## 3 Impact of Cold Plasma on Packaging Properties
### Mechanical Properties  
Mechanical properties such as tensile strength (TS) and elongation at break (EAB) of the films are key parameters in packaging applications to preserve food quality and integrity during handling, storage, and transportation [43, 52, 94]. The application of plasma to film induces physicochemical phenomena like etching, degradation, and cross-linking altering the mechanical properties of the films [52, 95]. The bombardment of plasma (ionic species) on the film surface cleaves C-C and C-H bonds and generates free radicals that create linkage with the surface radicals or participate in chain reactions resulting in the significant improvement in mechanical properties of the films [100, 106]. [PERSON], [PERSON] [106] reported that atmospheric cold plasma treatment for 45 s significantly increased the TS and EAB of a zein film. However, increasing the treatment time to 60 s was ineffective in improving the mechanical properties. The increase in TS and EAB of the zein film could be due to the cross-linking that occurred during plasma treatment. The plasma discharge could have oxidized oxygen into an ozone that transformed the free S-H group to S-S. Cross-linking by strong intermolecular and intramolecular S-S in the zein matrix may have resulted in the higher TS and EAB. Such findings for zein/chitosan film, zein, and zein/polylactic acid films were reported in the literature [46, 80]. [PERSON], [PERSON] [58] treated the corn starch-based film with DBD plasma and reported that with the increase in treatment time from 0 to 20 min, TS increased significantly. Similarly, [PERSON], [PERSON] [95] also demonstrated that TS of Ar plasma treated starch film increased significantly with the increase in treatment time from 0 to 12 min [95]. The increase in TS could be attributed to the probable introduction of cross-links like carbonyl groups after plasma treatment that promotes hydrogen bonding resulting in the enhanced structural integrity of the film matrix [58,95]. They also reported that improvements in TS could be due to the etching effect, which reduces some of the defects on the surface of the film that cause premature failure [95]. These studies showed that TS of the biopolymer films increased with an increase in plasma exposure time due to the longer chemical interaction between the plasma-generated radicals and the polymer surface. [PERSON], [PERSON] [49] studied the impact of applied voltage and plasma treatment time on the mechanical properties of polycaprolactone (PCL) grafted zein film. In general, TS increased with the increase in voltage and time. In particular, the plasma treatment for more than 15 s significantly enhanced the TS and EAB due to the intense chemical interaction between zein and PCL. However the application of a higher voltage of 100 V decreased the TS of the composite film. They also reported that the overall enhancement in EAB due to plasma treatment was negligible when compared to PCL film. This suggests that mechanical property is largely reliant on the bulk structure of the film rather than the surface layer [49]. Besides treatment time and voltage, the types of gases used to generate plasma reactive species also have an impact by altering the mechanical properties of the packaging film. [PERSON], [PERSON] [100] reported that the application of air and argon plasma for 5 and 10 min in whey protein film increased the TS significantly. Increasing the treatment time up to 15 min significantly increased the TS for air plasma treated film, however a decline was observed for argon plasma treated film. This could be due fact that the ionization yield of Ar plasma is higher than air plasma. Furthermore, Ar is more effective in crosslinking, with the formation of free radicals and double bonds presenting a higher impact on the mechanical properties of the films. During the formation of air plasma, a portion of electrical energy  
Figure 5: ATR-FTIR spectra: (**I**) air plasma treated corn starch/poly-\(\epsilon\)-caprolactone films. Reprinted with permission from Ref.