Natural product-based materials

Natural products derived from plants are diversified and could be classified under different categories based on their uses. Figure 1 illustrates natural products based on their most common uses and the industries that demand such raw and processed materials. A given plant could produce multiple benefits and could fall into more than one of those categories. This highlights that natural products have extensive uses in various industries and great potential to contribute to a diverse range of products. 

It is interesting to mention that the first truly synthetic (not based on natural products) polymer material was bakelite obtained in 1907 via polycondensation of phenol and formaldehyde. This material had good dielectric properties and was used mainly as an electrical insulator. The most famous polycondensation polymer is probably nylon belonging to the class of polyamides. Other common classes of polycondensation polymers are polyesters (like polyethylene terephthalate), polysiloxanes, polycarbonates, polysulfides, polyethers and polyimides. 

Cellulose is one of the most important natural polymers, a key source of sustainable materials on industry, and an almost inexhaustible raw material. Natural cellulose based materials have been used by our society for thousands of years and their use continues today. The first example was the fabrication of regenerated cellulose filaments by spinning a solution of cellulose in a mixture of copper hydroxide and aqueous ammonia [1]. The chemical modification of cellulose on an industrial scale led to a broad range of products based on cellulose. Since then the isolation, characterization, and search for applications of novel... 

The term polyurethane (PU) covers a number of polymer systems with one common element of chemistry, they contain an —NH—CO—O— linkage. Polyurethanes are used in a variety of applications where the need to form and mould the product into a desired shape makes the use of natural rubber based materials difficult. Such products include soles of shoes such as trainers, conveyor belts, foamed car seats and furniture, wiper blades in printers, etc. By changing the formulation it is possible to change a PU from being a hard material to being a very soft material. 

Adhesive raw materials come from two sources plant based and petroleum based. As was mentioned above, petroleum-based raw materials are becoming more expensive and harder to come by. This has led to a drive to find and manufacture adhesive components based on sustainable or renewable raw materials. Adhesives and sealants have a long history with natural product-based raw materials. The imfortu-nate situation is that adhesive bonds made with natural product-based raw materials are usually not dirrable. Thus, protein-based adhesives can be used to make interior-grade plywood, but synthetic adhesives are used to make exterior-grade plywood. Therefore, the drive to make adhesives cheaper is combined with the drive to make natural product-based adhesives more durable. 

The ease with which amines are extracted into aqueous acid combined with their regeneration on treatment with base makes it a simple matter to separate amines from other plant materials and ni trogen containing natural products were among the earliest organic compounds to be studied Their basic... 

Emulsion Adhesives. The most widely used emulsion-based adhesive is that based upon poly(vinyl acetate)—poly(vinyl alcohol) copolymers formed by free-radical polymerization in an emulsion system. Poly(vinyl alcohol) is typically formed by hydrolysis of the poly(vinyl acetate). The properties of the emulsion are derived from the polymer employed in the polymerization as weU as from the system used to emulsify the polymer in water. The emulsion is stabilized by a combination of a surfactant plus a coUoid protection system. The protective coUoids are similar to those used paint (qv) to stabilize latex. For poly(vinyl acetate), the protective coUoids are isolated from natural gums and ceUulosic resins (carboxymethylceUulose or hydroxyethjdceUulose). The hydroHzed polymer may also be used. The physical properties of the poly(vinyl acetate) polymer can be modified by changing the co-monomer used in the polymerization. Any material which is free-radically active and participates in an emulsion polymerization can be employed. Plasticizers (qv), tackifiers, viscosity modifiers, solvents (added to coalesce the emulsion particles), fillers, humectants, and other materials are often added to the adhesive to meet specifications for the intended appHcation. Because the presence of foam in the bond line could decrease performance of the adhesion joint, agents that control the amount of air entrapped in an adhesive bond must be added. Biocides are also necessary many of the materials that are used to stabilize poly(vinyl acetate) emulsions are natural products. Poly(vinyl acetate) adhesives known as "white glue" or "carpenter s glue" are available under a number of different trade names. AppHcations are found mosdy in the area of adhesion to paper and wood (see Vinyl polymers). 

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