Tuning the Mechanical Properties of Tapioca Starch by Plasticizers, Inorganic Fillers and Agrowaste-Based Fillers

Mechanical properties of tapioca starch-based films were tuned by different additives and additive combinations. The additives included plasticizers (glycerol, sorbitol, and citric acid), inorganic fillers (halloysite and kaolin), and agrowaste-based fillers (milled wood flour and rice bran). In addition, new biobased additives were prepared from wood flour and rice bran through liquefaction reaction. Through different additive combinations, starch-based materials with significant differences in tensile properties were designed. Addition of halloysite nanoclay resulted in materials with improved tensile strength at break and rather low strain at break. The effect of kaolin on tensile strength was highly dependent on the used plasticizer. However, in most combinations the addition of kaolin resulted in materials with intermediate tensile strength and strain at break values. The addition of milled wood flour and rice bran improved the tensile strength, while the addition of liquefied fillers especially liquefied rice bran increased the strain at break indicating that liquefied rice bran could have potential as a plasticizer for starch blends. 1. Introduction There is increasing interest in replacing nondegradable packaging materials with renewable and degradable polymeric materials. Starch-based materials are among the most promising renewable materials due to being abundant, renewable, low-cost, and nontoxic materials [1]. However, the inadequate mechanical properties and hydrophilicity limit the application range of starch-based material. The development of starch nanocomposites has attracted a lot of attention as a way to improve the mechanical properties and reduce the water absorption of starch materials [2]. In most studies 2？:？1 clays, especially montmorillonites with different surface modifications, were used as reinforcing phase due to their ability to be exfoliated [3, 4]. 1？:？1 aluminosilicate clay minerals, such as modified halloysite nanotubes, as well as kaolin have also been shown to enhance the mechanical properties of starch [5, 6]. The type of plasticizer and the organomodification of the nanoclays are important for the homogeneous distribution of the fillers and the clay exfoliation process [7, 8]. It was also shown that blending starch and nanoclay before addition of plasticizer improved the exfoliation process [9]. This allowed the starch to penetrate the silicate layers before the plasticizer did it. Mechanical properties of starch/montmorillonite composites could be additionally enhanced by using, for example, chitosan or polyvinyl