Aerobic biodegradation of starch–polyurethane flexible films under soil burial condition: Changes in physical structure and chemical composition

This paper documents the biodegradation behaviour of flexible films produced by physically blended and chemically grafted starch–polyurethane (PU) hybrid materials. Conversion of carbon content into carbon dioxide was measured after 180 days under soil burial condition. Changes in physical structure and chemical composition brought about by the biodegradation were measured using microscopic and spectroscopic methods. The results suggested that the starch component of the hybrid films provided sites for microorganisms to colonise and biodegrade. Films produced from physically blended starch–PU materials had faster biodegradation (72.5%, 180 days) compared with films produced using chemically grafted starch–PU (26.7, 180 days). The biodegradation of starch-only films was 86% under identical condition. Degradation of starch in films produced from physically blended starch–PU occurred first followed by degradation of polyester soft segments of PU. The slow degradation of films produced from chemically grafted starch–PU hybrids was due to covalently bonded structure. These starch–PU films had a sequentially progressing four-stage biodegradation process: (i) moisture uptake from environment and attachment of microorganisms, (ii) hydrolysis of the starch component, (iii) break down of the chemical structure into small molecular units, and (iv) degradation of the polyurethane component at a slower rate. This study demonstrates that the films produced from physically blended starch-PU hybrid materials have a potential as biodegradable flexible packaging.