Poly B-hydroxybutyrate–co-B-hydroxy valerate (PHBV): Structure, Properties & Usages

Poly(β-hydroxybutyrate-β-hydroxyvalerate) is abbreviated as PHBV. PHBV is a bio-based polymer with three primary characteristics: biodegradability, biocompatibility, and biodegradability (biosynthesis starting from renewable resources). These make PHBV an excellent substitute for non-degradable synthetic polymers and play an important role in the circular economy concept. However, PHBV has several shortcomings, limiting its commercial application. These include poor mechanical characteristics, limited heat stability, problematic processability, and high hydrophobicity. PHBV is used in specialty packaging, orthopedic devices, and controlled drug release. In the environment, PHBV is degraded by bacteria. Here we will learn more about the properties, structure, and application of PHBV and answer some important questions.

Key Takeaways: Poly(β-hydroxybutyrate-β-hydroxyvalerate), Polymer, Copolymerization, Specialized packaging, Orthopedic devices, Synthetic polymers, Hydrophobicity, PHBV, Biosynthesis

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What is Poly(β-hydroxybutyrate-β-hydroxyvalerate)?

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Poly(3-hydroxybutyrate-co-3-hydroxyvalerate), also known as poly(3-hydroxybutyric acid-co-3-hydroxyvalerate) or simply poly(hydroxybutyrate-co-3-hydroxyvalerate), is made by adding 3-hydroxyvalerate (HV) units to a PHB biopolymer.

Biodegradable Polymers Classification

PHBV is an aliphatic polyester and the chemical structure given by,

Chemical Structure of PHBV

• It is abbreviated as PHBV or PHBHV.
• It is a polyhydroxyalkanoate-type polymer.
• It is a biodegradable, non-toxic, biocompatible plastic made by bacteria.
• It is a good substitute for several non-biodegradable synthetic polymers.
• It can withstand UV rays and has adequate levels of alcohols, lipids, and oils.
• It is, however, a hard and brittle polymer with a lower melting temperature than PHB and the ability to dissolve in chlorinated solvents
• It's a linear aliphatic polyester that's thermoplastic that can be heated to soften.
• Copolymerization of 3-hydroxybutanoic acid and 3-hydroxypentanoic acid produces it.
• PHBV is used for specialty packaging, orthopedic devices, and controlled drug release
• (Controlled drug delivery technology is one of the fastest evolving fields of science in which chemists and chemical engineers are making a difference in human health care).
• In the environment, PHBV is despoiled by bacteria.

Also Read: Aniline

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Formation

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Under growth-limiting conditions, bacteria produce PHBV as storage molecules. Recombinant Escherichia coli(a bacteria) strains to manufacture it from glucose and propionate.

Many other bacteria, such as Paracoccus denitrificans and Ralstonia eutropha, can produce it as well. It's also possible to make it from genetically modified plants.

3-hydroxybutanoic acid and 3-hydroxypentanoic acid copolymerize to form PHBV. In the presence of an oligomeric aluminoxane catalyst, PHBV can also be made from butyrolactone and valerolactone.

The chemical reaction that results in the formation of PHBV is

Or, 

CH₃−CH(OH)−CH₂−COOH + CH₃−CH₂−CH(OH)CH₂COOH → [−O−CH(CH₃)CH₂−C(O)−O−CH(C₂H₅)−CH₂−C(O)−]n

In PHBV, 3-hydroxybutanoic acid, 3-hydroxypentanoic acid, and the monomers, are linked by ester bonds. The polymer's backbone is made up of carbon and oxygen atoms.

• The ratio of these two monomers in PHBV determines its properties. 
• Stiffness is provided by 3-hydroxybutanoic acid, while flexibility is provided by 3-hydroxypentanoic acid.
• By altering the monomer ratio, PHBV can be made to resemble either polypropylene or polyethylene.
• Melting point, water permeability, glass transition temperature (Tg), and tensile strength all rise when the ratio of 3-hydroxybutanoic acid to 3-hydroxypentanoic acid rises. Impact resistance, on the other hand, is diminished.

Also Read: Maltose

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Properties

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1. PHBV is a thermoplastic polymer that is a form of plastic made up of polymer resins that are soft when heated and hard when cooled. 
2. It is easily broken.
3. Has a low elongation at break, or fracture strain. So, its natural ability to withstand shape changes and start cracking.
4. It isn't very impact resistant. Hence it has a low power to withstand permanent deformation produced by a large force or shock applied in a short time.

Polyhydroxybutyrate (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) have different physical properties (PHBV). Some of them are given here:

Also Read: Micelle

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Uses of PHBV

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PHBV is used in manufacturing various products like

1. Controlled release of pharmaceuticals, medical implants, and repairs.
2. In specialty packaging, orthopedic devices.
3. In the production of customer goods bottles.
4. As it is biodegradable, it makes a viable replacement for non-biodegradable plastics.
5. It is beneficial to mankind because it is a biodegradable polymer that does not pollute the environment.

PHBV Uses

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Decomposition of PHBV

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• PHBV is broken down by bacteria.
• PHBV degrades into carbon dioxide and water when discarded.
• Microorganisms use PHBV as an energy source, similar to how humans use lipids.
• They create enzymes that break down it and devour it.
• The ester bond is cleaved by an elimination reaction, thus PHBV has limited temperature stability.
• Because hydrolytic breakdown happens slowly, it can be used in medical applications.

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Disadvantages of PHBV

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PHBV is a good alternative to synthetic non-biodegradable polymers generated from petroleum since it is biodegradable, biocompatible, and renewable.

The PHBV, on the other hand, has a significant drawback in it such as:

• Overly rigid,
• Brittle,
• Lacks exceptional mechanical qualities that are necessary for applications
• Expensive
• Thermal stability is poor
• Problems with processing

Also Check: High-Density Polyethylene

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Things to Remember

1. Poly(β-hydroxybutyrate-β-hydroxyvalerate) is also known as PHBV. It is a polyhydroxyalkanoate-type polymer.
2. PHBV is the result of the copolymerization of 3-hydroxybutyric acid and 3-hydroxypentanoic acid.
3. Poly-hydroxybutyrate-co-hydroxy valerate (PHBV) is an acronym for poly-hydroxybutyrate-co-hydroxy valerate.
4. The chemical reaction that causes PHBV to be produced is:
   CH₃−CH(OH)−CH₂−COOH + CH₃−CH₂−CH(OH)CH₂COOH → (−O−CH(CH₃)CH₂−C(O)−O−CH(C₂H₅)−CH₂−C(O)−]n
5. It is employed in specialized packaging, orthopedic devices, and drug release control.

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