Testing for sustainability

Explaining the importance of being able to prove claims made about a product’s environmental credentials and some of the tests used to substantiate sustainability.

by Nicola Pichel-Juan

In recent years there has been a significant backlash against so-called ‘greenwashing’, which has led to the introduction of legislation around the world that is intended to ensure that any claims made about the environmental or sustainable credentials of a product are accurate, fair, unambiguous and can be substantiated. The fashion industry is particularly coming under scrutiny – from consumers and legislative bodies – for some of the environmental claims being made from within the sector.

It is therefore more important than ever that organisations can back-up any claims they are making. In some cases, effective and clear communication combined with due diligence may be enough. However, where further evidence may be required, there are certain sustainability credentials that can be verified in a laboratory environment. This article will introduce some of the testing that can be conducted to validate the environmental credentials of a product.

Restricted substances

Organisations in the footwear supply chain have been managing ever more demanding restricted substances legislation in recent years. This legislation is intended to protect human health and the environment by restricting or eliminating substances that are persistent, bio-accumulative and toxic to the environment, carcinogenic, mutagenic, or toxic for reproduction. Testing can be used to confirm the absence/presence of a substance and, if present, to what degree. We have an extensive library of SATRA Bulletin articles and webinars produced by our chemistry team that examine this topic in greater detail, while focusing on specific substances and explaining what to look out for in particular materials.

Recycled polyester

There are well-established supply chain verification schemes that are used to certify that the polyester being used to manufacture a product is recycled rather than a virgin material. Laboratory analysis methods are now also being offered to confirm that polyester has been recycled from plastic bottles made from polyethylene terephthalate (PET). One such approach is by measuring the concentration of isophthalic acid, a compound typically added during the PET bottle manufacturing process which, in turn, can be used as a ‘marker’ in recycled polyester.

SATRA’s research into this testing has shown that using isophthalic acid as a marker for recycled polyester has its limitations, as isophthalic acid could also potentially be present in virgin polyester. We therefore recommend that if this test is carried out, it is done so only in conjunction with supply chain verification.

End-of-life

An area of growing interest is understanding what is likely to happen to an item at the end of its life in certain environments, and what impact that item might have on an environment. This concern takes into consideration whether the impact is on an intended end-of-life destination – for example, landfill, bioreactor or industrial composting facility – or an unintended destination, such as the sea, a river or a field. Many organisations are now developing materials and products that are intended to break down or biodegrade in a particular environment, and verifying that biodegradation can be carried out in a laboratory environment.

The ASTM D5511 (equivalent to ISO 15985) and ASTM D5526 tests are commonly used to measure the rate of ‘anaerobic biodegradation’ (the microbial degradation of organic compounds in the absence of oxygen). Materials that biodegrade anaerobically have the potential to be disposed of in bioreactors or anaerobic landfill sites, as they biodegrade, they breakdown into biogas. This gas can then be captured, purified and turned into biomethane which, in turn, can be used as a ‘green’ fuel.

Developing compostable items has been common in the packaging industry for a number of years, and there is a growing trend for single-use items (such as disposable coffee cups) to be marketed as ‘compostable’. More recently, compostable materials are starting to make their way into the fashion industry – for example, new tanning systems allow compostable leathers to be produced.

For a material to be certified as compostable, it must meet a number of different criteria: i) ‘characterisation’ – the material itself cannot contain any harmful substances, typically heavy metals and fluorine, ii) ‘biodegradability’ – it must biodegrade and release CO₂, iii) ‘disintegration’ – the material must break down into smaller pieces, iv) ‘compost quality’ – the resulting compost must be suitable to use as compost, which is usually verified by tests that try to grow plants in compost containing the material, and even potentially by tests exposing organisms such as earthworms to the compost, and v) ‘recognisability’ – the resulting compost must be recognised/accepted as compost – it must look, smell, and feel like compost.

Carbon content

Reducing CO₂ emissions is crucial to the mitigation of the worst effects of climate change, and it is being increasingly recognised that not all carbon is equal.

‘Bio-based carbon’ (also known as ‘modern’ or ‘recent’ carbon) comes from biomass such as plants and animals. Plants absorb carbon dioxide from the atmosphere and use it to make many compounds through the process of ‘photosynthesis’. The plant compounds are consumed by animals and humans who then ‘respire’ (breathe out) the bio-based carbon dioxide. Plants and animals eventually die and decompose, releasing further bio-based carbon back into the atmosphere. This is a natural cycle that occurs relatively quickly over a period of years or decades.

‘Fossil carbon’ is carbon that has been formed over a much longer period of time. Living organisms (plants and animals) die, their remains become buried and through heat and pressure over millions of years, fossil fuels such as oil and coal are created. Extracting and burning these fuels releases huge amounts of additional fossil carbon into the atmosphere, which means that more heat is trapped, and over time the planet gets warmer.

Although the warming effect from bio-based and fossil carbon is the same, bio-based carbon does not result in additional carbon being added into the atmosphere.

It is possible to test materials to measure their bio-based versus fossil-based carbon content using test methods such as ASTM D6866-22 – ‘Standard test methods for determining the bio-based content of solid, liquid and gaseous samples using radiocarbon analysis’ and ISO 16620-2:2019 – ‘Plastics. Bio-based content. Determination of bio-based carbon content.’ This concept is explained in more detail in the article ‘What is bio-based carbon?’

Microplastics and microfibres

Microplastics and microfibres ‘shedding’ from items during use, wear or, in the case of garments, while being washed, is a huge cause of concern. Microfibres and microplastics have been found everywhere from the Arctic to the peak of Mount Everest. Microplastics have even been found in human blood and heart tissue. The impact that these tiny fragments have on ecosystems and organisms is only at this time starting to be understood.

There are well-established tests for measuring microfibres shedding from garments during washing. So far, there has been less focus on the potential for microplastics to shed from outsoles in wear. However, this will almost certainly come under further scrutiny in the future, and SATRA is developing testing protocols to analyse microplastic loss from outsoles during wear.

Vegan verification and testing

While a vegan material is not always a sustainable material, the concept of ‘vegan’ is something that tends to be included as a sustainable credential. There are tests that can confirm the absence or presence of animal-derived substances in a material. This testing was covered in detail in the article ‘The challenges of vegan footwear’. However, a brief summary is provided here.

Fourier Transform Infrared spectroscopy (FTIR) and optical microscopy can be used to identify the potential presence of animal proteins. FTIR focuses infrared radiation onto the material and detects the wavelengths absorbed. The results are then compared to a library of known substances to provide a form of identification. Optical microscopy is used to identify fibrous materials such as textiles and leathers, by observing a small piece of material under a microscope to determine whether the fibres appear to be of animal origin.

Deoxyribonucleic acid (DNA) and protein analysis can be used to test for the presence of animal substances at a molecular level. The DNA analysis involves extracting molecules of DNA from the material being tested and analysing it for the presence of certain genetic markers which would indicate the presence of animal substances. The use of protein analysis for vegan verification is still in the early stages, but this could be potentially more reliable, as proteins are generally more stable than DNA.

None of the tests mentioned above are foolproof, and SATRA would recommend that testing is used to support supplier declarations and supply chain verification.

Durability

‘Durability’ is increasingly being recognised as an important factor in making sustainable products. A well-made, long-lasting item will have a much lower impact per wear or use, than an item that may be disposed of after only a few times of wearing. The concept of durability is written into both the draft European Product Environmental Footwear Category Rules (PEFCR) and the European Eco Label for footwear, which set certain durability standards considering properties such as upper to outsole bond strength and abrasion resistance of outsoles. Durability is also considered in the French EPR scheme for footwear, with discounts on EPR fees given to products achieving certain thresholds in testing.

Testing for durability and identifying potential points of weakness or failure in finished footwear and its constituent materials and components has been at the heart of SATRA’s activities since its foundation in 1919. SATRA is working to define what durability looks like from a sustainability perspective, to be truly able to identify those products that have been built to last.

It is also worth noting that any finished footwear item, material or component that is developed to be more sustainable – for instance, by having a lower carbon footprint – still needs to meet the performance that is required for its intended application.

Publishing Data

This article was originally published on page 14 of the February 2024 issue of SATRA Bulletin.

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