Biodegradable plastic designed to improve the soil quality and microbiological activity

Biodegradable plastic composites were produced from mixtures of polyvinyl alcohol (PVA) and starch, which were mixed with different natural fillers [sugarcane bagasse (SB), oat hulls (OH) or silkworm exuvia (SE)] and nutrients to stimulate the biodegrading microbiota. The physicochemical and biodegradability characteristics of the produced materials were studied, in addition to their influence over the microbiota involved in biodegradation. The SB-composite showed reduced solubility in water, a lower water absorption capacity and a slower mineralization rate when buried in a commercial substrate for seedlings production, as compared with those of the OH- and SE-composites. Scanning electron micrographs demonstrated the increased colonization of materials by the biodegrading microbiota over time, which were predominated by filamentous fungi in OH- and SE-composites, while the SB-composite was predominantly colonized by bacteria. A Fourier transform-infrared spectroscopy (FT-IR) analysis of the biodegraded materials highlighted the chemical differences in the protein and carbohydrate content between formulations, corroborating the activity of different microbial groups on their mineralization. Regardless of its composition, the mineralization rate of the materials was positively correlated with the microbial biomass carbon (C mic) and basal respiration (R-B) of the substrate. However, the correlation between the mineralization rate and the metabolic quotient of the substrate (qCO(2)) was negative for the OH- and SE-composites, while the SB-composite showed no significant correlation among these variables. The differences observed in the formulations indicated that biodegradable plastics can be designed for a given goal by selecting the most appropriate formulation. (C) 2018 Elsevier Ltd. All rights reserved.