Self-cleaning/dirt and water repellent smart clothes

Nanomaterials make possible to exceed the basic use of your clothes by integrating extra functionalities into the textile fibers.

How often have you thrown out a white shirt? If you are a business man, a bartender, waiter or a chef who must always look neatly and clean. However, washing white clothes, ironing shirts or avoiding stains in white garments is still challenging. Indeed, not always the most convenient garment, white shirts are still very popular, and we all like to wear them, to have that amazing feeling of looking impeccably clean.

Either for leisure or business, white garments are always wanted. At a wedding party or luxurious event, or when going on a date, you always include a white shirt. Working at restaurants, bars, labs or pharmacies when you deal with clients and you intend to show-off a neatly environment, you always choose white. Right?

Now just imagine having your white clothes impeccable white no matter where you are or what you are doing or what you are working with. No stains, no laundry, no dry cleaning, no ironing.

And I am not talking about those traditional methods based on coating textile surfaces with water-repellent agents that do not allow air to circulate freely through your clothes such as the so-known paraffin waxes [1][2], making heat and cold unbearable for you. When hot outside, sweat was kept inside of your garments and, when cold outside, humidity was formed inside [2]. Consequently, you used to feel yourself uncomfortable and unpleasant while wearing those water-repellent clothes.

I am talking about the use of one of the most promising revolution on the textile industry and fashion: the so-called nanotechnology. Recently, the fabrication of hydrophobic textiles with oil/water repellent properties by coating or impregnating the textiles surfaces, or directly integrating nanomaterials into textile fibers [3] has been receiving great attention in the textile industry. Nanoparticles can be incorporated during the fiber production in the whole fiber volume or only in the core of the “core-sheath” fiber. They can also be incorporated during finishing covalent or not covalent bound directly on the fiber surface, or incorporated in xero-gel or polymeric fiber coatings [4].

What it makes these nanoparticles so cool lies in their size and outstanding surface properties providing multiple special additional functionality to textiles and other materials. Many additional features such as hydrophobicity but also antibacterial activity, flame retardant properties, UV-protection, and others might be now incorporated in your clothes at low cost by using nanomaterials.

Probably you didn’t noticed yet but the number of textiles with oil/water repellent properties offered in the market has been rapidly growing and improving. Textiles containing carbon nanotubes, silicon dioxide (nano-SiO2), titanium dioxide (nano-TiO2), or silver (nano-Ag) nanomaterials have been largely used in shirts, towels, surgical cloths and medical masks. Besides textiles, there are hundreds of [5–7] containing nanomaterials that are commercially available and make part of our lives, such as sunscreens, cosmetics, foods, fertilizers, industrial catalysts, fuel cells, sports equipment, computer and television screens, or medical equipment [8].

Several studies have been conducted in order to better understand not only the undoubtable potential of using these nanoparticles but also their potential impact on health and environment. As such, we searched for more details about the findings they have been reported. Dermatological effects of nanoparticles are mainly focused on the question whether these particles are able to penetrate into or through the skin [3]. Dermal exposure is then proportional to the amount of nanoparticles released from textiles into the wearer’s sweat [9,10]. The penetration into or through the skin and consequently absorption into the body is then dependent on the dermal exposure and the dimensions of nanoparticles. In this line, studies have been evaluating the release of nanomaterials from textiles into artificial sweat [3]. There are also a few studies evaluating their release into washing water to test their environment impact.

Summing up their findings, nanoparticles released from the textiles into the sweat were shown to be too big to penetrate into the skin. Furthermore, although higher releases into the washing water were observed in comparison to those found in sweat, it is important to notice that these modified textiles are self-cleaning and no laundry is actually needed. This is another advantage of these water/dirt repellent garments as they reduce the waste of water and detergents, and save raw materials [11]. Even tough, these textiles have shown high durability by retaining the hydrophobic properties even after 30 laundering cycles [3]. Since we recognize the importance of being aware that nanoscale particles may be released unintentionally from textiles, we present a more detailed review of the studies in the following paragraphs aiming to further understand what has been observed so far.

Recent literature [12] suggests that nanoparticles may have a higher risk of toxicity due to their higher chemical reactivity and biological activity compared larger particles. Therefore, size is a key factor in determining the potential toxicity of a particle. However, other factors influencing toxicity include shape, chemical composition, surface structure, surface charge, aggregation and solubility [13].

Nano-TiO2 agglomerates with diameters ranging from ca. 60 nm to over 450 nm were released from washing and rinsing, or leaching of textiles [3,10,14, 15]. Crosera et al. (2017) [16], showed that when nanoparticles of TiO2 were dispersed in water, small aggregates were formed, and when dispersed in synthetic sweat, they immediately started to agglomerate in bigger clusters (about 730 nm). In addition, they demonstrated that no titanium permeation occurred after 24h of dermal exposure to nano-TiO2 both in intact and in damaged skin. Titanium was detectable only in the epidermis of the skin [16]. In accordance to this study, other authors [17–21] denied the nano-TiO2 capability to permeate the human skin. This has been explained by the accumulation of nanoparticles on the skin surface due to the great stability of the nano-TiO2 and its negligible ionization in the physiological condition. Moreover, the big size of the particles and their tendency to form aggregates further reduce the skin absorption capability [22]. Another study conducted by Kulthong et al. (2010) [15] showed that in some commercial fabric, nano-Ag could not be detected in any formulation of artificial sweat, neither in the fabric itself. Nano-Ag was released into artificial sweat at levels ranging from about 0.01 mg/kg to 0.5 mg/kg, depending on the sweat formulation, which was considerable lower than those observed in lab-prepared fabrics, also tested by the authors [15]. Overall, the majority of the released nano-Ag has been shown to be coarse particles larger than 450nm [4,23].

A study on human skin penetration of polymeric nanoparticles conducted by Alvarez-Romàn et al. (2004) [24] found that 20–200nm polystyrene nanoparticles were mainly accumulated in follicle openings. Similarly, Vogt et al. (2006) [25] showed that 40-nm, but not 750 or 1500 nm, nanoparticles were able to penetrate the perifollicular dermis through the hair follicle. Likewise, Larese et al. (2009) [26] showed that only nano-Ag smaller than 30nm were able to penetrate passively the skin, reaching the deepest layers of the stratum corneum and the outermost surface of the epidermis.

As already mentioned above, although sweat might facilitate transfer of nanoparticles to the skin surface [27], it remains unclear whether these particles can be absorbed by the body, since this absorbability is highly dependent on the dimensions of the released nanoparticles.

Nanoparticles-based textile garments are undoubtedly the new promising revolution on the textile industry and fashion. A growing interest in nanotechnology has already put several lines of nanoparticles-based products on the market worldwide. The potential of these nanoparticles is huge and came to stay forever.

Susana, PhD

References

Image: http://www.mfstek.com/sigmatek/]

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