**3. Thermoplastic starch (TPS)**

To produce a film based on starch, a high content of water or plasticizer is required (glycerol, sorbitol). These plasticized materials (application of mechanical and thermal energy) are known as thermoplastic starches [8].

The development and production of TPS is considered to be important for the reduction of the total quantity of synthetic plastic wastes in the world [24].

properties and is probably the most utilized hydrocolloid [13]. It can be used in flavor encapsulation, as a thickening agent or a filling agent, in bakery products, production of syrups, etc. Starch is also included in many other industries such as textiles, paper, cosmetics,

Currently, the negative environmental impact caused by synthetic polymer wastes, denomi‐ nated plastic materials, is well known and there is now a growing interest in biodegradable materials like starch to substitute the conventional plastic materials, such as polyethylene and polystyrene. A number of studies have reported the use of starch in the manufacture of fast

It is clear that one of the alternatives is the use of starch from nonconventional sources, particularly in countries where there is a high production of raw material for the production of this polymer. Nonconventional sources of starch have attracted much attention, given their diversity of properties, which allow their application in different industries, including the food

**Table 1** shows the amylose content, granule size, and gelatinization temperature of a few starches from nonconventional sources such as chestnut [15], kudzu [16], ramon [17], chayote [18], ‐parota [19], makal [20], sorghum [21], mango [22], and okenia [23], which could be considered for the production of biodegradable materials. In general, the new botanical sources

**Type of starch Amylose (%) Granule size (μm) Gelatinization temperature (°C) Reference Chestnut** 26.6 4–21 61.9 [15] **Kudzu** 22 2–20 64‐83 [16] **Ramon** 25.3 6.5–15 83.05 [17] **Chayote** 12.9 7–50 67.7 [18] **Parota** 17.5–21.3 20–28 76‐78 [19] **Makal** 23.6 12.4 78.4 [20] **Sorghum** 11.2–28.5 Not reported 70–75 [21] **Mango** 9–16 7‐28 77–80 [22] **Okenia** 26 Not reported 71.3 [23]

To produce a film based on starch, a high content of water or plasticizer is required (glycerol, sorbitol). These plasticized materials (application of mechanical and thermal energy) are

are always widely available in the countries, which produce them.

**Table 1.** Characteristics of starches from different botanical sources.

**3. Thermoplastic starch (TPS)**

known as thermoplastic starches [8].

plastics, pharmaceutical, and adhesives.

88 Composites from Renewable and Sustainable Materials

food utensils and packaging material [14].

industry.

TPS is a material which is obtained through the structural disruption (modification) occurring inside the starch granule when it is processed with a low water content and the action of shear force and temperature in the presence of plasticizers which do not evaporate easily during the processing [25].

To date, it is known that the techniques (extrusion, injection molding, and film casting) for processing starch‐based materials are similar to those used for conventional polymers. However, it is important to note that although the processing of starch is complicated, it can be achieved successfully if an appropriate formulation is developed and adequate processing conditions are established [26].

A simple and well‐established technique for producing sheets or films by extrusion is the use of a twin‐screw extruder with a slit or flat film die, followed by a takeoff device for orientation and collection [27, 28].

Foaming extrusion has mainly been used to produce loose‐fill packaging materials, in a similar way to the production of extruded expanded snack foods [29].

Twin‐screw extrusion is the most widely used and is preferred because of its ease of feeding, longer residence time, more extensive shear, and more flexible temperature control [30, 31].

The high viscosity and poor flow properties of starch‐based materials present difficulties during injection molding, while the lack of reliable parameters makes it difficult to design the optimum processing conditions [26].

Compression molding has been intensively investigated for processing starch‐based plastics, particularly in the production of foamed containers, and generally involves starch gelatiniza‐ tion, expanding, and drying. Apart from gelatinization agents, mold‐releasing agents such as magnesium stearate and stearic acid are also often used in formulations to prevent the starch sticking to the mold [26].

The casting technique for preparing starch films includes the preparation of a dispersion, gelatinization at 95°C, casting in acrylic or Teflon plates, and a drying period of approximately 24 h at 40–75°C [32–34]. Glycerol is the most used plastifier in the preparation of starch films. The resulting starch film can have a thickness between 0.02 and 0.10 mm [26].

Over the last few years, much research has focused on the modification of the starch in the production of a good thermoplastic material [35, 36]. A number of mixtures of TPS with biopolymers based on thermoplastic starch are being commercialized with a certain degree of success, by companies such as Mater Bi® (Novamont S.P.A., Italia) in Italy [www.mater‐bi.com], Carghill‐Down® in the U.S., and by others in Spain, Germany, France, Japan, Denmark, and Canada [37].
