A novel method for tuning the biodegradation rate of poly-3-hydroxybutyrate by adding acidified biochar or oxidized biochar

Abstract

This study revealed that the acidification and oxidation of biochar retarded the biodegradation of poly-3-hydroxybutyrate (PHB) films to a different extent. This finding is important as it both contributes to research efforts on PHB-based products and comprehending what happens to PHB and PHA (polyhydroxy acid) following their release into a natural environment. Herein, film samples were fabricated from neat poly-3-hydroxybutyrate and PHB supplemented with various forms of biochar (1 wt%) by extrusion and thermocompression. The properties of the films were investigated by optical microscopy, scanning electron microscopy (SEM), atomic force microscopy, differential scanning calorimetry, thermogravimetric analysis and X-ray diffraction. The PHB films underwent a biodegradation test in earth, the biological agent employed for this being natural mixed microflora in the form of garden soil. The course and extent to which they biodegraded were gauged by respirometry to determine the amount of carbon dioxide produced through microbial degradation. SEM, fluorescence microscopy and next-generation sequencing were carried out to study the microbial community involved in the biodegradation of the films. Investigation was also made of the environmental impacts of samples, discerning how they broke down in river sediment, in addition to which a phytotoxicity screening test was conducted. Analysis revealed that the thermal properties of the filled films were comparable to those of the neat PHB specimen. Respirometric data indicated the extent of PHB biodegradation could be adjusted by adding biochar, discerned as 87% in mineralization for the neat PHB material and 37% to 64% for the filled samples after 7 months. The rate of such biodegradation depended on how the biochar had been chemically modified. The hydrophilicity of the polymer surface did not relate to the lag phase or aforementioned biodegradation rate in the soil. Sequence analysis suggested that the biofilm communities that initially colonized the films were influenced by the type of biochar in their polymer matrices. Findings showed that the PHB materials supplemented with the modified biochar did not impact the cultivation of plants or the river environment. Notably, every film had degraded in river environment by over 50% in just a month.