Agropolymers

Agropolymers represent two large groups of polymers polysaccharides and protein-based polymers. Here, we describe both classes in detail. 

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ENSAM-INRA Montpellier, Joint Research Unit Agropolymers Engineering and Emerging Technologies, Montpellier, France, claire.bourlieu univ-montp2.fr... 

We can classify the different biodegradable and bio-based polymers into two major families agropolymers (categoiy a) and biodegradable polyesters (categories b and c). To illustrate the latter, the next section focuses on the description of biodegradable polyesters, from synthesis to application. 

Agropolymers are mainly extracted from plants. They are biopolymers, and for the most part they are biodegradable. There are different famihes such as polysaccharides, proteins, lignins and taimins. They share a relatively hydrophilic nature. Most of them can be processed directly, plasticized, used as fillers or chemically modified. 

The topic of cellulose and its derivatives has largely been discussed in many treatises. Cellulose is the most abundant agropolymer on Earth. It is a linear polymer made of units of D-glucose linked by P (1-4) bonds and synthesized by plants and bacteria. In order to obtain a thermoplastic material, cellulose is modified, e.g. by acetylation to obtain cellulose acetate. 

Protein-based materials have also been abundantly discussed in other publications [ZHA08], The next section of this chapter is, therefore, primarily oriented toward one example of an agropolymer starch. World production of starch-based materials for bioplastic applications is far from negligible. Put differently, it is greater than or ecpral to that of PLA. 

In order to preserve the final compostabihty, different blends of biodegradable materials have been developed. There is a vast body of literature available in this domain. We find certain associations with agropolymers such as proteins [ARV 99, FIS 00, OTA 99] or pectins [FIS 00], but most research focuses on blends of plasticized starches and biodegradable polyesters PCL, PHA, PBSA, PBAT, etc. These polyesters, described previously, are produced industrially. They exhibit interesting properties such as a more hydrophobic natiue, limited water permeability and improved mechanical properties, in comparison to polysaccharides. However, the cost of biodegradable polyesters is generally higher than that of starch... 

Bionanocomposites are an ecological alternative to conventional nanocomposites based on petroleum-derived polymers, as they are based on biodegradable polymers obtained from renewable resources. Biomass is the source of agropolymers like starch and cellulose and also of monomers used to chemically synthesize polymers like polylactic acid (PLA). Other kinds of biopolymers, e.g., xanthan gum and poly (hydroxyalkanoates), are produced by microorganisms. Even though most of the bionanocomposites reported in the hterature are based on layered sihcates, the number of examples illustrating the use of fibrous clays in the preparation of new bionanocomposites is growing rapidly. 

Like polymers, biodegradable polymers have been classified using distinct methods, including methods based on polymer origin (synthesis), renewability content, and biodegradability level. The most prominent and well-established method is the classification based on synthetic procedmes. In broad terms, these polymers are classified into two main categories (i) agropolymers (obtained from biomass) and (ii) biopolyesters (natural or synthetic biopolymers). Biopolyesters is itself a broad term that includes three subclasses (a) microbially produced polymers (b) polymers synthesized... 

Depending on their origins, biopolymers used as matrices in composite materials are divided into three main classes agropolymer based (renewable sources), microbially derived, and chemically synthesized. Some authors also mention a fourth class, which consists of blends of the aforementioned three classes. 

UMR1208 Agropolymer Engineering and Emerging Technologies Joint Research Unit, INRA/Agro.M/UM2/CIRAD, 2 place P. Viala, 34060, Montpellier Cedex, France... 

Chemical Composition. Along with additives such as plasticizers and moisture content, the chemical structure of the macromolecules used as agropolymers also affects their mechanical properties. For starch, the amylopectin... 

Among the different categories of biodegradable plastics obtained from agropolymers, both starch/polyesters blends and microbial biodegradable plastics satisfied the majority of requirements asked by the plastic packaging industries (material qualities, processability, performances, etc.). Other bioplastics based on natural polysaccharides or proteins are mainly interesting for their low cost but their non-reproduetive quality and lower performances are still a handicap. 

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