Evaluating the durability of SHP coating
The performance of the SHP materials after coating over the
surface of the fabric depends on how strongly the additives are
attached to the fibres. The stability of the additives after coating is
generally evaluated by subjecting the fabrics coated with all
additives by sonication process in a proper solvent [29]. By
employing this methodology, the fabrics were immersed in
ethanol, sonicated for 30 min. After sonication, the samples were
removed, air dried and their water contact angle was measured.
Fig. 7(a) and (b) shows the WCA of fabrics impregnated with iron
oxide and chromia nanoparticles after subjected to sonication
process, respectively. The obtained results show that there is a
reduction in the WCA values from 147.58 to 145.68 and 151.18 to
149.98 for iron oxide and chromia impregnated fabric, respectively.
The slight reduction in the WCA values can be attributed to the
removal of metal oxide nano particles which were loosely attached
on the fabrics during sonication process. From these results we can
infer that the prepared fabric is robust,the SHPadditives are strongly
attached to the fabric and shows its non-wettable character even in
the superhydrophobic region since the change in WCA value is very
less (18) after sonicating in ethanol for 30 min.
Tape-peeling test was also carried out to inspect the firm adhesion
of the nano-particles over the cotton fabric. Five cycles of attachment
and detachment of the adhesive tape over the SHP fabric was
performed and their morphology was inspected. The WCA results
shows that the nano-particles coated fabric losses its superhydrophobic
property and becomes hydrophobic. This is attributed to the
removal of nanoparticles from the coated fabric that can be clearly
understood from the SEM images [Fig. 7(c) and (d)]. Even though
there is a reduction in WCA,the iron oxide and chromia coated fabric
shows higher WCA of 141.78 and 142.48, respectively.
Further, the abrasion resistance of the coated fabric was
analysed by rubbing the cotton using sand paper. The sand paper
was mounted on an even surface and the SHP fabric was rubbed
over the sand paper with an applied load of 200 g over a length of
20 cm. After 20 cycles of rubbing, the coated fabric was tested for
WCA measurements. The morphology of the abraded surfaces of
cotton fabric coated with iron oxide and chromia shows that the
fabric fibres were found brokened to some extent [44,45] and
detached during rubbing process [Fig. 7(e) and (f)]. Regardless of
the damage, the coated fabric shows good WCA values of 139.18
and 1408 (iron oxide and chromia coated cotton).