The earth has finite resources in terms of fossil origin fuel and a finite capacity for disposal of waste. Biopolymers may offer a solution to both these issues in the long-term. The ideal biopolymer is both of renewable biological origin and biodegradable at the end of its life. In some cases material may be of a biological origin and not readily biodegradable, such as thermosets made from cashew nut shell liquid. On the other hand, polyvinyl alcohol is an example of a polymer of a synthetic origin and biodegradable.
Environmental degradation can involve enzymatic pathways and microorganisms such as bacteria and fungi, or chemical pathways such as hydrolysis. It is important that biopolymers have an adequate life span for applications - their biodegradability makes them ideal for use in resorbable medical products such as sutures, in short-term packaging applications for fast foods and fresh groceries, and for sanitary uses.
This review sets out to examine the current trends in biopolymer science. The different types of biological polymers are discussed. The chemistry and synthesis of some key biopolymers is described, including cellulose, hemicellulose, starch, polyhydroxyalkanoates (of bacterial origin), tannins (polyphenolic plant products), cashew nut shell liquid, rosins (from tree sap), lignin (from wood), and man made polylactides. Many other biopolymers are also being investigated, for example, alginates from seaweed and algae, and proteins such as casein and soybean. The abstracts at the end of this report cover an extensive range of materials and are fully indexed.
Commercially, bioplastics have proven to be relatively expensive and available only in small quantities. This has lead to limitations on applications to date. However, there are signs that this is changing, with increasing environmental awareness and more stringent legislation regarding recyclability and restrictions on waste disposal. Cargill Dow has a polylactic acid polymer in production (Natureworks). Metabolix has been working on polyhydroxyalkanoates (Biopol). Several companies have been developing starch products such as Avebe, Biop, Earthshell and Midwest Grain Products Inc. Polyols for polyurethane have been obtained from vegetable oils, etc.
Certification of compostability is now available from DIN CERTCO. The requirements for this standard are discussed in the report. Additives can compromise the environmentally-friendly status of a polymer and must be chosen with care. Thus natural fibre reinforcements are also discussed briefly here. Biocomposites have been developed comprising natural origin polymer matrices and natural fibres, such as sugar cane bagasse and jute.
This review is accompanied by over 400 abstracts from papers and books in the Rapra Polymer Library database, to facilitate further reading on this subject. A subject index and a company index are included.
1.2 Biodisintegratables or Biodeteriorating Polymers
1.4 Environmental Impact
1.5 Market Size
2. Synthesis of Biopolymers
2.4 Polyhydroxyalkanoates (PHA)
2.6 Cashew Nut Shell Liquid (CNSL)
2.6.1 The Structure of CNSL
2.6.2 Polymer Synthesis of CNSL
2.9 Polylactic Acids and Polylactides
3. Commercially Available Biopolymers
4. Uses of Biopolymers
4.1 General Uses
4.2 Uses of Specific Polymer Types
5. Manufacturing Technologies for Biopolymers
5.2 Manufacturing Methods
5.3.4 Flame Retardants
5.3.5 Blowing (Foaming) Agents
6. Fillers and Reinforcement for Biopolymers
7.The Markets and Economics for Biopolymers
9.The Chemistry and Biology of Polymer Degradation
Abbreviations and Acronyms
Mark Johnson is currently reading for a doctorate in Engineering Business Management (EngD) at the University of Warwick. Prior to this he worked as a production engineer in composite fabrication. The areas of study of his doctorate are biodegradable composites, their fabrication, performance, biodegradability and the factors affecting their uptake and usage by industry.
Dr. Leonard Mwaikambo
holds the post of Lecturer at the Sokoine University of Agriculture, Tanzania, and is currently a Research Fellow in the Department of Chemistry, University of Warwick. His research concerns the development of sustainably produced, recyclable natural fibre composites. He has keen interest in developing matrices based on polymerised natural oils and fats for composite manufacture.
Nick Tucker's interest in biopolymers was started by a request from the Rover Group to examine the potential effect of biodegradable polymers on end-of-life vehicle disposal. His current research portfolio now covers the economic manufacture and application of low environmental impact biodegradable composites from sustainable resources. In parallel with these activities, he runs the Sustainable Composites Network with the Biocomposites Centre at the University of Wales, Bangor.