**2.1. Biodegradable polymers**

**1. Introduction**

152 Composites from Renewable and Sustainable Materials

range of applications.

waste.

and bags.

**2. Classification of polymers**

Use of polymers has increased significantly over other types of materials, this more than anything because of its many possible applications, true reflection of the ease offered to

However, conventional polymers remain subject to very specific investigations, primarily aimed at improving their properties, as well as modifications that allow the expansion of its

That is, materials can be prepared with very different properties, for example, polymers with a great structural rigidity, due to a high proportion of aromatic structures in the molecular skeleton or flexible polymers with chains exclusively of the concatenation of aliphatic groups.

These polymers are primarily used for their advantages being chemically inert, lightweight, durable, comfortable and hygienic, and submit versatility of shape and size. It is undeniable that the introduction and advancement in the technology of synthetic polymer‐based petro‐

But nevertheless, to be synthetic compounds, nonbiodegradable and based on petroleum, use poses serious ecological problems, mainly due to the environmental pollution they cause, by manufacturing and incineration as its contribution to the generation and accumulation of

Since the last decades there has been a growing demand of friendly products environment, promoting the development of biodegradable materials based on biopolymers as lipids, polysaccharides, and proteins, which have been studied being renewable raw materials and inexpensive considered as an alternative to plastic nonbiodegradable and based on petroleum.

The replacement of synthetic plastics by biodegradable materials to obtain friendly products environment has not been achieved so far. However, if some synthetic polymers are replaced by other natural, in specific applications such as films, foams, covering, dishes, cups, spoons,

Although there are several elements that can be molecules of synthetic organic polymers, the

According to the process of obtaining, the polymers may be classified in to the following types: **•** Synthetic polymers are obtained by polymerization processes from raw materials of low molecular weight, for example nylon, polystyrene, polyvinyl chloride, and polyethylene.

**•** Semisynthetic polymers are the resultant product of chemical processes of some natural polymers. Examples of these are nitrocellulose, etonita, vulcanized rubber, to name a few.

main elements are carbon (C), hydrogen (H), oxygen (O), and nitrogen (N).

the design of new compositions with very different properties.

leum have brought many benefits to humanity.

Biopolymers are a new generation of materials that are still in development and that have attracted attention as possible replacement‐based materials of conventional plastics due to an increased interest in sustainable development [4–6].

These have been part of humanity since it exists, being that have been part of basic daily needs as fundamental as food and clothing, as well as medical materials, packaging, food additives, engineering plastics, chemicals for water treatment, among many others [7, 8].

Biopolymers used to obtain biodegradable materials have diverse provenances, such as products from vegetable origin (starches, celluloses, pectins, chitosan, zein, etc.); animal origin (casein, whey protein, and gelatin); microbial products (polyhydroxybutyrate and polyhy‐ droxyvalerate) and chemically synthesized polymers from the monomers of natural origin (polylactic acid) [9, 10].

Natural polymers more prominent have been sugar derivatives, polysaccharides, being starch the most used and representative. This is a thermoplastic biodegradable polymer highly hydrophilic, low cost, and high availability [11]. Starch is found in a variety of tissues botani‐ cals, including fruits, seeds, leaves, and tubers [12]. It consists essentially of a mixture of polysaccharides comprised of amylose and amylopectin and, a minority fraction (from 1 to 2%) not forming glycosidic [13]. Most starches in their glycosidic structure is made up of 20% amylose and the remaining 80% amylopectin.

Some application with this biopolymer has been its combination with synthetic polymers (such as polyvinyl alcohol, polyethylene), plasticizers (glycerin, sorbitol), nitrogenous bases, etc., to obtain a material partially biodegradable.

However, there are others polysaccharides obtained from various sources of natural resources (e.g., cellulose and chitosan) that also have been used by both its structure and its functional diversity [14].

The mixture of chitosan with aldehydes produces a harder material, biodegradable, insoluble in water and with high resistance to fats and oils [15]. Cellulose derivatives obtained by chemical modification by esterification of glucose, such as carboxymethylcellulose (CMC), hydroxypropylcellulose, and methylcellulose (MC), are used as food additives in the case of CMC, and in the pharmaceutical industry, the MC and hydroxypropylcellulose are used in pharmaceutical tablets for sustained release of granules.

The most important sectors that are intended to the biodegradable polymers are as follows:


However, the market of biodegradable polymers is an alternative market or replacement, intended to replace as a percentage of conventional materials for biodegradable materials. The demand is being generated from own production companies, appealing to a more ecological sense and responsible consumption, through the use of biodegradable materials. Nevertheless, given the evolution of the oil market with a view to 2020, it is estimated that replacement could reach almost 10% by weight, this involves managing areas for the cultivation of raw materials of which biopolymers are obtained and may present in a way as competitors in agricultural area for biofuels, livestock feed, and human food.

Even if the biopolymers are widely distributed in the nature, only limited number of plants and animals are used extensively for the production of commercial biopolymers. It points to a "exploitation" of natural resources that if not treated as a "management" of these; could become an excessive and irresponsible consumption on natural resources. So, all renewable resource must be replenished twice to meet the needs of current and future generations, and then, things that sustain life should also last in time, should be sustainable.
