**Chemical Modification of Starch with Synthetic**

**Chemical Modification of Starch with Synthetic**

DOI: 10.5772/intechopen.72384

#### Aurelio Ramírez Hernández Aurelio Ramírez Hernández Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.72384

#### **Abstract**

An alternative for solving the environmental pollution problems generated by conventional plastics, it is the chemical modifications graft-type of the starch with synthetic polymers of post-consumer and in situ polymerizations on the starch granules. The starch modified by this methodology allows to counteract the disadvantages of both polymers such as the little or no biodegradability of the synthetic polymer and the poor mechanical properties of the starch. In the present study, a review on the chemical modification of starch with synthetic polymers by grafting is carried out. Factors affecting the copolymerization reactions of starch-g-synthetic polymer were analyzed, for example, their chemical nature, solubility, size and length of polymer chains, temperature, catalyst and starch/amylose content, as well as their characterization chemistry and the potentials applications of this copolymer.

**Keywords:** starch, synthetic polymer, graft copolymer, biodegradable

### **1. Introduction**

process to modify the starch is the ionizing radiation process. The radiation ionizing can come from UV, gamma, or accelerated electrons; at first instance, this process was used with synthetic polymers, but today it is used with starch. The radiation produces free radicals that react

Figure 2. Relative comparison of process conditions and its effect on granular structure for physical treatments of starch.

Instituto Politécnico Nacional, Centro de Desarrollo de Productos Bióticos, Yautepec, Morelos,

with starch polymers to produce different properties on the ionized polymers.

Figure 1. Relative comparison of the physical and chemical treatments of starch.

Author details

2 Applications of Modified Starches

Mexico

Emmanuel Flores Huicochea

Address all correspondence to: efloreshu@outlook.com

Due to environmental pollution generated by conventional plastics such as polyethylene (PE), polypropylene (PP), vulcanized rubber, polystyrene (PS) and polyvinyl acetate (PVC), to name a few, several investigations have been carried out to generate materials that can compete or be an alternative to the excessive use of these plastics because these are not biodegradable. From this point of view, the use of natural polymers such as starch can contribute to reduce the negative impact of conventional plastics. However, materials made from starch alone generate plastics, which have important disadvantages such as their high affinity for moisture and poor mechanical properties. An alternative for solving these disadvantages is the chemical modifications of the starch with synthetic polymers of postconsumer and in situ polymerizations on the starch granules. These chemical modifications are called graft-type copolymerizations because the synthetic polymer chains are chemically bonded to the surface of the starch granule, as if these were hair extensions (**Figure 1**).

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

the natural and the synthetic polymer, that is, its hydrophilic and hydrophobic nature, will allow to propose a reaction medium to carry out a chemical interaction between these two polymers. For example, polyethylene is a non-polar semi-crystalline polyalkane, which would hardly carry out a copolymerization reaction with the starch by simply mixing both polymers. But the addition of some compatibilizing liquid between PE and starch could facilitate its chemical interaction [1]. Based on the commercial classification of the synthetic polymers and their functional group, the compatibility between the starch and each of the

Chemical Modification of Starch with Synthetic http://dx.doi.org/10.5772/intechopen.72384 5

For example, synthetic polymers classified commercially with numbers 2, 4, and 5 would be more difficult to combine with starch compared with classified numbers 1, 3 and 6. On the other hand, there is a great diversity of synthetic polymers classified with number 7 that present chemical compatibility with the starch. The degree of compatibility of the functional

Carboxylic acids > acid anhydrides > esters > acid halides > amides > nitriles > aldehydes > ketones > alcohols > mercaptans > amines > ethers > sulfides > alkenes > alkynes > halogenides

The chemical interaction of the starch with the functional groups of the synthetic polymers results in the production of graft-type copolymers. This type of chemical modification of starch is of great interest worldwide and represents an opportunity to recycle synthetic polymers or to generate materials that are more environmentally friendly and at the same time represent a chemical and physical challenge to improve the properties of starch. Starch graft copolymers are becoming important materials worldwide due to their potential applications

The solubility of the starch and the synthetic polymer in a given solvent plays a very important role in defining the process or the medium of copolymerization, that is, in homogeneous phase

**Synthetic polymer Commercial classification Functional group**

High-density polyethylene, HDPE 2 Alkane, ethyl

Low-density polyethylene, LDPE 4 Alkane, ethyl Polypropylene, PP 5 Alkane, propyl Polystyrene, PS 6 Aromatic, arylethyl

groups of the synthetic polymers with the starch has the following order:

in agriculture, medical, and food sectors [8], to mention a few examples.

Poly(ethylene terephthalate), PET 1 Ester

Polyvinyl chloride, PVC 3 Vinyl

Others 7\* —

This number is assigned to more than 100 synthetic polymers.

**Table 1.** Classification and functional group of synthetic polymers.

synthetic polymers could be predicted (**Table 1**).

> nitros > alkanes.

**2.2. Solubility**

\*

**Figure 1.** Graft copolymerization of starch-g-synthetic polymer.

Numerous investigations have been reported on physical modifications (i.e., blends or composites) between starch and synthetic polymers [1–5] and few investigations on chemical modifications of copolymerization between these two polymers [6, 7]. This represents a good opportunity to recycle the existing plastic or generate new biodegradable materials through copolymerization reactions. The modified starch by this methodology allows to counteract the disadvantages of both polymers such as the little or no biodegradability of the synthetic polymer and the poor mechanical properties of the starch, to mention some characteristics that generate a wide range of applications of the resulting copolymer. For this reason, the chemical and physical knowledge of synthetic polymer and starch is vital to propose and carry out a possible synthesis of starch-g-synthetic polymer. This chapter analyzes the chemical modification of starch with synthetic polymers by grafting, and factors that affecting the copolymerization reactions of starch-g-synthetic polymer are analyzed, for example, their chemical nature, solubility, size, and so on.
