Plasma-treated carbon nanotubes improve dispersion in polyurethane
Plasma functionalisation stops multi-walled carbon nanotubes agglomerating in polyurethane coatings, a dispersion problem that has limited their antimicrobial performance in solid films.
Multi-walled carbon nanotubes (MWCNTs) have demonstrated potential antimicrobial properties through mechanisms such as cell-wall penetration and oxidative stress. Incorporating MWCNTs into solid polyurethane coatings could impart these antimicrobial properties to the coatings. However, pristine MWCNTs tend to agglomerate, particularly in liquid media. To enhance their performance, achieving a stable and homogeneous dispersion of the particles is essential. Surface functionalization of MWCNTs using plasma-deposited organic coatings can reduce agglomeration and improve compatibility with solvents used in polyurethane synthesis, resulting in better dispersion in the final solid material.
To obtain MWCNTs with a high available surface area suitable for functionalization, the particles were synthesized in-house using a thermal chemical vapor deposition (CVD) furnace. The particles, grown in a forest-like structure on a stainless-steel substrate, were functionalized in a low-pressure RF plasma chamber. Three distinct plasma compositions (oxygen-rich, nitrogen-rich, and silicon-rich) were studied. The plasma-polymer coatings were characterized using X-ray photoelectron spectroscopy (XPS). Functionalized particles were dispersed in five different solvents commonly used in polyurethane chemistry through a sonication process. The dispersion quality and stability of these nanoparticle suspensions were examined through visual observation and dynamic light scattering (DLS). These suspensions were then used in the production of polyurethane coatings to create nanocomposites whose antimicrobial properties were investigated.
XPS characterization of the plasma-polymer coatings showed that nitrogen-rich plasma introduced amine, amide, and imine functional groups at the surface of the MWCNTs, oxygen-rich plasma yielded carboxyl and hydroxyl groups, and silicon-rich plasma produced siloxane groups and a silicon-chain structure. DLS results indicated that in water, oxygen-rich and nitrogen-rich functionalization improved dispersion and reduced agglomeration of the particles over a five-week period. The behavior of the particles was also studied in butyl acetate, ethyl acetate, and ethyl-ethoxypropionate, but functionalization showed no significant improvements. The nanofluids were used to create nanocomposite polyurethane coatings at three different MWCNT concentrations (0.1, 0.5, and 1.0 m%). Scanning electron microscopy (SEM) confirmed good dispersion of the particles in the bulk material and an embedded presence at the surface of the coatings. However, antibacterial testing following the ISO 22196:2011 protocol on these samples showed no significant antibacterial effect against E. coli and Staphylococcus epidermidis.
Source: Carbon Nanotubes Feed