Investigation of the effects of designed ZnO powders on the structure and properties of chitosan / polyvinyl alcohol biodegradable polymers

Biodegradable polymers exhibit great potential to be a critical part of the global sustainability solution; however, their application areas are limited due to their weak barrier properties, poor UV resistance, low thermal resistance, low mechanical strength and inadequate antibacterial properties. Although nano metal oxide powders are often used to improve the properties; they exhibit toxicity and phytotoxicity, and sometimes can cause processing difficulties via uncontrolled agglomeration. Accordingly, alternative additive forms that will be biocompatible, providing both excellent UV resistance and antibacterial effect, are needed to improve the properties of polymers. Recently, designed, biocompatible and environmentally benign micron size hexagonal platelet particles that are composed of fine primary particles, called as MicNo® , have been developed to exploit the advantages of both micron and nano size, while mitigating the adverse effects of nanoparticles. Consequently, the research objective of the present study was to evaluate effects of undoped MicNo® ZnO, Ag and a transition metal doped MicNo® ZnO particles on structure development and hence optical, mechanical and antibacterial properties of Chitosan/PVA films with respect to nano ZnO as a first time in the literature. XRD and SEM results showed that MicNo® particles can be distributed evenly throughout the film without demonstrating any uncontrolled agglomeration. In adiditon, FTIR results revealed that they exhibit stronger intermolecular bonding with the polymeric part with respect than the nanoparticles probably due to larger surface area to volume ratio. As a result, the MicNo® containing films exhibited the highest average tensile strength and elongation as 1.41 MPa and 43.54 %, respectively, among the doped films. This strength value refers to 206 % and 115 % improvement with respect to pristine and nanoparticle containing films, respectively. Furthermore, both undoped MicNo® ZnO, Ag and a transition metal doped MicNo® ZnO containing films exhibited higher UV-absorbance values than nano ZnO particle containing films. These results suggest that the UV resistance of the films can be improved much more effectively by MicNo® particles with respect to nanoparticles. This outstanding performance enhancement can be attributed to much more effective surface covering ability of unique hexagonal morphology of MicNo® particles with respect to speherical nano particles. Although the pristine films exhibited poor antibacterial activity, incorporation of ZnO particles into the films resulted in development of antibacterial effect. Against to both S. Aureus and E.Coli bacteria undoped MicNo® ZnO, Ag and a transition metal doped MicNo® ZnO particles exhibited very high antibacterial effect. Particularly against to S. Aureus, whereas nano ZnO containing films demonstrated 2.57 antibacterial R value, this value were 6.91, 7.72, 6.91 for undoped MicNo® ZnO, Ag and a transition metal doped MicNo® ZnO containing films, respectively. Consequently, MicNo® particles exhibit many advantages over nano particles and hence demonstrate a great potential as new generation additive systems for biodegradable polymers to extend their application areas.