Agro-polymers

Guilbert, S., Gontard, N. 2005. Agro-polymers for edible and biodegradable films Review of agricultural polymeric materials, physical and mechanical characteristics. In Innovations in Food Packaging, Han, J.H. (ed.). Elsevier Academic Press, Oxford, U.K., pp. 263-276. 

Chitin is the second most abundant agro-polymer produced in nature after cellulose. It appears in nature as ordered crystalline microfibrils forming structural components in the exoskeleton of arthropods or in the cell walls of fungi and yeasts [Rinaudo, 2006]. It is an acetylated polysaccharide composed of N-acetyl-D-glucosamine. 

Proteins are agro-polymers. They are an Important renewable resources produced by animals, plants, and bacteria. The term "protein" comes from the Greek, proteios, for "primary, first and foremost." A certain number of proteins have received much attention as biodegradable polymers but few have led to actual industrial scale-up due to the high production cost and the low... 

As it was previously said, biodegradable polymers tend to consist of ester, amide, or ether bonds. In general, biodegradable polymers can be separated into two main groups based on their structure and synthesis Agro-polymers, or those derived from biomass [7] and biopolyesters, which are those derived from microorganisms or synthetically made from either naturally or synthetic monomers (Fig 24.1). 

Biomass products From agro-resources Agro-polymers 1 From micro-organisms (obtained by extraction) From biotechnology (conventional synthesis from bio-derived monomers) 1 From petrochemical products (conventional synthesis from synthetic monomers)... 

Heat processing of agro-polymer-based materials like cellulose using techniques usually apphed for synthetic thermoplastic polymers such as extrusion, injection, molding, etc., is more cost effective. This process is often used for making flexible films... 

As cited in Guilbert and Gontard, 2005 [3], agro-polymers that have been proposed to formulate edible films or coatings are numerous (Cuq et at, 1995 Guilbert and Cuq, 1998). Plant polysaccharides such as cellulose and derivatives are used in various forms (simple or composite materials, single-layer or multi-layer films). The formulation of bioplastic or edible films implies the use of at least one component able to form a matrix having sufficient cohesion and continuity. They are polymers, which under preparation conditions, have the property to form crystalline or amorphous continuous structures [3]. 

Biodegradable polymers can be mainly classified as agro-polymers (starch, protein, etc.) and biodegradable polyesters (polyhydroxyalkanoates, poly(lactic acid), etc.). These latter, also called biopolyesters, can be synthesized from fossil resources but main productions can be obtained from renewable resources (Bordes et al. 2009). However for certain applications, biopolyesters cannot be fully competitive with conventional thermoplastics since some of their properties are too weak. Therefore, to extend their applications, these biopolymers have been formulated and associated with nano-sized fillers, which could bring a large range of improved properties (stiffness, permeability, crystallinity, thermal stability). The resulting nano-biocomposites have been the subject of many recent publications. Bordes etal. (2009) analyzed this novel class of materials based on clays, which are nowadays the main nanoflllers used in nanocomposite systems. 

Agriculture Derived/Agro-Resources -> Agro-polymers)... 

Biomass products from agro-resources (agro-polymers) These bioplastics are either synthesized naturally from plants and animals, or entirely synthesized from renewable resources. This class includes starch, cellulose, proteins, lignin, chitosan, poly lactic acid (PLA) and polyhydroxy-alkanoates/polyhydroxybutyrates. A recent breakthrough in this class of bioplastics is the development of technology to synthesize polymers like polyethylene, polypropylene and nylon from biological resources ... 

The potential use of agro-polymers in the plastics industry has long been recognized. Agro-polymers are extracted from either plants or animals. They could contribute to a reduction of dependence on fossil resources as agricultural resources are generally sustainable. Some of the polymers in this family... 

It is well known that polymers can generally be classified as either thermoset, thermoplastic, or rubbery. Most agro-polymers do not behave thermo-plastically without some additives and would typically degrade before a flow-able melt can be formed. It is therefore necessary to consider the synthesis route to render these materials ready for thermoplastic processing. 

Understanding how to process agro-polymers with similar properties to synthetic polymers requires an understanding of how these forces are manifested in proteins. The processability of proteins depends on their transition from the glassy to rubbery and viscous-flow states. These transitions are achieved with judicial application of heat, pressure, shear, chemical additives and plasticizers. Specific amino acid residues (primary protein structure) and initial structure (natural protein state) of the protein will influence each of these factors. Based on the structure of proteins and the requirement for thermoplastic processing, three broadly categorized processing requirements have been identified ... 

Selecting appropriate biopolymers for commercial use is a complicated task and involves careful consideration of the properties of the polymeric material. In the context of this chapter, the meaning of the term Characterization of Agro-polymers is twofold. Not only are the techniques used for... 

Mechanical properties can probably be regarded as the most signifieant aspeet of materials, as adequate mechanical properties are required for any application. This is not to say that other physical properties, such as density and thermal conductivity, can be neglected as these are also vital in materials selection. In understanding the mechanical properties of agro-polymers it is useful to compare their behaviour to that of synthetic polymers. 

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