Modelling biopolymer degradation in liquid medium fermentation | [Modelisation de la degradation des biopolymeres en fermentation en milieu liquide]

The development and the sale of biodegradable materials supposes that biodogradability can be scientifically measured. To solve this problem, it is necessary to set-up procedures, to fit the kinetics of biodegradation and to research the structural parameters of materials that influence the biodegradability of a polymer. In this present study, twenty materials, representing varied biodegradability levels (i.e., polyhydroxybutyrate-hydroxyvalerate, polycaprolactone, cellulose acetate, polylacticacid, polyethylene) were studied. A respirometric test under aerobic conditions, based on the CEN Draft, was set-up. The biodegradability of each plastic film has been evaluated by the percentage of carbon converted into CO2 during 35 days. The values of tbe CO2 production were plotted as cumulative function. In order to reduce the number of points the cumulative curve was modelled according to two functions: a Hill sigmoid and a Keursten model. The khi2 test shows that the biodegradation curve can be more accurately quantified with the first model than with the second one. Three kinetic parameters were determined for this model; one represents the maximal percentage of carbon converted into CO2, the second the half-life in days of the part degrading materials and the third the curve radius. In addition, each material was characterized by elementary analysis (% C, H, N, O), infrared spectra, film thickness, hydrophobicity and surface free energy. In order to compress and to keep the relevant information these parameters were submitted to a Principal Component Analysis. PCA finds linear combinations of variables that describe major trends in our data: The two principal components are closely relatod respectively to a chemical and a physical axis, which separate groups of materials. Materials showing a high biodegradability are related to high oxygen and nitrogen contents and low hydrophobicity. The thickness of material does not influence in our study the likeness to biodegradability Finally, this study establishes the correlation between the biodegradation and the structure of biopolymers.