Effect of the degree of acetylation, plasticizer concentration and relative humidity on cassava starch films properties

Abstract

The objective of this study was to develop films with reduced hygroscopicity and improved mechanical properties from acetylated cassava starch. For that, an acetylation procedure using acetic anhydride as the esterification reagent was performed, resulting in starch acetates with degrees of substitution (DS) of 0.6 (S0.6) and 1.1 (S1.1). Twelve films formulations were studied: native cassava starch (S), starch acetate S0.6 and S1.1, with two glycerol concentrations (0.25 g.100 g^-1 (25) and 0.30 g.100 g^-1 (30)). The films were conditioned at the relative humidities (RH) of 58% and 75% for 96 h before characterization. Water vapor permeability, water solubility, water sorption isotherms, microstructural analyses, and mechanical properties in different relative humidity and different glycerol concentration were performed. Starch acetate films (S1.1) resulted in lower water vapor permeability (2.35 ± 0.26 × 10^-7g/m.s.Pa) and water solubility (21.2 ± 0.16 g.100 g^-1) than native starch films (3.79 ± 0.26 × 10^-7 g/m.s.Pa and 25.46 ± 0.12 g.100 g^-1). S0.6 films showed higher tensile strength (8.42 ± 0.84 MPa) than S1.1 films (6.93 ± 0.55 MPa). The results indicated that acetylated starch can be used to produce films with improved mechanical properties, with less water solubility and permeability to water vapor, especially when starch acetate with 0.6 DS and low glycerol concentration are used. Chemical compounds used in this article: Starch, acetate (PubChem CID: 24832118); Acetic acid (PubChem CID: 176); Acetic anhydride (PubChem CID: 7918); Sulfuric acid (PubChem CID: 1118); Glycerol (PubChem CID: 753).

Keywords:
films; starch acetate; biodegradable; physical properties