As part of an IGF research project, scientists at the Hohenstein Institute and the Leibnitz Institute for Interactive Materials (DWI) have developed an antimicrobial treatment for wool fabrics and wool blend fabrics.

Many of the antimicrobial treatment substances available on the market today are very effective on cotton, polyester, polyamide and those kinds of mixtures of fibres, the Institute reports. By contrast, antimicrobial substances are often not effective at all, or only to a very limited extent, on wool and mixed fibres containing wool.

“By combining the use of different antimicrobial substances and technologies, we have achieved a really wide range of effectiveness. This will be especially of interest to manufacturers of high-quality functional textiles containing wool. However, we also see great potential for classic business suits or ladies' suits made of wool or mixed fabrics containing wool, as well as domestic and furnishing textiles,” explained Mihaela Szegedi, Project Leader at the Hohenstein Institute.

Different approaches

To find the best formulation, the researchers studied the combined use of ionic biopolymers, cationic polyelectrolytes, materials like silver and zinc and technologies such as layer-by-layer coating. The two research institutions pursued two different approaches in parallel.

At the Hohenstein Institute, researchers concentrated on producing a colloidal dispersion of mixed substances (a colloidal complex) in an aqueous dispersion medium. This is what a suspension is called in which the antimicrobial particles (1nm < size > 1μm) consist of two substances: the ionic biopolymer alginate (SA) and a type of silane quat (the cationic tetraoctadecyl silicon ammonium compound (TSA)).

The DWI developed a hydrogel coating made of polyamines and silver colloids and studied the effectiveness of the silver-release layers that were produced in situ in the treatment of pure woollen fabric and in fibre mixes.

Combined treatment

Following a two-stage gel cross-linking reaction to produce the colloidal complex from different SA:TSA % weight ratios, the antimicrobial effectiveness of the SA/TSA colloidal complexes was studied.

By using application techniques such as high-temperature exhaust and cold-pad-batch processes, followed by drying/fixing, alternating layers of the polyamine hydrogel, the silver colloids and the polyelectrolyte layers (SA, TSA) were applied and the range of effectiveness was evaluated at both research centres using different assessment matrices.

The tests showed that by combining two active components (silver ions and Si-quats) the growth of microorganisms (bacteria and fungi) on wool and on wool and polyester blends could be greatly reduced. The disadvantages of a combined treatment based on silver-release layers and alternating polyelectrolyte layers are discolouring and limited wash permanence.

Effectiveness

In the research project, a treatment based on colloidal complexes was developed for the first time specifically for wool and WO and PET fibre blends.

By applying colloidal layers of the SA/TSA complex (in a 1:2 ratio), together with a colloidal zinc-pyrithione formulation over the sol-gel coating, a strong antimicrobial effect was achieved which lasted even after 25 wash cycles. In addition to the wash permanence, a wider spectrum of effectiveness against bacteria and fungi was noted as a result of combining the two active components.

It was found that the effectiveness against Gram-positive and Gram-negative bioindicators can be increased by a higher proportion of TSA.

Fibre protection

Combining the use of the aqueous SA/TSA complex and colloidal silver in an exhaust process, or of commercial zinc-based colloids in a Foulard process, leads to a wide range of effectiveness and excellent hygiene protection for products containing wool.

This means that products based on animal protein fibres can be protected against the destructive effect of fungi, algae and bacteria. Woollen textiles that are frequently exposed to moisture can also be protected by this treatment from material damage such as mould or rotting.

www.hohenstein.de