Antimicrobial basalt: From rocks to threads

Scientists have developed effective antimicrobial glass and basalt fibers. The fibers are effective against different strains of bacteria and fungi and might be used in filters and textiles in the future.

Microbes and biocides - An innovation is on the way

Scientists from Germany have developed effective antimicrobial glass and basalt fibers. The fibers are effective against different strains of bacteria and fungi and might be used in filters and textiles in the future.

Bacteria and fungi can represent an enormous cost factor for an economy. They impact, among others, the health care system, the food industry, or the building materials industry, to mention a few. A wide variety of biocides are used to contain these dangerous pathogens. However, these are often expensive and can pollute the environment if, for example, they reach the groundwater. For this reason, work has been successfully carried out for years to anchor the antimicrobial active components firmly on surfaces or in substrates. In the textile sector, for example, silver nanoparticles are embedded in polyester fibers. However, the area of inorganic fibers, which are more resistant in many respects, has apparently remained unnoticed to date.

Production of the fibers and proof of effectiveness

Compared to organic fibers made of polyester, polyamide, etc., inorganic fibers are generally characterized by higher resistance to temperature, UV radiation, chemicals, aging, etc. This places them in a valuable position for use in corresponding environments or applications.

Inorganic fibers made of glass or basalt are manufactured at temperatures of up to 1,500 °C. Therefore only antimicrobial effective inorganic metal compounds can be used for embedding in the fiber. Organic antimicrobial agents such as quaternary ammonium compounds can also be used for surface functionalization.

For the tests, a suitable basalt deposit had to be found and various basalts had to be selected from various suppliers. Then the chemical components and viscosity were examined and numerous tests were carried out on the laboratory plant.

The addition of the inorganic metal compounds and their homogenization with the basalt material was carried out in an initial melting process. The resulting material could be processed into endless basalt fibers at a fiber drawing plant. The diameter of the fibers is between 10 µm and 30 µm.

Usually, textile fibers are provided with a sizing which, among other things, enables the subsequent textile processing. For inorganic fibers, silane sizing is usually used, which nevertheless increases the tensile strength by up to 50% and improves the fiber-matrix adhesion when used in fiber composites. In the tests, a sol-gel process was used for coating, which was additionally mixed with antimicrobially active substances.

The antimicrobial effectiveness was first tested according to DIN ISO 20743 standards with the bacterium Escherichia coli. Significant efficacy could already be established for the uncoated fibers. The reproducibility of the bacteria was completely suppressed.

Further fiber variants were tested according to ASTM E2149 standards. The testers found good to very good effectiveness against the bacteria Staphylococcus aureus and Pseudomonas aeruginosa as well as the fungus Aspergillus brasiliensis in particular.

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