The Role of ASTM D6868 in Bioplastics Testing and Certification

Bioplastics have emerged as a critical component in the transition toward a circular economy, offering alternatives to petroleum-based plastics that can reduce dependence on fossil fuels and lower carbon footprints. However, not all bioplastics are inherently biodegradable or compostable. Without rigorous, standardized testing, claims of environmental benefits remain unsubstantiated. ASTM D6868 is a pivotal standard in this landscape, providing a scientifically grounded framework for verifying the compostability of plastics under industrial conditions. This article examines the technical, regulatory, and practical dimensions of ASTM D6868, exploring how it underpins certification schemes, drives market confidence, and shapes the future of sustainable materials.

Understanding ASTM D6868: Scope and Purpose

Developed by ASTM International (formerly the American Society for Testing and Materials), ASTM D6868 is designed to assess the aerobic biodegradation of plastic materials under controlled composting conditions. The standard is formally titled "Standard Specification for Labeling of Plastics Designed to Be Aerobically Composted in Municipal or Industrial Facilities." It establishes the requirements for labeling plastics as compostable, ensuring that such products will disintegrate and biodegrade at rates comparable to known compostable materials (e.g., cellulose). The standard applies to plastics and plastic products intended for collection in municipal or industrial composting programs, including bags, food service items, and packaging.

ASTM D6868 is closely related to ASTM D6400, which covers similar requirements for compostable plastics. While D6400 focuses on the overall specification for compostable plastics, D6868 specifically addresses labeling and the testing protocols that support those labels. In practice, products seeking certification under programs like the Biodegradable Products Institute (BPI) or the Compost Manufacturing Alliance (CMA) often require testing to both D6868 and D6400 to ensure compliance.

Key Differences from Other Bioplastics Standards

ASTM D6868 should not be confused with other international standards such as EN 13432 (European standard for compostable packaging) or ISO 17088 (specification for compostable plastics). Although the core principles—biodegradation, disintegration, and ecotoxicity—are similar, nuances in test temperatures, duration, and allowable residuals exist. For instance, EN 13432 typically mandates a 12-week test for disintegration and up to 6 months for biodegradation, while ASTM D6868 requires a 180-day period under mesophilic or thermophilic conditions. Understanding these differences is crucial for manufacturers targeting global markets.

Detailed Testing Methodology Under ASTM D6868

The standard specifies a laboratory-based simulation of industrial composting. The process is broken down into three primary evaluation criteria: biodegradation, disintegration, and ecotoxicity. Below, each component is explained in detail.

1. Biodegradation: Measuring Microbial Conversion to CO₂

Biodegradation is quantified by respirometry—monitoring the carbon dioxide (CO₂) evolved as microorganisms consume the plastic material. The sample is mixed with mature compost (a microbial-rich inoculum) and incubated at 58°C ± 2°C (typical thermophilic composting temperature) for a maximum of 180 days. The amount of CO₂ produced is measured periodically and compared to the theoretical maximum carbon content of the sample. To pass, the material must achieve at least 90% absolute biodegradation relative to a positive control (e.g., cellulose) within 180 days. This means that 90% of the carbon in the plastic must be converted to CO₂, with the remainder likely incorporated into microbial biomass or humus.

Critical factors affecting test results include:

  • Sample morphology: Films, powders, or thin-walled items biodegrade faster than thick geometries.
  • Additives: Plasticizers, fillers, or pigments may inhibit microbial activity or alter carbon content calculations.
  • Inoculum quality: The compost used must be biologically active and free from inhibitory substances.

2. Disintegration: Physical Breakdown in a Composting Environment

Disintegration assesses the physical fragmentation of the material. A separate test is conducted by mixing the plastic specimen with fresh compost and maintaining composting conditions for 12 weeks. At the end of the period, the compost is sieved through a 2 mm mesh. The material must have no more than 10% of its original dry weight remaining on the sieve. This ensures that the product does not leave visible fragments that could accumulate in finished compost or cause aesthetic contamination.

3. Ecotoxicity: Safety of the Final Compost

Even if a plastic biodegrades and disintegrates, its residues could contain toxic substances harmful to plants or soil organisms. ASTM D6868 requires that the resulting compost be tested for ecotoxicity using plant germination and growth assays (often following OECD guidelines). The compost is mixed with a control growth medium, and seed germination rates and seedling biomass are compared. No statistically significant inhibition is allowed. Additionally, heavy metals and other regulated contaminants must fall below specified thresholds (e.g., for cadmium, lead, mercury).

Certification and Market Access

Compliance with ASTM D6868 is typically a prerequisite for certification by third-party organizations such as the Biodegradable Products Institute (BPI) in North America or DIN CERTCO in Europe. These organizations issue the universal "compostable" logo that consumers and waste processors recognize. For manufacturers, obtaining certification offers several advantages:

  • Regulatory compliance: Many U.S. states (e.g., California, Washington) have enacted laws requiring plastic products labeled as compostable to meet ASTM standards. Non-compliance can result in fines or removal from store shelves.
  • Consumer trust: A certified logo provides clear evidence that a product will break down in a commercial composting facility, reducing greenwashing concerns.
  • Access to composting infrastructure: Composting facilities often accept only certified compostable items, as they cannot risk contamination from non-compostable plastics.
  • Market differentiation: Early adopters of certified compostable materials can position themselves as sustainability leaders.

It is important to note that ASTM D6868 certification does not guarantee home compostability, as home piles operate at lower and more variable temperatures (often below 40°C). Separate standards, such as AS 5810 (Australia) or NF T51-800 (France), address home composting conditions.

Challenges and Limitations of Current Testing Approaches

Despite its robustness, ASTM D6868 is not without limitations. One significant challenge is the variability in industrial composting facilities. The standard's test conditions (constant 58°C, high moisture, continuous aeration) represent an optimized scenario. Real-world composting operations can experience temperature drops, uneven aeration, and shorter cycle times (often 30–60 days). Consequently, materials that pass the standard may not fully biodegrade in every facility. This discrepancy has led to criticism from waste management professionals and calls for testing at lower temperatures or shorter durations.

Another issue is the proliferation of oxo-degradable or fragmentation plastics that claim compostability without meeting the biodegradation threshold. These materials break into microplastics rather than converting to CO₂. ASTM D6868 specifically excludes them because they do not demonstrate true biodegradation. However, the standard does not explicitly test for microplastic formation, relying instead on the CO₂ end point.

Furthermore, the standard primarily addresses single polymers or simple blends. Multilayer films, coatings, and composites containing materials like biopolyethylene (bio-PE) or bio-polypropylene (bio-PP) are not biodegradable under this test because their polymer backbones are identical to conventional plastics. Developing standard methods for these novel materials remains an ongoing challenge for ASTM International.

Future Directions: Evolving Standards for a Growing Industry

The bioplastics sector continues to innovate, and ASTM D6868 must adapt. Several key developments are on the horizon:

  • Home compostable criteria: A separate standard, ASTM D8539, is being developed to address ambient-temperature biodegradation. This will help close the gap between laboratory tests and consumer expectations.
  • Marine and freshwater biodegradation: Emerging standards (e.g., ASTM D7991 for ocean water, D7473 for freshwater) may be integrated into certification schemes as concerns about plastic pollution in aquatic environments grow.
  • Anaerobic digestion: Some bioplastics may be better suited for controlled anaerobic digestion facilities (producing biogas). ASTM E2611 and D5526 cover anaerobic degradation, but harmonization with D6868 is still needed.
  • Real-time monitoring with advanced respirometry: New online CO₂ analyzers and automated systems allow for higher-resolution data, enabling faster certification decisions and better understanding of lag phases.
  • Inclusion of biodegradable additives: Standards are needed to verify that so-called "enhancement" additives actually accelerate biodegradation without leaving toxic residues.

In parallel, regulatory frameworks worldwide are tightening. The European Union's Single-Use Plastics Directive and the upcoming Packaging and Packaging Waste Regulation (PPWR) require compostable packaging to meet EN 13432. The United States Environmental Protection Agency (EPA) and state departments are developing guidance that leans on ASTM standards. International alignment efforts, such as those underway in ISO TC61/SC5/WG22, aim to reduce duplication and enable a single global testing framework.

Practical Implications for Manufacturers and End Users

For companies developing new bioplastic products, early engagement with ASTM D6868 testing is essential. The standard helps avoid costly redesigns by identifying formulation issues before scale-up. Additionally, manufacturers should consider the following strategic points:

  • Choose certified raw materials: Using compostable-certified resins from suppliers like BASF (Ecoflex), NatureWorks (Ingeo), or Novamont (Mater-Bi) simplifies downstream certification.
  • Plan for testing costs: Full certification including biodegradation, disintegration, and ecotoxicity can cost between $10,000 and $30,000 per product, depending on the material complexity and number of iterations.
  • Engage with certification bodies early: BPI, DIN CERTCO, and TÜV Austria provide pre-submission consultations to clarify requirements.
  • Educate customers: Labeling should clearly state "Certified Compostable under ASTM D6868" and recommend proper disposal in commercial composting facilities.

Composting facility operators also benefit from ASTM D6868. By requiring certified materials, they can confidently accept bioplastics without fear of contaminating the final compost product. Many facilities now run pilot programs to certify their own operational parameters against the standard, ensuring that materials labeled as compostable actually break down within their process time frames.

Conclusion

ASTM D6868 stands as a cornerstone of bioplastics quality assurance. It provides the scientific rigor needed to separate genuine compostable materials from misleading claims, supporting the growth of a reliable and transparent marketplace. As material science advances and environmental challenges mount, continuous refinement of this standard—along with harmonization with global norms—will be essential to fully realize the potential of bioplastics in waste reduction and resource recovery. Manufacturers, regulators, and consumers alike benefit from the clarity and accountability that ASTM D6868 delivers, making it not just a test method but a foundation for sustainable innovation.

Further reading: Visit ASTM International's official page for D6868 and the Biodegradable Products Institute for certification details.