## 3 Impact of Cold Plasma on Packaging Properties
### Molecular Properties of the Film  
Fourier Transform Infrared (FTIR) Study  
A microstructural study of the biopolymer-based film provides insight into the molecular interactions of the different components present in the film network. The understanding of molecular interactions is important as it influences the physical, thermal, and mechanical properties of the film. Cold plasma treatment is a novel technique used to enhance the structural features of the biopolymer-based film. One of the most prominent methods to investigate the structural changes in the biopolymer film is Fourier transform infrared (FTIR). It has been reported that plasma treatment induces a number of chemical reactions like molecular rearrangements, dehydration, and the hydrogenation of molecules [58]. The application of plasma creates a reactive site on the biopolymer film surface. [PERSON], [PERSON] [99] treated starch films with plasma (air and O\({}_{2}\)), and [PERSON], [PERSON] [100] treated gluten and whey protein with cold plasma. The FTIR showed that bands near 2940 cm\({}^{-1}\) and 2925 cm\({}^{-1}\) decreased and this was attributed to the abstraction of protons from the carbon atom of C-H of starch and proteins resulting in the creation of reactive sites on the biopolymers [43; 99; 100]. The studies have shown that the starch-based film treated with cold plasma incorporates oxygenated functional groups into the film matrix resulting in an increase in hydrogen bonding and crosslinking. [PERSON], [PERSON] [79] investigated the structural modification of corn starch/poly-\(\varepsilon\)-caprolactone films using FTIR and reported that the application of air plasma increased the intensity of peaks at approximately 3600-3000, 1265, and 1016 cm\({}^{-1}\) suggesting the increase in the oxygen-containing functional groups like O-H and C-O (Figure 5I). This increase in the peak intensity could be due to the interaction between oxygen-containing species in the plasma and the substrate [79]. A similar result was reported for corn starch film when treated with DBD where the increase in absorption bands at around 1016 cm\({}^{-1}\) (C-O-C), 1154, and 1081 cm\({}^{-1}\) (C-O-H) indicated an increase in C-O groups. A shift in the absorption bands at about 1648 and 1580 cm\({}^{-1}\) (\(\delta\) (O-H)) indicated an increase in hydrogen bonding and these phenomena could be attributed to surface oxygenation [58; 82; 99]. Further, [PERSON], [PERSON] [101] and [PERSON], [PERSON] [85] studied the impact of cold plasma on starch films with low (30%) to high (50-70%) amylose content and reported that the application of different types of plasma (such as Hexamethyldisiloxane cold plasma, DBD, and radiofrequency plasma) altered the short-range crystalline structure of starch. This was indicated by a band ratio 1047/1022, where a peak at 1047 cm\({}^{-1}\) denoted an ordered or crystalline structure and at 1022 cm\({}^{-1}\) represented the amorphous region of starch [102; 103]. As shown in Figure 5 II, after the plasma treatment the intensity at 1022 cm\({}^{-1}\) decreased and 1047/1022 increased for all of the films. This indicates that the etching phenomena allowed the plasma reactive species to penetrate and reorder the amylopeetin chains, thereby creating a highly ordered network in the starch film matrix [85; 101]. A study by [PERSON], [PERSON] [101] further reported that the peak at 3300 cm\({}^{-1}\) corresponding to the O-H group disappeared in all the plasma-treated films and this was attributed to the impact of plasma reactive species altering the water retention capability of the starch film by the formation of a coating on the film surface [101]. Similarly, [PERSON], [PERSON] [58] also reported that DBD plasma treatment of corn starch for 20 min demonstrated a reduction in the intensity of the peak in the range of 3500-3000 cm\({}^{-1}\) at approximately 3295 cm\({}^{-1}\), implying the possible dehydration of film during the plasma treatment and thereby reduced hydrophilicity [58].