THE CONVERSION OF POLYSACCHARIDES INTO POLYURETHANES - A REVIEW

The conversion of polysaccharides into polyurethanes, which has commanded considerable academic and industrial interest over the past 30 years, is reviewed from chemical, structure-property and economic viewpoints. The basic chemistry of polyurethanes and the morphological structure of segmented copolyurethane materials are described. The processes used to fabricate such materials are outlined and the properties required in polysaccharides used as feedstocks for polyurethanes are defined. Several methods of incorporating polysaccharides in polyurethanes are available including their use (i) in unmodified form, (ii) after derivatisation, (iii) after depolymerisation and derivatisation, and (iv) by conversion to non-carbohydrate polyols. (Routes (ii)-(iv) yield a very wide range of glycosidic and non-glycosidic polyol structures.) Specific examples of each route and the advantages of the polyol products for use in polyurethane formation are detailed. Advantages include low cost and structural versatility of the polyols which provide increased cross-linking, and solvent and fire resistance in derived polyurethanes. Some developments in the understanding of the formation of glycosides and their industrial-scale production are presented, together with an indication of the increasing variety of polysaccharide structures used. Methodologies for the production of solid polyurethanes with high carbohydrate contents, compared to foams of relatively low carbohydrate contents, are described together with the structure-property relationships in both types of materials. Finally, the future potential of biotechnology in providing novel carbohydrate structures is briefly considered.