The degradation process of starch-based polymers occurs through enzymatic action on the glucosidic linkages between the sugar groups. This enzymatic attack results in the shortening of polymer chains and the release of sugar units (monosaccharides, disaccharides, and oligosaccharides) that can be easily utilized in biochemical pathways.
Starch composites (10% starch)
Starch can be utilized as an eco-friendly additive or substitute material in conventional petroleum-based commodity plastics. When starch is incorporated into polymers derived from petroleum, such as polyethylene (PE), it expedites the disintegration of the blend, but not necessarily the biodegradation of the polyethylene component. The presence of starch hastens the disintegration or fragmentation of the synthetic polymer structure. As a result, microbial activity digests the starch, producing pores in the material that reduce its strength and facilitate its fragmentation.
Starch Composites (50% Starch)
Composites containing 50% starch, also known as plastified starch materials, have mechanical properties comparable to traditional plastics like PP, and are usually resistant to oils and alcohols. However, they break down when exposed to hot water. These materials consist mainly of corn starch, a renewable natural substance that makes up 40-80% of the composition, and may also contain performance-enhancing additives and other biodegradable materials.
Starch Composites (90% Starch)
Usually referred to as thermoplastic starch, these materials are stable in oils and fats, but their stability in hot/cold water depends on the type. They can be processed using traditional plastic techniques. At lower starch contents (less than 60%), the starch particles act as weak links in the plastic matrix and as sites for biological attack. This allows the polymer matrix to disintegrate into small fragments but not for the entire polymer structure to actually biodegrade.
Certain TPS grades are also fully water-soluble, along with the biodegradation of the polymers by sugar molecules. The wheat starch-aliphatic polyester blend, as studied by Lim et al. , demonstrated excellent biodegradability, with complete biodegradation within eight weeks in soil burial tests.
These blends exhibit excellent properties and are ideal for use as commodity biodegradable plastics. Polyvinyl alcohol (PVOH) is blended with starch to produce readily biodegradable plastics. Since PVOH is readily water-soluble, the starch/PVOH blends are degraded through hydrolysis and biodegradation of the sugar molecules.