Biopolymer or Bio-Derived Plastics

FIGURE 4.13 Dependence of the modulus of PVC on plasticizer content. DODP and DIDP are types of phthalates TPU is a thermoplastic PU. Sonrce Reproduced with permission from Pita et al. (2002). 

Most plasticizers including phthalates are not covalently linked (bonded or grafted) to PVC molecules and are free to leach out of the plastic product With plasticized packaging films in direct contact with food, leaching of plasticizer is a concern. 

A biopolymer or bioplastic is a polymer produced by a living organism. Cellulose is the most common biopolymer constituting about a third of all plant biomass. All living things produce other biopolymers such as polynucleotides and proteins. An example of a class of useful biopolymers are the so-called bacterial polyesters that are harvested from bacteria grown under specific conditions. 

A bio-derived plastic on the other hand is biopolymer that is chemically modified to improve its properties. Cellulose from plants can be acetylated to yield cellulose acetate, the bio-derived plastic used in cigarette filters. It can also be xanthated and extruded into cellophane (or Rayon), a bio-derived plastic. Chitin, a biopolymer from crab shells, can be processed (by converting the amide functionalities into amine functionalities) into its amine analog to obtain a bio-derived plastic, chitosan. 

There are a few examples of plasticizers such as epoxy plasticizers in PVC that are covalently linked to the polymer chain. 

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The terms biodegradable plastics and bio-based or bio-derived plastics were already defined in Chapter 4. Plastics can be classified in terms of the source of raw materials into four classes plastics based on fossil-fuel feed stocks, biopolymers made by living organisms, modified biopolymers, and bio-based plastics derived from renewable biomass feedstock. Members of each of these classes can be either inherently biodegradable or recalcitrant when placed in an appropriate biotic environment. BiodegradabiUty is a property or characteristic of plastics and is independent of the feedstock it is based on. This distinction was discussed in detail in Chapter 4 and is further illustrated in Figure 6.11. 

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