Petrochemical plastics has brought great progress for people's basic necessities of life and has been widely used in the fields of household appliances, packaging materials, construction facilities, medical equipment, etc. However, the degradation of petrochemical plastics can not be slowed down or even degraded. The problem of ecological white pollution Play more weight.
Picture source: Biocatalysis
How to develop and apply a biodegradable material that can replace petrochemical plastics has become a research hotspot of scientists.
Polyhydroxyalkanoates (PHA), a class of biodegradable plastics, stand out among a host of biodegradable materials due to their outstanding properties, and let's move closer to these materials.
Introduction
PHA is a kind of bio-based materials synthesized by microorganisms. It is the product of bacteria when the growth conditions are unbalanced. The physiological function of PHA is firstly as the storage source of carbon source and energy in bacteria. French scientist Lemoigne found that for the first time in Bacillus megaterium he found Poly-3-hydroxybutyrate (PHB) natural polymer
The greatest feature of PHA is that it can be decomposed by microorganisms in almost any environment (composting, soil and seawater) and is expected to be an environment-friendly polymer material, promising hope of solving 'white pollution'.
Picture source: danimerscientific
Synthesis method
Polyhydroxyalkanoates (PHA) synthesis methods biosynthesis and chemical synthesis of two kinds.
Biosynthetic method
Bacterial synthesis: Different microorganisms can convert different fermentation substrates to PHA under suitable conditions.
Genetic engineering: Introduction of the enzymes involved in the production of PHB from the genus Alcaligenes that are eutrophic bacteria into oil plants to obtain transgenic plants and cloning of synthetic PHB from the cells or plastids of these transgenic plants The gene approach eliminates the isolation of PHB from bacteria in the bacterial process Purification steps, can reduce the cost of synthesis.
Chemical synthesis method
Beta-butyrolactone ring-opening polymerization process in two ways:
method one: The bond between the carbonyl group and the oxygen atom in the lactone ring is broken and the racemate is rare in the product.
Way two: The bond between the β-carbon atom and the oxygen atom in the lactone ring is cleaved to produce enantiomerically occurring
Racemic effect.
Category
PHA because of its monomer is a chiral R-type hydroxy fatty acids, the monomer can have a variety of side chains, a variety of carbon chain length, so the polymerization of PHA is also diverse, there are more than 100 different single Body is reported.
Depending on the number of carbon atoms in the PHA monomer, PHA can be divided into two categories:
In the last ten years, PHAs composed of two or more monomers have drawn much attention, and therefore, according to the types of monomers, it can be said that the PHAs fall into two categories.
Different PHA performance comparison
Application areas
As a new functional material, PHA can be made into film, bottle and injection molding, also can be spun into fiber, made of fabric, so it can be widely used in plastic film, orthopedic surgery, personal hygiene products, drug controlled release, special packaging, etc. However, due to the current high cost, it is mainly used in biomedical and cosmetic fields such as surgical sutures and drug release systems.
Disposable plastic products made of PHA, the waste in the ecological environment is easily broken down by many microorganisms such as bacteria, fungi and algae into CO2 and H2O, do not pollute the environment.
Picture source: danimerscientific
Because PHA has good biocompatibility, it can be used as a carrier for surgical sutures and drug delivery systems in medicine, and cosmetic beads can be made in daily life.
Picture source: engineering
PHA can be used as a graft for animal and human tissues, and its stent made into certain tissues is implanted into the body.
It can be made into fixed skeleton materials such as bone nails, bone rods and the like in orthopedic surgery. It has the reinforcing effect. The rough surface can promote the growth of human tissues. The pores can be used for infiltration and exchange. When new tissues grow, the PHA Gradually degradation, decomposition of the product can be absorbed by the body, will not cause adverse reactions.
Skeletal soft tissue
PHA prosthetic heart valve
Image Source: Aquamarine Lab
PHA can be used to make decomposable fibers and textiles.
Using ordinary wet spinning method can be made into fibers, such as made of gauze, wound healing has an excellent effect; to PHA as material, can be made of medical gloves, dressing materials, tampons, medical films and other medical supplies.
Picture source: DuPont
Picture source: DuPont
Picture source: danimerscientific
PHA is optically active and has a chiral carbon in every building block that can be used for chromatographic analysis to separate optical isomers.
PHA has piezoelectric properties, can be made of piezoelectric components, for pressure sensors, ignition, acoustic instruments and oscillators, etc., but also as a transducer, especially in vivo transducers.
Picture source: wageningen
PHA gas barrier properties (CO2 and O2 can only be slowly transmitted), suitable for packaging materials.
Picture source: danimerscientific
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