Research by HTWK Leipzig
Compostable Packaging Films and the Microplastic Dilemma
Compostable packaging — cellulose films, starch-based blends, PLA — is marketed as the green alternative to fossil plastics. The promise: they return safely to nature once discarded. The reality: they can still generate microplastics.
Why Microplastics Form
True biodegradation means microorganisms metabolize material into water, CO₂, and biomass. But in most environments — soil, water, or compost — bioplastics don’t just vanish. They fragment, forming bio-microplastic particles (BMPs). The figure below shows a cellulose-based film breaking into fragments over 75 days in a simulated composting process at HTWK (Naegeli 2021).
Material-specific Issues
Cellulose films degrade under many conditions, but coatings and plasticizers can leave persistent residues. PLA requires high heat and humidity — typically only found in industrial composters. In soil or water, it fragments slowly, producing BMPs. Starch blends degrade unevenly: starch disappears, but polyesters remain (Cucina et al. 2021) . Alarmingly, recent studies show starch-based BMPs may disrupt gut microbiota and cause organ damage in lab animals (Liu et al. 2025) — a reminder that “bio” does not mean harmless.
Standards Leave Gaps
Certifications like EN 13432 focus only on fragments >2 mm, ignoring true microplastics. Tests are done with small, neatly cut samples under ideal lab conditions. Real packaging — like a stand-up pouch — is much larger, less exposed, and behaves very differently in composting facilities.
No such thing as a standard composting process
Industrial composting facilities vary widely — open windrows, closed containers, different bio-wastes, and different timeframes. Commercial pressures often mean shorter processing times than required by ISO standards. In our local site, large fragments of PBAT-PLA bags (30 × 30 mm) were still present after the 6-week cycle and had to be sieved out. But it is not practical to use a fine sieve to do this meaning that small particles can pass through the process and into the finished compost.
These findings reinforce what many recent studies have shown: compostable packaging is not guaranteed to disappear. Instead, it can leave behind microplastics, unless the right conditions — and infrastructure — are in place. Compostable ≠ consequence-free.
