## 3 Results
### Barrier Properties to Water Vapor and Oxygen Gas  
The values of WVP and OP of the TPS films are also shown in Table 3. The non-modified starch films exhibited WVP values ranging from 5.3 to 6.3 g.mm/kPa\(\cdot\)h\(\cdot\)m\({}^{2}\), close to the range reported by other authors for corn starch films [34, 40]. Films of TPS with 3 and 5 wt% CMFs exhibited slightly lower but still significant (\(p<0.05\)) WVP values than the neat TPS film, reaching percentages increases in the barrier performance of 6% and 15%, respectively. Since WVP of packaging materials is mainly affected by the solubility coefficient in the polymer matrix and also, but to a lesser extent, by the vapor diffusion rate [63], the permeability decrease attained in the film samples containing CMFs can be ascribed to the chemical interaction by -H bonds of cellulose with hydrophilic groups of the starch-glycerol matrix described above [4, 49, 64]. Other authors also reported a decrease in WVP of TPS films from different sources incorporated with cellulosic fractions [61, 65]. Furthermore, the CMF addition did not influence significantly (\(p>0.05\)) the WVP values of the TPSDH films, which already presented values remarkably lower (\(p<0.05\)) than the TPS samples. The latter lower permeability to water vapor of DH-modified starch can be ascribed to the large presence of intact starch granules, previously observed in the FESEM images, which would increase the tortuosity factor of the modified matrix, further limiting the diffusion of water molecules through the films. Other authors also reported lower values of VWP for DH-modified rice starch films [66]. As concerns the OP values, the incorporation of CMFs at contents of 3 and 5 wt% promoted a significant (\(p<0.05\)) OP decrease of approximately 30% with respect to the neat TPS film. This barrier enhancement can be attributed to the increase of the tortuosity factor \begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**Formulation**} & \multirow{2}{*}{**Moisture (\%)**} & **Solubility** & **WVP** & **OP \(\times\) 10\({}^{14}\)** \\  & & **(g Soluble Film\(\cdot\)100 g\({}^{-1}\) Film)** & **(g.mm.kPa\({}^{-1}\).h\({}^{-1}\).m\({}^{-2}\))** & **(cm\({}^{3}\).m\({}^{-1}\).s\({}^{-1}\).Pa\({}^{-1}\))** \\ \hline TPS & 7.7 \(\pm\) 0.1 \({}^{\text{a,1}}\) & 42 \(\pm\) 2 \({}^{\text{a,2}}\) & 6.3 \(\pm\) 0.2 \({}^{\text{ab,1}}\) & 9.0 \(\pm\) 0.3 \({}^{\text{a,1}}\) \\ TPS1 & 7.5 \(\pm\) 0.1 \({}^{\text{a,1}}\) & 28 \(\pm\) 1 \({}^{\text{b,2}}\) & 6.5 \(\pm\) 0.1 \({}^{\text{a,1}}\) & 9.2 \(\pm\) 0.4 \({}^{\text{a,1}}\) \\ TPS3 & 7.7 \(\pm\) 0.1 \({}^{\text{a,1}}\) & 37 \(\pm\) 4 \({}^{\text{ab,2}}\) & 5.9 \(\pm\) 0.2 \({}^{\text{b,1}}\) & 6.3 \(\pm\) 0.6 \({}^{\text{b,2}}\) \\ TPS5 & 7.1 \(\pm\) 0.2 \({}^{\text{b,1}}\) & 36 \(\pm\) 5 \({}^{\text{ab,2}}\) & 5.3 \(\pm\) 0.3 \({}^{\text{c,1}}\) & 6.4 \(\pm\) 0.1 \({}^{\text{b,2}}\) \\ TPSDH & 8.1 \(\pm\) 0.1 \({}^{\text{a,2}}\) & 55 \(\pm\) 8 \({}^{\text{b,1}}\) & 0.25 \(\pm\) 0.01 \({}^{\text{a,2}}\) & 8.7 \(\pm\) 0.5 \({}^{\text{a,1}}\) \\ TPSDH1 & 7.9 \(\pm\) 0.1 \({}^{\text{a,2}}\) & 80 \(\pm\) 8 \({}^{\text{a,1}}\) & 0.33 \(\pm\) 0.05 \({}^{\text{a,2}}\) & 8.8 \(\pm\) 0.4 \({}^{\text{a,1}}\) \\ TPSDH3 & 7.7 \(\pm\) 0.1 \({}^{\text{b,1}}\) & 73 \(\pm\) 12 \({}^{\text{ab,1}}\) & 0.31 \(\pm\) 0.02 \({}^{\text{a,2}}\) & 7.7 \(\pm\) 0.4 \({}^{\text{a,1}}\) \\ TPSDH5 & 7.9 \(\pm\) 0.1 \({}^{\text{a,2}}\) & 57 \(\pm\) 6 \({}^{\text{ab,1}}\) & 0.31 \(\pm\) 0.01 \({}^{\text{a,2}}\) & 8.4 \(\pm\) 0.1 \({}^{\text{a,1}}\) \\ \hline \end{tabular} Different subscript letters indicate significant differences between samples of the same group (TPS or TPSDH films). Different numbers indicated significant differences between TPS and TPSDH samples with the same ratio of CMF (Tukey test, \(p<0.05\)).  
\end{table} 
Table 3: Moisture, water solubility, water vapor permeability (WVP), and oxygen permeability (OP) of thermoplastic starch (TPS) and TPS modified by dry heating (TPSDH) films with different contents of cellulose microfibers (CMFs).