The present study was focused on improvement of the competitiveness of Azotobacter chroococcum 23 produced PHB in two directions: 1) seeking for convenient raw materials for PHB biosynthesis; 2) PHB blending with plasticizers in order to obtain PHB composite materials with controllable physical, thermal properties and biodegradability. Corn starch syrup (PHB content 10,2g/l and 9,8g/l, Yp/s 0,26g/g and Yp/s 0,28g/g on glucose and corn starch syrup consequently) was most convenient unrefined carbon source for PHB production . The effect of blend composition on the changes of most important factors of polymeric systems, influencing biodegradability, crystallinity and intrinsic viscosity was evaluated. An essential increase in PHB-based films flexibility was obtained using lower molecular weight plasticizers - dibutylsebacate (DBS), dioctylsebacate (DOS), polyethylen glycol (PEG) 300 upon plasticizer content 20 - 30 w.%.
Use of biodegradable polymers as a part of recycling can be offered as a sound argument and a partly solution for the plastic waste problem. Polyhydroxyalcanoates (PHAs) are natural biodegradable thermoplastics. One of such polymers is poly-b-hydroxybutyrate (PHB), accumulated by many bacteria as carbon and energy reserve material . The production of PHA from renewable resources, offers additional ecological advantages of the polymer as compared to thermoplastics and elastomers produced from fossil carbon sources . The suitability of a bacterium for the PHA production depends on many different factors such as stability and safety of the organism, growth and accumulation rates, achievable cell densities and PHA contents, extractability of PHA, molecular weights of accumulated PHA, range of utilizable carbon sources, costs of the carbon source and other components of the medium, and occurrence of by-products . As thermoplastic polymer PHA can be processed like other synthetic thermoplastics however some polymer properties thermal stability, brittlness and relatively high cost - are reasons limiting its processing and use.
Modification of PHB through blending with high and low molecular components provides a potentially relatively inexpensive and simple route to change and regulate properties of polymeric material and offers opportunities to obtain cost - competitive polymers as compared to traditional polymers and processable materials simultaneously preserving their specific property - ability to biodegrade. Various attempts have been made to blend PHB with synthetic and natural polymers [4-8] and determine the influence of the second component on the physical properties and biodegradability of the blends.
With an aim to improve the competitiveness of PHB an effect of unrefined carbon sources on A. chroococcum 23 growth, PHB production and polymer properties have been investigated. The influence of plasticizers on PHB physical properties and PHB-based films biodegradability have been investigated as well.