Investigation of the biological degradation of polymers

The increasing accumulation of plastic waste in the environment has posed a significant challenge for many years. As a potential solution, biodegradable plastics are being developed that can contribute in particular to reducing highly critical microplastics. However, a key barrier to adoption remains the often long residence time of these materials in industrial composting facilities.

The use of our testing techniques enables the targeted development of polymers with a defined and adjustable degradation rate. By combining microstructural diagnostics with modern analytical methods for investigating biological degradation, material understanding is significantly deepened and product development is accelerated. Materials can thus be specifically tailored to regulatory requirements and specific market needs.

Areas of application

• Material characterization and comparison
• Support in formulation development
• Quality assurance in production

Biological degradation

The biodegradability of plastics is governed by various standards and certifications. A distinction is made between industrially compostable plastics, home-compostable plastics, and biodegradable materials in soil. The central criterion is generally the rate of degradation under defined temperature and substrate conditions. Petroleum-based plastics can also meet the respective requirements.

Criteria for the compostability of plastics

Industrially compostable (DIN EN 13432)

• Degradation in industrial composting facilities at 55–60 °C
• After 3 months: 90% disintegration into particles < 2 mm
• After 6 months: 90% biologically degraded
• Evidence of undisturbed plant growth in the compost
• All constituents ecotoxicologically safe
• Petroleum-based plastics can also meet the requirements

Home-compostable:

• Requirements analogous to industrial compostability
• Degradation at lower temperatures (< 30 °C)
• After 6 months: 90% disintegration into particles < 2 mm
• After 12 months: 90% biologically degraded

Biodegradable in soil (DIN EN 17033)

• Requirements comparable to industrially compostable plastics
• Degradation at 20–28 °C (preferably 25 °C)
• After 24 months: 90% biologically degraded

Test Methods Employed

At Fraunhofer IMWS, qualitative and quantitative test methods are used for characterizing biological degradation. These can be combined with further material characterization techniques available at the institute, enabling comprehensive and in-depth material understanding from a single source.

Respirometer

Biological degradation is determined via the biological oxygen demand (BOD) as well as mineralization based on CO₂ release. The combination of both parameters allows a complete assessment of the biological degradation behavior as well as a carbon balance.

• Determination of specific oxygen consumption (coulometric method) as a function of time
• Calculation of the percentage of biological degradation
• Determination of CO₂ release via conductivity measurement in an absorber solution
• Constantly aerobic conditions without O₂ stress for microorganisms
• Constant CO₂ absorption
• Constant pressure in the closed system
• Constant temperature control from 5 °C to 50 °C (± 0.2 °C)