradable polymers in different waste management practices including anaerobic digestion, and considers topics such as the different types of biorefineries for renewable monomers used in producing the building blocks for biodegradable polymers.

1 Methods for evaluating the biodegradability of environmentally degradable polymers

Maarten van der Zee

1.1 Introduction

This chapter presents an overview of the current knowledge on experimental methods for monitoring the biodegradability of polymeric materials. The focus is, in particular, on the biodegradation of materials under environmental conditions. Examples of in vivo degradation of polymers used in biomedical applications are not covered in detail, but have been extensively reviewed elsewhere, e.g., [1–3]. Nevertheless, it is important to realise that the degradation of polymers in the human body is also often referred to as biodegradation.

A number of different aspects of assessing the potential, rate and degree of biodegradation of polymeric materials are discussed. The mechanisms of polymer degradation and erosion are reviewed, and factors affecting enzymatic and nonenzymatic degradation are briefly addressed. Particular attention is given to the various ways of measuring biodegradation, including complete mineralisation to gases (such as carbon dioxide (CO₂) and methane (CH₄)), water and possibly microbial biomass. Finally, some general conclusions are presented with respect to measuring the biodegradability of polymeric materials.

1.2 Background

There is a worldwide research effort to develop biodegradable polymers for agricultural applications or as a waste management option for polymers in the environment. Until the end of the 20^th century, most of the efforts were synthesis oriented and not much attention was paid to the identification of environmental requirements for, and testing of, biodegradable polymers. Consequently, many unsubstantiated claims of biodegradability were made, which has damaged the general acceptance.

An important factor is that the term biodegradation has not been applied consistently.

In the medical field of sutures, bone reconstruction and drug delivery, the term biodegradation has been used to indicate degradation into macromolecules that stay in the body but migrate (e.g., ultrahigh molecular weight (MW) polyethylene (PE) from joint prostheses), or hydrolysis into low MW molecules that are excreted from the body (bioresorption), or dissolving without modification of the MW (bioabsorption) [4, 5]. On the other hand, for environmentally degradable plastics, the term biodegradation may mean fragmentation, loss of mechanical properties, or sometimes degradation through the action of living organisms [6]. Deterioration or loss in physical integrity is also often mistaken for biodegradation [7]. Nevertheless, it is essential to have a universally acceptable definition of biodegradability to avoid confusion as to where biodegradable polymers can be used in agriculture or fit into the overall plan of polymer waste management. Many groups and organisations have endeavoured to clearly define the terms ‘degradation’, ‘biodegradation’ and ‘biode­gradability’. But there are several reasons why establishing a single definition among the international community has not been straightforward, including:

• The variability of an intended definition given the different environments in which the material is to be introduced and its related impact on those ­environments.
• The differences of opinion with respect to the scientific approach or reference points used for determining biodegradability.
• The divergence of opinion concerning the policy implications of various definitions.
• Challenges posed by language differences around the world.

As a result, many different definitions have officially been adopted, depending on the background of the defining organisation and their particular interests. However, of more practical importance are the criteria for calling a material ‘biodegradable’. A demonstrated potential of a material to biodegrade does not say anything about the time frame in which this occurs, nor the ultimate degree of degradation. The complexity of this issue is illustrated by the following common examples.

Low-density PE has been shown to biodegrade slowly to CO₂ (0.35% in 2.5 years) [8] and according to some definitions can thus be called a biodegradable polymer. However, the degradation process is so slow in comparison with the application rate that accumulation in the environment will occur. The same applies for polyolefin- starch blends which rapidly lose strength, disintegrate and visually disappear if exposed to microorganisms [9–11]. This is due to utilisation of the starch component, but the polyolefin fraction will nevertheless persist in the environment. Can these materials be called ‘biodegradable’?

1.3 Defining ‘Biodegradability’

In 1992, an international workshop on biodegradability was organised to bring together experts from around the world to achieve areas of agreement on definitions, standards and testing methodologies. Participants came from manufacturers, legislative authorities, testing laboratories, environmentalists and standardisation ­organisations in Europe, USA and Japan. Since this fruitful meeting, there is a general agreement concerning the following key points [12]:

• For all practical purposes of applying a definition, material manufactured to be biodegradable must relate to a specific disposal pathway such as composting, sewage treatment, denitrification and anaerobic sludge treatment.
• The rate of degradation of a material manufactured to be biodegradable has to be consistent with the disposal method and other components of the pathway into which it is introduced, such that accumulation is controlled.
• The ultimate end products of the aerobic biodegradation of a material manufactured to be biodegradable are CO₂, water and minerals, and the intermediate products should include biomass and humic materials. (Anaerobic biodegradation was discus...

Table of contents

• Title Page
• Copyright
• Contents
• Acknowledgments
• Preface
• References
• 1 Methods for evaluating the biodegradability of environmentally degradable polymers
• 2 Biodegradation behaviour of polymers in liquid environments
• 3 Environmental fate and ecotoxicity assessment of biodegradable polymers
• 4 Ecotoxicological aspects of the biodegradation process of polymers
• 5 International and national norms on biodegradability and certification procedures
• 6 General characteristics, processability, industrial applications and market evolution of biodegradable polymers
• 7 Polyhydroxyalkanoates
• 8 Starch-based technology
• 9 Lactic acid-based degradable polymers
• 10 Biodegradable Polyesters
• 11 Material formed from proteins
• 12 Enzyme catalysis in the synthesis of biodegradable polymers
• 13 Environmental life cycle of biodegradable plastics
• 14 The use of biodegradable polymers for the optimisation of models for the source separation and composting of organic waste
• 15 Collection of biowaste with biodegradable and compostable plastic bags and treatment in anaerobic digestion facilities: Advantages and options for optimisation
• 16 Principles, drivers, and analysis of biodegradable and biobased plastics
• 17 Biorefineries for renewable monomers
• 18 Research and development funding with the focus on biodegradable products
• Abbreviations
• Index