Learn more about biodegradable plastic

Why use PHB?

An alternative to petroleum based plastic is highly needed due to the current plastic pollution. Plastics are irreplaceable in our way of life and we are obligated to accommodate this need without leaving a permanent imprint on the planet. The petroleum based plastics worldwide mostly ends up polluting our environment. Therefore, the very use of biodegradable plastic such as poly-hydroxyalkanoates (PHA), including poly-hydroxybutyrate (PHB), as a substitution for petroleum based plastic is a huge step in the right direction ROCHMAN, C. M., COOK, A. M. & KOELMANS, A. A. 2016. Plastic debris and policy: Using current scientific understanding to invoke positive change. Environmental Toxicology and Chemistry, 35, 1617-1626..

There is a lot of potential in biodegradable plastics. Once the production of these environmental friendly plastics has been optimized, it is then possible to find applications where conventional plastics can be replaced. Because PHB is very expensive, we would have to first optimize the production. PHB has biocompatible properties, which could be used for creating implants or capsules for internal drug delivery. More examples of how the biocompatibility of PHB can be utilized in medicine can be seen at the perspectives site.

What is PHB’s properties?

PHB is used as a carbon source which are stored as granules in a wide variety of microorganisms. They usually accumulate it as intracellular carbon or energy that they use for a carbon source and stored reduction power. This generally occurs because of growth limiting nutrients such as oxygen, nitrogen, phosphate and sulfate. PHB is part of a large group of plastic polymers known as PHA’s.

PHA’s are microbial polyesters which contain 3-, 4-, 5-, and 6-hydroxycaboxylic acids that accumulate as an energy source JAMBUNATHAN, P. & ZHANG, K. C. 2016. Engineered biosynthesis of biodegradable polymers. Journal of Industrial Microbiology & Biotechnology, 43, 1037-1058..

Table 1: Shows poly-hydroxybutyrate's (PHB), Poly-lacticacid's (PLA), Poly-vinylchloride's (PVC) and Poly-ethyleneterephthalate's (PET) propeties: melting point, maximum service temperature, minimum service temperature, electrical and thermal conducter or insulator, embodied energy, CO2 footprint and price Granta’s teaching resources for materials and process education.

Melting Point171-182 ℃160 - 177 ℃100 - 260 ℃215 - 265 ℃
Maximum service temperature60 – 80 ℃45 - 55 ℃60 - 70 ℃66,9 - 86,9 ℃
Minimum service temperature-70 - -60 ℃-20 - -12 ℃-123 - -73,2 ℃-123 - -73,2 ℃
Electrical and thermal conductor or insulatorGood insulatorGood insulatorGood insulatorGood insulator
Embodied energy81,2 - 89,8 1000000*J/kg49 - 54,2 1000000*J/kg*55,4 - 61,2 1000000*J/kg80,9 - 89,5 1000000*J/kg
CO2 footprint4,14 - 4.58 kg/kg3,43 - 3,79 kg/kg2,37 - 2,62 kg/kg3,76 - 4,15 kg/kg
Price6,06 - 7,06 $/kg2,82 - 3,46 $/kg1,46 - 1,79 $/kg1,46 - 1,79 $/kg
Tensile strength35 - 40 MPa47 - 70 MPa40,7 - 65,1 MPa48,3 - 72,4 MPa
Elongation6 - 25 % strain2,5 - 6 % strain11,9 - 80 % strain30 - 300 % strain
Bio-derived material YesYesNoNo

Despite the large applicability of PHB in various fields, the plastic is not commonly used due to lack of research. A secretion system will reduce the overall costs and even minimize the CO2 footprint and embodied energy which nowadays is required, as seen at table 1 above.The production of PHB is 4 times higher than PET and PVC, which is one of the main reasons why PHB is still under development (table 1). PHB’s tensile strength is not as well as other plastic types, but the elongation is higher than PLA’s (table 1).

The melting point of PHB is almost the same as PLA, which makes it compatible for 3D printing. PHB has the possibility to be used as a substitute for PET, PVC and PLA due to the melting temperatures similiarities. It is also indicated through maximum temperature, minimum temperature and how good it is as an electrical and thermal conductor or insulator (table 1). One of PHB’s best properties is that it is a bio-derived material.

Some of the plastics commonly found in bandages are poly-vinylchloride and poly-ethylene. PHB has properties similar to these plastics which makes it a competent replacement for the backside of the bandage, as shown above. The fact that PHB is biocompatible makes the plastic suitable for partaking in covering a skin lesion and thereby protecting mechanically from further exposure to microorganisms (and microplastics).

A wound often heals better and more effectively when a traditional patch is applied, partly due to the fact it withholds moist GIL, E. S., PANILAITIS, B., BELLAS, E. & KAPLAN, D. L. 2013. Functionalized silk biomaterials for wound healing. Adv Healthc Mater, 2, 206-17.. PHB, as a framework for Bacto-Aid, could retain moisture. This could result in a synergistic effect, where the properties of spider silk combined with PHB creates the perfect healing conditions. It is though, important to do further studies of the moist’s impact on the different sub-elements of Bacto-Aid.