Nanocomposites Based on Cassava Starch and Chitosan-Modified Clay: Physico‑Mechanical Properties and Biodegradability in Simulated Compost Soil

Abstract

Organic-inorganic nanocomposites based on cassava starch, glycerol and chitosan-modified Veegum ® HS clay mineral at two different low polymer-to-clay ratios (2.5 and 5.0 wt.%) were prepared by extrusion producing flexible, transparent and homogeneous plastics as potential candidates for agricultural purposes. X-ray diffraction and transmission electron microscopy images revealed the presence of both intercalated and exfoliated nanocomposites in all samples, in which exfoliation is the predominant type of microscopic structure. Statistically significant improvements of over 20% on the tensile strength and Young's modulus were observed for samples containing chitosan-modified clay in comparison to pristine thermoplastic starch. Chitosan deeply affects the conversion of polymer carbon to CO 2 through biodegradation. Mineralization values for the sample loaded with 5.0 wt.% of chitosan-modified clay in simulated compost soil showed a reduction of almost 40% in comparison to thermoplastic starch, benefiting applications where delay degradation is required.Keywords: organic-inorganic hybrids, nanocomposites, extrusion, cassava starch, Veegum clay IntroductionPolymers produced from biodegradable resources have been intensely investigated over the past decades in an effort to decrease human reliance on fossil-based materials, especially over growing concerns about improper discard of these materials. [1][2][3] In particular, naturally occurring polymers or commonly known as biopolymers, macromolecules with large abundance across the globe, seem potential candidates to replace partially or totally oil-based plastics in many applications. 1,3 Among them, biopolymers made from or blends with starch appear in a growing number of reported studies as a potential material with a broad array of applications. In fact, starch possesses several properties desired in modern materials, such as large availability from different sources obtained in all regions, low cost associated to both cultivation/harvesting and also processing to obtain the final product and full biodegradability under regular disposal conditions. 4,5 Cassava starch is composed mainly of two types of polysaccharides, amylose and amylopectin. 1,6 Even though amylose to amylopectin ratio might not be constant depending on the cassava species, it is usually around 1:4, respectively.7 While both polysaccharides are constituted by the same monomer unit called α-D-glucopyranose, amylose possesses almost exclusively 1-4 α linkages, originating short linear chains ( Figure 1a). 1,8 On the other hand, amylopectin features not only the presence of 1-4 α linkages, but also 1-6 α linkages, yielding much larger and coiled structures (Figure 1b). 9 In order to transform cassava starch on a plastic material, it is necessary to disrupt its hierarchical coiled structure. 10 Addition of plasticizers such as glycerol or urea, among others, is often needed during the production Nanocomposites Based on Cassava Starch and Chitosan-Modified Clay J. Braz. Chem. Soc. 650 of ther...

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