TEACHING MATERIALS for Students: Spraying methods

2. New technologies for textile functionalization

2.6. Spraying methods

Liquid Flame spray (LFS) is a flame pyrolysis technique that allows the simultaneous synthesis and deposition of noble metal and metal oxide nanoparticles in a continuous process. A precursor for the desired nanoparticles to be formed is injected into a high-temperature flame and the produced nanoparticles are deposited onto a substrate.

Fig. 2.6.1 Schematics of the liquid flame spray setup used to deposit silver nanoparticles onto the fabrics

Using the LFS deposition process, silver nanoparticles were deposited onto fabrics, fabrics. Both fabrics are commonly used in hospital environments (first as bedding covers, and the second one as gowns in the operating room). It must be noted that the deposited nanoparticles can cause unwanted color change in the surface of different fabrics, therefore, it is important to consider this when choosing the substrate for nanoparticle deposition. Fabric samples coated with only silver and with both silver and plasma are shown in Figure (below the text).

Fig. 2.6.2 Silver nanoparticles deposited onto the fabrics (Fabric I is a,b; Fabric II is c,d) before plasma coating (10X).

A plasma polymer coating was also deposited onto the nanoparticle coated fabrics for better adhesion of nanoparticles. HMDSO was selected for the plasma coatings due to its hydrophobicity, low toxicity and transparent optical properties with good chemical and electrical stability.

The new ‘Touch’ test method that simulates the transfer of bacteria from one surface to another by touch was used for determining the antibacterial efficiency of the treated fabrics. The antibacterial results for both fabrics obtained from three repeated measurements are shown in figure below. Bacterial growth is evident in the reference samples that had no silver nanoparticles nor plasma coating. The growth of E. coli was inhibited in all the samples that had deposited silver nanoparticles. This was also the case even for samples with plasma coating on top of the nanoparticles. Since the antibacterial properties observed here are attributed to the release of silver, the plasma coating is either nonconformal, that is, it does not cover fully all the nanoparticles, or silver is released through the plasma coating or possible cracks in it. For gram-positive S. aureus, the coatings did not demonstrate antibacterial properties even for 20X coatings without any plasma coating on top.

Fig 2.6.3 Antibacterial results for fabrics I and II after 24 h incubation at room temperature. Bacterial growth

in the graph is given as 1, 2 and 3, corresponding to 10³–10⁴ CFU, 10⁴–10⁵ CFU and >10⁵ CFU, respectively.

‘Ref’ represents reference samples with no silver or plasma.

Reference:
K. J. Brobbey at al.: High-speed production of antibacterial fabrics using liquid flame spray, Textile Research Journal 2020, Vol. 90 (5–6) 503–511.