.jpeg)
Rubber waste, including natural and synthetic variants, along with textiles, wood, and leather, accounts for approximately 8% of the total Municipal Solid Waste (MSW or “trash”) managed by municipal waste systems. Of this, rubber content ranges from 0.5% to 2% of MSW. The volume of MSW is projected to grow significantly from 2 billion tons in 2020 to between 2.7 and 3.2 billion tons by 2030 and 2040, respectively. This waste is not confined to specific regions, with the largest contributors being China, the United States, India, Europe, Brazil, Russia, and Indonesia.
Recycling efforts are more prevalent for larger rubber products, such as tires, due to the economic and logistical feasibility of collecting, processing, and separating them. Smaller rubber items, like threads, are less commonly recycled due to higher challenges in handling and processing.
Spandex or elastane, made from polyurethane, is particularly challenging to recycle because of its chemical composition, heat sensitivity during recycling processes, and hard to separate because they are used in blended textiles. As such, reusing or downcycling remains the most viable approach for managing spandex waste.
Standardized compostability tests (e.g., ASTM methods) simulate municipal composting environments to evaluate decomposition. Materials passing these tests are considered both compostable and biodegradable, although they may also biodegrade under non-composting conditions too.
Unvulcanized natural rubber is not cured and is inherently biodegradable. However, vulcanization, a process that improves rubber’s strength, hardness, and durability, alters its biodegradability. Vulcanization involves adding agents (e.g., sulfur) that create crosslinks between polymer chains. While this enhances performance, it reduces biodegradability.
Research by Pattanawanidchai et al. (2024) demonstrated that biodegradability decreases with higher levels of vulcanizing agents. Over a 365-day period, unvulcanized rubber and rubber with low curative agents exhibited biodegradation rates of 54-59%, compared to only 28% for rubber with high levels of curative agents.
Yulastic natural rubber filaments strike a balance between durability and biodegradability, employing a vulcanization level comparable to low-curative formulations.
To evaluate biodegradability, a modified ASTM D5338 compostable testing for a period of 90-days was conducted, measuring CO₂ emissions over that period.
The graph below shows the biodegradation of YULASTIC natural rubber filament (33.2%) compared to (or normalized) to the cellulose (81.9%) control over a 90-day (3 month) period. The testing was not extended beyond 90 days.
Yulastic natural rubber filaments are 100% biobased, offering a sustainable alternative and replacement for petroleum-based spandex. Combining durability with reasonable decomposition rates under composting conditions, Yulastic provides a solution that balances performance and biodegradability.
Yulastic filament test samples were directly sent from Yulex’s authorized licensing manufacturer to RespirTek (Ocean Springs, Mississippi), where testing was conducted following ASTM D5338-15 test methods.
ASTM D5338-15 is a standardized method developed by ASTM International to evaluate the aerobic biodegradability of plastic materials under controlled composting conditions. This test measures levels of carbon dioxide (CO₂), water, and biomass within a composting system. Although there is no specific test standard for natural rubber materials, the industry universally adopts these methods for assessing textiles. The test simulates industrial composting conditions to determine how effectively a material decomposes.
Currently, for material to be classified as 100% compostable (and therefore 100% biodegradable), it must achieve at least 90% degradation within 180 days under these controlled conditions.
Total Organic Carbon (TOC) or Total Carbon Content is a critical metric in biodegradability studies, providing valuable insight into a material’s composition and potential environmental impact.
Both natural rubber and cellulose contain organic carbon:
During biodegradation, microorganisms metabolize the organic carbon, converting it into carbon dioxide (CO₂), water, and biomass. Cellulose is an established control in compost testing due to its ability to completely break down into simple sugars, which are readily consumed by bacteria, fungi, and other microorganisms under composting conditions. Additionally, cellulose is renewable and sourced from various plant-based materials, such as wood, cotton, or agricultural residues.
While not definitive, a higher TOC value in a test material indicates a greater likelihood that microorganisms can use it as a food source, facilitating its biodegradation.
