Biodegradation of polysaccharides, polyesters and proteins in soil based on the determination of produced carbon dioxide

•Reliable respirometric method for determination of biodegradation of biogenic polymers.•Determination of system boundaries, limits and calibration of the respirometric system.•Particle size is crucial for hardly biodegradable material such as polylactic acid.•High water solubility of proteins improves biodegradation.•Increased biodegradation of polylactic acid reinforced with microfibrillated cellulose compared to neat polylactic acid. The biodegradation of polymers can be determined by measuring the CO2 evolution from the biodegradation medium, for example soil. In this work, the biological degradation of cellulose (powder and fibers), polylactic acid (PLA, powder and films), a combination of both and lupin protein isolate (LPI, films) was investigated. Therefore, a reliable method using a respirometric system needed to be developed. The soil to sample ratio, the system boundaries concerning the maximum CO2 uptake and O2 consumption in addition to the change in electrical conductivity of the KOH absorbant solution caused by CO2 uptake were investigated. LPI-based films showed the highest biodegradation in %, followed by regenerated cellulose fibers (RC fibers). In case of PLA only the samples with powder morphology were biological degraded. The degradation of PLA films was highly increased to 68 % by addition of microfibrillated cellulose (MFC). The samples were analyzed before and after biodegradation using scanning electron microscopy (SEM) and gel permeation chromatography (SEC). The developed method was successful to validate the degree of biodegradation for a large variety of biogenic polymers and can be generally applied.