Poly-B-hydroxybutyrate (PHB): A Biodegradable Polymer of Microbial Origin - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 45

Polyamide 11 (Pa 11)
The PA 11 is a biopolymer derived from natural oil. It is also known under the trade
name Rilsan B. The PA 11 belongs to the technical polymers family and is not biode-
gradable. Its properties are similar to those of PA 12, although, emissions of greenhouse
gases and consumption of non renewable resources are reduced during its production.
It is used in high-performance applications like automotive fuel lines, pneumatic air-
brake tubing, electrical cable antitermite sheathing, flexible oil and gas pipes, control
fluid umbilicals, sports shoes, electronic device components, and catheters.
Poly b -hydroxybutyrate and other Polyhydroxyalkanoates
Initially world came to know about PHB by discovery of Maurice Lemoigne of the
Pasteur Institute, Paris in 1925 while studying Bacillus megaterium (Lemoigne, 1925).
When PHB was extracted from the bacteria it crystallizes to form a polymer with
similar properties to polypropylene as shown in Table 2 and is a biodegradable sub-
stitute for thermoplastics. The PHB is accumulated as a carbon reserve under nutrient
limitation.
The PHB was found to be part of a larger family of poly(hydroxyalkanoates) or
PHAs. The PHB is the first type of PHA to be identified (Lemoigne, 1925). The PHB is
microbial polyester accumulated as lipoidic inclusions and that is osmotically inert of
diameter 0.2 to 0.5 µm (Poirier et al., 1992). The P(3HB) inclusions contain approxi-
mately 97-98% P(3HB), 2% protein and 0.5% lipid. The lipid is a mixture of phospha-
tidic acid, triacetin, tributyrin, tripropionin, and other unidentified lipids (Kawaguchi
and Doi, 1990). The P(3HB) granules in vivo are noncrystalline but once isolated are
found to be 60-70 % crystalline.
In these microbial PHB, the ester bond is formed between carboxyl groups of one
monomer with the hydroxyl group of the neighboring monomer. The PHB is active
and isotactic due to the (R) stereochemical configuration (Ballistreri et al., 2001; Lee
et al., 1999).
Extracted PHB are broadly divided into three classes, on the basis of Molecular
weight (MW) after extraction, that are-
(a) Low MW (Reusch, 1995; Reusch et al., 1986; Reusch and Sadoff, 1983),
(b) High MW (Dawes, 1988; Dawes and Senior, 1973), and
(c) Ultra-high MW PHB (Kusaka et al., 1997).
The low MW PHB is widely accumulated by eukaryotes and archaebateria (Reusch,
1992; Reusch and Sadoff, 1983) and having MW < 12,000 Da. It is also called com-
plexed PHB (cPHB). The MW of high MW PHB is in the range of 200,000-30,00,000
Da which is actually depending on microorganism and growth conditions (Byrom,
1994). In contrast to low MW PHB which accumulated as chloroform insoluble in-
clusion, high MW PHB is accumulated as water insoluble and chloroform soluble
inclusion (Haung and Reusch, 1996). The Ultra high MW PHB is synthesized by re-
combinant E. coli when providing a specific growth condition (Kusaka et al., 1997).
The MW of these polymers is >30,00,000 Da. It is particular use for blending and
composite material.