# Attempts to Obtain Material Based on Polyvinyl Alcohol with Barrier Properties against Water Vapor
## 3 Results and Discussion
### PVA Film Modified with 0.75% CA, 0.2 g BW, CBS and 1.5% Gly, Thinner (PVA III)  
The film was well homogenized, was thin, 0.17 mm thick, easily detached from the Petri dish and was transparent with a slight tinge of white. The image of PVA III can be seen in Table 2. The WVTR values of this thermically treated film can be seen in Figure 4, compared to those of the PE and untreated pure PVA film. PVA III film treated at 125 \({}^{\circ}\)C achieved the best results, with WVTR values 5.8% lower than the pure PVA film after 34 days. The difference from the PE film is 6.96% for the PVA III film cured to 125 \({}^{\circ}\)C and 7.56% for the untreated PVA III film on day 34. The 150 \({}^{\circ}\)C heat treatment of the PVA III film was not effective, cracks may have appeared during modeling. The measured WVTR was 4.55% lower than the pure PVA and 8.21% higher compared to the PE. The results obtained suggest that obtaining a thinner film reduces the WVTR of PVA III film compared to the untreated PVA film, because the thickness of the film affects the partial equilibrium pressure of water on the inner surface of the film, giving it greater resistance to water transfer, in the case of hydrophilic films [37]. The values obtained with the film treated at 150 \({}^{\circ}\)C could be due to microcracks that may have occurred during modeling of the film. The PVA III film treated at 150 \({}^{\circ}\)C recorded statistically significant differences in the proportion of 95% (_p_ < 0.05) compared to the PVA III film as WVTR indicating that heat treatment at 150 \({}^{\circ}\)C did not improve the WVP of the PVA III film. The difference between the WVTR values of the modified and heat-treated films and the PVA film is statistically  
Figure 3: WVTR of untreated PE, PVA, PVA II films, and PVA II film heat treated at 125 \({}^{\circ}\)C and 150 \({}^{\circ}\)C (the results were obtained in triplicate. The average of the three determinations was reported, with a maximum error of 5%). significant at more than 99% (\(p<0.01\)) according to One-Way Anova, the Tukey model, which means that the WVP of the PVA film has been improved. PVA Film Modified with 0.75% CA and 1.5% Gly (PVA I) and PVA Film Modified with 0.75% CA, 0.2 g BW, CBS and 1.5% Gly (PVA III, Thinner) (PVA IV Double Layer)  
The films adhered quite well to each other, proving their compatibility, resulting in a fairly transparent film with a slight white tint and a thickness of 0.5 mm. During the heat treatment, the films did not break, but at 150 \({}^{\circ}\)C the double layer film yellowed slightly. The image of the film obtained can be seen in Table 2.  
The WVTR of the double layer film was calculated and can be seen in Figure 5, compared to that of the PE and pure PVA film. Heat treatment at 150 \({}^{\circ}\)C was not effective on PVA IV film, resulting in values 0.37%, higher than untreated PVA IV film at day 34. However, these are values that 6.77% lower than those achieved with pure PVA film. A PVA IV film cured at 125 \({}^{\circ}\)C prevents greater penetration of water through the film compared to an untreated PVA IV film. The difference recorded is 1.29%, and for pure PVA film the difference is 8.43% at day 34. The difference in WVTR values between PVA IV film treated at 125 \({}^{\circ}\)C and PE film is 4.33%, in favor of the PE film on the same day. PVA IV film achieved better results than PVA II and PVA III film. The formula adopted reduces the permeability of PVA film more effectively provides a better barrier to water vapor, which is achieved by the most hydrophobic layer in the double layer film. Compared to the other films, the WVTR values even approach those of PE film. The obtained results suggest that the formulation of a double layer film could be a viable strategy to reduce the permeability of PVA films. The results are consistent with those of [PERSON] et al. (2019) who prepared double layer films by thermocopression of a starch-based layer (cassava and corn) with another layer of PLA/poly(3-hydroxybutyrate-co-3-hydroxyvalerate).