How Scientists Are Decoding Biodegradable Plastics
The secret life of compostable plastics reveals surprises that could reshape our fight against pollution.
Imagine tossing a "compostable" plastic bag into your food waste bin, believing it will harmlessly return to nature. As it journeys through the industrial composting facility, what transformations does it truly undergo? Does it completely disappear, or could it be leaving behind an invisible environmental footprint? Scientists are now combining sophisticated analytical techniques to uncover the hidden story of biodegradable plastics, revealing complexities that challenge our simple solutions to the plastic pollution crisis.
The growing global production of biodegradable plastics (BPs) represents a promising response to the conventional plastic pollution crisis, with production reaching approximately 2.47 million tons in 2024 9 . These materials, including polylactic acid (PLA), polyhydroxyalkanoates (PHAs), and starch-based blends, are designed to break down faster than conventional plastics through the action of microorganisms, moisture, and heat 7 .
Unlike conventional plastics with their persistent C-C and C-H bonds, BPs incorporate hydrolysable ester and ether bonds that are more susceptible to microbial or hydrolytic attack 9 . However, this degradation doesn't always occur as completely or quickly as consumers might assume. Certification tests often occur under optimal laboratory conditions that don't always match real-world environments 2 .
The central challenge lies in understanding precisely how these materials break down in diverse environments and identifying what remains after degradation. This is where advanced analytical techniques become crucial for distinguishing between true biodegradation and mere fragmentation.
FTIR acts as a molecular fingerprinting tool. It identifies specific functional groups in plastic materials by measuring how chemical bonds vibrate when exposed to infrared light. Each polymer produces a unique infrared spectrum that allows researchers to determine chemical composition and observe changes as degradation occurs 1 . FTIR is particularly valuable for organic materials like plastics and requires minimal sample preparation 3 .
The EA-IRMS variant used in plastic analysis measures the relative abundances of carbon isotopes (¹²C vs. ¹³C) in a sample 5 . This provides crucial information about the origin of carbon atoms in biodegradable plastics and tracks how different components break down at varying rates. Unlike conventional mass spectrometry that identifies molecules, IRMS precisely measures isotope ratios that serve as tracers for biodegradation processes.
When combined, these techniques create a comprehensive picture of both the chemical structure (FTIR) and component-specific degradation pathways (IRMS) of biodegradable plastics.
A compelling 2023 study published in Applied Sciences exemplifies how researchers are applying these techniques to understand BP degradation in marine environments 5 . The experiment investigated the degradation of two types of Mater-Bi® shopping bags (ultra-lightweight and lightweight) in actual marine conditions to simulate what happens when these materials accidentally enter ocean ecosystems.
Researchers obtained compostable shopping bags compliant with the EN 13432 standard, along with conventional polyethylene bags as controls.
The bags were immersed at a 1-meter depth in the tourist marina of Chioggia, Italy, during summer months to simulate floating plastic pollution.
Samples were collected at six regular intervals over 73 days to track progressive degradation changes.
FTIR and IRMS analyses were performed to identify chemical changes and track differential degradation of components.
Results from both techniques were combined to develop a comprehensive understanding of the degradation mechanism and kinetics.
| Parameter | Specification | Significance |
|---|---|---|
| Location | Tourist marina of Chioggia, Italy | Real-world marine conditions |
| Depth | 1 meter | Simulates floating plastic debris |
| Duration | 73 days (with 6 sampling points) | Tracks progressive degradation |
| Water Temperature | 26.8 ± 1.1°C | Summer conditions enhance microbial activity |
| Salinity | 33.71 ± 1.03 PSU | Typical marine environment |
The FTIR spectra revealed progressive changes in specific absorption bands, indicating chemical modifications to both starch and polyester components. The IRMS data provided even more precise information, suggesting the bags had a mixed composition with 61-72% polyester content 5 .
Most remarkably, the isotopic approach enabled researchers to estimate that the complete degradation of the starch fraction would require 124 to 180 days in the studied marine environment, following zero-order kinetics 5 . This timeframe far exceeds what many consumers would expect from "compostable" plastics and highlights the importance of realistic degradation studies.
While the marine study demonstrated partial degradation of compostable bags, other research reveals a more concerning phenomenon: the potential for biodegradable plastics to generate microplastics (MPs) under certain conditions 2 6 .
A 2025 disintegration study of commercial biodegradable products found that while most tested items broke down effectively under simulated industrial composting, MPs were detected in compost undersieves for two of the ten products 6 . This finding is particularly significant because standard compostability certification tests do not assess fragments smaller than 2mm, creating a potential gap in our understanding of BP's environmental impact.
The problem may be more pronounced with some biodegradable plastics than others. Research indicates that plastics like PBAT can release substantially more plastic fragments in aquatic environments compared to conventional polyethylene 9 . The degradation process of BPs doesn't always lead to complete mineralization and can instead generate microplastic particles, especially under suboptimal conditions with low temperatures, limited oxygen, or low microbial activity 9 .
| Polymer Type | Common Applications | Relative Degradation Rate |
|---|---|---|
| PLA (Polylactic Acid) | Food containers, packaging |
|
| PHA (Polyhydroxyalkanoates) | Specialty packaging, medical devices |
|
| Starch Blends | Shopping bags, food service items |
|
| PBAT | Flexible films, bags |
|
Scientists studying biodegradable plastics rely on sophisticated reagents and materials to unravel the complex degradation processes. These research tools form the foundation of reliable plastic analysis.
| Research Solution | Function in Analysis | Application Example |
|---|---|---|
| ATR-FTIR Accessory | Enables direct analysis of solid samples without preparation | Surface characterization of degraded plastic films 2 |
| Isotopic Standards | Calibrate mass spectrometry measurements for accurate δ¹³C values | Quantifying component-specific degradation rates 5 |
| Synthetic Composting Medium | Simulates industrial composting conditions under controlled lab settings | Disintegration testing according to ISO 20200 6 |
| Enzyme Solutions | Mimic biological degradation processes | Studying specific enzymatic breakdown mechanisms 7 |
| Reference Polymer Materials | Provide baseline spectra for compound identification | FTIR spectral library matching 1 |
The combined application of FTIR and mass spectrometric techniques provides unprecedented insights into the complex journey of biodegradable plastics in the environment. These analytical approaches reveal that the degradation story is far more complicated than simple disappearance, involving nuanced processes of chemical transformation, fragmentation, and potential microplastic formation.
Ongoing research is increasingly focused on developing "sustainable-by-design" plastic materials that undergo more complete and predictable degradation across diverse environmental conditions 5 . The sophisticated analytical methods profiled here play a crucial role in this innovation cycle, providing the critical data needed to validate new material designs and ensure they truly deliver on their environmental promises.
As research advances, the integration of these analytical techniques with emerging technologies like machine learning algorithms for spectral analysis promises to further accelerate the development of next-generation biodegradable plastics 1 .
This scientific progress, coupled with responsible consumption and waste management practices, offers hope for genuinely effective solutions to the global plastic pollution crisis.
The hidden life of biodegradable plastics, once a mystery, is gradually being decoded through sophisticated analytical science—revealing both the promise and limitations of our current solutions while guiding the way toward truly sustainable materials for the future.