The Fibers in Your Closet: Understanding Cellulose Biodegradability and the Effects of Chemical Treatment

• Cotton’s key benefits: It’s naturally biodegradable, with microfibers breaking down in months, not centuries. Think 30-90% decomposition within just 15-90 days under suitable conditions.¹
• Chemical Impact: Dyes and finishes can slow things down, but even treated cotton vastly outpaces synthetics in returning to the earth. ^{1 2}
• Synthetic Problem: Polyester, nylon, and acrylic are plastics. They linger for decades, shedding microplastics that pollute our water and food chains.
• Your Closet, Your Choice: Opting for natural fibers like cotton, extending garment life, and proper end-of-life care (composting, recycling) makes a real difference.
• The Big Picture: Cotton is microplastic-free. The challenge is ensuring any added chemical treatments are equally biocompatible – a solvable problem, unlike the persistent plastic nature of synthetic fibers.

Did you know the cotton microfibers from your favorite T-shirt naturally disappear in a matter of months when left in nature? This natural property of cotton is essential, especially as we grapple with the overall fate and impact of our clothing. Cotton, being comprised of nearly all cellulose, is readily biodegradable under a variety of environmental conditions (e.g., in water, soil, compost, etc.). In fact, a new paper we published in collaboration with North Carolina State University confirms that cellulose-based materials like cotton can decompose by 30% to 90% within just 15 to 90 days under suitable conditions – even when chemically treated.¹  The main exception is in landfills with high solids and low moisture, where biodegradation occurs over decades.¹

Why this matters: Plastic pollution and textile waste represent growing global challenges, but cotton’s ability to return to the earth is a critical attribute that should not be overlooked. We’re all increasingly aware of plastic leakage – a massive challenge for the apparel industry.³ Large plastics (e.g., macroplastics) all eventually break down into microplastics, either when shed during washing and wearing of synthetic textiles or released as synthetic garments reach their end of life. Unfortunately, the long-term impact of these persistent synthetic materials and the true end-of-life fate of polyester clothing are often overlooked in sustainability frameworks like the Higg Materials Sustainability Index (Higg MSI).

This piece dives into the science of cellulose biodegradability, how chemical treatments affect it, and why cotton—being microplastic-free—is a more sustainable choice than synthetics. Our goal? To arm you with knowledge and practical steps for a more sustainable wardrobe and a healthier planet.

The Science of Cellulose Biodegradability

At the core of cotton’s natural cycle is cellulose. Simply put, cellulose is a natural polymer that forms the main structural component of cotton fibers and other plant-based materials. It’s what gives cotton its strength and durability.

But how does something so sturdy break down? This phenomenon is driven by enzymatic activity. As detailed in the “Biodegradability of Cellulose Fibers, Films, and Particles: A Review,” specialized enzymes, primarily produced by bacteria and fungi in the environment, are the key catalysts for cotton’s natural biodegradation. These enzymes essentially “unlock” the cellulose structure, breaking it down into simpler components that can be utilized by the ecosystem.¹

Several factors influence how quickly this natural decomposition occurs:

• Crystallinity: Cellulose contains both highly ordered (crystalline) and less ordered (amorphous) regions. Crystalline regions are more resistant to enzymatic attack, so a higher degree of crystallinity can slow biodegradation.¹
• Lignin Content: While cotton is virtually pure cellulose (~95%), other plant fibers contain lignin, a complex polymer that can shield cellulose from enzymes. Cotton’s very low lignin content is a key reason it is highly biodegradable compared to other plant-based materials.¹
• Environmental Conditions: The speed of biodegradation is heavily influenced by various environmental factors. Adequate moisture is crucial for microbial and enzymatic activity, while optimal temperatures promote microbial growth and enzyme function.¹

The Treatment Twist: How Chemical Finishes Affect Biodegradability

Cotton is well-established as a highly biodegradable material. However, its journey from raw fiber to finished garment often involves various chemical treatments—such as dyes for color, resins for wrinkle resistance, and softeners for feel—applied to enhance aesthetics, durability, and performance. This naturally raises a key question: how do these treatments affect cotton’s inherent biodegradability?

Our research indicates that chemical treatments can indeed influence the biodegradation process. Some finishes might create temporary barriers that make cellulose slightly harder for enzymes to access, potentially slowing decomposition.¹ Conversely, other treatments, like mercerization (a process using caustic soda to swell fibers), can alter the cellulose structure (from Cellulose I to Cellulose II), making it more accessible to enzymes and potentially accelerating biodegradation.⁴

The crucial takeaway, however, is that despite these treatments, research consistently shows that even treated cotton degrades significantly faster and more completely than synthetic fibers.¹ In fact, microfibers generated from dyed and finished cotton fabrics have been shown to biodegrade faster than an oak leaf—except in the case of durable press finishes, which may slow down the process.² Regardless of the dye or finish applied, the fundamental structure of cotton (~95% cellulose) supports its biocompatibility and eventual return to the ecosystem.¹

Cotton vs. Synthetics: A Tale of Two Waste Streams

When we consider the end-of-life of our clothing, the contrast between natural fibers like cotton and synthetic fibers becomes stark.

The Problem with Synthetic Fibers:

Synthetic fibers such as polyester and nylon are petroleum-based plastics inherently comprised of toxic compounds as part of their fundamental building blocks. These include substances like BPA (bisphenol A), PAHs (polycyclic aromatic hydrocarbons), and heavy metals, which pose risks to both human health and the environment.⁵ Their chemical structure, unlike natural cellulose, makes them extremely slow to degrade, persisting for decades or even centuries, whereas cotton can break down in months.^{6 7}

This persistence leads to significant environmental consequences. Improperly discarded synthetic garments or fibers shed during washing pollute our rivers and oceans, which may impact marine ecosystems.⁶ Microplastics released from these materials bypass wastewater treatment systems and contaminate waterways, where they are ingested by marine organisms, introducing toxic particles into the food chain. ^{5 6 [8]}Future studies are needed to understand the effects of these contaminants to human health when consumed through seafood, potentially leading to the accumulation of toxic substances in our bodies.⁹

Why Cotton Matters:

In contrast, cotton’s inherent biodegradability presents a more sustainable solution. As a cellulosic fiber, it naturally decomposes, returning to the soil and potentially enriching it.¹ Importantly, even cotton treated with common dyes and finishes degrades far more quickly and completely than synthetic alternatives, reducing its long-term environmental burden.¹

While the textile industry is developing more sustainable chemical treatments for all fibers, cotton’s advantage is its biodegradable base material. The focus for cotton becomes ensuring applied treatments are equally benign—a solvable challenge. For synthetics, however, the persistence of the base material itself remains the primary environmental problem.⁵

Practical Steps for a Sustainable Closet

Understanding the science is the first step. The next is taking action. Here are some practical ways to build a more sustainable closet and reduce textile waste:

1. Choose Natural Fibers: Prioritize clothing made from natural fibers like cotton. Cotton is a renewable and biodegradable material that breaks down more readily in the environment compared to synthetic fibers. Selecting 100% cotton or cotton-rich garments can help reduce the persistence of microplastics in ecosystems.
2. Embrace Durability and Longevity: Care for your garments properly to extend their lifespan. Extending garment life significantly reduces environmental impact; for instance, tripling the life of cotton pants can cut cumulative climate impacts by 31-41%.¹⁰ Keeping clothes in use longer is a powerful sustainability act.
3. Explore Composting: For 100% cotton items (or those with very high cotton content and natural trims) at their true end-of-life, composting is an excellent option. Undyed or naturally dyed cotton can break down in a home compost bin, returning nutrients to the soil and reducing textile waste.
4. Support Textile Recycling: Another option is textile recycling. Cotton Incorporated’s Blue Jeans Go Green™ program collects denim (predominantly cotton) and transforms it into new products like building insulation. This diverts waste from landfills and keeps the carbon stored in cotton fibers out of the atmosphere longer, contributing to a circular economy. Additionally, diverting cotton textiles from landfills helps reduce methane emissions (a greenhouse gas far more potent than CO₂) that would otherwise be produced as cotton decomposes under anaerobic conditions in landfills.

Conclusion

The science is clear: cellulose, cotton’s building block, readily biodegrades. As the most abundant polymer on earth, cellulose forms the foundation of plant cell walls, making it inherently compatible with natural ecosystems. By contrast, synthetic fibers like polyester and nylon are fundamentally incompatible with natural cycles, persisting as pollutants for generations. Cotton stands as a more sustainable alternative to synthetics, returning to the earth without leaving a legacy of microplastic pollution.

The path forward requires a dual approach:

• Continued innovation in more sustainable chemical treatments for all textiles.
• Conscious choices by us, the consumers.

By embracing natural fibers like cotton, extending garment life, and responsibly managing clothes at their end-of-life, we can collectively reduce textile waste. We can create a future where fashion doesn’t cost the earth, and our clothes, after a long, useful life, truly return to nature.

Want to see it for yourself? If you have an old, 100% cotton T-shirt beyond repair, try burying a piece in your yard or flower bed. Observe it over a few months. It’s a fascinating, hands-on way to witness cotton’s natural cycle and the power of cellulose biodegradability.

¹ Hubbe, M.A., Daystar, J.S., Venditti, R.A., Pawlak, J.J., Zambrano, M.C., Barlaz, M., Ankeny, M., Pires, S. (2025). Biodegradability of Cellulose Fibers, Films, and Particles: A Review. BioResources20(1), 2391-2458. Link

² Zambrano, M. C., Pawlak, J. J., Daystar, J., Ankeny, M., and Venditti, R. A. (2021). Impact of dyes and finishes on the aquatic biodegradability of cotton textile fibers and microfibers released on laundering clothes: Correlations between enzyme adsorption and activity and biodegradation rates. Marine Pollution Bull. 165, article112030.DOI: 10.1016/j.marpolbul.2021.112030. Link

³ Kounina, A., Daystar, J., Chalumeau, S., Devine, J., Geyer, R. Pires, S., Uday Sonar, S., Venditti, R., Boucher, J. (2024). The global apparel industry is a significant yet overlooked source of plastic leakage. Link

⁴ Wada, M., Ike, M., and Tokuyasu, K. (2010). Enzymatic hydrolysis of cellulose I is greatly accelerated via its conversion to the cellulose II hydrate form. Polym. Degrad. Stab. 95, 543-548. DOI: 10.1016/j.polymdegradstab.2009.12.014. Link

⁵ Wiesinger et al. (2024). LitChemPlast: An Open Database of Chemicals Measured in Plastics. Environmental Science & Technology Letters Vol11/Issue11, 1147–1160. Link

⁶ Marielis C. Zambrano et al. (2020). Aerobic Biodegradation in Freshwater and Marine Environments of Textile Microfibers Generated in Clothes Laundering: Effects of Cellulose and Polyester-Based Microfibers on the Microbiome. Marine Pollution Bulletin 151: p. 110826. Link

⁷ Marielis C. Zambrano et al. (2019). Microfibers Generated from the Laundering of Cotton, Rayon and Polyester Based Fabrics and Their Aquatic Biodegradation. Marine Pollution Bulletin 142: pp. 394-407. Link

⁸ Kala Senathirajah et al. (2021). Estimation of the Mass of Microplastics Ingested – A Pivotal First Step towards Human Health Risk Assessment. Journal of Hazardous Materials 404: p. 124004. Link

⁹ Roslan et al. (2024). Detection of microplastics in human tissues and organs: A scoping review. Journal of Global Health. Link

¹⁰ Pires et al. (2024). “Evaluating Cotton Apparel with Dynamic Life Cycle Assessment: The Climate Benefits of Temporary Biogenic Carbon Storage,” Bio Resources 19(3), 5074-5095. Link