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).

摘要 本研究旨在以乙酰化木薯淀粉为原料，制备吸湿性降低、力学性能提升的薄膜。为此，本研究采用乙酸酐作为酯化试剂开展乙酰化改性实验，得到取代度（degree of substitution, DS）分别为0.6（记为S0.6）与1.1（记为S1.1）的醋酸淀粉酯。共设置12组薄膜配方：原生木薯淀粉（S）、S0.6及S1.1醋酸淀粉酯，并搭配两种甘油浓度（0.25 g·100 g⁻¹（25）与0.30 g·100 g⁻¹（30））。所有薄膜在表征前均于相对湿度（relative humidity, RH）58%与75%条件下平衡96小时。本研究对薄膜的水蒸气透过率、水溶解度、吸水等温线、微观结构分析，以及不同相对湿度与甘油浓度下的力学性能进行了表征。结果显示，相较于原生木薯淀粉薄膜（水蒸气透过率为3.79±0.26×10⁻⁷ g/(m·s·Pa)，水溶解度为25.46±0.12 g·100 g⁻¹），S1.1醋酸淀粉酯薄膜的水蒸气透过率（2.35±0.26×10⁻⁷ g/(m·s·Pa)）与水溶解度（21.2±0.16 g·100 g⁻¹）均更低；而S0.6薄膜的拉伸强度（8.42±0.84 MPa）高于S1.1薄膜（6.93±0.55 MPa）。研究结果表明，乙酰化淀粉可用于制备力学性能更佳、水溶解度与水蒸气透过率更低的薄膜，尤其当采用取代度为0.6的醋酸淀粉酯且搭配低浓度甘油时效果更优。本文涉及的化学品如下：淀粉乙酸酯（PubChem CID：24832118）、乙酸（PubChem CID：176）、乙酸酐（PubChem CID：7918）、硫酸（PubChem CID：1118）与甘油（PubChem CID：753）。