|Posted: Dec 16, 2010
(Nanowerk Spotlight) "Nano Textiles" can be produced by a variety
of methods. The key difference among
them is whether synthetic nanoparticles are
integrated into the fibres or the textile, or
are applied as a coating on the surface,
and/or whether nanoparticles are added
to the nanoscale fibres or coating. However,
information about manufacturing
methods, the nanomaterials themselves
and the quantities used, as well as the "life
cycle" of the "nano-treated" textile for sale
is largely unavailable to the consumer. The
present dossier therefore clarifies nano-textile
manufacturing processes and application
areas, and gives an overview about
the potential effects on the environment
and health. Many questions remain unanswered,
however, there is a need for considerably
more research not only for product
development but also into the usefulness
and risks which nano-textiles give rise
to. The open questions have prompted the
Swiss Textile Federation to undertake a joint
project with the Swiss Federal Laboratories
for Materials Science and Technology (EMPA)
entitled "Nanosafe Textiles" and to initiate
discussions on the topic.
Manufacturing processes of fibres and textile surface patterns for nano textiles
In principle a distinction has to be made
as to whether the manufacturing process
involves the use of nanoparticles or whether
it uses nanostructures (nanometer-thin fibres,
nanoporous fibres) without synthetic
nanoparticles. Nanoparticles can be introduced
into a synthetic material (polymer)
and fibres can then be spun from the resulting
nanocomposite material, which have
a nanoscale, or larger, diameter. Nanometer-
thin fibres can however also be manufactured
from synthetic material or cellulose
without synthetic nanoparticles. In this
case the term nanofibre is used to refer to
the tiny diameter of the fibres.
Manufacture of nanofibres (NP: nanoparticles, CNT: carbon nanotubes).
A further possibility is the so-called "refining"
of chemical and natural fibres by which
nanoparticles themselves are either bonded
to the fibre surfaces or are embedded in
a coating on them. However, textiles and fibres
can also be refined by means of nanoscale
metal or polymer coatings, produced
by immersion, spraying or plasma processes
which do not contain synthetic nanoparticles.
As in the case of fibre manufacture
"nano" is used in this instance to refer to the
nanoscaling of the coating 1.
Application areas and products
The potential of nanotechnology in the development
of new materials in the textile industry
is considerable. On the one hand, existing
functionality can be improved using
nanotechnology and on the other, it could
make possible the manufacture of textiles
with entirely new properties or the combination
of different functions in one textile material 2.
Table 1 gives an overview of the improved
properties of textile materials that can
be achieved using nanotechnology, including
the type of nanomaterials used.
Foremost among the applications currently
feasible are, in particular dirt and/or waterrepellent
and antibacterial textiles and, although
they are as yet produced on a very
small scale, textiles which give UV radiation
protection and so-called "Cosmeto-textiles"
(e.g. ladies tights) with woven-in nano-capsules
containing special body care substances.
Bullet-proof vests containing carbon
nanotubes (CNT) are also currently available,
as are heat isolating and moisture-absorbent
"Smart clothes" are clothes in which the textile
structures themselves perform electronic
or electric functions. Despite all the promises,
however, they are not yet commercially
available. The scenario envisaged involves
electronic components which have been reduced
in size by means of nanotechnology
being completely fused with the textile material
resulting in that textile and non-textile components cannot be differentiated and
"foreign particles" can no longer be seen or
felt. At present initial trials are still focussing
on electronic devices or sensors, for example
to monitor body functions, being woven
into the textiles using conventional clothing
technology (e.g. pockets) 3.
Researchers are also investigating textile materials
made from nanofibres which can act
as a filter for pathogens (bacteria, viruses),
toxic gasses, or poisonous or harmful substances
in the air. Medical staff, fire fighters,
the emergency services or military personnel
could all benefit from protective garments
made from materials such as these. Certain
nanofibres can absorb a large amount of
moisture, hence textile materials are also being
studied for use in agriculture: soaked with
pesticides, they could be planted together
with seeds, rot at the end of the vegetation
period and at the same time fertilize the
ground. Futuristic visions even include textile
sensors which not only detect pathogens
by simply wiping a surface (e.g. of food or
surgical instruments), but record them and
warn the user, possibly by changing colour 4.
According to the manufacturers, there are
already quite a number of different nano textiles
on the international market. The
"Woodrow Wilson International Center for
Scholars" in the USA lists 156 articles under
the "clothing" category on its nano-product
database 5. Our own research 6 into the
European and Austrian market in particular,
found 82 products in the "clothing" category,
six in the category "interior textiles",
and eight in the Outdoors sector which have
nano-coating (tents, sleeping bags) and one
textile product with nano-silver for cleaning
purposes. Most of these products are advertised as having dirt or water-repellent properties,
e.g. coats and trousers for the Outdoors,
or shirts, ties and/or workwear garments
with "stain protection". However, there
is also a large group of antibacterial textiles
containing nano-silver. These consist principally
of odour-inhibiting clothing (underwear,
T-shirts, socks etc.), but also include
interior textiles products such as cushions,
blankets or mattress covers which, according
to the manufacturers at least, can be
bought on the retail market.
Overview of the nanomaterials used in textile applications research and possible functions which might be achieved through their use (slight adaptation from 2).
A study of scientific publications on nanotextiles
has been conducted with the summary
that many of the manufacturing methods
described are still at the research stage,
to some extent they are cost-intensive, and
that the integration of nanoparticles can have
a negative impact on other textile properties 2.
Nevertheless, nano-textiles with almost
all the properties cited in Table I are already
on the market. It can be assumed that the
term "nano" is often used for promotional
purposes and that several products do not
contain any nanomaterial or that nanotechnology
processes were not used in the manufacture.
However, this is not just true of the
textiles sector but is a phenomenon that applies
equally to many other "nano-products".
The "Hohenstein Quality Label for nanotechnology" in textiles
Germany's Hohenstein Institute is a private
research and service organisation focusing
on research, development, testing, consultation,
certification and basic and advanced
training, mainly for businesses in the textile
industry and associated areas. Together with
NanoMat, a network of research institutions
and suppliers of nanomaterials, a definition
of nanotechnology for the textile industry was
elaborated, which is also the basis for the
"Hohenstein Quality Label for nanotechnology":
"Nanotechnology refers to the systematically
arranged functional structures which
consist of particles with size-dependent properties."
7 A textile product therefore does not
qualify for the Hohenstein Quality Label
merely on the basis that it has nanoparticles
incorporated within the fibres or that the fibres
are enclosed in a nanoscale coating.
Rather, the nanoparticles or nanolayers in
or on the textile must be systematically arranged
(Figure 2) and thus demonstrably result
in a new function. At the same time there
must not be any negligible negative effect
on the textile properties.
Further parameters which the Hohenstein Institute
can test include resistance to care
treatments and wear comfort. These are indicated
separately on the quality label.
This quality label could be of value to consumers
and companies alike and allow a distinction
to be made as to whether a product
is a "genuine" nano-textile product or
whether the word "nano" is being used as
a powerful sales catchword for an otherwise
conventional product. Only four textile manufacturers
have so far taken advantage of
The "Hohenstein Quality Label for nanotechnology"
for textiles (as at 9.10.09).
Are synthetic nanoparticles released from nano-textiles?
As shown above, there are different manufacturing
processes by which nanoparticles
can be integrated in fibres or textiles, besides
which there can be variation in how tightly
woven the nanoparticles are into the textile
material (fibre or coating).
It is these factors
and the use to which the textile is subjected
that determine whether and to what extent
nanoparticles can be released from it. It is
known that textiles lose between 5% and 20%
of their weight during use as a result of abrasion,
mechanical influence, irradiation, water,
sweat, washing detergents or temperature
variations. The possibility therefore cannot
be ruled out that nano-textiles might release
individual nanoparticles, agglomerates
of nanoparticles or small particles of textile
with or without synthetic nanoparticles. To
date, however, there have been few experimental
investigations performed 1.
|Figure 2: Left: Nanoparticles systematically arranged on a textile. Right: By contrast, an unsystematic arrangement7
In the case of textiles made from fibres with
integrated nanoparticles, however, a lasting
functionality at least appears more likely
compared with nano-textiles in which nanoparticles
are only present in the surface coating
or which have been impregnated with
them. The few investigations there have been
with textiles containing nano-silver show that
some products lose up to 35% of the silver
in the washing water after only one wash 8 9.
It appears to be emerging that during the
production process of certain nanoparticles
occupational exposure can have negative effects
on the health. However there is currently
far too little data from laboratory and animal
tests to be able to conduct a comprehensive
risk assessment 10. Long and stiff
CNT in particular are currently regarded as
hazardous 11, which primarily affects those
involved in their manufacture and who
need to have appropriate protection from exposure.
The extent to which nanoparticles
woven into textiles may or may not be harmful
to consumers' health is as yet unknown.
As described above, the release of nanoparticles
from textiles as a result of use, aging,
abrasion etc. cannot be ruled out. Nevertheless,
suitable studies are absent to clarify the
exposure as well as the possible hazard potential.
Nano-silver is already used for its antimicrobial
properties in a wide range of consumer
products and hence also textiles. Some dubious
product value conflicts with potentially
negative effects on health 12. On the one
hand, materials with nano-silver particles (integrated
into textile fibres or as a fibre coating)
are used to manufacture textiles that are
relatively odourless, yet the effects on the natural
skin flora have not been tested (see below).
On the other hand, nano-silver is also
used for clothing which is supposed to
protect people suffering from neurodermatitis (atopic dermatitis) from becoming infected
with staphylococcus aureus, a bacterium
which is suspected of exacerbating the
symptoms of neurodermatitis. Clinical studies
have so far not confirmed an actual positive
effect of textiles with nano-silver in cases
of neurodermatitis 13.
The German Federal Institute for Risk Assessment
(BfR) does not see any advantage in the
reduction of bacteria on textiles and warns
against potential negative effects such as a
weakening of the immune system and the
possibility of silver-resistant bacterial strains
development. The Institute also fears that
consumers could develop a false sense of
security and neglect general hygiene (washing
Effects of nano-silver in textiles on skin flora
In recent years antibacterial textiles using
nano-silver have been developed to minimise
odour formation by reducing the number of
bacteria. Fresh sweat is initially entirely
odourless. It is only the influence of certain
bacteria of the skin flora that produces the
typical, and to some extent unpleasant, body
odour. Silber ions are effective against a
broad spectrum of bacteria 15 and this mechanism
is supposed to be used to kill the odourforming
bacteria. In other words, when contact
is made with the skin an unspecific effect
can be expected on the skin flora. The
Hohenstein Institutes have carried out in-vitro
tests with antibacterial textiles and examined
their effects on skin flora 16. The results
indicate that bacteria are evidently only killed
in very close and direct contact with antimicrobial-
treated fibres. In the case of human
skin flora this means that it can only be influenced
when it is in direct contact with the
treated fibre. However, since only a few textile
fibres have direct and, at most, temporary
points of contact with the skin, depending
on their construction and the type of fibre,
no dramatic transformation in the skin
flora is to be expected in respect of the number
of bacteria. Furthermore, investigations
with disinfectants show that approximately
20% of skin flora bacteria are located too
deep in the skin for them to reach 17. The bacteria
population is hence only reduced for
a short period and after some time the skin
bacteria are filled up again from deeper skin
depots (sweat pores, hair follicles) to make
up the deficit created 16. The same effect may
be expected where nano-silver is used. However,
more investigations are needed since
silver nanoparticles can also penetrate into
deeper skin layers because they are so
small 18, and release their antimicrobial effect
on the resident skin flora. To date there
have been no significant studies of the longterm
effects of nano-silver in textiles on natural
human skin flora.
As there have been no investigations on the
release of nanoparticles from textiles, their
potential risk to the environment cannot be
assessed. Most probably however nanoparticles
are released during washing, entering
the environment via the waste water. In this
case it is principally nano-silver's antimicrobial
properties which make it hazardous because
silver ions are toxic for aquatic organisms
as well as for microorganisms in the
soil. Damage to the bacteria used in the biological
purification of waste water in sewage
plants likewise cannot be ruled out (cf.12).
Initial studies substantiate the fact that nanosilver
can be released from textiles in differing
quantities and forms. One study has investigated
the quantities and forms of silver
(nano-sized or larger) which were released
from nine different fabrics into the water
whilst washing in the washing machine. It
concluded that the percentage of the released
silver varied considerably between individual
products (1.3 to 35%) and is dependent
on the manufacturing method 9. Products
which had the silver woven into the fibres released
very little silver. Silver was mostly released
from materials washed in the washing
machine in particle sizes of >450 nm,
which the authors interpreted as an indication
of the importance of the mechanical influence.
A product with conventional silver
refining (several µm-thick silver coatings of
the fibres) showed no significant differences
in respect to the distribution of sizes of the
silver particles released.
Nano-titanium dioxide, which is also used
in the manufacture of nano-textiles, also has
to be considered hazardous because of its
potential environmental impact. When water
and UV exposure are present nano-titanium
dioxide produces free oxygen radicals
which are toxic for aquatic microorganisms.
This can damage the ecological balance of
stretches of water. However, there are still no
investigations to the mechanisms of the toxicity
or the impact on natural ecosystems 19.
Notes and References
1 Som, C., Halbeisen, M. and K?hler, A., 2009,
Integration von Nanopartikeln in Textilien ? Absch?tzungen
zur Stabilit?t entlang des textilen
Lebenszyklus, 5.1.2009: EMPA
2 Siegfried, B., 2007, NanoTextiles: Functions,
nanoparticles and commercial applications,
December 2007: EMPA
3 Mecheels, S., Schroth, B. and Breckenfelder,
C., 2004, Smart Clothes ? Intelligente textile
Produkte auf der Basis innovativer Mikrotechnologie.
Expertensicht ? Beispiele ? Empfehlungen:
4 Ulrich, C., 2006, Nano-Textiles Are Engineering
a Safer World, Human Ecology, 2
5 nanotechproject.org, (as at 3.11.09).
6 Gre?ler, S., Nentwich, M., Simk?, M., Gazs?,
A. and Fiedeler, U., 2009, Nano-Konsumprodukte
in ?sterreich. NanoTrust Dossier No. 009,
7 www.hohenstein.de, (Zugriff 4.11.09).
8 Benn, T. M. and Westerhoff, P., 2008, Nanoparticle
Silver Released into Water from Commercially
Available Sock Fabrics, Environmental Science
& Technology 42(11), 4133-4139.
9 Geranio, L., Heuberger, M. and Nowack, B.,
2009, The Behavior of Silver Nanotextiles during
Washing, Environmental Science & Technology
10 Aitken, R. J., Hankin, S. M., Ross, B., Tran, C.
L., Stone, V., Fernandes, T. F., Donaldson, K.,
Duffin, R., Chaudhry, Q., Wilkins, T. A.,
Wilkins, S. A., Levy, L. S., Rocks, S. A. and Maynard,
A., 2009, EMERGNANO: A review of
completed and near completed environment,
health and safety research on nanomaterials
and nanotechnology, im Auftrag von: Defra,
Nr. TM/09/01: IOM.
11 Simk?, M., Gazs?, A., Fiedeler, U. and Nentwich,
M., 2009, Nanopartikel, Freie Radikale
und Oxidativer Stress. NanoTrust Dossier
No. 012, epub.oeaw.ac.at/ita/
12 Fries, R., Gre?ler, S., Simk?, M., Gazs?, A.,
Fiedeler, U. and Nentwich, M., 2010, Nanosilver.
NanoTrust Dossier No. 010en,
13 Birnie, A. J., Bath-Hextall, F. J., Ravenscroft, J.
C. and Williams, H. C., 2009, Interventions to
reduce Staphylococcus aureus in the management
of atopic eczema (Review), Cochrane Database
Syst. Rev. 2008 Jul 16; (3): CD003871.
14 BfR, 2006, 12. Sitzung des Arbeitskreises "Gesundheitliche
Bewertungen von Textilhilfsmitteln
und -farbmitteln" der Arbeitsgruppe "Textilien"
des BfR: Bundesinstitut f?r Risikobewertung
15 Wijnhoven, S. W. P., Peijnenburg, W. J. G. M.,
Herberts, C. A., Hagens, W. I., Oomen, A. G.,
Heugens, E. H. W., Roszek, B., Bisschops, J.,
Gosens, I., Van De Meent, D., Dekkers, S., De
Jong, W. H., Van Zijverden, M., Sips, A. J. A.
M. and Geertsma, R. E., 2009, Nano-silver ?
a review of available data and knowledge gaps
in human and environmental risk assessment,
Nanotoxicology 3(2), 109-138.
16 H?fer, D. and Mecheels, S., 2004, Textilien,
Hautflora und Geruch, No. 62: Hohensteiner
17 Haustein, U.-F., 1989, Bakterielle Hautflora,
Wirtsabwehr und Hautinfektionen, Dermatologische
Monatsschrift 175(11), 665-680.
18 Larese, F. F., D'Agostin, F., Crosera, M., Adami,
G., Renzi, N., Bovenzi, M. and Maina, G.,
2009, Human skin penetration of silver nanoparticles
through intact and damaged skin, Toxicology
19 Battin, T. J., Von der Kammer, F., Weilhartner,
A., Ottofuelling, S. and Hofmann, T., 2009,
Nanostructured TiO2: Transport Behavior and
Effects on Aquatic Microbial Communities under
Environmental Conditions, Environmental
Science & Technology 43(21), 8098-8104.
By NanoTrust, Austrian Academy of Sciences. NanoTrust Dossiers are published irregularly and contain the research results of the Institute of Technology Assessment in the framework of its research project NanoTrust. The Dossiers are made available to the public exclusively on epub.oeaw.ac.at/ita/nanotrust-dossiers.