3.4.1. Morphological Characterization

The elemental mapping on ZnAl-KET loaded patch obtained by EDX analysis showed that the hybrid was homogeneously dispersed in the polymeric matrix (Figure 6). This result suggested that the casting method used for patch preparation allowed to obtain a homogeneous final product, and this was very important as a guarantee that the drug (KET as a hybrid) was distributed homogeneously on the whole surface. Moreover, the patch showed a wrinkled surface due to the presence of ZnAl-KET crystals.

**Figure 6.** SEM analysis of ZnAl-KET loaded patch: micrograph (**A**), zinc mapping (**B**), aluminum mapping (**C**) and edx spectrum (**D**). Magnification 4999 X.

## 3.4.2. Mechanical Characterization

The presence and effect of ZnAl-KET in the NaCMC matrix were investigated in terms of mechanical properties. Mechanical parameters of the two patches, NaCMC (blank) and NaCMC loaded with ZnAl-KET, were estimated from stress-strain curves obtained by performing tensile tests at RT (Figure 7). Data are summarized in Table 2, while the stress-strain curves are reported in Figure 6. As already reported in Perioli et al. [23], the introduction of lamellar ZnAl-NO3 at 1% *wt.* in NaCMC, even in a small amount, was able to increase the mechanical properties of reference matrix. Specifically, at low humidity conditions, the produced patch showed increased tensile strength but limited deformability at the break, as already observed by Yadollahi et al. [28]. The ductility of the NaCMC film was indeed here recovered and greatly improved when KET was intercalated in ZnAl-NO3. The introduction of the drug into ZnAl-HTlc might enhance interfacial adhesion and compatibility between the NaCMC matrix and the layered nano clay, thus increasing tensile strength [29] and positively affecting the ductility of the produced patch. In particular, it could be considered that the presence of KET inhibited the possible restacking of the nano sheets that could appear in unmodified HTlcs, by maintaining the exfoliated state in water-soluble NaCMC before casting [30].

**Figure 7.** Stress–strain curves of NaCMC patch (NaCMC) and patch loaded with ZnAl-KET (NaCMC + ZnAl-KET).


**Table 2.** Mechanical properties of NaCMC patch and patch loaded with ZnAl-KET.

NaCMC: NaCMC patch; NaCMC + ZnAl-KET: patch loaded with ZnAl-KET; σ*max*: maximum stress; ε *at* <sup>σ</sup>*max*: deformation at the break for maximum stress; *EYoung*: elastic modulus.
