Is PHBV an example of biodegradable polymer?

In this brief discussion we will be highlighting some of the key aspects of poly(hydroxybutyrate-co-valerate) (PHBV) like its biodegradability, chemical nature, and production. We will further discuss the various uses of PHBV in different fields and know what makes it a better alternative to plastics. 

Is PHBV an example of biodegradable polymer? 

Biodegradable polymers are the ones that decompose by the naturally occurring bacteria within a certain span of time. The synthetic biodegradable polymers have structure and functional group similar to  the naturally occurring biopolymers and hence are easily recognised by many bacteria and fungi. 

Among the many biopolymers present in our nature, PHBV is one of the widely used owing to its biodegradability. PHBV is produced on a large scale by the industries using certain microorganisms in a controlled condition. It is the most biocompatible, biodegradable, compostable and sustainable polymer that is fine tuned to improve strength and elasticity depending on its applications. 

Biodegradable polymers are the need of the hour as the pollution caused by the polyethylene-based polymer is disturbing the environmental balance. The longer degradation of plastic material due to the inability to microbial decomposition is the reason why most plastic has been littered around the earth. 

Researchers are investigating naturally available material that can replace plastic in many of its applications. Naturally occurring plant or animal-based polymers such as cellulose, alginate, chitosan, and gelatine are highly biodegradable and have a variety of applications in tissue engineering. These biopolymers are biocompatible but lack the necessary strength to replace plastic. 

PHBV modified using physical and chemical methods can provide enough tensile and elasticity for its enhanced applications. 

How is PHBV made? 

PHBV is a polymer of two monomer units – 3-hydroxybutanoic acid and 3-hydroxypentanoic acid. There are many ways by which PHBV can be made. In an industrial set up, PHBV are made from butyrolactone and valerolactone in the presence of organic catalysts. The microbes synthesize PHBV and accumulate it as a nutrient store. The following lists some of the known microbes that produces PHBV. 

  • Recombinant Escherichia coli 
  • Paracoccus denitrificans 
  • Ralstonia eutropha 
  • Haloarchaea 
  • Gram negative bacteria 

The extent of biodegradability and biocompatibility depends on the type of microbes that are used for making PHBV. Haloarchaea can accumulate different variants of PHBV whereas PHBV produced by Gram negative bacteria can have endotoxin contaminants that need to be removed before its final processing. 

However, the purely formed PHBV does not come with enough mechanical strength, thermal properties and wettability thereby limiting its use in many applications. In order to overcome these drawbacks, PHBV is modified and combined with other biocompatible polymers or nanoparticles that can imbibe enough strength and flexibility for its application. 

Natural fibers, carbon nanotubes, nanoclays etc. are some of the strength inducing elements that can enhance the property of PHBV while still maintaining its native benefits. 

Photo courtesy: iStock. Bacteria

What are the applications of PHBV? 

PHBV being biocompatible, non-toxic, biodegradable and inert in nature, has many applications. Currently, its main usage is in the medical field where these are used as drug delivery systems, surgical sutures, medical packaging, and cardiovascular stents. 

PHBV are modified to be used for different applications and in industrial sectors they have uses ranging from single use disposable bags, containers, packaging, towels, diapers, and handkerchiefs. This was where plastics used to play a major role in providing leak proof durable objects. With the development of PHBV related products the use of plastic can be reduced to a great extent. 

This not only is a development towards an eco-friendlier option but will also take care of the current plastic waste problem. PHBV based materials also provide an efficient barrier to oxygen, showing chemical inertness with better mechanical properties. Hence it is a promising material for both industrial and medical applications. Its advance use has been noted in medical, agriculture and packaging fields. 

Is PHBV eco-friendly? 

PHBV possesses many eco-friendly properties that make it one of the best polymeric materials to replace plastics. With several modifications and reinforcement using nanoparticles, PHBV mechanical strength and durability can be enhanced to meet the demand. Currently replacing plastic with biodegradable material is the ultimate solution for a safe environment. 

Rather than depending on the non-renewable energy resources for plastic production, a renewable and sustainable bioplastic is the hope for everyone. Since PHBV is produced by microbes or naturally accruing molecules, these are promptly biodegradable. Several studies have demonstrated the biodegradability property in soil, water, and compost. 

Some of the studies have shown that its biodegradability is dependent on the temperature and is optimum at 40 deg Celsius. Furthermore, the degradation also depends on the molecular weight of the PHBV with low molecular weight PHBV degrading faster that the high molecular weight PHBV.

Conclusion

In this short report we have discussed the different aspects of the biopolymer PHBV and highlighted the different application of PHBV in the fields of medical, agriculture and industries. On a final note we have identified the properties that make PHBV preferable over plastic. 

Frequently asked question (FAQs): Poly(hydroxybutyrate-co-valerate) (PHBV) – a biodegradable polymer 

Is PHBV biodegradable? 

Biodegradability is the ability of any material to naturally decompose to simple elements such as water and carbon dioxide. Most naturally occurring things such as fruits and vegetables are easily degraded by the action of microbes. PHBV is made from naturally occurring microbes that accumulate it as their energy conserve. 

Being produced by microbes, this polymer is biodegradable, and its biodegradability is tested in soil, water, and compost which yields good results. Some studies have shown the effect of different temperatures on the biodegradability of PHBA. Others have proved that with reinforcements using synthetic fibers such as polyethylene, it has decreased its rate of biodegradation. 

HPBV integrated with natural fibers have, however, improved its stability, mechanical strength, and elasticity while still maintaining the biodegradability feature. 

Is PHBV made from microbial sources? 

PHBV is produced from microbes such as E. coli that accumulate it as energy reserve. Companies are also using genetically modified microbes to increase the yield and quality of PHA produced. However, these can also be produced by condensation reactions of two monomer units on a large-scale production. 

Is PHBV eco-friendly? 

PHBV is a naturally occurring biopolymer that is biocompatible, non-toxic and chemically inactive. What makes its use versatile is its ability to biodegrade under natural conditions by naturally occurring microbes. All these properties make this biopolymer eco-friendly. To add more, this polymer is naturally obtained from microbes unlike the plastics that use our valuable non-renewable resources. 

With the PHBV there is no issue of recyclability, overuse or over production and is a sustainable source as microbes can be made to replicate any number of times. 

Is PHBV better than plastic? 

PHBV is a naturally occurring biodegradable polymer that is made from naturally available microbes. They are in many ways better than plastic. They do not use the non-renewable petroleum-based products for its synthesis like plastics do. Plastic pollution has affected much wildlife owing to its overuse and non-biodegradability. 

Plastics also generate toxic leachates in landfills and emit hazardous chemicals when burned. PHBV on the other hand, is degraded easily as they have simple carbon chains which are utilized by microbes for their survival. 

Can PHBV be used for compost? 

PHBV can be composted where its biodegradability within 6 to 12 weeks is almost 90%. Its ability to biodegrade is even more than the PLA based biopolymers. PHBV is made from carbon and oxygen atoms which are easy to biodegrade under natural conditions. 

When buried in soil its degradability is only 35% while composting provides a much better condition due to the presence of worms and different bacteria that enhance its biodegradation. 

Which polymer is biodegradable? 

Polymers get degraded under both aerobic and anaerobic conditions by naturally occurring microbes that result in breakdown to natural by-products such as carbon dioxide, nitrogen, water, biomass, and inorganic salt. This makes these polymer biodegradables and cause no adverse effects to our environment. 

Polymers made from plant and animal sources include alginate, cellulose, and gelatine. Some synthetic polymers such as polylactic acid are biodegradable after industrial composting. 

Reference 

Batista, K.C., Silva, D.A.K., Coelho, L.A.F. et al. Soil Biodegradation of PHBV/Peach Palm Particles Biocomposites. J Polym Environ 18, 346–354 (2010). https://doi.org/10.1007/s10924-010-0238-4 

Kotnis, M.A., O’Brien, G.S. & Willett, J.L. Processing and mechanical properties of biodegradable Poly(hydroxybutyrate-co-valerate)-starch compositions. J Environ Polym Degr 3, 97–105 (1995). https://doi.org/10.1007/BF02067485 

Zaidi Zain, Mawad Damia, Crosky Alan. Soil Biodegradation of Unidirectional Polyhydroxybutyrate-Co-Valerate (PHBV) Biocomposites Toughened With Polybutylene-Adipate-Co-Terephthalate (PBAT) and Epoxidized Natural Rubber (ENR). Frontiers in Materials 6, 275 (2019). https://doi.org/10.3389/fmats.2019.00275 

Yun-Xuan Weng, Ying Wang, Xiu-Li Wang, Yu-Zhong Wang. Biodegradation behavior of PHBV films in a pilot-scale composting condition. Polymer Testing 29, 579-587 (2010). https://doi.org/10.1016/j.polymertesting.2010.04.002 

Policastro, G., Panico, A. & Fabbricino, M. Improving biological production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) co-polymer: a critical review. Rev Environ Sci Biotechnol 20, 479–513 (2021). https://doi.org/10.1007/s11157-021-09575-z 

Muniyasamy, S., Ofosu, O., John, M. J., Anandjiwala, R. D. (2016). Mineralization of Poly(lactic acid) (PLA), Poly(3-hydroxybutyrate-co-valerate) (PHBV) and PLA/PHBV Blend in Compost and Soil Environments. Journal of Renewable Materials, 4(2), 133–145.

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