Polyhydroxyalkanoates (PHA) is a general term for a class of macromolecule polyesters synthesized entirely by microorganisms. It has biodegradability and biocompatibility, so it is considered to be an environmentally friendly material and is widely used in agriculture, Environmental protection, biochemical, micro-electric materials, energy, medicine, medical materials and other fields.
The main PHA production companies in the world include Biomers of Germany, Kaneka of Japan, Danimer of the United States, RWDC of Singapore, Newlight of the United States, Ningbo Tianan Biomaterials, Blue Crystal Microorganisms, Zhuhai Meide Biotechnology, etc., including Guangdong Hefeng Biotechnology. Domestic and foreign companies such as Keneka, Danimer, and Jiangsu Lansu Biomaterials plan to build new PHA projects.
PHA can be divided into two types according to the number of carbon atoms of the monomer: short-chain PHA, whose monomer is composed of 3-5 carbon atoms, such as poly-3-hydroxybutyric acid (PHB), polyhydroxyvalerate (PHV), etc. ; Medium and long chain PHA, its monomer is composed of 6-14 carbon atoms, such as polyhydroxyhexanoate (PHHx), polyhydroxyoctanoate (PHO) and so on.
The PHA biosynthesis method mainly uses the self-metabolism of microorganisms to synthesize products, mainly microbial fermentation methods, including wild bacteria method and recombinant engineering bacteria method, followed by genetically modified plant method and activated sludge method. At present, the research on microbial fermentation method is the most extensive, and with the integrated application of synthetic biology and morphological engineering and other genetic manipulation methods and blue water biotechnology, it is helpful to promote the industrialization process of PHA; while the transgenic plant method and activated sludge method It is beneficial to reduce fermentation costs, but the low yield and difficulty in purification severely restrict the large-scale production and application of PHA.
At present, 4 types of PHA have been industrialized:
Poly 3-hydroxybutyrate (PHB). The discovery and development of PHB was the earliest. Its structure is highly regular, hard and brittle, and its mechanical properties and melting point are similar to those of polypropylene (PP); but it has a narrow processing window, low elongation at break, and high brittleness. Therefore, PHB usually cannot be used as a single material and needs to be modified to achieve the required performance.
Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). Compared with PHB, PHBV has higher hardness; but with the introduction of 3HV monomer, its ductility and toughness have been improved to a certain extent. However, PHBV still has a serious post-crystallization phenomenon, which is not conducive to processing and molding, and the brittleness is still relatively large.
Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx). PHBHHx belongs to short-chain and medium-long-chain copolymerization PHA. Compared with PHB, the introduction of long-chain monomer 3HHx reduces the hardness of the material, increases the ductility, and significantly improves the mechanical properties.
Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB). P34HB combines high strength and ductility, and has entered mass production. With the introduction of 4HB monomer, the thermal stability of P34HB is significantly improved, the processability is improved, and the material properties are adjustable (between the glass state and the rubber state). However, P34HB is sensitive to shear and temperature during processing, and needs to be modified to improve its performance and expand its application areas.
