Degradation of Film and Rigid Bioplastics During the Thermophilic Phase and the Maturation Phase of Simulated Composting

Abstract

The recent regulations, which impose limits on single use plastics and packaging, are encouraging the development of bioplastics market. Some bioplastics are labelled as compostable with the organic waste according to a specific certification (EN 13432), however the conditions of industrial composting plants are generally less favourable than the standard test conditions. Aiming at studying the effective degradation of marketable bioplastic products under composting, the current research stresses novel elements which can strongly influence bioplastics degradation: the simulation of industrial composting conditions and the thickness of bioplastic products, ranging between 50 and 500 µm. The research approaches these critical aspects simulating a composting test of 20 days of thermophilic phase followed by 40 days of maturation phase, on starch-based polymer Mater-Bi® (MB), polybutylene adipate terephthalate (PBAT), polylactic acid (PLA) of different thickness. Conventional low density polyethylene (LDPE) was introduced as negative control. An overall study with Fourier Transform InfraRed (FTIR), ThermoGravimetric Analysis (TGA), Gel Permeation Chromatography (GPC), Scanning Electron Microscope (SEM) and visual inspections was applied. Results highlighted that MB film presented the highest degradation rate, 45 ± 4.7% in terms of weight loss. Both MB and PBAT were subjected to physico-chemical features change, while LDPE presented slight degradation signs. The most critical observations have been done for PLA, which is strongly influenced both by thickness and thermophilic phase duration, shorter than the EN 13432 conditions.

End of Life of Biodegradable Plastics: Composting versus Re/Upcycling

“…[58] Then, oligomers and monomers generated from the hydrolysis pass through the microbial cellular membranes and are assimilated to produce energy, carbon dioxide, water, and new biomass. [22] De Hoe et al [59] report also that light-induced crosslinking reactions can take place along the PBAT macromolecular structures. In this case, the biodegradation rate tends to ChemSusChem Minireviews doi.org/10.1002/cssc.202101226 decrease with the increasing of crosslinking density beyond a certain limit threshold.…”

“…The chains in the crystalline regions are more resistant to hydrolysis than those in the amorphous regions. The relevance of the material thickness has been introduced by Ruggero et al: [22] a 500 μm PLA film only degraded by 3 % under thermophilic conditions [58°C and 50-55 relative humidity (RH%)] for 20 days followed by a maturation phase (37°C and 50-55 RH%) for 40 days. Therefore, it appears that the combination of a 20 day thermophilic phase and the 500 μm thickness of the material prevents a complete degradation within 2 months, and recirculation of macro-residues of bioplastics is necessary.…”

“… [58] Then, oligomers and monomers generated from the hydrolysis pass through the microbial cellular membranes and are assimilated to produce energy, carbon dioxide, water, and new biomass. [22] …”

“…The PBAT component, instead, takes a longer period to be completely assimilated by microorganisms and transformed into stable products, and it is much more sensitive to process conditions like an insufficient moistening content and short thermophilic phase. [ 22 , 64 ]…”

Biotechnological Aspects and Mathematical Modeling of the Biodegradation of Plastics under Controlled Conditions

“…In this scenario, composting systems are considered some of the most promising alternatives, due to the possibility of controlling important parameters, such as humidity, pH, aeration, and temperature [ 8 , 9 , 10 ]. In order to understand and optimize composting systems, simulated composting systems are often utilized [ 11 ].…”