Environmental biodegradability of recombinant structural protein

Yuya Tachibana,Haruna Misawa,Yuka Shibata,Senri Hayashi,Ken-ichi Kasuya,Alina Kudasheva,Sunita Darbe

doi:10.1038/s41598-020-80114-6

Yuya Tachibana, Haruna Misawa + Show 5 more

Open Access

https://doi.org/10.1038/s41598-020-80114-6

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Abstract

Next generation polymers needs to be produced from renewable sources and to be converted into inorganic compounds in the natural environment at the end of life. Recombinant structural protein is a promising alternative to conventional engineering plastics due to its good thermal and mechanical properties, its production from biomass, and its potential for biodegradability. Herein, we measured the thermal and mechanical properties of the recombinant structural protein BP1 and evaluated its biodegradability. Because the thermal degradation occurs above 250 °C and the glass transition temperature is 185 °C, BP1 can be molded into sheets by a manual hot press at 150 °C and 83 MPa. The flexural strength and modulus of BP1 were 115 ± 6 MPa and 7.38 ± 0.03 GPa. These properties are superior to those of commercially available biodegradable polymers. The biodegradability of BP1 was carefully evaluated. BP1 was shown to be efficiently hydrolyzed by some isolated bacterial strains in a dispersed state. Furthermore, it was readily hydrolyzed from the solid state by three isolated proteases. The mineralization was evaluated by the biochemical oxygen demand (BOD)-biodegradation testing with soil inocula. The BOD biodegradability of BP1 was 70.2 ± 6.0 after 33 days.

Highlights

Generation polymers needs to be produced from renewable sources and to be converted into inorganic compounds in the natural environment at the end of life
We evaluated the thermal and mechanical properties of the recombinant structural protein material BP1 using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), and three-point flexural testing, and we evaluated the biodegradability of BP1
With thermal stability beyond 180 °C and 10% weight loss at 285 °C, of BP1 has a potentially wide temperature range of applications including as a conventional engineering plastic

Summary

Introduction

Generation polymers needs to be produced from renewable sources and to be converted into inorganic compounds in the natural environment at the end of life. The poor mechanical and thermal properties of commercially available biodegradable polymers limit their adoption. The biodegradation of PLA is limited to high-temperature compost environments, and PLA does not show biodegradability in the natural environment Natural protein materials, such as silk, have been used for fiber material since ancient times. Chemical modification and polymer blending procedures were studied to endow the material with moldability and improved mechanical properties while maintaining biodegradability[13] Natural structural proteins, such as elastin, resilin, mussel byssus thread, squid suckerin, silks produced by various insects, and others are gaining attention due to their remarkable mechanical properties[14,15,16,17,18,19].

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