Use of Lignocellulosic Materials for PHA Production

Life of modern civilization is accompanied by accumulation of huge amounts of non-degradable solid waste materials. A major portion of this resistant waste is represented by synthetic polymers of petrochemical origin. The accumulation of plastic wastes has become a very important environmental issue1. Conventional synthetic polymers are problematic not only because of their long decomposition time, but they also release various toxic substances during the process of degradation. Hence, there is strong motivation to replace synthetic polymers with materials that can be readily eliminated from our biosphere in an “environmentally friendly” fashion2. Furthermore, the industrialized world is currently highly dependent on fossil resources as a supply of energy for industrial processes, and also substrate for the production of a wide range of chemicals and materials. Since the fossil fuels area is finite, its depletion results in a serious global problem. All carbon-based structural materials (such as plastics, foams, coating, and adhesives) owe their properties to long arrays of carbon–carbon bonds. Therefore, one of the challenges of the research today is to find an approach to produce a substitute for petrochemical-based polymers using sustainable renewable sources3. Polyhydroxyalkanoates (PHAs) are generally considered as an alternative to petrochemical-based synthetic polymers. These microbial polyesters are synthesized and accumulated as intracellular granules by some microorganisms belonging to the Bacteria and Archaea domains of life. These storage materials serve as the carbon and energy reserves of the producing microorganisms. PHAs are commonly grouped into two major categories: the shortchain-length (scl-) and the medium-chain-length (mcl-) PHAs. The repeat units of scl-PHAs are composed of hydroxy-acids having three to five carbon atoms, whereas, mcl-PHAs contain hydroxy-acids repeat units with six or more carbon atoms. In general, the scl-PHAs are more crystalline than the mcl-PHAs. As such, scl-PHAs usually exhibit thermoplastic-like properties, while mcl-PHAs behave like elastomers or adhesives4. Due to their physical characteristics, scl-PHAs can be used for manufacturing items for packaging or everyday plastics commodities. Therefore, they compete on the market with poly-(olefins) and, in the field of Use of Lignocellulosic Materials for PHA Production