**2. Starch**

Starch is a biodegradable and widely available natural resource [8], and constitutes the main source of carbohydrate reserves in plants. This polysaccharide is found in different parts of the plants and can be isolated from seeds, fruits, leaves, tubers, and roots [9].

The functionality of starch is largely due to its two components of high molecular weight: amylose and amylopectin. Most of the starches contain between 20 and 30% of amylose and 70 and 80% of amylopectin; these proportions depend on the plant source. Amylose molecules consist of approximately 200–20,000 glucose units joined by α‐1,4 glycoside bonds (**Figure 1**) in unbranched chains or coiled helix [10].

Thermoplastic Starch (TPS)‐Cellulosic Fibers Composites: Mechanical Properties and Water Vapor Barrier: A Review http://dx.doi.org/10.5772/65397 87

**Figure 1.** Segment of an amylose molecule [10].

**1. Introduction**

86 Composites from Renewable and Sustainable Materials

Current research studies have been focusing on the procurement of environmentally friendly materials with the aim of resolving the problems created by materials derived from petroleum. Starch is a promising biopolymer used in the production of biocomposite materials because it is renewable, completely biodegradable, and easily available at a low cost. Starch, in the form of its thermoplastic derivate (TPS), has been revealed as an appropriate candidate to be employed as a substitute of synthetic polymers traditionally used for packaging. Starch is not a real thermoplastic polymer, but can be processed after its gelatinization by mixing it with enough water and/or plasticizers [1, 2]. In most investigations the plasticization of the material is carried

TPS films are reported to have low permeability to gases, poor water vapor barrier properties,

Therefore, improving the resistance of TPS films to traction forces is a factor that must be taken into consideration for their use [5, 6]. The use of reinforcing agents in the starch matrix is an effective means of overcoming these drawbacks and several types of biodegradable reinforce‐ ments such as cellulosic fibers, whiskers, and cellulose nanofibers (CNF) have been utilized to develop new and inexpensive starch biocomposites. Cellulose is the most abundant, renewable polymer in the world; it is found in plant cell walls and it can also be synthesized by some bacteria. Its reinforcing property is remarkable [7]. Basically two types of nanoreinforcements

Improving the mechanical and water barrier properties by the addition of CNF (extracted from different botanical sources) can depend on the correct dispersion and the generation of an

This chapter provides the latest advances in green composite materials based on TPS and cellulose fibers and includes information on compositions, preparations, and the properties of "green" composite materials elaborated from TPS and cellulose fibers, with the focus on using

Starch is a biodegradable and widely available natural resource [8], and constitutes the main source of carbohydrate reserves in plants. This polysaccharide is found in different parts of

The functionality of starch is largely due to its two components of high molecular weight: amylose and amylopectin. Most of the starches contain between 20 and 30% of amylose and 70 and 80% of amylopectin; these proportions depend on the plant source. Amylose molecules consist of approximately 200–20,000 glucose units joined by α‐1,4 glycoside bonds (**Figure 1**)

the plants and can be isolated from seeds, fruits, leaves, tubers, and roots [9].

out by casting a dispersion of starch with glycerol [1, 3].

and must resist the tensions arising from their use in packaging [4].

can be obtained from cellulose: microfibrils (or CNF) and whiskers.

active nanoreinforcement/matrix interface.

in unbranched chains or coiled helix [10].

undervalued natural resources.

**2. Starch**

The structure of amylopectin is different from that of amylose; amylopectin molecules contain α‐1,4 and α‐1,6 glycosidic bonds, as can be seen in **Figure 2**. The glycosidic bonds join the glucose molecules in the main amylopectin chain. Branches of the main chain are often found, which are due to the α‐1,6 glycosidic bonds with other glucose molecules.

**Figure 2.** Segment of an amylopectin molecule [10].

The bonding points of the branches constitute between 4 and 5% of all the bonds [11]. Amy‐ lopectin molecules are significantly larger than the amylase molecules; some contain be‐ tween 10,000 and 20,000,000 glucose units. The molecular weight of amylose is between 0.1 and 1 million g/mol while that of amylopectin ranges between 10,000 and 1000 million g/mol [10].

One of the most important properties of natural starch is its semicrystallinity and amylopectin is the dominant component for crystallization in most starches. The significant commercial properties of starch, such as mechanical resistance and flexibility, depend on the resistance and character of the crystalline region, which in turn depend on the amylose/amylopectin ratio and thus on the type of plant; these properties also depend on the distribution of molecular weight, degree of branching, and the conformation process of each polymeric component [12].

Starch is versatile due to its variety of uses; it is also one of the most important ingredients at an industrial level. In the food industry, starch is used to provide a wide range of functional 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, plastics, pharmaceutical, and adhesives.

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 food utensils and packaging material [14].

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 industry.

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


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