Silk: natural biodegradable textile fiber

The subdivision of fibers in the textile panorama, although the latter is decidedly complex, is quite simple and immediately understandable based on the key distinction between natural fibers Vs chemical fibers, dividing the latter into artificial fibers and synthetic fibers

There are more and more attempts to make this scheme more complicated, for example by inserting new pseudo-categories with the primary purpose of confusing the final consumer.

Silk is a natural textile fiber of animal origin derived from the activity of a lepidopteran that in the form of a silkworm produces a filament to create a cocoon in order to implement a transformation from caterpillar to butterfly.

Silk is an eco-sustainable natural fiber that, when compared to synthetic and artificial fibers, highlights its high environmental protection value and zero release of polluting and harmful substances for humans

A material is biodegradable if it can decompose in nature into simpler elements and/or substances thanks to the enzymatic action of microorganisms and bacteria, atmospheric agents or sunlight.

The biodegradation process must be a completely natural process in which the original organic substances are transformed into inorganic molecules (mainly within the carbon cycle), to be reintroduced into the natural cycle as a primary element of the animal and plant life cycle. All of this presupposes the non-release of harmful and polluting substances

The European Environment Agency (EEA) defines biodegradability as: “the extent to which a substance can be decomposed by bacteria and fungi leaving residues of degradation that are not toxic”

However, Biodegradable is not synonymous with harmless or ecologically positive material. During biodegradation phenomena, harmful elements can be developed that can damage the environment and degrade over longer periods than the material from which they derive.

Biodegradation can be partial and incomplete and, even if it complies with the criteria specified by the various regulations, it could allow the accumulation of highly harmful parts with a very serious environmental impact

The European standard EN13432 of 2002, with reference to the requirements for packaging recoverable through composting and biodegradation, has tried to fill the gaps of Directive 94/62/CE by defining the characteristics that a material must have in order to be considered compostable.

A material is compostable if:

• From a metabolic point of view it converts into carbon dioxide by at least 90% within the first 6 months in an environment rich in carbon dioxide, according to the EN14046 standards
• If in contact with organic materials for a period of 3 months its mass is made up of parts smaller than 2 mm by 90% (EN14045), (Disintegrability)
• It has no negative effects on the composting process
• It satisfies a low concentration of heavy metals
• It respects the pH values
• It respects the salinity values
• It respects the values ​​of volatile solids
• It respects the concentration levels of nitrogen, phosphorus, magnesium and potassium

Each of these points must be verified to define a compostable material; therefore, any material that is biodegradable but does not comply with the other parameters (for example, produces high concentrations of volatile substances or has a high PH), is not compostable. A material that disintegrates into very small, non-degradable pieces is also not considered compostable

The protein composition of silk determines that it is considered compostable in ideal conditions.

If we insert the natural silk fiber into a composting system, it will decompose effectively and will also help to release elements such as nitrogen and essential nutrients that are particularly important for the quality of the process and the soil.
Decomposition times are different depending on the state in which the natural silk fiber is found (fiber, waste, yarn, fabric).

Nature created the silk filament to protect the vital activity of the silkworm from external atmospheric agents and at the same time to be difficult to attack, in a short time, by bacteria, fungi and microorganisms in general:

• maximum protection of the silk cocoon
• silk is naturally antibacterial and antifungal.

Its propensity to not accumulate humid micro-pockets in some cases can slow down but not modify its compostability.

Natural silk without chemical treatments or coating can be composted in domestic and industrial plants.

Natural silk fibre is a biodegradable material: once silk is left in the environment, its elements, thanks to the action of proteolytic enzymes (capable of breaking down protein bonds), will return to nature in the form of humus, feeding the soil and subsoil.

The biodegradability times are determined by different factors, including the form that the fibre takes:

• Short, medium time for natural free fibres (fibres, waste, yarns)
• Medium-long time for fabrics

Any treatments even if for organic fabrics (colouring, chemical and finishing) can affect these times.

An empirical test scheduled at our factories has allowed us to highlight in a real and documented way the aspects and times of complete and natural biodegradability of silk fiber:

• 2 samples of silk fiber were placed in an external lawn area in front of our offices, in the spring / summer period in direct contact with atmospheric phenomena, simulating abandonment in the environment
• A sample was placed on some unsealed ceramic tiles and a sample in direct contact with the ground
• After 15 days from positioning the fibers from a dispersed form assumed a single mass consistency and some primary forms of plants began to emerge with the presence of insects and small worms
• After 45 days plants and vegetables had extensively colonized the fibers in a mass in close contact with the ground, for the fibers placed on the ceramic tiles the process was of the same type even if partially slowed down
• After 60 days the fiber was completely incorporated into the ground and vegetation