Bacterial plastics

So far, the following building blocks can be produced microbially for polymerization purposes hydroxyalkanoic acids with many structural variations, lactic acid, succinic acid, (i )-3-hydroxypropionic acid, bioethylene produced from dehydration of bioethanol, 1,3-propanediol, and c/ s -3,5-cyclohexadiene-I,2-diols from microbial transformation of benzene and other chemicals. They have been successfully used for making various bacterial plastics. 

In this chapter, we will give an overview of these bacterial plastics. 

Fig. 1 Most common bio-based polymer building blocks for bacterial plastics...

Bacterial plastics Biosynthesized monomers Polymeri- zation approach M xlO W Poly- dispersity T .ec) r (°c) 7 Mechanical properties Young s Elongation Tensile modulus at break strength (MPa) (%) (MPa) References... 

Bacterial plastics have some weaknesses that need to be addressed. Modification of their structures can normally bring about the expected results. Chemical and physical modifications are commonly adopted to improve their properties (Table 3). 

Table 2 Microorganisms reported to degrade the bacterial plastics and some applications of bacterial plastics... 

Table 3 Structural and property modification of the bacterial plastics... 

A number of studies were made to produce structural alterations along the chain of bacterial plastics to improve the properties, among which copolymerization has been of primary interest (Aamer et al. 2008 Baki and Steinbiichel 2007 Hossein et al. 2008 Grimsdale and Miillen 2006 Table 3). 

The advantage of blending bacterial plastics with other polymers is to offset the relatively high cost and to further improve the physical properties, tailoring the plastic to a specific performance-cost profile (Table 3). 

Blending of the above-mentioned bacterial plastics 1 1 or 1 2 may bring about more improvements in their properties. Involvement of starch or cellulose that can bring down the cost of the bacterial plastics should be an area to which attention should be paid. The rapid expansion of PLA applications has shown how important cost is for the success of a bio-based polymer. In the end, it is not easy to convince customers to pay more for environmental reasons if they have a cheaper choice. 

Due to the possibility that petroleum supplies will be exhausted in the next decades to come, more and more attention has been paid to the production of bacterial plastics including polyhydroxyalkanoates (PHA), polylactic acid (PLA), poly(butylene succinate) (PBS), biopolyethylene (PE), poly(trimethylene terephthalate) (PTT), and poly(p-phenylene) (PPP). These are well-studied polymers containing at least one monomer synthesized via bacterial transformation. 

With the snpport of the above experts, we are able to offer the readers up-to-date information on the bacterial plastics. We are grateful to the authors who have contributed these excellent chapters. Our thanks also go to Springer for publishing this monograph, especially to Jutta Lindenbom for all his/her effort in helping us. 

Polyhydroxyalkanoates (PHAs), also known as microbial polyesters , or bacterial plastics are biosynthetic, biocomapatible, and biodegradable thermoplastics. They are bacterial storage polymers produced by various microorganisms (e.g., A.eutrophus, P.oleovorans, R.rubrum, Rb.spaeroides) in response to nutrient limitation occuring in the presence of an excess of carbon (see Chapters 9 and 10), and function as intracellular reserves of carbon and energy as well as ion sinks. 

---