During storage, transport and use personal protective equipment (PPE) for fall arrest may come into contact with chemical substances. While being transported, for example, in a car PPE may come into close proximity with engine oil, spare batteries or AdBlue. When used in industrial climbing, contact with chemical substances is also an issue, for example when cleaning special equipment or facilities or when handling motorized tools while climbing trees. Plastics are particularly affected by damage, as they are far more susceptible to chemical effects than metals. We want to address the question of how chemicals affect textile PPE and which substances are to be regarded as particularly critical.

 

IN LIGHT OF CURRENT EVENTS: One of the many consequences of the Corona epidemic is the increased use of disinfectants. In the rental area of climbing halls but also in private, the question for many climbers is whether and how such substances affect their ropes, slings, in short, their PPE. Our studies have shown, for example, that sargrotane does not reduce the strength of polyamide. Above all, strong acids and bases lead to changes in the properties of plastics. However, the relationships between the influence of chemical substances on textile PPE are complex and not easy to assess. You can find out more here in the article.

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CHEMICAL DAMAGE TO TEXTILE PPE 

Background

On principle, there are two different effects of chemicals on textiles:

  • Physical effect: if a medium does not react chemically with the plastic, it can still lead to a physical change in its properties. For example, this can result in surface changes and thus in the friction values, causing stiffening of the textile or swelling of the contaminated area. The changes resulting from a physical effect of the medium are reversible and can usually be remedied by washing out the chemical.
  • Chemical effect: the chemical reacts with the plastic and causes a decomposition reaction or a change in the molecular structure. The molecules of the chemical diffuse into the individual units of the polymer chain and weaken or break down its bonds. If there is a chemical reaction between the plastic and the medium, even small quantities can lead to pronounced changes in its mechanical properties.

The three main materials used in textile PPE are polyamide (PA), polyester, more precisely polyethylene terephthalate (PET) and ultra-high-molecular-weight polyethylene (UHMWPE), also known under the trade name Dyneema. Substances which cause changes to the properties of plastics can be divided into acids, bases, solvents, salts and oxidizing agents. By determining the pH value of the chemical, an initial rough indication of possible damage can be obtained. A substance with a pH value of 7, which corresponds to that of water, is considered neutral. The lower the pH value, the more acidic the substance is. The higher the pH value, the more alkaline the substance is. In Table 1, the pH limits show the range at which an acid or base can have a damaging effect on the plastic.

The table shows that strong acids and bases have a damaging effect, especially for polyamide.

Generally, a lot of information is available on the resistance of certain plastics to particular chemicals. Our incentive to carry out our own test series is to demonstrate the resistance of textile PPE to consumables in a test procedure suitable for the PPE. The test for consumables is of great importance in that the effects of a mixture of substances have not been well researched.

Method: How Were the Tests Performed? 

Not all contamination is equal. The effect of chemicals on textile PPE depends on many factors. On the one hand, the susceptibility to chemical substances depends on the material composition and the structure of the textile. On the other hand, the effect of the chemical is influenced by external conditions, such as the type of contamination, the temperature or the exposure time. We defined a worst-case scenario for our test to investigate the effect on our webbing. The exact test parameters are presented below.

  • Type of contamination: in practice, there are many routes by which chemicals may come into contact with PPE. From wetting by vapor to soaking the material in the substance, the range is great and the intensity of the contamination varies accordingly. For our test we decided to use an immersion bath to ensure diffusion of the chemical into the inner textile structures.
     
  • Exposure and reaction time: the exposure time describes the time period during which the textile is in direct contact with the chemical. We set a duration of 24 hours. The reaction time determines how long the chemical has time to dry and react with the material after direct contamination. We allowed a period of at least 72 hours in the climatic chamber.
     
  • Contamination and drying temperature: the temperature is a crucial factor for the reactivity of many chemicals, as an elevated temperature makes the molecular structures more mobile. This has a significant effect on the diffusibility of the chemical into the material, which is why the chemical resistance of plastics only applies to the specified temperature range. We chose to perform the contamination and drying at room temperature, i.e. 23°C (± 2°C) and a humidity of 50%, which corresponds to standard conditioning.

 

The Results of the Contamination Tests

The results table refers to the chemical resistance of textile materials to different substances at room temperature. Depending on the loss of strength, the harmfulness of the substance is divided into three categories:
 

  • Green, resistant: the textile retains its mechanical and physical properties. There is only slight or no damage to the textile, even after a long contamination period.
     
  • Orange, limited resistance: the textile retains its mechanical and physical properties over a longer period of time, or the loss of strength of the textile is within an acceptable range.
     
  • Red, not resistant: the textile loses its mechanical and physical properties after a short time. There is a strong damaging effect, which leads to the complete destruction of the textile at very low tensile loads.

We are endeavoring to expand this table to provide an overview of other substances and their chemical effects on textile PPE. However, caution is required when classifying the effects of substances:

  • the physical effect of chemicals can also have a major impact on their durability, as in the case of contamination of a kernmantle design. A stiffening of the sheath can be caused if the chemical penetrates into the sheath braid without penetrating into the core. Under mechanical load this stiffening can lead to a displacement of the sheath or to premature breakage of the sheath when falling over an edge.
     
  • Dyneema slings include some polyamide, which allows the textile composite to fail without the Dyneema deteriorating. The Dyneema threads are torn from the composite and thus can no longer sustain their maximum tensile strength. Therefore, even in the event of contamination with a chemical that is harmless to UHMWPE, caution is required and PPE should be discarded as a precaution.

 

Conclusion 

The effect of chemical substances on PPE is complex and not easy to assess. Therefore, contact between PPE and chemical substances should generally be avoided.

Even though some chemicals are only harmful for certain materials, PPE should be discarded in the event of contamination with strong acids and bases, e.g. hydrochloric acid, grip or pipe cleaners—regardless of the textiles involved.

Moreover, this list is only exemplary and when classifying other substances it is essential to take into account that the components and concentrations of mixtures of substances cannot always be determined.

 

Bibliography 

Koller, S.: Säureeinfluss auf Textilmaterial im Bergsport und deren Nachweisbarkeit, degree dissertation.

Polytron Kunststofftechnik GmbH & Co. KG (2011): Chemikalienbeständigkeit. Available online >