Mechanisms of degradation of plastics in natural and technical systems
C01: Formation and degradation of microplastics under simulated environmental stress
Iinvestigates the formation of secondary microplastics from macroplastics and its further degradation by exposure to UV radiation, water and mechanical forces. For this purpose, various plastics with and without additives are exposed to accelerated aging. The resulting materials are characterized in terms of mechanical properties and molecular structure. In this way, we are able to link crack formation and propagation with molecular weight, chain scissions and their end groups, additive concentration and migration. A wide range of different techniques including mechanical analysis, mass spectrometry and solid-state NMR spectroscopy will be used. By correlating the results of microscopic and macroscopic length scales, a deeper understanding of the mechanisms and time scales of the degradation of plastics in nature will be achieved.
C02: Degradation of biodegradable polymers and their clay nano-composites under environmentally relevant conditions
Biodegradable polymers are considered a smart solution for the microplastic problem. For packaging applications they are, however, often too brittle and to permeable for gases while their degradation is frequently not fast enough in relevant habitats and real natural environments. The overall objective of this proposal is to gain a comprehensive understanding of the degradation behaviour of conventional and tailored biodegradable polymers and their clay nanocomposites in limnic and terrestrial systems. This will allow developing biodegradable polymers and/or their clay nanocomposites that make no contribution to persistent secondary microplastic while meeting all technical and processing requirements for packaging.
C03: Enzymatic degradation of microplastics
Although most plastics are very biostable, there are clear evidences that microbes are able to degrade these materials enzymatically. By combining various experimental biochemical and biophysical techniques with computer simulations, we want to understand which properties an enzyme must have in order to attack and degrade plastics efficiently. In this respect, the recently discovered enzyme PETase, which is able to degrade poly(ethylene terephthalate) (PET), will serve as a model system. This enzyme is particularly interesting, since it is structurally and functionally closely related to a group of enzymes called cutinases, of which some representatives are also able to attack PET, although less efficiently. Other cutinases are however not able to degrade PET. Moreover, we want to search for new enzymes that degrade plastics such as for instance polystyrene.
C04: Impact of microbial diversity and biofilm formation on degradation mechanisms of microplastic particles in the environment
Microorganisms (MOs, prokaryotes and fungi) are central to the mineralization of microplastics (MP) in the environment and represent a huge and rather unstudied genetic and metabolic degradation potential. Thus, objectives of C04 are to identify new MP-degrading MOs, to elucidate their MP degradation pathways as well as to discover genes encoding for key enzymes associated with MP-degradation, and to understand biological degradation mechanisms in the environment. Pure culture screenings, degradation experiments with environmental samples and identification of key organisms, stable isotope probing with 13C-labelled MP to trace MP-13C-carbon flow and to get metagenomes of associated 13C-MP degraders, directed isolation, genomics and transcriptomics of pure cultures and environmental samples as well as gene expression studies will identify MP-degrading enzymes and MOs. Accelerated evolution will be utilized to generate high efficiency MP degraders. A further objective is to elucidate whether biofilms have the potential to inhibit UV-dependent plastic oxidation due to their UV-absorbing characteristics, and how microbial colonization affects mechanical stability and surface properties of plastics. Resulting insights are essential for the CRC 1357 and will foster an understanding of the role of MOs for the fate of MP in the environment, enable the identification of microbial MP degrader ‘hot spots’ in the environment, set the ground for the development of additives that speed up MP-degradation as well as the development of environmentally friendly plastics.
C05: Degradation and behaviour of plastics and microplastic particles in technical systems of water and waste management
The aim of sub-project C05 is the investigation of an important entry path for plastics from technical plants into the environment as microplastic (MP). Simultaneously a new approach will be explored for improved environmental compatibility of commodity plastics by avoidance or reduction of MP. For this purpose the surface properties of polyethylene, polypropylene, polystyrene, nylon, poly(ethylene terephthalate), polyisoprene and poly(vinyl chloride) will be modified by accelerators (in situ) for biofilm formation and thereby make the plastic under process conditions available for biodegradation. Following this concept also commodity plastics could become environmentally compatible with regard to MP-particle formation. With this the sub-project C05 reaches out beyond the descriptive studies on MP in technical plants and the environment.
The following central questions will be addressed in sub-project C05 with respect to MP-particles in technical plants for waster- and wastewater management:
- 1. Are in plants special degradation processes occuring?
- 2. What is the impact of the nature of the material, the composition, the size, the morphology and coatings of plastic particles on degradation processes in the plants?
- 3. Can the biodegradation be accelerated by controlled modification of particle surface before or in the plants?
- 4. What ecological consequence will have the spreading of modified particles in environment, in particular to soil?