Biodegradation kinetic modeling of pro-oxidant filled polypropylene composites under thermophilic composting conditions after abiotic treatment

This work aims at modeling and characterizing the kinetics of biodegradation of polypropylene loaded with cobalt stearate as pro-oxidant after abiotic treatment. Eight films of these composites were prepared using different pro-oxidant loadings. These films were treated abiotically using accelerated weathering for 40 h, and biotically using aerobic composting as per ASTM D 5338. The experimental data were analyzed using an eight-parameter Komilis model containing a flat lag phase. The model formulations involved hydrolysis of primary solid carbon and its subsequent mineralization. The first step was rate controlling and it included hydrolysis of slowly (Cₛ), moderately (Cₘ), and readily (Cᵣ) hydrolyzable carbon fractions in parallel. The model parameters were evaluated by means of nonlinear regression technique. The surface morphology of the films before and after the biodegradability test supported the biodegradation results. The model parameters and undegraded/hydrolyzable/mineralizable carbon evolutions involved moderately and readily hydrolyzable carbons but with the absence of slowly hydrolyzable carbon. These exhibit degradability in the range of 11.20-36.42% in 45 days. Biodegradability increases with progressive increase in pro-oxidant loading. The rate of degradation reaches maximum (0.322-0.897% per day) at around the 39th-12th day. For all the films, readily hydrolyzable carbon fractions and their hydrolysis rate constants (kᵣ) are appreciably increased with increasing pro-oxidant loading. All the films show the presence of growth phase because of their high initial readily hydrolyzable carbon fractions. The SEM images after the abiotic and subsequently biotic treatments were progressively rougher. The methods presented here can be used for the design and control of other similar systems.