The oxygen permeability (OP) of the HPMC film and HPMC based composite film were measured at 25 ± 2 C and 50 ± 5%
RH (ASTM D1434-88) using an oxygen permeation analyzer (Model 8500, Illinois Instruments, Johnsburg, IL, USA). Each film was greased at the rim and placed on the sample chamber with an exposed testing area of 100 cm2. Nitrogen gas flowed on one side and pure oxygen gas flowed on the other under the above conditions. The oxygen transmission rate (OTR)was recorded to calculate the OP by multiplying the OTR by the film thickness and dividing by the oxygen partial pressure difference (DP) according to the following equation: