The objective of this research was to develop a shellac-hydroproyl methyl cellulose (Sh-HPMC) composite film with enhanced water vapor barrier. Citric acid (CA) was used as an acid catalyst, to promote miscibility between HPMC and shellac. In a preliminary test, three different concentrations of CA (1000:1, 200:1, 100:1) were tested to identify the best Sh:CA ratio. Based on the Water vapor permeability properties and mechanical properties, Sh-CA (1000:1 ratio) had the most enhanced water vapor barrier and the lowest reduction in tensile strength compared to the pure HPMC film (control). In the later part of the research, the effect of shellac concentration in the Sh-HPMC composite films was studied by performing water vapor permeability (WVP) tests, tensile strength (TS), % elongation (%E), surface microscopy, and thermal gravimetric analysis (TGA). Among the four different concentration of Sh-HPMC (0.1, 0.5, 1.0, 1.5%), the 0.1% Sh-HPMC composite film had the highest moisture barrier as well as the best surface quality in the microscopic analysis. These result further suggested that the increase in the shellac concentration contributed to the reduction of TS and %E. However, 0.1% Sh-HPMC composite films had the lowest decrease in the mechanical properties compared to pure HPMC. Thermal properties of the pure HPMC were not compromised with the addition of Sh. The TGA results exhibited thermal stability for all the concentrations of Sh-HPMC. Overall, the increase in Sh concentration in the Sh-HPMC composite films produced brittle films due to poor miscibility between the complementary hydrophobic/hydrophilic character of Sh and HPMC polymers, respectively.
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