CO2 reacts with water, even when it forms part of another molecule as an ester group. Under the right conditions, this “hydrolysis” reaction can disintegrate polyesters into smaller molecules known as hydroxy-fatty acids ("omega hydroxy acids"). These are readily digested by various microbial species present in the environment, many of which produce enzymes to speed up the breakdown process. The only byproducts are biomass, CO2 and water (or methane in anaerobic conditions such as landfill or marine sediment).
Rapstrap PCL cable ties are very stable if kept clean & dry, and may be stored for over 10 years prior to use. Outdoors, they can be used for many months without significant deterioration, but will start being degraded within a few weeks once permanently exposed to moisture and microbes, such as when covered by damp soil. (Essentially, they behave similarly to wood when left outside.)
Common strains of fungi such as Fusarium and Aspergillus have been shown to rapidly digest PCL even in cold soil conditions; This ability has been attributed to the material’s unusually low melting and glass-transition temperatures.
In the tests shown here, our ties were placed in damp potting compost and left to over-winter in cool conditions at around 5C. Despite the low temperature, significant microbial colonisation still occurred in less than two months.
The exact fungal strain(s) seen forming clumps and wispy filaments is currently unknown. Interestingly, there is no sign of growth in the surrounding compost.
Because microbes capable of consuming polycaprolactone are widespread in the environment, the rate of biodegradation of the material itself is mostly determined by temperature and moisture.
Dry conditions are the major limiting factor. They are not conducive to microbial growth, and the underlying hydrolysis mechanism relies on the availability of water. In extremely arid environments (e.g., deserts), biodegradation may effectively stop altogether, regardless of temperature. (As was well understood by the Ancient Egyptians!)
Provided rapstrap PCL cable ties are exposed to moist surroundings in which microbial species can thrive, signs of biodegradation can be expected to be visible within a few weeks. Complete bio-assimilation may take anything from a few months to a few years, depending on local conditions.
After the initial colonisation stage, material degradation will commence, and will accelerate with increasing temperature. In the tests shown here, PCL cable ties were inserted into damp soil and left in mild conditions, typically around 15-20C. Significant microbial consumption was observed after just 12 weeks, with the ties clearly starting to disintegrate.
The light-brown cratering is where microbes were steadily eating away at the cable tie portion that was buried.