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Improved hygiene protection for wool and other textiles containing wool02.12.2014 - (idw) Hohenstein Institute
Scientists develop wash-resistant antimicrobial treatment for protein fibres
As part of an IGF research project (AiF No. 17150N), scientists
at the Hohenstein Institute in Bönnigheim and the Leibnitz Institute for Interactive
Materials (DWI) in Aachen have developed an antimicrobial treatment for wool and
other textiles containing wool.
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.
By contrast, antimicrobial substances are often not effective at all, or only to a very
limited extent, on wool and mixed fibres containing wool. And yet an antimicrobial
protective treatment would be particularly desirable here, because textiles containing
wool are generally washed less frequently than textiles made from other fibres, due
to the felting tendency of woollen fibres. Especially in the outdoor and sports sectors,
wool is currently experiencing a real renaissance, so Mihaela Szegedi, Project Leader
at the Hohenstein Institute, sees that as a particularly attractive area of application for
this innovative textile finish: "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
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 >
1m) consist of two substances: the ionic biopolymer alginate (SA) and a type of silane
quat (the cationic tetraoctadecyl silicon ammonium compound (TSA)). The experts
at the Hohenstein Institute worked out the best ratio for the concentration of the two
components, SA:TSA, and how to find the best way of applying and fixing ultra-thin
layers to textile substrates.
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.
Following a two-stage gel cross-linking reaction to produce the colloidal complex
(Figures 1a and 1b) from different SA:TSA % weight ratios, the antimicrobial
effectiveness of the SA/TSA colloidal complexes was studied. The interaction with the
fibre substrates was tested by measuring zeta potential and the pre-prototype was
optimised to improve wash permanence.
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
The tests showed that by combining two active components (silver ions and Siquats)
the growth of microorganisms (bacteria and fungi) on wool and on wool and
polyester blends could be greatly reduced. The application of silver-release layers (Ag/
polyamine), polyelectrolyte (SA) and Si-quat layers (TSA) resulted in a finish that had a
The disadvantages of a combined treatment based on silver-release layers and
alternating polyelectrolyte layers are discolouring and limited wash permanence.
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 zincpyrithione
formulation over the sol-gel coating, a strong antimicrobial effect was
achieved which lasted even after 25 wash cycles (Figure 3). Here, too, 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. Analysis by dynamic light scattering (DLS) and ATR-IR
spectroscopy indicates that the interaction of the anionic polyelectrolyte SA with the
TSA silane-quat components leads to the formation of colloidal structures (micelles) or
silesquioxane oligomers as a result of electrostatic interactions.
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.
This kind of synergistic treatment for textiles with a high woollen fibre content can
be of great benefit to textile manufacturers (domestic textiles, upholstery materials),
insulation producers, hosiery manufacturers and other fabric producers. Companies
in the technical textile sector, whose product range includes woollen fibre blends (car
seats), will also be able to benefit from the advantages of antimicrobial protection. The
specific formulations that are used are already licensed under the EU Biocidal Products
Regulation and can therefore be used as a combined treatment (based on aqueous
colloidal dispersions) by textile finishing companies.
We are grateful to the Research Association the Textile
Research Council, Reinhardtstraße 12 - 14, 10117 Berlin for its
financial support for IGF project 17150 N, which was provided
via the AIF as part of the programme to support "Industrial
Community Research and Development" (IGF), with funds from
the Federal Ministry of Economics and Technology (BMWi)
following an Order by the German Federal Parliament.
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