Development of a New Method for Obtaining the Bioplastics Based on Microbial Biopolymers and Lignin

Abstract

Background. The ever-increasing demand for plastic polymer products with simultaneous depleting fossil fuels such as oil and natural gas, as well as the growing problem of waste disposal, creates a need to find alternative technologies that meet current trends in both environmental and economic development. Bioplastic materials that are synthesized from renewable sources and have the ability to biodegrade are considered as such an alternative. The main obstacle of modern bioplastics which makes it impossible to completely replace traditional plastics is the high cost of production. In order to reduce the cost of existing biopolymers, production waste is added to the polymer matrix. One such waste is lignin – the second most common biopolymer. An additional way to reduce the cost of production is to find more cost-effective producers. Thus, although the classical microbial synthesis has fairly high productivity, the source of carbon for the cultivation of microorganisms are sugars obtained from agricultural raw materials which could cause a threat for food industry. The new producer for production of polyhydroxyalkanoates (PHA) is cyanobacteria, the carbon source of which is carbon (IV) oxide or gas emissions from enterprises, which reduces the cost of the target product.

Objective. Development of a method for obtaining bioplastics using products of microbial synthesis and lignin.

Methods. Cyanobacteria Nostoc commune was grown using a nutrient medium BG-11 with subsequent limitation of Nitrogen for the synthesis of PHA. Hydrolyzed lignin from hardwoods was combined with polylactic acid (PLA) or cyanobacteria-synthesized PHA in different ratios with further casting of the solution to determine the ability of lignin and polymer matrix to form polymer films.

Results. The content of PHA in the cells of cyanobacteria Nostoc commune, when grown in a nutrient medium limited to Nitrogen, reached 7.8%. The synthesized polymer films based on PLA and lignin were not homogeneous, and films based on PHA and lignin were fragile.

Conclusions. The possibility of obtaining PHA by using cyanobacteria of the Nostoc commune species under environmental conditions that differ from the optimal ones for both cultivation and PHA production is shown. The possibility of obtaining a biopolymer based on lignin and PLA is shown. To form homogeneous films, it is necessary to change the standard conditions for obtaining a mixture of components. The interaction of lignin with PHA forms a homogeneous polymer mixture, which is fragile and requires the addition of plasticizers to obtain the necessary properties.