Closed-loop strategy for valorization of starch : From starch to functionalized starch biomaterials and bioplastics

Sammanfattning: The desire to utilize renewable resources and avoid wastes drives us to develop new concepts for material design. Non-edible starch feedstocks and starch bioplastic wastes were previously considered useless. However, with a proper design and process chain, starch-rich biomasses are a promising resource for production and modification of future materials. Therefore, a top-down and closed-loop strategy for valorization of starch through a circle consisting of “StarchÞEnhancerÞNew starch product” is developed and demonstrated in this work. Starch, as a model for starch rich waste resources, was converted into valuable chemicals or carbon products through a two-step decomposition. The valorization products were then utilized as property enhancers in starch-rich biomaterials and bioplastics through design of “structure adapted utilization”: i.e., the obtained products were included in the design of starch-rich products aiming at property enhancement or introduction of new properties. This leads to the closed-loop strategy for valorization of starch.Through a two-step processing, starch was converted into two categories of value-added products: water soluble degradation products (mixture of glucose, levulinic acid (LA) and formic acid (FA)), and 0D nano-graphene oxide (nGO, smaller than 100 nm in all dimension). Specifically, in step one, through acid-catalyzed microwave-assisted reaction; starch was converted to a mixture of glucose, LA and FA in soluble phase and carbon spheres (C-spheres) as a solid residue phase. In step two, the insoluble C-spheres were further oxidized under oxygen-rich acidic conditions to obtain multifunctional nGO.Through “structure adapted utilization”, four routes were designed to efficiently utilize the two categories of value-added products as functional enhancers for new starch-rich products. On one hand, starch-derived biomedical scaffolds were developed in route 1 and 2: nGO could stabilize porous 3D starch scaffolds (route 1) and starch nanofibrous scaffolds (route 2), and meanwhile endorse them the ability to induce biomineralization. On the other hand, starch-rich (and fully starch-derivable) bioplastics were developed in route 3 and 4: nGO effectively compatibilized poly lactic acid/starch composites enhancing the mechanical performance and barrier properties (route 3) and the water soluble degradation products plasticized starch films reducing their brittleness (route 4).Along this closed-loop pathway, the material value of starch was significantly improved and minimum waste was derived, paving towards the sustainable environment and circular economy.