Types of Biodegradable Polymers/Plastics

• Cellulose: It is the most abundant of naturally occurring polymers comprising of at least one-third of the vegetable matter in the world. It’s produced from the renewable resources that are based on agriculture. Cellulosic materials are commonly used in textiles, fibers and packaging and are subdivided into two groups- regenerated and modified cellulose. Cellulose is readily biodegradable and is mineralized by variety of microorganisms.

• Starch: This another material obtained from agricultural resources. It’s a carbohydrate that is synthesized in the organs of plants as reserve food supply for periods of dormancy, germination and growth. It’s a condensation polymer of glucose. These materials are widely used in polymer blends and are available in commercial grades suitable for extrusion, injection/blow molding and thermoforming processes.
  
  

• Polyhydroxyalkanoates (Bacterial Polyesters): Polyhydroxyalkanoates (PHA’s), a class of bacterial polyesters are synthesized by a variety of naturally occurring bacteria by the process of fermentation of sugars and lipids. They are products of carbon assimilation employed by micro-organisms as a form of energy storage molecule to be metabolized when other common energy sources are not available. Polyhydroxybutyrate (PHB) is the most common type of polymer that falls in the category of polyhydroxyalkanoates. Several types of bacterial polyesters that are produced by biosynthesis are poly-3-hydroxybutyrate, poly-4-hydroxybutyrate, poly-3-hydroxyvalerate, poly-3-hydroxyhexanoate, poly-3-hydroxyheptanoate etc. and their respective copolymer combinations. Due to their ability to degrade naturally in variety of environments, they will find a lot of applications in disposal items such cups, containers as well packaging and agricultural mulching films to list a few.

• Polylactic Acid (PLA): Polylactic acid (PLA) is thermoplastic aliphatic polyester that can be synthesized from biologically produced lactic acid. Bacterial fermentation is used to produce lactic acid from corn starch or cane sugar which is further processed to produce lactide monomer. This monomer is polymerized by ring opening polymerization to produce polylactic acid. Because lactic acid is difficult to polymerize directly to high polymers in a single step on a commercial scale, most companies used a two-step process. Lactic acid is first oligomerised to a linear chain with a MW of less than 3,000 by removing water.
  
  The oligomer is then depolymerised to lactide, a cyclic dimer. This six-membered ring is purified and subjected to ring-opening polymerization to produce a PLA with a MW of greater than 50,000-110,000. The enantiomeric monomers (D and L) are polycondensed via its cyclic dimer (lactide) by ring-opening polymerization (ROP) to a high molecular weight polymer. Thus, this material can be made stereo specific or racemic to yield different properties. Compared to the other biodegradable polyesters, polylactic acid (PLA) is the product that at the present time has one of the highest potentials due to its availability in the market and its low price. PLA and its copolymers have been used widely in medicine and surgery for the controlled release of drugs, biodegradable surgical sutures and implants for fixation of fractures, primarily because of their high biocompatibility. Also, different properties associated with its tunability and its availability favor its actual developments in different packaging applications (trays, cups, bottle, films, etc.). PLA is considered to be fully biodegradable and generally undergoes hydrolytic degradation.
  
  

• Polycaprolactone (PCL): Polyvinyl Alcohol (PVA) is a semi-crystalline water soluble synthetic polymer made from polyvinyl acetate. This material is also found to be biodegradable and mineralized in various environments.
  
  
• Aliphatic Copolyesters (PBS and PBSA): Polyvinyl Alcohol (PVA) is a semi-crystalline water soluble synthetic polymer made from polyvinyl acetate. This material is also found to be biodegradable and mineralized in various environments.
  
  
• Aromatic Copolyesters: Compared with totally aliphatic copolyesters, aromatic copolyesters are often based on terephthalic diacid. BASF markets a product, Ecoflex®, which is a copolyester of butanediol, adipic acid, and dimethyl terephthalate. Eastman’s Eastar Bio Copolyester 14766 is similar aliphatic/aromatic copolyester.
  DuPont markets a modified PET known as Biomax. An increase of terephthalic acid content in these polymers tends to decrease the degradation rate.
  
  
• Polyvinyl Alcohol: Polyvinyl Alcohol (PVA) is a semi-crystalline water soluble synthetic polymer made from hydrolysis of polyvinyl acetate. This material is also found to be biodegradable and mineralized in various environments. The degree of solubility and biodegradability as well as other physical attributes can be controlled by varying the MW and the degree of hydrolysis of the polymer.